Adenylate cyclase activity in membrane fractions of adrenal tissue of human anencephalic fetuses.

There is greater basal and ACTH-stimulated adenylate cyclase activity in membrane fractions prepared from the neocortex of human fetal adrenal (HFA) tissue than in similar preparations from the fetal zone. In this study, the specific activity of adenylate cyclase was determined in membrane preparations of adrenal tissue obtained from anencephalic fetuses (n = 5) varying in gestational age from 17-43 weeks. The basal adenylate cyclase activity in membrane fractions of adrenals of anencephalics was 2.9 +/- 2.1 (mean +/- SEM) pmol mg protein-1 min-1, 3-5% of the average specific activity in membrane preparations of fetal zone or neocortex of normal fetuses. ACTH (10(-10)-10(-4) M) in the incubation mixture stimulated adenylate cyclase activity 2- to 5-fold in whole HFA membrane fractions. In contrast, ACTH, when added to adrenal membrane preparations of the anencephalics, did not stimulate adenylate cyclase activity. Furthermore, sodium fluoride or forskolin stimulated adenylate cyclase activity markedly in HFA membrane preparations of normal fetuses, but did not affect enzyme activity in adrenal membrane preparations of the anencephalics. In conclusion, the basal activity of adenylate cyclase in adrenal membrane preparations of anencephalics was low and unresponsive to brief exposure to ACTH, sodium fluoride, or forskolin. These findings as well as those of our previous investigations suggest that the expression of HFA adenylate cyclase may be regulated in part by ACTH.