Retinal nitro blue tetrazolium staining and catalase activity in rat models of diabetes

Recent studies have suggested that reactive oxygen species may be involved in the development of diabetic retinopathy.

Nitro blue tetrazolium (NBT) staining, a marker of reductants which may be induced by free radicals such as superoxide, and catalase activity, 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 diagnosis of diabetes. Streptozotocin (60 mg/kg) was injected i.p. at 8 weeks of age and the experiments were performed after 8 weeks of diabetes. Young Sprague-Dawley rats were fed a 50% galactose diet for 9, 12 or 22 months.

In trypsinized vessel preparations, more intense NBT staining was observed only in rats fed a galactose diet for 22 months. In cross sections, the number of stained vessels were increased in BB rats (p < 0.01), but not in rats with streptozotocin-induced diabetes. Catalase activity did not differ between any of the experimental groups and their matched controls.

Increased amount of NBT reductants in retinal vessels occurred in BB Wistar rats and to some extent in galactose-fed rats, indicating a possible role for free radicals in the development of diabetic retinopathy. There was no evidence of increased retinal H2O2 production or activation of catalase, indicating that this particular enzyme was not affected during the conditions studied.