Qom University of Medical Sciences Journal

Background and Objectives: Decarboxylated phytocannabinoids activate endocannabinoid system in the central nervous system and peripheral tissues via activation of cannabinoid receptors. In this investigation, the effect of interaction between decarboxylated phytocannabinoids and capsaicin at the central level and naloxone at the systemic level, was investigated on inflammatory rat paw edema induced by by sub-plantar injection.

Methods: In this experimental study, male Wistar rats (200-250g) were used. To study the effect of interaction with opioid system, intraperitoneal administration of hydroalcoholic extract (dose, 50mg/kg), naloxone (dose, 2mg/kg) and co-administration of the extract and naloxone were performed. To investigate the effect of interaction with vanilloid system, intrathecal administration of extract (0.01mg/10μl), capsaicin (0.002mg/10μl) and co-administration of extract and capsaicin were performed. Paw volume was measured before and one hour after sub-plantar administration of formalin using plethysmometer method in order to assess inflammatory edema.

Results: Intraperitoneal administration of extract alone or in combination with naloxone reduced the inflammatory rat paw edema volume (p<0.001). On the other hand, capsaicin increased rat paw edema volume (p<0.01), but intrathecal administration of extract alone and in combination with capsaicin decreased the inflammatory rat paw edema volume (p<0.01).

Conclusion: The results of this study showed that decarboxylated cannabinoids in hydroalcoholic extract decrease the capsaicin-induced inflammatory rat paw edema through activation of CB1 and CB2 receptors and desensitization of TRPV1 receptor. On the contrary, administration of naloxone has not antagonized the reduction effect of extract on inflammatory paw edema, and it is likely that the effect of the extract has not exerted through opioid receptors.