Microthrombi and hydraulic conductivity increase induced by laser/dye treatment

Abstract

To quantify microthrombi induced by photodynamic therapy, we measured thrombus initiation time, growth rate and microvessel occlusion time under laser/dye treatment. Rats (SD, 250‐300g) were anesthetized and kept warm on a heating pad. A midline incision (~2 inch) was made in the abdominal wall; the mesentery was gently taken out and arranged on a glass cover slip. Sodium fluorescein (NaF, 50 mg/kg in 1% BSA mammalian Ringer, ~0.5mg/ml in individual microvessels) was injected through the carotid artery simultaneously when the mesentery was exposed to a laser (495 nm, 0.38mW/mm2). Thrombi were initiated in microvessels (post‐capillary venules, n = 8) in 3.8 (±0.4 SE) min after laser/dye treatment; the mean thrombus growth rate was 0.038 vessel plane area/min; vessels were fully occluded in 25.5 (±2.2 SE) min. No flow was restored after 30 min laser off. We then tested the hypothesis that laser/NaF induced thrombosis was partially due to the increased hydraulic conductivity (Lp) by measuring Lp of a single microvessel under the same laser/dye treatment as for thrombosis. In ~5 min, Lp increased from a mean of 1.02 (±0.02 SE) to 2.12 (±0.25 SE, n = 13) × 10−7 cm/s/cmH2O (p = 0.002), no further increase after longer time exposure (up to 30 min). After laser was off for ~5min, Lp insignificantly decreased to 1.59 (±0.02 SE) ×10−7 cm/s/cmH2O (p = 0.07), no further decrease after 30 min off. The thrombosis is consistent with Lp increase.