Muscle Capillarization Research Articles

Capillarity and Angiogenic factors in Soleus Muscle Associated with Type II Diabetes Mellitus

Capillarity and Angiogenic factors in Soleus Muscle Associated with Type II Diabetes Mellitus

Myocyte vascular endothelial growth factor is required for exercise-induced skeletal muscle angiogenesis

We have previously shown, using a Cre-LoxP strategy, that vascular endothelial growth factor (VEGF) is required for the development and maintenance of skeletal muscle capillarity in sedentary adult mice. To determine whether VEGF expression is required for skeletal muscle capillary adaptation to exercise training, gastrocnemius muscle capillarity was measured in myocyte-specific VEGF gene-deleted (mVEGF(-/-)) and wild-type (WT) littermate mice following 6 wk of treadmill running (1 h/day, 5 days/wk) at the same running speed. The effect of training on metabolic enzyme activity levels and whole body running performance was also evaluated in mVEGF(-/-) and WT mice. Posttraining capillary density was significantly increased by 59% (P < 0.05) in the deep muscle region of the gastrocnemius in WT mice but did not change in mVEGF(-/-) mice. Maximal running speed and time to exhaustion during submaximal running increased by 20 and 13% (P < 0.05), respectively, in WT mice after training but were unchanged in mVEGF(-/-) mice. Training led to increases in skeletal muscle citrate synthase (CS) and phosphofructokinase (PFK) activities in both WT and mVEGF(-/-) mice (P < 0.05), whereas β-hydroxyacyl-CoA dehydrogenase (β-HAD) activity was increased only in WT mice. These data demonstrate that skeletal muscle capillary adaptation to physical training does not occur in the absence of myocyte-expressed VEGF. However, skeletal muscle metabolic adaptation to exercise training takes place independent of myocyte VEGF expression.

Striated muscle angio-adaptation requires changes in Vasohibin-1 expression pattern

Vasohibin-1 (VASH-1) was recently identified as a negative feedback regulator of angiogenesis. Here, we analyzed how the expression of the two active anti-angiogenic VASH-1 isoforms p36 and p42 was altered during physiological and pathological muscle angio-adaptation. Our results showed that VASH-1 protein expression was muscle-type specific, with higher levels detected in less vascularized muscles. In rat plantaris and heart muscles, the expression of VASH-1 protein was decreased in response to exercise training, a physiological pro-angiogenic stimulus leading to muscle capillary growth. Interestingly, expression patterns for p36 and p42 were different between plantaris and heart muscles. Next, we analyzed the time-course expression of VASH-1 isoforms in rat soleus muscles subjected to hindlimb unloading, a model that induces muscle capillary regression. Both p36 and p42 isoforms were increased, a signal in favor of some vessel destabilization and regression. Finally, we investigated VASH-1 expression in plantaris muscles from Zucker Diabetic Fatty rats (ZDF) that develop obesity and type-2 diabetes associated with a loss of capillaries in skeletal muscle. VASH-1 expression was higher in sedentary ZDF rats when compared to lean animals, suggesting its potential role during capillary regression. Interestingly, a physiological VASH-1 level was efficiently restored in spontaneously active ZDF animals where muscle capillarization was preserved. In conclusion, our results bring evidence that endogenous VASH-1 isoforms p36 and p42 are key actors of physiological and pathological muscle angio-adaptation.

Gene expression centroids that link with low intrinsic aerobic exercise capacity and complex disease risk

