REGULATION OF GLUT5 GENE-EXPRESSION IN RAT INTESTINAL-MUCOSA - REGIONAL DISTRIBUTION, CIRCADIAN-RHYTHM, PERINATAL-DEVELOPMENT AND EFFECT OFDIABETES

1. GLUT5 gene expression was studied in small intestine under a variet y of conditions characterized by altered intestinal absorption of mono saccharides. 2. RNA-blotting studies showed that GLUT5 mRNA was abunda ntly expressed in rat and rabbit intestine and kidney, but it was not detected in heart or brown adipose tissue. GLUT5 mRNA levels were high er in the upper segments of the small intestine (duodenum and proximal jejunum) than in the lower segments (distal jejunum and ileum). 3. Th e intestinal expression of GLUT5 mRNA in rat proximal jejunum showed c ircadian rhythm. A 12-fold increase in GLUT5 mRNA levels was detected at the end of the light cycle and at the beginning of the dark cycle w hen compared with the early light period. In keeping with this, GLUT5 protein content in brush-border membranes was also increased at the be ginning of the dark cycle compared with that in the light period. 4. I n streptozotocin-induced diabetes an 80% increase in GLUT5 mRNA levels in mucosa from the proximal jejunum was detected under conditions in which enhanced intestinal absorption of monosaccharides has been repor ted. 5. The intestinal expression of GLUT5 mRNA showed regulation duri ng perinatal development. Levels of GLUT5 mRNA were low during fetal l ife, increased progressively during the postnatal period and reached l evels comparable with the adult state after weaning. Weaning on to a h igh-fat diet partially prevented the induction of GLUT5 gene expressio n. 6. Our results indicate that GLUT5 gene expression is tightly regul ated in small intestine. Regulation involves maximal expression in the upper part of the small intestine, circadian rhythm, developmental re gulation dependent on the fat and carbohydrate content in the diet at weaning and enhanced expression in streptozotocin-induced diabetes. Fu rthermore, changes observed in intestinal GLUT5 expression correlate w ith reported alterations in intestinal absorption of fructose. This su ggests a regulatory role for GLUT5 in fructose uptake by absorptive en terocytes.