1
|
Damiani E, Casarotta E, Orlando F, Carsetti A, Scorcella C, Domizi R, Adrario E, Ciucani S, Provinciali M, Donati A. Effects of Normoxia, Hyperoxia, and Mild Hypoxia on Macro-Hemodynamics and the Skeletal Muscle Microcirculation in Anesthetised Rats. Front Med (Lausanne) 2021; 8:672257. [PMID: 34046421 PMCID: PMC8144325 DOI: 10.3389/fmed.2021.672257] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Accepted: 04/13/2021] [Indexed: 12/13/2022] Open
Abstract
Objectives: Excessive oxygen (O2) administration may have a negative impact on tissue perfusion by inducing vasoconstriction and oxidative stress. We aimed to evaluate the effects of different inhaled oxygen fractions (FiO2) on macro-hemodynamics and microvascular perfusion in a rat model. Methods: Isoflurane-anesthetised spontaneously breathing male Wistar rats were equipped with arterial (carotid artery) and venous (jugular vein) catheters and tracheotomy, and randomized into three groups: normoxia (FiO2 21%, n = 6), hyperoxia (FiO2 100%, n = 6) and mild hypoxia (FiO2 15%, n = 6). Euvolemia was maintained by infusing Lactate Ringer solution at 10 ml/kg/h. At hourly intervals for 4 h we collected measurements of: mean arterial pressure (MAP); stroke volume index (SVI), heart rate (HR), respiratory rate (by means of echocardiography); arterial and venous blood gases; microvascular density, and flow quality (by means of sidestream dark field videomicroscopy on the hindlimb skeletal muscle). Results: MAP and systemic vascular resistance index increased with hyperoxia and decreased with mild hypoxia (p < 0.001 in both cases, two-way analysis of variance). Hyperoxia induced a reduction in SVI, while this was increased in mild hypoxia (p = 0.002). The HR increased under hyperoxia (p < 0.05 vs. normoxia at 3 h). Cardiax index, as well as systemic O2 delivery, did not significantly vary in the three groups (p = 0.546 and p = 0.691, respectively). At 4 h, microvascular vessel surface (i.e., the percentage of tissue surface occupied by vessels) decreased by 29 ± 4% in the hyperoxia group and increased by 19 ± 7 % in mild hypoxia group (p < 0.001). Total vessel density and perfused vessel density showed similar tendencies (p = 0.003 and p = 0.005, respectively). Parameters of flow quality (microvascular flow index, percentage of perfused vessels, and flow heterogeneity index) remained stable and similar in the three groups. Conclusions: Hyperoxia induces vasoconstriction and reduction in skeletal muscle microvascular density, while mild hypoxia has an opposite effect.
Collapse
Affiliation(s)
- Elisa Damiani
- Anesthesia and Intensive Care Unit, Department of Biomedical Sciences and Public Health, Università Politecnica delle Marche, Ancona, Italy
| | - Erika Casarotta
- Anesthesia and Intensive Care Unit, Department of Biomedical Sciences and Public Health, Università Politecnica delle Marche, Ancona, Italy
| | - Fiorenza Orlando
- Experimental Animal Models for Aging Units, Scientific Technological Area, Istituto di Ricovero e Cura a Carattere Scientifico - Istituto Nazionale Ricovero e Cura Anziani, Ancona, Italy
| | - Andrea Carsetti
- Anesthesia and Intensive Care Unit, Department of Biomedical Sciences and Public Health, Università Politecnica delle Marche, Ancona, Italy.,Anesthesia and Intensive Care Unit, Azienda Ospedaliera Universitaria "Ospedali Riuniti Umberto I - Lancisi - Salesi" of Ancona, Ancona, Italy
| | - Claudia Scorcella
- Anesthesia and Intensive Care Unit, Azienda Ospedaliera Universitaria "Ospedali Riuniti Umberto I - Lancisi - Salesi" of Ancona, Ancona, Italy
| | - Roberta Domizi
- Anesthesia and Intensive Care Unit, Azienda Ospedaliera Universitaria "Ospedali Riuniti Umberto I - Lancisi - Salesi" of Ancona, Ancona, Italy
| | - Erica Adrario
- Anesthesia and Intensive Care Unit, Department of Biomedical Sciences and Public Health, Università Politecnica delle Marche, Ancona, Italy.,Anesthesia and Intensive Care Unit, Azienda Ospedaliera Universitaria "Ospedali Riuniti Umberto I - Lancisi - Salesi" of Ancona, Ancona, Italy
| | - Silvia Ciucani
- Anesthesia and Intensive Care Unit, Department of Biomedical Sciences and Public Health, Università Politecnica delle Marche, Ancona, Italy
| | - Mauro Provinciali
- Experimental Animal Models for Aging Units, Scientific Technological Area, Istituto di Ricovero e Cura a Carattere Scientifico - Istituto Nazionale Ricovero e Cura Anziani, Ancona, Italy
| | - Abele Donati
- Anesthesia and Intensive Care Unit, Department of Biomedical Sciences and Public Health, Università Politecnica delle Marche, Ancona, Italy.,Anesthesia and Intensive Care Unit, Azienda Ospedaliera Universitaria "Ospedali Riuniti Umberto I - Lancisi - Salesi" of Ancona, Ancona, Italy
| |
Collapse
|
2
|
