Antinociceptive effects of Randia siamensis extract and its constituent, pseudoginsenoside-RP1 in experimental animals.

Analgesic activities of Randia siamensis CRAIB (R. siamensis) extract and pseudoginsenoside-RP1, a constituent of the extract, were examined in the writhing test, hot plate test and Randall-Selitto test. Oral administration of R. siamensis extract dose-dependently decreased the number of writhings and stretchings induced by 0.6% acetic acid in the writhing test in mice. Moreover, in the Randall-Selitto test in rats, the extract raised the nociceptive threshold of the carrageenan-inflamed but not of non-inflamed paw. It did not affect the nociceptive response in the hot plate test in mice. The R. siamensis extract did not affect hexobarbital-induced sleep or spontaneous motor activity in mice, suggesting that it has no sedative effect. Pseudoginsenoside-RP1 produced similar effects to the R. siamensis extract, but its effective doses in the analgesic tests were lower than those with the extract. These results suggest that R. siamensis extract produces anti-nociceptive actions similar to those of a peripherally acting analgesic drug aspirin, and that pseudoginsenoside-RP1 may partly contribute, but is not the main contributor, to the antinociceptive action of the extract.