Leukocyte involvement in pulmonary localization of blood-borne microparticulates: relationship to altered lung fluid balance.

The lung lymph fistula preparation in sheep was used to study the influence of localization of blood-borne foreign microparticulates in the lung on lymph flow (Qlym); lymph-to-plasma total protein concentration ratios (L/P); pulmonary transvascular protein clearance (Qlym X L/P); and pulmonary hemodynamics. Test particles small enough to readily pass through capillary beds were infused intraarterially to avoid acute lung vascular injury by macroembolism. In sheep, tissue distribution patterns demonstrated that by 15 min after intravenous infusion of the gelatinized reticuloendothelial (RE) test lipid emulsion (0.8-1.0 micron) or gelatinized colloidal carbon (250 A), 30-35% of the injected particle dose localized in the lung, with approximately 15-22% in RE cell-rich organs such as the liver. Particle infusion resulted in an acute neutropenia in the absence of a decline in platelets. Electron microscopy revealed that the increased particulate localization in the lung reflected particle uptake by marginated phagocytic cells as well as the presence of microaggregates within the vascular space. Lung localization of both particulates resulted in approximately a 200-300% increase in both lymph flow and transvascular protein clearance. The hemodynamic response coupled with the pattern of transvascular protein clearance in relationship to lymph flow suggests that the alterations in fluid and protein flux were due to both an increase in microvascular pressure as well as an increase in lung vascular permeability. Marginated phagocytic cells which rapidly ingest the blood-borne foreign test particles may contribute to the altered lung fluid balance seen with the entrance of foreign or abnormal microparticulates in the blood.