EFFECT OF EXERCISE ON TISSUE ANTIOXIDANT CAPACITY AND HEART ELECTRICAL-PROPERTIES IN MALE AND FEMALE RATS

We studied the changes in the anti-oxidant capacity of tissues, such a s heart, liver, and blood In male and female rats, as a parameter for evaluating oxidative stress after either a prolonged (210 min) or an e xhausting bout of swimming, Furthermore, we also investigated exercise -induced changes in the electrophysiological properties, measured in v itro, of papillary muscle fibres. Small decreases of anti-oxidant capa cities after prolonged exercise [0.10 (SEM 0.04) in heart, 0.43 (SEM 0 .19) in liver, 0.22 (SEM 0.05) in blood] and greater decreases after e xhausting exercise [0.23 (SEM 0.04) in heart, 0.90 (SEM: 0.29) in live r, 0.34 (SEM 0.04) in blood] were found in tissues from the male rats. For the female rats, similar changes were found only in the blood [0. 11 (SEM 0.07) and 0.35 (SEM 0.06) for prolonged and exhausting exercis e, respectively]. Liver and heart anti-oxidant capacity remained uncha nged after prolonged exercise, while after exhausting swimming it unde rwent a decrease almost the same as found in the male rats: though the swimming time to exhaustion (endurance capacity) was much greater [70 6 (SEM 10) mill and 444 (SEM 32) min for the females and males, respec tively]. The duration of the action potential, recorded from papillary muscle fibres, underwent changes related to the decreases in heart an ti-oxidant capacity, In fact, the action potential duration (APD) was shorter only in preparations from the male rats after prolonged exerci se, but in all preparations after exhausting exercise. After such exer cise, the APD was similar for the male and female rats [37.1 (SEM 3.4) ms and 37.0 (SEM 3.6) ms, respectively]. Such a pattern was independe nt of stimulation frequency, since it was found substantially unchange d when the frequency was increased from 1 to 5 Hz. We concluded that t he different susceptibilities to the effects of physical exercise: exh ibited by tissues from these male and female rats might have been rela ted to different capacities to oppose oxidative stress effectively.