Analgesic and anti-ulcerogenic effects of a polar extract from leaves of Vernonia condensata.

An aqueous crude extract and a polar fraction derived from this extract were prepared from leaves of Vernonia condensata Baker and assessed in standard rodent models of algesia and ulcerogenesis. Oral pretreatment with the lyophilized crude extract (200 mg/kg) significantly reduced mouse writhing counts caused by the i.p. injection of increasing concentrations (0.6-1.2%) of acetic acid (0.1 ml/10 g). In doses ranging from 50 to 400 mg/kg, the crude extract inhibited dose-dependently mouse writhing induced by acetic acid (0.6%) (ED50 = 241 mg/kg) and also markedly increased the sleeping time induced by thiopental. The polar fraction, prepared by washing out the crude extract with chloroform, did not alter sleeping time but kept the analgesic activity (ED50 = 154 mg/kg), indicating that these effects are indeed dissociated. In contrast, the tail flick response in the immersion test was not modified by the crude extract or the polar fraction. The relative potency with which polar fraction and non-steroidal anti-inflammatory drugs inhibited mouse writhing caused by acetic acid in mice was indomethacin >> dypirone > polar fraction > aspirin. Furthermore, the combined polar fraction/aspirin or polar fraction/indomethacin treatments presented a marked synergistic effect, in contrast to what was observed when submaximal doses of indomethacin and aspirin were coadministered, suggesting that polar fraction and aspirin like drugs may have complementary analgesic actions. Finally, despite being able to potentiate the analgesic effect of indomethacin in mouse writhing caused by acetic acid, the pretreatment with the polar fraction (200 mg/kg, oral) significantly prevented indomethacin-induced ulcers in rats.(ABSTRACT TRUNCATED AT 250 WORDS)