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Kano Y, Miura S, Eshima H, Ezaki O, Poole DC. The effects of PGC-1α on control of microvascular Po2 kinetics following onset of muscle contractions. J Appl Physiol (1985) 2014; 117:163-70. [DOI: 10.1152/japplphysiol.00080.2014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
During contractions, regulation of microvascular oxygen partial pressure (Pmvo2), which drives blood-myocyte O2 flux, is a function of skeletal muscle fiber type and oxidative capacity and can be altered by exercise training. The kinetics of Pmvo2 during contractions in predominantly fast-twitch muscles evinces a more rapid fall to far lower levels compared with slow-twitch counterparts. Peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) improves endurance performance, in part, due to mitochondrial biogenesis, a fiber-type switch to oxidative fibers, and angiogenesis in skeletal muscle. We tested the hypothesis that improvement of exercise capacity by genetic overexpression of PGC-1α would be associated with an altered Pmvo2 kinetics profile of the fast-twitch (white) gastrocnemius during contractions toward that seen in slow-twitch muscles (i.e., slowed response kinetics and elevated steady-state Pmvo2). Phosphorescence quenching techniques were used to measure Pmvo2 at rest and during separate bouts of twitch (1 Hz) and tetanic (100 Hz) contractions in gastrocnemius muscles of mice with overexpression of PGC-1α and wild-type littermates (WT) mice under isoflurane anesthesia. Muscles of PGC-1α mice exhibited less fatigue than WT ( P < 0.01). However, except for the Pmvo2 response immediately following onset of contractions, WT and PGC-1α mice demonstrated similar Pmvo2 kinetics. Specifically, the time delay of the Pmvo2 response was shortened in PGC-1α mice compared with WT (1 Hz: WT, 6.6 ± 2.4 s; PGC-1α, 2.9 ± 0.8 s; 100 Hz: WT, 3.3 ± 1.1 s, PGC-1α, 0.9 ± 0.3 s, both P < 0.05). The ratio of muscle force to Pmvo2 was higher for the duration of tetanic contractions in PGC-1α mice. Slower dynamics and maintenance of higher Pmvo2 following muscle contractions is not obligatory for improved fatigue resistance in fast-twitch muscle of PGC-1α mice. Moreover, overexpression of PGC-1α may accelerate O2 utilization kinetics to a greater extent than O2 delivery kinetics.
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Affiliation(s)
- Yutaka Kano
- Department of Engineering Science, University of Electro-Communications, Chofu, Tokyo, Japan
| | - Shinji Miura
- Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, Shizuoka, Japan
| | - Hiroaki Eshima
- Department of Engineering Science, University of Electro-Communications, Chofu, Tokyo, Japan
| | - Osamu Ezaki
- Department of Human Health and Design, Showa Women's University, Tokyo, Japan; and
| | - David C. Poole
- Departments of Anatomy, Physiology, and Kinesiology, Kansas State University, Manhattan, Kansas
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Abstract
Muscular exercise requires transitions to and from metabolic rates often exceeding an order of magnitude above resting and places prodigious demands on the oxidative machinery and O2-transport pathway. The science of kinetics seeks to characterize the dynamic profiles of the respiratory, cardiovascular, and muscular systems and their integration to resolve the essential control mechanisms of muscle energetics and oxidative function: a goal not feasible using the steady-state response. Essential features of the O2 uptake (VO2) kinetics response are highly conserved across the animal kingdom. For a given metabolic demand, fast VO2 kinetics mandates a smaller O2 deficit, less substrate-level phosphorylation and high exercise tolerance. By the same token, slow VO2 kinetics incurs a high O2 deficit, presents a greater challenge to homeostasis and presages poor exercise tolerance. Compelling evidence supports that, in healthy individuals walking, running, or cycling upright, VO2 kinetics control resides within the exercising muscle(s) and is therefore not dependent upon, or limited by, upstream O2-transport systems. However, disease, aging, and other imposed constraints may redistribute VO2 kinetics control more proximally within the O2-transport system. Greater understanding of VO2 kinetics control and, in particular, its relation to the plasticity of the O2-transport/utilization system is considered important for improving the human condition, not just in athletic populations, but crucially for patients suffering from pathologically slowed VO2 kinetics as well as the burgeoning elderly population.
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Affiliation(s)
- David C Poole
- Departments of Kinesiology, Anatomy, and Physiology, Kansas State University, Manhattan, Kansas, USA.
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Mechanical ventilation reduces rat diaphragm blood flow and impairs oxygen delivery and uptake. Crit Care Med 2012; 40:2858-66. [PMID: 22846782 DOI: 10.1097/ccm.0b013e31825b933a] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVES Although mechanical ventilation is a life-saving intervention in patients suffering from respiratory failure, prolonged mechanical ventilation is often associated with numerous complications including problematic weaning. In contracting skeletal muscle, inadequate oxygen supply can limit oxidative phosphorylation resulting in muscular fatigue. However, whether prolonged mechanical ventilation results in decreased diaphragmatic blood flow and induces an oxygen supply-demand imbalance in the diaphragm remains unknown. DESIGN We tested the hypothesis that prolonged controlled mechanical ventilation results in a time-dependent reduction in rat diaphragmatic blood flow and microvascular PO2 and that prolonged mechanical ventilation would diminish the diaphragm's ability to increase blood flow in response to muscular contractions. MEASUREMENTS AND MAIN RESULTS Compared to 30 mins of mechanical ventilation, 6 hrs of mechanical ventilation resulted in a 75% reduction in diaphragm blood flow (via radiolabeled microspheres), which did not occur in the intercostal muscle or high-oxidative hindlimb muscle (e.g., soleus). There was also a time-dependent decline in diaphragm microvascular PO2 (via phosphorescence quenching). Further, contrary to 30 mins of mechanical ventilation, 6 hrs of mechanical ventilation significantly compromised the diaphragm's ability to increase blood flow during electrically-induced contractions, which resulted in a ~80% reduction in diaphragm oxygen uptake. In contrast, 6 hrs of spontaneous breathing in anesthetized animals did not alter diaphragm blood flow or the ability to augment flow during electrically-induced contractions. CONCLUSIONS These new and important findings reveal that prolonged mechanical ventilation results in a time-dependent decrease in the ability of the diaphragm to augment blood flow to match oxygen demand in response to contractile activity and could be a key contributing factor to difficult weaning. Although additional experiments are required to confirm, it is tempting to speculate that this ventilator-induced decline in diaphragmatic oxygenation could promote a hypoxia-induced generation of reactive oxygen species in diaphragm muscle fibers and contribute to ventilator-induced diaphragmatic atrophy and contractile dysfunction.
