Cholinergic and anticholinesterase activities of total protein extract of Morinda morindoïdes on isolated rabbit duodenum

Abstract

Traditional herbal medicines such as Morinda morindoïdes are used for treatment of intestinal disorders including constipation in Ivory Coast. The aim of present study was to investigate the effect of total protein of Morinda morindoïdes extract (PT-Mm) on rabbit duodenum contractility and the involved possible mechanism(s). PT-Mm was extracted according to the saturation method of Dawson with ammonium sulfate. The cholinergic effect of the extract was determined by the in vitro organ bath method. The acetylcholinesterase (AChE) extracted from rabbit duodenum and it activity was determined by Ellman’s assay using acetylthiocholine (ASCh) as substrate. PT-Mm concentrations (40, 80, 120 and 200 μg/mL) showed dose-dependent effect a both tonicity and amplitude of the duodenum spontaneous contractions. The effective concentration which induces 50% effect of PT-Mm (EC₅₀) was obtained with 68.57 ± 0.89 μg/mL. The antagonist tests carried out showed a considerable reduction (90%) in the amplitudes of duodenal contractions in the presence of atropine, but with nifedipine, the contractions were completely inhibited. PT-Mm also exerted non-competitive inhibition on AChE (Vmax = 5687 mM/min and K_M = 578 μM). These results suggest that PT-Mm could stimulate duodenum smooth muscle contraction because it contains anti-AChE and cholinomimetic substances which, through muscarinic receptors, increase Ca²⁺ mobilization from extracellular. Therefore, PT-Mm could be used as a laxative, due to its stimulating effects on duodenal contractility.

Keywords: Morinda morindoides, acetylcholinesterase, duodenum, contraction