Effects of synthetic rat C-peptide in normal and diabetic rats

The effects of synthetic rat C-peptide 1 and C-peptide 2 on plasma insulin and blood glucose concentrations in the rat were studied. Infusion of rat C-peptide (500 micrograms X h-1 X kg-1) diminished glucose induced increase of plasma insulin by 56% (15.2 +/- 0.9 versus 6.6 +/- 0.6 ng/ml, p less than 0.01, mean +/- SEM). Somatostatin infused at a rate of 50 micrograms X h-1 X kg-1 body weight inhibited glucose-induced insulin secretion by 33%. In the presence of a mixture of both C-peptides or somatostatin, blood glucose after intravenous glucose was higher than in the control experiments. In alloxan-diabetic rats, C-peptide (160 micrograms/kg) significantly increased and prolonged the hypoglycaemic effect of exogenous insulin. It is suggested that C-peptide may not be a biologically inert substance.