Yartsev VN. Paradoxical effects of acidosis on the noradrenaline-induced and neurogenic constriction of the rat tail artery at low temperatures. Can J Physiol Pharmacol 2021; 99:1036-1047. [PMID: 33857387 DOI: 10.1139/cjpp-2020-0740] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Although vasodilatation evoked by acidosis at normal body temperature is well known, the reports regarding effect of acidosis on the reactivity of the isolated arteries at low temperatures are nonexistent. This study tested the hypothesis that the inhibitory effect of acidosis on the neurogenic vasoconstriction may be increased by cooling. Using wire myography, we recorded the neurogenic contraction of the rat tail artery segments to the electrical field stimulation in the absence and in the presence of 0.03-10.0 µmol/L noradrenaline. The experiments were conducted at 37 °C or 25 °C and pH 7.4 or 6.6 which was decreased by means of CO2. Noradrenaline at concentration of 0.03-0.1 µmol/L significantly potentiated the neurogenic vasoconstriction at 25 °C, and the potentiation was not inhibited by acidosis. Contrary to our hypothesis, acidosis at a low temperature did not affect the noradrenaline-induced tone and significantly increased the neurogenic contraction of the artery segments in the absence and presence of noradrenaline. These effects of acidosis were partly dependent on the endothelium and L-type Ca2+ channels activation. The phenomenon described for the first time might be of importance for the reduction in the heat loss by virtue of decrease in the subcutaneous blood flow at low ambient temperatures.
Collapse
Affiliation(s)
- Vladimir N Yartsev
- Laboratory of Physiology of Cardiovascular and Lymphatic Systems, Pavlov Institute of Physiology, Russian Academy of Sciences, St. Petersburg, Russia.,Laboratory of Physiology of Cardiovascular and Lymphatic Systems, Pavlov Institute of Physiology, Russian Academy of Sciences, St. Petersburg, Russia
| |
Collapse
|
3
|
Cooper IR, Liu S, DeLorey DS. Effects of sex and exercise training on β-adrenoreceptor-mediated opposition of evoked sympathetic vasoconstriction in resting and contracting muscle of rats. J Appl Physiol (1985) 2020; 130:114-123. [PMID: 33090912 DOI: 10.1152/japplphysiol.00726.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This study investigated the hypothesis that β-adrenoreceptor-mediated inhibition of sympathetic vasoconstriction would be enhanced in female compared with male rats, and that endurance exercise training would augment β-adrenoreceptor-mediated inhibition of sympathetic vasoconstriction in male and female rats. Sprague-Dawley rats were randomized into sedentary (male: n = 7; female: n = 8) and exercise-trained (male: n = 9; female: n = 9) groups. Following 4 wk of exercise training or being sedentary, rats were anesthetized and surgically instrumented for stimulation of the lumbar sympathetic chain, muscle contraction and measurement of arterial blood pressure and femoral artery blood flow (FBF). Femoral vascular conductance (FVC) was calculated as FBF/mean arterial pressure. The percentage change of FVC in response to sympathetic stimulation delivered at 2 and 5 Hz was measured at rest and during contraction of the triceps surae muscles before and after β-adrenoreceptor blockade (propranolol: 0.075 mg·kg-1 iv). We found that, at rest, β-adrenoreceptor blockade decreased (main effect of drug, 2 Hz: P < 0.001; 5 Hz: P < 0.001) sympathetic vasoconstriction. During contraction, sympathetic vasoconstrictor responsiveness was lower (main effect of sex, 2 Hz: P = 0.001; 5 Hz: P = 0.023) in female compared with male rats, and sympatholysis was enhanced (main effect of sex, 2 Hz: P = 0.001; 5 Hz: P < 0.001) in female rats. β-adrenoreceptor blockade decreased (main effect of drug, 2 Hz: P = 0.049; 5 Hz: P < 0.001) evoked sympathetic vasoconstriction in contracting muscle. The present study demonstrated that β-adrenoreceptors do not blunt sympathetic vasoconstriction in resting or contracting skeletal muscle of male or female rats. Sympatholysis was enhanced in female rats; however, this was not attributable to β-adrenoreceptor-mediated blunting of sympathetic vasoconstriction.NEW & NOTEWORTHY β-adrenoreceptors do not inhibit sympathetic vasoconstriction in resting or contracting muscle of male or female rats, regardless of training status. Sympatholysis was enhanced in female, compared to male rats; however, β-adrenoreceptors were not responsible for the enhanced sympatholysis. These findings indicate that β-adrenoreceptors do not contribute to the regulation of sympathetic vasoconstriction in resting and contracting skeletal muscle and suggest that β-adrenoreceptors do not underlie sex differences in the neural control of the circulation.
