Endothelin-1 stimulates aldosterone synthesis in Conn's adenomas via both A and B receptors coupled with the protein kinase C- and cyclooxygenase-dependent signaling pathways

Background: The mechanisms and factors leading to enhanced aldosterone secr etion and ultimately to neoplastic transformation of the adrenal cortex are poorly defined. Angiotensin-II (Ang-II) and endothelin-1 (ET-1) have emerg ed as likely candidates among potential aldosterone secretagogues and adren ocortical growth-promoting factors, We therefore compared the effects of An g-II and ET-1 on steroid hormone secretion of Conn's adenomas, Methods: Ten Conn's adenomas that showed responsiveness to Ang-II blockade in vivo were recruited, Fragments of the tumors were collected immediately after surgical excision, and dispersed cells were obtained by collagenase d igestion and mechanical disaggregation, Steroid hormones secreted by disper sed Conn's adenoma cells were assayed by quantitative high-performance liqu id chromatography or radioimmunoassay, Results: Both Ang-II and ET-1 (10(-9) mol/L) similarly enhanced the overall steroid hormone production. ET-1 raised the release of pregnenolone las ev aluated by blocking its further metabolism by cyanoketone), corticosterone, 18-hydroxycorticosterone, and aldosterone, without affecting that of 11-de oxycortisol, cortisol, and Il-deoxycorticosterone. The hormonal responses t o ET-1 were partially reversed by 10(-7) mol/L of either the ETA-receptor a ntagonist BQ-123 or the ETB-receptor antagonist BQ-788 and were abolished w hen both antagonists were used together, The aldosterone response to the se lective activation of ETA and ETB receptors was studied in three Conn's ade nomas by exposing dispersed cells to ET-1 (10(-9) mol/L) plus BQ-788 (10(-7 ) mol/L) and to the ETB -receptor agonist BQ-3020 (10(-8) mol/L), Both trea tments raised aldosterone output by about 2-fold. ETA receptor-mediated ald osterone response was abolished by the protein kinase (PK) C inhibitor calp hostin C (10(-5) mol/L), ETB receptor-mediated secretory response was lower ed by either calphostin C and the cyclooxygenase (COX) inhibitor indomethac in (10(-5) or 10(-4) mol/L) and was completely suppressed when these two we re combined. The PKA inhibitor H-89 and the lipoxygenase inhibitor phenidon e were ineffective, Conclusions: Collectively, our findings indicate that Ang-II and ET-1 equip otently stimulate both early and late steps of aldosterone synthesis in Con n's adenoma cells, The secretagogue effect of ET-1 occurs via the activatio n of ETA and ETs receptors, which are coupled with the PKC-dependent and th e PKC- and COX-dependent signaling pathways, respectively.