The maintenance of optimal steroidogenesis in adrenocortical cells primarily depends on the chronic action of cAMP. Herein we examine the effects of prostaglandin E2 (PGE2) on the differentiated functions of bovine adrenocortical (BAC) cells in primary culture. PGE2 (10 microM) treatment for 3 h stimulated steroidogenesis and cAMP production by over 100-fold. In addition, the cAMP antagonist Rp-cAMP (1 mM) inhibited PGE2 stimulation of steroidogenesis by 60%. This observation suggests that the cAMP second messenger system is responsible for much of the PGE2-activated steroid hormone synthesis. Chronic treatment of BAC cells with PGE2 caused induction of 3 beta-hydroxysteroid dehydrogenase and steroid 17 alpha-hydroxylase cytochrome P-450 expression as determined by the examination of enzyme activity, enzyme levels by immunoblotting, and specific messenger RNA (mRNA) levels by Northern analysis. The positive effects of PGE2 on expression of 3 beta-hydroxysteroid dehydrogenase and 17 alpha-hydroxylase cytochrome P-450 were similar to the effects seen after ACTH treatment of BAC cells. In addition, treatment of BAC cells with PGE2 for 3 days caused a 3-fold induction of ACTH receptors as determined by increased cell binding of [125I]ACTH. Finally, we determined that BAC cells produced PGE2 and that the level of synthesis increased 10-fold after treatment with the hormone angiotensin II. Taken together these data indicate that PGE2 is a positive regulator of BAC cell differentiation acting on ACTH receptors, steroid metabolizing enzymes, and steroidogenesis. The ability of BAC cells to produce PGE2 leaves open the possibility for paracrine and autocrine regulation within the adrenal.