Leukotrienes but not complement mediate limb ischemia-induced lung injury

Reperfusion after limb ischemia leads to sequestration of polymorphonuclear leukocytes (PMN) in the lungs and to leukocyte-(WBC) and thromboxane-(Tx) dependent respiratory dysfunction. This study examines the intermediary role of the chemoattractants leukotriene (LT)B₄ and complement (C) fragments. Anesthetized sheep with chronic lung lymph fistulae underwent 2 hours of tourniquet ischemia of both hind limbs. In untreated controls (n = 7), 1 minute after tourniquet release, mean pulmonary artery pressure (MPAP) rose from 13 to 38 mmHg (p < 0.05) and returned to baseline within 30 minutes. Pulmonary artery wedge pressure was unchanged from 3.6 mmHg. There were increases in plasma LTB₄ levels from 2.46 to 9.34 ng/ml (p < 0.01), plasma TxB₂ levels from 211 to 735 pg/ml (p < 0.05), and lung lymph TxB₂ from 400 to 1005 pg/ml (p < 0.05). C3 levels were 96% of baseline values. Thirty minutes after reperfusion, lung lymph flow (Q̇L) increased from 4.3 to 8.3 ml/30 minutes (p < 0.05), lymph/plasma protein ratio was unchanged from 0.6, and the lymph protein clearance increased from 2.6 to 4.6 ml/30 minutes (p < 0.05), data consistent with increased microvascular permeability. WBC count fell within the first hour from 6853 to 3793/mm³ (p < 0.01). Lung histology showed leukosequestration, 62 PMN/10 high-power fields (HPF) and proteinaceous exudates. In contrast to this untreated ischemic group, animals treated with the lypoxygenase inhibitor diethylcarbamazine (n = 5) demonstrated a blunted reperfusion-induced rise in MPAP to 17 mmHg (p < 0.05). There were no increases in LTB₄, TxB₂, Q̇L or lymph protein clearance (p < 0.05). WBC count was unchanged and lung leukosequestration was reduced to 40 PMN/10 HPF (p < 0.05). Decomplementation with cobra venom factor (n = 4) resulted in plasma C3 levels, 10% of baseline, but tourniquet release still led to pulmonary hypertension, elevated LTB₄, TxB₂ levels, and a decline in WBC count similar to that of untreated ischemic control animals. Histology showed 46 PMN/10 HPF sequestered in the lungs. Further, bilateral hind limb ischemia in either genetically sufficient (n = 10) or deficient (n = 10) C5 mice led to significant lung leukosequestration of 108 and 106 PMN/10 HPF, respectively, compared with 42 and 47 PMN/10 HPF in sham C5(+) and C5(-) mice (n = 20) (p < 0.01). These results suggest that the lung leukosequestration and increased microvascular permeability after lower torso ischemia are mediated by the chemotactic agent LTB₄, but not by the complement system.