Plasma concentrations and transperitoneal transport of native insulin and C-peptide in patients on continuous ambulatory peritoneal dialysis.

The insulin and C-peptide response to glucose (50 g), given intraperitoneally or enterally, and the elimination rate of these compounds has been studied in five nondiabetic patients on continuous ambulatory peritoneal dialysis (CAPD). The fasting C-peptide concentrations were three to ten times the normal values, whereas the fasting plasma insulin concentrations were within normal limits. After intraperitoneal glucose administration, a more marked hyperglycemia (P less than 0.05) and a more long lasting hyperinsulinemia (P less than 0.05) were found than after the enteral glucose load. The relative change in plasma C-peptide was slower and less pronounced in both experiments. Estimated total body clearance (Kt) for insulin was higher than for C-peptide (P less than 0.01), but dialysis clearance (Kd) for C-peptide was higher than for insulin in both experiments (P less than 0.01). The markedly elevated fasting C-peptide concentrations in plasma can be explained only partly by the absence of normal kidney function and suggests a continuously increased production of C-peptide during CAPD treatment. This was not reflected by the fasting plasma insulin concentrations. C-peptide measurements in plasma and dialysate during CAPD could be helpful in evaluating the beta-cell function in patients in need of exogenous insulin.