RETINAL NITRO BLUE TETRAZOLIUM STAINING AND CATALASE ACTIVITY IN RAT MODELS OF DIABETES

Background: Recent studies have suggested that reactive oxygen species may be involved in the development of diabetic retinopathy. Methods: Nitro blue tetrazolium (NBT) staining, a marker of reductants which ma y be induced by free radicals such as superoxide, and catalase activit y, as an indirect measure of hydrogen peroxide (H2O2) generation, were studied in the rat retina in three conditions known to cause diabetes -like retinopathy, i.e. rats with spontaneous diabetes (the BB Wistar rat), rats with streptozotocin-induced diabetes mellitus, and rats fed on galactose. Male Wistar BB rats were studied 4-10 weeks after diagn osis of diabetes. Streptozotocin (60 mg/kg) was injected i.p. at 8 wee ks of age and the experiments were performed after 8 weeks of diabetes . Young Sprague-Dawley rats were fed a 50% galac-tose diet for 9, 12 o r 22 months. Results: In trypsinized vessel preparations, more intense NBT staining was observed only in rats fed a galactose diet for 22 mo nths. In cross sections, the number of stained vessels were increased in BB rats (p<0.01), but not in rats with streptozotocin-induced diabe tes. Catalase activity did not differ between any of the experimental groups and their matched controls. Conclusions: Increased amount of NB T reductants in retinal vessels occurred in BB Wistar rats and to some extent in galactose-fed rats, indicating a possible role for free rad icals in the development of diabetic retinopathy. There was no evidenc e of increased retinal H2O2 production or activation of catalase, indi cating that this particular enzyme was not affected during the conditi ons studied.