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Sakamoto R, Kamoda T, Sato K, Ogoh S, Katayose M, Neki T, Iwamoto E. Acute aerobic exercise enhances cerebrovascular shear-mediated dilation in young adults: the role of cerebral shear. J Appl Physiol (1985) 2024; 136:535-548. [PMID: 38153849 DOI: 10.1152/japplphysiol.00543.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Revised: 12/22/2023] [Accepted: 12/22/2023] [Indexed: 12/30/2023] Open
Abstract
Exercise-induced increases in shear rate (SR) acutely improve peripheral endothelial function, but the presence of this mechanism in cerebral arteries remains unclear. Thus, we evaluated shear-mediated dilation of the internal carotid artery (ICA), which is an index of cerebrovascular endothelial function, before and after exercise. Shear-mediated dilation was measured with 30 s of hypercapnia in 16 young adults before and 10 min after 30 min of sitting rest (CON) or three cycling exercises on four separate days. The target exercise intensity was 80% of oxygen uptake at the ventilatory threshold. To manipulate the ICA SR during exercise, participants breathed spontaneously (ExSB, SR increase) or hyperventilated without (ExHV, no increase in SR) or with ([Formula: see text], restoration of SR increase) addition of CO2 to inspiratory air. Shear-mediated dilation was calculated as a percent increase in diameter from baseline. Doppler ultrasound measures ICA velocity and diameter. The CON trial revealed that 30 min of sitting did not alter shear-mediated dilation (4.34 ± 1.37% to 3.44 ± 1.23%, P = 0.052). ICA dilation after exercise compared with preexercise levels increased in the ExSB trial (3.32 ± 1.37% to 4.74 ± 1.84%, P < 0.01), remained unchanged in the ExHV trial (4.07 ± 1.55% to 3.21 ± 1.48%, P = 0.07), but was elevated in the [Formula: see text] trial (3.35 ± 1.15% to 4.33 ± 2.12%, P = 0.04). Our results indicate that exercise-induced increases in cerebral shear may play a crucial role in improving cerebrovascular endothelial function after acute exercise in young adults.NEW & NOTEWORTHY We found that 30-min cycling (target intensity was 80% of the ventilatory threshold) with increasing shear of the internal carotid artery (ICA) enhanced transient hypercapnia-induced shear-mediated dilation of the ICA, reflecting improved cerebrovascular endothelial function. This enhancement of ICA dilation was diminished by suppressing the exercise-induced increase in ICA shear via hyperventilation. Our results indicate that increases in cerebral shear may be a key stimulus for improving cerebrovascular endothelial function after exercise in young adults.
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Affiliation(s)
- Rintaro Sakamoto
- Graduate School of Health Sciences, Sapporo Medical University, Sapporo, Japan
- Japan Society for the Promotion of Science, Tokyo, Japan
| | - Tatsuki Kamoda
- Graduate School of Health Sciences, Sapporo Medical University, Sapporo, Japan
| | - Kohei Sato
- Graduate School of Health Sciences, Sapporo Medical University, Sapporo, Japan
| | - Shigehiko Ogoh
- Department of Biomedical Engineering, Toyo University, Kawagoe, Japan
| | - Masaki Katayose
- Graduate School of Health Sciences, Sapporo Medical University, Sapporo, Japan
- School of Health Sciences, Sapporo Medical University, Sapporo, Japan
| | - Toru Neki
- School of Health Sciences, Sapporo Medical University, Sapporo, Japan
| | - Erika Iwamoto
- School of Health Sciences, Sapporo Medical University, Sapporo, Japan
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Carter HH, Pienaar O, Coleman A, Cheng JL, MacDonald MJ, Naylor LH, Green DJ. The effects of water temperature on cerebral blood flow during aquatic exercise. Eur J Appl Physiol 2024; 124:219-225. [PMID: 37419991 PMCID: PMC10786737 DOI: 10.1007/s00421-023-05264-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2022] [Accepted: 06/20/2023] [Indexed: 07/09/2023]
Abstract
PURPOSE Recent studies suggest that episodic increases in cerebral blood flow (CBF) may contribute to the improvement in brain health associated with exercise training. Optimising CBF during exercise may enhance this benefit. Water immersion in ~ 30-32 °C augments CBF at rest and during exercise; however, the impact of water temperature on the CBF response has not been investigated. We hypothesised that cycle ergometry in water would increase CBF compared to land-based exercise, and that warm water would attenuate the CBF benefits. METHODS Eleven young heathy participants (nine males; 23.8 ± 3.1 yrs) completed 30 min of resistance-matched cycle exercise in three separate conditions; non-immersion (Land), 32 °C and 38 °C water immersion up to the level of the waist. Middle cerebral artery velocity (MCAv), blood pressure, and respiratory measures were assessed throughout the exercise bouts. RESULTS Core temperature was significantly higher in the 38 °C immersion than 32 °C (+ 0.84 ± 0.24 vs + 0.04 ± 0.16, P < 0.001), whilst mean arterial pressure was lower during 38 °C exercise compared to Land (84 ± 8 vs 100 ± 14 mmHg, P < 0.001) and 32 °C (92 ± 9, P = 0.03). MCAv was higher in 32 °C immersion compared to the Land and 38 °C conditions throughout the exercise bout (68 ± 10 vs 64 ± 11 vs 62 ± 12 cm/s, P = 0.03 and P = 0.02, respectively). CONCLUSION Our findings suggest that cycle exercise in warm water attenuates the beneficial impact of water immersion on CBF velocity due to redistribution of blood flow to subserve thermoregulatory demand. Our findings suggest that, whilst water-based exercise can have beneficial effects on cerebrovascular function, water temperature is a key determinant of this benefit.
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Affiliation(s)
- Howard H Carter
- School of Sport Science, Exercise and Health, The University of Western Australia, Crawley, WA, 6009, Canada
| | - Oliver Pienaar
- School of Sport Science, Exercise and Health, The University of Western Australia, Crawley, WA, 6009, Canada
| | - Alexander Coleman
- School of Sport Science, Exercise and Health, The University of Western Australia, Crawley, WA, 6009, Canada
| | - Jem L Cheng
- Department of Kinesiology, McMaster University, Hamilton, ON, Canada
| | | | - Louise H Naylor
- School of Sport Science, Exercise and Health, The University of Western Australia, Crawley, WA, 6009, Canada
| | - Daniel J Green
- School of Sport Science, Exercise and Health, The University of Western Australia, Crawley, WA, 6009, Canada.
- School of Humans Sciences (M408), 35 Stirling Highway, Crawley, Perth, WA, 6009, Canada.
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Carr JMJR, Hoiland RL, Fernandes IA, Schrage WG, Ainslie PN. Recent insights into mechanisms of hypoxia-induced vasodilatation in the human brain. J Physiol 2023. [PMID: 37655827 DOI: 10.1113/jp284608] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2023] [Accepted: 08/07/2023] [Indexed: 09/02/2023] Open
Abstract
The cerebral vasculature manages oxygen delivery by adjusting arterial blood in-flow in the face of reductions in oxygen availability. Hypoxic cerebral vasodilatation, and the associated hypoxic cerebral blood flow reactivity, involve many vascular, erythrocytic and cerebral tissue mechanisms that mediate elevations in cerebral blood flow via micro- and macrovascular dilatation. This contemporary review focuses on in vivo human work - with reference to seminal preclinical work where necessary - on hypoxic cerebrovascular reactivity, particularly where recent advancements have been made. We provide updates with the following information: in humans, hypoxic cerebral vasodilatation is partially mediated via a - likely non-obligatory - combination of: (1) nitric oxide synthases, (2) deoxygenation-coupled S-nitrosothiols, (3) potassium channel-related vascular smooth muscle hyperpolarization, and (4) prostaglandin mechanisms with some contribution from an interrelationship with reactive oxygen species. And finally, we discuss the fact that, due to the engagement of deoxyhaemoglobin-related mechanisms, reductions in O2 content via haemoglobin per se seem to account for ∼50% of that seen with hypoxic cerebral vasodilatation during hypoxaemia. We further highlight the issue that methodological impediments challenge the complete elucidation of hypoxic cerebral reactivity mechanisms in vivo in healthy humans. Future research is needed to confirm recent advancements and to reconcile human and animal findings. Further investigations are also required to extend these findings to address questions of sex-, heredity-, age-, and disease-related differences. The final step is to then ultimately translate understanding of these mechanisms into actionable, targetable pathways for the prevention and treatment of cerebral vascular dysfunction and cerebral hypoxic brain injury.
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Affiliation(s)
- Jay M J R Carr
- Centre for Heart, Lung and Vascular Health, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Ryan L Hoiland
- Department of Anesthesiology, Pharmacology and Therapeutics, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, British Columbia, Canada
- Collaborative Entity for Researching Brain Ischemia (CEREBRI), University of British Columbia, Vancouver, British Columbia, Canada
| | - Igor A Fernandes
- Department of Health and Kinesiology, Purdue University, Indiana, USA
| | - William G Schrage
- Department of Kinesiology, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
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Saha PS, Knecht TM, Arrick DM, Watt MJ, Scholl JL, Mayhan WG. Prenatal exposure to alcohol impairs responses of cerebral arterioles to activation of potassium channels: Role of oxidative stress. ALCOHOL, CLINICAL & EXPERIMENTAL RESEARCH 2023; 47:87-94. [PMID: 36446735 PMCID: PMC9974881 DOI: 10.1111/acer.14980] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Revised: 10/24/2022] [Accepted: 11/17/2022] [Indexed: 11/23/2022]
Abstract
BACKGROUND Potassium channels play an important role in the basal tone and dilation of cerebral resistance arterioles in response to many stimuli. However, the effect of prenatal alcohol exposure (PAE) on specific potassium channel function remains unknown. The first goal of this study was to determine the influence of PAE on the reactivity of cerebral arterioles to activation of ATP-sensitive potassium (KATP ) and BK channels. Our second goal was to determine whether oxidative stress contributed to potassium channel dysfunction of cerebral arterioles following PAE. METHODS We fed Sprague-Dawley dams a liquid diet with or without alcohol (3% EtOH) for the duration of their pregnancy (21 to 23 days). We examined in vivo responses of cerebral arterioles in control and PAE male and female offspring (14 to 16 weeks after birth) to activators of potassium channels (Iloprost [BK channels] and pinacidil [KATP channels]), before and following inhibition of oxidative stress with apocynin. RESULTS We found that PAE impaired dilation of cerebral arterioles in response to activation of potassium channels with iloprost and pinacidil, and this impairment was similar in male and female rats. In addition, treatment with apocynin reversed the impaired vasodilation to iloprost and pinacidil in PAE rats to levels observed in control rats. This effect of apocynin also was similar in male and female rats. CONCLUSIONS PAE induces dysfunction in the ability of specific potassium channels to dilate cerebral arterioles which appears to be mediated by an increase in oxidative stress. We suggest that these alterations in potassium channel function may contribute to the pathogenesis of cerebral vascular abnormalities and/or behavioral/cognitive deficits observed in fetal alcohol spectrum disorders.
