Normal and castor oil-induced intestinal transit and castor oil-induced diarrhoea tests were carried out in mice while gastric emptying and enteropooling tests were conducted in rats following the administration of distilled water (10 ml/kg, p.o.), C. bicolor extract (1–50 mg/kg, p.o.) and loperamide (5 mg/kg, p.o.). The probable mechanisms of action of C. bicolor was investigated following pre-treatment with yohimbine (10 mg/kg, s.c.; α2-adrenoceptor antagonist), pilocarpine (1 mg/kg, s.c.; non-selective muscarinic receptor agonist), prazosin (1 mg/kg, s.c.; α1-adrenoceptor antagonist) and propranolol (1 mg/kg, i.p.; non-selective β-adrenoceptor antagonist) 15 min prior to administration of C. bicolor extract (50 mg/kg, p.o.). After 30 min of pre-treatment with these drugs, the mice were subjected to the castor oil-induced intestinal transit test.
C. bicolor extract did not produce significant (p>0.05) effect on normal intestinal transit unlike loperamide which caused significant (p<0.001) inhibition (61.57%). The extract caused significant (p<0.001) dose-dependent inhibition of castor oil-induced intestinal transit with peak effect, 100% inhibition, elicited at the dose of 50 mg/kg compared to 86.97% inhibition for loperamide. Yohimbine and pilocarpine most significantly (p<0.001) reversed this effect of the extract. In the castor oil-induced diarrhoea test, the extract (1 mg/kg) and loperamide significantly (p<0.05, 0.01) delayed the onset of diarrhoea. For diarrhoea score, the extract (1 and 50 mg/kg) inhibited diarrhoea development (47.53% and 43.83% inhibition, respectively) like loperamide (5 mg/kg; 54.94%). The in vivo antidiarrhoeal index of the extract at 1 and 50 mg/kg was 50.07% and 42.81% respectively compared to 58.15% for loperamide.
The results obtained in this study suggest that the aqueous leaf extract of C. bicolor possess antidiarrhoeal activity due to its anti-motility effect possibly via antagonist action on intestinal muscarinic receptors and agonist action on intestinal α2-adrenoceptors. This justifies the use of the extract in traditional medicine for the treatment of diarrhoea.
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