Insulin secretion, insulin action and non-insulin-dependent glucose uptake in pancreas transplant recipients

To assess individual factors responsible of overall glucose tolerance after successful pancreas transplantation, an i.v. glucose tolerance test, with frequent blood sampling and tolbutamide administration to elicit a second insulin response was used to estimate insulin sensitivity (SI) and glucose effectiveness (SG) with Bergman's minimal model. Insulin secretion was calculated from the combined insulin-C-peptide kinetics method. These parameters were quantified in identically immunosupressed transplants: ISPx, four segmental pancreas recipients with impaired glucose tolerance; TSPx, five segmental pancrease recipients with normal glucose tolerance; WPx, five whole pancreas recipients with normal glucose tolerance; and in two controls groups, Kx, eight nondiabetic kidney recipients, and Ns, eight normal subjects. All participants had normal fasting plasma glucose and normal glycosylated hemoglobin A1C levels. The glucose tolerance KG value was significantly reduced only in ISPx compared with Ns (P < 0.05). SI was reduced by 60% in ISPx, WPx, and Kx compared with normal subjects (P < 0.05), whereas SI was reduced by 30% in TSPx compared with normal controls (P = NS). The reduction in SG was the same in all pancreas transplanted groups, as compared to Kx and Ns (by 33% and 40%, respectively, P < 0.05). The first-phase insulin secretion (0-5 min) was markedly reduced in ISPx and TSPx compared with Ns (by 76% and 50%), to Kx (by 84% and 66%) and to WPx (by 73% and 45%), respectively (P < 0.05), but similar to Ns in WPx. The overall incremental insulin secretion was reduced in ISPx compared with Ns, WPx, and Kx (by 38%, 62%, and 73%, respectively, P < 0.05) and reduced in TSPx compared to WPx and Kx (by 47% and 67%, respectively, P < 0.05) Ns secreted 43% of the total amount of insulin during the first phase the corresponding value was only 13% in ISPx vs. 24% in TSPx, 24% in Kx, and 25% in WPx, respectively (P < 0.05). In conclusion, after pancreas transplantation, the overall glucose tolerance is determined by the net effect of reductions in insulin sensitivity and glucose effectiveness and in the adaptability of the beta-cells to ensure sufficient insulin secretion. beta-cell function was impaired in both the whole pancreas and segmental transplant recipients, and the failure to increase insulin secretion sufficiently leads to glucose intolerance.