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Affiliation(s)
- Partha S. Saha
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069
| | - Tiffany M. Knecht
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069
| | - Denise M. Arrick
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069
| | - Michael J. Watt
- Department of Anatomy, University of Otago, Dunedin, New Zealand
| | - Jamie L. Scholl
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069
| | - William G. Mayhan
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069
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Morse CJ, Boerman EM, McDonald MW, Padilla J, Olver TD. The role of nitric oxide in flow-induced and myogenic responses in 1A, 2A, and 3A branches of the porcine middle cerebral artery. J Appl Physiol (1985) 2022; 133:1228-1236. [PMID: 36227166 PMCID: PMC9715271 DOI: 10.1152/japplphysiol.00209.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2022] [Revised: 09/13/2022] [Accepted: 10/09/2022] [Indexed: 12/15/2022] Open
Abstract
Myogenic and flow-induced reactivity contribute to cerebral autoregulation, with potentially divergent roles for smaller versus larger arteries. The present study tested the hypotheses that compared with first-order (1A) branches of the middle cerebral artery, second- and third-order branches (2A and 3A, respectively) exhibit greater myogenic reactivity but reduced flow-induced constriction. Furthermore, nitric oxide synthase (NOS) inhibition may amplify myogenic reactivity and abolish instances of flow-induced dilation. Isolated porcine cerebral arteries mounted in a pressure myograph were exposed to incremental increases in intraluminal pressure (40-120 mmHg; n = 41) or flow (1-1,170 µL/min; n = 31). Intraluminal flows were adjusted to achieve 5, 10, 20, and 40 dyn/cm2 of wall shear stress at 60 mmHg. Myogenic tone was greater in 3A versus 1A arteries (P < 0.05). There was an inverse relationship between myogenic reactivity and passive arterial diameter (P < 0.01). NOS inhibition increased basal tone to a lesser extent in 3A versus 1A arteries (P < 0.01) but did not influence myogenic reactivity (P = 0.49). Increasing flow decreased luminal diameter (P ≤ 0.01), with increased vasoconstriction at 10-40 dyn/cm2 of shear stress (P < 0.01). However, relative responses were similar between 1A, 2A, and 3A arteries (P = 0.40) with and without NOS inhibition conditions (P ≥ 0.29). Whereas NOS inhibition increases basal myogenic tone, and myogenic reactivity was less in smaller versus larger arteries (range = ∼100-550 µM), neither NOS inhibition nor luminal diameter influences flow-induced constriction in porcine cerebral arteries.NEW & NOTEWORTHY This study demonstrated size-dependent heterogeneity in myogenic reactivity in porcine cerebral arteries. Smaller branches of the middle cerebral artery exhibited increased myogenic reactivity, but attenuated NOS-dependent increases in myogenic tone compared with larger branches. Flow-dependent regulation does not exhibit the same variation; diameter-independent flow-induced vasoconstrictions occur across all branch orders and are not affected by NOS inhibition. Conceptually, flow-induced vasoconstriction contributes to cerebral autoregulation, particularly in larger arteries with low myogenic tone.
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Affiliation(s)
- Cameron J Morse
- Department Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Erika M Boerman
- Department Medical Physiology and Pharmacology, University of Missouri, Columbia, Missouri
| | - Matthew W McDonald
- Department Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Jaume Padilla
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri
- Department Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - T Dylan Olver
- Department Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
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Hoiland RL, Caldwell HG, Carr JMJR, Howe CA, Stacey BS, Dawkins T, Wakeham DJ, Tremblay JC, Tymko MM, Patrician A, Smith KJ, Sekhon MS, MacLeod DB, Green DJ, Bailey DM, Ainslie PN. Nitric oxide contributes to cerebrovascular shear-mediated dilatation but not steady-state cerebrovascular reactivity to carbon dioxide. J Physiol 2021; 600:1385-1403. [PMID: 34904229 DOI: 10.1113/jp282427] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Accepted: 12/07/2021] [Indexed: 12/15/2022] Open
Abstract
Cerebrovascular CO2 reactivity (CVR) is often considered a bioassay of cerebrovascular endothelial function. We recently introduced a test of cerebral shear-mediated dilatation (cSMD) that may better reflect endothelial function. We aimed to determine the nitric oxide (NO)-dependency of CVR and cSMD. Eleven volunteers underwent a steady-state CVR test and transient CO2 test of cSMD during intravenous infusion of the NO synthase inhibitor NG -monomethyl-l-arginine (l-NMMA) or volume-matched saline (placebo; single-blinded and counter-balanced). We measured cerebral blood flow (CBF; duplex ultrasound), intra-arterial blood pressure and P aC O 2 . Paired arterial and jugular venous blood sampling allowed for the determination of trans-cerebral NO2 - exchange (ozone-based chemiluminescence). l-NMMA reduced arterial NO2 - by ∼25% versus saline (74.3 ± 39.9 vs. 98.1 ± 34.2 nM; P = 0.03). The steady-state CVR (20.1 ± 11.6 nM/min at baseline vs. 3.2 ± 16.7 nM/min at +9 mmHg P aC O 2 ; P = 0.017) and transient cSMD tests (3.4 ± 5.9 nM/min at baseline vs. -1.8 ± 8.2 nM/min at 120 s post-CO2 ; P = 0.044) shifted trans-cerebral NO2 - exchange towards a greater net release (a negative value indicates release). Although this trans-cerebral NO2 - release was abolished by l-NMMA, CVR did not differ between the saline and l-NMMA trials (57.2 ± 14.6 vs. 54.1 ± 12.1 ml/min/mmHg; P = 0.49), nor did l-NMMA impact peak internal carotid artery dilatation during the steady-state CVR test (6.2 ± 4.5 vs. 6.2 ± 5.0% dilatation; P = 0.960). However, l-NMMA reduced cSMD by ∼37% compared to saline (2.91 ± 1.38 vs. 4.65 ± 2.50%; P = 0.009). Our findings indicate that NO is not an obligatory regulator of steady-state CVR. Further, our novel transient CO2 test of cSMD is largely NO-dependent and provides an in vivo bioassay of NO-mediated cerebrovascular function in humans. KEY POINTS: Emerging evidence indicates that a transient CO2 stimulus elicits shear-mediated dilatation of the internal carotid artery, termed cerebral shear-mediated dilatation. Whether or not cerebrovascular reactivity to a steady-state CO2 stimulus is NO-dependent remains unclear in humans. During both a steady-state cerebrovascular reactivity test and a transient CO2 test of cerebral shear-mediated dilatation, trans-cerebral nitrite exchange shifted towards a net release indicating cerebrovascular NO production; this response was not evident following intravenous infusion of the non-selective NO synthase inhibitor NG -monomethyl-l-arginine. NO synthase blockade did not alter cerebrovascular reactivity in the steady-state CO2 test; however, cerebral shear-mediated dilatation following a transient CO2 stimulus was reduced by ∼37% following intravenous infusion of NG -monomethyl-l-arginine. NO is not obligatory for cerebrovascular reactivity to CO2 , but is a key contributor to cerebral shear-mediated dilatation.
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Affiliation(s)
- Ryan L Hoiland
- Department of Anesthesiology, Pharmacology and Therapeutics, Faculty of Medicine, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada.,Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada.,Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.,International Collaboration on Repair Discoveries (ICORD), University of British Columbia, Vancouver, British Columbia, Canada
| | - Hannah G Caldwell
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Jay M J R Carr
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Connor A Howe
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Benjamin S Stacey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Tony Dawkins
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, UK
| | - Denis J Wakeham
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, UK
| | - Joshua C Tremblay
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Michael M Tymko
- Neurovascular Health Laboratory, University of Alberta, Edmonton, Alberta, Canada
| | - Alexander Patrician
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Kurt J Smith
- Integrative Physiology Laboratory, Department of Kinesiology and Nutrition, College of Applied Health Sciences, University of Illinois, Chicago, IL, USA.,Cerebrovascular Health, Exercise, and Environmental Research Science (CHEERS) Laboratory, School of Exercise Science, Physical and Health Education, Faculty of Education, University of Victoria, Victoria, British Columbia, Canada
| | - Mypinder S Sekhon
- Division of Critical Care Medicine, Department of Medicine, Faculty of Medicine, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada
| | - David B MacLeod
- Human Pharmacology and Physiology Lab, Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA
| | - Daniel J Green
- School of Human Sciences (Exercise and Sport Sciences), University of Western Australia, Nedlands, Western Australia, Australia
| | - Damian M Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Philip N Ainslie
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
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Caldwell HG, Carr JMJR, Minhas JS, Swenson ER, Ainslie PN. Acid-base balance and cerebrovascular regulation. J Physiol 2021; 599:5337-5359. [PMID: 34705265 DOI: 10.1113/jp281517] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Accepted: 10/19/2021] [Indexed: 12/22/2022] Open
Abstract
The regulation and defence of intracellular pH is essential for homeostasis. Indeed, alterations in cerebrovascular acid-base balance directly affect cerebral blood flow (CBF) which has implications for human health and disease. For example, changes in CBF regulation during acid-base disturbances are evident in conditions such as chronic obstructive pulmonary disease and diabetic ketoacidosis. The classic experimental studies from the past 75+ years are utilized to describe the integrative relationships between CBF, carbon dioxide tension (PCO2 ), bicarbonate (HCO3 - ) and pH. These factors interact to influence (1) the time course of acid-base compensatory changes and the respective cerebrovascular responses (due to rapid exchange kinetics between arterial blood, extracellular fluid and intracellular brain tissue). We propose that alterations in arterial [HCO3 - ] during acute respiratory acidosis/alkalosis contribute to cerebrovascular acid-base regulation; and (2) the regulation of CBF by direct changes in arterial vs. extravascular/interstitial PCO2 and pH - the latter recognized as the proximal compartment which alters vascular smooth muscle cell regulation of CBF. Taken together, these results substantiate two key ideas: first, that the regulation of CBF is affected by the severity of metabolic/respiratory disturbances, including the extent of partial/full acid-base compensation; and second, that the regulation of CBF is independent of arterial pH and that diffusion of CO2 across the blood-brain barrier is integral to altering perivascular extracellular pH. Overall, by realizing the integrative relationships between CBF, PCO2 , HCO3 - and pH, experimental studies may provide insights to improve CBF regulation in clinical practice with treatment of systemic acid-base disorders.
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Affiliation(s)
- Hannah G Caldwell
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan, Kelowna, Canada
| | - Jay M J R Carr
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan, Kelowna, Canada
| | - Jatinder S Minhas
- Cerebral Haemodynamics in Ageing and Stroke Medicine (CHiASM) Research Group, NIHR Leicester Biomedical Research Centre, University of Leicester, Leicester, UK
| | - Erik R Swenson
- Pulmonary, Critical Care and Sleep Medicine Division, University of Washington, and VA Puget Sound Healthcare System, Seattle, WA, USA
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan, Kelowna, Canada
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Claassen JAHR, Thijssen DHJ, Panerai RB, Faraci FM. Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation. Physiol Rev 2021; 101:1487-1559. [PMID: 33769101 PMCID: PMC8576366 DOI: 10.1152/physrev.00022.2020] [Citation(s) in RCA: 289] [Impact Index Per Article: 96.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Brain function critically depends on a close matching between metabolic demands, appropriate delivery of oxygen and nutrients, and removal of cellular waste. This matching requires continuous regulation of cerebral blood flow (CBF), which can be categorized into four broad topics: 1) autoregulation, which describes the response of the cerebrovasculature to changes in perfusion pressure; 2) vascular reactivity to vasoactive stimuli [including carbon dioxide (CO2)]; 3) neurovascular coupling (NVC), i.e., the CBF response to local changes in neural activity (often standardized cognitive stimuli in humans); and 4) endothelium-dependent responses. This review focuses primarily on autoregulation and its clinical implications. To place autoregulation in a more precise context, and to better understand integrated approaches in the cerebral circulation, we also briefly address reactivity to CO2 and NVC. In addition to our focus on effects of perfusion pressure (or blood pressure), we describe the impact of select stimuli on regulation of CBF (i.e., arterial blood gases, cerebral metabolism, neural mechanisms, and specific vascular cells), the interrelationships between these stimuli, and implications for regulation of CBF at the level of large arteries and the microcirculation. We review clinical implications of autoregulation in aging, hypertension, stroke, mild cognitive impairment, anesthesia, and dementias. Finally, we discuss autoregulation in the context of common daily physiological challenges, including changes in posture (e.g., orthostatic hypotension, syncope) and physical activity.
