Antinociceptive and anti-inflammatory effects of Olax subscorpioidea Oliv. (Olacaceae) leaf extract in rodents: possible mechanisms of antinociceptive action

Background: Olax subscorpioidea Oliv. (Olacaceae) is a medicinal plant commonly used in traditional medicine to relieve pain in inflammatory processes. Objective: In the present study, the in vivo anti-inflammatory and antinociceptive effects of aqueous leaf extract of Olax subscorpioidea (OLS) and its possible mechanisms of action were investigated. Methods: OLS (50, 100, 200, and 400 mg/kg, p.o.) was administered 1 h before injection of 0.6%v/v acetic acid (10 ml/kg, i.p.), 1%v/v formalin (20 µl) or tail flick tests to evaluate antinociceptive effect while acute anti-inflammatory effect was investigated using xylene-induced ear and carrageenan-induced paw edema models, chronic anti-inflammatory effect was investigated using the complete Freund's adjuvant (CFA) test in rats. Results: OLS (50-400 mg/kg) significantly (P<0.001) reduced acetic acid-induced writhes (68.28%, 50 mg/kg), duration of paw licking/biting by 73.10% (early phase) and 70.50% (late phase), 50 mg/kg) in formalin-test, while also increasing reaction latency by 79.73 and 92.47% at 150 and 180 min, respectively, in tail-flick test, at 400 mg/kg, in comparison to vehicle-treated, control. The antinociceptive effect elicited by the extract was prevented by pretreatment of mice with metergoline (5-HT2 receptor antagonist), sulpiride (dopamine D2 receptor antagonist) and glibenclamide (K-ATP sensitive channels blocker). The extract (400 mg/kg) or diclofenac (20 mg/kg) inhibited carrageenan-induced oedema by 73.08% and 80.77%, respectively, 5 h post-carrageenan injection. Moreover, OLS (400 mg/kg) significantly reduced CFAinduced chronic inflammation by 85.30%, on day 12 post-CFA injection which was similar to the effect of celecoxib (76.50% inhibition). Conversely, OLS failed to inhibit xylene-induced ear edema. Conclusion: Olax subscorpioidea possesses antinociceptive effect through interaction with 5-HT2, dopamine D2 and sensitive potassium ATP channels as well anti-inflammatory effect. Thus confirm its folkloric uses in the treatment of painful and inflammatory conditions.