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Macananey O, O'Shea D, Warmington SA, Green S, Egaña M. Gymnasium-based unsupervised exercise maintains benefits in oxygen uptake kinetics obtained following supervised training in type 2 diabetes. Appl Physiol Nutr Metab 2012; 37:599-609. [PMID: 22563745 DOI: 10.1139/h2012-012] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Supervised exercise (SE) in patients with type 2 diabetes improves oxygen uptake kinetics at the onset of exercise. Maintenance of these improvements, however, has not been examined when supervision is removed. We explored if potential improvements in oxygen uptake kinetics following a 12-week SE that combined aerobic and resistance training were maintained after a subsequent 12-week unsupervised exercise (UE). The involvement of cardiac output (CO) in these improvements was also tested. Nineteen volunteers with type 2 diabetes were recruited. Oxygen uptake kinetics and CO (inert gas rebreathing) responses to constant-load cycling at 50% ventilatory threshold (V(T)), 80% V(T), and mid-point between V(T) and peak workload (50% Δ) were examined at baseline (on 2 occasions) and following each 12-week training period. Participants decided to exercise at a local gymnasium during the UE. Thirteen subjects completed all the interventions. The time constant of phase 2 of oxygen uptake was significantly faster (p < 0.05) post-SE and post-UE compared with baseline at 50% V(T) (17.3 ± 10.7 s and 17.5 ± 5.9 s vs. 29.9 ± 10.7 s), 80% V(T) (18.9 ± 4.7 and 20.9 ± 8.4 vs. 34.3 ± 12.7s), and 50% Δ (20.4 ± 8.2 s and 20.2 ± 6.0 s vs. 27.6 ± 3.7 s). SE also induced faster heart rate kinetics at all 3 intensities and a larger increase in CO at 30 s in relation to 240 s at 80% V(T); and these responses were maintained post-UE. Unsupervised exercise maintained benefits in oxygen uptake kinetics obtained during a supervised exercise in subjects with diabetes, and these benefits were associated with a faster dynamic response of heart rate after training.
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Affiliation(s)
- Oscar Macananey
- Department of Physiology, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin 2, Ireland
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McDonough P, Padilla DJ, Kano Y, Musch TI, Poole DC, Behnke BJ. Plasticity of microvascular oxygenation control in rat fast-twitch muscle: effects of experimental creatine depletion. Respir Physiol Neurobiol 2012; 181:14-20. [PMID: 22285799 PMCID: PMC3296908 DOI: 10.1016/j.resp.2012.01.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2011] [Revised: 01/09/2012] [Accepted: 01/10/2012] [Indexed: 10/14/2022]
Abstract
Aging, heart failure and diabetes each compromise the matching of O2 delivery (Q˙O2)-to-metabolic requirements (O2 uptake, V˙O2) in skeletal muscle such that the O2 pressure driving blood-myocyte O2 flux (microvascular PO2, PmvO2) is reduced and contractile function impaired. In contrast, β-guanidinopropionic acid (β-GPA) treatment improves muscle contractile function, primarily in fast-twitch muscle (Moerland and Kushmerick, 1994). We tested the hypothesis that β-GPA (2% wt/BW in rat chow, 8 weeks; n=14) would improve Q˙O2-to-V˙O2 matching (elevated PmvO2) during contractions (4.5V @ 1Hz) in mixed (MG) and white (WG) portions of the gastrocnemius, both predominantly fast-twitch). Compared with control (CON), during contractions PmvO2 fell less following β-GPA (MG -54%, WG -26%, P<0.05), elevating steady-state PmvO2 (CON, MG: 10±2, WG: 9±1; β-GPA, MG 16±2, WG 18±2 mmHg, P<0.05). This reflected an increased Q˙O2/V˙O2 ratio due primarily to a reduced V˙O2 in β-GPA muscles. It is likely that this adaptation helps facilitate the β-GPA-induced enhancement of contractile function in fast-twitch muscles.
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Affiliation(s)
- Paul McDonough
- Department of Kinesiology, University of Texas at Arlington, Arlington, TX 76019, USA
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Koga S, Kano Y, Barstow TJ, Ferreira LF, Ohmae E, Sudo M, Poole DC. Kinetics of muscle deoxygenation and microvascular Po2 during contractions in rat: comparison of optical spectroscopy and phosphorescence-quenching techniques. J Appl Physiol (1985) 2012; 112:26-32. [DOI: 10.1152/japplphysiol.00925.2011] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The overarching presumption with near-infrared spectroscopy measurement of muscle deoxygenation is that the signal reflects predominantly the intramuscular microcirculatory compartment rather than intramyocyte myoglobin (Mb). To test this hypothesis, we compared the kinetics profile of muscle deoxygenation using visible light spectroscopy (suitable for the superficial fiber layers) with that for microvascular O2 partial pressure (i.e., PmvO2, phosphorescence quenching) within the same muscle region (0.5∼1 mm depth) during transitions from rest to electrically stimulated contractions in the gastrocnemius of male Wistar rats ( n = 14). Both responses could be modeled by a time delay (TD), followed by a close-to-exponential change to the new steady level. However, the TD for the muscle deoxygenation profile was significantly longer compared with that for the phosphorescence-quenching PmvO2 [8.6 ± 1.4 and 2.7 ± 0.6 s (means ± SE) for the deoxygenation and PmvO2, respectively; P < 0.05]. The time constants (τ) of the responses were not different (8.8 ± 4.7 and 11.2 ± 1.8 s for the deoxygenation and PmvO2, respectively). These disparate (TD) responses suggest that the deoxygenation characteristics of Mb extend the TD, thereby increasing the duration (number of contractions) before the onset of muscle deoxygenation. However, this effect was insufficient to increase the mean response time. Somewhat differently, the muscle deoxygenation response measured using near-infrared spectroscopy in the deeper regions (∼5 mm depth) (∼50% type I Mb-rich, highly oxidative fibers) was slower (τ = 42.3 ± 6.6 s; P < 0.05) than the corresponding value for superficial muscle measured using visible light spectroscopy or PmvO2 and can be explained on the basis of known fiber-type differences in PmvO2 kinetics. These data suggest that, within the superficial and also deeper muscle regions, the τ of the deoxygenation signal may represent a useful index of local O2 extraction kinetics during exercise transients.
