EFFECTS OF HYPOBARIC HYPOXIA ON ANTIOXIDANT ENZYMES IN RATS

1. The present study was undertaken to investigate the effects of hypo baric hypoxia, equivalent to an altitude of 5500 m, on antioxidant enz ymes in rats. 2. Malondialdehyde levels in serum, heart, lung, liver a nd kidney of hypobaric-hypoxic rats were all significantly higher than in control rats by day 21 of exposure (P < 0.05), indicating increase d oxidative stress. 3. Superoxide dismutase (SOD) catalyses the conver sion of the superoxide anion to H2O2 and O-2. The concentration of imm unoreactive Mn-SOD in the serum of hypobaric-hypoxic rats was raised s ignificantly from day 5 onwards, whereas in liver and lung, it had dec reased significantly by day 21 (P < 0.05). 4. Glutathione peroxidase ( GSH-Px) catalyses H2O2 and certain lipid peroxides. By day 21, GSH-Px activity had increased significantly in the heart and lungs, but decre ased significantly in the liver (P < 0.05). 5. Catalase catalyses H2O2 . Catalase activity in the liver and kidney of hypobaric-hypoxic rats was significantly decreased on day 1 (P < 0.05) though levels then rec overed. 6. Mn-SOD mRNA in the liver of hypobaric-hypoxic rats was indu ced during the experiment, the effect being exceptionally marked, espe cially during the first 3 days of exposure to hypobaric hypoxia. 7. Th ese results suggest that the liver may be more vulnerable than the oth er organs tested to oxidative stress under hypobaric hypoxia.