Antinociceptive effect of aqueous extracts from the bark of Croton guatemalensis Lotsy in mice.

Croton guatemalensis Lotsy (CGL), known as "copalchi" in Chiapas, Mexico, is used for the treatment of fever, abdominal pain and malaria and also as a remedy for chills and for treating rheumatism. The aim of this study was to evaluate whether aqueous extracts from the bark of this plant possesses indeed antinociceptive properties by using two different animal models of nociception, the acetic acid-induced writhing test and the hot plate model. The results showed that i.p. administration of this extract (0, 100, 200 and 400 mg/kg) 30 min prior testing had significant dose-dependent antinociceptive effects in the acetic acid-induced writhing test and that the reduction of writhings (85.5 % as compared to the control) at the highest dose tested is similar to that exhibited by dipyrone (250 mg/kg). This effect was not reversed by naloxone, a non-selective opioid receptor antagonist, suggesting that the endogenous opioid system does not underlie the antinociceptive effects of CGL in the acetic acid-induced writhing test. No effects were however observed in the hot-plate model. Our results indicate that aqueous extracts from Croton guatemalensis bark contain pharmacologically active constituents endowed with antinociceptive activity. It is suggested that cyclooxygenase inhibition might be at least partially involved in the antinociceptive effects of this extract.