C-type natriuretic peptide (CNP), the third member of natriuretic peptides, has recently been discovered from the porcine brain. Using a polyclonal antiserum to CNP, we demonstrated that CNP-like immunoreactivity (CNP-LI) is present mainly in the central nervous system. Recently, however, we have discovered the production and secretion of CNP in vascular endothelial cells. These observations suggested that CNP may act not only as a neuropeptide but also as a local regulator of vascular tone or growth. In order to further clarify the pathophysiological significance of CNP, we aimed at the preparation of a monoclonal antibody to CNP. A monoclonal antibody to CNP, KY-CNP-I, has been produced. This monoclonal antibody belongs to the immunoglobulin G1 subclass and has high affinity for CNP. Using this monoclonal antibody, we established a specific radioimmunoassay (RIA) for CNP. The RIA detected CNP-LI in rat brain extracts and culture media conditioned with bovine endothelial cells. In addition, the pretreatment of cultured aortic smooth muscle cells with KY-CNP-I attenuated cyclic GMP production induced by GNP in vitro. The preadministration of KY-CNP-I to rats also attenuated plasma cyclic GMP increase after intravenous injection of CNP in vivo. These results indicate that this monoclonal antibody is a useful tool to clarify the pathophysiological role of CNP as a neuropeptide and as a local vascular regulator.
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