Intestinal absorption of sucrose in man: interrelation of hydrolysis and monosaccharide product absorption.

Disaccharides are hydrolyzed by their specific enzymes present in the intestinal mucosa (1-3). Although some current textbooks still state that these enzymes are secreted into the intestinal lumen (4-7), the concentrations of monosaccharide products free in intestinal contents during disaccharide absorption in vitro (8-10) have been found insufficient to support the concept of intraluminal hydrolysis. In addition, the low disaccharidase activity of intestinal contents during the absorption process in vivo (11-13) strongly suggests that the disaccharide either enters the cell before being hydrolyzed or else is hydrolyzed at the cell surface by mucosa-bound enzyme. The released monosaccharide products presumedly are then transported across the intestinal cell (8, 14, 15). Little information is available that relates disaccharide hydrolysis to absorption of the component monosaccharides. Wilson and Vincent (14) commented on the accumulation of monosaccharides in the mucosal medium during the process of disaccharide absorption in hamster gut sac preparations, and Dahlqvist and Thomson have reported that large amounts of free fructose accumulate intraluminally during sucrose absorption in the intact rat (16). Despite these findings in animals, Dahlqvist and Borgstr6m found little free intraluminal monosaccharides during the process of disaccharide absorption in man (12). It was recently demonstrated, however, that appreciable