Background: Vernonia amygdalina is well known as a medicinal plant in folk medicine as anti-diabetic, anthelmintic, antimalarial, laxative/purgative, and expectorant amongst others. Aim: This study was conducted to investigate the mechanisms of action of the anti-nociceptive and anti-inflammatory of Vernonia amygdalina. Materials and Methods: Methanol extract of Vernonia amygdalina leaf (MEVa) was evaluated for anti-nociceptive effect and possible mechanisms of action in the presence naloxone (1mg/kg), atropine (2mg/kg) and prazosin (1mg/kg) using acetic acid writhing test in mice. The anti-inflammatory effect was evaluated in carrageenan hind paw edema and carrageenan air pouch models. protein concentration, malondialdehyde, glutathione and superoxide dismutase assays were carried out for its anti-oxidative activities in inflammation. Hematoxylin and eosin staining were used to assess the level of inflammation. Results: From the acetic acid writhing test results, MEVa (50,100mg/kg) showed significant anti-nociceptive effect. Naloxone reversed the antinociceptive effect in comparison to atropine and prazosin. MEVa (50, 100 and 200 mg/kg) showed dose dependent inhibition of oedema (41.4, 63.0, 68.6%) at 4 h post carrageenan injection. In the carrageenan air pouch model, MEVa (200 mg/kg) reduced fluid exudation, infiltrating leucocytes and protein concentration. MEVa reduced MDA and prevented the depletion of GSH while increasing SOD activities. The histological study showed a reduction in the infiltration of inflammatory cells in MEVa-treated groups. Conclusion: Vernonia amygdalina might be carrying out its anti-nociceptive mechanism via the opioidergic system and its anti-inflammatory mechanism via reduction of leucocyte migration and lipid peroxidation.
Key words: Vernonia amygdalina, opioidergic system, anti-inflammatory, anti-nociceptive, malondialdehyde
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