Comparison of oral glucose loading and intravenous glucagon injection as stimuli to C-peptide secretion in normal men

In 10 healthy men, we have compared the respective effects of an intravenous injection of glucagon (1 mg) and an oral glucose load (75 G) in eliciting the release of C-peptide and insulin from the pancreas. Serum C-peptide and insulin concentrations increased respectively to median values of 190% and 500% at 6 minutes after glucagon injection, and 344% and 794% at 30 minutes and 268% and 278% at 60 minutes following glucose ingestion. The oral glucose load was as effective as glucagon injection in testing beta cell function and was free from the unpleasant side effects (nausea, vomiting, syncope) commonly associated with glucagon. We conclude that oral glucose loading is probably the test of choice to elicit C-peptide release when screening populations of normal subjects for adequacy of beta cell function.