RAPID ENHANCEMENT OF BRUSH-BORDER GLUCOSE-UPTAKE AFTER EXPOSURE OF RAT JEJUNAL MUCOSA TO GLUCOSE

Background-Increased jejunal glucose transport after ingestion of carb ohydrate rich diets may reflect higher concentrations of lumenal gluco se. Normal processing of carbohydrate causes wide fluctuations in gluc ose concentration in the jejunal lumen and this raises the question of whether the high lumenal concentrations seen at peak digestion affect glucose uptake. Aims-To study the effects of 30 minute exposure of ra t jejunal mucosa to glucose on sodium-glucose transporter (SGLT1) medi ated glucose transport across the brush border membrane. Methods-Jejun al mucosa was exposed in vitro or in vivo to 25 mM glucose or 25 mM ma nnitol for 30 minutes. In addition, isolated villus enterocytes were i ncubated with mannitol or glucose for the same time. Brush border memb rane vesicles were isolated from these preparations and phlorizin sens itive H-3-D-glucose accumulation was measured. Results-Lumenal glucose in vivo significantly enhanced SGLT1 mediated glucose uptake by 49.2- 57.2%. For jejunal loops in vitro, the increase was 32.0-85.2%. Kineti c analysis disclosed a 50% greater V-max for glucose uptake in each pr eparation. The facilitated and passive components of uptake were, howe ver, unaffected by prior exposure to glucose. Incubation of villus ent erocytes with 25 mM glucose did not influence glucose uptake by brush border membranes. Finally, exposure of intact mucosa to 25 mM galactos e, a non-metabolised sugar also transported by SGLT1, did not alter gl ucose transport. Conclusions-Lumenal glucose promotes glucose transpor t by brush border membrane within 30 minutes. An intact mucosa is nece ssary for upregulation and evidence suggests that the response is medi ated by locally acting mechanisms.