Carbohydrate Metabolism in the Rat Epididymis: Evidence that Glucose is Taken up by Tissue Slices and Isolated Cells by a Process of Facilitated Transport

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Abstract
An examination has been made of factors which influence the rate at which exogenous glucose is utilized by tissue slices and isolated cells prepared from the epididymis of rats with ligated efferent ducts. The uptake of exogenous glucose by tissue slices was unaffected by the addition of testosterone, dihydrotestosterone or carnitine but was reduced by theophylline and, in the caput epididymidis, was stimulated by insulin. Mannose was also utilized by epididymal tissue but fructose and galactose were utilized little, if at all. Galactose, arabinose and 1-0-methylglucose were ineffective in altering the rate at which exogenous glucose was taken up by isolated cells, whereas 3-0-methylglucose, 5-thio-D-glucose and 2-deoxy-D-glucose reduced the rate of glucose uptake, as did phloridzin and phloretin which inhibit membrane transport of hexoses in other tissues. The reduced rate of glucose uptake by epididymal cells in the presence of the nonmetabolizable sugar, 3-0-methylglucose, was shown to be due to competitive inhibition. By comparing the distribution space of glucose in isolated cells with that of substances which are normally excluded from entry into cells, it was evident that the extra- and intracellular concentrations of glucose were greatly displaced from equilibrium values. It is concluded that glucose enters epididymal cells with difficulty but that uptake occurs by a process of facilitated transport.