Steroid hydroxylase gene expression in the ovine fetal adrenal gland following ACTH infusion

Abstract

Abstract. Between 90 and 120 days of gestation (term = 147±5), when plasma cortisol concentrations in the fetus are at a minimum, levels of mRNA encoding the steroidogenic enzymes 17α-hydroxylase (P-45017α) and cholesterol side-chain cleavage (P-450scc) are also very low. Over the following 30 days, P-45017α and P-450scc gene expression increases concurrent with increasing fetal cortisol concentration. The hypothesis tested in this study was that cortisol biosynthesis is minimal in the period 90-120 days because of insufficient ACTH. Fetuses were cannulated between 98-102 days of gestation. Following recovery, 7 fetuses received 24-h ACTH infusions (12 μg/24 h) and 5 fetuses received 24-h vehicle infusions; 4 ACTH-infused and 4 vehicle-infused fetuses were then sacrificed immediately after cessation of the infusion. The other fetuses were left in utero for 3 days prior to sacrifice. Fetal blood samples were analysed for ACTH and cortisol and the adrenals processed for hybridization histochemistry and Northern blot analysis. ACTH, but not vehicle, induced significant increases in the width of the adrenal cortex and in the levels of P-45017α and P-450scc mRNA. Concurrently, fetal plasma ACTH and cortisol concentrations also increased significantly. In adrenals from fetuses left in utero for 3 days after cessation of the ACTH infusion, P-45017α and P-450scc mRNA levels returned to control levels. Plasma ACTH and cortisol levels also approximated basal values. P-450c21 mRNA levels did not vary significantly at any time with the treatments. It can be concluded that the major regulatory influence on ACTH in the 90-120 day fetus is via increased gene expression of P-45017α and P-450scc but not P-450c21.