Lack of effect of improved glycemic control on C-peptide secretion in patients without residual B-cell function.

Ten patients with insulin-dependent diabetes mellitus underwent a program of intensification of therapy that resulted in marked improvement in glycemic control. C-peptide secretion in response to a test meal and to an intravenous glucagon challenge was used to assess pancreatic B-cell function in terms of residual endogenous insulin secretion. Patients, who had diabetes for a mean (+/- SEM) of 8.4 +/- 1.9 yr, had minimal or no C-peptide response at baseline evaluation. C-peptide responses remained unchanged when reassessed after 2, 4, and 6 mo of improved glycemic control.