Modification of antinociceptive action of Ukrain by endogenous nitric oxide in the writhing syndrome test in mice

The effects of L-arginine, the physiological precursor of nitric oxide (NO), and inhibitors of NO-synthase on the antinociceptive action of Ukrain (4.75, 9.5, and 19.0 mg/kg i.p.) were investigated using the writhing syndrome test in mice. It was found that L-arginine (0.1 or 1.0 mg/kg i.p.) significantly decreased or enhanced the antinociceptive effect of Ukrain, depending on the combination administered. In addition, the inhibitors of NO-synthase NG-nitro-L-arginine methyl ester (L-NAME) (1.0 and 10 mg/kg i.p.), 7-nitroindazole (1.0 mg/kg i.p.) and NG-monomethyl-L-arginine acetate (L-NMMA) (1.0 mg/kg i.p.) significantly enhanced Ukrain-induced antinociception. These results suggest that endogenous NO can modify the antinociceptive effect of Ukrain.