Differential effects of ambient blood glucose level and degree of obesity on basal serum C-peptide level and the C-peptide response to glucose and glucagon in non-insulin-dependent diabetes mellitus.

We student basal, glucose- and glucagon-induced insulin secretion in non-insulin diabetes mellitus (NIDDM) patients in relation to body mass index (BMI) and fasting serum glucose (FBS) level. A total of 46 NIDDM patients and 22 control subjects with varying degrees of BMI and FBS were given 100 g of oral glucose and 1 mg of intravenous glucagon on separate days. C-peptide response to glucose, but not basal serum C-peptide and C-peptide response to glucagon, was significantly lower in NIDDM than in controls (P < 0.001). FBS was inversely correlated with C-peptide response to glucose in NIDDM patients (r = -0.67, P < 0.001), but not with basal C-peptide level and C-peptide response to glucagon. On the other hand, BMI was positively correlated with basal serum C-peptide level both in NIDDM (r = 0.60, P < 0.001) and in control subjects (r = 0.74, P < 0.001). In 15 poorly controlled NIDDM patients, the tests were repeated after insulin treatment for 10-14 days. C-peptide response to glucose significantly increase, but not to a level in control subjects, after glycemic control. Basal serum C-peptide level and the C-peptide response to glucagon decreased after glycemic control to significantly lower levels than those in the baseline and those in control subjects. These results suggest that beta cell secretory reserve is reduced in moderate to severe NIDDM patients.