Nitric oxide (NO) produced by the enzyme nitric oxide synthase (NOS) is critically involved in the cardiopulmonary transition from fetal to neonatal life. In congenital diaphragmatic hernia (CDH) this transition often does not occur normally, resulting in persistent pulmonary hypertension of the newborn (PPHN). We sought to determine if pulmonary NOS expression is altered in a rat model of CDH induced by maternal ingestion of the herbicide 2,4-dichlorophenyl-p-nitrophenyl ether (Nitrofen) on day 9 of gestation (term = 22 days). Sixty-three percent of Nitrofen-exposed fetuses developed CDH. Endothelial NOS (eNOS) and neuronal NOS (nNOS) protein expression were assessed in ipsilateral CDH lungs and in control lungs (Nitrofen-treated, no hernia) at 20 d gestation using immunoblot analyses. eNOS and nNOS have been immunohistochemically localized to rat pulmonary endothelium and bronchiolar epithelium, respectively, and we have previously demonstrated that their expression normally increases during late gestation to be maximal near term. eNOS protein expression was decreased in CDH versus control lung (58 +/- 6 versus 100 +/- 6% of control, n = 5). In contrast, nNOS protein abundance was similar. Factor VIII-associated antigen expression was comparable in CDH and control lung, indicating that the change in eNOS is not related to differences in endothelial cell density. eNOS mRNA abundance was evaluated in semiquantitative reverse transcription-polymerase chain reaction assays. Paralleling the decline in eNOS protein expression, eNOS mRNA was decreased in CDH versus control lung (22 +/- 8 versus 100 +/- 31% of control, n = 4).(ABSTRACT TRUNCATED AT 250 WORDS)