Antinociceptive activity of ethanolic extract and isolated compounds of Urtica circularis

Ethnopharmacological relevance: Urtica circularis (Hicken) Soraru is a medicinal plant commonly used in traditional medicine to relieve pain in inflammatory processes. Aim of the study: In the present study, the in vivo antinociceptive effect of Urtica circularis ethanolic extract and its isolated compounds has been investigated. Materials and methods: Antinociceptive activity was evaluated through writhing, formalin and hot plate tests in mice. The phytochemical analysis was performed. Results: The extract produced significant inhibition on nociception induced by acetic acid (ED50: 72.2 mg/kg, i.p.) and formalin (ED50: 15.8 mg/kg, i.p.) administered intraperitoneally and also orally. Atropine diminished the activity of the extract in the acetic acid test. In this model, at dose of 10 mg/kg i.p., vitexin was the most active of the isolated compounds (inhibition of 91%), and chlorogenic acid, caffeic acid and vicenin-2 (6,8-di-C-glucosyl apigenin) produced an inhibition of 72%, 41% and 41%, respectively, whereas apigenin did not show any activity. Conclusions: These results suggest that Urtica circularis extract produced antinociception possibly related to the presence of vitexin, chlorogenic, caffeic acid and vicenin-2. The activation of cholinergic systems seems to be involved in the mechanism of antinociception of the extract. (C) 2011 Elsevier Ireland Ltd. All rights reserved.