Portal and cubital serum insulin during oral, portal and cubital glucose tolerance tests.
Oral, intracubital, and intraportal glucose tolerance tests have been performed on 7 non-obese non-diabetics, and glucose and insulin concentrations have been followed in the peripheral and portal blood. A significant rise in portal glucose and insulin was found 1/2-2 min after oral glucose intake. There was no lag between the rise in insulin and glucose concentrations. The portal glucose concentration after oral glucose intake was significantly higher than after cubital glucose infusion for 45 min, although the peripheral glucose concentrations were identical. In the cubital vein the insulin concentration after oral glucose intake was significantly higher than after i.v. glucose infusion, but in the portal blood there was no difference. After portal glucose infusion the cubital insulin concentration did not differ significantly from the concentration after i.v. glucose infusion. Thus, it seems unlikely that a high portal glucose concentration is responsible for the higher peripheral insulin concentration after oral glucose intake. A high portal glucose concentration does not seem to influence the hepatic uptake or release of glucose.