Postnatal lung function in preterm lambs: effects of a single exposure to betamethasone and thyroid hormones.

Abstract

We determined the effect of a single direct fetal injection of corticosteroid and thyroid hormones on postnatal pulmonary function in preterm lambs. Initially fetal sheep (126 days' gestation) randomly received saline solution, betamethasone (Celestone Soluspan, 0.5 mg/kg), betamethasone plus triiodothyronine (5 micrograms/kg), or betamethasone plus thyroxine (15 micrograms/kg) as a single injection. Forty-eight hours later (128 days' gestation) the fetuses were delivered and ventilated for 50 minutes. In a second protocol fetuses were delivered at 128 days' gestation, after only 24 hours of hormone exposure. Betamethasone treatment improved compliance nearly twofold after 24 or 48 hours of exposure. Efficiency of ventilation also improved after steroid therapy; this effect was augmented 48 hours after thyroxine exposure (but not triiodothyronine). No thyroxine effect was noted after 24 hours of exposure. Maximal lung volume increased by 80% after steroid treatment and doubled in response to combination betamethasone and thyroxine therapy. Alveolar pool sizes of saturated phosphatidylcholine and surfactant protein A were comparable for all groups exposed for 48 hours. A single fetal exposure to betamethasone improves postnatal pulmonary function after 24 or 48 hours. Addition of thyroxine (but not triiodothyronine) augments this effect at 48 hours.