Depressor and natriuretic activities of several atrial peptides

Mammalian atria contain peptides that have depressor and natriuretic activities. Four peptides, atriopeptin I to III (AP I to III) and α-human atrial natriuretic factor (α-hANP), were synthesized and assayed in the urethane-anesthetized rat for cardiovascular changes and natriuretic activities. All four peptides produced depressor responses and natriuresis. The relative activities were: α- hANP = AP III > AP II > AP I . The disappearance of iodinated AP III from plasma was rapid, with an estimated half-life of 2.5 min. Atriopeptin III was degraded by tissue homogenates, the relative activities being: kidney > liver > lung > plasma > heart. The HPLC profile of AP III suggested that smaller peptide fragments were formed after incubation with kidney homogenates. The degradation of AP III was inhibited by bestatin, an aminopeptidase inhibitor, and SQ 20881, a carboxypeptidase inhibitor.