Evans blue dye in the assessment of permeability-surface area product in perfused rat lungs

Evans blue dye (EBD) has been used extensively as a marker of extravascular protein leakage. We assessed the utility of EBD as an albumin marker in the measurement of permeability-surface area product (PS) in perfused rat lungs and compared the results with PS values obtained using 125I-labeled albumin. In isolated perfused rat lungs, PS was measured by exposure to a perfusate containing EBD (600 micrograms/ml) and 125I-albumin (I microCi) for exactly 3 min, followed by washout of the intravascular space with fresh perfusate for 6 min. In lungs from normal rats, we found that PS obtained by EBD (PS-EBD) was fivefold higher than PS obtained by 125I-albumin (PS-125I) [1.92 +/- 0.32 (SE) vs. 0.42 +/- 0.03 x 10(-2) cm3.min-1.g-1, P < 0.05]. Similarly, in rats pretreated with Salmonella enteritidis lipopolysaccharide (2 mg/kg iv), PS-EBD was much higher than PS-125I (2.01 +/- 0.30 vs. 0.59 +/- 0.08 x 10(-2) cm3.min-1.g-1, P < 0.01). This discrepancy between PS-EBD and PS-125I was not explained by differences in the amount of free marker in perfusate, because the albumin-binding rate for both markers was very high. In addition, prolonged perfusion (40 min) with EBD did not significantly affect pulmonary vasoreactivity or water content in rat lungs. A detailed comparison of the kinetics of lung tissue uptake of EBD followed by parallel uptake of both markers up to 60 min of perfusion.(ABSTRACT TRUNCATED AT 250 WORDS)