Antagonism of antinociceptive effect of hydro-ethanolic extract of Hypericum perforatum Linn. by a non selective opioid receptor antagonist, naloxone.

Hydro-ethanolic crude extract of Hypericum perforatum Linn. family hypericaceae (St. John's Wort) aerial parts (Hp. Cr) was studied for its possible antinociceptive effect against acetic acid-induced abdominal constriction assay in mice. Hp. Cr (10-20 mg kg(-1)), opium (10-30 mg kg(-1)), morphine (0.75-3.0 mg kg(-1)) and aspirin (50-100 mg kg(-1)) showed dose-dependent antinociceptive effect. In animals treated with naloxone (0.5 mg kg(-1)), the antinociceptive effect of Hp. Cr was significantly reduced similar to that of opium, while effect of aspirin remained unchanged. These results suggest that the antinociceptive effect of Hypericum perforatum may be mediated through activation of opioid receptors.