Myosin ATPase in young and old mammalian myocardium: responses to exercise in cold and thermo neutral environment.

Resting levels of blood lactate (La) were significantly lower at 35 degrees C than at 25 degrees C in the trained (Tr) rats while untrained (UTr) rats maintained higher levels. Extent of decrease in blood glucose (Glu) in Tr rats was lower in cold (C) than in thermo neutral (N) water in young but not in old. Training in C had no impact on young right and left ventricles (RV and LV). UTr old rats showed loss in LV Glu at both the temperatures. Old trainees had reduced RV Glu in C while no change was observed at N. Substrate changes were concomitant with altered myosin ATPase activity. Young ventricles showed higher ATPase activity in LV than in RV, and training in C evoked elevations in RV enzyme. The results suggest that training may enhance the functional and biochemical activity in terms of higher myosin ATPase activity in N, as against a C environment, and the effect is better pronounced in LV. Anaerobic condition is felt more in C as seen through elevated blood La.

Responses of aging brain to physical exercise: changes in the substrates of energy metabolism.

Responses of aging brain to physical training was evaluated by quantifying the substrates, glucose, lactic acid, and nucleic acids in cerebral cortex (CC) and medulla oblongata (MO) of the brain in rats. Rats of 1 month (young), 6 months (adult), 12 months (middle-aged) and 18 months (old) of age were swim-trained for 30 days. Glucose content of CC and MO increased with training whereas blood glucose decreased in trained young and adult animals with middle-aged and old animals maintaining constant blood glucose. Brain lactate in these two regions decreased with training in all age groups. However, the old animals showed an elevation in blood lactic acid in trained state, while the other age groups showed a decrease. Nucleic acid content, decreased with age, especially the RNA content in MO showing a larger depletion. However, there was no discernible influence of physical exercise on these parameters. Physical training has influenced the aging brain's adaptability, as seen by increase in its glucose content in young animals and also possible utilization of lactate as an additional substrate in old animals as evidenced by an increase in blood lactic acid.

Interaction of exercise and age on substrates of carbohydrate metabolism.

Changes in blood lactate, pyruvate, glucose and tissue glycogen were used as indices to evaluate the extent of effects of physical conditioning in young and old male rats. Rats were trained on a running wheel and swimming tank for 10 weeks. Biochemical estimations of lactic acid (LA) pyruvic acid (PA) and glucose (GL) in plasma and glycogen in cardiac and slow-twitch soleus (SOL) and fast-twitch extensor digitorum longus (EDL) skeletal muscles of trained animals were conducted and compared with those of sedentary control rats. Blood parameters showed a decrease upon training in both young and old rats, though of variable significances, between exercise types. Glycogen levels in the cardiac and skeletal muscles increased in all groups with the exception in SOL of older trained animals. Hepatic glycogen exhibited an insignificant increase in all groups. Results suggest that, though the trends of responses of both young and old rats to exercise follow a comparable path, the magnitudes of changes are definitely impressed upon appreciably by increasing age.

Changes in cardiac lactate dehydrogenase isoenzymes following experimental necrosis in rats.

Following a subcutaneous injection of isoproterenol (ISO) into adult rats (30 mg/100 g, B.W.), the cardiac total lactate dehydrogenase (LDH) activity was decreased by about 53.81% in less than 24 H. Restoration of myocardial LDH activity was seen at 24 H and 48 H. LDH-I activity exceeded LDH-V in the control heart, while LDH-I, LDH-II and LDH-III decreased at 48 H following ISO injection. These changes were associated with concomitant elevation in LDH-V activity. Percentage M-LDH was less than H-LDH till 12 H in the necrotic heart muscle but exceeded the latter at 24H and 48 H. Similar changes were marked in absolute H-LDH and M-LDH activities when compared with the total LDH activity. Histopathological studies revealed and confirmed the occurrence of infarcts. The results indicate the potential of myocardial tissue for efficient shifting of H-LDH synthesis to M-LDH synthesis in the necrotic heart.