Metabolic handling of intraduodenal vs. intravenous glucose in humans

To determine whether the route of glucose administration affects whole body glucose metabolism, 14 healthy volunteers were randomly infused with intra duodenal (id) or intravenous (iv) glucose at 6 mg.kg(-1).min(-1) for 180 mi n. Infused glucose was labeled with [2-H-3] glucose in a first series of pa ired experiments designed to characterize kinetic parameters to be used in a second series of experiments in which [3-H-3]- and [U-C-14] glucose label ing was used to characterize the metabolic fate of infused glucose. Experim ents with [2-H-3] glucose showed that, after a lag period of only 20 min, i d absorption averaged 105 +/- 3% of infusion. During the final hour of id a nd iv infusion of [3-H-3] glucose, tissue uptake averaged 98 +/- 3 and 107 +/- 4% of infusion, respectively, and was equally divided between glycolysi s ((H2O)-H-3 production) and storage (uptake-glycolysis). Glucose oxidation ((CO2)-C-14), total carbohydrate oxidation (indirect calorimetry), and net carbohydrate balance were also similar, but the thermic effect of glucose was significantly greater after id infusion. Because insulin and estimated portal vein glucose levels were similar during the final 80 min of both inf usions, our results suggest that hepatic glucose storage (and therefore mus cle storage estimated as whole body minus liver storage) is not affected by the route of glucose administration.