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Affiliation(s)
- Jurgen A H R Claassen
- Department of Geriatrics, Radboud University Medical Center, Donders Institute for Brain, Cognition, and Behaviour, Nijmegen, The Netherlands
| | - Dick H J Thijssen
- Department of Physiology, Radboud Institute for Health Sciences, Nijmegen, The Netherlands
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom
| | - Ronney B Panerai
- Department of Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom
- >National Institute for Health Research Leicester Biomedical Research Centre, University of Leicester, Leicester, United Kingdom
| | - Frank M Faraci
- Departments of Internal Medicine, Neuroscience, and Pharmacology, Carver College of Medicine, University of Iowa, Iowa City, Iowa
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9
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Caldwell HG, Howe CA, Hoiland RL, Carr JMJR, Chalifoux CJ, Brown CV, Patrician A, Tremblay JC, Panerai RB, Robinson TG, Minhas JS, Ainslie PN. Alterations in arterial CO 2 rather than pH affect the kinetics of neurovascular coupling in humans. J Physiol 2021; 599:3663-3676. [PMID: 34107079 DOI: 10.1113/jp281615] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Accepted: 06/08/2021] [Indexed: 12/11/2022] Open
Abstract
KEY POINTS We investigated the influence of arterial P C O 2 ( P aC O 2 ) with and without acute experimental metabolic alkalosis on neurovascular coupling (NVC). We assessed stepwise iso-oxic alterations in P aC O 2 prior to and following intravenous NaHCO3 to acutely elevate arterial pH and [HCO3 - ]. The NVC response was not altered following NaHCO3 between stepwise P aC O 2 stages; therefore, NVC is acutely mediated by P aC O 2 rather than the prevailing arterial [H+ ]/pH. The NVC response was attenuated by 27-38% with -10 mmHg P aC O 2 and the absolute peak change was reduced by -19% with +10 mmHg P aC O 2 irrespective of acutely elevated arterial pH/[HCO3 - ]. The NVC kinetics (i.e. time to peak) were markedly slower with hypercapnia versus hypocapnia (24 ± 5 vs. 7 ± 5 s, respectively) likely indicating an influence of resting cerebrovascular tone on NVC responsiveness. ABSTRACT Elevations in cerebral metabolism necessitate appropriate coordinated and localized increases in cerebral blood flow (i.e. neurovascular coupling; NVC). Recent pre-clinical work indicates that arterial P C O 2 ( P aC O 2 ) mediates NVC independently of arterial/extracellular pH; this has yet to be experimentally tested in humans. The goal of this study was to investigate the hypotheses that: (1) the NVC response would be unaffected by acute experimentally elevated arterial pH; rather, P aC O 2 would regulate any changes in NVC; and (2) stepwise respiratory alkalosis and acidosis would each progressively reduce the NVC response. Ten healthy males completed a standardized visual stimulus-evoked NVC test during matched stepwise iso-oxic alterations in P aC O 2 (hypocapnia: -5, -10 mmHg; hypercapnia: +5, +10 mmHg) prior to and following intravenous NaHCO3 (8.4%, 50 mEq/50 ml) that elevated arterial pH (7.406 ± 0.019 vs. 7.457 ± 0.029; P < 0.001) and [HCO3 - ] (26.2 ± 1.5 vs. 29.3 ± 0.9 mEq/l; P < 0.001). Although the NVC response was collectively attenuated by 27-38% with -10 mmHg P aC O 2 (stage post hoc: all P < 0.05), this response was unaltered following NaHCO3 (all P > 0.05) irrespective of the higher pH (P = 0.002) at each matched stage of P aC O 2 (P = 0.417). The absolute peak change was reduced by -19 ± 41% with +10 mmHg P aC O 2 irrespective of acutely elevated arterial pH/[HCO3 - ] (stage post hoc: P = 0.022). The NVC kinetics (i.e. time to peak) were markedly slower with hypercapnia versus hypocapnia (24 ± 5 vs. 7 ± 5 s, respectively; stage effect: P < 0.001). Overall, these findings indicate that temporal patterns in NVC are acutely regulated by P aC O 2 rather than arterial pH per se in the setting of acute metabolic alkalosis in humans.
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Affiliation(s)
- Hannah G Caldwell
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada
| | - Connor A Howe
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada
| | - Ryan L Hoiland
- Department of Anesthesiology, Pharmacology, and Therapeutics, Vancouver General Hospital, West 12th Avenue, University of British Columbia, Vancouver, BC, V5Z 1M9, Canada.,Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | - Jay M J R Carr
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada
| | - Carter J Chalifoux
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada
| | - Courtney V Brown
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada
| | - Alexander Patrician
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada
| | - Joshua C Tremblay
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada
| | - Ronney B Panerai
- Cerebral Haemodynamics in Ageing and Stroke Medicine (CHiASM) Research Group, Leicester Biomedical Research Centre, University of Leicester, Leicester, UK
| | - Thompson G Robinson
- Cerebral Haemodynamics in Ageing and Stroke Medicine (CHiASM) Research Group, Leicester Biomedical Research Centre, University of Leicester, Leicester, UK
| | - Jatinder S Minhas
- Cerebral Haemodynamics in Ageing and Stroke Medicine (CHiASM) Research Group, Leicester Biomedical Research Centre, University of Leicester, Leicester, UK
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada
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Carr JMJR, Caldwell HG, Ainslie PN. Cerebral blood flow, cerebrovascular reactivity and their influence on ventilatory sensitivity. Exp Physiol 2021; 106:1425-1448. [PMID: 33932955 DOI: 10.1113/ep089446] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2021] [Accepted: 04/26/2021] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the topic of this review? Cerebrovascular reactivity to CO2 , which is a principal factor in determining ventilatory responses to CO2 through the role reactivity plays in determining cerebral extra- and intracellular pH. What advances does it highlight? Recent animal evidence suggests central chemoreceptor vasculature may demonstrate regionally heterogeneous cerebrovascular reactivity to CO2 , potentially as a protective mechanism against excessive CO2 washout from the central chemoreceptors, thereby allowing ventilation to reflect the systemic acid-base balance needs (respiratory changes in P aC O 2 ) rather than solely the cerebral needs. Ventilation per se does not influence cerebrovascular reactivity independent of changes in P aC O 2 . ABSTRACT Alveolar ventilation and cerebral blood flow are both predominantly regulated by arterial blood gases, especially arterial P C O 2 , and so are intricately entwined. In this review, the fundamental mechanisms underlying cerebrovascular reactivity and central chemoreceptor control of breathing are covered. We discuss the interaction of cerebral blood flow and its reactivity with the control of ventilation and ventilatory responsiveness to changes in P C O 2 , as well as the lack of influence of ventilation itself on cerebrovascular reactivity. We briefly summarize the effects of arterial hypoxaemia on the relationship between ventilatory and cerebrovascular response to both P C O 2 and P O 2 . We then highlight key methodological considerations regarding the interaction of reactivity and ventilatory sensitivity, including the following: regional heterogeneity of cerebrovascular reactivity; a pharmacological approach for the reduction of cerebral blood flow; reactivity assessment techniques; the influence of mean arterial blood pressure; and sex-related differences. Finally, we discuss ventilatory and cerebrovascular control in the context of high altitude and congestive heart failure. Future research directions and pertinent questions of interest are highlighted throughout.
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Affiliation(s)
- Jay M J R Carr
- Centre for Heart, Lung and Vascular Health, University of British Columbia - Okanagan Campus, British Columbia, Canada
| | - Hannah G Caldwell
- Centre for Heart, Lung and Vascular Health, University of British Columbia - Okanagan Campus, British Columbia, Canada
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, University of British Columbia - Okanagan Campus, British Columbia, Canada
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Green DJ, Smith K, Maslen BA, Cox KL, Lautenschlager NT, Pestell CF, Naylor LH, Ainslie PN, Carter HH. The Impact of 6-Month Land versus Water Walking on Cerebrovascular Function in the Aging Brain. Med Sci Sports Exerc 2021; 53:2093-2100. [PMID: 33867500 DOI: 10.1249/mss.0000000000002685] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
INTRODUCTION To examine the hypothesis that exercise training induces adaptation in cerebrovascular function, we recruited 63 older adults (62 ± 7 yr, 46 females) to undertake 24 wk of either land walking or water walking, or participate in a nonexercise control group. This is the first multi-interventional study to perform a comprehensive assessment of cerebrovascular function in response to longer term (6-month) training interventions, including water-based exercise, in older healthy individuals. METHODS Intracranial blood flow velocities (middle cerebral artery (MCAv) and posterior cerebral artery) were assessed at rest and in response to neurovascular coupling, hypercapnic reactivity, and cerebral autoregulation. RESULTS We observed no change in resting MCAv in response to either training intervention (pre vs post, mean (95% confidence interval), land walking: 65 (59-70) to 63 (57-68) cm·s-1, P = 0.33; water walking: 63 (58-69) to 61 (55-67) cm·s-1, P = 0.92) compared with controls and no change in neurovascular coupling (land walking: P = 0.18, water walking: P = 0.17). There was a significant but modest improvement in autoregulatory normalized gain after the intervention in the water-walking compared with the land-walking group (P = 0.03). Hypercapnic MCAv reactivity was not different based on exercise group (land: P = 087, water: P = 0.83); however, when data were pooled from the exercise groups, increases in fitness were correlated with decreases in hypercapnic reactivity (r2 = 0.25, P = 0.003). CONCLUSIONS Although exercise was not associated with systematic changes across multiple domains of cerebrovascular function, our data indicate that exercise may induce modest changes in autoregulation and CO2 reactivity. These findings should encourage further studies of the longer-term implications of exercise training on cerebrovascular health.
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Affiliation(s)
- Daniel J Green
- School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Perth, WA, AUSTRALIA
| | - Kurt Smith
- School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Perth, WA, AUSTRALIA
| | - Barbara A Maslen
- School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Perth, WA, AUSTRALIA
| | | | | | - Carmela F Pestell
- School of Psychological Science, University of Western Australia, Perth, WA, AUSTRALIA
| | - Louise H Naylor
- School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Perth, WA, AUSTRALIA
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, British Columbia, CANADA
| | - Howard H Carter
- School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Perth, WA, AUSTRALIA
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Caldwell HG, Howe CA, Chalifoux CJ, Hoiland RL, Carr JMJR, Brown CV, Patrician A, Tremblay JC, Panerai RB, Robinson TG, Minhas JS, Ainslie PN. Arterial carbon dioxide and bicarbonate rather than pH regulate cerebral blood flow in the setting of acute experimental metabolic alkalosis. J Physiol 2021; 599:1439-1457. [DOI: 10.1113/jp280682] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2020] [Accepted: 12/14/2020] [Indexed: 12/11/2022] Open
Affiliation(s)
- Hannah G. Caldwell
- Centre for Heart, Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Connor A. Howe
- Centre for Heart, Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Carter J. Chalifoux
- Centre for Heart, Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Ryan L. Hoiland
- Department of Anesthesiology Pharmacology and Therapeutics Vancouver General Hospital University of British Columbia Vancouver BC Canada
- Department of Cellular and Physiological Sciences University of British Columbia Vancouver BC Canada
| | - Jay M. J. R. Carr
- Centre for Heart, Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Courtney V. Brown
- Centre for Heart, Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Alexander Patrician
- Centre for Heart, Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Joshua C. Tremblay
- Centre for Heart, Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Ronney B. Panerai
- Cerebral Haemodynamics in Ageing and Stroke Medicine (CHIASM) Research Group Leicester Biomedical Research Centre University of Leicester Leicester UK
| | - Thompson G. Robinson
- Cerebral Haemodynamics in Ageing and Stroke Medicine (CHIASM) Research Group Leicester Biomedical Research Centre University of Leicester Leicester UK
| | - Jatinder S. Minhas
- Cerebral Haemodynamics in Ageing and Stroke Medicine (CHIASM) Research Group Leicester Biomedical Research Centre University of Leicester Leicester UK
| | - Philip N. Ainslie
- Centre for Heart, Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
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Carr JMJR, Hoiland RL, Caldwell HG, Coombs GB, Howe CA, Tremblay JC, Green DJ, Ainslie PN. Internal carotid and brachial artery shear‐dependent vasodilator function in young healthy humans. J Physiol 2020; 598:5333-5350. [DOI: 10.1113/jp280369] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Accepted: 09/07/2020] [Indexed: 12/12/2022] Open
Affiliation(s)
- Jay M. J. R. Carr
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia – Okanagan Campus Kelowna British Columbia Canada
| | - Ryan L. Hoiland
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia – Okanagan Campus Kelowna British Columbia Canada
- Department of Anesthesiology Pharmacology and Therapeutics Vancouver General Hospital University of British Columbia Vancouver British Columbia Canada
| | - Hannah G. Caldwell
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia – Okanagan Campus Kelowna British Columbia Canada
| | - Geoff B. Coombs
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia – Okanagan Campus Kelowna British Columbia Canada
| | - Connor A. Howe
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia – Okanagan Campus Kelowna British Columbia Canada
| | - Joshua C. Tremblay
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia – Okanagan Campus Kelowna British Columbia Canada
| | - Daniel J. Green
- School of Human Sciences (Sport and Exercise Sciences) The University of Western Australia Crawley Western Australia Australia
| | - Philip N. Ainslie
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia – Okanagan Campus Kelowna British Columbia Canada
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Iwamoto E, Hanson BE, Bock JM, Casey DP. Intermittent hypoxia enhances shear-mediated dilation of the internal carotid artery in young adults. J Appl Physiol (1985) 2020; 129:603-611. [DOI: 10.1152/japplphysiol.00274.2020] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
We explored the effects of cyclic intermittent hypoxia (IH) on shear-mediated dilation of the internal carotid artery (ICA), a potential index of cerebral endothelial function, in young adults. Cyclic IH increased blood flow and shear rate in the ICA and, as a result, increased shear-mediated dilation of the ICA. These data suggest that cyclic IH could potentially be applied as a nonpharmacological therapy to optimize cerebral vascular health.
