[Histopathogenesis of diabetic retinopathy]

Morphology and enzyme activities of the retinal capillaries in mice with the obese-hyperglycaemic syndrome (gene symbol ob)

The retinal capillary bed from 67 obese-hyperglycaemic mice and 64 lean litter mates was isolated by trypsin digestion and investigated with respect to structure and enzyme activities. There was no significant difference in the ratio between numbers of endothelial and mural cells. The capillary walls did not show any obvious structural differences and microaneurysms were not observed. The retinal vessels from the obese-hyperglycaemic mice, however, displayed significantly higher activities of the enzymes hydroxyacyl-CoA-dehydrogenase, asparate aminotransferase (ASAT) and adenylate kinase than their lean litter mates. The activities of glutathione reductase, glucose-6-phosphate dehydrogenase (G-6-PDH) and phosphofructokinase were similar in the two experimental groups. It is suggested that the present data reflect early metabolic disturbances related to diabetic retinopathy.

Morphology and enzyme activities of the retinal capillaries in streptozotocin-diabetic mice

Male lean mice belonging to the obese-hyperglycemic strain were made diabetic by intravenous injection of streptozoticin. The retinal capillary bed freed by trypsin digestion was studied with regard to morphology and the activity of some enzymes. There was a significant increase in the ratio between the endothelial and mural cells which was interpreted as indicating mural pericyte disappearance. The activities of adenylate kinase, aspartate-aminotransferase and hydroxyacyl-CoA-dehydrogenase in the retinal vessels of the diabetic animal were significantly higher than in vessels from the control animals. No differences were found in the activities of glucose-6-phosphate dehydrogenase, glutathione reductase and phosphofructokinase between the two animal groups. It is suggested that these results reflect early morphological and metabolic changes of the retinal vessels, preceding the well known clinical picture of diabetic retinopathy.

Macular retinal capillary hemodynamics in diabetic patients

Macular retinal capillary hemodynamics was evaluated in 39 nonhypertensive insulin-dependent diabetic patients and 24 age-matched control subjects using the blue field entopic simulation technique. A statistically significant 25% increase in macular capillary flow velocity was observed among the diabetic eyes along with a 37% decrease in the density of the entoptically perceived leukocytes. When the eyes of diabetic patients were graded according to the modified composite scale of Klein et al, capillary flow velocity was elevated in the group without retinopathy as well as in those with mild background retinopathy and those with preproliferative or proliferative retinopathy. The density of the entopically perceived leukocytes was more severely reduced in those with retinopathy than in those without retinopathy but was poorly correlated with the composite grading scale. These results are consistent with the concept that in diabetes, capillary obstruction, either transient or permanent, may focally occur within the retina associated with vasodilation in the adjacent microvasculature because of relative tissue hypoxia.

Diabetic capillaropathy

Diabetic capillaropathy is defined and reviewed. A number of physiological and pathological variables, such as aging, venous stasis, and environment, may affect the thickness of the capillary basal lamina. Since these effects have not been adequately measured, it is impossible to know precisely what increment diabetes mellitus adds to the basal lamina. Because of these variables and technical difficulties, the detection of early diabetes is impossible at this time. However, the ultrastructure of the peripheral capillaries in the late stages of diabetes provides a means of detecting the presence of widespread capillaropathy when clinical evidence is difficult to obtain or uncertain.