Structural and biochemical adaptive changes in rat lungs after exposure to hypoxia.

Rats exposed to 10 to 11 per cent oxygen for 7 days develop tolerance to hyperoxia and can survive for prolonged periods in 100 per cent oxygen. This preexposure to hypoxia is associated with a 180 per cent increase in the activity of the mangani superoxide dismutase but no increase in activity of copper-zinc superoxide dismutase, glucose-6-phosphate dehydrogenase, or the mitochondrial enzymes, cytochrome oxidase and succinate cytochrome c reductase. Cyanide-insensitive oxygen uptake is also increased after this exposure to hypoxia suggesting that an enhanced rate of production of partially reduced species of oxygen may occur. Morphometric and morphologic studies of lung structure demonstrate that no substantial change in cell population characteristics occur in the lungs of animals exposed to hypoxia, but there are ultrastructure changes in the cytoplasm of pulmonary capillary endothelial cells consistent with focal hypertrophy and enhanced metabolic activity of these cells.