Hexose metabolism in pancreatic islets: Effect of D-glucose upon D-fructose metabolism

In the light of recent findings on the effect of D-glucose upon D-fructose phosphorylation by human B-cell glucokinase, the influence of the aldohexos e upon the metabolism of the ketohexose was investigated in rat pancreatic islets. D-glucose, although slightly decreasing D-[5-H-3]fructose utilizati on, augmented the oxidation of the ketohexose, indicating that the aldohexo se stimulates preferentially the oxidative, as distinct from anaerobic, mod ality of glycolysis. Such was not the case in parotid cells, taken as repre sentative of functionally nonglucose-responsive cells. In the islets expose d to D-fructose, D-glucose also decreased the fractional contribution of th e pentose shunt to the generation of CO2 and D-glyceraldehyde 3-phosphate f rom the ketohexose, and increased the inflow into the Krebs cycle of dicarb oxylic metabolites relative to that of fructose-derived acetyl-CoA. This gl ucose-induced remodeling of D-fructose metabolism may optimize the insulin secretory response of islet cells to these hexoses, e.g. after food intake.