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Antenatal Triiodothyronine Improves Neonatal Pulmonary Function in Preterm Lambs

Departments of Obstetrics, Gynecology, and Reproductive Sciences, Physiology, and Pediatrics, Temple University School of Medicine; Departments of Obstetrics/Gynecology and Pediatrics, Jefferson Medical College, Philadelphia, Pennsylvania; Division of Maternal-Fetal Medicine, Department of Obstetrics, Gynecology, and Reproductive Sciences, Temple University School of Medicine, 3401 N. Broad Street, 7-OPD, Philadelphia, PA 19140

Thomas F. Miller, BS

Jiang Yuxin, MD

Clotilda Farina, MD

Avinash Chander, PhD

Thomas H. Shaffer, PhD

Marla R. Wolfson, PhD

Departments of Obstetrics, Gynecology, and Reproductive Sciences, Physiology, and Pediatrics, Temple University School of Medicine; Departments of Obstetrics/Gynecology and Pediatrics, Jefferson Medical College, Philadelphia, Pennsylvania

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.

Key Words: Triiodothyronine • fetal maturation • fetal lamb • pulmonary function • lung

Journal of the Society for Gynecologic Investigation, Vol. 5, No. 3, 122-126 (1998)
DOI: 10.1177/107155769800500303


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