Mast cells and leukotrienes mediate neutrophil sequestration and lung edema after remote ischemia in rodents

Reperfusion of ischemic hindlimbs leads to leukotriene B₄ (LTB₄) and polymorphonuclear neutrophil (PMN)-dependent lung injury. Pulmonary mast cells are capable of synthesizing LTB₄ and are potential mediators of this inflammatory response. This study tests their role in PMN sequestration and pulmonary edema after hindlimb ischemia. Anesthetized, mast cell-sufficient mice (n = 8) or their congeneic mast cell-deficient strain (n = 8) were subjected to 3 hours of hindlimb ischemia. After another 3 hours of reperfusion, plasma LTB₄ levels rose to 651 pg/ml, higher than sham ischemic control (n = 8) values of 202 pg/ml (p < 0.05). At this time there was sequestration of neutrophils in the pulmonary microcirculation (54 PMN/10 high-power fields [HPF]) and an increase in lung wet/dry weight ratio ( W D) of 4.4. Both these values were higher (p < 0.05) than those in sham ischemic animals that showed sequestration of 18 PMN/10 HPF and a lung W D of 3.1. In contrast, mast cell-deficient mice showed an attenuation of ischemia- and reperfusion-induced rise in plasma LTB₄ (507 pg/ml), fewer sequestered neutrophils (34 PMNs/10 HPF), and a reduction in lung W D to 3.9 (all p < 0.05). To test the role of lung LTB₄ in determining PMN sequestration, rats (n = 78) were subjected to 3 hours of hindlimb ischemia. After 3 hours of reperfusion, plasma and bronchoalveolar lavage (BAL) LTB₄ concentrations rose to 956 and 211 pg/ml, respectively-higher than sham values of 460 and 121 pg/ml (both p < 0.05). After 4 hours, plasma LTB₄ levels had returned to baseline, whereas BAL LTB₄ had increased further to 658 pg/ml, indicating lung origin. Treatment of other rats by localized lung lavage of the lipoxygenase inhibitor diethylcarbamazine (80 mg/kg in 0.1 ml twice) prevented the ischemia- and reperfusion-induced rise in BAL LTB₄ (267 pg/ml) and limited local neutrophil sequestration (from 51 PMN/10 HPF after saline aspiration to 36 PMN/10 HPF) and lung W D (from 4.5 to 4.1) (all p < 0.05). The data indicate that after hindlimb ischemia pulmonary mast cells and localized LTB₄ synthesis mediate, in part, the lung inflammatory response.