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Affiliation(s)
- Shunsaku Koga
- Applied Physiology Laboratory, Kobe Design University, Kobe
| | - Yutaka Kano
- The University of Electro-Communications, Chofu; and
| | - Thomas J. Barstow
- Departments of Kinesiology and Anatomy and Physiology, Kansas State University, Manhattan, Kansas
| | - Leonardo F. Ferreira
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida; and
| | | | - Mizuki Sudo
- The University of Electro-Communications, Chofu; and
| | - David C. Poole
- Departments of Kinesiology and Anatomy and Physiology, Kansas State University, Manhattan, Kansas
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Portha B, Giroix MH, Tourrel-Cuzin C, Le-Stunff H, Movassat J. The GK rat: a prototype for the study of non-overweight type 2 diabetes. METHODS IN MOLECULAR BIOLOGY (CLIFTON, N.J.) 2012; 933:125-59. [PMID: 22893405 DOI: 10.1007/978-1-62703-068-7_9] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Type 2 diabetes mellitus (T2D) arises when the endocrine pancreas fails to secrete sufficient insulin to cope with the metabolic demand because of β-cell secretory dysfunction and/or decreased β-cell mass. Defining the nature of the pancreatic islet defects present in T2D has been difficult, in part because human islets are inaccessible for direct study. This review is aimed to illustrate to what extent the Goto Kakizaki rat, one of the best characterized animal models of spontaneous T2D, has proved to be a valuable tool offering sufficient commonalities to study this aspect. A comprehensive compendium of the multiple functional GK abnormalities so far identified is proposed in this perspective, together with their time-course and interactions. A special focus is given toward the pathogenesis of defective β-cell number and function in the GK model. It is proposed that the development of T2D in the GK model results from the complex interaction of multiple events: (1) several susceptibility loci containing genes responsible for some diabetic traits; (2) gestational metabolic impairment inducing an epigenetic programming of the offspring pancreas and the major insulin target tissues; and (3) environmentally induced loss of β-cell differentiation due to chronic exposure to hyperglycemia/hyperlipidemia, inflammation, and oxidative stress.
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Affiliation(s)
- Bernard Portha
- Laboratoire B2PE (Biologie et Pathologie du Pancréas Endocrine), Unité BFA (Biologie Fonctionnelle et Adaptive), Université Paris-Diderot, CNRS EAC 4413, Paris, France.
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58
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Poole DC, Copp SW, Hirai DM, Musch TI. Dynamics of muscle microcirculatory and blood-myocyte O(2) flux during contractions. Acta Physiol (Oxf) 2011; 202:293-310. [PMID: 21199399 DOI: 10.1111/j.1748-1716.2010.02246.x] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The O(2) requirements of contracting skeletal muscle may increase 100-fold above rest. In 1919, August Krogh's brilliant insights recognized the capillary as the principal site for this increased blood-myocyte O(2) flux. Based on the premise that most capillaries did not sustain RBC flux at rest, Krogh proposed that capillary recruitment [i.e. initiation of red blood cell (RBC) flux in previously non-flowing capillaries] increased the capillary surface area available for O(2) flux and reduced mean capillary-to-mitochondrial diffusion distances. More modern experimental approaches reveal that most muscle capillaries may support RBC flux at rest. Thus, rather than contraction-induced capillary recruitment per se, increased RBC flux and haematocrit within already-flowing capillaries probably elevate perfusive and diffusive O(2) conductances and hence blood-myocyte O(2) flux. Additional surface area for O(2) exchange is recruited but, crucially, this may occur along the length of already-flowing capillaries (i.e. longitudinal recruitment). Today, the capillary is still considered the principal site for O(2) and substrate delivery to contracting skeletal muscle. Indeed, the presence of very low intramyocyte O(2) partial pressures (PO(2)s) and the absence of intramyocyte PO(2) gradients, whilst refuting the relevance of diffusion distances, place an even greater importance on capillary hemodynamics. This emergent picture calls for a paradigm-shift in our understanding of the function of capillaries by de-emphasizing de novo'capillary recruitment'. Diseases such as heart failure impair blood-myocyte O(2) flux, in part, by decreasing the proportion of RBC-flowing capillaries. Knowledge of capillary function in healthy muscle is requisite for identification of pathology and efficient design of therapeutic treatments.
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Affiliation(s)
- D C Poole
- Departments of Kinesiology, Anatomy and Physiology, Kansas State University, Manhattan, KS, USA.
