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PubMed1999

Norepinephrine response to exercise at the same relative intensity before and after endurance exercise training.

It is well documented that endurance exercise training results in a blunted norepinephrine (NE) response to exercise of a given absolute exercise intensity. However, it is not clear what effect training has on the catecholamine response to exercise of the same relative intensity because previous studies have provided conflicting results. The purpose of the present study was, therefore, to determine the catecholamine response to exercise of the same relative exercise intensity before and after endurance exercise training. Six women and three men [age 28 +/- 8 (SD) yr] performed 10 wk of training. Maximal O2 uptake (VO2 max) was determined during treadmill exercise. Fifteen-minute treadmill exercise bouts were performed at 60, 65, 70, 75, 80, and 85% of VO2 max before and after training. VO2 max was increased by 20% (from 39.2 +/- 7.7 to 46.9 +/- 8.1 ml. kg-1. min-1; P < 0.05) in response to training. Plasma NE concentrations were higher (P < 0.05) during exercise at the same relative intensity after, compared with before, training at 65-85% of VO2 max. Differences between heart rates and plasma epinephrine concentrations after, compared with before, training were not statistically significant. These results provide evidence that the NE response to exercise is dependent on the absolute as well as the relative intensity of the exercise.

Adult↗

PubMedDate not supplied

Influence of aerobic exercise training and relaxation training on physical and psychologic health following stressful life events.

An experiment was conducted to determine whether aerobic exercise training or relaxation training would be effective for reducing the deleterious effects of life stress on physical and psychologic health. Over 1000 college students were surveyed, and 55 of those who reported experiencing a high number of negative life events over the preceding year were assigned to an aerobic exercise training condition, a relaxation training condition, or a no-treatment control condition. Physical and psychologic health were assessed with self-report measures before, halfway through, immediately following, and 8 weeks after the 11-week training (and control) period. Heart rate data collected during a treadmill test indicated that the aerobic exercise training was effective for improving cardiovascular fitness. Psychologic measures indicated that the exercise training condition was more effective than the other two conditions for reducing depression during the first 5 weeks of training. No differences were found among the conditions on self-report measures of physical health. These findings suggest that aerobic exercise training may be useful for reducing the severity and duration of depressive reactions following stressful life change.

Adaptation, Psychological↗

PubMed2000

Enhanced L-type Ca2+ channel current density in coronary smooth muscle of exercise-trained pigs is compensated to limit myoplasmic free Ca2+ accumulation.

We hypothesized that enhanced voltage-gated Ca2+ channel current (VGCC) density in coronary smooth muscle cells of exercise-trained miniature Yucatan pigs is compensated by other cellular Ca2+ regulatory mechanisms to limit net myoplasmic free Ca2+ accumulation. Whole-cell voltage clamp experiments demonstrated enhanced VGCC density in smooth muscle cells freshly dispersed from coronary arteries of exercise-trained vs. sedentary animals. In separate experiments using fura-2 microfluorometry, we measured depolarization-induced (80 mM KCl) accumulation of myoplasmic free Ba2+ and free Ca2+. Both maximal rate and net accumulation of free Ba2+ in response to membrane depolarization were increased in smooth muscle cells isolated from exercise-trained pigs, consistent with an increased VGCC density. Depolarization also produced an enhanced maximal rate of free Ca2+ accumulation in cells of exercise-trained pigs; however, net accumulation of free Ca2+ was not significantly increased suggesting enhanced Ca2+ influx was compensated to limit net free Ca2+ accumulation. Inhibition of sarco-endoplasmic reticulum Ca2+-transporting ATPase (SERCA; 10 microM cyclopiazonic acid) and/or sarcolemmal Na+-Ca2+ exchange (low extracellular Na+) suggested neither mechanism compensated the enhanced VGCC in cells of exercise-trained animals. Local Ca2+-dependent inactivation of VGCC, assessed by buffering myoplasmic Ca2+ with EGTA in the pipette and using Ca2+ and Ba2+ as charge carriers, was not different between cells of sedentary and exercise-trained animals. Our findings indicate that increased VGCC density is compensated by other cellular Ca2+ regulatory mechanisms to limit net myoplasmic free Ca2+ accumulation in smooth muscle cells of exercise-trained animals. Further, SERCA, Na+-Ca2+ exchange and local Ca2+-dependent inactivation of VGCC do not appear to function as compensatory mechanisms. Additional potential compensatory mechanisms include Ca2+ extrusion via plasma membrane Ca2+-ATPase, mitochondrial uptake, myoplasmic Ca2+-binding proteins and other sources of VGCC inactivation.