A strong link exists between low aerobic exercise capacity and complex metabolic diseases. To probe this linkage, we utilized rat models of low and high intrinsic aerobic endurance running capacity that differ also in the risk for metabolic syndrome. We investigated in skeletal muscle gene-phenotype relationships that connect aerobic endurance capacity with metabolic disease risk factors. The study compared 12 high capacity runners (HCRs) and 12 low capacity runners (LCRs) from generation 18 of selection that differed by 615% for maximal treadmill endurance running capacity. On average, LCRs were heavier and had increased blood glucose, insulin, and triglycerides compared with HCRs. HCRs were higher for resting metabolic rate, voluntary activity, serum high density lipoproteins, muscle capillarity, and mitochondrial area. Bioinformatic analysis of skeletal muscle gene expression data revealed that many genes up-regulated in HCRs were related to oxidative energy metabolism. Seven mean mRNA expression centroids, including oxidative phosphorylation and fatty acid metabolism, correlated significantly with several exercise capacity and disease risk phenotypes. These expression-phenotype correlations, together with diminished skeletal muscle capillarity and mitochondrial area in LCR rats, support the general hypothesis that an inherited intrinsic aerobic capacity can underlie disease risks.—Kivelä, R., Silvennoinen, M., Lehti, M., Rinnankoski-Tuikka, R., Purhonen, T., Ketola, T., Pullinen, K., Vuento, M., Mutanen, N., Sartor, M. A., Reunanen, H., Koch, L. G., Britton, S. L., Kainulainen, H. Gene expression centroids that link with low intrinsic aerobic exercise capacity and complex disease risk.

Gastrocnemius Muscle Capillarization Is Increased In SOD1-G93A Mice

Gastrocnemius Muscle Capillarization Is Increased In SOD1-G93A Mice

Gastrocnemius fatigue is increased and blood flow is reduced in adult skeletal myocyte‐specific VEGF‐deficient mice

Adult skeletal muscle‐specific VEGF gene‐deleted mice demonstrate exercise limitation, but muscle capillarity is maintained. To determine if exercise impairment is due to reduced skeletal muscle blood flow, gastrocnemius flow at rest and during electrically stimulated (ES) muscle contraction was assessed with fluorescent microspheres. Myocyte‐specific VEGF gene deletion was tamoxifen‐induced (D0‐D4, i.p.) in 4 month old VEGFLoxP X HSA‐Cre‐ERT2(+) and (−) mice. On day 21 post‐tamoxifen gastrocnemius VEGF is reduced by 94%. At this time point the gastrocnemius complex of one leg was stimulated via the sciatic nerve (10 volts) and force monitored by a pressure transducer connected to the tendon. 15 μ microspheres (0.2 ml, 1 x 106 beads/ml) were delivered into the aorta via the left carotid artery during the first minute of contractions. VEGFLoxP X HSA‐Cre‐ERT2(+) mice had 76% less resting gastrocnemius flow than control (Cre −). Only control mice increased blood flow during ES (by 60%). Time to reach 50% of initial force was reduced in VEGF‐deficient mice [156+/−31 (sd) sec.] compared to controls [475+/−246 (sd) sec.]. These data suggest that reduced skeletal myocyte‐specific VEGF expression in adult mice attenuates both basal and contraction‐induced blood flow, and this vascular alteration may contribute to the greater muscle fatigue.

Recreational football as a health promoting activity: a topical review

The present review addresses the physiological demands during recreational football training and the effects on central health variables that influence the risk of life-style diseases of young and middle-aged men. Recent studies have established that recreational football, carried out as small-sided games can be characterized as having a high aerobic component with mean heart rates of 80-85% of maximum heart rate, which is similar to values observed for elite football players. In addition, the training includes multiple high-speed runs, sprints, turns, jumps and tackles, which provide a high impact on muscles and bones. Recreational football training in untrained men results in marked improvements in maximum aerobic power, blood pressure, muscle capillarization and intermittent exercise performance, and those effects are similar to interval training and more pronounced than moderate-intensity continuous running and strength training. Further, recreational football training enhances fat oxidation during exercise and results in a higher fat loss than interval training and strength training, and results in marked muscle hypertrophy and elevates bone mass, more than interval and continuous running. Taken together, recreational football appears to effectively stimulate musculoskeletal, metabolic and cardiovascular adaptations of importance for health and thereby reduces the risk of developing life-style diseases.