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59
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Dominguez JM, Davis RT, McCullough DJ, Stabley JN, Behnke BJ. Aging and exercise training reduce testes microvascular PO2 and alter vasoconstrictor responsiveness in testicular arterioles. Am J Physiol Regul Integr Comp Physiol 2011; 301:R801-10. [PMID: 21677264 DOI: 10.1152/ajpregu.00203.2011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Testicular function and associated testosterone concentration decline with advancing age, and an impaired O₂ supply may contribute, in part, to this reduction. We hypothesized that there would be a reduced microvascular Po₂ (Po₂(m)) in the testes from aged rats, and this reduced Po₂(m) would be associated with impaired vasomotor control in isolated resistance arterioles. In addition, given the positive effect of exercise on microvascular Po₂ and arteriolar function, we further hypothesized that there would be an enhanced Po₂(m) in the testes from aged animals after aerobic exercise training. Testicular Po₂(m) was measured in vivo via phosphorescence quenching in young and aged sedentary (SED) and exercise-trained (ET; 15 m/min treadmill walking, 15-degree incline, 5 days/wk for 10 wk) male Fischer-344 rats. Vasoconstriction to α-adrenergic [norepinephrine (NE) and phenylephrine (PE)] and myogenic stimuli in testicular arterioles was assessed in vitro. In the SED animals, testicular Po₂(m) was reduced by ∼50% with old age (aged SED 11.8 ± 1.9 vs. young SED 22.1 ± 1.1 mmHg; P = 0.0001). Contrary to our hypothesis, exercise training did not alter Po₂(m) in the aged group and reduced testicular Po₂(m) in the young animals, abolishing age-related differences (young ET, 10.0 ± 0.8 vs. aged ET, 10.7 ± 0.9 mmHg; P = 0.37). Vasoconstrictor responsiveness to NE and PE was diminished in aged compared with young (NE: young SED, 58 ± 2 vs. aged SED, 47 ± 2%; P = 0.001) (PE: young SED, 51 ± 3 vs. aged SED, 36 ± 5%; P = 0.008). Exercise training did not alter maximal vasoconstriction to NE in young or aged groups. In summary, advancing age is associated with a reduced testis Po₂(m) and impaired adrenergic vasoconstriction. The diminished testicular microvascular driving pressure of O₂ and associated vascular dysfunction provides mechanistic insight into the old age-related decrease in testicular function, and a reduced Po₂(m) may contribute, in part, to reduced fertility markers after exercise training.
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Affiliation(s)
- James M Dominguez
- Department of Applied Physiology and Kinesiology, Center for Exercise Science, University of Florida, Gainesville, Florida, USA
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60
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Nie J, Xue B, Sukumaran S, Jusko WJ, DuBois DC, Almon RR. Differential muscle gene expression as a function of disease progression in Goto-Kakizaki diabetic rats. Mol Cell Endocrinol 2011; 338:10-7. [PMID: 21356272 PMCID: PMC3093670 DOI: 10.1016/j.mce.2011.02.016] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/16/2010] [Revised: 01/26/2011] [Accepted: 02/17/2011] [Indexed: 11/23/2022]
Abstract
The Goto-Kakizaki (GK) rat, a polygenic non-obese model of type 2 diabetes, is a useful surrogate for study of diabetes-related changes independent of obesity. GK rats and appropriate controls were killed at 4, 8, 12, 16 and 20 weeks post-weaning and differential muscle gene expression along with body and muscle weights, plasma hormones and lipids, and blood cell measurements were carried out. Gene expression analysis identified 204 genes showing 2-fold or greater differences between GK and controls in at least 3 ages. Array results suggested increased oxidative capacity in GK muscles, as well as differential gene expression related to insulin resistance, which was also indicated by HOMA-IR measurements. In addition, potential new biomarkers in muscle gene expression were identified that could be either a cause or consequence of T2DM. Furthermore, we demonstrate here the presence of chronic inflammation evident both systemically and in the musculature, despite the absence of obesity.
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Affiliation(s)
- Jing Nie
- Department of Biological Sciences, State University of New York at Buffalo, Buffalo, N.Y. 14260 USA
| | - Bai Xue
- Department of Biological Sciences, State University of New York at Buffalo, Buffalo, N.Y. 14260 USA
| | - Siddharth Sukumaran
- Department of Biological Sciences, State University of New York at Buffalo, Buffalo, N.Y. 14260 USA
| | - William J. Jusko
- Department of Pharmaceutical Sciences, State University of New York at Buffalo, Buffalo, N.Y. 14260 USA
- New York State Center of Excellence in Bioinformatics and Life Sciences
| | - Debra C. DuBois
- Department of Biological Sciences, State University of New York at Buffalo, Buffalo, N.Y. 14260 USA
- Department of Pharmaceutical Sciences, State University of New York at Buffalo, Buffalo, N.Y. 14260 USA
| | - Richard R. Almon
- Department of Biological Sciences, State University of New York at Buffalo, Buffalo, N.Y. 14260 USA
- Department of Pharmaceutical Sciences, State University of New York at Buffalo, Buffalo, N.Y. 14260 USA
- New York State Center of Excellence in Bioinformatics and Life Sciences
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Wilkerson DP, Poole DC, Jones AM, Fulford J, Mawson DM, Ball CI, Shore AC. Older Type 2 diabetic males do not exhibit abnormal pulmonary oxygen uptake and muscle oxygen utilization dynamics during submaximal cycling exercise. Am J Physiol Regul Integr Comp Physiol 2011; 300:R685-92. [DOI: 10.1152/ajpregu.00479.2010] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
There are reports of abnormal pulmonary oxygen uptake (V̇o2) and deoxygenated hemoglobin ([HHb]) kinetics in individuals with Type 2 diabetes (T2D) below 50 yr of age with disease durations of <5 yr. We examined the V̇o2 and muscle [HHb] kinetics in 12 older T2D patients with extended disease durations (age: 65 ± 5 years; disease duration 9.3 ± 3.8 years) and 12 healthy age-matched control participants (CON; age: 62 ± 6 years). Maximal oxygen uptake (V̇o2max) was determined via a ramp incremental cycle test and V̇o2 and [HHb] kinetics were determined during subsequent submaximal step exercise. The V̇o2max was significantly reduced ( P < 0.05) in individuals with T2D compared with CON (1.98 ± 0.43 vs. 2.72 ± 0.40 l/min, respectively) but, surprisingly, V̇o2 kinetics was not different in T2D compared with CON (phase II time constant: 43 ± 17 vs. 41 ± 12 s, respectively). The Δ[HHb]/ΔV̇o2 was significantly higher in T2D compared with CON (235 ± 99 vs. 135 ± 33 AU·l−1·min−1; P < 0.05). Despite a lower V̇o2max, V̇o2 kinetics is not different in older T2D compared with healthy age-matched control participants. The elevated Δ[HHb]/ΔV̇o2 in T2D individuals possibly indicates a compromised muscle blood flow that mandates a greater O2 extraction during exercise. Longer disease duration may result in adaptations in the O2 extraction capabilities of individuals with T2D, thereby mitigating the expected age-related slowing of V̇o2 kinetics.
