Analgesic effect of Irvingia gabonensis stem bark extract

Irvingia gabonensis is used medicinally in most parts of tropical Africa for the treatment of a number of ailments. In West Africa the Mende tribe of Sierra Leone uses the stem bark to relieve pain. In order to establish a pharmacological rationale for the traditional use of this plant as a remedy for pain, the water and ethanol extracts of the powdered stem bark were screened for analgesic activity and compared with standard analgesic drugs. The water extract and morphine protected the mice from heat-induced pain. In contrast, the ethanol extract and metamizole sodium showed very low level of analgesic activity in this test. However, using tail pressure as a source of pain, the water and ethanol extracts, metamizole sodium and morphine offered protection to the mice against pain stimuli. Morphine and the water extract were more potent as analgesic agents in heat than non-heat pain test. The analgesic effects of the water extract and morphine were blocked by a non-selective opioid receptor antagonist, naloxone in both tests, whereas the analgesic effects of the ethanol extract and metamizole sodium were not antagonized by the same dose of the opioid antagonist. The data presented in this study suggest that the active principle(s) in the water extract has analgesic profile similar to that of the narcotic analgesic and the ethanol extract might contain compound(s) that behave like non-narcotic analgesic agent. These findings provide for the first time the pharmacological basis for the folkloric use of Irvingia gabonensis in the relief of pain.