The Antinociceptive Effect of Intraperitoneally Administered Nonselective Nitric Oxide Synthase Inhibitor on the Rat Formalin Test

Abstract

Background: Nitric oxide (NO) is involved in the transmission and modulation of nociceptive information at the peripheral, spinal cord and supraspinal levels. We conducted this experiment to assess the antinociceptive effects of a nonselective nitric oxide synthase (NOS) inhibitor, N-nitro-L-arginine methyl ester (L-NAME), on the modulation of pain in rats subjected to the formalin test. Methods: Formalin 5% was injected in the right hind paw after intraperitoneal (IP) injection of various doses of L-NAME (0.5 mg/kg, 1.5 mg/kg with and without L-arginine 100 mg/kg, 5.0 mg/kg). The number of flinches was measured. Results: Formalin injected into the rat hind paw induced a biphasic nociceptive behavior. IP injected L-NAME diminished the nociceptive behaviors in a dose-dependent manner during phases 1 and 2. The concomitant injection of L-arginine reversed the antinocipetive effect of L-NAME. Conclusions: The data demonstrates that a nonselective NOS inhibitor, L-NAME, possesses antinociceptive properties in rats subjected to the formalin test, and the antinociceptive effect of L-NAME is reversed by the concomitant administration of L-arginine. (Korean J Pain 2006; 19: 142-145)