Anti-inflammatory and analgesic activities of the aqueous extract of Leonotis leonurus leaves in rats

Leonotis leonurus (L.) R. BR. Lamiaceae is extensively for the treatment of various ailments and in the Eastern Cape province of South Africa, it is used for the treatment of effects of gastrointestinal parasites in animals. There is, however, scanty information on the pharmacological activities of this plant. The aqueous extract from the leaf of L. leonurus was investigated for its analgesic and antiinflammatory properties. Carrageenan and histamine-induced rat paw oedema were conducted to evaluate anti-inflammatory activity, while acetic acid-induced writhing test was conducted to assess the analgesic activity of the plant. The extract was administered intraperitoneally (i.p) to rats at graded doses of 50, 100, 200 mg/kg body weight (BWt). Indomethacin (10 mg/kg BWt) was used as reference drug, whereas the vehicle (2 mg/kg BWt of 0.9% normal saline in Tween-80) was used as negative control. Acute toxicity was tested in rats at doses of 200, 400, 800 and 1600 mg/kg BWt. Compared with the control, the plant extract at 100 and 200 mg/kg BWt significantly (P < 0.05) reduced the formation of carrageenan - induced oedema, while with histamine-induced oedema the difference was insignificant (P > 0.05). In the acetic acid-induced writhing model, the plant extract produced a significant (P < 0.05) reduction in the number of writhes with all test doses and at 100 and 200 mg/kg BWt, the extract produced results that were similar to those of Indomethacin. This study revealed the potential of L. leonurus leaf aqueous extract in reducing pain and inflammation, suggesting that it has some antiinflammatory and analgesic activities, hence, justifying its ethno-veterinary uses. The acute toxicity test showed that the plant is relatively safe to use.Key words: Analgesic, anti-inflammation, indomethacin, Leonotis leonurus, rats