Proadrenomedullin N-Terminal 20 Peptide (PAMP), Acting Through PAMP(12–20)-Sensitive Receptors, Inhibits Ca 2+ -Dependent, Agonist-Stimulated Secretion of Human Adrenal Glands

Abstract

Abstract —Proadrenomedullin N-terminal 20 peptide (PAMP) is a 20–amino acid hypotensive peptide expressed in the adrenal medulla. We investigated the localization and function of PAMP receptors in the human adrenal gland. Autoradiography showed the presence of [ 125 I]PAMP-binding sites in both zona glomerulosa and adrenal medulla that were displaced by cold PAMP and PAMP(12–20) but not by other preproadrenomedullin-derived peptides. PAMP, but not PAMP(12–20), counteracted, in a concentration dependent manner, both aldosterone response of zona glomerulosa cells and catecholamine response of adrenal medulla cells to BAYK-8644, the selective agonist of voltage-activated Ca 2+ channels, as well as to K + and angiotensin II. PAMP(12–20) partially reversed this antisecretagogue effect of PAMP. Collectively, these findings suggest (1) that PAMP inhibits Ca 2+ -dependent, agonist-stimulated aldosterone and catecholamine secretion, acting via specific receptors and through a mechanism involving the impairment of Ca 2+ influx; and (2) that PAMP(12–20) acts as a weak antagonist of PAMP receptors, thereby suggesting that both C- and N-terminal sequences of the PAMP molecule are required for this peptide to exert its antisecretagogue action on the human adrenal gland.