Evaluation of anti-motility and anti-secretory effects of Annona muricata leaves extract in castor oil-induced diarrhoeic rats

Abstract

Diarrhoea is a debilitating gastrointestinal disorder commonly affecting all age groups in the developing world due to lifestyle, hygiene and environmental factors. Most drugs used in the treatment of this disease have side effects and are out of reach in many rural areas. Hence a need to search for more tolerable, affordable and effective anti-diarrhoeal drugs from medicinal plants. The study evaluated the anti-motility and anti-secretory properties and phytochemical constituents of the leaves of Annona muricata. The dried coarse leaves were cold-macerated in methanol (95%v/v) and the resulting extract partitioned successively in n-hexane, ethyl acetate, n-butanol and water to afford their respective fractions using the solvent partition method. Phytochemical screening was conducted using standard methods while acute toxicity of the extract was carried out by the method of Lorke. The anti-motility and antisecretory studies were evaluated using the castor oil-induced diarrhea model in experimental rats. The extraction of the leaves and fractionation of methanol extract yielded 3.5%w/w of the extract and 0.46, 1.45, 0.62 and 0.62%w/w of the n-hexane, ethyl acetate n-butanol and aqueous partitions respectively. The acute toxicity study indicated that there were no unusual behavioural changes and mortality at an administered dose of 5000 mg of extract per kg of mice. The extract (200 and 400 mg/kg) exhibited non-dose-dependent anti-diarrheal activity. The extract and its ethyl acetate fraction (200 and 400 mg/kg) elicited a significant anti-motility activity (p < 0.05) compared to untreated. Pre-treatment of rats with ethyl acetate fraction (400 mg/kg) significantly inhibited the action of carbachol on gastric emptying (82.0 ± 5.0% vs. 28.1 ± 8.2%),) and gastrointestinal transit (83.5 ± 7.6%, vs 30.10 ± 5.2%) but with no significant effect on the actions of serotonin and metoclopramide. The extract and ethyl acetate fraction of A. muricata demonstrated a significant anti-motility activity which could be mediated by the anticholinergic effect of its phytoconstituents.