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Affiliation(s)
- Erika Iwamoto
- Human Integrative and Cardiovascular Physiology Laboratory, Department of Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, Iowa
- School of Health Sciences, Sapporo Medical University, Sapporo, Japan
| | - Brady E. Hanson
- Human Integrative and Cardiovascular Physiology Laboratory, Department of Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, Iowa
| | - Joshua M. Bock
- Human Integrative and Cardiovascular Physiology Laboratory, Department of Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, Iowa
| | - Darren P. Casey
- Human Integrative and Cardiovascular Physiology Laboratory, Department of Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, Iowa
- Abboud Cardiovascular Research Center, University of Iowa, Iowa City, Iowa
- Fraternal Order of Eagles Diabetes Research Center, Carver College of Medicine, University of Iowa, Iowa City, Iowa
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15
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Sancho M, Welsh DG. K IR channels in the microvasculature: Regulatory properties and the lipid-hemodynamic environment. CURRENT TOPICS IN MEMBRANES 2020; 85:227-259. [PMID: 32402641 DOI: 10.1016/bs.ctm.2020.01.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
Abstract
Basal tone and perfusion control is set in cerebral arteries by the sensing of pressure and flow, key hemodynamic stimuli. These forces establish a contractile foundation within arterial networks upon which local neurovascular stimuli operate. This fundamental process is intimately tied to arterial VM and the rise in cytosolic [Ca2+] by the graded opening of voltage-operated Ca2+ channels. Arterial VM is in turn controlled by a dynamic interaction among several resident ion channels, KIR being one of particular significance. As the name suggests, KIR displays strong inward rectification, retains a small outward component, potentiated by extracellular K+ and blocked by micromolar Ba2+. Cerebrovascular KIR is unique from other K+ currents as it is present in both smooth muscle and endothelium yet lacking in classical regulatory modulation. Such observations have fostered the view that KIR is nothing more than a background conductance, activated by extracellular K+ and which passively facilitates dilation. Recent work in cell model systems has; however, identified two membrane lipids, phosphatidylinositol 4,5-bisphosphate (PIP2) and cholesterol, that interact with KIR2.x, to stabilize the channel in the preferred open or silent state, respectively. Translating this unique form of regulation, recent studies have demonstrated that specific lipid-protein interactions enable unique KIR populations to sense distinct hemodynamic stimuli and set basal tone. This review summarizes the current knowledge of vascular KIR channels and how the lipid and hemodynamic impact their activity.
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Affiliation(s)
- Maria Sancho
- Robarts Research Institute and the Department of Physiology & Pharmacology, University of Western Ontario, London, ON, Canada
| | - Donald G Welsh
- Robarts Research Institute and the Department of Physiology & Pharmacology, University of Western Ontario, London, ON, Canada.
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Karamian P, Burford J, Farzad S, Blair NP, Shahidi M. Alterations in Retinal Oxygen Delivery, Metabolism, and Extraction Fraction During Bilateral Common Carotid Artery Occlusion in Rats. Invest Ophthalmol Vis Sci 2019; 60:3247-3253. [PMID: 31343655 PMCID: PMC6660186 DOI: 10.1167/iovs.19-27227] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Purpose The purpose of the current study was to investigate alterations in retinal oxygen delivery, metabolism, and extraction fraction and elucidate their relationships in an experimental model of retinal ischemia. Methods We subjected 14 rats to permanent bilateral common carotid artery occlusion using clamp or suture ligation, or they underwent sham procedure. Within 30 minutes of the procedure, phosphorescence lifetime imaging was performed to measure retinal vascular oxygen tension and derive arterial and venous oxygen contents, and arteriovenous oxygen content difference. Fluorescent microsphere and red-free retinal imaging were performed to measure total retinal blood flow. Retinal oxygen delivery rate (DO2), oxygen metabolism rate (MO2), and oxygen extraction fraction (OEF) were calculated. Results DO2 and MO2 were lower in ligation and clamp groups compared to the sham group, and also lower in the ligation group compared to the clamp group (P ≤ 0.05). OEF was higher in the ligation group compared to clamp and sham groups (P ≤ 0.03). The relationships of MO2 and OEF with DO2 were mathematically modeled by exponential functions. With moderate DO2 reductions, OEF increased while MO2 minimally decreased. Under severe DO2 reductions, OEF reached a maximum value and subsequently MO2 decreased with DO2. Conclusions The findings improve knowledge of mechanisms that can maintain MO2 and may clarify the pathophysiology of retinal ischemic injury.
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Affiliation(s)
- Preny Karamian
- Department of Ophthalmology, University of Southern California, Los Angeles, California, United States
| | - James Burford
- Department of Ophthalmology, University of Southern California, Los Angeles, California, United States
| | - Shayan Farzad
- Department of Ophthalmology, University of Southern California, Los Angeles, California, United States
| | - Norman P Blair
- Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, Illinois, United States
| | - Mahnaz Shahidi
- Department of Ophthalmology, University of Southern California, Los Angeles, California, United States
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Abstract
Cerebral small vessel disease (SVD) is characterized by changes in the pial and parenchymal microcirculations. SVD produces reductions in cerebral blood flow and impaired blood-brain barrier function, which are leading contributors to age-related reductions in brain health. End-organ effects are diverse, resulting in both cognitive and noncognitive deficits. Underlying phenotypes and mechanisms are multifactorial, with no specific treatments at this time. Despite consequences that are already considerable, the impact of SVD is predicted to increase substantially with the growing aging population. In the face of this health challenge, the basic biology, pathogenesis, and determinants of SVD are poorly defined. This review summarizes recent progress and concepts in this area, highlighting key findings and some major unanswered questions. We focus on phenotypes and mechanisms that underlie microvascular aging, the greatest risk factor for cerebrovascular disease and its subsequent effects.
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Affiliation(s)
- T Michael De Silva
- Department of Physiology, Anatomy and Microbiology, School of Life Sciences, La Trobe University, Melbourne Campus, Bundoora, Victoria 3086, Australia;
| | - Frank M Faraci
- Departments of Internal Medicine, Neuroscience, and Pharmacology, Francois M. Abboud Cardiovascular Center, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA;
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18
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Hoiland RL, Fisher JA, Ainslie PN. Regulation of the Cerebral Circulation by Arterial Carbon Dioxide. Compr Physiol 2019; 9:1101-1154. [DOI: 10.1002/cphy.c180021] [Citation(s) in RCA: 101] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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19
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Smith KJ, Hoiland RL, Grove R, McKirdy H, Naylor L, Ainslie PN, Green DJ. Matched increases in cerebral artery shear stress, irrespective of stimulus, induce similar changes in extra-cranial arterial diameter in humans. J Cereb Blood Flow Metab 2019; 39:849-858. [PMID: 29125372 PMCID: PMC6501503 DOI: 10.1177/0271678x17739220] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The mechanistic role of arterial shear stress in the regulation of cerebrovascular responses to physiological stimuli (exercise and hypercapnia) is poorly understood. We hypothesised that, if shear stress is a key regulator of arterial dilation, then matched increases in shear, induced by distinct physiological stimuli, would trigger similar dilation of the large extra-cranial arteries. Participants ( n = 10) participated in three 30-min experimental interventions, each separated by ≥48 h: (1) mild-hypercapnia (FICO2:∼0.045); (2) submaximal cycling (EX; 60%HRreserve); or (3) resting (time-matched control, CTRL). Blood flow, diameter, and shear rate were assessed (via Duplex ultrasound) in the internal carotid and vertebral arteries (ICA, VA) at baseline, during and following the interventions. Hypercapnia and EX produced similar elevations in blood flow and shear rate through the ICA and VA ( p < 0.001), which were both greater than CTRL. Vasodilation of ICA and VA diameter in response to hypercapnia (5.3 ± 0.8 and 4.4 ± 2.0%) and EX (4.7 ± 0.7 and 4.7 ± 2.2%) were similar, and greater than CTRL ( p < 0.001). Our findings indicate that matched levels of shear, irrespective of their driving stimulus, induce similar extra-cranial artery dilation. We demonstrate, for the first time in humans, an important mechanistic role for the endothelium in regulating cerebrovascular response to common physiological stimuli in vivo.
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Affiliation(s)
- Kurt J Smith
- 1 Cardiovascular Research Group, School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Perth, Australia
| | - Ryan L Hoiland
- 2 Centre for Hearth Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Vancouver, BC, Canada
| | - Ryan Grove
- 1 Cardiovascular Research Group, School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Perth, Australia
| | - Hamish McKirdy
- 1 Cardiovascular Research Group, School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Perth, Australia
| | - Louise Naylor
- 1 Cardiovascular Research Group, School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Perth, Australia
| | - Philip N Ainslie
- 2 Centre for Hearth Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Vancouver, BC, Canada
| | - Daniel J Green
- 1 Cardiovascular Research Group, School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Perth, Australia.,3 Research Institute for Sport and Exercise Sciences, John Moores Liverpool University, UK
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Iwamoto E, Bock JM, Casey DP. Hypercapnia-induced shear-mediated dilation in the internal carotid artery is blunted in healthy older adults. Am J Physiol Heart Circ Physiol 2018; 315:H1279-H1286. [DOI: 10.1152/ajpheart.00335.2018] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
This study aimed to elucidate the effect of aging on shear-mediated dilation of the common and internal carotid arteries (CCA and ICA, respectively). Hypercapnia-induced shear-mediated dilation in the CCA and ICA were assessed in 10 young (5 women and 5 men, 23 ± 1 yr) and 10 older (6 women/4 men, 68 ± 1 yr) healthy adults. Shear-mediated dilation was induced by two levels of hypercapnia (target end-tidal Pco2, +5 and +10 mmHg from individual baseline values) and was calculated as the percent rise in peak diameter from baseline diameter. There were no differences in shear-mediated dilation between young and older adults in either artery under lower levels of hypercapnia (CCA: 2.8 ± 0.6 vs. 2.0 ± 0.3%, P = 0.35; ICA: 4.6 ± 0.8 vs 3.6 ± 0.4%, P = 0.37). However, shear-mediated dilation in response to higher levels of hypercapnia was attenuated in older compared with young adults in the ICA (4.5 ± 0.5 vs. 7.9 ± 1.2%, P < 0.01) but not in the CCA (3.7 ± 0.6 vs. 4.5 ± 0.8%, P = 0.35). Shear-mediated dilation was significantly correlated to the percent change in shear rate in the ICA (young: r = 0.55, P = 0.01; older: r = 0.49, P = 0.03) but not in the CCA in either young or older adults (young: r = −0.30, P = 0.90; older: r = 0.16, P = 0.50). These data indicate that aging attenuates shear-mediated dilation of the ICA in response to higher levels of hypercapnia, and shear rate is an important stimulus for hypercapnic vasodilation of the ICA in both young and older adults. The present results may provide insights into age-related changes in the regulation of cerebral circulation in healthy adults. NEW & NOTEWORTHY We explored the effect of aging on shear-mediated dilation in the common and internal carotid arteries (CCA and ICA, respectively) in healthy adults. Our findings suggest that 1) aging attenuates shear-mediated dilation of the ICA but not the CCA and 2) shear rate is an important stimulus for hypercapnic vasodilation of the ICA in young and older adults. These findings may provide insights into the age-related changes in cerebrovascular regulation of healthy adults.