Collapse
Affiliation(s)
- Ian R Cooper
- Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Sixue Liu
- Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Darren S DeLorey
- Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Alberta, Canada
| |
Collapse
|
4
|
Affiliation(s)
| | - Naima Covassin
- Department of Cardiovascular Diseases (N.C., V.K.S.), Mayo Clinic, Rochester, MN
| | - Virend K Somers
- Department of Cardiovascular Diseases (N.C., V.K.S.), Mayo Clinic, Rochester, MN
| |
Collapse
|
5
|
Cooper IR, Just TP, DeLorey DS. β-Adrenoreceptors do not oppose sympathetic vasoconstriction in resting and contracting skeletal muscle of male rats. Appl Physiol Nutr Metab 2019; 44:1230-1236. [DOI: 10.1139/apnm-2019-0130] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Sympathetic nervous system (SNS) vasoconstriction is primarily achieved through the binding of norepinephrine (NE) to α-adrenoreceptors. However, NE may also bind to β-adrenoreceptors and cause vasodilation that may oppose/blunt SNS-mediated vasoconstriction. Therefore, this study investigated the hypothesis that β-adrenoreceptor–mediated vasodilation opposes evoked vasoconstriction in resting and contracting skeletal muscle. Male (n = 9) Sprague–Dawley rats were anesthetized and surgically instrumented for stimulation of the lumbar sympathetic chain and measurement of arterial blood pressure and femoral artery blood flow. The percentage change of femoral vascular conductance in response to sympathetic chain stimulation delivered at 2 and 5 Hz was determined at rest and during triceps surae skeletal muscle contraction before (control) and after β-adrenoreceptor blockade (propranolol; 0.075 mg·kg−1, intravenously). β-Adrenoreceptor blockade did not alter (P > 0.05) baseline hemodynamics or the hyperemic response to exercise. At the 2 Hz stimulation frequency, sympathetic vasoconstriction was similar (P > 0.05) in control and β-blockade conditions in resting (control, −34% ± 6%; β-blockade, −33% ± 8%) and contracting (control, −16% ± 6%; β-blockade, −14% ± 7%) muscle. At the 5 Hz stimulation frequency, sympathetic vasoconstrictor responsiveness was reduced (main effect of drug, P < 0.05) following β-blockade (rest: control, −52% ± 7%; β-blockade, −51% ± 9%; contraction: control, −32% ± 11%; β-blockade, −29% ± 13%). Novelty These data indicate that β-adrenoreceptor blockade did not augment sympathetic vasoconstriction at rest or during exercise. The study demonstrates that β-adrenoreceptors do not oppose evoked sympathetic vasoconstriction in resting or contracting skeletal muscle or contribute to functional sympatholysis.