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Affiliation(s)
- D. P. Wilkerson
- School of Sport and Health Sciences, St. Luke's Campus, University of Exeter, Exeter, Devon, United Kingdom
| | - D. C. Poole
- School of Sport and Health Sciences, St. Luke's Campus, University of Exeter, Exeter, Devon, United Kingdom
- Departments of Kinesiology, Anatomy and Physiology, Kansas State University, Manhattan, Kansas; and
| | - A. M. Jones
- School of Sport and Health Sciences, St. Luke's Campus, University of Exeter, Exeter, Devon, United Kingdom
| | - J. Fulford
- Diabetes and Vascular Medicine, Institute of Biomedical and Clinical Science, Peninsula Medical School, University of Exeter, and Peninsula National Institute for Health Research, Clinical Research Facility, Devon, United Kingdom
| | - D. M. Mawson
- Diabetes and Vascular Medicine, Institute of Biomedical and Clinical Science, Peninsula Medical School, University of Exeter, and Peninsula National Institute for Health Research, Clinical Research Facility, Devon, United Kingdom
| | - C. I. Ball
- Diabetes and Vascular Medicine, Institute of Biomedical and Clinical Science, Peninsula Medical School, University of Exeter, and Peninsula National Institute for Health Research, Clinical Research Facility, Devon, United Kingdom
| | - A. C. Shore
- Diabetes and Vascular Medicine, Institute of Biomedical and Clinical Science, Peninsula Medical School, University of Exeter, and Peninsula National Institute for Health Research, Clinical Research Facility, Devon, United Kingdom
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62
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Hirai DM, Copp SW, Ferreira LF, Musch TI, Poole DC. Nitric oxide bioavailability modulates the dynamics of microvascular oxygen exchange during recovery from contractions. Acta Physiol (Oxf) 2010; 200:159-69. [PMID: 20384595 DOI: 10.1111/j.1748-1716.2010.02137.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
AIM lowered microvascular PO(2) (PO(2) mv) during the exercise off-transient likely impairs muscle metabolic recovery and limits the capacity to perform repetitive tasks. The current investigation explored the impact of altered nitric oxide (NO) bioavailability on PO(2) mv during recovery from contractions in healthy skeletal muscle. We hypothesized that increased NO bioavailability (sodium nitroprusside: SNP) would enhance PO(2) mv and speed its recovery kinetics while decreased NO bioavailability (l-nitro arginine methyl ester: l-NAME) would reduce PO(2) mv and slow its recovery kinetics. METHODS PO(2) mv was measured by phosphorescence quenching during transitions (rest-1 Hz twitch-contractions for 3 min-recovery) in the spinotrapezius muscle of Sprague-Dawley rats under SNP (300 microm), Krebs-Henseleit (CONTROL) and l-NAME (1.5 mm) superfusion conditions. RESULTS relative to recovery in CONTROL, SNP resulted in greater overall microvascular oxygenation as assessed by the area under the PO(2) mv curve (PO(2 AREA) ; CONTROL 3471 ± 292 mmHg s; SNP: 4307 ± 282 mmHg s; P < 0.05) and faster off-kinetics as evidenced by the mean response time (MRToff; CONTROL 60.2 ± 6.9 s; SNP: 34.8 ± 5.7 s; P < 0.05), whereas l-NAME produced lower PO(2 AREA) (2339 ± 444 mmHg s; P < 0.05) and slower MRToff (86.6 ± 14.5s; P < 0.05). CONCLUSION no bioavailability plays a key role in determining the matching of O(2) delivery-to-O(2) uptake and thus the upstream O(2) pressure driving capillary-myocyte O(2) flux (i.e. PO(2) mv) following cessation of contractions in healthy skeletal muscle. Additionally, these data support a mechanistic link between reduced NO bioavailability and prolonged muscle metabolic recovery commonly observed in ageing and diseased populations.
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Affiliation(s)
- D M Hirai
- Department of Anatomy and Physiology, Kansas State University, Manhattan, KS 66506-5802, USA
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63
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Copp SW, Hageman KS, Behnke BJ, Poole DC, Musch TI. Effects of type II diabetes on exercising skeletal muscle blood flow in the rat. J Appl Physiol (1985) 2010; 109:1347-53. [PMID: 20798267 DOI: 10.1152/japplphysiol.00668.2010] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The purpose of the present investigation was to examine the muscle hyperemic response to steady-state submaximal running exercise in the Goto-Kakizaki (GK) Type II diabetic rat. Specifically, the hypothesis was tested that Type II diabetes would redistribute exercising blood flow toward less oxidative muscles and muscle portions of the hindlimb. GK diabetic (n = 10) and Wistar control (n = 8, blood glucose concentration, 13.7 ± 1.6 and 5.7 ± 0.2 mM, respectively, P < 0.05) rats were run at 20 m/min on a 10% grade. Blood flows to 28 hindlimb muscles and muscle portions as well as the abdominal organs and kidneys were measured in the steady state of exercise using radiolabeled 15-μm microspheres. Blood flow to the total hindlimb musculature did not differ between GK diabetic and control rats (161 ± 16 and 129 ± 15 ml·min(-1)·100 g(-1), respectively, P = 0.18). Moreover, there was no difference in blood flow between GK diabetic and control rats in 20 of the individual muscles or muscle parts examined. However, in the other eight muscles examined that typically are comprised of a majority of fast-twitch glycolytic (IIb/IIdx) fibers, blood flow was significantly greater (i.e., ↑31-119%, P < 0.05) in the GK diabetic rats. Despite previously documented impairments of several vasodilatory pathways in Type II diabetes these data provide the first demonstration that a reduction of exercising muscle blood flow during submaximal exercise is not an obligatory consequence of this condition in the GK diabetic rat.
