Effects of vitamin A on malformations of neural-crest-controlled organs induced by nitrofen in rats.

Vitamin A (vit A) alleviates the effects of nitrofen in exposed rat pups. The present study examines the effects of early exposure to vitamin A on the neural-crest-related cardiovascular, thymic, parathyroid, and thyroid malformations previously reported in the rat model of congenital diaphragmatic hernia (CDH). Pregnant rats were exposed on gestational day 9.5 to 100 mg 2-4-dichlorophenyl-p-nitrophenyl ether (nitrofen) alone or followed by 15,000 IU vit A. Controls were treated only with oil or oil + vit A. The fetuses were recovered near term and diaphragmatic, lung, heart, and thymic malformations were sought after dissection. The parathyroids and thyroid were histologically investigated. The hearts were also examined for protein, DNA, and proportion of proliferating cells. None of the control fetuses had malformations, whereas 41% of nitrofen and 27% of nitrofen + vit A fetuses had CDH. Anomalies of the heart outflow tract and pharyngeal arteries were seen in 64% and 43%, respectively, in both groups. Heart and thymic hypoplasia, which were severe in the nitrofen group with significant decreases of total DNA and percent proliferating cells, were significantly improved in the nitrofen + vit A group. The hypoplastic thymus was malformed in 53% and 27% of fetuses, respectively, and the parathyroids were abnormal in 48% and 35%, respectively. Only minimal anomalies of the thyroid were found. The significant improvement of heart and thymic hypoplasia associated with vit A was not seen for the other variables studied, but there was a trend in this direction for all of them. Vit A definitely improved heart hypoplasia induced by nitrofen by stimulating myogenesis. It also improved thymic hypoplasia, but had limited beneficial effects on malformations of the cardiac outflow tract and pharyngeal derivatives that accompany CDH in rats exposed to nitrofen.