Urinary sorbitol measurement and the effect of an aldose reductase inhibitor on its concentration in the diabetic state

The amounts of sorbitol (SOR) excreted in 24-h urine were determined on two groups, i.e., diabetic and nondiabetic patients, using an improved method in which ion exchange resin column processing was applied, and these levels were compared with SOR levels in whole blood. Urinary SOR concentration was also determined in diabetic and normal rats in the same manner and its relationship to aldose reductase (AR) activity in whole blood was investigated. Changes in SOR levels in urine and whole blood were compared in diabetic rats after administration of an AR inhibitor (ARI). Whole blood SOR levels and urinary SOR excretion were significantly higher in diabetic patients than in nondiabetic patients. The same results were obtained in the animal models. In diabetic rats, the urinary SOR excretion was about five times higher than that in control rats, and the AR activity in whole blood was also significantly higher. The increase in urinary SOR excretion and whole blood SOR levels, as well as AR activity, in blood in the diabetic state was inhibited by ARI administration. The influence of the diabetic state and the efficacy of the ARI were more marked in urinary SOR excretion than in whole blood SOR levels. These data indicate that determinations of urinary SOR excretion and AR activity are easily measurable and of benefit to assessing the diabetic condition.