Plantaris muscle capillarity is reduced in pulmonary TNFα over‐expressing mice

Chronic lung inflammation may contribute to abnormal skeletal muscle microvessel structure and function. To test the hypothesis that elevated pulmonary, and, as a result, systemic tumor necrosis factor‐α (TNFα) levels could contribute to skeletal muscle capillary rarefaction, transgenic mice that over‐express TNFα under the control of the lung‐specific SP‐C promoter were studied. Hind limb muscle mass and capillarity, body weight and exercise capacity in 4–5 month old SP‐C/TNFα (Tg, n=7) and littermate, control (C, n=7) mice were evaluated. Serum TNFα in Tg mice was increased (Tg 29.6±3.6 vs. C 5.2±2.9 pg/ml, p&lt;0.001). Maximal running speed was reduced by 18% in Tg vs. C mice (31±1 vs 38±1 m/min, respectively, p&lt;0.01). Body weight, and heart, gastrocnemius, plantaris and soleus mass were not different between Tg and C groups. Plantaris muscle capillary‐to‐fiber (C:F) ratio was 10% lower in Tg vs. C mice (1.32±0.06 vs. 1.46±0.01, respectively, p&lt;0.05). C:F was not altered in the gastrocnemius (Tg 1.51±0.04 vs. C 1.50±0.02) or soleus (Tg 1.63±0.06 vs. C 1.73±0.01, p=0.15). These data suggest that chronically elevated circulating TNFα may contribute to skeletal muscle pathology in part by capillary rarefaction in some, but not all, hind limb locomotor muscles.

Abnormality of capillarity and oxidative enzyme activity in slow muscle of type 2 diabetic rats

Type 2 diabetes mellitus is tightly linked to impaired skeletal muscle glucose uptake and storage. The 3‐D capillarity, the myosin heavy chain isoforms (MyHC) transformation and succinate dehydrogenase (SDH) activity in the soleus muscle were determined between Goto‐Kakizaki (GK) rats, a spontaneous, non‐obese type 2 diabetes model and age matched Wistar rats (Con)(9 months old). The volume, diameter and tortuosity of the capillary in soleus muscle of GK were significantly lower than those of Con. Thus, the morphological microvascular alterations in the soleus muscle were observed in diabetes rats. Although the soleus muscle of Con was composed of both type I and type IIa MyHCs, all the muscle fibers of the GK were type I MyHC. Furthermore, the SDH activity of type I MyHC fiber in GK decreased significantly compared with that of Con. These results indicate that microvascular alterations and changes in the MyHC of skeletal muscles in diabetic rats may be due to impairment in glucose metabolism. This study was supported by Grants‐in‐Aid for Scientific Research (19300196 and 21700559) from the Japanese Ministry of Education, Culture, Sports, Science and Technology.

Effects of Estradiol, Angiotensin-Converting Enzyme Inhibitor and Exercise Training on Exercise Capacity and Skeletal Muscle in Old Female Rats

Physical fitness is closely related to cardiovascular health. We examined the effects of estradiol, angiotensin-converting enzyme inhibitor, exercise training, and their combination on exercise capacity as well as skeletal muscle fiber type and capillarity in old female rats. Twelve-month-old female Wistar-Kyoto rats were allocated to six groups: control (C), treatment with 17 beta-estradiol (0.025 mg/kg/dose, i.p. twice a week) (Est), perindopril (2 mg/kg/day) (Per), exercise training on a treadmill (15 m/min, 10 grade incline, 60 min/day, 5 days/week) (Exe), and combinations of a drug and exercise training (Exe+Est and Exe+Per). Following 6-month interventions, the rats were submitted to a stepwise exercise test on a treadmill. Moreover, fiber type and capillarity in both the soleus and gastrocnemius muscles were examined. Exercise capacity, capillary density, and the percentage of type I fiber significantly increased in Exe, Exe+Est, and Exe+Per compared to C. There were no significant differences in exercise capacity, capillary density, and percentage of type I fiber among C, Est, and Per. The combination of exercise training and perindopril further increased capillary density in both the soleus and gastrocnemius muscles, and the percentage of type I fiber in the gastrocnemius muscle compared to exercise training alone. We found that in old female rats, chronic treatment with estradiol or perindopril affected neither untrained exercise capacity nor exercise capacity acquired as a result of exercise training. However, we found that perindopril promotes adaptive changes of skeletal muscle in response to exercise such as increases in capillary density and the percentage of type I fiber.

