Effects of Polysaccharides Extracted from Stem Barks on the Spontaneous Contractile Activity of the Ileal Smooth...

Decoctions of stem barks from Aucoumea klaineana, Canarium schweinfurthii, Pentadesma butyracea and Scorodophloeus zenkeri are used against affections of irritable bowel syndrome in Gabonese traditional medicine. In the present study, we aim to determine whether the bark polysaccharides may contribute to the activity of these plants against the symptoms of gastrointestinal disorders. To this end, we investigated the structure and the pharmacological activity of polysaccharides extracted from their stem barks. The pectic and hemicellulose polysaccharides were isolated, and their sugar compositions were determined by gas chromatography. In addition, analysis by MALDI-TOF mass spectrometry of oligosaccharides released after digestion with an endo-xylanase indicated that glucuronoarabinoxylans are the main hemicellulose of stem barks. We then evaluated the influence of the polysaccharide fractions on the spontaneous contractile activity of rat ileal smooth muscle and the cholinergic system. Spasmolytic activity of pectic fractions from all stem barks, as well as lemon polygalacturonic acid, were observed, indicating that these extracts exhibit a myorelaxant activity. In contrast, the bark hemicellulose fractions, as well as commercially available beechwood glucuronoxylan and wheat arabinoxylan, were demonstrated to be able to increase the basal contractile activity of smooth muscle. These data show that, beyond physicochemical effects affecting the bowel water content, plant polysaccharides have also an impact on the spontaneous smooth muscle contractility, the main mechanism involved in the pathophysiology of gastrointestinal disorders.