C-type natriuretic peptide: The endothelial component of the natriuretic peptide system

C-type natriuretic peptide (CNP) is a 22-amino-acid peptide, structurally related to but genetically distinct from atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). Whereas ANP and BNP are ligands for a guanylyl cyclase-coupled receptor, the NPR-A receptor, CNP is a specific ligand for the NPR-B receptor. In addition to clearance by the NPR- C receptor, CNP is subject to degradation by the ectoenzyme neutral endopeptidase 24.11 (NEP), which is widely distributed in the kidney, lung, heart, and endothelial cells. Although initially identified in porcine brain, CNP immunoreactivity has been found in human vascular endothelial cells, plasma, and kidney. CNP has potent systemic cardiovascular actions, which include reductions in cardiac filling pressures and output, secondary to vasorelaxation and decreases in venous return, but has minimal renal actions. Unlike ANP, CNP is a selective endothelium-independent venodilator. However, it is also a potent coronary vasodilator. Expression of the CNP gene by the endothelial cells, the presence of CNP receptors on vascular smooth muscle cells (VSMCs), and the antimitogenic effect of CNP on VSMCs suggest that CNP is produced by the endothelium and acts on adjacent VSMCs serving as an autocrine/paracrine endothelium-derived vasoregulatory system.