Studies of adrenal steroidogenic enzymes in guinea pigs

In the present study we found that 3 beta-hydroxysteroid dehydrogenase 4-ene-5-ene-isomerase (3 beta-HSD), 17-hydroxylase and 17,20-lyase (P-450c17), and 21-hydroxylase (P-450c21) activities in a suspension of cells from guinea pig zona reticularis (RE) were 10- to 15-fold less than those measured in cells from zona fasciculata-glomerulosa (FG). Whereas the secretion of cortisol and C-19 steroids was remarkably increased during treatment of FG cells with adrenocorticotropic hormone (ACTH), no response could be detected when using cells from zona RE. By contrast, the measurement of a series of C-21 and C-19 steroids shows that the concentrations of several steroids were greater in the zona RE than in the zona FG. In addition, using Northern blot analysis, we have observed that the basal steady-state levels of mRNA for cholesterol side-chain cleavage (P-450scc), 3 beta-HSD, P-450c21, P-450c17, and P-450c11 were in the same range in the two zones and an administration of ACTH caused, in both zona FG and zona RE, a two- to threefold decrease in P-450c17 and P-450c21 steady-state mRNA levels, whereas P-450c11, 3 beta-HSD, and P-450scc steady-state mRNA levels remained unchanged. Our data suggest the presence of some factor(s) capable of rapidly deactivating the steroidogenic enzymes in the zona RE.