The effect of dexamethasone administration at different stages of gestation on maternal plasma steroid concentrations in the baboon (Papio cynocephalus).

Dexamethasone administration at different stages of gestation in the baboon was studied for its effect on maternal steroid hormone concentrations. Dexamethasone (2 mg i.m. at 12 h intervals for three doses) was administered at early (days 37-39), mid (days 76-85) or late (days 112-123) gestation and morning blood samples were collected before, during and after dexamethasone suppression for 6 consecutive days. Dexamethasone treatment, at all stages of pregnancy, resulted in a significant decline in maternal serum cortisol concentrations, which rapidly return to normal concentrations after treatment. Progesterone concentrations were not affected by dexamethasone at any stage of gestation. Serum concentrations of oestradiol, testosterone and androstenedione were unchanged following dexamethasone administration in early pregnancy. A trend toward lower serum oestradiol was observed following dexamethasone administration in both mid and late gestation, but this was not significant. Both testosterone and androstenedione were significantly decreased following dexamethasone in both mid and late pregnancy and recovered to pretreatment concentrations within a few days after cessation of treatment. These results confirm other studies which demonstrate that adrenal precursors (maternal or fetal) are a major contributor to maternal serum concentrations of oestradiol. They also demonstrate that these adrenal precursors increase serum concentrations of testosterone and androstenedione in the pregnant baboon. Since these changes are only evident after that time (>40 days) when the fetal adrenal is steroidogenically competent, a role for fetal adrenal involvement in maternal serum androgen concentrations is suggested.