Insulin secretory capacity and the regulation of glucagon secretion in diabetic and non-diabetic alcoholic cirrhotic patients

Abstract

Background/Aims: Insulin secretion is increased in cirrhotic patients without diabetes but decreased in cirrhotic patients with diabetes. Increased glucagon secretion is found in both groups. Our aim was to determine: 1) whether alterations in insulin secretion are due to changes in maximal secretory capacity or altered islet B-cell sensitivity to glucose, and 2) whether regulation of glucagon secretion by glucose is disturbed. Methods: Insulin, C-peptide and glucagon levels were measured basally and during 12, 19 and 28 mmol/l glucose clamps, and in response to 5 g intravenous arginine basally and after 35 min at a glucose of 12, 19 and 28 mmol/l in 6 non-diabetic alcoholic cirrhotic patients, six diabetic alcoholic cirrhotic patients and six normal controls. Results: Fasting insulin, and C-peptide levels were higher in cirrhotic patients than controls but not different between diabetic and non-diabetic patients. C-peptide levels at t=35 min of the clamp increased more with glucose concentration in non-diabetic cirrhotic patients than controls; there was little increase in diabetic cirrhotic patients. At a blood glucose of ≈ mmol/l the 2–5 min C-peptide response to arginine (CP ARG) was similar in all groups, but enhancement of this response by glucose was greater in non-diabetic cirrhotic patients and impaired in diabetic cirrhotic patients. Maximal insulin secretion (CP ARG at 28 mmol/l glucose) was 49% higher in the non-diabetic cirrhotic patients than controls ( p<0.05); in diabetic cirrhotic patients it was 47% lower ( p<0.05). The glucose level required for half-maximal potentiation of (CP ARG) was not different in the three groups. Cirrhotic patients had higher fasting glucagon levels, and a greater 2–5-min glucagon response to arginine, which was enhanced by concomitant diabetes ( p<0.001 vs controls). Suppression of plasma glucagon by hyperglycaemia was markedly impaired in diabetic cirrhotic patients (glucagon levels at 35 min of 28 mmol/l glucose clamp: diabetics, 139 ×/ ÷ 1.25 ng/l, non-diabetic cirrhotic patients, 24 × ÷1.20, controls, 21×/÷1.15, p<0.001). Suppression of arginine-stimulated glucagon secretion by glucose was also impaired in diabetic cirrhotic patients, and to a lesser extent in non-diabetic cirrhotic patients. Conclusions: Insulin secretory abnormalities in diabetic and non-diabetic cirrhotic patients are due to changes in maximal secretory capacity rather than altered B-cell sensitivity to glucose. The exaggerated glucagon response to arginine in alcoholic cirrhotic patients is not aboli0shed by hyperglycaemia/hyperin-sulinaemia. In diabetic alcoholic cirrhotic patients, the inhibitory effect of glucose on basal glucagon secretion is also markedly impaired.