Metabolic response of equine muscle to intermittent maximal exercise

Four thoroughbred horses performed 4 gallops (G1-G4) with intervals of 5 min. With one exception, gallops were sustained at maximal speed over 620 m. Muscle biopsy samples of the middle gluteal and brachiocephalicus were taken before, during, and after exercise and assayed for ATP and intermediary metabolites. The results showed a major involvement of the brachiocephalicus, in addition to the middle gluteal, during galloping. In three horses, who were clearly fatigued, muscle ATP decreased by up to 50% by the end of G4. This was matched by an equal rise in inosine 5'-monophosphate. Pronounced accumulations of glycerol 3-phosphate, glycerol, and lactate (up to 204 mmol X kg dry muscle-1) occurred with exercise. In the fourth horse, which was less fatigued, a decrease in ATP and increases in intermediary metabolites were much less. Postexercise there was little or no recovery in muscle ATP or lactate during 30 min. The decreases in ATP are consistent with a high activity of adenosine 5'-monophosphate deaminase in horse muscle and indicative also of the high level of anaerobic stress of the exercise program. There was evidence to suggest that the increase in muscle glycerol resulted from hydrolysis of glycerol 3-phosphate and not from the utilization of triglyceride.     

Metabolic response of trained and untrained women during high-intensity intermittent cycle exercise

The metabolic response to two different forms of high-intensity intermittent cycle exercise was investigated in young women. Subjects (8 trained and 8 untrained) performed two bouts of high-intensity intermittent exercise: short sprint (SS) (8-s sprint, 12-s recovery) and long sprint (LS) (24-s sprint, 36-s recovery) for 20 min on two separate occasions. Both workload and oxygen uptake were greater in the trained subjects but were not significantly different for SS and LS. Plasma glycerol concentrations significantly increased during exercise. Lactate concentrations rose over the 20 min and were higher for the trained women. Catecholamine concentration was also higher postexercise compared with preexercise for both groups. Both SS and LS produced similar metabolic response although both lactate and catecholamines were higher after the 24-s sprint. In conclusion, these results show that high-intensity intermittent exercise resulted in significant elevations in catecholamines that appear to be related to increased venous glycerol concentrations. The trained compared with the untrained women tended to show an earlier increase in plasma glycerol concentrations during high-intensity exercise.     

Reproducibility of cardiac biomarkers response to prolonged treadmill exercise

Abstract

We examined the reproducibility of alterations in cardiac biomarkers after two identical bouts of prolonged exercise in young athletes. Serum high-sensitivity cardiac troponin T (hs-cTnT) and N-terminal pro-brain natriuretic peptide (NT-proBNP) levels were assessed before and after exercise. Significant rises in median hs-cTnT and NT-proBNP occurred in both trials. While the absolute changes in hs-cTnT were smaller after trial 2, the pattern of change was similar and the delta scores were significantly related. However, the change in NT-proBNP was not correlated between trials. The hs-cTnT release demonstrates some consistency after exercise although the blunted hc-cTnT response requires further study.     

Metabolic effects of treadmill exercise training on the diabetic heart.

This study determined whether exercise training in rats would prevent the accumulation of lipids and depressed glucose utilization found in hearts from diabetic rats. Diabetes was induced by intravenous streptozotocin (60 mg/kg). Trained diabetic rats were run on a treadmill for 60 min, 27 m/min, 10% grade, 6 days/wk for 10 wk. Training of diabetic rats had no effect on glycemic control but decreased plasma lipids. In vivo myocardial long-chain acylcarnitine, acyl-CoA, and high-energy phosphate levels were similar in sedentary control, sedentary diabetic, and trained diabetic groups. The levels of myocardial triacylglycerol were similar in sedentary control and diabetic rats but decreased in trained diabetic rats. Hearts were perfused with buffer containing diabetic concentrations of glucose (22 mM) and palmitate (1.2 mM). D-[U-14C] glucose oxidation rates (14CO2 production) were depressed in hearts from sedentary diabetic rats relative to sedentary control rats. Hearts from trained diabetic rats exhibited increased glucose oxidation relative to those of sedentary diabetic rats, but this improvement was below that of the sedentary control rats. [9,10(-3)H]palmitate oxidation rates (3H2O production) were identical in all three groups. These findings suggest that exercise training resulted in a partial normalization of myocardial glucose utilization in diabetic rats.     

