EFFECTS OF CORTICOSTEROIDS IN PRETERM SHEEP ON ADAPTATION AND SYMPATHOADRENAL MECHANISMS AT BIRTH

This study investigates the effects of prenatal corticosteroid adminis tration on newborn sympathoadrenal mechanisms involved in postnatal ad aptation. Randomly assigned preterm (122-125 days) fetal sheep were tr eated with hydrocortisone or saline for 60 h and delivered by cesarean section. We examined postnatal physiological adaptation, sympathoadre nal responses, cardiac beta-receptor density, and the receptor-cyclase system. We observed increased ventilatory, cardiovascular, and metabo lic responses function in the corticosteroid-treated animals despite a marked attenuation in the anticipated surge of plasma catecholamine c oncentrations and a decrease in epinephrine secretion rate, which is n ormally seen at birth. Myocardial beta-adrenergic receptor density and affinity states were comparable in both groups. Basal and agonist-med iated adenylyl cyclase activity in myocardial tissue was increased in the corticosteroid-treated animals. We speculate that the increase in myocardial adenylyl cyclase activity may be accompanied by similar cha nges in other organ systems and that this could account for the augmen tation in respiratory, cardiovascular, and metabolic responses in the corticosteroid-treated animals.