Effects of hyperoncotic albumin on endothelial barrier properties of rat lung

Abstract

We have determined the effect of concentrated albumin on lung endothelial hydraulic conductivity (Lp) by our split-drop technique. We anesthetized 39 rats (2% halothane and pentobarbital sodium, 30 mg/kg ip; Sprague-Dawley, 500 g), then isolated and blood perfused their lungs. At constant inflation pressure (5 cmH2O) and stopped blood flow, we viewed subpleural venules (diameter, 20 microns) by microscopy and video. By micropuncture, we first microinfused a venule for 6 min with albumin that was either isoncotic (4 g/dl) or hyperoncotic (6 g/dl) with respect to rat plasma. In the same venule we then injected and split an oil drop with 4 g/dl albumin. From the rates of movement of the split oil drop at different vascular pressures, we determined Lp for 4 g/dl albumin. In venules that were previously microinfused for 6 min with 4 g/dl albumin, Lp for 4 g/dl albumin did not differ from that of noninfused controls (5.4 +/- 0.8 x 10(-7) ml.cm-2.s-1.cmH2O-1). However, after a similar microinfusion of 6 g/dl albumin, the Lp immediately increased more than two times above baseline (P < 0.01) but returned to baseline after 15 min. Lp for 4 g/dl albumin was not affected by hyperoncotic preinfusions of either neutral dextran or immunoglobulin G. We conclude that concentrated albumin caused a reversible increase of the lung endothelial barrier conductivity.