Leukocyte effects on microcirculation in artificially perfused rat lungs

Evidence indicates that leukocyte microvascular flow obstructions play an important role in no-reflow phenomena after ischemia and that leukocytes may cause significant disturbances of capillary perfusion in low flow states. In the present study, a cell-free colloid perfusion (20-60 ml.kg-1.min-1) of isolated ventilated rat lungs was interrupted by bolus injections of leukocytes in varying numbers. Leukocyte effects on flow resistance, tracer gas exchange, and micromorphology were evaluated. The vast majority of the infused leukocytes remained trapped in the lungs after repeated infusions regardless of the number of leukocytes given, although leukocyte trapping decreased at the higher flow rates. The functional and morphological analyses showed that the polymorphonuclear granulocytes had a greater tendency than the mononuclear cells to become permanently trapped in the pulmonary capillaries. The tracer gas analyses indicated that the trapped leukocytes were scattered in the alveolar capillary networks and did not cause complete exclusion of flow from the affected alveoli. This was probably due to the anatomy of the pulmonary microvasculature, with its abundancy in interconnecting pathways.