Permeability in atherosclerosis: fluorescence test in green light with trypan blue.

A new microscopic fluorescence method for trypan blue at 570 nm has been used to follow the entry of albumin into the atheromatous rabbit aorta. Permeability into the inner aortic wall increases before the onset of gross lesions and seems just to precede intraendothelial deposition of lipid. Thereafter, permeability of the inner wall progressively increases until streaks or small plaques develop. These raised lesions stain and fluoresce variably, some intensely so while others are almost unreactive. This variability might reflect the difference between progressive and quiescent lesions. However, a zone of increased permeability surrounds many raised lesions, suggesting that the edge is a major site of growth and progression.