Yukihiro Nakabou

Diabetes and glucose transporter gene expression in rat small intestine

The expressions of Na(+)-dependent glucose transporter (SGLT1) and five facilitative glucose transporter genes (GLUT1-5) in the small intestine of streptozotocin (STZ)-induced diabetic rats were examined by RNA blotting analysis. The transcripts of SGLT1 mRNA gave bands of 4.5 Kilobases (Kb) and 2.8Kb (very faint band). The levels of SGLT1 mRNA were significantly increased in 30- and 60-day STZ rats, but not changed in acute diabetic rats (2- to 10- day STZ rats). The GLUT2 mRNA levels changed in parallel with the D-galactose transport activity, being increased about 4-fold in 5-day STZ rats. The transcripts of GLUT5 mRNA gave three bands of 5.1Kb, 2.8Kb and 2.OKb, whose levels were significantly reduced in 30- and 60-day STZ rats. These results suggest that the facilitative glucose transporter (GLUT2), in addition to the Na(+)-dependent glucose transporter (SGLT1), may play an important role in intestinal glucose transport in diabetic rats.

Developmental changes in intestinal glucose transporter mRNA levels

Developmental changes in glucose transporter mRNA levels in the jejunum of rats of different ages were examined by using slot blot RNA analysis. The level of SGLT1 mRNA did not change significantly through life. The GLUT5 mRNA level was highest in 10-day-old rats and then decreased reaching the adult level by day 20 after birth. The GLUT2 mRNA level was low in rats of 5 and 10 days old, but then increased progressively reaching the adult value by day 25 after birth. These results indicate that the expressions of intestinal facilitative glucose transporter genes change markedly in the third week after birth.

Effect of food intake on intestinal absorption and mucosal hydrolases in alloxan diabetic rats

The relation between food intake and enzyme activity of the small intestine and rate of intestinal absorption were studied in rats 15 days after induction of alloxan diabetes. Diabetic rats were given an ad lib. semisynthetic diet or a restricted diet on the basis of either daily intake or body weight. The rates of absorption of 5 mMD-galactose and L-valine were determined in vitro by the everted sac method. The rates of absorption of the substances, expressed per unit weight or per length of intestine, were higher in diabetic rats than in controls, regardless of the amount of food consumed. Maltase and sucrase activities were significantly increased in diabetic rats, regardless of the amount of food consumed. The activity of intestinal alkaline phosphatase was increased in diabetic rats fed ad lib., but not in those on a restricted diet. These findings suggest that in alloxan diabetic rats the increased disaccharidase activity in the small intestine is due to insulin deficiency, and that the increased activity of alkaline phosphatase is only a secondary effect of insulin deficiency, caused by increased food intake resulting from insulin deficiency.

Inhibition of glucose absorption by phlorizin affects intestinal functions in rats

BACKGROUND To investigate the mechanism of regulation of intestinal disaccharidase activity and glucose absorption, the effect of dietary intake of phlorizin, a potent and specific inhibitor of intestinal glucose transport, on intestinal disaccharidase activity and Na(+)-dependent glucose transporter was examined in rats. METHODS Jejunal disaccharidase activity and the number of Na(+)-dependent glucose transporters were determined in rats maintained on a low-starch diet, a high-starch diet, or low-starch diets containing various amounts of phlorizin (0.1%-0.9% wt/wt). RESULTS Jejunal disaccharidase activity increased in a dose- and time-dependent manner. Stimulation of jejunal disaccharidase activity only occurred when phlorizin was added to starch-containing diets, not when it was added to a carbohydrate-free diet. Addition of the same amount of phloretin and glucose (constituents of phlorizin), to the diet failed to increase disaccharidase activity. The maximum binding of phlorizin to brush border membrane vesicles was increased in the rats fed phlorizin, whereas the dissociation constant remained unchanged, suggesting an increase of glucose transporter expression. CONCLUSIONS Dietary phlorizin increased the jejunal disaccharidase activity and Na(+)-dependent glucose transporter expression. The trigger for these changes may have been due to an increased luminal glucose content.

Role of liver‐type glucose transporter (GLUT2) in transport across the basolateral membrane in rat jejunum

To obtain information on the regulation of glucose transport across the basolateral membrane (BLM) of intestinal epithelial cells, we measured the number of [3H]cytochalasin B binding sites and the level of liver‐type glucose transporter (GLUT2) protein in the BLM in the jejunum of rats (i) with diabetes (ii) given a high‐carbohydrate diet or (iii) with experimental hyperglycemia (12 h infusion of a high‐glucose solution). A glucose uptake and the number of d‐glucose inhibitable [3H]cytochalasin B binding sites in BLM vesicles were significantly increased in all three conditions. Western blot analysis showed that the amount of GLUT2 protein in BLM vesicles was increased in rats with diabetes and those given a high‐carbohydrate diet, but not in those with experimental hyperglycemia. These results suggest that there is a mechanism for rapid regulation of glucose transport in the BLM that does not depend on change in the amount of GLUT2.

Changes in brush-border enzyme activities of intestinal epithelial cells isolated from the villus-crypt axis during the early phase of alloxan diabetes in rats

The sucrase activity in enterocytes isolated from the villus crypt axis was found to increase in all regions of the villus from day 2 after induction of diabetes, and the increase continued until day 4. In contrast, alkaline phosphatase activity increased mainly in the apical one-third of the villus-crypt column, and the increase occurred abruptly on day 4 with increase in food intake.

Differential mechanisms of induction of ornithine decarboxylase in rat intestine by l- and d-amino acids

A single intragastric administration of glycine, L- and D-alanine, and L-and D-serine into rats resulted in a more than 20-fold stimulation of intestinal mucosal ornithine decarboxylase (ODC) within 4 h. The stimulation of ODC activity was accompanied by an increase in the amount of immunoreactive ODC protein. The induction of ODC by D-amino acids was in all likelihood attributable to an enhanced accumulation of ODC-specific mRNA species as revealed by Northern blot and dot-blot hybridization analyses. However, the induction by glycine and L-amino acids was not explainable by changes of mRNA since the changes in mRNA contents were only marginal. Since the turnover rates of L-serine-induced and D-serine-induced intestinal ODC protein were the same as the non-induced control, we concluded that the induction by glycine and L-amino acids was brought about by an increased efficiency of translation of the ODC message.