Protein, cell, and LTB4 concentrations of lung edema fluid produced by high capillary pressures in rabbit

We previously demonstrated disruptions of the pulmonary capillary endothelium and alveolar epithelium at transmural pressures (Ptm) of 52.5 cmH2O in rabbit by electron microscopy. In the present study, we determined the characteristics of the alveolar edema fluid in this condition by carrying out bronchoalveolar lavage after blood perfusion for 10 min at Ptm of 12.5 (low), 32.5 (intermediate), and 52.5 cmH2O (high). At low Ptm, where our previous studies showed no ultrastructural changes, the volume of alveolar fluid obtained by urea dilution was very small, and the concentrations of proteins, cells, and leukotriene B4 (LTB4) in the bronchoalveolar lavage fluid (BALF) were low. However, at high Ptm the volume of alveolar fluid and the concentrations of total protein and cells in the BALF were greatly increased. The amount of LTB4 in the BALF also increased substantially from 6.0 to 49.5 micrograms (P < 0.001). Intermediate changes were seen at intermediate Ptm. We concluded that exposing pulmonary capillaries to high Ptm results in a high-permeability form of edema. In addition, the presence of LTB4 suggests that chemical mediators are released, possibly as the result of exposure of the reactive capillary endothelial basement membrane, as demonstrated by electron microscopy.