Metabolic and secretory response to D-fructose in pancreatic islets from adult rats injected with streptozotocin during the neonatal period

The metabolic and secretory responses to D-glucose and/or D-fructose were m easured in pancreatic islets prepared from either control rats or animals t hat had been injected with streptozotocin during the neonatal period (STZ r ats). The STZ rats displayed higher plasma D-glucose concentrations, but lo wer plasma insulin concentrations, islet insulin content, as well as basal and nutrient-stimulated insulin release. This coincided with lower rates of D-[U-C-14]hexose oxidation and D-[5-H-3]hexose utilization. In both contro l and STZ rats, D-fructose failed to affect significantly the metabolism of D-glucose, while the aldohexose increased the ratio between D-[U-C-14]fruc tose oxidation and D-[5-H-3]fructose conversion to (HOH)-H-3. Such a ratio was higher than that found with radioactive D-glucose in islets exposed to both hexoses, whether in control or STZ rats, indicating a far-from-negligi ble contribution of fructokinase to the phosphorylation of D-fructose. Desp ite these analogies between both the respective fate of D-glucose and D-fru ctose and the reciprocal metabolic effects of the two hexoses in islets fro m control and STZ rats, the secretory response to the ketohexose in islets from STZ rats was preferentially suppressed, relative to that evoked by the aldohexose. This gives support to the idea that the insulinotropic action of D-fructose may not be entirely accounted for by its nutritional value in islet cells. (C) 1999 Academic Press.