Insulin Regulation of Hepatic Glucose Transporter Protein Is Impaired in Chronic Pancreatitis

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Abstract
Objective The effect of chronic pancreatitis and insulin on the expression of the hepatic facilitative glucose transporter protein (GLUT-2) was determined in rats. Summary Background Data Chronic pancreatitis is associated with diabetes mellitus or impaired glucose tolerance. Suppression of hepatic glucose production (HGP) by insulin is impaired, although the mechanism is unknown. Methods Normal rats, rats with chronic pancreatitis induced 12 to 16 weeks earlier by oleic acid injection into the pancreatic ducts, and sham-operated rats were studied. Isolated, single-pass liver perfusion was performed, during which glucagon (1.2 pM) was infused, with or without insulin (0.6 or 1.2 nM). The suppression of HGP production by insulin was compared with changes in GLUT-2 in the membrane fraction of liver biopsies obtained before and after hormone perfusion. Results Glycogen-rich (fed) livers of normal rats (n = 16) demonstrated a dose-dependent suppression of hepatic glucose production by insulin (50 ± 5% HGP induced by glucagon alone during 1.2-nM insulin perfusion) and a dose-dependent decrease in GLUT-2 (30 ± 13% of basal level during 1.2-nM insulin perfusion). Sham-operated rats (n = 6) also showed reductions in HGP (51 ± 4%) and GLUT-2 (14 ± 10%) during 1.2-nM insulin perfusion. In contrast, rats with chronic pancreatitis (n = 6) showed no suppression of HGP during 1.2-nM Insulin perfusion, and an increase in GLUT-2 (+20 ± 6%) after insulin perfusion (p < 0.02 vs. sham). Conclusions Insulin suppresses glucagon-stimulated HGP in normal and sham-operated rats, and this reduction in HGP is associated with a decrease in the membrane-bound quantity of GLUT-2. In chronic pancreatitis, insulin suppression of HGP is absent, and this is accompanied by an increase in GLUT-2 in the hepatocyte membrane. The authors conclude that the insulin-mediated change in the level of hepatocyte GLUT-2 is impaired in chronic pancreatitis, and may contribute to the altered glucose metabolism observed commonly in this disease.

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