Metabolic and Secretory Interactions between D-Glucose and D-Fructose in Islets from GK Rats

Abstract

The metabolism of d-glucose and/or d-fructose was investigated in both pancreatic islets and parotid cells of control and hereditarily diabetic Goto-Kakizaki (GK) rats. In the islets from GK rats, a preferential alteration of the oxidative response to d-glucose coincided with an impaired secretory response to the aldohexose. Such a metabolic alteration was not found in the parotid cells of GK rats. Whether in islet or parotid cells, d-fructose little affected the catabolism of glucose in either control or GK rats. The metabolism of d-fructose and the effect of d-glucose thereupon were essentially comparable in control and GK rats in both pancreatic islets and parotid cells. In both cell types, the comparison between the metabolism of d-glucose and d-fructose in cells simultaneously exposed to the two hexoses suggested a far from negligible contribution of fructokinase to the phosphorylation of d-fructose. Although the catabolism of the ketohexose and its modulation by d-glucose were closely comparable in islets from control and GK rats, the insulinotropic action of the ketohexose, relative to that of the aldohexose, was severely impaired in the GK rats. The present work thus emphasizes the specificity of the alteration in d-glucose metabolism in islets, as opposed to extrapancreatic cells, of GK rats. It also reveals in the islets of GK rats a further secretory anomaly apparently not attributable to the impairment of nutrient catabolism in the islet cells of these diabetic animals.