[A scanning electron microscopic study of experimental endothelial injury and regeneration following photochemically induced thrombosis in rat retinal venules].

The natural course of retinal venous obstruction and of endothelial injury and regeneration following photochemically induced thrombosis in Wistar-Kyoto rats was studied by scanning electron microscopy utilizing the freeze-splitting method. The eyes were examined ophthalmoscopically and histologically at 30 min, 6, 24 h, 2, 3, 4 and 5 days after the insult. At 30 minutes after the irradiation, the vascular lumen of retinal venule was completely occluded with a large amount of fibrous materials considered to be fibrin mesh-work and a mass of deformed erythrocytes. By 6 hours after the irradiation, the fibrous materials had decreased and deformed erythrocytes had also decreased in number. On the other hand, multi-layered platelets with pseudopods aggregated over the irradiated area. Similar platelet aggregation was also seen at 24 hours after the irradiation, however, fibrous materials and deformed erythrocytes were rarely observed. These aggregates persisted for up to 2 days after the irradiation, when exposure of the subendothelium was also observed. By 3 days after the irradiation, there had been no platelet aggregates and the injured area was reendothelialized. But the endothelial surface was rugged and had many crater-like pores. In addition, some of these endothelial cells protruded or were elevated toward the lumen. Endothelial abnormalities such as rugged surface and crater-like pores were also found at 5 days after the irradiation. These findings suggested that rapid thrombolysis was caused by activation of the local fibrinolytic system, that the injured area was rapidly reendothelialized within about 3 days but that mild endothelial damage still existed for more than 5 days.