Augmented polyol pathway activity and retinal pigment epithelial permeability in the diabetic BB rat

In the present study we investigated the relationship between an augmented polyol pathway and the breakdown of the blood-retinal barrier in the spontaneously diabetic BB rat. Permeability experiments were performed in diabetic and age-matched non-diabetic BB rats in a longitudinal fashion using horseradish peroxidase. Increased permeability of horseradish peroxidase across the retinal pigment epithelium was noted after 6 months of diabetes. Abnormalities of the basal plasmalemmal infoldings of the retinal pigment epithelium were noted in the control animals and appeared to be exaggerated in diabetic rats. Simultaneous quantitative ultrastructural immunohistochemistry, using an affinity purified anti-BB rat aldose reductase antibody and protein-A gold, revealed a significant increase in the aldose reductase immunoreactivity of the retinal pigment epithelium in diabetic animals. These findings suggest that an augmented polyol pathway activity may play a role in the pathogenesis of the blood-retinal barrier breakdown at the level of the retinal pigment epithelium in the diabetic BB rat.