Glucagon inhibits ACTH-stimulated cortisol secretion from dispersed human adrenocortical cells by activating unidentified receptors negatively coupled with the adenylate cyclase cascade

We have investigated the direct effect of glucagon on collagenase-dispersed adrenocortical cells obtained from consenting patients undergoing unilater al adrenalectomy and nephrectomy for renal cancer. Dispersed cells, actuall y a mixture of zona glomerulosa and zona fasciculata-reticularis (ZF/R) cel ls, were incubated with glucagon (from 10(-10) to 10(-6) M) alone or in the presence of 10(-9) M angiotensin-ll, 10(-10) M ACTH or 10(-5) M forskolin, and the effects on aldosterone, cortisol and cyclic-AMP (cAMP) production were measured by radioimmune assay. Glucagon concentration-dependently inhi bited ACTH-stimulated cortisol production and ACTH- or forskolin-enhanced c AMP release, minimal and maximal effective concentrations being 10(-9) and 10(-7) M. The effects of glucagon were suppressed by 10(-5) M Des-His(1)-[G lu(9)]glucagon amide, an antagonist of glucagon receptors (glucagon-A). Rev erse transcription-polymerase chain reaction did not reveal the presence of specific glucagon-receptor mRNA in the human adrenal cortex. However, auto radiography demonstrated the presence of [I-125]glucagon binding sites in t he ZF/R, which were displaced by glucagon but not by ACTH. Taken together, these findings suggest that glucagon, through the activation of unidentifie d receptors located on ZF/R cells, inhibits adenylate cyclase, thereby damp ening glucocorticoid response to ACTH.