Effect of betamethasone administration to the pregnant baboon at 0.75 gestation on placental eNOS distribution and activity

Betamethasone is frequently administered to pregnant women at risk of premature labor to accelerate fetal lung maturation. Maternally administered betamethasone produces pronounced changes in the fetal peripheral vasculature, raises fetal blood pressure and produces fetal growth restriction. Endothelial nitric oxide synthase (eNOS) plays an important role in regulating vascular tone. We hypothesized that effects of betamethasone on the fetal vasculature include decreased eNOS activity. We determined a significant depression of total placental eNOS protein measured by ELISA (betamethasone treated vs control, 0.48±0.28 vs 1.57±0.45, p<0.05) and immunohistochemistry in both syncytiotrophoblast and vascular endothelium. Following betamethasone exposure, eNOS mRNA and enzyme activity showed decreasing trends which were not statistically significant. eNOS protein was higher in the placentas of both control and betamethasone treated baboons in the presence of a female fetus compared with a male fetus. The same effect of the sex of the fetus was observed in the betamethasone group for eNOS mRNA. In conclusion, maternally administered betamethasone produces a consistent decrease in several indices of placental eNOS function that may play a role in the altered cardiovascular dynamics and fetal growth retardation produced by betamethasone administration in late pregnancy.