The sorbitol pathway. Enzyme localization and content in normal and diabetic nerve and cord

The enzymes of the sorbitol pathway, aldose reductase and sorbitol dehydrogenase, were investigated in sciatic nerve and spinal cord. The substrate specificities of spinal cord aldose reductase indicates that it is a variant of TPN L-hexonate dehydrogenase which possesses poor polyol forming ability. In contrast, the cauda equina and sciatic nerve aldose reductase have a true aldose reductase with considerable polyol forming ability. The distribution of the latter enzyme is associated with the presence of Schwann cells. Wallerian degeneration experiments are compatible with the localization of true aldose reductase in the Schwann cell and sorbitol dehydrogenase in the axon. There was no change in the levels of sorbitol dehydrogenase in diabetic nerves, a 30 per cent decrease occurred in the aldose reductase content. This decrease suggests a metabolic abnormality of the Sehwann cell, possibly resulting from alrered cellular integrity, which may have important implication for the otiology of diabetic neuropathy.

Effects of insulin on metabolism of perfused livers of rats made acutely diabetic by anti-insulin serum injection

Livers were taken from fed rats injected ninety to 120 minutes earlier with guinea pig anti-insulin serum and were perfused for four hours with and without addition of insulin to the medium. Glucose-l-C-14, glucose-6-C-14, and acetate-H-3 were added as tracers. The major changes from normal were (1) decreased initial glycogen content, (2) decreased fatty acid synthesis, and (3) decreases in oxidation to CO2 of both glucose-l-C-14 and glucose-6-C-14. Fatty acid synthesis was correlated with initial glycogen content, which varied widely even though the degree of hyperglycemia of the donor animal was quite consistent. Insulin added to the perfusate restored normal rates of glucose oxidation and stimulated fatty acid synthesis, although normal lipogenesis was not achieved. The data are consistent with mediation of the antiserum effects on the liver by plasma elevation of either unesterified fatty acid or glucagon.