Summary
Arterial thrombosis may be initiated in an experimental animal by a photochemical
reaction between transmural green light and i.v. administered Rose Bengal, a photosensitizer
dye. In this study, scanning electron microscopy has been used to reveal the nature
of vessel injury and the cellular composition of the photochemically induced thrombus.
A 5 mm segment of the guinea pig femoral artery was occluded by a thrombus about 10
min after irradiation with green light in the presence of systemically administered
Rose Bengal. Electron microscopy revealed that following photochemical reaction, endothelial
cells first contract and, with further irradiation, become detached from the vessel
wall, with their cell membrane being destroyed at the irradiated site where an occlusive
platelet-rich thrombus was formed. Endothelial cell injury and vessel occlusion could
be completely inhibited by the aminothiol, DL-cysteine administered i.v. 1 min after
Rose Bengal. The mechanism of endothelial injury in this model appears to be by singlet
molecular oxygen, 1O2 formed by energy transfer from the photo-excited dye to O2.