Antinociceptive activity of ethanolic extract and isolated compounds of Urtica circularis

Urtica circularis (Hicken) Sorarú is a medicinal plant commonly used in traditional medicine to relieve pain in inflammatory processes. In the present study, the in vivo antinociceptive effect of Urtica circularis ethanolic extract and its isolated compounds has been investigated. Antinociceptive activity was evaluated through writhing, formalin and hot plate tests in mice. The phytochemical analysis was performed. The extract produced significant inhibition on nociception induced by acetic acid (ED50: 72.2mg/kg, i.p.) and formalin (ED50: 15.8mg/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 10mg/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. 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.