Sex differences in plasma corticosterone in mouse fetuses are mediated by differential placental transport from the mother and eliminated by maternal adrenalectomy or stress.

The effect of changes in maternal corticosterone concentrations, induced by maternal stress, maternal adrenalectomy or both, on concentration of corticosterone in serum and in adrenals of mouse (Mus domesticus) fetuses was examined. Higher baseline serum corticosterone concentrations were found in female fetuses than in male fetuses; however, there was no sex difference in the content of corticosterone in adrenals collected from these fetuses. Sex differences were observed in the fetal response to changes in maternal concentrations of serum corticosterone resulting from stress (bright light and heat) or adrenalectomy, and both factors eliminated the sex difference in corticosterone in fetal serum. When females were injected i.v. with [3H]corticosterone on day 17 of pregnancy, significantly more 3H was recovered from the serum of female than of male fetuses 15 min after the injection, while more 3H was recovered from placentae of male fetuses. This finding suggests that the difference in serum corticosterone in male and female mouse fetuses is due to greater transport of corticosterone from maternal blood across the placenta of female than of male fetuses.