Leukotrienes but not Complement Mediate Limb Ischemia-Induced Lung Injury

Abstract

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 less than 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 less than 0.01), plasma TxB2 levels from 211 to 735 pg/ml (p less than 0.05), and lung lymph TxB2 from 400 to 1005 pg/ml (p less than 0.05). C3 levels were 96% of baseline values. Thirty minutes after reperfusion, lung lymph flow (QL) increased from 4.3 to 8.3 ml/30 minutes (p less than 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 less than 0.05), data consistent with increased microvascular permeability. WBC count fell within the first hour from 6853 to 3793/mm3 (p less than 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 less than 0.05). There were no increases in LTB4, TxB2, QL or lymph protein clearance (p less than 0.05). WBC count was unchanged and lung leukosequestration was reduced to 40 PMN/10 HPF (p less than 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 less than 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.