Hormonal regulation of the adrenocortical cell

Monolayer cultures of bovine and human adrenocortical cells have been used to study regulation of growth and function. Homogeneous bovine adrenocortical cells exhibit a finite life span of ~60 generations in culture. Full maintenance of differentiated function (steroid hormone synthesis) requires an inducer such as ACTH and antioxidizing conditions. Full induction of differentiated function occurs only when cellular hypertrophy is stimulated by growth factors such as fibroblast growth factor and serum. ACTH and other agents that increase cellular cAMP inhibit replication but do not block growth factor-induced cellula hypertrophy. ACTH and growth factors together result in a hypertrophied, hyperfunctional cell. Replication ensues only when desensitization to the growth inhibitory effects of ACTH occurs. Cultures of the definitive and fetal zones of the human fetal adrenal cortex synthesize the steroids characteristic of the two zones in vivo. ACTH stimulates production of dehydroepiandrosterone (DHA), the major steroid product of the fetal zone, and of cortisol, the characteristic steroid product of the definitive zone. Prolonged ACTH treatment of fetal zone cultures results in a preferential increase in cortisol production so that the pattern of steroid synthesis becomes that of the definitive zone. The preferential increase in cortisol production by fetal zone cultures results from induction of 3β-hydroxysteroid dehydrogenas, Δ(4,5) isomerase activity, which is limiting in fetal zone cells. ACTH thus causes a phenotypic change in fetal zone cells to that of definitive zone cells. In both bovine and human adrenocortical cells, the principal effect of ACTH is to induce full expression of differentiated function. This occurs only under conditions where growth substances and nutrients permit full amplication.