EFFECTS OF HYPERONCOTIC ALBUMIN ON ENDOTHELIAL BARRIER PROPERTIES OF RAT LUNG

We have determined the effect of concentrated albumin on lung endothel ial hydraulic conductivity (L(p)) by our split-drop technique. We anes thetized 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 vi ewed subpleural venules (diameter, 20 mum) 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 respe ct 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 L(p) or 4 g/dl al bumin. In venules that were previously microinfused for 6 min with 4 g /dl albumin, L(p) for 4 g/dl albumin did not differ from that of nonin fused controls 5.4 +/- 0.8 x 10(-7) ml.cm-2.s-1.cmH2O-1). However, aft er a similar microinfusion of 6 g/dl albumin, the L(p) immediately inc reased more than two times above baseline (P < 0.01) but returned to b aseline after 15 min. L(p) for 4 g/dl albumin was not affected by hype roncotic preinfusions of either neutral dextran or immunoglobulin G. W e conclude that concentrated albumin caused a reversible increase of t he lung endothelial barrier conductivity.