Hepatic insulin extraction is difficult to measure in humans; as a result, the interrelationship between defective insulin secretion and insulin insensitivity in the pathogenesis of glucose intolerance in cirrhosis remains unclear. To reassess this we used recombinant human C-peptide to measure C-peptide clearance in cirrhotic patients and controls and thus derive C-peptide and insulin secretion rates after a 75-gm oral glucose load and during a 10 mmol/L hyperglycemic clamp. Cirrhotic patients were confirmed as insulin-insensitive during a euglycemic clamp (glucose requirement: 4.1 ± 0.1 mg/kg/min vs. 8.1 ± 0.5 mg/kg/min; p < 0.001), which also demonstrated a low insulin metabolic clearance rate (p < 0.001). Although intolerant after oral glucose, the cirrhotic patients had glucose requirements identical to those of controls during the hyperglycemic clamp (cirrhotic patients: 6.1 ± 1.0 mg/kg/min; controls: 6.3 ± 0.7 mg/kg/min), suggesting normal intravenous glucose tolerance.
C-peptide MCR was identical in cirrhotic patients (2.93 ± 0.16 ml/min/kg) and controls (2.96 ± 0.24 ml/min/kg). Insulin secretion was higher in cirrhotic patients, both fasting (2.13 ± 0.26 U/hr vs. 1.09 ± 0.10 U/hr; p < 0.001) and from min 30 to 90 of the hyperglycemic clamp (5.22 ± 0.70 U/hr vs. 2.85 ± 0.22 U/hr; p < 0.001). However, with oral glucose the rise in serum C-peptide concentration was relatively delayed, and the insulin secretion index (secretion/area under 3-hr glucose curve) was not elevated. Hepatic insulin extraction was reduced both in fasting and during the hyperglycemic clamp (p < 0.001).
Thus hypersecretion and decreased insulin clearance contribute to the four- to sixfold increased insulin levels in cirrhotic patients (fasting and after oral or intravenous glucose). In response to intravenous glucose, this hyperinsulinemia compensates for peripheral-tissue insulin insensitivity, accounting for normal rates of glucose disposal. In response to oral glucose, compensation is only partial, glucose intolerance being most marked in those cirrhotic patients with a lower insulin secretory response (r = −0.76, p < 0.02). (HEPATOLOGY 1991;14:103–111.)