THE ROLE OF INSULIN IN THE INTESTINAL-ABSORPTION OF GLUCOSE IN THE RAT

1. Acute pre-treatment with either mannoheptulose or streptozotocin-bo th compounds acting as powerful suppressors of insulin secretion-cause d a significant decrease on the in vivo rate of intestinal glucose abs orption following an intragastric [U-C-14]glucose administration. 2. M annoheptulose treatment also lowered the rate of whole-body oxidation of the administered tracer. 3. Insulin had no effect on the metabolic fate of [U-C-14]glucose by isolated enterocytes. 4. However, the rate of glucose uptake, measured by the oxidation of [1-C-14]glucose to (CO 2)-C-14 in the presence of phenazine methosulphate, was decreased by i nsulin at concentrations of 50-200 munits/ml. 5. In addition, the rate of transport of [U-C-14]glucose by brush-border membrane vesicles was also inhibited by insulin at high concentrations (100-1000 munits/ml) . 6. This indicated that insulin acts by inhibiting glucose transport in isolated in vitro preparations. 7. Acute pre-treatment with either mannoheptulose or streptozotocin caused a significant decrease in the rate of gastric emptying, measured as the distribution of [H-3]inulin along the gastrointestinal tract, following an intragastric glucose lo ad. 8. It is concluded that insulin secretion modulates intestinal glu cose absorption in vivo by enhancing gastric emptying in spite of the inhibitory effects of glucose transport observed with in vitro prepara tions.