Animals↗

PubMed1999

Vasomotor responses of soleus feed arteries from sedentary and exercise-trained rats.

Our goals were to determine the nature of endothelium-dependent and -independent vascular responses in isolated soleus feed arteries (SFA) and to test the hypothesis that these responses would be altered by exercise training. Exercise-trained rats ran 30 m/min, up a 15% grade, 1 h/day, 5 days/wk for 10-12 wk, while sedentary control rats were confined to normal cage activity. SFA were isolated, cannulated, and pressurized at 90 cmH2O. After a 1-h equilibration period, the dose-response relationships to constrictors, endothelium-dependent dilators, and endothelium-independent dilators were examined. SFA developed spontaneous tone, demonstrated myogenic reactivity by maintaining vessel diameter in the face of large changes in intraluminal pressure, and constricted in a dose-dependent manner to norepinephrine and potassium chloride. SFA dilated in a dose-dependent manner to the endothelium-dependent dilators acetylcholine and increased flow and to the endothelium-independent dilator sodium nitroprusside. SFA did not dilate to the putative endothelium-dependent dilators bradykinin, substance P, and clonidine or to adenosine. Dilation to acetylcholine was attenuated markedly by arginine analogs and less by 20 mM KCl, but it was unaltered by indomethacin. These results indicate that SFA respond to a number of vasoactive substances, consistent with the hypothesis that SFA participate in the control of vascular resistance. However, exercise training does not appear to elicit a stimulus adequate to alter vasomotor responses in SFA.

Animals↗

PubMed1987

Exercise training reduces depression and increases the performance of pleasant activities in hemodialysis patients.

This study compares the effects of a structured exercise training program to the therapeutic benefits of a 'support' group on the depressed mood and reduced performance of pleasant activities by hemodialysis patients. After 6 months of an aerobic exercise training program, the 10 exercisers showed a significant increase in maximal aerobic capacity (VO2max) and a significant decrease in dysphoric mood when compared to 7 patients attending the support group. Support group participants reported a significant decrease in pleasant activities while there was no change in the exercisers. Eighteen months after the exercise training program, the exercisers reported continued low levels of depressed mood, and were performing significantly more pleasant activities than they reported prior to the exercise program. The results of this study suggest an exercise training program may be useful in the psychosocial rehabilitation of some hemodialysis patients.

Activities of Daily Living↗

PubMed2000

Exercise training restores adenosine-induced relaxation in coronary arteries distal to chronic occlusion.

