Water deprivation enhances the inhibitory effect of natriuretic peptides on cAMP synthesis in rat renal glomeruli.

This study investigates the effect of water deprivation on the expression of atrial natiruretic peptide (ANP)(1-28) binding sites in rat kidney. Water deprivation increased the B(max) of glomerular binding sites for ANP(1-28) and C-type natriuretic peptide (CNP)(1-22) without modifying their affinity, an effect that was prevented in the presence of C-atrial natriuretic factor (C-ANF), suggesting that natriuretic peptide receptor-C (NPR-C) binding sites might be enhanced. Our results indicate that ANP(1-28), CNP(1-22), and C-ANF inhibit cAMP synthesis directly stimulated by forskolin or by the physiological agonists histamine and 5-hydroxytryptamine. The inhibitory effect was found to be significantly greater in water-deprived rats than in controls. Our observations suggest that this effect must be attributed to the 67-kDa NPR-C-like protein, because the 67- and 77-kDa NPR-C-like proteins show high and low affinities for CNP(1-22), respectively, and the enhanced inhibitory effect of CNP on cAMP generation in water-deprived rats was detected at subnanomolar concentrations. In addition, using affinity cross-linking studies we have observed that water deprivation increases the expression of the 67-kDa NPR-C-like protein, and HS-142, which binds to NPR-A and the 77-kDa NPR-C-like but not the 67-kDa protein, reduced ligand internalization without affecting cAMP inhibition by ANP(1-28). Finally, we have found that ligand binding to the 67-kDa NPR-C-like protein is reduced by GTPgammaS, suggesting that this receptor is associated with a G protein in renal glomeruli. The enhanced inhibitory role of natriuretic peptides on cAMP synthesis induced by water deprivation may influence glomerular function in the rat kidney.