Antinociceptive Effect of Hydroalcoholic Extract of Iranian Green tea in the Formalin Test in Rats

Background: Tea (Camellia sinensis) has been utilised, since time immemorial, as a beverage possessing encouraging health benefits. Little scientific evidence exists in literature on the effect of this plant on pain. Objectives: To investigate the antinociceptive activity of Iranian green tea extract. Materials and Methods: The hydroalcoholic extract was administered to male Wistar rats. Formalin paw test was used to evaluate the antinociceptive activity. Plant extract (25, 50, 100 and 200 mg/kg, i.p.) (n = 6 for each group) or vehicle (n = 6) was administered 30 min before the subplantar formalin injection. Results: The extract caused a significant dose-related (50, 100, 200 mg /kg, i.p.) inhibition of the first phase and onset of chronic phase (200 mg /kg, i.p.) of formalin induced nociception. The results showed that the pre-treatment of rats with naloxone (1 mg/kg, i.p.) significantly (P < 0.001) reversed antinociception by Green tea extract (GTE) (200 mg/kg, i.p.) in the inflammatory phase and had no effect on phase 1. Conclusions: These results indicate that GTE produces dose-related antinociception in chemical pain model and one of its possible mechanisms involves opioid pathways.