Atrial natriuretic factor: Structural requirements of the peptide for receptor binding, biological activity, and cGMP stimulation

Abstract

AbstractThe atrial natriuretic factor (ANF) family of peptides possesses diverse functional properties including smooth‐muscle relaxation, inhibition of aldosterone biosynthesis, and hypotensive activities. These separate activities are most likely mediated by the binding of the peptide to specific receptors located in the target organs. The present study was initiated to more closely examine the relationship between biological activity and the requirements of the various receptors for interaction with ANF and with ANF analogs. Binding affinities (Ki) were measured in plasma membranes isolated from rabbit kidney cortex, aorta, and adrenal, and in cultured rabbit aortic vascular smooth muscle cells (VSMC) using 125I‐Tyr‐28‐ANF (1–28) as the ligand. The VSMC were also utilized to quantitate stimulation of cGMP synthesis. Vasorelaxation (pD2) was measured in histamine‐contracted rabbit aortic rings. The activities of 19 ANF (5–28) analogs were compared, and a significant correlation between pD2 and Ki (r = −.83; p < 0.01) was obtained. The (D)Phe‐8 and Asn‐13 analogs were exceptions to this correlation; pD2 = 7.1 and 7.2, and pKi = 6.0 and 8.1, respectively. All analogs examined possessed comparable affinities in the four receptor assays. Conversely, comparison of vasorelaxant and cGMP stimulatory activities resulted in a much larger separation of activities. Tyr‐8 ANF (5–27) did not stimulate cGMP synthesis but relaxed smooth muscle (pD2 = 7.9), while ANF (7–23) was 500‐fold less active than ANF (5–28) in the vasorelaxant assay (pD2 = 6.1 and 8.9, respectively) but equipotent in the cGMP system. These and other experiments suggest the presence of ANF receptor subtypes and question the causative role of cGMP for inducing vasorelaxation of histamine‐constricted aortic rings.