THE EFFECTS OF CORTICOSTEROIDS AND THYROTROPIN-RELEASING-HORMONE ON NEWBORN ADAPTATION AND SYMPATHOADRENAL MECHANISMS IN PRETERM SHEEP

OBJECTIVES: We examined the effect of prenatal corticosteroids and thy rotropin-releasing hormone on postnatal adaptation and sympathoadrenal function in preterm lambs. STUDY DESIGN: Catheterized fetal lambs rec eived saline solution (n = 6), corticosteroids alone (n = 8), or corti costeroids plus thyrotropin-releasing hormone (n = 6) for 60 hours. Th e lambs were delivered by cesarean section at a gestational age of 130 +/- 1 days. Ventilatory, cardiovascular, and metabolic responses and plasma catecholamine concentrations were measured for 2 hours after bi rth. Statistical anaysis was performed by use of independent t tests o r analysis of variance. RESULTS: Ventilatory function and cardiac cont ractility were significantly improved in both corticosteroid and corti costeroid plus thyrotropin-releasing hormone animals. Lambs treated wi th corticosteroid plus thyrotropin-releasing hormone had significantly higher aortic pressure and left ventricular blood pressure than eithe r of the other groups. The postnatal norepinephrine and epinephrine su rge was blunted in response to corticosteroid and corticosteroid plus thyrotropin-releasing hormone treatment. There were no differences in metabolic responses among the three groups. CONCLUSIONS: In premature lambs prenatal exposure to corticosteroids and thyrotropin-releasing h ormone improves postnatal cardiovascular adaptation more than corticos teroids alone.