Abstract
Adenylate cyclase activity was studied in crude adrenal membranes from fetal and newborn rats. Basal adenylate cyclase activity was higher in fetal than in newborn rats. ACTH(1-24) (1 mumol/l), guanosine (beta,gamma-imido diphosphate) (Gpp(NH)p) (10 mumols/l) and forskolin (100 mumols/l) stimulated the activity of the enzyme at all stages studied. The sensitivity of the enzyme to ACTH was maximal on days 17 and 19 of gestation. When Gpp(NH)p was added to ACTH(1-24), the response was significantly higher than that induced by Gpp(NH)p alone. Forskolin and Gpp(NH)p alone increased the adenylate cyclase activity and the sensitivity of the enzyme to these compounds was higher in newborn rats than in fetuses. Treatment of 21-day-old rat fetuses with ACTH increased the response of adenylate cyclase to Gpp(NH)p alone or to forskolin whereas treatment with dexamethasone did not modify the response of the enzyme to either Gpp(NH)p alone or forskolin. Our results show that the change in the responsiveness of adenylate cyclase takes place immediately after birth during the first week and ACTH is able to induce a maturation of the fetal adrenal adenylate cyclase system.
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