Thyroid hormones in the pathogenesis of lung hypoplasia and immaturity induced in fetal rats by prenatal exposure to nitrofen

Abstract

Background/Purpose: Nitrofen is believed to act on prenatally exposed fetuses by changing maternal or fetal thyroid hormone physiology. The aim of this study was to determine whether the amounts of circulating and lung tissue T3 and T4 are decreased in rat fetuses with nitrofen-induced pulmonary hypoplasia and diaphragmatic hernia. Methods: Timed-pregnant rats were given 100 mg of nitrofen in oil on gestational day 9.5, and their fetuses were recovered on the 21st day. Lung weight to body weight ratio was determined. Hormonal studies consisted in measurement of plasma T3, T4, and TSH, and of T3, T4, and DNA in lung tissue. Suitable groups of control fetuses prenatally exposed to oil were used for comparison. Results: The lungs of nitrofen-treated fetuses were hypoplastic and those who had congenital diaphagmatic hernia were even more so. Nitrofen treatment led to decreased plasma T3 and T4 levels without TSH changes. T3 and T4 in lung tissue were apparently decreased in treated fetuses when expressed by weight, but these differences disappeared when expressed by DNA (cell content). Conclusions: Lung hypoplasia and immaturity induced by nitrofen treatment are not related to decreased levels of thyroid hormones in tissue near term. This should be kept in mind when proposing hormonal treatment for prenatal induction of lung maturation.