EFFECTS OF INCREMENTAL CORTISOL AND ADRENALECTOMY ON PLASMA CORTICOSTEROID-BINDING CAPACITY IN FETAL SHEEP

The effects of incremental cortisol infusion or fetal adrenalectomy on plasma corticosteroid-binding capacity (CBC) were examined in sheep f etuses during late gestation (term approximate to 150 days). Cortisol, infused from day 120 at 1.5 mg/day for the first 3 days, 2.5 mg/day f or the next 5 days, and 3.5 mg/day for the final 2 days, stimulated a significant rise in plasma CBC and immunoreactive corticosteroid bindi ng globulin (CBG). There was a significant positive correlation betwee n individual values for total plasma cortisol concentrations and CBC v alues. In contrast, fetal adrenalectomy at day 115 prevented the rise in plasma CBC found in intact fetuses at term. These experiments show that exogenous cortisol, given in a manner that mimics the prepartum r ise in fetal plasma cortisol, stimulates CBG biosynthesis, whereas abo lition of the cortisol rise prevents the increase in CBG. The study pr ovides strong support for the proposal that the prepartum increase in CBG biosynthesis in fetal sheep occurs in response to the progressive rise in adrenal cortisol output by the fetus towards term.