Peripheral Insulin Parallels Changes in Insulin Secretion More Closely than C-Peptide after Oral and Intravenous Glucose Administration

Abstract

The relationship between changes in peripheral plasma insulin, C-peptide levels, and the pancreatic insulin secretory rate (ISR) during isoglycemic oral and iv glucose loading and IVGTT were studied in 17 normal subjects. Pancreatic ISR was calculated according to a two-compartment model of distribution for C-peptide. Whereas the plasma insulin levels in OGTT increased 5.2±0.7-fold over the basal level at 15 min, and the plasma C-peptide concentrations increased to only 3.1±0.3-fold above the basal value at 15 min after the stimulus, the corresponding pancreatic ISR increased reaching a peak value at 8.0±1.0-fold over the basal level at 15min.Peripheral insulin concentrations paralleled changes in ISR more closely than C-peptide.In IVGTT, the ISR was more closely reflected by changes in peripheral insulin than in C-peptide levels. In conclusion, changes in pancreatic ISR after oral and iv glucose administration are more accurately reflected by parallel changes in peripheral plasma insulin than in plasma C-peptide levels.