Effects of spontaneous portal-systemic shunting on insulin metabolism

Insulin degradation was measured by the C-peptide/insulin ratio in 19 patients with portal vein block with extensive spontaneous portal-systemic shunting but minimal liver cell damage: 13 patients with biopsy-proved cirrhosis and 12 controls. Blood obtained fasting and for 3 hr after oral glucose was assayed for glucose, insulin, and C-peptide. Fasting C-peptide and insulin levels in patients with portal vein block and those in controls did not differ. Eight of 13 cirrhotic patients had fasting hyperinsulinemia with a significantly reduced C-peptide/insulin ratio. After glucose administration, the C-peptide/insulin ratio in portal vein block patients with normal aspartate transaminase levels did not differ from control values. In portal vein block patients with elevated asparatate transaminase levels, the C-peptide/insulin ratio was significantly reduced only from 60 min onwards. All the cirrhotic patients showed a significantly reduced C-peptide/insulin ratio after glucose administration. It is suggested that portal-systemic shunting of blood in the presence of a normal liver does not influence hepatic insulin metabolism and that the hyperinsulinemia of cirrhosis is a feature of parenchymal liver damage. In addition, insulin degradation was abnormal in all cirrhotic patients at high insulin secretion rates, even when fasting insulin levels were normal.