4.3 The polyol pathway

Sorbitol is not strictly a sugar since it lacks a keto or aldehyde group. It is normally a minor component of dietary carbohydrates, but it is also prepared synthetically and used as a sweetener. In addition, it is formed in our own metabolism from glucose (Figure 4.3-1). Degradation occurs via dehydrogenation to fructose.

Aldose reductase can also reduce galactose, giving rise to galactitol. It is believed that accumulation of sorbitol in diabetes and of galactitol in galactosemia occurs in the lens of the eye and in peripheral nerves, and that this contributes to the formation of cataract and to nerve damage in the two diseases. Therefore, inhibitors of aldose reductase are being used—with fairly limited success—in the therapy of diabetes.

Formation of fructose from glucose via the polyol pathway occurs in the seminal vesicles (part of the male sexual organs), and fructose is found in the sperm. It serves as a supply of fuel to these cells in their quest of an oocyte; the fructose is not utilized by the other tissues the sperm will get into contact with.

Now, if that is the case, then inhibitors of aldose reductase should be great as a pill for males, shouldn't they? However, I have not seen any studies on their effects on male fertility.