[Insulin extraction by the isolated perfused rat liver using infusion conditions of a biphasic insulin concentration...

Rat liver was perfused in vitro at 37 degrees C in an open system with Krebs-Ringer-Bicarbonate buffer, pH 7.4, in the presence of 20 vol% freshly prepared bovine erythrocytes. A biphasic insulin concentration profile, imitating the glucose induced insulin secretion of the isolated perfused rat pancreas was infused by means of a gradient mixer into the portal vein of the liver. The quality of the infused gradient was tested in a series of preliminary experiments by dye-infusion into the portal vein. It could be shown by synchronous fractionation of medium samples immediatly prior and after liver passage and by subsequent radioimmunological insulin determination that the biphasic profile of the infused insulin gradient was preserved after a single liver passage. The insulin concentration in the portal vein under experimental conditions ranged from 0 to 3.2 ng insulin/ml perfusate. About 70-80% of the insulin was removed by the liver. It could be further demonstrated that the hepatic insulin removal rate is rising with increasing insulin concentration in the liver input. The highest hepatic insulin removal rate obtained under the used portal insulin concentrations amounted to 2 ng insulin/min X g liver ww.