Atrial-Natriuretic-Peptide Modulators - Dissociation Of Receptor-Binding And Particulate Guanylate-Cyclase Activity

Prazosin stimulated I-125-rANP(102-126) binding to bovine adrenal zona glomerulosa membranes (BAZGM) allosterically by converting the lower-affinity state binding sites into the higher-affinity state. The modulatory effect could be mimicked by guanabenz and LY193422, and was concentration-dependent. SC-50 (concentration required to stimulate binding by 50%) values for guanabenz, prazosin, and LY193422 were 13, 25, and 1.8-mu-M, respectively. Prazosin (30-mu-M) enhanced I-125-ANP(102-126) binding by decreasing the K(D) from 251 +/- 24 to 97.4 +/- 8.3 pM without affecting the Bmax. Competitive inhibition of I-125-rANP binding by ANP analogs was potentiated by prazosin (30-mu-M) and LY193422 (50-mu-M). The modulator-stimulated I-125-rANP(102-126) binding was reversible by the addition of unlabelled ANP analogs during incubation. Previously, we also demonstrated that these modulators potentiated the ANP-mediated inhibition of ACTH-induced aldosterone synthesis in rat adrenal zona glomerulosa cells [Horng, J.S., Steinberg, M.I., Wyss, V.L., Wiest, S.A., Schirmer, E.W., McCowan, J.R., and Yu, M.J.: Atrial natriuretic peptide (ANP) receptor modulators: Effects of prazosin and guanabenz analogs on ANP receptor binding and in vitro biological activity. FASEB Journal 3:A733, 1989; Yu, M.J., McCowan, J.R., Steinberg, M.I., Wiest, S.A. Wyss, V.L., and Horng, J.S.: Atrial natriuretic peptide receptor modulators: Effect of disubstituted quinazolines on receptor binding and in vitro biological activity. Journal of Medicinal Chemistry 33:348-353, 1990]. However, neither prazosin nor LY193422 affected basal or ANP-induced particulate guanylate cyclase activity in rabbit glomeruli. This is the first study to our knowledge in which ANP modulators were demonstrated to potentiate ANP-mediated response independent of cGMP. Our studies suggest that potentiation of ANP-mediated inhibition of aldosterone synthesis by these analogs does not involve particulate guanylate cyclase and that these modulators induce a cyclase-uncoupled, high affinity ANP receptor in the adrenal gland, which might be different from cyclase-uncoupled ANP clearance receptor.