Beneficial effects of recreational football on the cardiovascular risk profile in untrained premenopausal women

The present study examined the cardiovascular health effects of 16 weeks of recreational football training in untrained premenopausal women in comparison with continuous running training. Fifty healthy women were matched and randomized to a football (FG, n=25) or a running (RG, n=25) group and compared with a control group with no physical training (CO, n=15). Training was performed for 1 h twice a week. After 16 weeks, systolic and diastolic blood pressure was reduced (P<0.05) in FG (7+/-2 and 4+/-1 mmHg) and systolic blood pressure was lowered (P<0.05) in RG (6+/-2 mmHg). After 16 weeks, resting heart rate was lowered (P<0.05) by 5+/-1 bpm both in FG and RG, and maximal oxygen uptake was elevated (P<0.05) by 15% in FG and by 10% in RG (5.0+/-0.7 and 3.6+/-0.6 mL/min/kg, respectively). Total fat mass decreased (P<0.05) by 1.4+/-0.3 kg in FG and by 1.1+/-0.3 kg in RG. After 16 weeks, pulse pressure wave augmentation index (-0.9+/-2.5 vs 4.2+/-2.4%), skeletal muscle capillarization (2.44+/-0.15 vs 2.07+/-0.05 cap/fib) and low-density lipoprotein/high-density lipoprotein cholesterol ratio were improved (P<0.05) in FG, but not altered in RG. No changes were observed in CO. In conclusion, regular recreational football training has significant favorable effects on the cardiovascular risk profile in untrained premenopausal women and is at the least as efficient as continuous running.

Detraining losses of skeletal muscle capillarization are associated with vascular endothelial growth factor protein expression in rats

The purposes of this study were as follows: (1) to examine basal vascular endothelial growth factor (VEGF) protein concentrations following 10 weeks of endurance training and after 7 days of detraining; and (2) to examine the acute VEGF protein response to a single 1 h exercise work bout in trained and detrained animals in relationship to changes in capillary indices following training and detraining. Thirty-three Sprague-Dawley rats were randomized into the following six groups: (1) control-basal; (2) control-acute exercise; (3) trained-basal; (4) trained-acute exercise; (5) detrained-basal; and (6) detrained-acute exercise. Groups 3-6 performed endurance training on a rodent treadmill three times per week for 10 weeks. Following the training intervention, rats in groups 5 and 6 remained cage confined (i.e. detrained) for 7 days. As expected, training increased soleus and plantaris muscle capillarity and attenuated the VEGF response to acute exercise. Seven days of detraining, however, resulted in a regression of capillary contacts and individual capillary-to-fibre ratio in the plantaris and soleus muscles compared with the trained group (P < 0.05). Restoration of the VEGF protein response to acute exercise was evident in both muscles, but only statistically significant in the plantaris muscle (P < 0.05). This is the first study to demonstrate the temporal relationship between VEGF protein expression and skeletal muscle capillarity within the first week of detraining. The findings of the present investigation are consistent with the hypothesis that reduced capillarity impairs oxygen availability to the working muscles. The results indicated that training-induced angiogenic remodelling was reversible following 1 week of detraining and may be modulated by VEGF.

The estimation error of skeletal muscle capillary supply is significantly reduced by 3D method

Capillary supply of individual skeletal muscle fibers is usually evaluated from two-dimensional (2D) images of thin transverse sections by the number of capillary profiles around a fiber (CAF). This method is inherently inaccurate and the resulting capillary length measurement errors can be avoided by using an alternative three-dimensional (3D) approach where the mean length of capillaries around individual muscle fibers per fiber length (Lcap/Lfib) is measured from 3D images acquired by confocal microscopy. We quantified the error of the 2D method and its reduction by using a 3D approach in realistic geometrical models of muscle fiber capillary bed and in true muscle samples. In models we showed that Lcap/Lfib was sensitive to different arrangements of capillaries, while CAF underestimated capillarization since it could not detect the increased length of capillary bed. In true muscle samples, we detected statistically significant differences in the capillary supply of control and denervated rat soleus muscles by both 2D and 3D methods. Lcap/Lfib was larger than CAF in control muscles reflecting their more complicated capillary bed. Thus, 3D approach is more sensitive in agreement with the analysis of geometrical models. We conclude that the 3D method, though technically more demanding than 2D method, represents a more precise approach to evaluation of muscle capillarization. Moreover, the 3D method could be applied to other organs and we suggest potential medical applications.

