Antenatal Triiodothyronine Improves Neonatal Pulmonary Function in Preterm Lambs

Abstract

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 μg of triiodothyronine (T₃) 2 weeks before delivery.

Methods: Nine fetal lambs were given 100 μg of intra-amniotic T₃ 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 T₃, and thyroxine (T₄) 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 venilation in T₃-treated group (P < .05). Functional residual capacity increaed 69% (P < .05) without a change in specific compliance. The tracheal fluid and pulmonary phospholipids and tracheal fluid and plasma T₃ and T₄ levels were not different between the two groups.

Conclusion: A single 100 μg dose of antenatal T₃ 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 T₃ improved lung function via accelerated structural development of the lung with an alternative possible effect on parenchymal connective tissue matrix.