Dilatation and endothelial proliferation of retinal capillaries in streptozotocin-diabetic rats: quantitative electron microscopy.

The capillaries in normal and short term (30 days) streptozotocin-diabetic rats were studied with quantitative light and electron microscopy. The streptozotocin treatment caused capillary dilatation, endothelial proliferation, and endothelial swelling. These ultrastructural changes occurred in existing capillaries, since light microscopy showed no significant change in the frequency of capillaries per unit area of retina. Endothelial cell proliferation was evidenced by a significant increase in the number of endothelial junctions. Capillaries with one endothelial function were most severely dilated, and their number significantly decreased by endothelial proliferation. Unlike the normal rats, the streptozotocin-treated animals showed no significant correlation between the mean lumen area and the number of endothelial junctions. The increase in size of the capillaries and their lumens was expected to reduce the width of the capillary walls. The thickness of capillary basement membrane was reduced as expected. However, the observed capillary wall width remained within normal limits, due to both capillary proliferation and endothelial swelling. In addition, some interesting qualitative alterations were observed in mural cells, neurons, and the endothelial junctions.