The effect of hyperoxic exposure on antioxidant enzyme activities of alveolar type II cells in neonatal and adult rats.

Neonatal animals of several species are more tolerant of hyperoxic exposure than are adults, but the mechanisms of increased neonatal tolerance are unknown, as are the cell types, if any, that contribute to oxygen resistance. We studied the effect of in vivo exposure to 85% oxygen for 72 h on the activities of the antioxidant enzymes, glutathione peroxidase, catalase and superoxide dismutase (SOD), in alveolar type II cells and whole lung from adult and neonatal rats. Baseline antioxidant enzyme activities were generally lower in neonatal type II cells compared with adults. Baseline enzyme activities did not differ in neonatal type II cells and lung homogenates except for lower catalase activity in type II cells. Hyperoxic exposure resulted in 35-38% increases in antioxidant enzyme activities in neonatal whole lung. In neonatal type II cells, SOD activity increased by 170% after hyperoxia, whereas catalase and glutathione peroxidase were not significantly changed. In the adult whole lung, hyperoxic exposure resulted in increases in only glutathione peroxidase activity, whereas in adult type II cells there was a significant decrease in SOD activity after O2 exposure. Therefore, although baseline antioxidant enzyme activities were not higher in neonatal type II cells compared with whole lung, there were differences in the antioxidant enzyme responses of adult and neonatal type II cells to hyperoxia, particularly with respect to SOD. The ability of the neonatal type II cell to respond to hyperoxia with an early increase in SOD activity may contribute to the enhanced oxygen tolerance of the neonate.