Cardiovascular effects of treadmill exercise in physiological and pathological preclinical settings

Exercise adaptations result from a coordinated response of multiple organ systems, including cardiovascular, pulmonary, endocrine-metabolic, immunologic, and skeletal muscle. Among these, the cardiovascular system is the most directly affected by exercise, and it is responsible for many of the important acute changes occurring during physical training. In recent years, the development of animal models of pathological or physiological cardiac overload has allowed researchers to precisely analyze the complex cardiovascular responses to stress in genetically altered murine models of human cardiovascular disease. The intensity-controlled treadmill exercise represents a well-characterized model of physiological cardiac hypertrophy because of its ability to mimic the typical responses to exercise in humans. In this review, we describe cardiovascular adaptations to treadmill exercise in mice and the most important parameters that can be used to quantify such modifications. Moreover, we discuss how treadmill exercise can be used to perform physiological testing in mouse models of disease and to enlighten the role of specific signaling pathways on cardiac function.     

Effects of treadmill exercise to exhaustion on the insulin response to hyperglycemia in untrained men

The effects of a single bout of exercise to exhaustion on pancreatic insulin secretion were determined in seven untrained men by use of a 3-h hyperglycemic clamp with plasma glucose maintained at 180 mg/100 ml. Clamps were performed either 12 h after an intermittent treadmill run at approximately 77% maximum O2 consumption or without prior exercise. Arterialized blood samples for glucose, insulin, and C-peptide determination were obtained from a heated hand vein. The peak insulin response during the early phase (0-10 min) of the postexercise clamp was higher (81 +/- 8 vs. 59 +/- 9 microU/ml; P less than 0.05) than in the nonexercise clamp. Incremental areas under the insulin (376 +/- 33 vs. 245 +/- 51 microU.ml-1.min) and C-peptide (17 +/- 2 vs. 12 +/- 1 ng.ml-1.min) curves were also greater (P less than 0.05) during the early phase of the postexercise clamp. No differences were observed in either insulin concentrations or whole body glucose disposal during the late phase (15-180 min). Area under the C-peptide curve was greater during the late phase of the postexercise clamp (650 +/- 53 vs. 536 +/- 76 ng.ml-1.min, P less than 0.05). The exercise bout induced muscle soreness and caused an elevation in plasma creatine kinase activity (142 +/- 32 vs. 305 +/- 31 IU/l; P less than 0.05) before the postexercise clamp. We conclude that in untrained men a bout of running to exhaustion increased pancreatic beta-cell insulin secretion during the early phase of the hyperglycemic clamp. Increased insulin secretion during the late phase of the clamp appeared to be compensated by increased insulin clearance.     

Changes in ventilation in response to ramp changes in treadmill exercise load

These experiments examined the changes in ventilation during a 40-s ramp increase in exercise load, produced by increasing either the speed of the treadmill or the grade, to equivalent end-points of oxygen uptake. Six subjects underwent five trials each for grade and speed, while ventilation was monitored breath-by-breath. For each subject, ventilation versus time for all five of the speed trials was plotted on a single graph and fitted by linear regression. The data for the grade trials were similarly treated. For all subjects, the slope of the regression line for the speed plots was found to be significantly (P < 0.05) greater than that for the grade plots. We concluded that these experimental results support the hypothesis that the neural drive to ventilation persists as exercise continues and is proportionately related to the frequency of limb movement.     

