INTERLEUKIN 1 REDUCES GLYCOLYTIC UTILIZATION OF GLUCOSE BY PANCREATIC ISLETS

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Culture of rat pancreatic islets with interleukin-1 (IL-1) results in up-regulation of the inducible isoform of nitric oxide synthase (iNOS) and overproduction of nitric oxide (NO). This is associated with reversible inhibition of both glucose-induced insulin secretion and islet glucose oxidation, and these effects are prevented by the iNOS inhibitor NG-monomethyl-arginine (NMMA). IL-1 also induces accumulation of nonesterified arachidonic acid in islets by an NO-dependent mechanism, as demonstrated by isotope dilution mass spectrometry and one potential explanation for that effect would involve an IL-1-induced enhancement of islet glycolytic flux. We have therefore examined effects of IL-1 on islet glycolytic utilization of glucose and find that culture of islets with IL-1 in medium containing 5.5 mM glucose results in suppression of islet glucose utilization subsequently measured at glucose concentrations between 6 and 18 mM. The IL-1-induced suppression of islet gluc ose utilization is associated with a decline in islet glucokinase mRNA content, as determined by competitive RT-PCR, and in glucokinase protein synthesis, as determined by immuno-precipitation experiments, and all of these effects are prevented by NMMA. These findings suggest that IL-1 can down-regulate islet glucokinase, which is the primary component of the islet glucose-sensor apparatus, by an NO-dependent mechanism. Because reductions in islet glucokinase levels are known to cause a form of type II diabetes mellitus, these observations raise the possibility that factors which increase islet NO levels might contribute to development of glucose intolerance.