Effect of exercise duration on characteristics of mitochondrial population from rat liver

Young male rats were sacrificed either at rest or immediately after a single bout of swimming lasting either 5 or 8 h. Mitochondrial population, obtained by centrifugation (10,000g for 10 min) from liver homogenates freed from debris and nuclei, was resolved by differential centrifugation into three fractions. Homogenates and mitochondrial preparations were examined for their protein content, oxidative capacity (by cytochrome oxidase activity), peroxidative processes (by thiobarbituric acid reactive substance and hydroperoxide levels), antioxidant status (by reduced glutathione and vitamin E levels and whole antioxidant capacity), and susceptibility to in vitro oxidative stress. In all groups, the antioxidant level was smaller and oxidative capacity, lipid peroxidation, and susceptibility to oxidants were greater in the heavy mitochondrial fraction. Exercise of shorter duration did not significantly affect most of the parameters; only the resulting homogenate glutathione level and susceptibility to oxidative stress decreased and increased, respectively, compared with control values. In contrast, more prolonged exercise was associated with increased lipid peroxidation and susceptibility to oxidative stress and decreased antioxidant levels in all preparations. The contribution of each fraction to the whole mitochondrial population was also modified in that the heavy fraction decreased and light fractions increased. These results suggest that liver antioxidant defence systems are able to withstand oxidative challenge due to low-intensity exercise of moderate duration. In contrast, the free radical production associated with long-lasting exercise causes oxidative injury in cellular components and in particular induces protein degradation in the heavy mitochondrial fraction characterized by higher susceptibility to oxidative stress.