We previously reported that canine collateral-dependent coronary arteries exhibit impaired relaxation to adenosine but not sodium nitroprusside. In contrast, exercise training enhances adenosine sensitivity of normal porcine coronary arteries. These results stimulated the hypothesis that chronic coronary occlusion and exercise training produce differential effects on cAMP- versus cGMP-mediated relaxation. To test this hypothesis, Ameroid occluders were surgically placed around the proximal left circumflex coronary artery (LCx) of female Yucatan miniature swine 8 wk before initiating sedentary or exercise training (treadmill run, 16 wk) protocols. Relaxation to the cAMP-dependent vasodilators adenosine (10(-7) to 10(-3) M) and isoproterenol (3 x 10(-8) to 3 x 10(-5) M) were impaired in collateral-dependent LCx versus nonoccluded left anterior descending (LAD) arterial rings isolated from sedentary but not exercise-trained pigs. Furthermore, adenosine-mediated reductions in simultaneous tension and myoplasmic free Ca(2+) were impaired in LCx versus LAD arteries isolated from sedentary but not exercise-trained pigs. In contrast, relaxation in response to the cAMP-dependent vasodilator forskolin (10(-9) to 10(-5) M) and the cGMP-dependent vasodilator sodium nitroprusside (10(-9) to 10(-4) M) was not different in LCx versus LAD arteries of sedentary or exercise-trained animals. These data suggest that chronic occlusion impairs receptor-dependent, cAMP-mediated relaxation; receptor-independent cAMP- and cGMP-mediated relaxation were unimpaired. Importantly, exercise training restores cAMP-mediated relaxation of collateral-dependent coronary arteries.

Adenosine↗

PubMed2000

Exercise training prevents maturation-induced decreases in insulin receptor substrate-1 and phosphatidylinositol 3-kinase in rat skeletal muscle.

We have previously reported that exercise training prevents a maturation-induced decrease in insulin sensitivity and suggested that an improvement of insulin sensitivity by exercise training was attributable, in part, to an increase in insulin-sensitive GLUT-4 on the skeletal muscle plasma membrane. In this study, we examined the effects of maturation and exercise training on the gene expression and protein content of the components of post-insulin receptor signal transduction in rat skeletal muscle. Rats aged 3 weeks were sedentary or trained by voluntary running through 4 or 27 weeks of age, and then the rats in both the sedentary and trained groups were killed and the gastrocnemius muscle was immediately removed for analysis of mRNA and protein content. The concentration of mRNA and protein for insulin receptor substrate-1 (IRS-1) in sedentary rats significantly decreased with maturation (49% and 63%, respectively, at age 27 weeks v age 4 weeks), but in trained rats they did not decrease with maturation. Although the level of phosphatidylinositol 3-kinase (PI 3-kinase) mRNA in sedentary rats was not altered with maturation, PI 3-kinase protein in sedentary rats significantly decreased with maturation (73% at 27 weeks v 4 weeks). However, PI 3-kinase protein in trained rats did not decrease with maturation. These results suggest that the prevention of maturation-induced decreases in the protein content of IRS-1 and PI 3-kinase is involved in the mechanisms responsible for the improvement of insulin sensitivity by exercise training, and exercise training may affect transcriptional regulation of the IRS-1 gene and posttranscriptional regulation of PI 3-kinase expression.

Animals↗

PubMed1984

Effect of exercise training on whole-body insulin sensitivity and responsiveness.

Exercise training causes a decline in basal and glucose-stimulated plasma insulin levels and improves glucose tolerance. Furthermore evidence has been presented for effects on both insulin receptors and postreceptor events. However, it is unclear how these changes affect the in vivo dose-response relationship between insulin levels and whole-body glucose utilization. The aim was to examine the effect of exercise training on this relationship and distinguish between changes in insulin sensitivity and responsiveness. Euglycemic clamps were performed in trained (ET, running 1 h/day for 7 wk), sedentary (CON), and sedentary food-restricted ( SFR ) rats. ET rats showed no increase in maximal net glucose utilization in response to insulin (ET 29.5 +/- 0.6 vs. CON 28.2 +/- 1.5 mg X kg-1 X min-1, NS), whereas insulin sensitivity was increased as indicated by the insulin concentration causing half-maximal stimulation (ED50) (49 +/- 20 for ET and 133 +/- 30 mU/l for CON). Thus 7 wk of moderate exercise training resulted in a significant shift of whole-body insulin sensitivity to place ED50 well within the physiological range of insulin concentrations. This would undoubtedly result in improved glucose disposal in the postprandial state and emphasizes the potential benefit of exercise in obesity and type II diabetes.