Collapse
Affiliation(s)
- Ian R. Cooper
- Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, AB T6G 2H9, Canada
- Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, AB T6G 2H9, Canada
| | - Timothy P. Just
- Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, AB T6G 2H9, Canada
- Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, AB T6G 2H9, Canada
| | - Darren S. DeLorey
- Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, AB T6G 2H9, Canada
- Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, AB T6G 2H9, Canada
| |
Collapse
|
6
|
Fukuda M, Isobe-Sasaki Y, Sato R, Miura T, Mizuno M, Ono M, Kiyono K, Yamamoto Y, Hayano J, Ohte N. The angiotensin II type 1 receptor blocker azilsartan can overwhelm the sympathetic nerve activation stimulated by coadministration of calcium channel blockers. J Renin Angiotensin Aldosterone Syst 2019; 20:1470320319839525. [PMID: 30915878 PMCID: PMC6437324 DOI: 10.1177/1470320319839525] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Objective: In our recent study, non-Gaussianity of heart rate variability (λ25s), an indicator of sympathetic nerve activity, did not change during two-day treatment with the angiotensin II type 1 receptor blocker (ARB) azilsartan. Coadministration of calcium channel blockers (CCBs) might affect the study results. Methods: In this subanalysis, 20 patients with chronic kidney disease (14 men; age 61±15 years) were divided into three groups: patients with coadministration of L-type CCB, patients without coadministration of CCB, and patients with coadministration of sympathoinhibitory (L/T- or L/T/N-type) CCB. λ25s was calculated separately in daytime and nighttime. Results: Daytime λ25s at baseline was higher in patients with L-type CCB coadministration (0.62±0.18, n = 5) compared with those without CCB (0.49±0.13, n = 11) and those with sympathoinhibitory CCB (0.46±0.06, n = 4). The relationship between the changes in daytime λ25s and systolic blood pressure was positive in patients with L-type CCB coadministration, whereas the relationship was inverse in the other two groups. A larger decrease in daytime λ25s was shown in patients with L-type CCB coadministration compared with those in the other two groups. Conclusions: CCBs, as well as diuretics, are recommended as second-line antihypertensive agents. Our results suggested that ARBs can overwhelm the activation of sympathetic nerve activity stimulated by coadministration of L-type CCBs.
Collapse
Affiliation(s)
- Michio Fukuda
- Department of Cardio-Renal Medicine and Hypertension, Nagoya City University Graduate School of Medical Sciences, Japan
- Michio Fukuda, Nagoya City University Graduate School of Medical Sciences, Department of Cardio-Renal Medicine and Hypertension, Division of Nephrology and Dialysis Center, 1 Kawasumi, Mizuho-ku, Nagoya, 467-8601, Japan. Email
| | - Yukako Isobe-Sasaki
- Department of Cardio-Renal Medicine and Hypertension, Nagoya City University Graduate School of Medical Sciences, Japan
| | - Ryo Sato
- Department of Cardio-Renal Medicine and Hypertension, Nagoya City University Graduate School of Medical Sciences, Japan
| | - Toshiyuki Miura
- Department of Cardio-Renal Medicine and Hypertension, Nagoya City University Graduate School of Medical Sciences, Japan
| | - Masashi Mizuno
- Department of Cardio-Renal Medicine and Hypertension, Nagoya City University Graduate School of Medical Sciences, Japan
| | - Minamo Ono
- Department of Cardio-Renal Medicine and Hypertension, Nagoya City University Graduate School of Medical Sciences, Japan
| | - Ken Kiyono
- Department of Mechanical Science and Bioengineering, Osaka University, Japan
| | - Yoshiharu Yamamoto
- Department of Physical and Health Education, University of Tokyo Graduate School of Education, Japan
| | - Junichiro Hayano
- Department of Medical Education, Nagoya City University Graduate School of Medical Sciences, Japan
| | - Nobuyuki Ohte
- Department of Cardio-Renal Medicine and Hypertension, Nagoya City University Graduate School of Medical Sciences, Japan
| |
Collapse
|
7
|
A non-invasive magnetic resonance imaging approach for assessment of real-time microcirculation dynamics. Sci Rep 2017; 7:7468. [PMID: 28784990 PMCID: PMC5547069 DOI: 10.1038/s41598-017-06983-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2017] [Accepted: 06/21/2017] [Indexed: 11/17/2022] Open
Abstract
We present a novel, non-invasive magnetic resonance imaging (MRI) technique to assess real-time dynamic vasomodulation of the microvascular bed. Unlike existing perfusion imaging techniques, our method is sensitive only to blood volume and not flow velocity. Using graded gas challenges and a long-life, blood-pool T1-reducing agent gadofosveset, we can sensitively assess microvascular volume response in the liver, kidney cortex, and paraspinal muscle to vasoactive stimuli (i.e. hypercapnia, hypoxia, and hypercapnic hypoxia). Healthy adult rats were imaged on a 3 Tesla scanner and cycled through 10-minute gas intervals to elicit vasoconstriction followed by vasodilatation. Quantitative T1 relaxation time mapping was performed dynamically; heart rate and blood oxygen saturation were continuously monitored. Laser Doppler perfusion measurements confirmed MRI findings: dynamic changes in T1 corresponded with perfusion changes to graded gas challenges. Our new technique uncovered differential microvascular response to gas stimuli in different organs: for example, mild hypercapnia vasodilates the kidney cortex but constricts muscle vasculature. Finally, we present a gas challenge protocol that produces a consistent vasoactive response and can be used to assess vasomodulatory capacity. Our imaging approach to monitor real-time vasomodulation may be extended to other imaging modalities and is valuable for investigating diseases where microvascular health is compromised.
