Endothelial albumin permeability measured with a new technique in perfused rabbit lung

This study describes two methods of measuring the albumin permeability-surface area product (PS) of the pulmonary microvascular endothelium in isolated, perfused rabbit lungs. Both involve direct sampling of lung tissue to measure how much labeled albumin has entered the extravascular space during a known exposure period. In one, the traditional "multiple-sample" method, extravascular albumin is measured for several different exposure times to determine the kinetics of transcapillary albumin movement, and PS is calculated from that data. We found single-exponential kinetics, with a half time of 77 min and a PS of 2.28 X 10(-3) cm3 . min-1 . g blood-free wet lung-1. The second, "single-sample" method, is a new modification that involves exposing the tissue to labeled albumin for only 3 min, followed by a 3-min vascular washout. Tissue is then analyzed for extravascular albumin and PS calculated assuming the interstitial albumin concentration is essentially zero. The PS obtained was 2.44 X 10(-3) cm3 . min-1 . g blood-free wet lung-1, not significantly different from the value obtained using the more accepted method. Possible sources of error in the new method are discussed, and we conclude that it is an easy, quick, reliable way of accurately measuring macromolecular PS in the lung and presumably other organs as well.