Orexin a stimulates cortisol secretion from human adrenocortical cells through activation of the adenylate cyclase-dependent signaling cascade

Orexins A and B are two hypothalamic peptides that increase food intake and body weight and probably play a role in the sleep regulation. They act thr ough two subtypes of G protein-coupled receptors, called OX1-R and OX2-R. O X1-R selectively binds orexin-A, whereas OX2-R is nonselective for both ore xins. Orexins did not affect the in vitro secretion of either catecholamine or aldosterone from human adrenals. Conversely, orexin A, but not orexin B , concentration dependently increased basal cortisol secretion from dispers ed adrenocortical cells; the maximal effective concentration was 10(-8) mol /L. Orexin A (10(-8) mol/L) enhanced the cortisol response to maximal effec tive concentrations (10(-9) mol/L) of angiotensin II and endothelin-1, but only to low concentrations of ACTH (10(-12)/10(-11) mol/L). Orexin A (10(-8 ) mol/L) increased basal cAMP release by dispersed adrenocortical cells, an d the effect was blocked by the adenylate cyclase inhibitor SQ-22536. The c ortisol response to 10-8 mol/L orexin A was unaffected by the ACTH receptor antagonist corticotropin-inhibiting peptide, but was abolished by either S Q-22536 or the protein kinase A inhibitor H-89. RT-PCR demonstrated high le vels of OX1-R messenger ribonucleic acid and very low levels of OX2-R messe nger ribonucleic acid in human adrenal zona fasciculata-reticularis and adr enal medulla. Collectively, our findings suggest that orexins selectively s timulate glucocorticoid secretion from human adrenocortical cells, acting t hrough OX1-R coupled with the adenylate cyclase-dependent signaling pathway .