Collapse
|
8
|
Just TP, DeLorey DS. Sex differences in sympathetic vasoconstrictor responsiveness and sympatholysis. J Appl Physiol (1985) 2017; 123:128-135. [PMID: 28473610 DOI: 10.1152/japplphysiol.00139.2017] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Revised: 04/10/2017] [Accepted: 04/29/2017] [Indexed: 11/22/2022] Open
Abstract
Sex differences in the neurovascular control of blood pressure and vascular resistance have been reported. However, the mechanisms underlying the modulatory influence of sex have not been fully elucidated. Nitric oxide (NO) has been shown to inhibit sympathetic vasoconstriction in resting and contracting skeletal muscle, and estrogen modulates NO synthase (NOS) expression and NO bioavailability. Therefore NO-mediated inhibition of sympathetic vasoconstriction may be enhanced in females. Thus the purpose of the present study was to investigate the hypothesis that sympathetic vasoconstrictor responsiveness would be blunted and NO-mediated inhibition of sympathetic vasoconstriction would be enhanced in females compared with males. Male (M; n = 8) and female (F; n = 10) Sprague-Dawley rats were anesthetized and surgically instrumented for measurement of arterial blood pressure and femoral artery blood flow and stimulation of the lumbar sympathetic chain. The percentage change of femoral vascular conductance in response to sympathetic chain stimulation delivered at 2 and 5 Hz was determined at rest and during triceps surae muscle contraction before (control) and after NOS blockade [Nω-nitro-l-arginine methyl ester (l-NAME), 10 mg/kg iv]. At rest, sympathetic vasoconstrictor responsiveness was augmented (P < 0.05) in female compared with male rats at 2 Hz [F: -33 ± 8% (SD); M: -26 ± 6%] but was not different at 5 Hz (F: -55 ± 7%; M: -47 ± 7%). During muscle contraction, evoked vasoconstriction was similar (P > 0.05) in females and males at 2 Hz (F: -12 ± 5%; M: -13 ± 5%) but was blunted (P < 0.05) in females compared with males at 5 Hz (F: -24 ± 5%; M: -34 ± 8%). l-NAME increased (P < 0.05) sympathetic vasoconstrictor responsiveness in both groups at rest and during contraction. Contraction-mediated inhibition of vasoconstriction (sympatholysis) was enhanced (P < 0.05) in females compared with males; however, sympatholysis was not different (P > 0.05) between males and females in the presence of NOS blockade, indicating that NO-mediated sympatholysis was augmented in female rats. These data suggest that sex modulates sympathetic vascular control in resting and contracting skeletal muscle and that a portion of the enhanced sympatholysis in female rats was NO dependent.NEW & NOTEWORTHY Sex differences in the neurovascular regulation of blood pressure and vascular resistance have been documented. However, our understanding of the underlying mechanisms that mediate these differences is incomplete. The present study demonstrates that female rats have an enhanced capacity to inhibit sympathetic vasoconstriction during exercise (sympatholysis) and that NO mediates a portion of the enhanced sympatholysis.
Collapse
Affiliation(s)
- Timothy P Just
- Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Darren S DeLorey
- Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Alberta, Canada
| |
Collapse
|
9
|
Just TP, DeLorey DS. Exercise training and α1-adrenoreceptor-mediated sympathetic vasoconstriction in resting and contracting skeletal muscle. Physiol Rep 2016; 4:4/3/e12707. [PMID: 26869686 PMCID: PMC4758927 DOI: 10.14814/phy2.12707] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Exercise training (ET) increases sympathetic vasoconstrictor responsiveness and enhances contraction‐mediated inhibition of sympathetic vasoconstriction (i.e., sympatholysis) through a nitric oxide (NO)‐dependent mechanism. Changes in α2‐adrenoreceptor vasoconstriction mediate a portion of these training adaptations, however the contribution of other postsynaptic receptors remains to be determined. Therefore, the purpose of this study was to investigate the effect of ET on α1‐adrenoreceptor‐mediated vasoconstriction in resting and contracting muscle. It was