Photochemically induced cerebral infarction. II. Edema and blood-brain barrier disruption.

Alterations in the blood-brain barrier to proteins, and regional water and electrolyte content were documented in a rat model of photochemically induced small-vessel thrombosis leading to infarction. Horseradish peroxidase (HRP) or Evans blue was given immediately following a 2-min photochemical sensitization period. At 5 min following irradiation, multifocal sites of peroxidase extravasation were noted within the irradiated area. Ultrastructural examination revealed endothelial cells filled with HRP which in some cases extended into the basal lamina and extracellular spaces. At 15 min, protein leakage was more pronounced within the irradiated zone and reaction product was also apparent within the subarachnoid and perivascular spaces of brain regions remote from the site of irradiation. Widespread staining on the surface of the irradiated hemisphere was apparent in rats perfused 8 h following Evans blue infusion. Water content increased significantly by 15 min within the irradiated zone but not in brain regions remote from this site. Although vasogenic edema is an early event in this stroke model, increases in water content are restricted to the irreversibly damaged site. In contrast, protein tracer escaping from microvessels coursing within the irradiated zone was widely distributed. These findings implicate endothelial barrier dysfunction in the genesis of tissue injury in this model. Morphological evidence for the capability of macromolecules to escape from a site of evolving infarction and to migrate to distances remote from the area of primary microvascular damage is also discussed.