Changes in the responsiveness of adrenal cells from foetal goats at different times during pregnancy

To understand the factors responsible for the increased pre-partum output of cortisol from the adrenal glands of the goat foetus, we measured changes in responsiveness to ACTH in vitro of dispersed adrenal cells from foetal goats of various gestational ages and we determined the output of cortisol (F) and corticosterone (B) in the presence of exogenous progesterone (P4) and 17 alpha-hydroxyprogesterone (17 alpha-OHP4). The increment in F output after ACTH increased 5-fold between day 100 and days 147 or 154 (term). This increase was not associated with changes in the ED50 for ACTH stimulation of F output. The basal and ACTH-stimulated output of F was similar to that of B at day 100 but 5-7 times greater than that of B at day 154. There was a significant effect of ACTH on P4 output on days 77, 100 and 147 but net utilization of P4 by the cells at term. The ratio of exogenous P4: 17 alpha-OHP4 converted to F varied with gestation and increased from 0.11 at day 100 to 0.99 at day 154. Exogenous P4 was converted to B at all stages of pregnancy. We conclude that in the goat there is an increase in the responsiveness of foetal adrenal cells to ACTH between day 100 of gestation and term. One factor associated with this change in adrenal responsiveness may be an increase in the activity of the enzyme 17 alpha-hydroxylase.