383 CORTICOSTEROID BINDING GLOBULIN (CBG) IN FETAL AND NEWBORN SHEEP

Abstract

To examine the ontogeny and regulation of CBG in the perinatal period, we determined plasma cortisol binding capacity using a charcoal absorption assay. CBG capacity increased progressively from 1.6 μg/dl at 75 days to 7.1 μg/dl at 141 days (n=249), with the greatest increase from 121 days to term. There was a similar increase in CBG (+41.1%) and total proteins (+36.7%) in 6 fetuses during the 4-6 days before spontaneous delivery. After birth, both CBG and proteins decreased during the first half day; thereafter CBG decreased (t½=5 days) to 1.0 μg/dl at 14 days while proteins did not change. In 7 fetuses with loss of pituitary function there was no increase in CBG during the 22-35 days after surgery. Infusions of hydrocortisone for 2 days, estradiol for 5 days, prolactin for 5-8 days and ACTH for 3 days to intact fetuses did not affect CBG levels. We conclude that the pituitary controls the major increase in CBG after 121 days; there is an additional prepartum increase in all serum proteins with labor. The pituitary hormone(s) which stimulate CBG production are not identified, but this hormonal influence apparently ceases with birth.