Metabolic response to carbohydrate ingestion during exercise in males and females

The present study investigated potential sex-related differences in the metabolic response to carbohydrate (CHO) ingestion during exercise. Moderately endurance-trained men and women (n = 8 for each sex) performed 2 h of cycling at approximately 67% Vo(2 max) with water (WAT) or CHO ingestion (1.5 g of glucose/min). Substrate oxidation and kinetics were quantified during exercise using indirect calorimetry and stable isotope techniques ([(13)C]glucose ingestion, [6,6-(2)H(2)]glucose, and [(2)H(5)]glycerol infusion). In both sexes, CHO ingestion significantly increased the rates of appearance (R(a)) and disappearance (R(d)) of glucose during exercise compared with WAT ingestion [males: WAT, approximately 28-29 micromol x kg lean body mass (LBM)(-1) x min(-1); CHO, approximately 53 micromol x kg LBM(-1) x min(-1); females: WAT, approximately 28-29 micromol x kg LBM(-1) x min(-1); CHO, approximately 61 micromol x kg LBM(-1) x min(-1); main effect of trial, P < 0.05]. The contribution of plasma glucose oxidation to the energy yield was significantly increased with CHO ingestion in both sexes (from approximately 10% to approximately 20% of energy expenditure; main effect of trial, P < 0.05). Liver-derived glucose oxidation was reduced, although the rate of muscle glycogen oxidation was unaffected with CHO ingestion (males: WAT, 108 +/- 12 micromol x kg LBM(-1) x min(-1); CHO, 108 +/- 11 micromol x kg LBM(-1) x min(-1); females: WAT, 89 +/- 10 micromol x kg LBM(-1) x min(-1); CHO, 93 +/- 11 micromol x kg LBM(-1) x min(-1)). CHO ingestion reduced fat oxidation and lipolytic rate (R(a) glycerol) to a similar extent in both sexes. Finally, ingested CHO was oxidized at similar rates in men and women during exercise (peak rates of 0.70 +/- 0.08 and 0.65 +/- 0.06 g/min, respectively). The present investigation suggests that the metabolic response to CHO ingestion during exercise is largely similar in men and women.     

Metabolic response to green tea extract during rest and moderate-intensity exercise

BackgroundGreen tea catechins have been hypothesized to increase energy expenditure and fat oxidation by inhibiting catechol-O-methyltransferase (COMT) and thus promoting more sustained adrenergic stimulation. Metabolomics may help to clarify the mechanisms underlying their putative physiological effects.ObjectiveThe study investigated the effects of 7-day ingestion of green tea extract (GTE) on the plasma metabolite profile at rest and during exercise.MethodsIn a placebo-controlled, double-blind, randomized, parallel study, 27 healthy physically active males consumed either GTE (n=13, 1200 mg catechins, 240 mg caffeine/day) or placebo (n=14, PLA) drinks for 7 days. After consuming a final drink (day 8), they rested for 2 h and then completed 60 min of moderate-intensity cycling exercise (56%±4% VO₂max). Blood samples were collected before and during exercise. Plasma was analyzed using untargeted four-phase metabolite profiling and targeted profiling of catecholamines.ResultsUsing the metabolomic approach, we observed that GTE did not enhance adrenergic stimulation (adrenaline and noradrenaline) during rest or exercise. At rest, GTE led to changes in metabolite concentrations related to fat metabolism (3-β-hydroxybutyrate), lipolysis (glycerol) and tricarboxylic acid cycle (TCA) cycle intermediates (citrate) when compared to PLA. GTE during exercise caused reductions in 3-β-hydroxybutyrate concentrations as well as increases in pyruvate, lactate and alanine concentrations when compared to PLA.ConclusionsGTE supplementation resulted in marked metabolic differences during rest and exercise. Yet these metabolic differences were not related to the adrenergic system, which questions the in vivo relevance of the COMT inhibition mechanism of action for GTE.