IN VITRO AND IN VIVO ACTIVITIES OF THE STEM BARK EXTRACT OF Anacardium occidentale LINN. ON GUT MOTILITY IN LABORATORY RODENTS

Abstract

Diarrhoea is a disease characterised by gut smooth muscle dysfunction associated with increased motility. Anacardium occidentale (Ao) stem bark possesses strong anti-diarrhoeal effect; however the mechanism of this effect has not been fully elucidated. This study was designed to investigate the anti-diarrhoeal mechanisms of Anacardium occidentale stem bark in laboratory rodents.

The Ao was collected from a farm in Abeokuta, Ogun State and authenticated at the Department of Botany, University of Ibadan, Ibadan (UIH No.: 22599). The Ao methanol extract (AoME) was obtained by Soxhlet extraction. Solvent partitioning of AoME with Hexane (AoHF), ethylacetate (AoEF) and methanol (AoMF) was carried out. The three fractions were subjected to Gas Chromatography-Mass Spectrometer (GC-MS). The in vitro activity of AoME was evaluated on isolated Guinea Pig Ileum (GPI). Gastrointestinal Transit (GT) was measured using distance travelled by charcoal meal. Gastric Emptying (GE) was measured using phenol red. Diarrhoea was induced with castor oil. The AoME and its three fractions (0.0067-5.30 mg/mL) were tested on GPI. Interaction of AoEF with acetylcholine (1.8-14.6 x 10-6 M), histamine (3.0-2.4 x 10-6 M), serotonin (0.9-6.9 x 10-6 M), atropine (10-4 M), hexamethonium (10-3 M) and L-NAME (200 x 10-6 M) were investigated on GPI. Twenty-five male Wistar rats (160.0-174.0 g) used for GT experiment were distributed into 5 groups (n=5) and treated as follows; control (normal saline, 1 mL/kg), AoME (200, 400 and 800 mg/kg) and AoEF (400 mg/kg). Sixty male Swiss mice (15.0-21.0 g) used for Gastric Emptying (GE) and anti-diarrhoeal studies were distributed into 12 groups (n=5); control (distilled water, 1 mL/kg), loperamide (2.5 mg/kg), AoME (200, 400 and 800 mg/kg), AoEF (400 mg/kg), carbachol (10 mg/kg), serotonin (10 mg/kg), metoclopramide (30 mg/kg), AoEF+carbachol, AoEF+serotonin and AoEF+metoclopramide. Data were subjected to descriptive statistics and ANOVA at α0.05.

The GC-MS analysis of AoEF revealed 15 components of which oleic (45.51%) and 11-octadecenoic acids (20.57%) were prominent. The AoME, AoEF, AoMF and AoHF exerted concentration-dependent relaxation of GPI (IC50:1.5 x 10-4, 1.3 x 10 -5, 1.7 x 10-5 and 1.5 x 10-5 mg/mL, respectively). Atropine reduced the relaxant effect of AoEF (2.7±0.3 vs 5.0±0.05 mm) The AoEF reduced the contractile activities of acetylcholine (EC50: 0.3 x 10-5 vs 6.8 x 10-5 M), histamine (EC50: 0.1 x 10-6 against 9.4 x10-6 M) and serotonin (EC50: 0.1 x 10-6 vs 5.7 x 10-6M) on GPI. The GT was significantly decreased by AoEF (47.9 ± 3.5%) and AoME (200, 400 and 800 mg/kg) (56.9±1.8, 51.9±1.2, 49.9±0.4%) compared to control (70.4±2.0%). The AoME (200, 400 and 800 mg/kg) significantly delayed onset of diarrhoea (134.0±5.2, 157.1±8.9, 219.0±10.6 min) compared to control (62.6±3.0 min). The AoEF inhibited the effect of carbachol on GT (29.0±2.6 vs 74.3±6.6 %) and GE (26.1±3.1 against 74.8±5.9 %).

Anarcardium occidentale stem bark inhibited the contraction of guinea pig ileum smooth muscle and reduced gastrointestinal transit in vivo. These effects were mediated via mechanisms related to inhibition of acetylcholine, histamine and serotonin receptors in the stomach and ileum.