OBJECTIVE: We set out to examine the short-term regulation of the intestinal sodium/glucose cotransporter SGLT1 by its substrate glucose and sweet taste analogs.
SUMMARY BACKGROUND DATA: Intestinal SGLT1 is a putative target for antidiabetic therapy; however, its physiological regulation is incompletely understood, limiting its application as a pharmacological target. While it is clearly regulated by dietary composition over a period of days, its short-term regulation by nutrients is unknown.
METHODS: Sprague-Dawley rats were anesthetized, and the duodenum cannulated. D-glucose, D-fructose, saccharin, D-mannitol, and water were infused for 3 hours, before harvest of proximal jejunum for SGLT1 analysis with Western blotting and quantitative polymerase chain reaction. In further experiments, the receptor region was identified by D-glucose infusion of isolated regions. Lastly, the vagus was de-afferented with capsaicin, and 5HT3-receptor activation of vagal afferents inhibited using ondansetron, before repeating experiments using water or D-glucose infusion.
RESULTS: Infusion of D-glucose led to 2.9-fold up-regulation in SGLT1 compared with water or iso-osmotic D-mannitol; this effect was replicated by D-fructose or saccharin. This response was strongest following isolated infusions of duodenum and proximal jejunum, with a blunted effect distally; topography matched the expression profile of sweet taste receptor T1R2/T1R3. The reflex was abolished by capsaicin pretreatment, and blunted by ondansetron.
CONCLUSIONS: The agonist response implicates the luminal-based sweet-taste receptor T1R2/T1R3, with the reflex apparently involving vagal afferents. The proximal nature of the sensor coincides with the excluded biliopancreatic limb in Roux-en-Y gastric bypass, and this may provide a novel explanation for the antidiabetic effect of this procedure.
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