ANTI-NOCICEPTIVE ACTIVITY AND POSSIBLE MECHANISMS OF ACTION OF AQUEOUS ROOT EXTRACT OF STROPHANTHUS HISPIDUS DC (APOCYNACEAE)

Background: Decoction of the root of Strophanthus hispidus is highly valued in Africa herbal medicine for the treatment of skin diseases, leprosy, ulcers, malaria, dysentery, gonorrhea and in the management of inflammation. Objective: The present study aimed to evaluate the anti-nociceptive effect of the aqueous root extract of Strophanthus hispidus focusing on central involvement as well as exploring the possible mechanisms of action in Swiss albino mice of both sexes. Methods: The aqueous extract was administered in doses of 50, 100, and 200 mg kg^-1 via oral route to the animals used in the various models- acetic acid-induced writhing, formalin, Haffner’s tail clip, hot plate and tail immersion tests. Results: In each of the models, the aqueous root extract of Strophanthus hispidus each possesses a significant (p< 0.05, p< 0.01, p< 0.001) anti-nociceptive effect in a dose-dependent manner. The anti-nociceptive activity of the extract may be mediated through central and peripheral mechanisms. The involvement of opioid and dopamine (D₂) receptors in anti-nociception were also established.  The effect of the extract was comparable to that produced by peripheral analgesics, the NSAIDs (aspirin) and centrally acting analgesic opioids (morphine), both used as positive control in several models to access anti-nociception. Conclusion: These findings showed that S. hispidus possesses anti-nociceptive effect mediated both peripherally and centrally.