Abstract:
Pleurotus ostreatus. (Jacquin: Fries) P. Kummer (Tricholomataceae) was subjected to an antinociceptive activity-guided fractionation procedure in order to identify the fraction having highest activity. Three extracts, namely, acetone, dichloromethane, and hexane, were prepared at room temperature using fresh P. ostreatus., and 500 mg/kg was orally administered to male rats. The acetone extract showed significant antinociceptive activity with the hot-plate assay (male, 68%; p < 0.05), whereas dichloromethane and hexane extracts did not show significant activity. The same dose of acetone extract with female rats in the diestrous stage also showed prolongation of reaction time using the hot-plate test (female, 54%; p < 0.05). None of the extracts showed a significant increase in reaction time with the tail-flick test. The acetone extract was further fractionated by solvent partition to obtain four fractions (hexane, dichloromethane, ethyl acetate, and aqueous). Of these extracts, only the aqueous fraction showed marked prolongation in reaction time with the hot-plate test (500 mg/kg dose) on both male rats and on female rats in the diestrous stage (male, 37%; female, 26%). The aqueous fraction, following purification on a reverse phase column, yielded AqFrA-1, AqFrA-2, and AqFrA-3. Oral administration of a 500 mg/kg dose of these three fractions also showed marked prolongation in reaction time with the hot-plate test after 1 h of treatment (AqFrA-1, 26%; AqFrA-2, 69%; AqFrA-3, 101%). The effect was highest in AqFrA-3 at 1 h of treatment, and the effect lasted for 3 h. Hence, we can conclude that the compounds responsible for the activity have very high polarity. The acetone extract of P. ostreatus. did not induce a membrane-stabilizing effect and did not cause prostaglandin inhibition. Naloxone blocked the antinociceptive activity in the hot-plate test upon feeding of 500 mg/kg of acetone extract of P. ostreatus., indicating the mechanism of action is via opioid receptor mediation.