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Affiliation(s)
- Steven W Copp
- Department of Kinesiology, Kansas State University, Manhattan, KS 66506-5802, USA
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Hanson MS, Stephenson AH, Bowles EA, Sprague RS. Insulin inhibits human erythrocyte cAMP accumulation and ATP release: role of phosphodiesterase 3 and phosphoinositide 3-kinase. Exp Biol Med (Maywood) 2010; 235:256-62. [PMID: 20404042 DOI: 10.1258/ebm.2009.009206] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In non-erythroid cells, insulin stimulates a signal transduction pathway that results in the activation of phosphoinositide 3-kinase (PI3K) and subsequent phosphorylation of phosphodiesterase 3 (PDE3). Erythrocytes possess insulin receptors, PI3K and PDE3B. These cells release adenosine triphosphate (ATP) when exposed to reduced O(2) tension via a signaling pathway that requires activation of the G protein, Gi, as well as increases in cAMP. Although insulin inhibits ATP release from human erythrocytes in response to Gi activation by mastoparan 7 (Mas 7), no effect on cAMP was described. Here, we investigated the hypothesis that insulin activates PDE3 in human erythrocytes via a PI3K-mediated mechanism resulting in cAMP hydrolysis and inhibition of ATP release. Incubation of human erythrocytes with Mas 7 resulted in a 62 +/- 7% increase in cAMP (n = 9, P < 0.05) and a 306 +/- 69% increase in ATP release (n = 9, P < 0.05), both of which were attenuated by pre-treatment with insulin. Selective inhibitors of PDE3 (cilostazol) or PI3K (LY294002) rescued these effects of insulin. These results support the hypothesis that insulin activates PDE3 in erythrocytes via a PI3K-dependent mechanism. Once activated, PDE3 limits Mas 7-induced increases in intracellular cAMP. This effect of insulin leads, ultimately, to decreased ATP release in response to Mas 7. Activation of Gi is required for reduced O(2) tension-induced ATP release from erythrocytes and this ATP release has been shown to participate in the matching of O(2) supply with demand in skeletal muscle. Thus, pathological increases in circulating insulin could, via activation of PDE3 in erythrocytes, inhibit ATP release from these cells, depriving the peripheral circulation of one mechanism that could aid in the regulation of the delivery of O(2) to meet tissue metabolic need.
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Affiliation(s)
- Madelyn S Hanson
- Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, St Louis, MO 63104, USA.
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Aging impacts microvascular oxygen pressures during recovery from contractions in rat skeletal muscle. Respir Physiol Neurobiol 2009; 169:315-22. [PMID: 19833236 DOI: 10.1016/j.resp.2009.10.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2009] [Revised: 09/28/2009] [Accepted: 10/06/2009] [Indexed: 11/20/2022]
Abstract
Aging-induced alterations in peripheral circulatory control during contractions reduce the microvascular partial pressure of O(2) (P(O)(2)mv; which reflects the dynamic balance in the O(2) delivery-to-O(2) uptake ratio), resulting in exaggerated intramuscular metabolic disturbances and premature fatigue. However, the extent to which this altered P(O)(2)mv during contractions is associated with prolongated muscle metabolic recovery is not known. We tested the hypothesis that the aging-induced speeding of the P(O)(2)mv on-kinetics would presage slowed P(O)(2)mv off-kinetics. The spinotrapezius muscle was exposed in six young (6-8 months) and seven old (26-28 months) male Fischer 344xBrown Norway F1-hybrid rats. The P(O)(2)mv kinetic profile was measured via phosphorescence quenching at rest, during electrically stimulated contractions (1Hz, 7-9V, 2ms pulse duration, 180s), and throughout recovery (180s). Aged rats which evidenced faster P(O)(2)mv on-kinetics (reduced mean response time (MRTon), young: 27.3+/-3.6s, old: 19.2+/-1.6s; P<0.05) exhibited markedly slowed P(O)(2)mv off-kinetics (increased MRToff, young: 46.5+/-5.9s, old: 84.8+/-7.9s; P<0.05). Accordingly, a greater degree of P(O)(2)mv on-off asymmetry (MRToff-MRTon) in the aged muscle was observed (young: 19.1+/-4.5s, old: 65.6+/-8.6s; P<0.01). We conclude that aging-induced speeding of the P(O)(2)mv on-kinetics does indeed presage a slowed P(O)(2)mv off-kinetics, which likely compromises muscle metabolic recovery and may reduce subsequent contractile performance. Moreover, the greater degree of P(O)(2)mv on-off asymmetry in the aged muscle suggests a mechanistic link between impaired microvascular oxygenation and altered muscle metabolic responses during exercise transitions.
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Sperandio PA, Borghi-Silva A, Barroco A, Nery LE, Almeida DR, Neder JA. Microvascular oxygen delivery-to-utilization mismatch at the onset of heavy-intensity exercise in optimally treated patients with CHF. Am J Physiol Heart Circ Physiol 2009; 297:H1720-8. [PMID: 19734359 DOI: 10.1152/ajpheart.00596.2009] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Impaired muscle blood flow at the onset of heavy-intensity exercise may transiently reduce microvascular O(2) pressure and decrease the rate of O(2) transfer from capillary to mitochondria in chronic heart failure (CHF). However, advances in the pharmacological treatment of CHF (e.g., angiotensin-converting enzyme inhibitors and third-generation beta-blockers) may have improved microvascular O(2) delivery to an extent that intramyocyte metabolic inertia might become the main locus of limitation of O(2) uptake (Vo(2)) kinetics. We assessed the rate of change of pulmonary Vo(2) (Vo(2)(p)), (estimated) fractional O(2) extraction in the vastus lateralis (approximately Delta[deoxy-Hb+Mb] by near-infrared spectroscopy), and cardiac output (Qt) during high-intensity exercise performed to the limit of tolerance (Tlim) in 10 optimally treated sedentary patients (ejection fraction = 29 + or - 8%) and 11 controls. Sluggish Vo(2)(p) and Qt kinetics in patients were significantly related to lower Tlim values (P < 0.05). The dynamics of Delta[deoxy-Hb+Mb], however, were faster in patients than controls [mean response time (MRT) = 15.9 + or - 2.0 s vs. 19.0 + or - 2.9 s; P < 0.05] with a subsequent response "overshoot" being found only in patients (7/10). Moreover, tauVo(2)/MRT-[deoxy-Hb+Mb] ratio was greater in patients (4.69 + or - 1.42 s vs. 2.25 + or - 0.77 s; P < 0.05) and related to Qt kinetics and Tlim (R = 0.89 and -0.78, respectively; P < 0.01). We conclude that despite the advances in the pharmacological treatment of CHF, disturbances in "central" and "peripheral" circulatory adjustments still play a prominent role in limiting Vo(2)(p) kinetics and tolerance to heavy-intensity exercise in nontrained patients.
