Chronic and acute exercise do not alter Ca2+ regulatory systems and ectonucleotidase activities in rat heart.
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The purpose of this investigation was to examine the effects of chronic and acute exercise on the main components involved in excitation-contraction coupling and relaxation in rat heart. Sixty male Wistar rats were divided into a sedentary (S) and three 12-wk treadmill-trained groups (T-1, moderate intensity; T-2, high intensity; T-3, interval running). After 12-wk, 15 rats from the S group and 15 rats from the T-2 group were subjected to a single treadmill-exercise session until exhaustion before being killed at 0, 24, or 48 h (acute exercise). The remaining animals were killed 48 h after the last standard exercise session (chronic exercise). The efficacy of the training programs was confirmed by an increase in treadmill endurance time and in skeletal muscle citrate synthase activity. None of the exercise programs modified heart weight or cardiac oxidative capacity. [(3)H]PN200-110 and [(3)H]ryanodine binding to cardiac homogenates indicated that the density of L-type and sarcoplasmic reticulum (SR) Ca(2+) channels was the same in S and trained rats. The SR Ca(2+)-ATPase activity was also unmodified. Finally, the activities of the ectoenzymes Mg(2+)-ATPase and 5'-nucleotidase, which are involved in degradation of extracellular nucleotides, were not affected by either of the running programs. After the acute exercise session, no changes were detected in either of the tested parameters in heart homogenates of S and T-2 animals. We conclude that neither treadmill-exercise training for 12 wk nor exhaustive exercise alters the density of Ca(2+) channels involved in excitation-contraction coupling or the SR Ca(2+)-ATPase and the ectonucleotidase activities in rat heart. (+info)
Training-induced elevation in FABP(PM) is associated with increased palmitate use in contracting muscle.
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To evaluate the effects of endurance training in rats on fatty acid metabolism, we measured the uptake and oxidation of palmitate in isolated rat hindquarters as well as the content of fatty acid-binding proteins in the plasma membranes (FABP(PM)) of red and white muscles from 16 trained (T) and 18 untrained (UT) rats. Hindquarters were perfused with 6 mM glucose, 1,800 microM palmitate, and [1-(14)C]palmitate at rest and during electrical stimulation (ES) for 25 min. FABP(PM) content was 43-226% higher in red than in white muscles and was increased by 55% in red muscles after training. A positive correlation was found to exist between succinate dehydrogenase activity and FABP(PM) content in muscle. Palmitate uptake increased by 64-73% from rest to ES in both T and UT and was 48-57% higher in T than UT both at rest (39.8 +/- 3.5 vs. 26.9 +/- 4. 4 nmol. min(-1). g(-1), T and UT, respectively) and during ES (69.0 +/- 6.1 vs. 43.9 +/- 4.4 nmol. min(-1). g(-1), T and UT, respectively). While the rats were resting, palmitate oxidation was not affected by training; palmitate oxidation during ES was higher in T than UT rats (14.8 +/- 1.3 vs. 9.3 +/- 1.9 nmol. min(-1). g(-1), T and UT, respectively). In conclusion, endurance training increases 1) plasma free fatty acid (FFA) uptake in resting and contracting perfused muscle, 2) plasma FFA oxidation in contracting perfused muscle, and 3) FABP(PM) content in red muscles. These results suggest that an increased number of these putative plasma membrane fatty acid transporters may be available in the trained muscle and may be implicated in the regulation of plasma FFA metabolism in skeletal muscle. (+info)
Aging and acute exercise enhance free radical generation in rat skeletal muscle.
