Magnitude of hyperoxic stress and degree of lung maturity determine the nature of pulmonary antioxidant response in the guinea pig.

The ability of the immature lung to induce antioxidant defences in response to hyperoxic stress was examined. Preterm guinea pigs (65 days gestation, term = 68 d) were exposed to either 21% O2, 85% O2 or 95% O2 for 72 hours. Exposure to 85% O2 increased lung catalase, glutathione peroxidase and manganese superoxide dismutase activities in comparison to air controls. Exposure to 95% O2 resulted only in an increase in glutathione peroxidase activity. Bronchoalveolar lavage fluid GSH concentration was increased by a similar amount by both exposure regimes, while lung copper/zinc superoxide dismutase activity was unchanged by either treatment. Comparison of the antioxidant response of term and preterm animals exposed to 85% O2 for 72 hours indicated a greater response in the lung of the preterm animals. Manganese superoxide dismutase activity was elevated in both term and preterm animals, while catalase and glutathione peroxidase activities were elevated only in preterm animals. The extent of microvascular permeability as indicated by bronchoalveolar lavage fluid protein concentration, was lower in preterm animals than in term animals. We conclude that the immature lung can respond to hyperoxic stress by antioxidant induction and that the nature of the response is dependent, in part, both on the severity of the stress and on the maturity of the lung.