A Crossover Study to Assess the 2 Glucose Tolerance Tests on Incretin, Beta-cell function and Insulin Sensitivity in Japanese Healthy and Type 2 Diabetes Subjects - Two Glucose Tolerance Tests on Incretin, beta-cell function and Insulin Sensitivity in Japanese T2DM Patients

Hypersecretion of glucagon and reduced insulin secretion both contribute to hyperglycemia in type 2 diabetes (T2DM). However, the relative contributions of impaired glucagon and insulin secretions in glucose excursions at the various stages of T2DM development remain to be determined. In OGTT, T2DM showed a rise in glucagon at 0-30min, unlike NGT and IGT, along with reduced insulin. In MTT, all three groups showed a rise in glucagon at 0-30min, with that in T2DM being highest, while T2DM showed a significant reduction in insulin. Linear regression analyses revealed that glucose area under the curve (AUC)0-120 min was associated with glucagon-AUC0-30 min and insulin-AUC0-30 min in both OGTT and MTT. Total and biologically intact GIP and GLP-1 levels were similar among the three groups. Disordered early phase insulin and glucagon secretions but not incretin secretion are involved in hyperglycemia after ingestion of nutrients in T2DM of even a short duration.