The Effects of Adrenocorticotropin, Guanylylimidodiphosphate, Dibutyryl Adenosine 3′,5′-Monophosphate, and Exogenous Substrates on Corticosteroid Output by Ovine Fetal Adrenal Cells at Different Times in Pregnancy*

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Abstract
To examine the factors responsible for the changing responsiveness of ovine fetal adrenals during pregnancy, we incubated dispersed adrenal cells obtained from fetal sheep on days 50, 100, and 130 of pregnancy and at term with ACTH (1–24), a GTP analog [guanosine 5′-(β,γ-imido)triphosphate], dibutyryl cAMP, and potential substrates for corticosteroid production, pregnenolone, progesterone, 17α-hydroxypregnenolone, and 17α-hydroxyprogesterone (17OHP4). We determined the output of cortisol (F), corticosterone (B) and progesterone (p4) by these cells during in vitro incubation. ACTH stimulated F and B output on day 50 and at term, but not in midpregnancy. The mean F to B output ratio for all concentrations of ACTH rose from 3.3 on day 50 to 11.3 at term. The GTP analog stimulated F, B, and P4 output at term, but not on day 100 or 130. Dibutyryl cAMP stimulated F and B output on day 50 and at term and stimulated P4 output at all stages of pregnancy examined. Exogenous 17OHP4 was converted to F at all times in pregnancy. The relative conversion of P4 to F and 17OHP4 to F (conversion quotient) rose from 0.09 on day 100 to 0.80 at term. P4 was converted to B at all times in gestation. At term, formation of F from Δ4 substrates (P4) and 17OHP4) was greater than that from Δ5 substrates (pregnenolone and 17αOHpregnenolone). We conclude that (1) the output of F in response to ACTH was highest on day 50 and at term pregnancy; 2) the loss of response in midpregnancy may be associated with a defect in GTP and cAMP generation and with reduced 17α-hydroxylase activity; and 3) at term, 17α-hydroxylase appears to be less limiting to F production than in midgestation, but Δ5 3β-hydroxysteroid dehydrogenase may be more so.