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Reactive oxygen species (ROS) are implicated in the mechanism of biological aging and exercise-induced oxidative damage. The present study examined the effect of an acute bout of exercise on intracellular ROS production, lipid and protein peroxidation, and GSH status in the skeletal muscle of young adult (8 mo, n = 24) and old (24 mo, n = 24) female Fischer 344 rats. Young rats ran on a treadmill at 25 m/min and 5% grade until exhaustion (55.4 +/- 2.7 min), whereas old rats ran at 15 m/min and 5% grade until exhaustion (58.0 +/- 2.7 min). Rate of dichlorofluorescin (DCFH) oxidation, an indication of ROS and other intracellular oxidants production in the homogenate of deep vastus lateralis, was 77% (P < 0.01) higher in rested old vs. young rats. Exercise increased DCFH oxidation by 38% (P < 0.09) and 50% (P < 0.01) in the young and old rats, respectively. DCFH oxidation in isolated deep vastus lateralis mitochondria with site 1 substrates was elevated by 57% (P < 0.01) in old vs. young rats but was unaltered with exercise. Significantly higher DCFH oxidation rate was also found in aged-muscle mitochondria (P < 0.01), but not in homogenates, when ADP, NADPH, and Fe(3+) were included in the assay medium without substrates. Lipid peroxidation in muscle measured by malondialdehyde content showed no age effect, but was increased by 20% (P < 0.05) with exercise in both young and old rats. Muscle protein carbonyl formation was unaffected by either age or exercise. Mitochondrial GSH/ GSSG ratio was significantly higher in aged vs. young rats (P < 0.05), whereas exercise increased GSSG content and decreased GSH/GSSG in both age groups (P < 0.05). These data provided direct evidence that oxidant production in skeletal muscle is increased in old age and during prolonged exercise, with both mitochondrial respiratory chain and NADPH oxidase as potential sources. The alterations of muscle lipid peroxidation and mitochondrial GSH status were consistent with these conclusions. (+info)
Mechanism-based modeling of rebound tachycardia after chronic l-propranolol infusion in spontaneous hypertensive rats.
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The aims of the study were to characterize the rate and extent of the rebound effect after abrupt cessation of a chronic exposure of l-propranolol in spontaneous hypertensive rats, using exercise-induced tachycardia as a pharmacodynamic endpoint. Thirty-two spontaneous hypertensive rats were randomized to receive either placebo or 4 or 8 mg/kg/day s.c. infusion of l-propranolol for 11 days using osmotic minipumps. The heart rate was measured after standardized physical exercise before and during drug exposure and over 12 days after cessation, using a computerized tail-cuff method. Blood samples were collected after each effect measurement during the infusion. A similar reduction in exercise tachycardia was registered for the two doses. No apparent tolerance development was found, but both doses showed a clear rebound effect of similar extent and intensity. The maximal rebound effect was observed on the second day after cessation and was found to have a duration of about 6 days. A mechanism-based model was developed to describe the rate and extent of changes in beta-adrenoceptor up- and down-regulation with increased sensitivity of the transducer complex. The half-life of disappearance of up-regulated beta-adrenoceptors was estimated to be 2.0 days (1.0-3.9 days). The effect-versus-time data was analyzed by nonlinear mixed-effect modeling with the program NONMEM. A dose-dependent reduction in the growth of body weight was observed during drug treatment, which was reversible. A dose- and time-dependent increase in the alpha(1)-acid glycoprotein concentration was also observed. (+info)
Reliability of recall of physical activity in the distant past.
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Substantial data exist supporting the role of physical activity in the etiology of several chronic diseases. Many chronic diseases begin developing 20-30 years before they become clinically evident. Since researchers often must rely on recall to characterize the long term habits of study participants, the accuracy of recall of physical activity is an important methodological issue in etiologic studies. The purpose of this study was to examine the quality of recall of physical activity in the distant past in a cohort of western New York residents followed since 1960. Paired t tests and intraclass correlation coefficients (ICCs) were used to compare "original" (1960) and "recalled" (1992-1996) reports of weekday (occupational) and free-day (leisure time) physical activity. Results showed that the recalled reports underestimated past weekday activities when overall activity was examined; estimates closer to the originals were found when levels of activity were examined. Recall was best for weekday light (ICC = 0.43) and weekday moderate (ICC = 0.45) activity in both sexes and free-day hard activity in females (ICC = 0.45). Most participants underestimated past free-day activity, but males overestimated free-day hard activity. Correlations for free-day activity were highest for summer sports in females (ICC = 0.29) and winter sports in both sexes (ICC = 0.39) and were low for walking and "other activity." Considering the length of time between the original interviews and the recall interviews, the correlations found here are remarkable and close to those found in other studies where recall intervals were 10 years or less. (+info)
Effect of verbascoside on decreasing concentration of oxygen free radicals and lipid peroxidation in skeletal muscle.
