Glucose tolerance depends on insulin secretion, insulin action (the ability of insulin to increase glucose uptake by tissues or to inhibit release of glucose by the liver and the kidney) and glucose effectiveness (the ability of glucose to stimulate its own uptake and to suppress its own release). Impaired glucose tolerance is a consequence of impairment in either or all of these processes. An ideal therapeutic agent for diabetes mellitus should increase insulin secretion, improve insulin action, enhance glucose effectiveness and restore postprandial glucagon suppression. The incretin hormone, Glucagon-Like-Peptide-1 (GLP-1) holds the promise of being such an agent. Studies to date have confirmed that pharmacological doses of GLP-1 suppress glucagon release and potentiate post-prandial insulin-secretion. However, when glucose is delivered intravenously, GLP-1 does not seem to affect insulin sensitivity and glucose effectiveness. We propose to study the effect of GLP-1 on splanchnic glucose uptake in persons with type 1 diabetes when glucose is delivered enterally. Our hypotheses is that pharmacological doses of GLP-1 and/or the direct delivery of glucose into the intestine improve splanchnic glucose uptake.
The specific aims of the study are to determine whether type 1 diabetes alters splanchnic glucose uptake in age and weight-matched controls, to determine whether GLP-1 alters splanchnic glucose uptake, and to determine whether intravenous versus intra-duodenal delivery of glucose will alter splanchnic glucose uptake in healthy volunteers.
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