hypothesized that α1‐adrenoreceptor‐mediated sympatholysis would be enhanced following ET. Male Sprague Dawley rats were randomized to sedentary (S; n = 12) or heavy‐intensity treadmill ET (n = 11) groups. Subsequently, rats were anesthetized and instrumented for lumbar sympathetic chain stimulation and measurement of femoral vascular conductance (FVC) at rest and during muscle contraction. The percentage change in FVC in response to sympathetic stimulation was measured in control, α1‐adrenoreceptor blockade (Prazosin; 20 μg, IV), and combined α1 and NO synthase (NOS) blockade (l‐NAME; 5 mg·kg−1IV) conditions. Sympathetic vasoconstrictor responsiveness was increased (P < 0.05) in ET compared to S rats at low, but not high (P > 0.05) stimulation frequencies at rest (S: 2 Hz: −25 ± 4%; 5 Hz: −45 ± 5 %; ET: 2 Hz: −35 ± 7%, 5 Hz: −52 ± 7%), whereas sympathetic vasoconstrictor responsiveness was not different (P > 0.05) between groups during contraction (S: 2 Hz: −11 ± 8%; 5 Hz: −26 ± 11%; ET: 2 Hz: −10 ± 7%, 5 Hz: −27 ± 12%). Prazosin blunted (P < 0.05) vasoconstrictor responsiveness in S and ET rats at rest and during contraction, and abolished group differences in vasoconstrictor responsiveness. Subsequent NOS blockade increased vasoconstrictor responses (P < 0.05) in S at rest and during contraction, whereas in ET vasoconstriction was increased (P < 0.05) in response to sympathetic stimulation at 2 Hz at rest and unchanged (P > 0.05) during contraction. ET enhanced (P < 0.05) sympatholysis, however the training‐mediated improvements in sympatholysis were abolished by α1‐adrenoreceptor blockade. Subsequent NOS inhibition did not alter (P > 0.05) sympatholysis in S or ET rats. In conclusion, ET augmented α1‐adrenoreceptor‐mediated vasoconstriction in resting skeletal muscle and enhanced α1‐adrenoreceptor‐mediated sympatholysis. Furthermore, these data suggest that NO is not required to inhibit α2‐adrenoreceptor‐ and nonadrenoreceptor‐mediated vasoconstriction during exercise.
Collapse
Affiliation(s)
- Timothy P Just
- Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB, Canada
| | - Darren S DeLorey
- Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB, Canada
| |
Collapse
|
10
|
Ganesh T, Estrada M, Duffin J, Cheng HL. T2* and T1 assessment of abdominal tissue response to graded hypoxia and hypercapnia using a controlled gas mixing circuit for small animals. J Magn Reson Imaging 2016; 44:305-16. [PMID: 26872559 DOI: 10.1002/jmri.25169] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Accepted: 01/12/2016] [Indexed: 01/13/2023] Open
Abstract
PURPOSE To characterize T2* and T1 relaxation time response to a wide spectrum of gas challenges in extracranial tissues of healthy rats. MATERIALS AND METHODS A range of graded gas mixtures (hyperoxia, hypercapnia, hypoxia, and hypercapnic hypoxia) were delivered through a controlled gas-mixing circuit to mechanically ventilated and intubated rats. Quantitative magnetic resonance imaging (MRI) was performed on a 3T clinical scanner; T2* and T1 maps were computed to determine tissue response in the liver, kidney cortex, and paraspinal muscles. Heart rate and blood oxygen saturation (SaO2 ) were measured through a rodent oximeter and physiological monitor. RESULTS T2* decreases consistent with lowered SaO2 measurements were observed for hypercapnia and hypoxia, but decreases were significant only in liver and kidney cortex (P < 0.05) for >10% CO2 and <15% O2 , with the new gas stimulus, hypercapnic hypoxia, producing the greatest T2* decrease. Hyperoxia-related T2* increases were accompanied by negligible increases in SaO2 . T1 generally increased, if at all, in the liver and decreased in the kidney. Significance was observed (P < 0.05) only in kidney for >90% O2 and >5% CO2 . CONCLUSION T2* and T1 provide complementary roles for evaluating extracranial tissue response to a broad range of gas challenges. Based on both measured and known physiological responses, our results are consistent with T2* as a sensitive marker of blood oxygen saturation and T1 as a weak marker of blood volume changes. J. Magn. Reson. Imaging 2016;44:305-316.
