In vitro activity of methanol extract of Citrullus lanatus Thunb. (Curcubitaceae) fruit rind on isolated gastrointestinal tissues of rabbit and guinea pig

Abstract

The small intestine undergoes segmental contractions and peristaltic waves causing onward movement of its contents [1]. Stimulation of parasympathetic division of the autonomic nervous system usually causes contractions by releasing acetylcholine, which increases activity of myenteric plexus, or by direct excitatory effect on smooth muscle of the gut [2]. This research evaluates effects of methanol extract of Citrullus lanatus (watermelon) fruit rind on isolated gastrointestinal tissues of rabbit and guinea pig. Phytochemical screening was evaluated for presence of chemical constituents. Flavonoids, steroids, alkaloids, carbohydrates, saponins and triterpenes were found to be present while anthraquinones were absent. The oral median lethal dose was established to be safe up to the highest dose of 5000 mg/kg in swiss albino mice. Intrinsic activities of MECL fruit rind on isolated guinea-pig ileum and rabbit jejunum were evaluated. MECL showed biphasic response on isolated gastrointestinal tissues where at lower log concentrations (-1.40 x 10^-6 – 1.20 x 10^-6 g/ml); spasmolytic effect was recorded on the microdynamometer, while higher log concentrations (1.51 x 10^-6 – 1.60 x 10^-6 g/ml) produced spasmogenic response. MECL was interacted with acetylcholine (1x 10^-5 mg/ml), histamine (1x 10^-5 mg/ml) and antagonists like atropine (1x10^-5 mg/ml) and mepyramine. The action of MECL on gastrointestinal tissue may be linked partly to its direct inhibitory effect on cholinergic receptor binding sites, propuls ion of gastrointestinal muscle or due to activity of phytoconstituents present. Biphasic effects of MECL on isolated gastrointestinal tissue validates its use traditionally for treating diarrhoea and constipation in Northern Nigeria.

Keywords: Diarrhoea, Citrullus lanatus (watermelon) fruit rind, acetylcholine, atropine, biphasic response