Plasma insulin, C-peptide and glucagon concentrations in patients with insulin-independent diabetes treated with chlorpropamide.

The effect of chlorpropamide on blood glucose, plasma insulin, C-peptide and glucagon levels was studied in 21 patients with insulin-independent diabetes. A metabolic profile of these parameters was obtained throughout a normal day in seven newly-diagnosed diabetic patients (group A), before, and 3 to 8 weeks after treatment with chlorpropamide was established, and in 14 patients on longterm therapy with chlorpropamide (seven taking less than 250 mg. chlorpropamide--group B; seven taking 250-375 mg.--group C), before, and two weeks after withdrawal of the drug. In group A, correction of hyperglycaemia was not accompanied by a significant rise in the mean plasma insulin and C-peptide levels but a fall was observed in the mean plasma pancreatic glucagon concentrations. In groups B and C, withdrawal of chlorpropamide produced no significant change in plasma insulin, C-peptide or glucagon levels, although the mean blood glucose increased. This study supports an extrapancreatic effect of chlorpropamide to lower blood glucose after prolonged administration. In the short-term, it is possible that chlorpropamide may influence the secretion of pancreatic glucagon.