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Affiliation(s)
- Priscila Abreu Sperandio
- Pulmonary Function and Clinical Exercise Physiology Unit (SEFICE), Division of Respiratory Diseases, Department of Medicine, Federal University of Sao Paulo (UNIFESP), São Paulo
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Behnke BJ, Ferreira LF, McDonough PJ, Musch TI, Poole DC. Recovery dynamics of skeletal muscle oxygen uptake during the exercise off-transient. Respir Physiol Neurobiol 2009; 168:254-60. [PMID: 19619675 DOI: 10.1016/j.resp.2009.07.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2009] [Revised: 07/10/2009] [Accepted: 07/13/2009] [Indexed: 11/26/2022]
Abstract
UNLABELLED The time course of muscle .V(O2) recovery from contractions (i.e., muscle .V(O2) off-kinetics), measured directly at the site of O(2) exchange, i.e., in the microcirculation, is unknown. Whereas biochemical models based upon creatine kinase flux rates predict slower .V(O2) off- than on-transients [Kushmerick, M.J., 1998. Comp. Biochem. Physiol. B: Biochem. Mol. Biol.], whole muscle .V(O2) data [Krustrup, et al. J. Physiol.] suggest on-off symmetry. PURPOSE We tested the hypothesis that the slowed recovery blood flow (Qm) kinetics profile in the spinotrapezius muscle [Ferreira et al., 2006. J. Physiol.] was associated with a slowed muscle .V(O2) recovery compared with that seen at the onset of contractions (time constant, tau approximately 23s, Behnke et al., 2002. Resp. Physiol.), i.e., on-off asymmetry. METHODS Measurements of capillary red blood cell flux and microvascular pressure of O(2) (P(O2) mv) were combined to resolve the temporal profile of muscle .V(O2) across the moderate intensity contractions-to-rest transition. RESULTS Muscle .V(O2) decreased from an end-contracting value of 7.7+/-0.2 ml/100 g/min to 1.7+/-0.1 ml/100g/min at the end of the 3 min recovery period, which was not different from pre-stimulation .V(O2). Contrary to our hypothesis, muscle .V(O2) in recovery began to decrease immediately (i.e., time delay <2s) and demonstrated rapid first-order kinetics (tau, 25.5+/-2.6s) not different (i.e., symmetrical to) to those during the on-transient. This resulted in a systematic increase in microvascular P(O2) during the recovery from contractions. CONCLUSIONS The slowed Qm kinetics in recovery serves to elevate the Qm/.V(O2) ratio and thus microvascular P(O2) . Whether this Qm response is obligatory to the rapid muscle .V(O2) kinetics and hence speeds the repletion of high-energy phosphates by maximizing conductive and diffusive O(2) flux is an important question that awaits resolution.
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Affiliation(s)
- Brad J Behnke
- Department of Applied Physiology & Kinesiology, University of Florida, Gainesville, FL 32611, USA.
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Copp SW, Ferreira LF, Herspring KF, Hirai DM, Snyder BS, Poole DC, Musch TI. The effects of antioxidants on microvascular oxygenation and blood flow in skeletal muscle of young rats. Exp Physiol 2009; 94:961-71. [PMID: 19502293 DOI: 10.1113/expphysiol.2009.048223] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Alterations of skeletal muscle redox state via antioxidant supplementation have the potential to impact contractile function and vascular smooth muscle tone. The effects of antioxidants on the regulation of muscle O(2) delivery-O(2) utilization (Q(O(2)m/V(O(2)m)) matching (which sets the microvascular partial pressure of O(2); P(O(2)mv)) in young healthy muscle are not known. Therefore, the purpose of this study was to test the effects of acute antioxidant supplementation on rat spinotrapezius muscle force production, blood flow, V(O(2)m) and P(O(2)mv) (phosphorescence quenching). Anaesthetized male Fischer 344 x Brown Norway rats (6-8 months old) had their right spinotrapezius muscles either exposed for measurement of blood flow and (n = 13) or exteriorized for measurement of muscle force production (n = 6). Electrically stimulated 1 Hz twitch contractions (approximately 7-9 V) were elicited for 180 s, and measurements were made before and after acute intra-arterial antioxidant supplementation (76 mg kg(-1) ascorbic acid, 52 mg kg(-1) tempol) dissolved in saline and infused over 30 min. The principal effects of antioxidants were a approximately 25% decrease (P < 0.05) in contracting spinotrapezius muscle force production concurrent with reductions in muscle blood flow and V(O(2)m) at rest and during contractions (P < 0.05 for both). Antioxidant supplementation reduced the resting baseline P(O(2)mv) (before, 29.9 +/- 1.2 mmHg; after, 25.6 +/- 1.3 mmHg; P < 0.05), and this magnitude of depression was sustained throughout the rest-to-exercise transition (steady-state value before, 16.4 +/- 0.7 mmHg; after, 13.6 +/- 0.9 mmHg; P < 0.05). In addition, the time constant of the P(O(2)mv) decrease was reduced after antioxidant supplementation (before, 23.4 +/- 4.3 s; after, 15.6 +/- 2.7 s; P < 0.05). These results demonstrate that antioxidant supplementation significantly impacts the control of (Q(O(2)m/V(O(2)m)) in young rats at rest and during contractions.