Animals↗

PubMed1998

Low dose dobutamine echocardiography predicts improvement in functional capacity after exercise training in patients with ischemic cardiomyopathy: prognostic implication.

OBJECTIVES: This study sought to investigate whether the identification of hibernating myocardium by low dose dobutamine stress echocardiography (LDSE) may predict an improvement in functional capacity after moderate exercise training in patients with ischemic cardiomyopathy. Another objective was to assess whether exercise training may affect the outcome. BACKGROUND: There is evidence that exercise training improves left ventricular (LV) function as well as functional capacity in patients with a previous myocardial infarction and LV dysfunction. We hypothesized that the magnitude of these improvements might be related to the extent of hibernating myocardium. METHODS: We studied 71 consecutive patients 56+/-9 years old (mean +/- SD) with chronic heart failure secondary to ischemic cardiomyopathy (LV ejection fraction [LVEF] <40%). All patients were in sinus rhythm and were clinically stable during the previous 3 months. Patients were randomized into two matched groups. Group T (n = 36) underwent exercise training at 60% of peak oxygen uptake (Vo2) three times a week for 10 weeks. Group C (n = 35) did not exercise. At study entry and end, all patients underwent an exercise test with gas exchange analysis and LDSE (5 to 20 microg/kg body weight per min). RESULTS: At baseline, a positive contractile response (CS+) to LDSE was observed in 317 of 576 segments in group T and 291 of 560 segments in group C. After 10 weeks, peak Vo2 and peak work rate increased only in trained patients (peak Vo2: from 16.2+/-3 to 20.8+/-4 ml/kg per min; work capacity: from 108+/-20 to 131+/-25 W, p < 0.001 vs. group C for both). The presence of CS+ at baseline was associated with a sensitivity of 70% and a specificity of 77% for predicting an increase in the functional capacity after exercise training. Positive and negative predictive values of LDSE were 84% and 59%, respectively. Independent predictors of cardiac events were a pre-to-posttraining difference in LVEF at peak dobutamine infusion and the presence of a viable response at baseline (p = 0.004 and 0.008, respectively). The log-rank test demonstrated that trained patients had a significantly lower probability of cardiac events during follow-up than sedentary control patients (p < 0.001). CONCLUSIONS: The presence of hibernating myocardium as assessed by LDSE predicts the magnitude of improvement in functional capacity after moderate exercise training in patients with chronic heart failure. A significant increase in functional capacity after exercise training is associated with a lower incidence of cardiac events during follow-up.

Adult↗

PubMed1994

Exercise training in a patient with congestive heart failure on continuous dobutamine.

We present a 53-yr-old man with congestive heart failure who underwent 32 wk of exercise training. The patient was on a continuous infusion of dobutamine for 10 months prior to exercise training, which was subsequently discontinued at wk 24 of exercise training. Symptom-limited graded exercise tests were performed at baseline, wk 12, wk 24, and wk 32 of exercise training. While on a continuous infusion of dobutamine, the patient's oxygen consumption and exercise duration were increased during the exercise training period. Additionally, the patient was able to maintain these changes for 8 wk while continuing to exercise after the discontinuation of the dobutamine therapy.

Dobutamine↗

PubMed1998

Effect of exercise training on passive stiffness in locomotor skeletal muscle: role of extracellular matrix.

