A methanolic extract from Senna garrettiana (S. garrettiana) heartwood was prepared and then a fractionation process was performed to obtain hexane, dichloromethane, ethyl acetate, and aqueous fractions. An antinociceptive screening of each fraction was carried out using the acetic acid-induced writhing in mice. Among all the fractions, the ethyl acetate fraction showed the highest activity on the writhing test. The ethyl acetate fraction was separated to obtain a piceatannol-rich extract. The S. garrettiana extract contains 11.70 % w/w and 39.16 % w/w piceatannol in the ethyl acetate fraction and the piceatannol-rich extract, respectively. The analgesic activities of the ethyl acetate fraction (50, 100 and 200 mg/kg) and the piceatannol-rich extract (10, 20 and 40 mg/kg) were evaluated by the acetic acid-induced writhing test, hot-plate test and formalin test. The antipyretic activity of these extracts was assessed on yeast’s-induced pyrexia in rats. The acute toxicity was also investigated. In the acute toxicity study, no lethality was observed after the oral administration of methanolic extract of S. garrettiana heartwood even at a high dose of 5 g/kg in mice. The oral administration of the ethyl acetate fraction decreased the number of writhings in a dose dependent manner with 54.9 %, 68.5 %, and 71.0 % inhibition, respectively. A similar result was also observed after the oral administration of the piceatannol-rich extract with 53.1%, 69.2% and 80.3% inhibition, respectively. In the formalin test, either the ethyl acetate fraction or the piceatannol-rich extract significantly diminished the licking time in both the early and late phases. Neither the ethyl acetate nor the piceatannol-rich extract had any effect on heat-induced pain. The ethyl acetate fraction at the same dosage range significantly decreased the rat rectal temperature at 2, 3 and 4 hrs. The piceatannol-rich extract at a dose of 20 and 40 mg/kg suppressed the rectal temperature over the same time intervals. These results demonstrated that the ethyl acetate fraction and the piceatannol-rich extract from S. garrettiana heartwood possessed analgesic and antipyretic activities with an apparently similar efficacy. The probable mechanism(s) of analgesic actions might be mediated by both the peripheral and central mechanisms.
