Proadrenomedullin N-terminal 20 peptide (PAMP), acting through PAMP(12-20)-sensitive receptors, inhibits Ca2+-dependent, agonist-stimulated secretion of human adrenal glands

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 [I-125]PAMP-binding sites in both zona glomerulosa and adrenal medulla that were displaced by cold PAMP and PAMP(12-20) but not by other preproadrenamedullin-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 Ca2+ channels, as well as to K+ and angiotensin Il, PAMP(12-20) partially reversed this antisecretagogue effect of PAMP. Collectively, these findings suggest (1) that PAMP inhibits Ca2+-dependent, agonist-stimulated aldosterone and catecholamine secretion, acting via specific receptors and through a mechanism involving the impairment of Ca2+ 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.