Collapse
Affiliation(s)
- Tameshwar Ganesh
- Translational Biology & Engineering Program, Ted Rogers Centre for Heart Research, Toronto, Canada.,Leslie Dan Faculty of Pharmacy, University of Toronto, Canada.,Physiology & Experimental Medicine, Hospital for Sick Children Research Institute, Toronto, Canada
| | - Marvin Estrada
- Lab Animal Services, Hospital for Sick Children, Toronto, Canada
| | - James Duffin
- Department of Anesthesia, University of Toronto, Canada
| | - Hai Ling Cheng
- Translational Biology & Engineering Program, Ted Rogers Centre for Heart Research, Toronto, Canada.,Leslie Dan Faculty of Pharmacy, University of Toronto, Canada.,Physiology & Experimental Medicine, Hospital for Sick Children Research Institute, Toronto, Canada.,The Edward S. Rogers Sr. Department of Electrical & Computer Engineering, University of Toronto, Canada.,Institute of Biomaterials & Biomedical Engineering, University of Toronto, Canada
| |
Collapse
|
11
|
Marshall JM. Interactions between local dilator and sympathetic vasoconstrictor influences in skeletal muscle in acute and chronic hypoxia. Exp Physiol 2015; 100:1400-11. [DOI: 10.1113/ep085139] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Revised: 06/18/2015] [Accepted: 06/19/2015] [Indexed: 12/14/2022]
Affiliation(s)
- Janice M. Marshall
- School of Clinical & Experimental Medicine; Centre for Cardiovascular Science, University of Birmingham; B15 2TT UK
| |
Collapse
|
12
|
Mansukhani MP, Kara T, Caples SM, Somers VK. Chemoreflexes, sleep apnea, and sympathetic dysregulation. Curr Hypertens Rep 2015; 16:476. [PMID: 25097113 DOI: 10.1007/s11906-014-0476-2] [Citation(s) in RCA: 73] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Obstructive sleep apnea (OSA) and hypertension are closely linked conditions. Disordered breathing events in OSA are characterized by increasing efforts against an occluded airway while asleep, resulting in a marked sympathetic response. This is predominantly due to hypoxemia activating the chemoreflexes, resulting in reflex increases in sympathetic neural outflow. In addition, apnea - and the consequent lack of inhibition of the sympathetic system that occurs with lung inflation during normal breathing - potentiates central sympathetic outflow. Sympathetic activation persists into the daytime, and is thought to contribute to hypertension and other adverse cardiovascular outcomes. This review discusses chemoreflex physiology and sympathetic modulation during normal sleep, as well as the sympathetic dysregulation seen in OSA, its extension into wakefulness, and changes after treatment. Evidence supporting the role of the peripheral chemoreflex in the sympathetic dysregulation seen in OSA, including in the context of comorbid obesity, metabolic syndrome, and systemic hypertension, is reviewed. Finally, alterations in cardiovascular variability and other potential mechanisms that may play a role in the autonomic imbalance in OSA are also discussed.
Collapse
Affiliation(s)
- Meghna P Mansukhani
- Sleep Medicine, Affiliated Communities Medical Center, 101 Willmar Avenue SW, Willmar, MN, USA,
| | | | | | | |
Collapse
|
13
|
Rook W, Johnson CD, Coney AM, Marshall JM. Prenatal Hypoxia Leads to Increased Muscle Sympathetic Nerve Activity, Sympathetic Hyperinnervation, Premature Blunting of Neuropeptide Y Signaling, and Hypertension in Adult Life. Hypertension 2014; 64:1321-7. [DOI: 10.1161/hypertensionaha.114.04374] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Adverse conditions prenatally increase the risk of cardiovascular disease, including hypertension. Chronic hypoxia in utero (CHU) causes endothelial dysfunction, but whether sympathetic vasoconstrictor nerve functioning is altered is unknown. We, therefore, compared in male CHU and control (N) rats muscle sympathetic nerve activity, vascular sympathetic innervation density, and mechanisms of sympathetic vasoconstriction. In young (Y)-CHU and Y-N rats (≈3 months), baseline arterial blood pressure was similar. However, tonic muscle sympathetic nerve activity recorded focally from arterial vessels of spinotrapezius muscle had higher mean frequency in Y-CHU than in Y-N rats (0.56±0.075 versus 0.33±0.036 Hz), and the proportions of single units with high instantaneous frequencies (1–5 and 6–10 Hz) being greater in Y-CHU rats. Sympathetic innervation density of tibial arteries was ≈50% greater in Y-CHU than in Y-N rats. Increases in femoral vascular resistance evoked by sympathetic stimulation at low frequency (2 Hz for 2 minutes) and bursts at 20 Hz were substantially smaller in Y-CHU than in Y-N rats. In Y-N only, the neuropeptide Y Y1-receptor antagonist BIBP3226 attenuated these responses. By contrast, baseline arterial blood pressure was higher in middle-aged (M)-CHU than in M-N rats (≈9 months; 139±3 versus 126±3 mm Hg, respectively). BIBP3226 had no effect on femoral vascular resistance increases evoked by 2 Hz or 20 Hz bursts in M-N or M-CHU rats. These results indicate that fetal programming induced by prenatal hypoxia causes an increase in centrally generated muscle sympathetic nerve activity in youth and hypertension by middle age. This is associated with blunting of sympathetically evoked vasoconstriction and its neuropeptide Y component that may reflect premature vascular aging and contribute to increased risk of cardiovascular disease.
