Adaptations of glutathione antioxidant system to endurance training are tissue and muscle fiber specific

The effect of endurance training on glutathione (GSH) status and antioxidant enzyme system was investigated in skeletal muscle, heart, and liver of female Sprague-Dawley rats pair fed an isocaloric diet. Ten weeks of treadmill training (25 m/min, 10% grade for 2 h/day, 5 days/wk) increased citrate synthase activity in the deep vastus lateralis (DVL) and soleus muscles by 79 and 39%, respectively (P < 0.01), but not in the heart or liver. In DVL, GSH content was increased 33% (P < 0.05) with training, accompanied by a 64% (P < 0.05) increase in glutamate content but no change in cysteine. Trained rats showed a 62 and 27% higher GSH peroxidase (GPX) and superoxide dismutase (SOD) activity, respectively (P < 0.05), in DVL compared with control rats. In contrast, GSH content and glutathione reductase (GR) activity in soleus declined with training (P < 0.05), whereas activities of GPX and SOD remained unchanged. Training did not alter GSH status in the liver or plasma but significantly decreased the GSH-to-glutathione disulfide ratio in the heart. In addition, GR activity in the liver and GSH sulfur-transferase activity in the heart and DVL were significantly lower in the trained vs. control rats. DVL muscle had threefold higher gamma-glutamyltranspeptidase activity compared with other tissues; however, no significant alteration was observed in the activity of gamma-glutamyltranspeptidase or gamma-glutamylcysteine synthetase in the liver, heart, or skeletal muscle. These data indicate that endurance training can cause tissue- and muscle fiber-specific adaptation of antioxidant systems and that GSH homeostasis in extrahepatic tissues may be determined by utilization and uptake of GSH via the gamma-glutamyl cycle.