Proadrenomedullin N-terminal 20 peptide inhibits aldosterone secretion of human adrenocortical and Conn's adenoma cells: comparison with adrenomedullin effect.

Adrenomedullin (ADM) and proadrenomedullin N-terminal 20 peptide (PAMP) are two vasoactive peptides, which are highly expressed in human adrenal gland. Autoradiography showed the presence of abundant [125I]ADM and [125I]PAMP binding sites in both the outer cortex and medulla of human adrenals. ADM, but not PAMP binding was completely displaced by the specific CGRP1 receptor antagonist CGRP(8-37). ADM and PAMP concentration-dependently inhibited angiotensin-II (ANG-II)-stimulated, but not basal aldosterone secretion of dispersed human adrenocortical cells. PAMP was significantly more potent than ADM (IC50, 0.98 x 10(-11) vs. 3.16 x 10(-9) mol/L). CGRP(8-37) abolished the inhibitory action of ADM, without affecting that of PAMP. Qualitatively analogous findings were obtained using aldosteronoma dispersed cells. However, tumor cells were more sensitive than normal adrenocortical cells (IC50 were 1.32 x 10(12) and 1.51 x 10(-9) mol/L for PAMP and ADM, respectively). Moreover, PAMP was found to also depress basal aldosterone secretion (IC50, 4.27 x 10(-11) mol/L). Neither basal nor ANG-II-stimulated cortisol production by both normal and tumorous adrenocortical cells was altered by ADM or PAMP. Collectively, these findings confirm that ADM (CGRP1) and PAMP receptors are present in the human outer adrenal cortex and allow us to draw the following conclusions: 1) because of its potency, PAMP may a better candidate for being considered a physiological regulator of aldosterone secretion than ADM; and 2) under pathological conditions, both peptides may be capable of reversing overproduction of aldosterone.