Disappearance rate of endogenous human C-peptide from blood.

Glucagon (1 mg) and glucose (60 ml of 50% solution) were infused over 60 min to three normal and one obese subjects and two insulinoma patients. Plasma C-peptide immunoreactivity (CPR) and immunoreactive insulin (IRI) increased during the infusion. Half time of CPR after cessation of the infusion was 20.1 +/- 4.0 min, and that of IRI 9.8 +/- 1.3 min, respectively. This difference partly explains the higher molar concentration in plasma of CPR than IRI.