Relationship between changes in lactase activity and monosaccharide uptake in the small intestine of the rat during development.

The relationship between changes in intestinal lactase activity and monosaccharide uptake was studied in rats of different ages using the technique of intestinal everted sacs. In the postweaning period there is a sharp decrease in the rate of glucose and galactose uptake by the small intestinal mucosa. This change occurs simultaneously with a decrease in lactase activity in the tissue. The kinetic analysis showed a lower Vmax for monosaccharide uptake in the 50-days-old rats as compared with the fifteen-days-old animals, with no change in the apparent Kt. The addition of Tris+ (40 mM) to the incubation media was found to produce a decrease in Vmax for monosaccharide uptake only in the suckling rats but not in the 50-days-old animals; the K1 remained unchanged. Tris+, at the concentration used had previously been shown to completely inhibit lactase activity in homogenates of small intestinal mucosa. These observations lead us to postulate the lactase in the suckling rat might possess a translocating role for sugar, in addition to its hydrolytic function. The decrease in sugar uptake after weaning could be explained by the disappearance of this role.