Evidence for low muscle capillary supply as a pathogenic factor in chronic compartment syndrome

There is a paucity of data regarding the pathogenesis of chronic exertional compartment syndrome (CECS), its consequences for the muscles and the effects of treatment with fasciotomy. We analyzed biopsies from the tibialis anterior muscle, from nine patients, obtained during a decompressing fasciotomy and during follow-up 1 year later. Control biopsies were obtained from nine normal subjects. Muscle capillarity, fiber-type composition and fiber area were analyzed with enzyme- and immunohistochemistry and morphometry. At baseline, CECS patients had lower capillary density (273 vs 378 capillaries/mm(2) , P=0.008), lower number of capillaries around muscle fibers (4.5 vs 5.7, P=0.004) and lower number of capillaries in relation to the muscle fiber area (1.1 vs 1.5, P=0.01) compared with normal controls. The fiber-type composition and fiber area did not differ, but focal signs of neuromuscular damage were observed in the CECS samples. At 1-year follow-up after fasciotomy, the fiber area and the number of fibers containing developmental myosin heavy chains were increased, but no enhancement of the capillary network was detected. Thus, morphologically, patients with CECS seemed to have reduced microcirculation capacity. Fasciotomy appeared to trigger a regenerative response in the muscle, however, without any increase in the capillary bed.

Angiomotin p80/p130 ratio: a new indicator of exercise‐induced angiogenic activity in skeletal muscles from obese and non‐obese rats?

Skeletal muscle capillarisation responds to physiological and pathological conditions with a remarkable plasticity. Angiomotin was recently identified as a new pro-angiogenic molecule. Angiomotin is expressed as two protein isoforms, p80 and p130. Whereas p80 stimulates endothelial cell migration and angiogenesis, p130 is rather characteristic of stabilized and matured vessels. To date, how angiomotin expression is physiologically regulated in vivo remains largely unknown. We thus investigated (1) whether angiomotin was physiologically expressed in skeletal muscle; (2) whether exercise training, known to stimulate muscle angiogenesis, affected angiomotin expression; and (3) whether such regulation was altered in obesity, a pathological situation often associated with an impaired angiogenic activity and some capillary rarefaction in skeletal muscle. Two models of obesity were used: a high fat diet regime and Zucker Diabetic Fatty rats (ZDF). Our results provide evidence that angiomotin was expressed both in capillaries and myofibres. In non-obese rats, the p80 isoform was increased in plantaris muscle in response to endurance training whereas p130 was unaffected. In obese animals, no change was observed for p80 whereas training significantly decreased p130 expression. Exercise training induced angiogenesis in plantaris from both obese and non-obese rats, possibly through the modulation of angiomotin level and its consequences on RhoA-ROCK signalling. In conclusion, any increase in p80 or decrease in p130, as respectively observed in non-obese and obese animals, led to an increased ratio between p80 and p130 isoforms. This increased angiomotin p80/p130 ratio might then directly reflect the enhanced angiogenic ability of skeletal muscle in response to exercise training.

