Structural correlates of arterial endothelial permeability in the Evans blue model

Normal young pigs were injected intravenously with azo dye Evans blue, which is preferentially and consistently taken up by focal areas in the aorta known to be areas of enhanced permeability. Ferritin was intravenously injected into these animals, and its uptake was quantitated at the electron microscope level at 1, 5 and 15 min after administration. The number of vesicles, large inclusions or vacuoles, and junctions, both labelled and unlabelled, were counted in areas of normal and enhanced permeability. The results have revealed that the number of ferritin grains per vesicle is the same in both areas. However, the percentage of vesicles containing ferritin is significantly higher in areas of enhanced permeability.