Role of adenylate cyclase-cyclic AMP-dependent signal transduction in the ACTH-induced biphasic growth effect of rat adrenocortical cells in primary culture.

ABSTRACT

ACTH has a biphasic effect on the proliferation of fetal rat adrenocortical cells in primary culture. Dramatic changes occurred during the first 72 h of ACTH stimulation, when incorporation of bromodeoxyuridine was used as an indicator of proliferation. The primary effect of ACTH was the inhibition of proliferation during the first 24 h, which was followed by an intense stimulatory phase during the third day of ACTH treatment. Cycloheximide (a protein synthesis inhibitor) prevented both the inhibitory and the stimulatory effects of ACTH, but did not affect the basal proliferation of unstimulated zona glomerulosa-like cells. Although adrenocortical cells stimulated with cyclic AMP (cAMP) derivatives, 8-bromo cAMP (8-Br cAMP) or dibutyryl cAMP ((Bu)2cAMP), differentiated morphologically into fasciculata-like cells, and secreted corticosterone and 18-OH-deoxycorticosterone, as did ACTH-stimulated cells, neither of the derivatives inhibited proliferation during the first 24 h of treatment. In contrast to ACTH, (Bu)2cAMP had a stimulatory effect on bromodeoxyuridine incorporation during the first 24 h of treatment. 8-Br cAMP did not change proliferation during the 24 h of treatment, but had a stimulatory effect after 72 h, which was not seen with (Bu)2cAMP. Thus, these results suggest that (1) differentiation, steroid hormone synthesis and the mitogenic effect of ACTH are transduced through the cAMP-mediated system, (2) the antimitogenic effect of ACTH is transduced via a cAMP-independent pathway and (3) both antimitogenic and mitogenic effects of ACTH are dependent on protein synthesis.