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 intraduodenal (id) or intravenous (iv) glucose at 6 mg x kg(-1) x min(-1) for 180 min. Infused glucose was labeled with [2-(3)H]glucose in a first series of paired experiments designed to characterize kinetic parameters to be used in a second series of experiments in which [3-(3)H]- and [U-(14)C]glucose labeling was used to characterize the metabolic fate of infused glucose. Experiments with [2-(3)H]glucose showed that, after a lag period of only 20 min, id absorption averaged 105 +/- 3% of infusion. During the final hour of id and iv infusion of [3-(3)H]glucose, tissue uptake averaged 98 +/- 3 and 107 +/- 4% of infusion, respectively, and was equally divided between glycolysis ((3)H(2)O production) and storage (uptake-glycolysis). Glucose oxidation ((14)CO(2)), 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 infusions, our results suggest that hepatic glucose storage (and therefore muscle storage estimated as whole body minus liver storage) is not affected by the route of glucose administration.