C-peptide response to glucagon in type 2 diabetes mellitus: a comparison with oral glucose tolerance test

C-peptide immunoreactivity (CPR) response during glucagon test (intravenous injection of 1 mg glucagon) was compared with CPR response during 75 g oral glucose tolerance test (oGTT) in 58 patients with newly-diagnosed, untreated type 2 (non-insulin-dependent) diabetes mellitus. Both tests were also repeated after blood glucose was well controlled with sulfonylurea or insulin in 17 patients. CPR secretory response was estimated by delta CPR, i.e. the difference between maximal and basal levels of CPR during each test. In the 58 untreated patients, the mean fasting plasma glucose (FPG) level was 12.8 +/- 0.6 mmol/L (M +/- SE), and there was no significant correlation between delta CPR during glucagon test and delta CPR during oGTT. The therapy for diabetes mellitus in 17 patients resulted in a fall in FPG (from 15.1 +/- 0.5 to 6.7 +/- 0.3 mmol/L) and a marked increase in delta CPR during oGTT (from 0.28 +/- 0.06 to 1.18 +/- 0.17 nmol/L, P < 0.01), but did not influence delta CPR during glucagon test (from 0.39 +/- 0.06 to 0.42 +/- 0.06 nmol/L, N.S.). In these patients, delta CPR during glucagon test before therapy correlated significantly with delta CPR during oGTT after therapy. Of the 13 patients who showed impaired CPR response during oGTT (delta CPR < 0.5 nmol/L) but substantial response during glucagon test (delta CPR > or = 0.5 nmol/L), 12 were successfully controlled without insulin therapy.(ABSTRACT TRUNCATED AT 250 WORDS)