RECEPTOR-SPECIFIC LIGANDS DISTINGUISH NATRIURETIC PEPTIDE RECEPTOR-A AND RECEPTOR-C IN PRIMATE TISSUES

Systemic clearance of atrial natriuretic peptide (ANP) is in part due to neutral endopeptidase (NEP) proteolysis and natriuretic peptide rec eptor-C (NPR-C) mediated endocytosis. Biological responses to ANP are primarily mediated by the membrane guanylyl cyclase-A/natriuretic pept ide receptor-A (NPR-A). Analogs of ANP selective for NPR-A and/or resi stant to NEP may have increased activity in those tissues where NPR-C and NEP are coexpressed with NPR-A. The analog of ANP termed vANP; [(R 3D, G9T, R11S, M12L, G16R)ANP] is selective for human NPR-A with at le ast 10,000 fold reduction in affinity for human NPR-C. We report that rat NPR-A is insensitive to 10 nM vANP demonstrating the limitations o f this species in evaluating human therapeutic candidates. As an alter native approach we tested the binding and potency of receptor-selectiv e and NEP-resistantANP analogs in rhesus monkey tissues. Competition b inding studies with a simplified version of vANP, sANP [(G9T, R11S, G1 6R)rANP], in rhesus monkey kidney and lung membrane preparations shows displacement of I-125-ANP from only a fraction of the total ANP recep tor population, 30 and 85%, respectively. The remaining ANP binding si tes can be occupied with the NPR-C selective ligand cANP(4-23). These data strongly suggest that only two classes of ANP receptor are presen t in these membrane preparations, NPR-A and NPR-C. The NEP resistant s ANP derivative called sANP(TAPR) was 8 fold more potent (ED50 = 0.6 nM ) than rANP (ED50 = SnM) in stimulating cGMP production in the lung me mbrane preparation. Our results demonstrate that the rhesus monkey nat riuretic peptide receptors reflect the pharmacology of the human recep tors, and that this species may be suitable to determine the role of N PR-C and NEP in peptide clearance and attenuating functional responses .