Pancreatic beta cell secretion during oral and intravenous glucose administration.

The contribution of decreased hepatic insulin extraction to the relative hyperinsulinemia after oral glucose load as compared to intravenous glucose load was studied in 6 normal weight male volunteers by means of an analysis of the relationship between peripheral venous concentrations of insulin and C-peptide following similar glycemic stimuli after oral and intravenous glucose administration. The incremental areas under the insulin and C-peptide curves were higher during oral as compared to intravenous glucose administration, 436 (251--762) per cent and 267 (124-378) per cent respectively (mean and range). The ratio between corresponding incremental areas of insulin and C-peptide were 53 (17--103 per cent higher during oral glucose load. These findings suggest that the augmented peripheral insulin levels after oral glucose administration are caused by a combination of increased beta cell secretion and decreased hepatic insulin extraction.