Abstract
Nitric oxide (NO) is a major endothelium-derived relaxing factor (EDRF) released in response to vasodilating amines, peptides, proteins, ionophores, and nucleotides. EDRF is an important regulator of smooth muscle tone and platelet aggregation and adhesion. Histamine and acetylcholine relax the intact norepinephrine-constricted guinea pig pulmonary artery by an EDRF-dependent mechanism in a medium free of amino acids. N omega-Monomethylarginine (N-MeArg; 0.25 mM) inhibited this relaxation by 64-73%. Inhibition by N-MeArg developed rapidly and was immediately and completely reversed by excess L-arginine but not by D-arginine or by citrulline. N-MeArg did not diminish relaxation induced by nitroprusside, an NO-generating agent, indicating that N-MeArg acts on endothelium rather than on smooth muscle. These observations strongly suggest that, in the intact guinea pig pulmonary artery, EDRF originates from enzymatic action on the guanido nitrogen(s) of an endogenous pool of arginine. This is strikingly similar to the origin of reactive nitrogen intermediates in activated macrophages.
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