Inhibition of acute and chronic pain in male rats by aqueous extract of Hypericum perforatum L

Introduction: Hypericum perforatum L was coded in medicinal plants research center of Shaheed Beheshti university and using decoction method was extracted. There are many reports concerning the antidepressant effects of Hypericum perforatum L. (HP), but there are few studies indicating its antinociceptive effects of Hypericum specially Hypericum perforatum L. Materials & Methods: In this experimental study 70 male Sprague- Dawely rats weighing 200-230g were used for all experiments. Both chronic (formalin test) and acute (tail flick test) pain models were used. In this study aqueous extract of HP extract was administered intraperitoneally (i.p.) to evaluate its antinociceptive effect. Intraperitoneally (i.p.) administration of aqueous HP extract was assessed in three doses (200, 400 and 800 mg/kg). Antinociceptive effects compared with sodium salicylate (SS) as a positive control. The 50% letal dose (LD50) of the extract was about 6000 mg/kg. Findings: Results of the experiments show that administration of 300 mg/kg of SS i.p. had no effect on tail-flick latency, while all doses of HP extract increased it. In both phases of formalin test, all doses of HP extract alleviated the animal’s nociception, but SS 300 mg/kg produced antinociception only in the second phase of formalin test. Conclusion: It seems that HP extract effects on both acute and chronic pain. Its peripheral and central mechanisms of action remain to be elucidated.