Microvessel hyperpermeability and thrombosis induced by light/dye treatment

To investigate the structural mechanisms by which light/dye treatment induces microvascular hyperpermeability and thrombosis, we quantified thrombus initiation time, thrombus growth rate, and microvessel occlusion time in post-capillary venule of rat mesentery. We also measured the microvessel hydraulic conductivity (Lp) under the same light/dye treatment. With the light intensity of 0.37 mW/mm², thrombus was initiated in 3.8 ± 0.4 min, with a growth rate 3.9% ± 0.3% of the vessel mid-plane area/min, and microvessels were completely occluded in 29.3 ± 2.2 min (SE, n=8); in 3.5 ± 0.3 min, Lp increased from a mean of 0.98 ± 0.08 to 2.07 ± 0.21 × 10^-7 cm/s/cmH₂O (SE, n = 11). Lp didn´t increase further after longer time exposure (up to 30 min). Combination of experimental results with predictions from an interendothelial cleft model suggests that the most likely mechanism by which light/dye induces hyperpermeability and thrombosis is degradation of the endothelial glycocalyx layer of the microvessel wall.