The effect of prenatal dexamethasone treatment on oxygen toxicity in the newborn rat.

To determine whether prenatal corticosteroid therapy had adverse effects on the tolerance of the newborn lung to prolonged high O2 exposure, pregnant rats were given injections of dexamethasone (0.2 mg/kg) at 48 and 24 hours prior to parturition, and the newborn pups were placed in 96% to 98% O2 for the first seven days of life. Dexamethasone treatment resulted in significant decreases in body weight (-17%), lung weight (-30%), lung weight/body weight (-22%), and lung DNA (-18%) compared to untreated rat pups. Despite this growth inhibition, the dexamethasone-treated pups had improved survival in hyperoxia (36/48 = 75% vs 29/48 = 60% for untreated rats, P = .055). In addition, substantial "catch-up" lung growth had occurred by seven days and was complete in 28-day-old rats. Dexamethasone did not interfere with normal pulmonary antioxidant enzyme responses to hyperoxia. Thus, prenatal dexamethasone did not compromise the relative tolerance of the newborn to pulmonary O2 toxicity.