The purpose of this study was to evaluate the effect of endurance exercise training on both locomotor skeletal muscle collagen characteristics and passive stiffness properties in the young adult and old rat. Young (3-mo-old) and senescent (23-mo-old) male Fischer 344 rats were randomly assigned to either a control or exercise training group [young control (YC), old control (OC), young trained (YT), old trained (OT)]. Exercise training consisted of treadmill running at approximately 70% of maximal oxygen consumption (45 min/day, 5 days/wk, for 10 wk). Passive stiffness (stress/strain) of the soleus (Sol) muscle from all four groups was subsequently measured in vitro at 26 degreesC. Stiffness was significantly greater for Sol muscles in OC rats compared with YC rats, but in OT rats exercise training resulted in muscles with stiffness characteristics not different from those in YC rats. Sol muscle collagen concentration and the level of the nonreducible collagen cross-link hydroxylysylpyridinoline (HP) significantly increased from young adulthood to senescence. Although training had no effect on Sol muscle collagen concentration in either age group, it resulted in a significant reduction in the level of Sol muscle HP in OT rats. In contrast, exercise had no effect on HP in the YT animals. These findings indicate that 10 wk of endurance exercise significantly alter the passive viscoelastic properties of Sol muscle in old but not in young adult rats. The coincidental reduction in the principal collagen cross-link HP also observed in response to training in OT muscle highlights the potential role of collagen in influencing passive muscle viscoelastic properties.

Aging↗

PubMed1989

Effect of exercise training on energy balance of orchidectomized rats.

The purpose of the present study was to investigate both the respective and interactive roles of exercise training and testosterone on energy balance. Male rats were divided into sedentary and exercise-trained groups. Each group formed was further divided into a sham-operated group, an orchidectomized group, or an orchidectomized group treated with testosterone. Rats were exercised on a motor-driven treadmill for 1 h/day over 28 consecutive days, after which rats were killed. Energy balance measurements, body composition analyses, and serum testosterone assay were then performed. The weight, protein content, and cytochrome-c oxidase activity of interscapular brown adipose tissue (IBAT) were also measured. Results indicate that total food intake, final body weight, and body weight gain were generally lower in exercise-trained rats than in sedentary animals. In orchidectomized rats treated with testosterone, gains of both fat and protein were lower in exercise-trained than in sedentary animals. There was no difference in metabolizable energy intake and body energy gain between trained and sedentary rats that underwent orchidectomy without replacement therapy. In orchidectomized groups of rats, energy gain was lower in trained rats that were treated with testosterone than in those that did not receive any treatment. Furthermore, in trained orchidectomized rats treated with testosterone, both energetic efficiency and energy density of body weight gain were lower than those of trained orchidectomized rats that were not treated. Finally, a significant reduction in IBAT weight was observed in exercise-trained animals, whereas neither exercise nor the various hormonal manipulations affected IBAT protein content and cytochrome-c oxidase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue, Brown↗

PubMed1999

Effects of exercise training on oxygen uptake kinetic responses in women with type 2 diabetes.

OBJECTIVE: Women with uncomplicated type 2 diabetes have both a decreased maximal oxygen consumption (VO2max) and slowed oxygen uptake (VO2) kinetics at the onset of exercise compared with nondiabetic women. These abnormalities are seen not only at maximal workloads, but also at the onset of low-level exercise. To evaluate the hypothesis that VO2max and VO2 kinetics would improve with exercise training in untrained people with type 2 diabetes, we measured these parameters in premenopausal sedentary women before and after 3 months of supervised exercise training. RESEARCH DESIGN AND METHODS: A total of 8 women with type 2 diabetes, 9 overweight nondiabetic women, and 10 lean nondiabetic women were studied. At baseline and after 3 months of exercise training, subjects underwent bicycle ergometer testing to obtain VO2max and VO2 kinetics data. RESULTS: On entry, women with type 2 diabetes had the lowest VO2max and slowest VO2 kinetics of the three groups. After exercise training, the women with type 2 diabetes improved their VO2max more than the lean and overweight control women: 28 vs. 5 and 8%, respectively (P < 0.05 for the diabetic group vs. both control groups). In the group with diabetes, VO2 kinetics improved by 39 and 22% at 20 and 30 W, respectively. For the control subjects, VO2 kinetics did not improve at any workload in either group. CONCLUSIONS: Despite beginning with the lowest VO2max and slowest VO2 kinetics, subjects with type 2 diabetes benefited more from an exercise training program than did control subjects. These findings suggest that in addition to its known metabolic effects, exercise training in individuals with type 2 diabetes may be an effective therapy to improve the cardiovascular response to exercise and to overcome low-level exercise impairment as reflected by improved VO2max and VO2 kinetics. If the ability to make circulatory adjustments at the beginning of exercise at low workloads is improved by an exercise training program, as suggested by the VO2 kinetics data, the clinical significance of exercise for people with type 2 diabetes is clear.

