Antenatal triiodothyronine improves neonatal pulmonary function in preterm lambs

OBJECTIVE: To characterize 1) pulmonary gas exchange, 2) pulmonary function, 3) lung fluid and tissue phospholipid content, and 4) thyroid hormone in the premature lamb (0.85 of term) after intra-amniotic administration of 100 mu g of triiodothyronine (T-3) 2 weeks before delivery. 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, tracheal 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 lambs had significantly higher mean arterial pH and lower PCO2 than controls (P<.05) with a trend toward higher mean PO2. The dynamic lung compliance was increased by 54% with a 40% proportional increase in tidal volume and minute ventilation in the T-3-treated group (p<.05). Functional residual capacity increased 69% (P<.05) without a change in specific compliance. The tracheal fluid and pulmonary phospholipids and tracheal 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 significantly improves neonatal gas exchange and lung compliance. The improvement in lung function was not accompanied by an increase in pulmonary surfactant production. It is inferred that T-3 improved lung function via accelerated structural development of the lung with an alternative possible effect on parenchymal connective tissue matrix. Copyright (C) 1988 by the Society for Gynecologic Investigation.