ACTIVATED EOSINOPHILS INCREASE VASCULAR-PERMEABILITY AND RESISTANCE IN ISOLATED PERFUSED RAT LUNGS

The effects of eosinophils activated with phorbol myristate acetate (PMA) on isolated perfused rat lungs were examined. Eosinophils were obtained from lungs of rats infected with Toxocara canis by bronchoalveolar lavage, incubated with PMA, and administered to an isolated perfused rat lung preparation. Vascular endothelial permeability was assessed by measuring the capillary filtration coefficient (K(f,c)) in the perfused lungs. In lungs receiving either no eosinophils (control) or nonactivated eosinophils, there were no changes in pulmonary hemodynamics or K(f,c). However, in lungs receiving 2 x 106 eosinophils activated with PMA, there was a transient 4.8-fold increase in pulmonary vascular resistance that peaked at 30 min, primarily due to the constriction of small arteries and veins. After the initial pressor response, K(f,c) was increased to 7.5 times control at 130 min and resulted in marked lung edema, increased wet-dry weight ratios, and edema on histologic examination. Pulmonary arterial pressure and K(f,c) responses were dose related for eosinophil numbers between 1 x 106 and 4 x 106 cells. Peak airway pressure (Paw) during constant tidal volume ventilation also increased in lungs receiving activated eosinophils compared to the control and nonactivated eosinophil groups. These findings indicate that activated eosinophils are potent effector cells and can cause pulmonary vasoconstriction, bronchoconstriction, and vascular endothelial injury without widespread plugging of capillaries by aggregated eosinophils.