The Enzyme Activity of Dogs' Intestinal Juice and Its Relation to Intestinal Digestion

Abstract

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Studies of Intestinal Digestion and Absorption in the Human1

“…It is therefore tempting to draw the conclusion that the presence of disaccharide splitting enzymes in the succus entericus is of no importance for the absorption of the disaccharides, the action of these enzymes being confined to the intestinal cells. This opinion is in accord with the conclusions drawn by Cajori (42) in experiments on intestinal loops of dogs that sucrose and lactose are absorbed much more rapidly than would be predicted on the basis of the enzymatic activity of the intestinal juice. Based on a study on a comparison of the concentration of lactase in the intestinal content and in the mucosal cells Heilskov (43) has recently arrived at the opposite conclusion, i.e., the lactase is secreted to and acts in the intestinal content.…”

Sugar malabsorption due to deficiencies of disaccharidase activities and of monosaccharide transport.

“…But studies in man during the past decade (Borgstrom, Dahlqvist, Lundh, and Sjovall, 1957; Dahlqvist and Borgstrom, 1961) demonstrated that disaccharidase activity in the intestinal lumen was extremely limited and did not account for the amount of carbohydrate absorbed. They further indicated that the majority of disaccharides were absorbed unhydrolysed and split intracellularly, a fact that accorded well with experimental findings (Cajori, 1933;Fridhandler and Quastel, 1955).…”

“…But studies in man during the past decade (Borgstrom, Dahlqvist, Lundh, and Sjovall, 1957; Dahlqvist and Borgstrom, 1961) demonstrated that disaccharidase activity in the intestinal lumen was extremely limited and did not account for the amount of carbohydrate absorbed. They further indicated that the majority of disaccharides were absorbed unhydrolysed and split intracellularly, a fact that accorded well with experimental findings (Cajori, 1933;Fridhandler and Quastel, 1955).The problem of localization of the sugar-splitting enzymes was brought nearer its solution by Miller and Crane (1961), who were able to separate the brush-border from the rest of the intestinal mucosa of the hamster, and found that the whole of the enzyme activity of the mucosa was accounted for by this layer. (-galactosidase (lactase) activity had been localized in the microsomes of the rat intestinal mucosa by Doell and Kretchmer (1962), while Dahlqvist and Brun (1962), employing histochemical methods for the recognition of invertase and trehalase in various animal tissues, associated their activity with cytoplasmic granules.…”

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

“…Although some current textbooks still state that these enzymes are secreted into the intestinal lumen (4)(5)(6)(7), the concentrations of monosaccharide products free in intestinal contents during disaccharide absorption in vitro (8)(9)(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)(12)(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).…”