Dietary induction of intestinal fructose absorption in weaning rats.

The onset of developmentally induced changes in rat intestinal nutrient absorption is well known: brushborder glucose and fructose transporters appear during prenatal and postweaning periods, respectively. The onset of diet-induced regulation, however, is unknown. To test the hypothesis that intestinal glucose and fructose transport is regulated by diet during weaning and postweaning, we fed rats experimental diets containing high (65%) glucose, high fructose, high sucrose, or no carbohydrate. In 16-d-old rats, 6 d of dietary fructose but not glucose modestly increased fructose absorption in everted sleeves of small intestine (SI) over control (mother-fed with access to chow) rats (p = 0.02). In 21-d-old (age when sucrase is present) rats, dietary fructose and sucrose each dramatically enhanced (p = 0.004) fructose absorption over control rats and rats fed high glucose or carbohydrate-free diets. In 35- (postweaning) and 60-d-old rats, dietary fructose and sucrose, but not glucose, stimulated fructose absorption (p < 0.005) over rats fed a carbohydrate-free diet. In all age groups, intestinal glucose absorption was independent of diet (p > or = 0.12), and experimental rats grew at the same rate as control rats. Absorption of fructose or glucose was 2-3 times greater in the proximal and middle than in the distal SI. Intestinal fructose, but not glucose, absorption can be induced by diet even during early weaning, and dietary fructose followed by sucrose is the most potent inducer. Thus, mechanisms of diet regulation can change ontogenetically, and early introduction of certain diets can induce appearance of certain nutrient transporters.