CHANGES IN C19-STEROID METABOLISM BY OVINE PLACENTAS DURING CORTISOL ADMINISTRATION

Placental cotyledons were removed from 23 ewes of 120-130 days of gestation immediately before and at intervals up to 24 h after the initiation of cortisol administration. The fetuses received 0, 4.8 or 24.0 mg cortisol/24 h i.v. Samples of arterial and venous umbilical blood were collected from each fetus at 12 h intervals for cortisol determination by competitive protein-binding radioassay. Placental microsomes prepared from the fetal cotyledons were incubated with radioactive dehydroepiandrosterone, androstenedione and testosterone along with appropriate cofactors to measure the aromatizing activity (estrone and estradiol synthesis). The infusion of cortisol into fetuses 2-3 weeks prior to parturition significantly increased plasma cortisol levels to those normally found in fetuses at birth. The correlations between umbilical arterial cortisol levels and corresponding aromatizing rates were not significant. The data suggest that although the increased cortisol levels may have an effect on aromatizing activity, the effect is not consistently significant and probably does not account for the increase in maternal and fetal plasma estrogen surges before ovine parturition.