In previous studies, the aqueous extract of Trema guineensis
(Ulmaceae) was shown to increase rabbit duodenal contractions. The aim of this study was to evaluate the mechanism of the stimulation of the rabbit duodenum by the aqueous extract of Trema guineensis
The in vitro
organ bath method was used in our experiments. The enzyme was extracted from rabbit duodenum. The acetylcholinesterase (AChE) activity was determined by Ellman's assay using acethylthiocholine iodide as substrate. The rate of hydrolysis of acetylcholinesterase was monitored at 412 nm using a spectrophotometer.
The effective concentration which induces 50% effect of Hypo+ (EC50) was obtained with 8 x10-2
mg/ml of Hypo+. The tests carried out in the presence of atropine showed a considerable reduction in the amplitudes of intestinal contractions. Hypo+ exerted mixed competitive inhibition on acetylcholinesterase (Vmax
= 8.33 µM/min and KM
= 6.25 x 10-4
M). These results indicate that the crude extract of Trema guineensis contains anti-AChE and cholinomimetic substances. These two properties can explain the increase of duodenal contraction by Hypo+.
These results support the use of Trema guineensis as a laxative due to its stimulating effects on duodenal contractility.