Abstract
High serum C-peptide inu-nunoreactivity (CPR) due to the presence of proinsulin-like component (PLC)-insulin antibody complex which cross-reacts with human C-peptide antiserum, is often observed in insulin-treated diabetics. The CPR extracted from the serum using polyethylene glycol (the so-coiled free-CPR) is considered to express more accurately the C-peptide concentration in the serum of insulintreated diabetics with insulin antibody.
Serum CPR and free-CPR levels were measured during 50 g oral glucose tolerance tests (OGTT) in 10 adult-onset diabetics nerver on insulin, 8 insulin-treated diabetics without insulin antibody, and 19 insulin-treated diabetics with insulin antibody.
A significant correlation was noted between the CPR and free-CPR levels in the adult-onset diabetics and insulin-treated diabetics without insulin antibody (r=0.97, p<0.005). No significant difference was observed between the CPR and free-CPR levels during OGTT in these two groups. In the insulin-treated diabetics with insulin antibody, the average levels of CPR during OGTT were 3.1±0.5 ng/ml (M±SE)(at fasting) and 4.1±0.6ng/ml (at peak, 120 min after glucose), while the average levels of free-CPR were 1.1±0.1 ng/ml, 1.8±0.3 ng/ml, respectively. Moreover, the fasting free-CPR level in these patients was significantly lower than the fasting CPR level in 9 normal subjects (2.0±0.1ng/ml, p<0.005). The free-CPR response during OGTT in these diabetics with insulin antibody was markedly lower and more delayed than the CPR response in normal subjects, and was also lower than that in adult-onset diabetics.
These results suggest that determinations of the serum free-CPR are more meaningful in assessing the endogenous insulin secretory capacity to various stimuli of insulin-treated diabetics with high serum CPR.
