L-leucyl-L-arginine, naltrindole and D-arginine block antinociception elicited by L-arginine in mice with carrageenin-induced hyperalgesia.

1. Intraplantar injection of carrageenin into the mouse hind paw produced hyperalgesia when measured by the paw pressure test (Randall & Selitto method). 2. Subcutaneous administration of L-arginine (100-1,000 mg kg-1), a possible precursor of kyotorphin which is an endogenous analgesic neuropeptide, inhibited carrageenin-induced hyperalgesia in a dose-dependent manner. This effect was blocked by subcutaneous administration of naloxone, naltrindole, a selective delta-opioid receptor antagonist (enkephalin antagonist), and D-arginine. 3. Intracerebroventricular administration of L-leucyl-L-arginine inhibited the antinociceptive effect of systemically administered L-arginine in hyperalgesic mice. 4. Intracerebroventricular administration of L-arginine (3 and 30 micrograms per mouse) and kyotorphin (300 ng-3 micrograms per mouse) produced antinociception in hyperalgesic mice. The antinociceptive effects of L-arginine but not kyotorphin were blocked by intracerebroventricular administration of D-arginine. 5. These results suggest that L-arginine-induced antinociception is mediated by activation of 'kyotorphinergic' nerves followed by activation of the 'opioidergic' (possible 'enkephalinergic') nerves in the central nervous system.