ACTH-induced inhibition of the action of angiotensin II in bovine zona glomerulosa cells. A modulatory effect of cyclic AMP on the angiotensin II receptor.

Both angiotensin II and adrenocorticotropic hormone (ACTH) are well known to play a crucial role on the regulation of aldosterone production in adrenal glomerulosa cells. Recent observations suggest that the steroidogenic action of ACTH is mediated via the cAMP messenger system, whereas angiotensin II acts mainly through the phosphoinositide pathway. However, there have been no reports concerning the interaction between the cAMP messenger system activated by ACTH and the Ca2+ messenger system induced by angiotensin II. Both ACTH and angiotensin II simultaneously act on adrenal cells for regulating steroidogenesis under physiological conditions. Thus the present experiments were performed to examine the effect of ACTH on the action of angiotensin II by measuring angiotensin II receptor activity, cytosolic Ca2+ movement, and aldosterone production. The major findings of the present study are that short-term exposure to a high dose of ACTH (10(-7) M) inhibited 125I-angiotensin II binding to bovine adrenal glomerulosa cells, decreased the initial spike phase of Ca2+]i induced by angiotensin II, and inhibition of angiotensin II-induced aldosterone production. Low dose of ACTH (10(-10) M), which did not increase cAMP formation, did not affect angiotensin II receptor activity. These studies have shown that angiotensin II receptors of bovine adrenal glomerulosa cells can be down-regulated by 1 mM dibutyryl cyclic AMP, as well as by effectors which are able to activate cAMP formation (10(-7) M ACTH and 10(-5) M forskolin). The rapid decrease in angiotensin II receptors induced by 10(-7)M ACTH was associated with a decreased steroidogenic responsiveness and a decreased rise in the Ca2+]i response induced by angiotensin II. These studies show that the cAMP-dependent processes activated by ACTH have the capacity to interfere with signal transduction mechanisms initiated by receptors for angiotensin II.