Adult↗

PubMed2004

Effect of exercise training in patients with heart failure: a pilot study on autonomic balance assessed by heart rate variability.

BACKGROUND: Heart rate variability (HRV) is decreased in patients with congestive heart failure (CHF) and is a prognostic marker in this disease. Exercise training is now regarded as an important part of the treatment of patients with CHF, but the effect on HRV and the association between this effect and the effect on neurohormones are not well assessed. METHODS: Heart rate recording was performed in 12 patients with CHF (mean age 67+/-8 years) with CHF NYHA functional class III, before and after 12 weeks of exercise training. The association with exercise capacity and serum levels of atrial natriuretic peptide was assessed. We also evaluated the correlation between HRV and survival at follow-up 87 months later. RESULTS: At baseline there was a significant correlation between mean heart rate and work performed during max cycle test (r=0.650, P=0.022) and the HRV parameter standard deviation normal to normal (SDNN) (r=0.678, P=0.015). After exercise training there was a significant increase in work performed (30.3+/-14.2 versus 38.1+/-14.1 kJ), 6-min walk test (502+/-88 versus 552+/-59 m, P=0.006) and SDNN (117.3+/-40.7 versus 128.6+/-42.3 ms, P=0.028). At 87 months of follow-up, there was a borderline significant difference between survivors and non-survivors. Only the survivors had a significant increase in SDNN after exercise training. CONCLUSION: This pilot study demonstrates an improvement with regard to parameters for HRV after exercise training in patients with CHF. The study suggests that the positive effect of exercise training in patients with CHF involves an attenuation of the reduced HRV response, and that this improvement might have prognostic significance.

Aged↗

PubMed1995

Does exercise training play a role in the treatment of essential hypertension?

Endurance exercise training reduces systolic and diastolic blood pressures in approximately 75% of people who have essential hypertension; these reductions are approximately 10 mmHg for both systolic and diastolic blood pressures. Exercise training at intensities of 40-70% VO2max appears to lower systolic blood pressure somewhat more and diastolic blood pressure to the same degree as higher-intensity training. Additional benefits of endurance exercise training on other risk factors for coronary heart disease make such training an efficacious intervention for people who have mild-to-moderate elevations in blood pressure.

Blood Pressure↗

PubMed1998

Myocardial adaptation to exercise training: a view through positron emission tomography.

Myocardial adaptation to exercise training includes changes in morphology, energy metabolism and autonomic control. Positron emission tomography (PET) provides a tool for investigating tissue perfusion, metabolism and neurotransmission in vivo. Combined with echocardiography, magnetic resonance imaging and assessment of cardiovascular autonomic nervous function, this technology allows us to study the effects of exercise training on cardiac physiology in a noninvasive way. For example, exercise-induced increases in coronary blood flow have been quantified in myocardial segments supplied by angiographically normal as well as diseased vessels. Recent studies have shown that adaptive changes of energy substrate utilization occur in the athlete's heart. Simulation of physical exercise by dobutamine infusion has been used to study demand-induced changes in cardiac energetics and efficiency. Studies on the dysfunctionally hibernating myocardium have outlined the consequences of exercise-induced ischaemia, whereas in heart failure exercise training may normalize myocardial hypoperfusion and sympathetic denervation. In conclusion, PET has matured to a very informative clinical research tool which, particularly in combination with other imaging modalities, has brought into attention previously unaccessible features of cardiovascular physiology.

