Increased cytochrome oxidase activity in the diabetic rat retinal pigment epithelium

We have investigated the effects of diabetes on retinal oxidative metabolism. Since activity of the mitochondrial enzyme, cytochrome oxidase, has been demonstrated to be a reliable indicator of oxidative metabolism and physiological activity, we used cytochemical techniques to study the activity of this enzyme in spontaneously diabetic, streptozotocin-diabetic, and control rat retinas. Light microscope results showed an increase in staining for cytochrome oxidase activity in the diabetic RPE cell layer as compared with the control. Quantitative electron microscope analysis showed a significant increase in RPE cells with highly reactive mitochondria as compared with the controls. Mitochondrial staining within the diabetic photoreceptor and retinal vascular endothelial cells was normal. RPE cell volume and surface area, as well as number and volume of mitochondria, were unchanged. This increase in oxidative enzyme activity is further evidence of RPE cell alteration in diabetes.