Proabsorptive action of gum arabic: Regulation of nitric oxide metabolism in the basolateral potassium channel of the small intestine

Background: Gum arabic, a high-molecular-weight natural polysaccharide, has been shown to have proabsorptive properties in animal models of gastrointe stinal disease that involve nitric oxide (NO). Gum arabic may indirectly re gulate NO metabolism by creating an outward NO gradient, thus altering othe r intracellular NO-dependent mechanisms such as gating of the potassium (K) channel. This hypothesis was further investigated using the K+ channel bl ocker, glybenclamide. Methods: Following intraperitoneal injection of 4.5 mg/kg glybenclamide or saline, the jejunum of anesthetized rats was perfused with a standard oral rehydration solution in the presence or absence of 2.5 g/L gum arabic, as w ell as 1 mmol/L L-arginine to enhance NO production. Sodium, net water, and glucose absorption and unidirectional water movement were determined. Results: Gum arabic showed regulatory capacity for NO-dependent metabolism by reducing net water absorption in the absence of arginine, and sodium abs orption after arginine stimulation, in the absence of glybenclamide. Additi on of gum arabic to oral rehydration solution. in glybenclamide pretreated animals, and in the absence of arginine, normalized sodium absorption, but was less effective in restoring net water transport. Injection of glybencla mide sharply decreased all absorption markers in arginine supplemented oral rehydration solution, which were at least partially restored by addition o f gum arabic to the oral rehydration solution. In the presence of glybencla mide, the effects of arginine became antiabsorptive, as had those observed in preceding studies with high arginine concentration. Gum arabic partially or fully reversed alterations produced by perfused 1 mmol/L arginine. Conclusions: Some of the effects of gum arabic on the small intestine are l ikely caused by its ability to remove NO as it diffuses into the lumen, thu s reducing NO concentration in the enterocyte and indirectly affecting the absorptive/secretory response of the gut, which leads to normalization of a bsorptive function. These findings are consistent with the previously shown gum arabic-scavenging properties of NO and support a potential therapeutic role for this product.