Fibrinolysis and diabetic retinopathy.

The spontaneous fibrinolytic activity of the blood is abnormally low significantly more often in persons with diabetes mellitus than in nondiabetic controls. The fibrinolytic response stimulated by venous occlusion is poor six times more frequently in diabetics than in controls, and the fibrinolytic activity of the endothelial cells is abnoramlly low in one-fourth of the diabetics tested. These changes are not related to the duration of diabetes. However, if patients with long-standing diabetes (greater than 10 years) are separated into those with retinopathy and those without, it is found that those who remain free from opthalmoscopically visible retinopathy have an almost normal fibrinolytic response on stimulation, while the others have a significantly lower response. This difference seems to be caused by a faulty plasminogen activator release mechanism. Compared with the other diabetics, those with retinopathy also have a significantly increased level of fibrinogen and of alpha2-macroglobulin, a protein that acts as an inhibitor of fibrinolysis. These findings imply a poor defense mechanism against fibrin deposits in the vessel walls in diabetes, which might contribute to the development of diabetic microangiopathy.