N(G)-MONOMETHYL-L-ARGININE CAUSES NITRIC-OXIDE SYNTHESIS IN ISOLATED ARTERIAL RINGS - TROUBLE IN PARADISE

Arginine analogs are commonly used as inhibitors of the synthesis of endothelium-derived relaxing factor, nitric oxide. However, their effect on nitric oxide levels is rarely measured. Using a chemiluminescence assay for nitric oxide, we found that NG-monomethyl-l-arginine enhanced, rather than reduced, nitric oxide synthesis in pulmonary arterial and aortic rings. NG-monomethyl-l-arginine inhibited relaxation to the endothelium-dependent vasodilator A23187 in aortic but not pulmonary arterial rings. In contrast, Nω-nitro-l-arginine did not stimulate nitric oxide synthesis and it inhibited relaxation to A23187 in all rings. We conclude that NG-monomethyl-l-arginine is a partial agonist for nitric oxide synthesis. © 1992.