Permeability of inner and outer layers of rat and rabbit aortic wall. Two new microscopic test with trypan blue

Two new permeability tests are described for use with intravenously injected trypan blue. One depends on the demonstration of trypan blue by its specific red fluorescence in green light at 570 nm, while the other is a surface microscopy technique at low magnification, using illumination from a fibre-optics light source. The routes of entry of the trypan blue-albumin complex into the rat and rabbit aorta appear to be from both the inner and outer surfaces. Over the period 1/4-24 h after injection of the dye, more entered from the outer surface than the inner surface in the rat aorta and rather more in the rabbit thoracic aorta. The arch of the rabbit aorta showed in general rather greater entry from the inner surface. Trypan blue that has entered the aortic wall is partly taken up by the elastic lamellae. Elastic competes successfully for the dye and captures it from the trypan blue-albumin complex; this uptake is blocked by deamination with nitrous acid.