Erythrocyte-leukocyte interactions in the vascular bed of isolated perfused rat lungs

An earlier study of perfused rat lungs showed that leukocytes, given as bolus injections, seemed to become more or less permanently trapped in the pulmonary microvascular bed under erythrocyte-free perfusion. The aim of the present study was, therefore, to investigate the rheologic effects of erythrocytes on the leukocyte microcirculation of perfused rat lungs. Leukocyte and erythrocyte suspensions were given as bolus injections during cell-free, constant pressure perfusion of ventilated rat lungs. Leukocyte numbers were counted in samples of the venous effluent and flow resistance changes were computed from registrations of flow rate, arterial and venous pressures. The preparations showed a continuous efflux of leukocytes which had been trapped in the pulmonary microcirculation before the perfusion was started. A bolus infusion of erythrocytes (3 ml, hematocrit: 30%) caused a transient flow resistance increase during the passage of the erythrocyte bolus through the vascular bed. This initial peak was accompanied by an increased venous efflux of leukocytes and followed by a lower second peak, attributed to a redistribution of trapped leukocytes in the capillary bed. Infusions of mixed cell suspensions (20-30 x 10(6) leukocytes in 30% hematocrit) caused a transient resistance increase similar to that caused by erythrocytes and a sustained resistance increase, less persistent than that caused by leukocytes. The present data suggest that the infusion of erythrocytes caused a re-distribution and an increased efflux of leukocytes, pooled in the pulmonary microcirculation. The rheological effects of erythrocytes could, hypothetically, result from mechanical interactions with the leukocytes in the pulmonary microvessels.