Adaptation, Physiological↗

PubMed2005

Effect of mild endurance exercise training and pravastatin on peripheral vasodilatation of forearm resistance vessels in patients with coronary artery disease.

BACKGROUND: Improved endothelial function may contribute to the beneficial effects of cholesterol lowering therapy in patients with coronary artery disease (CAD), but results of the effect of statin therapy on endothelial function are disparate in these patients. Exercise training has been reported to improve endothelial function of patients at risk of or with established CAD. The goal of the study was to compare the effect of mild exercise training or statin therapy on forearm endothelial function in CAD patients with average cholesterol levels. DESIGN AND METHODS: Twenty-eight sedentary male patients with angiographically documented CAD and average pretreatment total plasma cholesterol levels (5.1+/-0.9 mmol/l) aged 42-75 years were included. They were randomly assigned in a 2 : 1 order to either statin therapy (pravastatin, 40 mg daily) or exercise training therapy (mild endurance exercise three or more times a week). The effects of 10 weeks of either treatment on endothelium-dependent and independent vasodilation of forearm resistance vessels was assessed by plethysmography. Cardiopulmonary exercise testing was performed at baseline and after 10 weeks. RESULTS: Ten weeks of pravastatin therapy significantly reduced low-density lipoprotein cholesterol (from 3.8+/-0.6 to 3.1+/-0.6 mmol/l at study end, P=0.04) and the ratio of total to high-density lipoprotein cholesterol (from 4.9+/-0.8 to 3.7+/-0.7 mmol/l, P=0.002). Exercise training did not significantly modify the lipid profile. Peak oxygen consumption, maximal achieved workload and exercise duration tended to improve in the exercise training group but remained unchanged in the pravastatin-treated group. Neither 10 weeks of pravastatin nor mild endurance exercise training improved endothelium-dependent or independent vasomotor function in forearm resistance vessels. CONCLUSIONS: In patients with CAD and average cholesterol levels, 10 weeks of treatment with mild endurance exercise training or with pravastatin failed to improve endothelium-dependent or independent vasomotor function in forearm resistance vessels.

Adult↗

PubMed1997

Effects of exercise training on glucose transport and cell surface GLUT-4 in isolated rat epitrochlearis muscle.

The effects of exercise training on maximal glucose transport activity and cell surface GLUT-4 were examined in rat epitrochlearis muscle. Five days of swim training (2 x 3 h/day) produce a significant increase in citrate synthase activity (24.5 +/- 0.6 vs. 20.1 +/- 0.7 micromol x min(-1) x g(-1)), GLUT-4 content (22.9 +/- 0.8 vs. 17.4 +/- 0.4% GLUT-4 standard), and glycogen levels (54.3 +/- 9.4 vs. 28.6 +/- 9.4 micromol/g). Maximally, insulin-stimulated glucose transport activity and cell surface GLUT-4 are increased by 55 (1.50 +/- 0.11 vs. 0.97 +/- 0.10 micromol x ml(-1) x 20 min(-1)) and 48% [12.0 +/- 0.8 vs. 8.1 +/- 0.9 disintegrations x min(-1) (dpm) x mg(-1)], respectively, in exercise-trained epitrochlearis muscles. In contrast, hypoxia-stimulated glucose transport activity and cell surface GLUT-4 are reduced by 38 (0.78 +/- 0.08 vs.1.25 +/- 0.14 micromol x ml(-1) x 20 min(-1)) and 40% (5.7 +/- 0.9 vs. 9.4 +/- 1.2 dpm/mg), respectively, in exercise-trained epitrochlearis muscles. These results demonstrate that changes in insulin- and hypoxia-stimulated glucose transport activity after exercise training are fully accounted for by the appearance of cell surface GLUT-4 and support the concept of two intracellular pools of GLUT-4. Finally, we propose that high levels of muscle glycogen with exercise training may contribute to the decrease in hypoxia-stimulated glucose transport activity.

Animals↗