Inhibition of Experimentally-induced Pain and Inflammation by Methanol Root Extract of Nauclea Latifolia in Wistar Rats

In many African countries, rural and semi-urban dwellers use decoctions of N. latifolia Smith (Rubiaceae) root to treat diseases that are associated with pain, fever and/or inflammation. This study investigated the ability of methanol root extract of Nauclea latifolia (MRENL) to inhibit experimentally-induced pain and inflammation in Wistar rats. Dried and pulverized roots of N. latifolia (65 g) was exhaustively extracted with methanol (500 ml), in a Soxhlet apparatus. Qualitative phytochemical screening and acute toxicity test of MRENL were done following standard procedures. The extract was tested for analgesic activity, using the acetic acid-induced writhing, hot plate, tail immersion and formalin tests, while its anti-inflammatory potential was determined by the carrageenan-induced paw oedema, In the above models MRENL was tested at 400 and 800 mg/kg while acetylsalicylic acid (ASA) served as the reference drug. The antioxidant activity of MRENL was estimated, using the DPPH photometric assay. The phytochemical screening detected alkaloids, flavonoids, tannins, saponins, glycosides and phenols in MRENL. The acute toxicity test recorded neither death nor morbidity, even at the maximum dose of 4000 mg/kg. The results of the acetic acid-induced writhing showed lower number of writhes in the extract-treated groups when compared with the untreated control. The hot plate and the tail immersion tests showed higher pain reaction time in the MRENL-treated rats, when compared with the control. In the formalin test, there was lower number of clinches by the extract-treated rats, when compared with the untreated control, at both phases of the test. There was also reduction of carrageenan-induced paw oedema in rats treated with MRENL when compared with the control. The extract exhibited concentration-dependent antioxidant activity in the DPPH assay. Overall, the activities of MRENL in this study were significant (p < 0.05), dose-related and comparable with ASA, thus supporting the ethnomedical use of Nauclea latifolia root in alleviating pain and inflammation.