Reduction of C-peptide secretion in noninsulin-dependent diabetic patients with long duration of insulin treatment.

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Abstract
The responses of serum free C-peptide immunoreactivity (CPR) during a 100 g oral glucose tolerance test (OGTT) on diabetic patients undergoing different kinds and durations of treatment were examined. None of the patients were ketosis-prone or had any history of nephropathy and they all developed diabetes when over the age of 30. The .SIGMA.serum free CPR (the sum of serum free CPR values during OGTT) of group A (duration of insulin treatment was less than 5 yr, n = 10) was higher than that of group B (duration of insulin treatment was 5 yr or more, n = 10) (P < 0.005). The .SIGMA.serum free CPR of group C (treatment with an oral hypoglycemic agent for less than 5 yr, n = 9) was not statistically different from that of group D (treatment with an oral hypoglycemic agent for 5 yr or more, n = 11). There were no statistical differences between group A and group B in age at onset, duration of diabetes, daily insulin dose, relative body wt index, serum creatinine or .SIGMA.BG (the sum of blood glucose values during OGTT). Just before the start of insulin treatment, there were no significant differences between the 2 groups in the following: fasting blood values (all 10 patients measured in group A and 9 patients in group B) and blood glucose and plasma immunoreactive insulin (IRI) responses (7 patients measured in group A and 6 in group B). Among those with plasma IRI measured on the previous occasion, .SIGMA.serum free CPR was higher in group A than in group B (P < 0.025) at the time of the present study. A negative correlation was noted between the duration of insulin treatment and .SIGMA.serum free CPR in insulin-treated patients (r = -0.39, P < 0.05). Pancreatic .beta.-cell function in insulin-treated noninsulin-dependent diabetic patients is likely to be inversely correlated with the duration of insulin treatment.