Hind limb ischemia and reperfusion have been shown to result in high plasma levels of leukotriene B4 (LTB4) and polymorphonuclear neutrophil (PMN) sequestration in the pulmonary microvasculature. This study tests whether LTB4 is derived from PMNs and its role in mediating ischemic plasma- induced diapedesis. Plasma derived from rabbit hind limbs after 3 hours of tourniquet ischemia and 10 minutes of reperfusion (n = 6) showed an increased LTB4 level of 560 pg/ml, higher than sham plasma values of 106 pg/ml (p < 0.05). Introduction of ischemic plasma in abraded skin chambers placed on the dorsum of normal rabbits (n = 6) led after 3 hours to PMN diapedesis of 1175 PMN/mm3, associated with a further increase in LTB4 levels to 820 pg/ml (both p < 0.05). In contrast, ischemic plasma derived from neutropenic animals (n = 4; nitrogen mustard, 2 mg/kg; PMNs < 30/mm3) contained lower levels of LTB4, 160 pg/ml (p < 0.05). When introduced in skin chambers in normal rabbits (n = 4), this plasma induced accumulations of only 163 PMN/mm3, accompanied by a smaller increase in LTB4 levels in the blister fluid after 3 hours, 397 pg/ml (both p < 0.05). A correlation was found between LTB4 levels in ischemic plasma and PMN accumulations in blister fluid (r = 0.92; p < 0.05). Intravenous pretreatment of rabbits (n = 4) used in the blister chamber bioassay with the LT receptor antagonist FPL-55712, 40 μg/kg/hr, attenuated diapedesis induced by ischemic and ischemic-neutropenic plasma, 103 and 35 PMN/mm3, respectively (both p < 0.05). Pretreatment with superoxide dismutase, 1500 units/kg, and catalase, 5000 units/kg, both conjugated to polyethylene glycol (n = 4), prevented ischemic plasma-induced LTB4 synthesis, as well as ischemic plasma-induced diapedesis, 12 PMN/mm3 (p < 0.05). Finally, pretreatment with allopurinol, 25 mg/kg, was similarly effective in preventing LTB4 synthesis and PMN migration. These data suggest that oxygen free radicals are essential for ischemia-induced PMN synthesis of LTB4 that in turn mediates their diapedesis.
|Number of pages||7|
|State||Published - 1992|