 Normally, insulin is secreted from the pancreas in pulses into the portal vein which brings blood into the liver in variable amounts, closely related to ingestion of meals.For induction and maintenance of insulin-dependent enzymes essential for glucose metabolism in the liver (e.g.hepatic glucokinase, phosphofructokinase, and pyruvate kinase), the hepatocytes require a defined insulin level (200-500 µU/ml in the portal vein) concomitant with high glucose levels (which acts as a bimolecular signal).