Figure 2.
AIRs to arginine as a function of the prestimulus plasma glucose concentration (18). The glucose-potentiation slope (GPS), calculated as the difference in the AIR at fasted and 230 mg/dl glucose levels divided by the difference in plasma glucose, is impaired in the islet vs. normal group (0.11 ± 0.01 vs. 0.76 ± 0.07; P < 0.0001; panel A), but not in the pancreas-kidney or kidney transplant vs. kidney donor group (0.71 ± 0.16 vs. 0.64 ± 0.04 vs. 0.90 ± 0.20; NS). β-Cell sensitivity to glucose is determined as the PG50, the plasma glucose level at which half-maximal insulin secretion was achieved, using the y-intercept (b) of the GPS to solve the equation AIRmax/2 = GPS × PG50 + b as represented by the dashed lines in panels A and B. Because the impairment of GPS in the islet group was proportional to the reduction in AIRmax, no difference existed in PG50 between the islet vs. normal groups (134 ± 21 vs. 143 ± 9 mg/dl; NS; panel A), nor did any differences exist in PG50 across the pancreas-kidney, kidney transplant, and kidney donor groups (148 ± 13 vs. 163 ± 10 vs. 148 ± 7 mg/dl; NS; panel B).