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Affiliation(s)
- Erika Iwamoto
- Human Integrative and Cardiovascular Physiology Laboratory, Department of Physical Therapy and Rehabilitation Science, Carver College of Medicine, University of Iowa, Iowa City, Iowa
- School of Health Sciences, Sapporo Medical University, Sapporo, Japan
| | - Joshua M. Bock
- Human Integrative and Cardiovascular Physiology Laboratory, Department of Physical Therapy and Rehabilitation Science, Carver College of Medicine, University of Iowa, Iowa City, Iowa
| | - Darren P. Casey
- Human Integrative and Cardiovascular Physiology Laboratory, Department of Physical Therapy and Rehabilitation Science, Carver College of Medicine, University of Iowa, Iowa City, Iowa
- Abboud Cardiovascular Research Center, Carver College of Medicine, University of Iowa, Iowa City, Iowa
- Fraternal Order of Eagles Diabetes Research Center, Carver College of Medicine, University of Iowa, Iowa City, Iowa
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Tykocki NR, Boerman EM, Jackson WF. Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles. Compr Physiol 2017; 7:485-581. [PMID: 28333380 DOI: 10.1002/cphy.c160011] [Citation(s) in RCA: 212] [Impact Index Per Article: 30.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Vascular tone of resistance arteries and arterioles determines peripheral vascular resistance, contributing to the regulation of blood pressure and blood flow to, and within the body's tissues and organs. Ion channels in the plasma membrane and endoplasmic reticulum of vascular smooth muscle cells (SMCs) in these blood vessels importantly contribute to the regulation of intracellular Ca2+ concentration, the primary determinant of SMC contractile activity and vascular tone. Ion channels provide the main source of activator Ca2+ that determines vascular tone, and strongly contribute to setting and regulating membrane potential, which, in turn, regulates the open-state-probability of voltage gated Ca2+ channels (VGCCs), the primary source of Ca2+ in resistance artery and arteriolar SMCs. Ion channel function is also modulated by vasoconstrictors and vasodilators, contributing to all aspects of the regulation of vascular tone. This review will focus on the physiology of VGCCs, voltage-gated K+ (KV) channels, large-conductance Ca2+-activated K+ (BKCa) channels, strong-inward-rectifier K+ (KIR) channels, ATP-sensitive K+ (KATP) channels, ryanodine receptors (RyRs), inositol 1,4,5-trisphosphate receptors (IP3Rs), and a variety of transient receptor potential (TRP) channels that contribute to pressure-induced myogenic tone in resistance arteries and arterioles, the modulation of the function of these ion channels by vasoconstrictors and vasodilators, their role in the functional regulation of tissue blood flow and their dysfunction in diseases such as hypertension, obesity, and diabetes. © 2017 American Physiological Society. Compr Physiol 7:485-581, 2017.
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Affiliation(s)
- Nathan R Tykocki
- Department of Pharmacology, University of Vermont, Burlington, Vermont, USA
| | - Erika M Boerman
- Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri, USA
| | - William F Jackson
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan, USA
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Hu X, De Silva TM, Chen J, Faraci FM. Cerebral Vascular Disease and Neurovascular Injury in Ischemic Stroke. Circ Res 2017; 120:449-471. [PMID: 28154097 PMCID: PMC5313039 DOI: 10.1161/circresaha.116.308427] [Citation(s) in RCA: 256] [Impact Index Per Article: 36.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Revised: 10/13/2016] [Accepted: 10/26/2016] [Indexed: 12/13/2022]
Abstract
The consequences of cerebrovascular disease are among the leading health issues worldwide. Large and small cerebral vessel disease can trigger stroke and contribute to the vascular component of other forms of neurological dysfunction and degeneration. Both forms of vascular disease are driven by diverse risk factors, with hypertension as the leading contributor. Despite the importance of neurovascular disease and subsequent injury after ischemic events, fundamental knowledge in these areas lag behind our current understanding of neuroprotection and vascular biology in general. The goal of this review is to address select key structural and functional changes in the vasculature that promote hypoperfusion and ischemia, while also affecting the extent of injury and effectiveness of therapy. In addition, as damage to the blood-brain barrier is one of the major consequences of ischemia, we discuss cellular and molecular mechanisms underlying ischemia-induced changes in blood-brain barrier integrity and function, including alterations in endothelial cells and the contribution of pericytes, immune cells, and matrix metalloproteinases. Identification of cell types, pathways, and molecules that control vascular changes before and after ischemia may result in novel approaches to slow the progression of cerebrovascular disease and lessen both the frequency and impact of ischemic events.
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Affiliation(s)
- Xiaoming Hu
- Center of Cerebrovascular Disease Research, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213
| | - T. Michael De Silva
- Biomedicine Discovery Institute, Department of Pharmacology, 9 Ancora Imparo Way, Monash University, Clayton, Vic, Australia
| | - Jun Chen
- Center of Cerebrovascular Disease Research, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213
| | - Frank M. Faraci
- Departments of Internal Medicine and Pharmacology, Carver College of Medicine, University of Iowa, Iowa City Veterans Affairs Healthcare System, Iowa City, IA, USA
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Raignault A, Bolduc V, Lesage F, Thorin E. Pulse pressure-dependent cerebrovascular eNOS regulation in mice. J Cereb Blood Flow Metab 2017; 37:413-424. [PMID: 26823473 PMCID: PMC5381440 DOI: 10.1177/0271678x16629155] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Arterial blood pressure is oscillatory; whether pulse pressure (PP) regulates cerebral artery myogenic tone (MT) and endothelial function is currently unknown. To test the impact of PP on MT and dilation to flow (FMD) or to acetylcholine (Ach), isolated pressurized mouse posterior cerebral arteries were subjected to either static pressure (SP) or a physiological PP (amplitude: 30 mm Hg; frequency: 550 bpm). Under PP, MT was significantly higher than in SP conditions ( p < 0.05) and was not affected by eNOS inhibition. In contrast, under SP, eNOS inhibition increased ( p < 0.05) MT to levels observed under PP, suggesting that PP may inhibit eNOS. At a shear stress of 20 dyn/cm2, FMD was lower ( p < 0.05) under SP than PP. Under SP, eNOS-dependent [Formula: see text] production contributed to FMD, while under PP, eNOS-dependent NO was responsible for FMD, indicating that PP favours eNOS coupling. Differences in FMD between pressure conditions were abolished after NOX2 inhibition. In contrast to FMD, Ach-induced dilations were higher ( p < 0.05) under SP than PP. Reactive oxygen species scavenging reduced ( p < 0.05) Ach-dependent dilations under SP, but increased ( p < 0.05) them under PP; hence, under PP, Ach promotes ROS production and limits eNOS-derived NO activity. In conclusion, PP finely regulates eNOS, controlling cerebral artery reactivity.
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Affiliation(s)
- Adeline Raignault
- 1 Faculty of Medicine, Department of Pharmacology, Université de Montréal, Montreal, Quebec, Canada.,2 Montreal Heart Institute Research Center, Montreal, Quebec, Canada
| | - Virginie Bolduc
- 1 Faculty of Medicine, Department of Pharmacology, Université de Montréal, Montreal, Quebec, Canada.,2 Montreal Heart Institute Research Center, Montreal, Quebec, Canada
| | - Frédéric Lesage
- 2 Montreal Heart Institute Research Center, Montreal, Quebec, Canada.,3 Ecole Polytechnique de Montréal, Montreal, Quebec, Canada
| | - Eric Thorin
- 1 Faculty of Medicine, Department of Pharmacology, Université de Montréal, Montreal, Quebec, Canada.,2 Montreal Heart Institute Research Center, Montreal, Quebec, Canada.,4 Faculty of Medicine, Department of Surgery, Université de Montréal, Montreal, Quebec, Canada
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Jensen LJ, Nielsen MS, Salomonsson M, Sørensen CM. T-type Ca 2+ channels and autoregulation of local blood flow. Channels (Austin) 2017; 11:183-195. [PMID: 28055302 DOI: 10.1080/19336950.2016.1273997] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
L-type voltage gated Ca2+ channels are considered to be the primary source of calcium influx during the myogenic response. However, many vascular beds also express T-type voltage gated Ca2+ channels. Recent studies suggest that these channels may also play a role in autoregulation. At low pressures (40-80 mmHg) T-type channels affect myogenic responses in cerebral and mesenteric vascular beds. T-type channels also seem to be involved in skeletal muscle autoregulation. This review discusses the expression and role of T-type voltage gated Ca2+ channels in the autoregulation of several different vascular beds. Lack of specific pharmacological inhibitors has been a huge challenge in the field. Now the research has been strengthened by genetically modified models such as mice lacking expression of T-type voltage gated Ca2+ channels (CaV3.1 and CaV3.2). Hopefully, these new tools will help further elucidate the role of voltage gated T-type Ca2+ channels in autoregulation and vascular function.
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Affiliation(s)
- Lars Jørn Jensen
- a Departments of Veterinary Clinical and Animal Sciences , University of Copenhagen , Copenhagen , Denmark
| | - Morten Schak Nielsen
- b Department of Biomedical Sciences, Faculty of Health and Medical Sciences , University of Copenhagen , Copenhagen , Denmark
| | - Max Salomonsson
- b Department of Biomedical Sciences, Faculty of Health and Medical Sciences , University of Copenhagen , Copenhagen , Denmark
| | - Charlotte Mehlin Sørensen
- b Department of Biomedical Sciences, Faculty of Health and Medical Sciences , University of Copenhagen , Copenhagen , Denmark
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McBryde FD, Malpas SC, Paton JFR. Intracranial mechanisms for preserving brain blood flow in health and disease. Acta Physiol (Oxf) 2017; 219:274-287. [PMID: 27172364 DOI: 10.1111/apha.12706] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Revised: 02/03/2016] [Accepted: 05/06/2016] [Indexed: 12/19/2022]
Abstract
The brain is an exceptionally energetically demanding organ with little metabolic reserve, and multiple systems operate to protect and preserve the brain blood supply. But how does the brain sense its own perfusion? In this review, we discuss how the brain may harness the cardiovascular system to counter threats to cerebral perfusion sensed via intracranial pressure (ICP), cerebral oxygenation and ischaemia. Since the work of Cushing over 100 years ago, the existence of brain baroreceptors capable of eliciting increases in sympathetic outflow and blood pressure has been hypothesized. In the clinic, this response has generally been thought to occur only in extremis, to perfuse the severely ischaemic brain as cerebral autoregulation fails. We review evidence that pressor responses may also occur with smaller, physiologically relevant increases in ICP. The incoming brain oxygen supply is closely monitored by the carotid chemoreceptors; however, hypoxia and other markers of ischaemia are also sensed intrinsically by astrocytes or other support cells within brain tissue itself and elicit reactive hyperaemia. Recent studies suggest that astrocytic oxygen signalling within the brainstem may directly affect sympathetic nerve activity and blood pressure. We speculate that local cerebral oxygen tension is a major determinant of the mean level of arterial pressure and discuss recent evidence that this may be the case. We conclude that intrinsic intra- and extra-cranial mechanisms sense and integrate information about hypoxia/ischaemia and ICP and play a major role in determining the long-term level of sympathetic outflow and arterial pressure, to optimize cerebral perfusion.
