The present study establishes the analgesic and anti-pyretic activities of the ethanolic extract of leaves of Catharanthus roseus in the models used. Since antipyretic and analgesic activities are commonly mentioned as characteristic of drugs or compounds which have an inhibitory effect on prostaglandin biosynthesis, the yeast induced hyperthermia in rat model was, therefore, employed to investigate the antipyretic activity of this plant. It was found that the ethanolic extract at the dose of 100, 200 and 400 mg/kg b.w. showed a significant decrease in rectal temperature similar to that shown by the standard drug, paracetamol. This result seems to support the view that the extract has an inhibitory effect on prostaglandin biosynthesis because prostaglandin is believed to be a regulator of body temperature. The analgesic activity of ethanolic extract was evaluated using the hot plate method and acetic acid induced writhing test in mice. The hot plate method is useful in detecting centrally acting analgesics, whereas writhing method is useful to detect peripheral analgesic effects. Acetic acid, which is used as an inducer for writhing syndrome, causes algesia by liberation of endogenous substances, which then excite the pain nerve endings. The fact that ethanolic extract of Catharanthus roseus showed analgesic activity in both the models studied, indicate that this effect could be due to the presence of two components; one acting centrally and the other via peripheral route. As the phytochemical screening has shown the presence of alkaloids and flavonoids, its potent activity may be attributed to the presence of these phytoconstituents.
