Muscle energetics during prolonged cycling after exercise hypervolemia

This study examined the question of whether increases in plasma volume (hypervolemia) induced through exercise affect muscle substrate utilization and muscle bioenergetics during prolonged heavy effort. Six untrained males (19-24 yr) were studied before and after 3 consecutive days of cycling (2 h/day at 65% of peak O2 consumption) performed in a cool environment (22-23 degrees C, 25-35% relative humidity). This protocol resulted in a 21.2% increase in plasma volume (P less than 0.05). During exercise no difference was found in the blood concentrations of glucose, lactate, and plasma free fatty acids at either 30, 60, 90, or 120 min of exercise before and after the hypervolemia. In contrast, blood alanine was higher (P less than 0.05) during both rest and exercise with hypervolemia. Measurement of muscle samples extracted by biopsy from the vastus lateralis muscle at rest and at 60 and 120 min of exercise indicated no effect of training on high-energy phosphate metabolism (ATP, ADP, creatine phosphate, creatine) or on selected glycolytic intermediate concentrations (glucose 1-phosphate, glucose 6-phosphate, fructose 6-phosphate, lactate). In contrast, training resulted in higher (P less than 0.05) muscle glucose and muscle glycogen concentrations. These changes were accompanied by blunting of the exercise-induced increase (P less than 0.05) in both blood epinephrine and norepinephrine concentrations. Plasma glucagon and serum insulin were not affected by the training. The results indicate that exercise-induced hypervolemia did not alter muscle energy homeostasis. The reduction in muscle glycogen utilization appears to be an early adaptive response to training mediated either by an increase in blood glucose utilization or a decrease in anaerobic glycolysis.     

Muscle and blood redox status after exercise training in severe COPD patients

Beneficial effects of exercise training in patients with chronic obstructive pulmonary disease (COPD) are acknowledged. However, high-intensity exercise may enhance muscle oxidative stress in severe COPD patients. We hypothesized that high-intensity exercise training of long duration does not deteriorate muscle redox status. In the vastus lateralis and blood of 18 severe COPD patients and 12 controls, before and after an 8-week training program, protein oxidation and nitration, antioxidant systems, and inflammatory cytokines were examined. At baseline, COPD patients showed greater muscle oxidative stress and superoxide dismutase activity and circulating inflammatory cytokines than controls. Among COPD patients, muscle and blood protein carbonylation levels were correlated. Both groups showed training-induced increase in VO(2) peak and decreased blood lactate levels. After training, among the COPD patients, blood protein nitration levels were significantly reduced and muscle protein oxidation and nitration levels did not cause impairment. Muscle and blood levels of inflammatory cytokines were not modified by training in either patients or controls. We conclude that in severe COPD patients, high-intensity exercise training of long duration improves exercise capacity while preventing the enhancement of systemic and muscle oxidative stress. In addition, in these patients, resting protein oxidation levels correlate between skeletal muscle and blood compartments.     

Muscle metabolism during prolonged physical exercise in dogs

In order to provide reference data, adenine nucleotide, creatine phosphate, glycogen, glycolytic intermediates and lactate muscle contents were measured in 49 dogs under resting conditions and during prolonged physical exercise of moderate intensity performed until exhaustion. Both the resting and exercise values of the measured variables were remarkably similar to those described in human subjects, except muscle lactate content which achieved higher values during submaximal exercise in dogs than in men.     

Effects of acute exercise and prolonged exercise training on blood pressure, vasopressin and plasma renin activity in spontaneously hypertensive rats

The purpose of this study was to investigate the effect of swimming training on systolic blood pressure (BPs), plasma and brain vasopressin (AVP), and plasma renin activity (PRA) in spontaneously hypertensive rats (SHR) during rest and after exercise. Resting and postexercise heart rate, as well as blood parameters such as packed cell volume (PCV), haemoglobin concentration (Hb), plasma sodium and potassium concentrations ([Na+], [K+]) osmolality and proteins were also studied. Hypophyseal AVP had reduced significantly after exercise in the SHR, whereas PRA had increased significantly in the Wistar-Kyoto (WKY) strain used as normotensive controls. Plasma AVP concentration increased in both strains. By the end of the experiment, training had reduced body mass and BPs by only 10% and 6%, respectively. Maximal oxygen uptake was increased 10% and plasma osmolality 2% by training. The postexercise elevation of heart rate was not significantly attenuated by training. A statistically significant reduction in postexercise plasma osmolality (10%) and [Na+] (4%) was observed. These results suggested that swimming training reduced BPs. Plasma and brain AVP played a small role in the hypertensive process of SHR in basal conditions because changes in AVP contents did not correlate with those of BPs. Moreover, there were no differences between SHR and WKY in plasma, hypophyseal and hypothalamic AVP content in these basal conditions. Finally, during moderate exercise a haemodilution probably occurred with an increase of plasma protein content. This was confirmed by the exercise-induced increase of plasma AVP and the reduction of hypophyseal AVP content, suggesting a release of this hormone, which probably contributed to the water retention and haemodilution.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunomodulatory effect of selenosemicarbazides and selenium inorganic compounds, distribution in organs after selenium supplementation

Antioxidant properties of selenium producing a protective barrier against free radicals play an important role in numerous metabolic and immunologic processes associated with oxidation- reduction reactions which take place during intracellular digestion of phagocyted bacteria. The aim of our study was to examine the properties of an organic compound of selenium, 4-(o-tolilo)- selenosemicarbazide of p-chlorobenzoic acid in terms of its retention in organs, effect on erythropoesis and phagocytic abilities of neutrophiles as well as antioxidant properties in neutrophiles tested with NBT test. This compound as well as inorganic sodium selenate was given to Swiss mice at the dose of 10^–3 g Se/kg for the period of 10 days. The concentrations of selenium in livers of mice treated with sodium selenate and selenosemicarbazide were found to be higher than in controls (18,7 g lg^–1 and 23.2 g lg^–1 vs. 12 g lg^–1, respectively). Analysis of blood cells count has shown a significant decrease in neutrophile levels in both groups treated with selenium. The influence of selenium compounds on phagocytosis and especially NBT test has been determined (3.8% of positive cells in the controls vs. 2.2% and 0.9% in the groups treated with sodium selenate and selenosemicarbazide, respectively). Our preliminary investigations suggest that selenosemicarbazides are biologically active compounds and can modify neutrophile functions.     

