Annual Meeting of the North American Society for Pediatric Gastroenterology and Nutrition; Orlando, October 22-24, 1998
INDUCTION OF INTESTINAL FRUCTOSE TRANSPORT AND GLUT5 mRNA EXPRESSION IN HYPOTHYROID PUPS
Intestinal fructose transport typically increases two to three fold after weaning in rats allowed to wean normally but can be enhanced during early weaning (15-21 d of age) by precocious introduction of high fructose diets. Increases in serum thyroxine levels coincide with the onset of weaning. To investigate the potential role of the thyroxine surge in the enhancement of fructose uptake by diet, we made rat pups hypothyroid by giving the dam 0.01% propyl-thiouracil as drinking water from the 18th d of gestation. Hypothyroid pups and their age-matched euthyroid controls were then gavage fed high fructose or high glucose solutions (2ml/100g body weight), twice a day, starting at 17 d of age for three days. Pups were returned to the dams after gavage feeding. Pups that were not gavage fed but allowed to wean normally with the dam were used as controls in each of the two groups. Serum thyroxine levels in the hypothyroid pups were five fold lower than those in age matched controls. Regardless of the thyroid status, intestinal fructose uptake per mg (p=0.0001) and per cm (p=0.0001) in both proximal and middle small intestine was 2.0 to 2.5 fold higher in pups gavage fed high fructose compared to those in pups fed high glucose solutions or in pups allowed to wean normally with the dam. Intestinal glucose uptake per mg (p=0.013) and per cm (p<0.0001) increased significantly in hypothyroid but not euthyroid pups fed high fructose solutions. Northern blot analysis showed higher levels of GLUT5 mRNA in pups fed high fructose solutions and paralleled the increase in fructose uptake. Thus, the thyroxine surge is not necessary for the precocious induction of intestinal fructose uptake and GLUT5 mRNA expression by dietary fructose during weaning.
Transport/Cell Biology/Nutrition© 1998 Lippincott Williams & Wilkins, Inc.