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 I-125-labeled albumin. In isolated perfused rat lungs, PS was measured by exposure to a perfusate containing EBD (600 mu g/ml) and I-125- albumin (1 mu Ci) 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 (PSEBD) was fivefold higher than PS obtained by I-125-albumin (PS-I-125) [1.92 +/- 0.32 (SE) vs. 0.42 +/- 0.03 X 10(-2) cm(3).min(-1).g(-1), P < 0.05]. Similarly, in rats pretreated with Salmonella enteritidis lipopolysaccharide (2 mg/kg iv), PSEBD was much higher than PS-I-125 (2.01 +/- 0.30 VS. 0.59 +/- 0.08 X 10(-2) cm(3).min(-1).g(-1), P < 0.01). This discrepancy between PSEBD and PS-I-125 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 the two markers showed an initial phase of rapid lung uptake of EBD, followed by parallel uptake of both markers up to 60 min of perfusion. We conclude that although EBD does not cause obvious lung injury, it is not a reliable marker for measurement of vascular permeability in perfused rat lungs. This is most likely due to rapid binding of EBD to lung tissue proteins.