ANTENATAL TRIIODOTHYRONINE IMPROVES NEONATAL PULMONARY-FUNCTION IN PRETERM LAMBS

OBJECTIVE: To characterize 1) pulmonary gas exchange, 2) pulmonary fun ction, 3) lung fluid and tissue phospholipid content, and 4) thyroid h ormone in the premature lamb (0.85 of term) after intra-amniotic admin istration of 100 mu g of triiodothyronine (T-3) 2 weeks before deliver y. METHODS: Nine fetal lambs were given 100 mu g of intra-amniotic T-3 under ultrasound guidance at 112+/-1 days' gestation and delivered at 126+/-1 days (term=149 days). Five saline-injected animals served as controls. Arterial blood gases, pulmonary mechanics, and lung volumes were compared between groups for 1 hour after delivery. At delivery, t racheal fluid and blood was taken for T-3, and thyroxine (T-4) levels. Tracheal fluid and lung tissues were assayed for total phosphorus and disaturated phosphatidylcholine. RESULTS: Triiodothyronine-treated la mbs had significantly higher mean arterial pH and lower PCO2 than cont rols (P<.05) with a trend toward higher mean PO2. The dynamic lung com pliance was increased by 54% with a 40% proportional increase in tidal volume and minute ventilation in the T-3-treated group (p<.05). Funct ional residual capacity increased 69% (P<.05) without a change in spec ific compliance. The tracheal fluid and pulmonary phospholipids and tr acheal fluid and plasma T-3 and T-4 levels were not different between the two groups. CONCLUSION: A single 100 mu g dose of antenatal T-3 si gnificantly improves neonatal gas exchange and lung compliance. The im provement in lung function was not accompanied by an increase in pulmo nary surfactant production. It is inferred that T-3 improved lung func tion via accelerated structural development of the lung with an altern ative possible effect on parenchymal connective tissue matrix. Copyrig ht (C) 1988 by the Society for Gynecologic Investigation.