L-NG-MONOMETHYL ARGININE AND L-NG-NITRO ARGININE INHIBIT NON-ADRENERGIC, NONCHOLINERGIC RELAXATION OF THE MOUSE ANOCOCCYGEUS MUSCLE

The effects of L-N(G)-monomethyl arginine (L-NMMA) and L-N(G)-nitro arginine (L-NOARG) on non-adrenergic, non-cholinergic (NANC) relaxations of the mouse anococcygeus were investigated. L-NMMA (10-200 μM) produced a concentration-related inhibition of the NANC repsonse; the inhibitory effect of 50 μM L-NMA was completely reversed by L-arginine but not D-arginine (both 100 μM). L-NOARG (1-50 μM) also produced a concentration-related inhibition of the NANC response and was some 30-50 times more potent than L-NMMA; again, the effects of 10 μM L-NOARG were reversed by 100 μM L-, but not D-, arginine. By itself 100 μM L-arginine did not relax the tissue, but did cause a slight potentiation of the NANC response. Sodium nitroprusside (0.01-10 μM), hydroxylamine (0.1-100 μM), sodium azide (1-100 μM) and nitric oxide (3-120 μM) all relaxed carbachol-induced tone; relaxations to submaximal concentrations of these nitrovasodilators were unaffected by either 50 μM L-NMMA or 10 μM L-NOARG. L-NOARG 10 μM did not inhibit, but rather potentiated, contractions of the mouse anococcygeus due to of its sympathetic nerves. The inhibitory effects of 10 μM L-NOARG on NANC relaxations were reversed by L-arginine (by 131%), L-citrulline (by 75%), L-arginine methyl ester (by 46%) and L-homoarginine (by 22%), but were unaffected by a variety of other amino acids and their derivatives (all at 100 μM). The results provide strong evidence that NANC relaxations of the mouse anococcygeus are mediated by an endogenous nitrate material, probably derived from L-arginine, and confirm that L-NOARG provides a very useful and potent drug for the investigation of endogenous nitrate function.