Renal extraction of insulin and C-peptide in man before and after a glucose meal.

It was recently shown that the early rise in arterial insulin concentration after an oral glucose meal is largely because of a decreased extraction of the hormone. The kidney is a major site for extraction of insulin and C-peptide. We therefore measured the renal extraction of insulin and C-peptide in eight healthy individuals before and after ingestion of 75 g of glucose. Arterial, renal venous and hepatic venous catheters were inserted. Splanchnic and renal plasma flow were measured, as well as arterial, hepatic venous and renal venous concentrations of insulin and C-peptide. Renal fractional extraction of insulin increased significantly, from 21% to a maximum of 48% after the meal while the renal fractional extraction of C-peptide did not change significantly. Renal blood flow decreased slightly but significantly after the meal. It is concluded that renal fractional extraction of insulin increases and that renal blood flow decreases after a glucose meal.