Antinociceptive activity of Syzygium jambos leaves extract on rats

Syzygium jambos (L.) Alston (Myrtaceae) (syn Eugenia jambos) is a widespread medicinal plant traditionally used in sub-Saharan Africa to treat several diseases. The analgesic potential of leaf hydro-alcoholic extracts was assessed in rats. Hot plate and formalin tests were used to estimate cutaneous nociception whereas measurements of forelimb grip force were done to assess muscular nociception under normal and inflammatory conditions. In the hot plate test, Syzygium jambos extract produced a significant increase in the withdrawal response latencies in a dose-dependant manner (10-300 mg/kg i.p.) and with a maximal effect (analgesic efficacy) similar to that of morphine. The extract (100-300 mg/kg i.p.) significantly reduced pain scores in all the phases of the formalin test with an analgesic efficacy higher than that shown by diclofenac. Although the extract (300 mg/kg) did not alter grip force in intact rats, it reversed the reduction in grip force induced by bilateral injection carrageenan in the forelimb triceps. This analgesic effect of the extract on muscle hyperalgesia was not antagonized, but enhanced, by naloxone. Thus, the Syzygium jambos extract has remarkable analgesic effects on both cutaneous and deep muscle pain that is not mediated by opioid receptors.