Signaling pathways involved in the A and B receptor-mediated cortisol secretagogue effect of endothelins in the human adrenal cortex

Endothelins (ETs) are a family of 21-amino acid hypertensive peptides, whic h together with their receptors ETA and ETB are expressed in human adrenal cortex. Evidence has been provided that ETs exert a potent secretagogue eff ect on human adrenocortical cells, acting through both ETA and ETB receptor s. Therefore, it seemed worthwhile to study the signaling cascades mediatin g the cortisol secretagogue effect of the two receptor subtypes. Normal adr enal glands were obtained from consenting patients undergoing unilateral ne phrectomy with ipsilateral adrenalectomy for renal cancer. Dispersed zona f asciculata-reticularis (ZF/R) cells were obtained by collagenase digestion and mechanical disaggregation. The selective activation of ETA and ETB rece ptors was obtained by exposing dispersed cells to ET-1 plus the ETB recepto r antagonist BQ-788 and to the selective ETB receptor agonist BQ-3020, resp ectively. ETA and ETB receptors about equally contributed to the cortisol r esponse of dispersed ZF/R cells to ETs. The phospholipase (PL) C inhibitor U-73122 abolished ETA-mediated secretory response, but only partially preve nted the ETB-mediated one. The phosphatidylinositol 3-kinase inhibitor wort mannin and the protein kinase (PK) C inhibitor calphostin-C significantly b lunted the secretory responses ensuing from the activation of both receptor subtypes, while the Ca2+-channel blocker nifedipine was ineffective. The E TB receptor-, but not the ETA receptor-mediated cortisol response was parti ally reversed by the cyclooxygenase (COX) inhibitor indomethacin, which whe n added together with U-73122 abolished it. The inhibitors of adenylate cyc lase, PKA, tyrosine kinase and lipoxygenase did not affect the secretory re sponse to the activation of either receptor subtype. ETA-receptor activatio n raised inositol triphosphate (IP3) production from dispersed ZF/R cells, while ETB-receptor stimulation enhanced both IF, and prostaglandin-E-2 prod uction. Collectively, our findings indicate that ETs stimulate cortisol sec retion from human ZF/R cells, acting through ETA receptors exclusively coup led with PLC/PKC-dependent pathway and ETB receptors coupled with both PLC/ PKC- and COX-dependent cascades.