Physician-writers in the age of blogging

Muscle atrophy, fiber-type shifting, reduced contractility, metabolic alterations, capillarization defect, and mitochondrial modifications are important adaptations in COPD. Skelatal muscle dysfunction is one of the most devastating systemic manifestations of COPD which eventually leads to increase in morbidity and mortality. In this study we aimed to demonstrate the effects of COPD on both muscles and nerves in neurologically normal patients with different degrees of airflow limitations, using current electrophysiological methods.Electrophysiological examinations were performed using a Keypoint EMG machine with subjects lying supine on a bed at a room temperature. Tests were nerve conduction studies, motor unit potential (MUP) analysis, interference pattern (IP) analysis and macro EMG (mEMG) analysis on the right side in the upper and lower extremities. Multi-motor unit potential (m-MUP) analysis and interference pattern (IP) analysis revealed some changes in biceps brachii (BB) and tibialis anterior (TA) muscles, but macro EMG (mEMG) analysis was similar except for increased fiber density at TA muscles in COPD patients. Increased ulnar and sural sensory latency, decreased ulnar sensory velocity, and increased ulnar motor latency values were found in COPD. There was increased motor unit potential (MUP) turn and phase values in BB muscles and increased MUP turn and decreased MUP duration, area, area/amplitude ratio and size index values in TA muscles in COPD patients. As a conclusion, in COPD more nerve conduction abnormalities and more MUP abnormalities which reflected muscle fiber diameter changes were observed by the use of electrophysiological methods including multi MUP - IP analysis and mEMG analysis.

Global deletion of thrombospondin‐1 increases cardiac and skeletal muscle capillarity and exercise capacity in mice

Thrombospondin-1 (TSP-1) is a known inhibitor of angiogenesis; however, a skeletal muscle phenotype of TSP-1 null mice has not been investigated. The purposes of this study were to compare and contrast TSP-1 null and wild-type mice by examining the following: (1) capillarity in the skeletal and cardiac muscles; (2) fibre type composition and oxidative enzyme activity in the hindlimb; and (3) the consequences of TSP-1 gene deletion for exercise capacity. In TSP-1 null mice, maximal running speed was 11% greater and time to exhaustion during submaximal endurance running was 67% greater compared with wild-type mice. Morphometric analyses revealed that TSP-1 null mice had higher (P < 0.05) capillarity in the heart and skeletal muscle than wild-type mice, whereas no differences for fibre type composition or oxidative enzyme activity were present between the two groups. Cardiac function, as measured by transthoracic echocardiography, revealed no difference in myocardial contractility but greater left ventricular end-diastolic and systolic dimensions, corresponding to an elevated heart mass in the TSP-1 null mice. The results of this study indicate that TSP-1 is an important endogenous negative regulator of angiogenesis that prevents excessive capillarization in the heart and skeletal muscles. The increased capillarity alone was sufficient to increase (P < 0.05) exercise capacity. These data demonstrate that the capillary-to-muscle interface is a critical factor that limits oxygen transport during exercise.

Skeletal Myocyte-specific VEGF Gene Deletion In Adult Mice Leads To Impaired Exercise Capacity Without Evidence Of Capillary Regression Or Altered In Vitro Muscle Contraction

Vascular endothelial growth factor (VEGF) is involved in controlling skeletal muscle capillarity, an essential component of exercise capacity. PURPOSE: Determine the mechanisms by which skeletal myocyte VEGF maintains exercise capacity. METHODS: Inducible, skeletal myocyte-specific VEGF gene-deleted mice were generated by crossing VEGFLoxP mice with HSA-CreERT2 mice (skmVEGF-/-) in which cre recombinase is under control of a human skeletal actin (HSA) sequence and can be conditionally induced with tamoxifen. VEGF levels were measured in several organs and in the gastrocnemius muscle by ELISA, 2 and 7 weeks after tamoxifen delivery to adult (skmVEGF-/-) and control (VEGF+/+) mice. Exercise capacity was evaluated by recording the maximum running speed and time to exhaustion. Contractile function in isolated EDL and soleus muscles was assessed by peak force, time to fatigue and the force-frequency relationship. RESULTS: SkmVEGF-/- mice showed 95% and 92% reductions in skeletal muscle VEGF protein 2 and 7 weeks after tamoxifen delivery, respectively, with no reduction in other organs. Two-weeks after tamoxifen, maximum running speed (-10%) and endurance capacity (-47%) were reduced in skmVEGF-/- mice compared to controls. Seven weeks post-tamoxifen, maximum running speed remained low in skmVEGF-/- mice, with a non-significant trend towards lower endurance capacity. Body and muscle weights, muscle cross-sectional areas, peak force or time to fatigue and capillary to fiber ratios were not different between skmVEGF-/- mice and VEGF+/+ at either time point. Analysis of skeletal muscle force-frequency relationships also did not reveal any difference at 2 weeks in the EDL or soleus, though by 7 weeks a significant right shift in the force-frequency curve was observed in the EDL. CONCLUSION: Mice with VEGF-deficient skeletal myocytes exhibit a limitation to exercise that does not stem from an inability of the muscle to contract or the number of capillaries that supply muscle fibers.