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AIM: To detect the effects of verbascoside on decreasing the concentration of oxygen free radicals (OFR) and lipid peroxidation in skeletal muscle resulting from exhaustive exercise. METHODS: Electron spin resonance (ESR) technique and thiobarbituric acid reaction (TBAR) method were used to detect the concentration of OFR in intact gastrocnemius muscle and the contents of milondialdehyde (MDA) in muscle homogenate. RESULTS: Verbascoside decreased the concentration of OFR (P < 0.05) and the level of lipid peroxidation (P < 0.05) in muscle caused by exercise. CONCLUSION: Verbascoside has the effects of reducing oxidative stress in muscle caused by exhaustive exercise by decreasing the concentration of free radicals and the level of lipid peroxidation. (+info)
Association of low back pain with self-reported risk factors among patients seeking physical therapy services.
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BACKGROUND AND PURPOSE: This study investigated the magnitude of association between low back pain (LBP) and self-reported factors thought to increase the risk of LBP. SUBJECTS AND METHODS: Questionnaires were completed by 150 patients who were receiving physical therapy for LBP and by 138 patients who were being treated for other reasons. The solicited information was used to estimate odds ratios and 95% confidence intervals for the LBP-risk factor association. RESULTS: Low back pain was positively associated with smoking status, pregnancy, industrial vibration exposure, and time spent in a car (odds ratios > or = 2.21). Daily lifting, body mass index, activity level, and time sitting or standing showed at most a weak positive association with LBP. Comparisons with estimated associations from other studies were made. CONCLUSION AND DISCUSSION: Data from this study support a statistically significant association between LBP and some factors found in other research to increase the risk of LBP. Study findings may have implications for targeting at-risk groups for back care education or intervention programs. (+info)
Impact of acute exercise intensity on pulsatile growth hormone release in men.
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To investigate the effects of exercise intensity on growth hormone (GH) release, 10 male subjects were tested on 6 randomly ordered occasions [1 control condition (C), 5 exercise conditions (Ex)]. Serum GH concentrations were measured in samples obtained at 10-min intervals between 0700 and 0900 (baseline) and 0900 and 1300 (exercise+ recovery). Integrated GH concentrations (IGHC) were calculated by trapezoidal reconstruction. During Ex subjects exercised for 30 min (0900-0930) at one of the following intensities [normalized to the lactate threshold (LT)]: 25 and 75% of the difference between LT and rest (0.25LT and 0.75LT, respectively), at LT, and at 25 and 75% of the difference between LT and peak (1.25LT and 1.75LT, respectively). No differences were observed among conditions for baseline IGHC. Exercise+recovery IGHC (mean +/- SE: C = 250 +/- 60; 0.25LT = 203 +/- 69; 0.75LT = 448 +/- 125; LT = 452 +/- 119; 1.25LT = 512 +/- 121; 1.75LT = 713 +/- 115 microg x l(-1) x min(-1)) increased linearly with increasing exercise intensity (P < 0.05). Deconvolution analysis revealed that increasing exercise intensity resulted in a linear increase in the mass of GH secreted per pulse and GH production rate [production rate increased from 16. 5 +/- 4.5 (C) to 32.1 +/- 5.2 microg x distribution volume(-1) x min(-1) (1.75LT), P < 0.05], with no changes in GH pulse frequency or half-life of elimination. We conclude that the GH secretory response to exercise is related to exercise intensity in a linear dose-response pattern in young men. (+info)