CHANGES IN THE REDOX STATE IN THE RETINA AND BRAIN DURING THE ONSET OF DIABETES IN RATS

Diabetic retinopathy is thought to result from chronic changes in the metabolic pathways of the retina. Hyperglycemia leads to increased int racellular glucose concentrations, alterations in glucose degradation and an increase in lactate/pyruvate ratio. We measured lactate content in retina and other ocular and non-ocular tissues from normal and dia betic rats in the early stages of strepto-zotocin-induced diabetes. Th e intracellular redox state was calculated from the cytoplasmic [lacta te]/[pyruvate] ratio. Elevated lactate concentration were found in ret ina and cerebral cortex from diabetic rats. These concentrations led t o a significant and progressive decrease in the NAD(+)/NADH ratio, sug gesting that altered glucose metabolism is an initial step of retinopa thy. It is thus possible that tissues such as cerebral cortex have mec hanisms that prevent the damaging effect of lactate produced by hyperg lycemia and/or alterations of the intracellular redox state.