Effect of intermittent hypoxia on pro- and antioxidant balance in rat heart during high-intensity chronic exercise

The purpose of the present study was to elucidate the influence of sessions of intermittent hypoxic training (IHT) alone and in combination with high-intensity chronic exercise on lipid peroxidation and antioxidative defense system in rat heart. High-intensity chronic exercise was performed as swimming training with load that corresponded to ~ 75% VO_2max(30 min/day, 5 days/wk, for 4 wk). IHT consisted of repeated episodes of hypoxia (12% O₂, 15 min), interrupted by equal periods of recovery (5 sessions/day, for 2wk). Sessions of IHT were applied during the first two weeks and during the last two weeks of chronic exercise. It was shown that long-term training was accompanied by the accumulation of thiobarbituric acid reactive substances (TBARS) in myocardium. IHT attenuated the increase in TBARS content caused by high-intensity chronic exercise and it enhanced myocardial reduced glutathione concentration, activities of superoxide dismutase, catalase, and glutathione peroxidase in comparison with trained animals only. No significant changes were found in glutathione reductase, glucose-6-phosphate dehydrogenase activities. Our results suggest that intermittent hypoxic stimuli may induce a state of preconditioning that protects the heart from oxidative stress evoked by high-intensity chronic exercise.