First-Phase Insulin Secretion Restoration and Differential Response to Glucose Load Depending on the Route of Administration in Type 2 Diabetic Subjects After Bariatric Surgery

OBJECTIVE - The purpose of this study wits to elucidate the mechanism,. of diabetes reversibility after malabsorptive bariatric surgery. RESEARCH DESIGN AND METHODS - Peripheral insulin sensitivity and P cell function after either intravenous (IVGTT) or oral glucose tolerance (OGTT) test,; and minimal model analysis were assessed in nine obese, type 2 diabetic subjects before and I month after biliopancreatic diversion and compared with those in six normal-weight control subjects. Insulin-dependent whole-body glucose disposal was measured by the euglycemic clamp, and glucose-do:pendent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) were also measured. RESULTS - The first phase of insulin secretion alter the IVGTT was fully normalized after the operation. The disposition index from OGTT data was increased about 10 fold and became similar to the values found in control subjects, and the disposition index from IVGTT data increased about 3.5-fold, similarly to what happened after the euglycemic clamp. The area under the curve (AUC) for GIP decreased about four times (from 3,000 +/- 816 to 577 +/- 155 pmol . l (1).min, P < 0.05). On the contrary, the AUC for GLPI almost tripled (from 150.4 +/- 24.4 to 424.4 +/- 64.3 pmol .l (1).min, P<0.001). No significant correlation was found between GIP or GLPI percent changes and modification of the sensitivity indexes independently of the route of glucose administration. CONCLUSIONS - Restoration of the first-phase insulin secretion and normalization of insulin sensitivity in type 2 diabetic subjects after malabsorptive bariatric surgery seem to be related to the reduction of the effect of some intestinal factor(s) resulting from intestinal bypass.