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Affiliation(s)
- F. D. McBryde
- Department of Physiology; Faculty of Medical and Health Sciences; University of Auckland; Auckland New Zealand
- School of Physiology, Pharmacology & Neuroscience; Biomedical Sciences; University of Bristol; Bristol UK
| | - S. C. Malpas
- Department of Physiology; Faculty of Medical and Health Sciences; University of Auckland; Auckland New Zealand
| | - J. F. R. Paton
- Department of Physiology; Faculty of Medical and Health Sciences; University of Auckland; Auckland New Zealand
- School of Physiology, Pharmacology & Neuroscience; Biomedical Sciences; University of Bristol; Bristol UK
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De Silva TM, Faraci FM. Reactive Oxygen Species and the Regulation of Cerebral Vascular Tone. STUDIES ON ATHEROSCLEROSIS 2017. [DOI: 10.1007/978-1-4899-7693-2_6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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Microvascular Dysfunction and Cognitive Impairment. Cell Mol Neurobiol 2016; 36:241-58. [PMID: 26988697 DOI: 10.1007/s10571-015-0308-1] [Citation(s) in RCA: 106] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2015] [Accepted: 11/19/2015] [Indexed: 12/18/2022]
Abstract
The impact of vascular risk factors on cognitive function has garnered much interest in recent years. The appropriate distribution of oxygen, glucose, and other nutrients by the cerebral vasculature is critical for proper cognitive performance. The cerebral microvasculature is a key site of vascular resistance and a preferential target for small vessel disease. While deleterious effects of vascular risk factors on microvascular function are known, the contribution of this dysfunction to cognitive deficits is less clear. In this review, we summarize current evidence for microvascular dysfunction in brain. We highlight effects of select vascular risk factors (hypertension, diabetes, and hyperhomocysteinemia) on the pial and parenchymal circulation. Lastly, we discuss potential links between microvascular disease and cognitive function, highlighting current gaps in our understanding.
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Tarumi T, Zhang R. Cerebral hemodynamics of the aging brain: risk of Alzheimer disease and benefit of aerobic exercise. Front Physiol 2014; 5:6. [PMID: 24478719 PMCID: PMC3896879 DOI: 10.3389/fphys.2014.00006] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2013] [Accepted: 01/05/2014] [Indexed: 11/17/2022] Open
Abstract
Alzheimer disease (AD) and cerebrovascular disease often coexist with advanced age. Mounting evidence indicates that the presence of vascular disease and its risk factors increase the risk of AD, suggesting a potential overlap of the underlying pathophysiological mechanisms. In particular, atherosclerosis, endothelial dysfunction, and stiffening of central elastic arteries have been shown to associate with AD. Currently, there are no effective treatments for the cure and prevention of AD. Vascular risk factors are modifiable via either pharmacological or lifestyle intervention. In this regard, habitual aerobic exercise is increasingly recognized for its benefits on brain structure and cognitive function. Considering the well-established benefits of regular aerobic exercise on vascular health, exercise-related improvements in brain structure and cognitive function may be mediated by vascular adaptations. In this review, we will present the current evidence for the physiological mechanisms by which vascular health alters the structural and functional integrity of the aging brain and how improvements in vascular health, via regular aerobic exercise, potentially benefits cognitive function.
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Affiliation(s)
- Takashi Tarumi
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas Dallas, TX, USA ; Department of Internal Medicine, University of Texas Southwestern Medical Center Dallas, TX, USA
| | - Rong Zhang
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas Dallas, TX, USA ; Department of Internal Medicine, University of Texas Southwestern Medical Center Dallas, TX, USA ; Department of Neurology and Neurotherapeutics, Alzheimer's Disease Center, University of Texas Southwestern Medical Center Dallas, TX, USA
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Abstract
The cerebrovascular regulation involves highly complex mechanisms to assure that the brain is perfused at all times. These mechanisms depend on all components of the neurovascular units: neurons, glia, and vascular cells. All these cell types can produce nitric oxide (NO), a powerful vasodilator through different NO synthases. Many studies underlined the key role of NO in the maintenance of resting cerebral blood flow (CBF) as well as in the mechanisms that control cerebrovascular tone: autoregulation and neurovascular coupling. However, although the role of NO in the control of CBF has been largely investigated, the complexity of the NO system and the lack of specific NO synthase inhibitors led to still unresolved questions such as the origin of NO and the pathways by which it controls the vascular tone. In this chapter, the role of NO in the regulation of CBF is critically reviewed and discussed in the context of the neurovascular unit and the general principles of cerebrovascular regulation.
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Laughlin MH, Davis MJ, Secher NH, van Lieshout JJ, Arce-Esquivel AA, Simmons GH, Bender SB, Padilla J, Bache RJ, Merkus D, Duncker DJ. Peripheral circulation. Compr Physiol 2013; 2:321-447. [PMID: 23728977 DOI: 10.1002/cphy.c100048] [Citation(s) in RCA: 174] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Blood flow (BF) increases with increasing exercise intensity in skeletal, respiratory, and cardiac muscle. In humans during maximal exercise intensities, 85% to 90% of total cardiac output is distributed to skeletal and cardiac muscle. During exercise BF increases modestly and heterogeneously to brain and decreases in gastrointestinal, reproductive, and renal tissues and shows little to no change in skin. If the duration of exercise is sufficient to increase body/core temperature, skin BF is also increased in humans. Because blood pressure changes little during exercise, changes in distribution of BF with incremental exercise result from changes in vascular conductance. These changes in distribution of BF throughout the body contribute to decreases in mixed venous oxygen content, serve to supply adequate oxygen to the active skeletal muscles, and support metabolism of other tissues while maintaining homeostasis. This review discusses the response of the peripheral circulation of humans to acute and chronic dynamic exercise and mechanisms responsible for these responses. This is accomplished in the context of leading the reader on a tour through the peripheral circulation during dynamic exercise. During this tour, we consider what is known about how each vascular bed controls BF during exercise and how these control mechanisms are modified by chronic physical activity/exercise training. The tour ends by comparing responses of the systemic circulation to those of the pulmonary circulation relative to the effects of exercise on the regional distribution of BF and mechanisms responsible for control of resistance/conductance in the systemic and pulmonary circulations.
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Affiliation(s)
- M Harold Laughlin
- Department of Medical Pharmacology and Physiology, and the Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, USA.
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Bolduc V, Thorin-Trescases N, Thorin E. Endothelium-dependent control of cerebrovascular functions through age: exercise for healthy cerebrovascular aging. Am J Physiol Heart Circ Physiol 2013; 305:H620-33. [PMID: 23792680 DOI: 10.1152/ajpheart.00624.2012] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Cognitive performances are tightly associated with the maximal aerobic exercise capacity, both of which decline with age. The benefits on mental health of regular exercise, which slows the age-dependent decline in maximal aerobic exercise capacity, have been established for centuries. In addition, the maintenance of an optimal cerebrovascular endothelial function through regular exercise, part of a healthy lifestyle, emerges as one of the key and primary elements of successful brain aging. Physical exercise requires the activation of specific brain areas that trigger a local increase in cerebral blood flow to match neuronal metabolic needs. In this review, we propose three ways by which exercise could maintain the cerebrovascular endothelial function, a premise to a healthy cerebrovascular function and an optimal regulation of cerebral blood flow. First, exercise increases blood flow locally and increases shear stress temporarily, a known stimulus for endothelial cell maintenance of Akt-dependent expression of endothelial nitric oxide synthase, nitric oxide generation, and the expression of antioxidant defenses. Second, the rise in circulating catecholamines during exercise not only facilitates adequate blood and nutrient delivery by stimulating heart function and mobilizing energy supplies but also enhances endothelial repair mechanisms and angiogenesis. Third, in the long term, regular exercise sustains a low resting heart rate that reduces the mechanical stress imposed to the endothelium of cerebral arteries by the cardiac cycle. Any chronic variation from a healthy environment will perturb metabolism and thus hasten endothelial damage, favoring hypoperfusion and neuronal stress.
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Affiliation(s)
- Virginie Bolduc
- Departments of Surgery and Pharmacology, Université de Montréal, and Centre de recherche, Montreal Heart Institute, Montreal, Quebec, Canada
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Craig J, Martin W. Dominance of flow-mediated constriction over flow-mediated dilatation in the rat carotid artery. Br J Pharmacol 2013; 167:527-36. [PMID: 22537086 DOI: 10.1111/j.1476-5381.2012.02006.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND AND PURPOSE The shearing forces generated by flow generally evoke dilatation in systemic vessels but constriction in the cerebral circulation. The aim of this study was to determine the effects of flow on the conduit artery delivering blood to the brain in the rat, that is, the carotid artery. EXPERIMENTAL APPROACH Carotid artery segments were mounted in a pressure myograph and pressurized to 100 mmHg. Changes in vessel diameter to flow (0.5-10 mL·min⁻¹ for 2-10 min) at constant pressure were then measured using a video dimension analyser. KEY RESULTS Following the induction of tone, the onset of flow evoked a transient dilatation followed by a powerful constriction that was sustained until the termination of flow. Endothelial denudation or treatment with indomethacin, N(G)-nitro-L-arginine methyl ester, or the combination of apamin and TRAM-34 showed that the initial flow-mediated dilatation arose from the combined actions of endothelium-derived NO and endothelium-derived hyperpolarizing factor (EDHF). The flow-mediated constriction, which increased in magnitude with increasing flow rate and duration of flow, was also endothelium dependent, but was unaffected by treatment with superoxide dismutase, BQ-123, indomethacin, HET0016 or carbenoxolone. Flow-mediated constriction therefore appeared not to involve superoxide anion, endothelin-1, a COX product, 20-HETE or gap-junctional communication. CONCLUSIONS AND IMPLICATIONS Although a weak, transient flow-mediated dilatation is observed in the rat carotid artery, the dominant response to flow is a powerful and sustained constriction. Whether this flow-mediated constriction in the carotid artery serves as an extracranial mechanism to regulate cerebral blood flow remains to be determined.
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Affiliation(s)
- John Craig
- College of Medical, Veterinary and Life Sciences, West Medical Building, University of Glasgow, UK
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De Silva TM, Faraci FM. Effects of angiotensin II on the cerebral circulation: role of oxidative stress. Front Physiol 2013; 3:484. [PMID: 23316164 PMCID: PMC3539653 DOI: 10.3389/fphys.2012.00484] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2012] [Accepted: 12/11/2012] [Indexed: 12/31/2022] Open
Abstract
Oxidative stress has emerged as a key component of many diseases that affect the vasculature. Oxidative stress is characterized as a cellular environment where the generation of oxidant molecules overwhelms endogenous anti-oxidant defense mechanisms. NADPH oxidases are a family of enzymes whose primary purpose is generation of reactive oxygen species (oxidant molecules) and therefore are likely to be key contributors to oxidative stress. Hypertension is associated with oxidative stress in the vasculature and is a major risk factor for stroke and cognitive abnormalities. Angiotensin II (Ang II) is the main effector peptide of the renin-angiotensin system (RAS) and plays a critical role in promoting oxidative stress in the vasculature. In the cerebral circulation, Ang II has been implicated in reactive oxygen species generation, alterations to vasomotor function, impaired neurovascular coupling, inflammation, and vascular remodeling. Furthermore, studies in humans have shown that cerebral blood flow is altered during hypertension and therapeutically targeting the RAS improves cerebral blood flow. Importantly, many of the aforementioned effects have been shown to be dependent on NADPH oxidases. Thus, Ang II, NADPH oxidases and oxidative stress are likely to play key roles in the pathogenesis of hypertension and associated cerebrovascular disease. This review will focus on our current understanding of the contribution of Ang II and NADPH oxidases to oxidative stress in the cerebral circulation.
