The analgesic effects and mechanisms of orally administered eugenol.

In the present study, the antinociceptive profiles of eugenol were examined in ICR mice. Eugenol administered orally (from 1 to 10 mg/kg) showed an antinociceptive effect in a dose-dependent manner as measured in the acetic acid-induced writhing test. Duration of antinociceptive action of eugenol maintained at least for 30 min. Moreover, the cumulative response time of nociceptive behaviors induced by an intraplantar formalin injection was reduced by eugenol treatment during the 2(nd) phases. Furthermore, the cumulative nociceptive response time for intrathecal injection of substance P (0.7 μg) or glutamate (20 μg) was diminished by eugenol. Intraperitoneal pretreatment with yohimbine (α2-adrenergic receptor antagonist) or naloxone (opioid receptor antagonist) attenuated antinociceptive effect induced by eugenol in the writhing test. However, methysergide (5-HT serotonergic receptor antagonist) did not affect antinociception induced by eugenol in the writhing test. Our results suggest that eugenol shows an antinociceptive property in various pain models. Furthermore, this antinociceptive effect of eugenol may be mediated by α2-adrenergic and opioidergic receptors, but not serotonergic receptor.