Changes in membrane fluidity and lipid peroxidation of skeletal muscle mitochondria after exhausting exercise in rats

We studied the effects of exhausting exercise and exercise training on skel etal muscle mitochondrial membrane fluidity and lipid peroxidation in rats. The first part of the study involved 60 untrained rats divided into six eq ual groups. Of the total number 10 rats were sedentary and acted as control s. The remaining 50 rats exercised to exhaustion and were sacrificed at 0-h , 24-h, 48-h, 72-h, and 96-h post-exercise. The second part of the study in volved 40 rats which were divided into four equal groups. Of these 10 rats were sedentary and acted as controls. The remaining 30 rats underwent 8 wee ks of exercise training. They were then subjected to a single period of exh austing exercise and were sacrificed at 0-h, 24-h and 48-h post-exercise. M embrane fluidity was measured using the fluorescence polarization method. L ipid peroxidation was estimated by determining the thiobarbituric acid-reac tive substances (TBARS) in mitochondria. In the untrained rats, mitochondri al fluorescence polarization and TBARS contents were significantly increase d post-exercise compared with the sedentary controls (P < 0.05). They did n ot return to near control levels until 96 h and 48 h, respectively. In the trained rats, fluorescence polarization was raised compared with the sedent ary controls but this was significantly lower than those measured at the sa me times of the untrained group post-exercise (P < 0.05). Exhausting exerci se decreased membrane fluidity and increased lipid peroxidation in rat skel etal muscle mitochondria. These effects were relieved to some extent by exe rcise training.