Muscle‐specific VEGF deficiency greatly reduces exercise endurance in mice

Vascular endothelial growth factor (VEGF) is required for vasculogenesis and angiogenesis during embryonic and early postnatal life. However the organ-specific functional role of VEGF in adult life, particularly in skeletal muscle, is less clear. To explore this issue, we engineered skeletal muscle-targeted VEGF deficient mice (mVEGF-/-) by crossbreeding mice that selectively express Cre recombinase in skeletal muscle under the control of the muscle creatine kinase promoter (MCKcre mice) with mice having a floxed VEGF gene (VEGFLoxP mice). We hypothesized that VEGF is necessary for regulating both cardiac and skeletal muscle capillarity, and that a reduced number of VEGF-dependent muscle capillaries would limit aerobic exercise capacity. In adult mVEGF-/- mice, VEGF protein levels were reduced by 90 and 80% in skeletal muscle (gastrocnemius) and cardiac muscle, respectively, compared to control mice (P < 0.01). This was accompanied by a 48% (P < 0.05) and 39% (P < 0.05) decreases in the capillary-to-fibre ratio and capillary density, respectively, in the gastrocnemius and a 61% decrease in cardiac muscle capillary density (P < 0.05). Hindlimb muscle oxidative (citrate synthase, 21%; beta-HAD, 32%) and glycolytic (PFK, 18%) regulatory enzymes were also increased in mVEGF-/- mice. However, this limited adaptation to reduced muscle VEGF was insufficient to maintain aerobic exercise capacity, and maximal running speed and endurance running capacity were reduced by 34% and 81%, respectively, in mVEGF-/- mice compared to control mice (P < 0.05). Moreover, basal and dobutamine-stimulated cardiac function, measured by transthoracic echocardiography and left ventricular micromanomtery, showed only a minimal reduction of contractility (peak +dP/dt) and relaxation (peak -dP/dt, tau(E)). Collectively these data suggests adequate locomotor muscle capillary number is important for achieving full exercise capacity. Furthermore, VEGF is essential in regulating postnatal muscle capillarity, and that adult mice, deficient in cardiac and skeletal muscle VEGF, exhibit a major intolerance to aerobic exercise.

Reduced Skeletal Muscle Capillarization and Glucose Intolerance

Reduced capillarization in hemiparetic skeletal muscle of chronic stroke patients can limit insulin, glucose, and oxygen supply to muscle, thereby contributing to impaired glucose metabolism and cardiovascular deconditioning. We hypothesized that compared to sedentary controls, stroke subjects have reduced skeletal muscle capillarization that is associated with glucose intolerance and reduced peak oxygen consumption (Vo(2peak)). Twelve chronic stroke subjects (ages, 62.1+/-2.8 years), and matched sedentary controls with impaired (n=12) or normal (n=12) glucose tolerance underwent oral glucose tolerance tests, exercise tests, and vastus lateralis biopsies. Stroke subjects had lower capillarization in hemiparetic muscle than in nonparetic muscle and normal glucose tolerant controls ( approximately 22 and approximately 28%, respectively; P<0.05) and had similar bilateral capillarization, compared to controls with impaired glucose tolerance. Capillary density in hemiparetic muscle inversely correlated with 120-minute glucose (r=-0.70, P<0.01) and glucose area under the curve (r=-0.78, P<0.01). Vo(2peak) was approximately 40% lower in stroke subjects, compared to controls (P<0.001), but did not correlate with capillarization (P=n.s.). Hemiparetic muscle capillarization is reduced after stroke, and reduced capillarization is associated with glucose intolerance in stroke and control subjects. Interventions to increase skeletal muscle capillarization may prove beneficial for improving glucose metabolism in chronic stroke patients.