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Affiliation(s)
- T Michael De Silva
- Department of Internal Medicine, Cardiovascular Center, The University of Iowa Carver College of Medicine Iowa City, IA, USA
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Koller A, Toth P. Contribution of flow-dependent vasomotor mechanisms to the autoregulation of cerebral blood flow. J Vasc Res 2012; 49:375-89. [PMID: 22739136 PMCID: PMC3586555 DOI: 10.1159/000338747] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2011] [Accepted: 04/04/2012] [Indexed: 11/19/2022] Open
Abstract
Regulation of cerebral blood flow (CBF) is the result of multilevel mechanisms to maintain the appropriate blood supply to the brain while having to comply with the limited space available in the cranium. The latter requirement is ensured by the autoregulation of CBF, in which the pressure-sensitive myogenic response is known to play a pivotal role. However, in vivo increases in pressure are accompanied by increases in flow; yet the effects of flow on the vasomotor tone of cerebral vessels are less known. Earlier studies showed flow-sensitive dilation and/or constriction or both, but no clear picture emerged. Recently, the important role of flow-sensitive mechanism(s) eliciting the constriction of cerebral vessels has been demonstrated. This review focuses on the effect of hemodynamic forces (especially intraluminal flow) on the vasomotor tone of cerebral vessels and the underlying cellular and molecular mechanisms. A novel concept of autoregulation of CBF is proposed, suggesting that (in certain areas of the cerebrovascular tree) pressure- and flow-induced constrictions together maintain an effective autoregulation, and that alterations in these mechanisms may contribute to the development of cerebrovascular disorders. Future studies are warranted to explore the signals, the details of signaling processes and the in vivo importance of these mechanisms.
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Affiliation(s)
- Akos Koller
- Department of Pathophysiology and Gerontology, Medical School, University of Pécs, Pécs, Hungary.
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35
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Bonnin P, Leger PL, Villapol S, Deroide N, Gressens P, Pocard M, Renolleau S, Baud O, Charriaut-Marlangue C. Dual action of NO synthases on blood flow and infarct volume consecutive to neonatal focal cerebral ischemia. Exp Neurol 2012; 236:50-7. [PMID: 22531298 DOI: 10.1016/j.expneurol.2012.04.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2011] [Revised: 03/23/2012] [Accepted: 04/04/2012] [Indexed: 11/15/2022]
Abstract
Research into neonatal ischemic brain damage is impeded by the lack of a complete understanding of the initial hemodynamic mechanisms resulting in a lesion, particularly that of NO-mediated vascular mechanisms. In a neonatal stroke rat model, we recently show that collateral recruitment contributes to infarct size variability. Non-specific and selective NO synthase (NOS) inhibition was evaluated on cerebral blood-flow changes and outcome in a P7 rat model of arterial occlusion (left middle cerebral artery electrocoagulation with 50 min occlusion of both common carotid arteries). Blood-flow changes were measured by using ultrasound imaging with sequential Doppler recordings in both internal carotid arteries and basilar trunk. Cortical perfusion was measured by using laser Doppler flowmetry. We showed that global NOS inhibition significantly reduced collateral support and cortical perfusion (collateral failure), and worsened the ischemic injury in both gender. Conversely, endothelial NOS inhibition increased blood-flows and aggravated volume lesion in males, whereas in females blood-flows did not change and infarct lesion was significantly reduced. These changes were associated with decreased phosphorylation of neuronal NOS at Ser(847) in males and increased phosphorylation in females at 24h, respectively. Neuronal NOS inhibition also increased blood-flows in males but not in females, and did not significantly change infarct volumes compared to their respective PBS-treated controls. In conclusion, both nNOS and eNOS appear to play a key role in modulating arterial blood flow during ischemia mainly in male pups with subsequent modifications in infarct lesion.
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Affiliation(s)
- Philippe Bonnin
- Univ Paris Diderot, Sorbonne Paris Cité, AP-HP, Hôpital Lariboisière, Physiologie Clinique - Explorations-Fonctionnelles, 75010 Paris, France
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Kreis D, Schulz D, Stein M, Preuss M, Nestler U. Assessment of parameters influencing the blood flow velocities in cerebral arteries of the rat using ultrasonographic examination. Neurol Res 2012; 33:389-95. [PMID: 21535938 DOI: 10.1179/1743132810y.0000000010] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
Abstract
OBJECTIVES Rat models of cerebrovascular diseases are used for a variety of human pathologies comprising ischemic stroke or subarachnoid hemorrhage. Whereas in neuro-intensive care, Doppler ultrasonographic examination of major cerebral arteries is a common diagnostic tool, only few data exist concerning the animal model. We therefore studied cerebral blood flow velocities in the rat by ultrasonographic triplex mode. METHODS Female Wistar rats underwent a large craniectomy and baseline values for blood flow velocities were obtained by 399 examinations in 52 animals. Vessel diameters were assessed by 301 examinations in 39 animals. Finally, in 26 animals, continuous measurements of blood flow velocities were performed. For a duration of more than 30 minutes, values in the anterior trunk, the left carotid artery and the basilar artery were obtained every 60-90 seconds with simultaneous detection of heart rate. RESULTS Blood flow velocities in the anterior part of cerebral circulation were faster than those in the posterior part and showed higher standard deviation. Flow velocities in arteries belonging to the anterior circulation changed in relation to carotid flow velocity and heart rate, whereas the velocity in the basilar artery showed much lower correlation to carotid flow velocity or heart rate. DISCUSSION Ultrasonographic triplex mode examination of cerebral vessels offers a reproducible method to study rat cerebral blood flow velocities and vessel diameters. In combination with monitoring of systemic hemodynamic parameters, it can provide a detailed description of the vascular response to drugs, experimental stroke or subarachnoid hemorrhage.
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Affiliation(s)
- Dorothee Kreis
- Department of Neurosurgery, Justus Liebig University, Giessen, Germany
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Kim KJ, Filosa JA. Advanced in vitro approach to study neurovascular coupling mechanisms in the brain microcirculation. J Physiol 2012; 590:1757-70. [PMID: 22310311 DOI: 10.1113/jphysiol.2011.222778] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
An understanding of the signalling events underlying neurovascular coupling mechanisms in the brain is a crucial step in the development of novel therapeutic approaches for the treatment of cerebrovascular-associated disorders. In this study we present an enhanced in vitro brain slice preparation from male Wistar rat cortical slices that incorporates haemodynamic variables (flow and pressure) into parenchymal arterioles resulting in the development of myogenic tone (28% from maximum dilatation). Moreover, we characterized flow-induced vascular responses, resulting in various degrees of vasoconstrictions and the response to 10 mM K(+) or astrocytic activation with the mGluR agonist, t-ACPD (100 μM), resulting in vasodilatations of 33.6±4.7% and 38.6±4.6%, respectively. Using fluorescence recovery, we determined perfusate velocity to calculate diameter changes under different experimental pH conditions. Using this approach, we demonstrate no significant differences between diameter changes measured using videomicroscopy or predicted from the velocity values obtained using fluorescence recovery after photobleaching. The model is further validated by demonstrating our ability to cannulate arterioles in two brain regions (cortex and supraoptic nucleus of the hypothalamus). Altogether, we believe this is the first study demonstrating successful cannulation and perfusion of parenchymal arterioles while monitoring/estimating luminal diameter and pressure under conditions where flow rates are controlled.
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Affiliation(s)
- Ki Jung Kim
- Department of Physiology, Georgia Health Sciences University, Augusta, GA 30912, USA
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Güresir E, Vasiliadis N, Dias S, Raab P, Seifert V, Vatter H. The effect of common carotid artery occlusion on delayed brain tissue damage in the rat double subarachnoid hemorrhage model. Acta Neurochir (Wien) 2012; 154:11-9. [PMID: 21986833 DOI: 10.1007/s00701-011-1191-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2011] [Accepted: 09/27/2011] [Indexed: 12/20/2022]
Abstract
OBJECTIVE Delayed ischemic brain tissue damage in the time course of cerebral vasospasm in the rat double-subarachnoid hemorrhage (SAH) model has been described before. However, in order to enhance hemodynamic insufficiency during cerebral vasospasm (CVS), we performed-in a modification to the standard double-hemorrhage model-an additional unilateral common carotid artery occlusion (CCAO), expecting aggravation of brain-tissue damage in areas particularly sensitive to hypoxia. METHODS CVS was induced by injection of 0.25 ml autologous blood twice in the cisterna magna of Sprague-Dawley rats with and without unilateral CCAO. The animals were examined on days 2, 3, 4 and 5, and compared with the sham-operated control group without SAH. The functional deficits were graded between 0 and 3. Perfusion weighted imaging (PWI) at 3 Tesla magnetic resonance (MR) tomography was performed to assess cerebral blood flow (CBF). The brains were fixed, stained and evaluated for histological changes. RESULTS On day 5, the neurological state was significantly worse in rats with SAH. The relative CBF/muscle blood ratio was significantly decreased by SAH and lowest in rats with CCAO and SAH (4.5 ± 1.1 vs 2.7 ± 0.6) compared with sham (7.9 ± 1.5; p < 0.001). Basilar artery (BA) diameter was 79 ± 5 μm (SAH) vs 147 ± 4 μm (sham, p < 0.001). Neuronal cell count in the hippocampal areas CA1-CA4 was significantly reduced by SAH on day 5 (p < 0.001) and lowest in rats with SAH and CCAO. CONCLUSIONS CCAO leads to an aggravation of CVS-related delayed brain tissue damage in the modified rat double-SAH model.
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Affiliation(s)
- Erdem Güresir
- Department of Neurosurgery, Johann Wolfgang Goethe-University Frankfurt am Main, Germany.
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Montalcini T, Gorgone G, Gazzaruso C, Romeo S, Bosco D, Pujia A. Brachial artery diameter measurement: a tool to simplify non-invasive vascular assessment. Nutr Metab Cardiovasc Dis 2012; 22:8-13. [PMID: 22176922 DOI: 10.1016/j.numecd.2011.09.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/05/2011] [Revised: 09/02/2011] [Accepted: 09/12/2011] [Indexed: 11/16/2022]
Abstract
AIM The mechanisms of vascular remodeling have attracted great interest since it is a phenomenon related to cardiovascular diseases. We would like to examine studies that contributed to clarify the remodeling mechanisms, to explore the different faces of atherosclerosis process. DATA SYNTHESIS A number of invasive and non-invasive vascular assessment methods were developed, to detect the early sign of atherosclerosis. It became clear that the invasive tests were not applicable to large-scale studies. Consequently, a non-invasive test was developed. Studies showed that the endothelial function evaluation is a predictor of future cardiac events in individuals at cardiovascular risk and in those with established disease. However, analyzing several works, an interesting concept emerged, i.e., the inverse relation between endothelium-dependent dilation and vessel size, since large vessel tend not to dilate significantly. This notion emphasized the role of basal diameter on vascular response. In particular, as brachial artery diameter is the measure on which FMD is based, it could add more information in clinical evaluation, simplifying the assessment. Several studies showed that morphological change of brachial artery is a better indicator of the extent of coronary disease rather than FMD. Other studies showed that brachial diameter has predictive significance in the stratification of cardiovascular risk. CONCLUSION Brachial diameter is a useful and simple tool. It should be incorporated into the overall assessment of cardiovascular risk but further studies are warranted to determine the final place of brachial diameter assessment in routine clinical setting.
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Affiliation(s)
- T Montalcini
- Clinical Nutrition Unit, Department of Clinical and Exp. Medicine, University Magna Graecia, Catanzaro, Italy.
