β-cell function during insulin-modified intravenous glucose tolerance test successfully assessed by the C-peptide minimal model

The insulin-modified intravenous glucose tolerance test (IM-IVGTT) is increasingly used to measure insulin sensitivity. However, the assessment of beta-cell secretion is usually made using rough indices. The aim here is to evaluate the ability of the minimal model of C-peptide secretion and kinetics recently proposed for the standard IVGTT (S-IVGTT) to also assess beta-cell function during the IM-IVGTT. C-peptide and glucose data from the IM-IVGTT in 15 normal humans were analyzed. The results show that the same rich beta-cell picture from the S-IVGTT can be obtained during an IM-IVGTT. In particular, in each individual, the time course of beta-cell secretion can be reconstructed and the functional indices of glucose control on first-phase (Phi(1)), second-phase (Phi(2)), and basal (Phi(b)) insulin secretion can be estimated (Phi(1) = 191 +/- 29, Phi(2) = 10.9 +/- 1.4.10(-9).min(-1), and Phi(b) = 5.7 +/- 1.0.10(-9).min(-1), mean +/- SE). Finally, the comparison between IM-IVGTT and S-IVGTT Phi(1), Phi(2), and Phi(b) values suggest they are not affected by insulin administration. Copyright (C) 1999 by W.B. Saunders Company.