Mechanism of fat-induced attenuation of glucose-induced insulin secretion from mouse pancreatic islets

In order to investigate the mechanism behind fat-induced inhibition of glucose-induced insulin secretion a selection of enzymes that may participate in regulation of pancreatic islet glucose oxidation was studied in islets isolated from mice that had been fed on a laboratory chow diet or on a high-fat diet for 10-12 weeks. At 20 mmol/L glucose production of (CO2)-C-14 from [U-C-14]-glucose was decreased 50% in islets from fat-fed mice. At 3.3 mmol/L glucose the glucose oxidation rate was similar in the two groups. The fatinduced decrease in glucose oxidation rate was correlated with a 35% decrease in the maximal glucokinase activity. The K-m for glucose was unchanged. No differences between the diet groups were found in the activities of hexokinase, phosphofructo-1-kinase, glucose 6-phosphatase or mitochondrial glycerophosphate dehydrogenase. After preincubation with 20 mmol/L glucose the activity of cytosolic Ca2+-independent as well as Ca2+-dependent phospholipase A(2) was unchanged by fat-feeding. However, the activity of lysophospholipase was significantly increased by fat-feeding, which may result in lowered concentrations of islet lysophosphatidylcholine (lysoPC). It is concluded that in fat induced diabetic animals a decrease in islet glucokinase may contribute considerably to the decrease in islet glucose oxidation rate. Furthermore, the study raises the possibility that changes in islet lysoPC may contribute to the fat-induced attenuation of glucose-induced insulin secretion.