Digestion and absorption of sugars and sugar substitutes in rat small intestine

The bioavailability of newly developed sugar substitutes was observed by measuring the transmural potential difference (delta PD) evoked by Na+-dependent active transport of glucose, which is supposed to be produced by the hydrolysis of sugar substitutes. delta PD was measured using everted intestinal sac prepared from jejunum of adult rats and compared with the digestibility of sugar substitutes in the mucosal homogenate of everted sac. delta PDs evoked by glucose, maltose or maltosylfructose had almost the same levels, however, the delta PD evoked by sucrose was a little lower. delta PDs evoked by maltitol or palatinose were low, and delta PDs evoked by fructo-oligosaccharides were negligible. The hydrolyzing activities of these sugars and sugar substitutes by the mucosal homogenate were correlated with the delta PDs. A significant positive correlation was observed between delta PDmax of various sugars and sugar substitutes and the Vmax of their corresponding hydrolyzing activities. Also, a significant positive correlation was observed between Kt and Km values of these sugars. These results suggest that the absorption of sugar substitutes is dependent on digestibility by membrane digestive enzymes.