title: Potentiation of the vasorelaxant activity of nitric oxide by hydroxyguanidine: implications for the nature of endothelium-derived relaxing factor.
abstract: 1. We recently demonstrated that NG-hydroxy-L-arginine (L-HOArg) is a substrate for the constitutive nitric oxide (NO) synthase present in bovine aortic endothelial cells cultured on microcarrier beads (EC). Furthermore, L-HOArg reacts chemically with NO released from these cells to form a potent and more stable vasodilator. This is most likely through a reaction with the hydroxyguanidino group. 2. Here, we studied the interaction of a simpler molecule, hydroxyguanidine (HOG) with NO. 3. HOG (10 microM), like L-HOArg (10 microM) or NG-hydroxy-D-arginine (D-HOArg, 10 microM), potentiated and stabilized the relaxant activity of authentic NO. 4. When NO was bubbled through the solution of HOG, a new compound was formed. It had similar physicochemical properties to those of the previously described L-HOArg/NO adduct. It was also a potent vasodilator and its action was inhibited by oxyhaemoglobin (10 microM), indicating formation of a NO-containing substance. 5. Moreover, HOG (10 microM) was not a substrate for the constitutive NO synthase present in the microsomal fraction of EC and did not affect the flow-induced or bradykinin-stimulated generation of prostacyclin, as measured by 6-keto-PGF1 alpha. 6. We also studied the effect of HOG on the endothelium-derived relaxing factor (EDRF) released from the column of EC. HOG (10 microM) potentiated and stabilized the relaxations of rabbit aortic strips induced by EDRF released by bradykinin (5-20 pmol) or ADP (5-10 nmol). These relaxations were inhibited by NG-nitro-L-arginine methyl ester (L-NAME, 10 microM) and L-arginine (L-Arg, 1 mM) reversed the inhibitory effects of L-NAME. 7. HOG (10 iM) augmented the basal (flow-induced) EC-dependent relaxations which were also inhibited by L-NAME (10 1M) and the effects of L-NOArg were reversed by L-Arg (1 mM).8. Thus, the hydroxyguanidino moiety of L-HOArg is involved in the reaction with NO. Moreover, the comparable reaction of the hydroxyguanidino compounds with NO on the one hand and with flowinduced and agonist-triggered EDRF on the other, strongly supports their common identity.
mesh_terms: D000594:Amino Acid Oxidoreductases / Q000378:metabolism; D000818:Animals; D001011:Aorta; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D002417:Cattle; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D004357:Drug Synergism; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011464:Epoprostenol / Q000096:biosynthesis; D006146:Guanidines / Q000494:pharmacology*; D006898:Hydroxylamines; D066298:In Vitro Techniques; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D019331:NG-Nitroarginine Methyl Ester; D009569:Nitric Oxide / Q000378:metabolism / Q000494:pharmacology*; D019001:Nitric Oxide Synthase; D011817:Rabbits; D014664:Vasodilation / Q000187:drug effects*
chemical_list: D006146:Guanidines; D006898:Hydroxylamines; D009569:Nitric Oxide; C029604:hydroxyguanidine; D001120:Arginine; D011464:Epoprostenol; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases; D019331:NG-Nitroarginine Methyl Ester