Regulation of rat intestinal GLUT2 mRNA abundance by luminal and systemic factors.

Fructose in the lumen of the small intestine is transported across the brush border membrane by GLUT5, then across the basolateral membrane by GLUT2, which also transports glucose. Diets containing high fructose (HF) specifically enhance intestinal GLUT5 expression in neonatal rats, but there is little information concerning the dietary regulation of GLUT2 expression during early development. In this study, we perfused for 1-4 h 100 mM fructose, glucose (HG), alpha-methylglucose, or mannitol solutions into the jejunum of anaesthetized 20-day-old rat pups. GLUT2 mRNA abundance increased only in HF- and HG-perfused intestines, an effect inhibited by actinomycin D but not by cycloheximide. Bypassed (Thiry-Vella) intestinal loops were constructed, then pups were fed either HF or low-carbohydrate diets for 5 days. GLUT2 mRNA abundance increased significantly in both bypassed and anastomosed intestines of Thiry-Vella pups fed HF. In contrast, GLUT5 mRNA abundance increased only in the anastomosed segment. In sham-operated pups, GLUT2 and GLUT5 mRNA abundance increased in both intestinal regions that corresponded to the bypassed and anastomosed regions of Thiry-Vella pups. SGLT1 mRNA abundance was independent of diet and intestinal region in both Thiry-Vella and sham-operated pups. Unlike GLUT5 expression, which is regulated at the level of transcription only by luminal fructose, GLUT2 mRNA expression is transcriptionally regulated by luminal fructose and glucose as well as by systemic factors released during their absorption.