Prevention by granulocyte depletion of increased vascular permeability of sheep lung following endotoxemia.

To see whether circulating granulocytes are necessary for the lung vascular reaction to endotoxin, we measured the endotoxin response in chronically instrumented sheep before and after granulocyte depletion with hydroxyurea. Granulocyte depletion did not affect the pulmonary hypertension caused by endotoxin (peak mean pulmonary artery pressures = 38 +/- 2 cm H2O before depletion and 42 +/- 2 after depletion, P = NS). The late phase increase in lung lymph flow after endotoxin was significantly lower in the granulocytopenic animals as reflected by lung lymph flow (mean steady state lymph flow before depletion = 30.6 +/- 2.0 SE ml/h; mean steady state lymph flow after granulocyte depletion = 15.4 +/- 1.0; P less than 0.01) even though late phase pulmonary vascular pressures were similar before and after granulocyte depletion. Lung lymph protein clearance (lymph flow x lymph/plasma protein concentration) was also significantly lower after granulocyte depletion (mean steady state before depletion = 2.14 +/- 1.4 SE ml/h; and after depletion = 10.4 +/- 1.0; P less than 0.01). We conclude that circulating granulocytes are necessary for the development of increased lung vascular permeability to fluid and protein following endotoxin. The pulmonary vasopressor effects of endotoxin in sheep are independent of granulocytes.