ANTIOXIDANTS, TISSUE-DAMAGE, AND ENDURANCE IN TRAINED AND UNTRAINED YOUNG MALE-RATS

It is well known that physical training permits an animal to respond s uccessfully to exercise loads of various types, intensities, and durat ions. Furthermore, the trained animal can sustain the activity for a l ong period before the fatigue becomes limiting. The effects of physica l training on the antioxidant defenses of tissues and on their suscept ibility to damage induced by exhaustive exercise have been investigate d. Therefore, untrained rats were sacrificed either at rest or immedia tely after swimming to exhaustion. Rats trained to swim for 10 weeks w ere also sacrificed, 48 hr after the last exercise, either at rest or after exhaustive swimming. Homogenates of liver, heart, and muscle mer e used for biochemical determinations. Mitochondrial and sarcoplasmic (SR) or endoplasmic (ER) reticulum integrity was assessed with measure ments of respiratory control index and latency of alkaline phosphatase activity. Lipid peroxidation was measured by determination of malondi aldehyde and hydroperoxides. Additionally, the effect of training on t he antioxidant protection systems of tissues was examined by determini ng the glutathione peroxidase and glutathione reductase activity and t he overall antioxidant capacity. Mitochondrial, SR, and ER integrity a nd lipid peroxidation were similar in trained and untrained at rest an imals, whereas the glutathione peroxidase and glutathione reductase ac tivity and the overall antioxidant capacity of tissues were greater in trained animals. The exhaustive exercise gave rise to tissue damage i rrespective of the trained state, as documented by similar loss of SR and ER integrity, and by increase in lipid peroxidation found in exhau sted trained and untrained rats. Because exercise endurance capacity w as greatly increased by training, our results suggest that free radica l-induced damage in muscle could be one of the factors terminating mus cle effort. In effect, the greater antioxidant level should allow trai ned muscle to withstand oxidative processes more effectively, thus len gthening the time required so that the cell. function is sufficiently damaged as to make further exercise impossible. (C) 1996 Academic Pres s, Inc.