COMMON REABSORPTION SYSTEM OF 1,5-ANHYDRO-D-GLUCITOL, FRUCTOSE, AND MANNOSE IN RAT RENAL TUBULE

1,5-Anhydro-D-glucitol (AG) is a major polyol, 99.9% of which is reabs orbed by the kidney. However, such reabsorption is inhibited by compet ition with glucose excreted in excess, i.e., glucosuria. Under such co nditions, AG is excreted into the urine. We administered various types of sugars to rats by continuous intravenous infusion for two hours to evaluate the competition between AG and these sugars for renal reabso rption in vivo. The reabsorption of AG was significantly inhibited by competition with fructose and mannose. The excretion of AG in the 120 min after a load of 3.64 mmol of fructose was 1.99 +/- 0.33 mu mol, th at after 3.64 mmol of mannose loading was 2.34 +/- 0.43 mu mol. These levels were comparable to the AG excretion observed after the administ ration of the same amount of glucose (3.87 +/- 0.61 mu mol). No compet ition was observed with sucrose, xylose, myoinositol or galactose. The reabsorption of fructose and mannose was significantly inhibited by t he presence of AG (P < 0.001) after a mixed load. Results suggest that AG is reabsorbed in the renal tubule by an AG/fructose/mannose-commen transport system that is distinct from the major glucose reabsorption system. These findings may help to clarify the specific transport sys tems for various sugars in the renal tubule, as well as their physiolo gical importance.