Collapse
Affiliation(s)
- William Rook
- From the School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, B15 2TT UK (W.R., A.M.C., J.M.M.); and Centre for Biomedical Sciences Education, Queens University, Belfast, Northern Ireland, UK (C.D.J.)
| | - Christopher D. Johnson
- From the School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, B15 2TT UK (W.R., A.M.C., J.M.M.); and Centre for Biomedical Sciences Education, Queens University, Belfast, Northern Ireland, UK (C.D.J.)
| | - Andrew M. Coney
- From the School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, B15 2TT UK (W.R., A.M.C., J.M.M.); and Centre for Biomedical Sciences Education, Queens University, Belfast, Northern Ireland, UK (C.D.J.)
| | - Janice M. Marshall
- From the School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, B15 2TT UK (W.R., A.M.C., J.M.M.); and Centre for Biomedical Sciences Education, Queens University, Belfast, Northern Ireland, UK (C.D.J.)
| |
Collapse
|
14
|
Freet CS, Stoner JF, Tang X. Baroreflex and chemoreflex controls of sympathetic activity following intermittent hypoxia. Auton Neurosci 2013; 174:8-14. [PMID: 23305890 DOI: 10.1016/j.autneu.2012.12.005] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2012] [Revised: 11/25/2012] [Accepted: 12/15/2012] [Indexed: 11/29/2022]
Abstract
There is a large amount of evidence linking obstructive sleep apnea (OSA), and the associated intermittent hypoxia that accompanies it, with the development of hypertension. For example, cross-sectional studies demonstrate that the prevalence of hypertension increases with the severity of OSA (Bixler et al., 2000; Grote et al., 2001) and an initial determination of OSA is associated with a three-fold increase for future hypertension (Peppard et al., 2000). Interestingly, bouts of intermittent hypoxia have also been shown to affect sympathetic output associated with the baroreflex and chemoreflex, important mechanisms in the regulation of arterial blood pressure. As such, the possibility exists that changes in the baroreflex and chemoreflex may contribute to the development of chronic hypertension observed in OSA patients. The aim of the current article is to briefly review the response of the baroreflex and chemoreflex to intermittent hypoxic exposure and to evaluate evidence for the hypothesis that modification of these autonomic reflexes may, at least in part, support the comorbidity observed between chronic hypertension and OSA.
Collapse
Affiliation(s)
- Christopher S Freet
- The Pennsylvania State University College of Medicine, Department of Neural and Behavioral Sciences, Hershey, PA 17033, USA.
| | | | | |
Collapse
|
15
|
Billaud M, Lohman AW, Straub AC, Parpaite T, Johnstone SR, Isakson BE. Characterization of the thoracodorsal artery: morphology and reactivity. Microcirculation 2012; 19:360-72. [PMID: 22335567 DOI: 10.1111/j.1549-8719.2012.00172.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
OBJECTIVES In this paper, we describe the histological and contractile properties of the thoracodorsal artery (TDA), which indirectly feeds the spinotrapezius muscle. METHODS We used immunolabelling techniques to histologically characterize the TDA while the contractile properties were assessed using pressure arteriography. RESULTS Our results demonstrate that the TDA is composed of approximately one to two layers of smooth muscle cells, is highly innervated with adrenergic nerves, and develops spontaneous tone at intraluminal pressures above 80 mmHg. The reactivity of the TDA in response to various contractile agonists such as phenylephrine, noradrenaline, angiotensin II, serotonin, endothelin 1, and ATP, as well as vasodilators, shows that the TDA exhibits a remarkably comparable reactivity to what has been observed in mesenteric arteries. We further studied the different components of the TDA response to acetylcholine, and found that the TDA was sensitive to TRAM 34, a blocker of the intermediate conductance potassium channel, which is highly suggestive of an endothelium-dependent hyperpolarization. CONCLUSIONS We conclude that the TDA exhibits comparable characteristics to other current vascular models, with the additional advantage of being easily manipulated for molecular and ex vivo vasoreactivity studies.
Collapse
Affiliation(s)
- Marie Billaud
- Robert M. Berne Cardiovascular Research Center, University of Virginia School of Medicine, Charlottesville, Virginia 22908, USA
| | | | | | | | | | | |
Collapse
|