Molecular physiology of natriuretic peptide signalling.

The natriuretic peptide family consists of three homologous members, atrial (ANP), B-type (BNP) and C-type natriuretic peptides (CNP). These small peptides activate specific membrane-bound guanylyl cyclase (GC) receptors (GC-A and GC-B), thus modulating cellular functions via the intracellular second messenger, cyclic GMP. Since the original discovery of cardiac ANP more than two decades ago, the application of gene targeting technology in mice has provided new valuable information regarding the molecular physiology and diverse biological functions of natriuretic peptides and their receptors. The GC-A and ANP gene knock-outs demonstrated that this signalling system is not only essential in the maintenance of normal blood pressure and volume, but also has local, growth-moderating functions within the heart itself. Disruption of the genes encoding BNP, CNP or the CNP-receptor, GC-B, demonstrated that these "natriuretic peptides" are in fact unlikely to physiologically regulate renal sodium excretion but instead may exert important autocrine/paracrine cGMP-mediated effects on cellular proliferation and differentiation in different tissues. Notably, the intestinal peptide uroguanylin, which activates a third guanylyl cyclase (GC-C), exerts diuretic/natriuretic activity and links the intestine and kidney in an endocrine way to modulate renal function in response to oral salt load. Reviewed here is the physiology and biochemistry of natriuretic peptides and their guanylyl cyclase receptors, with special focus on the information gained to date from targeted disruption of specific members of this peptide family, their receptors, or effector molecules in the murine system.