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Affiliation(s)
- Steven W Copp
- Department of Kinesiology, Kansas State University, Manhattan, KS 66506-5802, USA
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Poole DC, Barstow TJ, McDonough P, Jones AM. Control of oxygen uptake during exercise. Med Sci Sports Exerc 2008; 40:462-74. [PMID: 18379208 DOI: 10.1249/mss.0b013e31815ef29b] [Citation(s) in RCA: 152] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Other than during sleep and contrived laboratory testing protocols, humans rarely exist in prolonged metabolic steady states; rather, they transition among different metabolic rates (V O2). The dynamic transition of V O2 (V O2 kinetics), initiated, for example, at exercise onset, provides a unique window into understanding metabolic control. This brief review presents the state-of-the art regarding control of V O2 kinetics within the context of a simple model that helps explain the work rate dependence of V O2 kinetics as well as the effects of environmental perturbations and disease. Insights emerging from application of novel approaches and technologies are integrated into established concepts to assess in what circumstances O2 supply might exert a commanding role over V O2 kinetics, and where it probably does not. The common presumption that capillary blood flow dynamics can be extrapolated accurately from upstream arterial measurements is challenged. From this challenge, new complexities emerge with respect to the relationships between O2 supply and flux across the capillary-myocyte interface and the marked dependence of these processes on muscle fiber type. Indeed, because of interfiber type differences in O2 supply relative to V O2, the presence of much lower O2 levels in the microcirculation supplying fast-twitch muscle fibers, and the demonstrated metabolic sensitivity of muscle to O2, it is possible that fiber type recruitment profiles (and changes thereof) might help explain the slowing of V O2 kinetics at higher work rates and in chronic diseases such as heart failure and diabetes.
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Affiliation(s)
- David C Poole
- Department of Kinesiology, Anatomy and Physiology, Kansas State University, Manhattan, KS 66506-5802, USA.
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Ferreira LF, Koga S, Barstow TJ. Dynamics of noninvasively estimated microvascular O2 extraction during ramp exercise. J Appl Physiol (1985) 2007; 103:1999-2004. [PMID: 17823295 DOI: 10.1152/japplphysiol.01414.2006] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Utilization of near-infrared spectroscopy (NIRS) in clinical exercise testing to detect microvascular abnormalities requires characterization of the responses in healthy individuals and theoretical foundation for data interpretation. We examined the profile of the deoxygenated hemoglobin signal from NIRS {deoxygenated hemoglobin + myoglobin [deoxy-(Hb+Mb)] ≈ O2 extraction} during ramp exercise to test the hypothesis that the increase in estimated O2 extraction would be close to hyperbolic, reflecting a linear relationship between muscle blood flow (Q̇m) and muscle oxygen uptake (V̇o2m) with a positive Q̇m intercept. Fifteen subjects (age 24 ± 5 yr) performed incremental ramp exercise to fatigue (15–35 W/min). The deoxy-(Hb+Mb) response, measured by NIRS, was fitted by a hyperbolic function [ f( x) = ax/( b + x), where a is the asymptotic value and b is the x value that yields 50% of the total amplitude] and sigmoidal function { f( x) = f0 + A/[1 + e−(− c+ dx)], where f0 is baseline, A is total amplitude, and c is a constant dependent on d, the slope of the sigmoid}, and the goodness of fit was determined by F test. Only one subject demonstrated a hyperbolic increase in deoxy-(Hb+Mb) ( a = 170%, b = 193 W), whereas 14 subjects displayed a sigmoidal increase in deoxy-(Hb+Mb) ( f0 = −7 ± 7%, A = 118 ± 16%, c = 3.25 ± 1.14, and d = 0.03 ± 0.01). Computer simulations revealed that sigmoidal increases in deoxy-(Hb+Mb) reflect a nonlinear relationship between microvascular Q̇m and V̇o2m during incremental ramp exercise. The mechanistic implications of our findings are that, in most healthy subjects, Q̇m increased at a faster rate than V̇o2m early in the exercise test and slowed progressively as maximal work rate was approached.
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Affiliation(s)
- Leonardo F Ferreira
- Department of Anatomy and Physiology and Kinesiology, Kansas State University, Manhattan, KS 66506-0302, USA
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Bauer TA, Reusch JEB, Levi M, Regensteiner JG. Skeletal muscle deoxygenation after the onset of moderate exercise suggests slowed microvascular blood flow kinetics in type 2 diabetes. Diabetes Care 2007; 30:2880-5. [PMID: 17675540 DOI: 10.2337/dc07-0843] [Citation(s) in RCA: 154] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
OBJECTIVE People with type 2 diabetes have impaired exercise responses even in the absence of cardiovascular complications. One key factor associated with the exercise intolerance is abnormally slowed oxygen uptake (VO2) kinetics during submaximal exercise. The mechanisms of this delayed adaptation during exercise are unclear but probably relate to impairments in skeletal muscle blood flow. This study was conducted to compare skeletal muscle deoxygenation (deoxygenated hemoglobin/myoglobin [HHb]) responses and estimated microvascular blood flow (Qm) kinetics in type 2 diabetic and healthy subjects after the onset of moderate exercise. RESEARCH DESIGN AND METHODS Pulmonary VO2 kinetics and [HHb] (using near-infrared spectroscopy) were measured in 11 type 2 diabetic and 11 healthy subjects during exercise transitions from unloaded to moderate cycling exercise. Qm responses were calculated using VO2 kinetics and [HHb] responses via rearrangement of the Fick principle. RESULTS VO2 kinetics were slowed in type 2 diabetic compared with control subjects (43.8 +/- 9.6 vs. 34.2 +/- 8.2 s, P < 0.05), and the initial [HHb] response after the onset of exercise exceeded the steady-state level of oxygen extraction in type 2 diabetic compared with control subjects. The mean response time of the estimated Qm increase was prolonged in type 2 diabetic compared with healthy subjects (47.7 +/- 14.3 vs. 35.8 +/- 10.7 s, P < 0.05). CONCLUSIONS Type 2 diabetic skeletal muscle demonstrates a transient imbalance of muscle O2 delivery relative to O2 uptake after onset of exercise, suggesting a slowed Qm increase in type 2 diabetic muscle. Impaired vasodilatation due to vascular dysfunction in type 2 diabetes during exercise may contribute to this observation. Further study of the mechanisms leading to impaired muscle oxygen delivery may help explain the abnormal exercise responses in type 2 diabetes.
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Affiliation(s)
- Timothy A Bauer
- Division of Cardiology, University of Colorado at Denver and Health Sciences Center, Denver, Colorado, USA
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