硒元素对平菇菌丝体GSH-Px、SOD及MDA的影响

于培养基中加入一定量的亚硒酸钠溶液 ,分别测定了 2个品种平菇菌丝体内GSH Px、SOD活性及MDA含量。结果表明 :3 0、60mg/L组菌丝体内GSH Px、SOD活性极显著升高 (P <0 .0 1 )而MDA含量明显降低 (P <0 .0 5 ) ,随着硒水平的升高 ,GSH Px、SOD活性呈下降趋势而MDA含量则显著升高 (P <0 .0 5 )。因此 ,在培养富硒平菇菌丝体时应适当考虑培养基的硒浓度。     

Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate

The purpose of this study was to determine whether the postponement of fatigue in subjects fed carbohydrate during prolonged strenuous exercise is associated with a slowing of muscle glycogen depletion. Seven endurance-trained cyclists exercised at 71 +/- 1% of maximal O2 consumption (VO2max), to fatigue, while ingesting a flavored water solution (i.e., placebo) during one trial and while ingesting a glucose polymer solution (i.e., 2.0 g/kg at 20 min and 0.4 g/kg every 20 min thereafter) during another trial. Fatigue during the placebo trial occurred after 3.02 +/- 0.19 h of exercise and was preceded by a decline (P less than 0.01) in plasma glucose to 2.5 +/- 0.5 mM and by a decline in the respiratory exchange ratio (i.e., R; from 0.85 to 0.80; P less than 0.05). Glycogen within the vastus lateralis muscle declined at an average rate of 51.5 +/- 5.4 mmol glucosyl units (GU) X kg-1 X h-1 during the first 2 h of exercise and at a slower rate (P less than 0.01) of 23.0 +/- 14.3 mmol GU X kg-1 X h-1 during the third and final hour. When fed carbohydrate, which maintained plasma glucose concentration (4.2-5.2 mM), the subjects exercised for an additional hour before fatiguing (4.02 +/- 0.33 h; P less than 0.01) and maintained their initial R (i.e., 0.86) and rate of carbohydrate oxidation throughout exercise. The pattern of muscle glycogen utilization, however, was not different during the first 3 h of exercise with the placebo or the carbohydrate feedings. The additional hour of exercise performed when fed carbohydrate was accomplished with little reliance on muscle glycogen (i.e., 5 mmol GU X kg-1 X h-1; NS) and without compromising carbohydrate oxidation. We conclude that when they are fed carbohydrate, highly trained endurance athletes are capable of oxidizing carbohydrate at relatively high rates from sources other than muscle glycogen during the latter stages of prolonged strenuous exercise and that this postpones fatigue.     

Muscle and blood ammonia and lactate responses to prolonged exercise with hyperoxia

Investigations using nonsteady-state and fatiguing exercise protocols have demonstrated a strong relationship between ammonia and lactate metabolism and have suggested a cause and effect relationship between these two variables. We investigated the lactate-ammonia response using prolonged exercise and inspiration of hyperoxic gas (60% O2-40% N2). The exercise consisted of either 70-75% maximal O2 uptake (VO2 max) for 40 min (series 1, n = 6) or 75-80% VO2max for 30 min (series 2, n = 6) with the subjects inspiring room air on one occasion and hyperoxia in the other test. In both series blood ammonia rose continuously throughout the exercise regardless of the inspired gas treatment; in contrast blood lactate did not increase after 10 min with room air, and with hyperoxia blood lactate was reduced. Muscle lactate and ammonia (series 2; vastus lateralis) had responses similar to the blood data. The data demonstrated no apparent lactate-ammonia relationship with prolonged exercise or in response to hyperoxia, suggesting that ammonia production can be independent of lactate metabolism. The data also suggest that type I fibers can be a major source of ammonia in humans.     

Selenium supplementation of Chinese women with habitually low selenium intake increases plasma selenium, plasma glutathione peroxidase activity, and milk selenium, but not milk glutathione peroxidase activity

Twenty-one pregnant women living in Xichang County, China, a selenium-deficient area, were divided into two groups and given either a placebo (n = 10) as yeast or selenium-enriched yeast tablets (n = 11) to provide 100 microg selenium per day. This supplementation was begun the last trimester of pregnancy and continued for 3 months after parturition. Plasma selenium levels and glutathione peroxidase (GPX) activity steadily declined in supplemented women, but a curvilinear response occurred in milk selenium and GPX activity in both supplemented and deficient women and in plasma selenium and GPX activity in deficient women. The milk selenium levels were higher in supplemented women but there were no differences in the milk GPX activity between the two groups of women. The plasma alpha-tocopherol concentrations declined after parturition in both groups but no differences were found between the two groups of women. Plasma thiobarbituric acid reactive substances declined in supplemented women but showed a curvilinear response in unsupplemented women, suggesting peroxidative stress in these women. GPX, selenium, and peroxidative responses in plasma and milk following parturition is advocated as a new method to assess selenium status of lactating women.