Anti-nociceptive and anti-inflammatory activities of the methanol extract of Waltheria americana Linn. leaf in experimental animals

Background: Waltheria americana has been used in African folklore for the treatment of minor and complicated ailments like pain, fever, and rheumatism. Aim: To investigate the analgesic and anti-inflammatory potentials of Waltheria americana and its possible mechanism of action in Swiss mice and Wistar rats, respectively. Materials and Methods: Methanol extract of Waltheria americana leaf was evaluated for anti-nociceptive activities (using tail flick, formalin-induced paw licking, and acetic acid-induced writhing tests in mice) and possible mechanisms of action using atropine (5 mg/kg ip), prazosin (1 mg/kg po), glibenclamide (8 mg/kg po), propranolol (40 mg/kg po), naloxone (2 mg/kg ip), nifedipine (10 mg/kg po) using acetic acid, and tail-flick models of analgesia. The anti-inflammatory effect was evaluated in carrageenan-induced paw edema and cotton pellet-induced granuloma tests. Results: Acute toxicity revealed no mortality in the mice up to a dose of 2,000 mg/kg. The phytochemistry revealed the presence of alkaloids, flavonoids, saponins, and terpenoids. The extract (100 or 200 mg/kg) produced inhibition (p < 0.05) both in the formalin-induced paw licking and acetic acid-induced writhing tests. In the thermal test, the extract (200 mg/kg) significantly increased the withdrawal latency. There was a reversal of the analgesic effect of the extract with the cholinergic and opioidergic blockers that significantly produced changes in the analgesic effects of the extract. The extract produced dose-related inhibition of cotton pellet-induced granuloma in rats and carrageenan-induced paw edema in rats. Conclusion: The extract produced anti-inflammatory potentials and anti-nociception through mechanisms that may depend on the cholinergic and opioidergic system.