Depletion of sorbitol and fructose from young and older rat lenses

Fasting for as little as 24 hr markedly reduced the levels of sorbitol and fructose in the adult rat lens. This depletion was found in both young (1 month) and older (8-12 month) rats. Two modes of depletion were examined: decreased synthesis and metabolic breakdown. The role of diffusion was discussed. In vitro experiments showed that in both age groups, decreased glucose in the medium resulted in a proportional decrease in glucose and sorbitol in the lens; the lenticular fructose level was not changed. In contrast to reports showing decreased glycolysis with age, the sorbitol-synthetic capacity of rat lenses was undiminished with age. Acceleration of glycolytic flux in lenses in vitro resulted in decreases in fructose, and to a lesser extent in sorbitol, in both age groups. These findings indicated that fructose can be removed from lenses by metabolism; and that, especially in the older lenses, glycolysis may represent a major route by which fructose, and hence sorbitol, are eliminated during fasting.