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Petzold GC, Murthy VN. Role of astrocytes in neurovascular coupling. Neuron 2011; 71:782-97. [PMID: 21903073 DOI: 10.1016/j.neuron.2011.08.009] [Citation(s) in RCA: 285] [Impact Index Per Article: 21.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/15/2011] [Indexed: 10/17/2022]
Abstract
Neural activity is intimately tied to blood flow in the brain. This coupling is specific enough in space and time that modern imaging methods use local hemodynamics as a measure of brain activity. In this review, we discuss recent evidence indicating that neuronal activity is coupled to local blood flow changes through an intermediary, the astrocyte. We highlight unresolved issues regarding the role of astrocytes and propose ways to address them using novel techniques. Our focus is on cellular level analysis in vivo, but we also relate mechanistic insights gained from ex vivo experiments to native tissue. We also review some strategies to harness advances in optical and genetic methods to study neurovascular coupling in the intact brain.
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Affiliation(s)
- Gabor C Petzold
- German Center for Neurodegenerative Diseases (DZNE), Ludwig-Erhard-Allee 2, 53175 Bonn, Germany.
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Toth P, Rozsa B, Springo Z, Doczi T, Koller A. Isolated human and rat cerebral arteries constrict to increases in flow: role of 20-HETE and TP receptors. J Cereb Blood Flow Metab 2011; 31:2096-105. [PMID: 21610722 PMCID: PMC3208155 DOI: 10.1038/jcbfm.2011.74] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Elevation of intraluminal pressure increases vasomotor tone, which thought to have a substantial role in regulation of cerebral blood flow (CBF). Interestingly, responses of cerebral vessels to increases in flow varied and have not been studied in human cerebral arteries. We hypothesized that increases in flow elicit constrictions of isolated human and rat cerebral arteries and aimed to elucidate the underlying mechanisms. Human cerebral arteries and rat middle cerebral arteries constricted to increases in flow (P<0.05). Simultaneous increase in intraluminal flow+pressure further reduced the diameter compared with pressure-induced changes (P<0.05), leading to constant estimated CBF. Flow-induced constrictions were abolished by HET0016 (inhibitor of synthesis of 20-hydroxyeicosatetraenoic acid (20-HETE) or inhibition of COXs or blocking TP (thromboxane A(2)/prostaglandin H(2), receptors and attenuated by scavenging reactive oxygen species (ROS). Flow-enhanced ROS formation was significantly reduced by HET0016. In conclusion, in human and rat cerebral arteries (1) increases in flow elicit constrictions, (2) signaling mechanism of flow-induced constriction of cerebral arteries involves enhanced production of ROS, COX activity, and mediated by 20-HETE via TP receptors, and (3) we propose that simultaneous operation of pressure- and flow-induced constrictions is necessary to provide an effective autoregulation of CBF.
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Affiliation(s)
- Peter Toth
- Department of Physiology, New York Medical College, Valhalla, New York 10595, USA
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Abstract
Endothelial cells exert an enormous influence on blood vessels throughout the circulation, but their impact is particularly pronounced in the brain. New concepts have emerged recently regarding the role of this cell type and mechanisms that contribute to endothelial dysfunction and vascular disease. Activation of the renin-angiotensin system plays a prominent role in producing these abnormalities. Both oxidative stress and local inflammation are key mechanisms that underlie vascular disease of diverse etiology. Endogenous mechanisms of vascular protection are also present, including antioxidants, anti-inflammatory molecules, and peroxisome proliferator-activated receptor-γ. Despite their clear importance, studies of mechanisms that underlie cerebrovascular disease continue to lag behind studies of vascular biology in general. Identification of endogenous molecules and pathways that protect the vasculature may result in targeted approaches to prevent or slow the progression of vascular disease that causes stroke and contributes to the vascular component of dementia and Alzheimer's disease.
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Affiliation(s)
- Frank M Faraci
- Dept. of Internal Medicine, Carver College of Medicine, Univ. of Iowa, Iowa City, Iowa 52242-1081, USA.
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Koller A, Kaley G. Shear Stress Dependent Regulation of Vascular Resistance in Health and Disease: Role of Endothelium. ACTA ACUST UNITED AC 2009. [DOI: 10.3109/10623329609024701] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Drouin A, Thorin E. Flow-induced dilation is mediated by Akt-dependent activation of endothelial nitric oxide synthase-derived hydrogen peroxide in mouse cerebral arteries. Stroke 2009; 40:1827-33. [PMID: 19286591 PMCID: PMC3692461 DOI: 10.1161/strokeaha.108.536805] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND AND PURPOSE Endothelial nitric oxide synthase produces superoxide under physiological conditions leading to hydrogen peroxide (H(2)O(2)) -dependent dilations to acetylcholine in isolated mouse cerebral arteries. The purpose of this study was to investigate whether H(2)O(2) was involved in flow-mediated dilation (FMD). METHODS Cerebral arteries were isolated from 12+/-2-week-old C57Bl/6 male mice. FMD (0 to 10 microL/min, 2-microL step increase at constant internal pressure) was induced in vessels preconstricted with phenylephrine (30 micromol/L). Simultaneously to diameter acquisition, H(2)O(2) or nitric oxide production was detected by the fluorescent dyes CMH(2)CFDA or 4,5-diaminofluorescein diacetate, respectively. Results are expressed as mean+/-SEM of 6 to 8 mice. RESULTS FMD (at 10 microL/min, 25+/-3% of maximal diameter) was prevented (P<0.05) by endothelium removal (6+/-1%) or endothelial nitric oxide synthase inhibition with N-nitro-L-arginine (11+/-1%) but not by the specific nitric oxide scavenger 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl3-oxide (24+/-3%). Addition of PEG-catalase and silver diethyl dithio-carbamate (superoxide dismutase inhibitor) reduced (P<0.05) FMD to 10+/-2% and 15+/-1%, respectively. Simultaneously to FMD, H(2)O(2)-associated rise in fluorescence (+133+/-19 a.u.) was prevented by N-nitro-L-arginine, PEG-catalase, and silver diethyl dithio-carbamate (+55+/-10, +64+/-4, and +50+/-10 a.u., respectively; P<0.05). Inhibition of FMD by PEG-catalase was fully restored by the addition of tetrahydrobiopterin, a cofactor of endothelial nitric oxide synthase (23+/-3%); this functional reversal in dilation was associated with the simultaneous increase in nitric oxide-associated fluorescence (+418+/-58 a.u., P<0.05), which was prevented by 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl3-oxide (+93+/-26 a.u.). Akt inhibition with triciribine prevented FMD and H(2)O(2)-associated rise in fluorescence (3+/-1% and +23+/-4% a.u., respectively; P<0.05), but not acetylcholine-induced dilation. CONCLUSIONS In healthy C57Bl/6 mouse cerebral arteries, Akt-dependent activation of endothelial nitric oxide synthase-derived H(2)O(2) mediates flow-dependent dilation.
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Affiliation(s)
- Annick Drouin
- Institut de Cardiologie de Montréal, Centre de Recherche, Montréal, Québec, Canada
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Hoi Y, Gao L, Tremmel M, Paluch RA, Siddiqui AH, Meng H, Mocco J. In vivo assessment of rapid cerebrovascular morphological adaptation following acute blood flow increase. J Neurosurg 2009; 109:1141-7. [PMID: 19035734 DOI: 10.3171/jns.2008.109.12.1141] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
OBJECT Pathological extremes in cerebrovascular remodeling may contribute to basilar artery (BA) dolichoectasia and fusiform aneurysm development. Factors regulating cerebrovascular remodeling are poorly understood. To better understand hemodynamic influences on cerebrovascular remodeling, we examined BA remodeling following common carotid artery (CCA) ligation in an animal model. METHODS Rabbits were subjected to sham surgery (3 animals), unilateral CCA ligation (3 animals), or bilateral CCA ligation (5 animals). Transcranial Doppler ultrasonography and rotational angiography were used to compute BA flow, diameter, wall shear stress (WSS), and a tortuosity index on Days 0, 1, 4, 7, 14, 28, 56, and 84. Basilar artery tissues were stained and analyzed at Day 84. Statistical analysis was performed using orthogonal contrast analysis, repeated measures analysis of variance, or mixed regression analysis of repeated measures. Statistical significance was defined as a probability value < 0.05. RESULTS Basilar artery flow and diameter increased significantly after the procedure in both ligation groups, but only the bilateral CCA ligation group demonstrated significant differences between groups. Wall shear stress significantly increased only in animals in the bilateral CCA ligation group and returned to baseline by Day 28, with 52% of WSS correction occurring by Day 7. Only the bilateral CCA ligation group developed significant BA tortuosity, occurring within 7 days postligation. Unlike the animals in the sham and unilateral CCA ligation groups, the animals in the bilateral CCA ligation group had histological staining results showing a substantial internal elastic lamina fragmentation. CONCLUSIONS Increased BA flow results in adaptive BA remodeling until WSS returns to physiological baseline levels. Morphological changes occur rapidly following flow alteration and do not require chronic insult to affect substantial and significant structural transformation. Additionally, it appears that there exists a flow-increase threshold that, when surpassed, results in significant tortuosity.
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Affiliation(s)
- Yiemeng Hoi
- Toshiba Stroke Research Center, State University of New York at Buffalo, New York 14214, USA
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Busija DW, Bari F, Domoki F, Horiguchi T, Shimizu K. Mechanisms involved in the cerebrovascular dilator effects of cortical spreading depression. Prog Neurobiol 2008; 86:379-95. [PMID: 18835324 PMCID: PMC2615412 DOI: 10.1016/j.pneurobio.2008.09.008] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2008] [Revised: 05/23/2008] [Accepted: 09/05/2008] [Indexed: 10/21/2022]
Abstract
Cortical spreading depression (CSD) leads to dramatic changes in cerebral hemodynamics. However, mechanisms involved in promoting and counteracting cerebral vasodilator responses are unclear. Here we review the development and current status of this important field of research especially with respect to the role of perivascular nerves and nitric oxide (NO). It appears that neurotransmitters released from the sensory and the parasympathetic nerves associated with cerebral arteries, and NO released from perivascular nerves and/or parenchyma, promote cerebral hyperemia during CSD. However, the relative contributions of each of these factors vary according to species studied. Related to CSD, axonal and reflex responses involving trigeminal afferents on the pial surface lead to increased blood flow and inflammation of the overlying dura mater. Counteracting the cerebral vascular dilation is the production and release of constrictor prostaglandins, at least in some species, and other possibly yet unknown agents from the vascular wall. The cerebral blood flow response in healthy human cortex has not been determined, and thus it is unclear whether the cerebral oligemia associated with migraines represents the normal physiological response to a CSD-like event or represents a pathological response. In addition to promoting cerebral hyperemia, NO produced during CSD appears to initiate signaling events which lead to protection of the brain against subsequent ischemic insults. In summary, the cerebrovascular response to CSD involves multiple dilator and constrictor factors produced and released by diverse cells within the neurovascular unit, with the contribution of each of these factors varying according to the species examined.
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Affiliation(s)
- David W Busija
- Department of Physiology and Pharmacology, Wake Forest University Health Sciences, Medical Center Boulevard, Winston-Salem, NC 27157-1010, USA.
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du Plessis AJ. Cerebrovascular injury in premature infants: current understanding and challenges for future prevention. Clin Perinatol 2008; 35:609-41, v. [PMID: 19026331 DOI: 10.1016/j.clp.2008.07.010] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Cerebrovascular insults are a leading cause of brain injury in premature infants, contributing to the high prevalence of motor, cognitive, and behavioral deficits. Understanding the complex pathways linking circulatory immaturity to brain injury in premature infants remains incomplete. These mechanisms are significantly different from those causing injury in the mature brain. The gaps in knowledge of normal and disturbed cerebral vasoregulation need to be addressed. This article reviews current understanding of cerebral perfusion, in the sick premature infant in particular, and discusses challenges that lie ahead.
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Affiliation(s)
- Adré J du Plessis
- Department of Neurology, Children's Hospital Boston, Boston, MA 02115, USA.
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