Effects of early embryonal exposure to dexamethasone on malformations of neural-crest derivatives induced by nitrofen in rats.

Abstract

Prenatal corticosteroids reverse to some extent lung and heart hypoplasia in nitrofen-exposed rat pups. The present study examines the effects of early exposure to dexamethasone on the neural crest-related malformations of the cardiovascular system, thymus, parathyroids, and thyroid observed in this model. Pregnant rats were exposed on gestational day 9.5 to either 100 mg 2-4-dichlorophenyl-p-nitrophenyl ether (nitrofen) alone or followed on days 10.5 and 11.5 by 0.4 mg/kg dexamethasone (dexa) i.p. Controls were treated with either oil alone or oil+dexa alone. The fetuses were recovered near term and diaphragmatic, lung, heart, and thymic malformations were sought after dissection. The parathyroids and thyroid were histologically investigated. Control fetuses had no malformations whereas 68% of nitrofen and 65% of nitrofen + dexa fetuses had congenital diaphragmatic hernias (CDH). Heart-outflow tract and pharyngeal artery anomalies were seen in 62% and 61%, respectively in both groups. Heart hypoplasia, which was severe in the nitrofen group, was fully reversed in nitrofen+dexa pups. In contrast, thymic hypoplasia was of similar severity in both groups. The hypoplastic thymus was malformed in 29% and 39%, the parathyroids in 50% and 41%, and the thyroid in 25% and 16% of fetuses, respectively. These differences were not significant. Early exposure to dexa in rat fetuses previously treated with nitrofen thus does not produce any benefit on the incidence or severity of malformations of the cardiac outflow tract and pharyngeal derivatives that accompany CDH in rats exposed to nitrofen. However, even administered so early, this medication prevents heart hypoplasia, suggesting a favorable effect on early heart organogenesis.