Absence of degenerative changes in retinal and uveal capillary pericytes in diabetic rats

Ultrastructural morphometric techniques were used to quantify pericyte degeneration in retinal and uveal capillaries of streptozotocin-diabetic rats in order to assess the suitability of this small rodent model of diabetes for studies of the pathogenesis of microvascular eye disease in diabetic humans. Male, Sprague-Dawley rats were killed by intraaortic perfusion of fixative 6 and 9 mos after induction of diabetes with 50 mg/kg streptozotocin. No differences were evident between diabetics and age-matched controls in capillary circumference, numbers of endothelial cells per capillary, and capillary cytoplasmic area of retinal, choroidal, and iridial vessels. Capillary basement membrane width and the percentage of the capillary circumference covered by pericytes were increased in retinas of diabetic vs age-matched control rats after 9 mos of diabetes (P less than 0.05), but no differences were evident in the number of pericyte processes per capillary and the percentage of vessels with pericyte nuclei. No differences in pericyte distributions were observed between control and diabetic rats in the choriocapillaris and iris after 9 mos of diabetes. These findings indicate that retinal capillary basement membrane thickening precedes any evidence of pericyte degenerative changes and suggest that pericyte degeneration analogous to that associated with human diabetic microangiopathy does not occur in this experimental animal model.