Distribution and functional significance of the endothelin receptor subtypes in the rat adrenal gland

Endothelins (ET) are a family of vasoactive peptides that act via two subtypes of receptors, named ETA and ETB. ET-1 binds to both ETA and ETB, whereas the isopeptide ET-3 preferentially binds to ETB. The localization of ETA and ETB receptors in the rat adrenal gland and their involvement in the adrenal secretagogue effect of ETs has been studied in vitro. Autoradiographic assessment of the selective displacement of [I-125]ET-1, [I-125]ET-3 and [I-125]BQ-3020 (an ETB agonist) by BQ-123 or BQ-788 (specific antagonists of ETA and ETB, respectively) indicates that the zona glomerulosa and adrenal medulla possess both ETA and ETB, whereas the zona fasciculata/reticularis is exclusively provided with ETB. ET-1, ET-3 and BQ-3020 enhance aldosterone and corticosterone secretion by dispersed cells of the zona glomerulosa and zona fasciculata/reticularis, respectively. BQ-123 does not affect the secretagogue action of these three agonists, whereas BQ-788 completely annuls it. ET-1 induces a marked rise in catecholamine release by fragments of the adrenal medulla, and both BQ-123 and BQ-788 partially reverse this effect. ET-3 and BQ-3020 elicit a catecholamine release that is less intense than that produced by ET-1; this response is unaffected by BQ-123 and abolished by BQ-788. Thus, in the rat, the corticosteroid secretagogue effect of ETs seems to be exclusively mediated by the ETB receptor subtype, and the catecholamine secretagogue action by both ETA and ETB. The functional relevance of ETA receptors present in the zona glomerulosa remains to be investigated.