Disruption of blood-retinal barrier in experimental diabetic rats: An electron microscopic study

Permeability pattern of retinal capillaries in streptozotocin-diabetic rats, maintained for 1-6 months, was studied with the electron microscope, using horseradish peroxidase as a tracer. A reaction product of horseradish peroxidase was confined to the capillary lumina and to a small number of vesicles on the luminal portion of the endothelial cells in control rats and diabetic rats maintained for 1 month. In diabetic rats maintained for 2-6 months, reaction product was observed in the basement membrane of endothelial cells and pericytes and extended to the extracellular spaces around the capillaries. The number of reaction product-labeled vesicles in the capillary endothelial cells was greatly increased in diabetic rats maintained for 2 months, as compared with that in control rats and diabetic rats maintained for 1 month. Reaction product was also found in the intercellular junctions of capillary endothelial cells from the luminal to the abluminal portion in diabetic rats maintained for 3-6 months. The increased permeability in retinal capillaries of diabetic rats preceded the thickening of the basement membrane, and seemed to play an important role in the development of diabetic retinopathy.