NG-monomethyl-L-arginine and NG-nitro-L-arginine inhibit endothelium-dependent relaxations in human isolated omental arteries

The L-arginine analogues NG-monomethyl-l-arginine (l-NMMA, 10−4 m) and NG-nitro-L-arginine methyl ester (l-NAME, 10−4 m), which specifically inhibit the synthesis of nitric oxide from l-arginine, significantly reduced acetylcholine-induced endothelium-dependent relaxations in rings of human omental arteries. The inhibitory potency of l-NMMA and l-NAME was similar. Addition of l-NMMA or l-NAME to the organ bath did not induce any significant changes in the resting tension of the tissues. The effects of l-NMMA were reversed by l-arginine (3 × 10−4 m). The l-NMMA enantiomer, d-NMMA (10−4 m), did not influence either the basal tone of the preparation or the relaxing effects of acetylcholine. Arterial relaxations induced by sodium nitroprusside (10−6 m) were not influenced by incubation with l-NMMA or l-NAME. These results suggest that endothelium-dependent relaxations in human omental arteries are mediated by the endogenous and substrate-specific generation of nitric oxide from l-arginine.