Plasma C-peptide response to arginine in insulin-dependent diabetic subjects.

Plasma C-peptide concentrations have been determined in the basal state and in response to intravenous arginine in 10 insulin-dependent diabetics. Five patients had fasting C-peptide levels above 0.08 pmol/ml and responded to the arginine infusion with a rise in C-peptide levels of more than 0.2 pmol/ml (responsive diabetics). The remaining 5 patients had fasting C-peptide below 0.03 pmol/ml and showed no C-peptide response to arginine (nonresponsive diabetics). Fasting blood glucose and the rise in blood glucose in response to arginine were higher in non-responsive than in responsive diabetics. The magnitude of blood glucose rise in response to arginine was inversely correlated with increments in plasma C-peptide. In addition, the fasting levels of FFA and 3-hydroxybutyrate were significantly lower in C-peptide responsive than in nonresponsive patients. These data give further support to the concept that measurements of fasting plasma C-peptide permit to distinguish secretors from nonsecretors, and demonstrate that residual beta-cell function is associated with a lesser degree of aminoacid-induced hyperglycemia.