NEUTROPHIL LIPOXYGENASE ACTIVATION AND LEUKOSEQUESTRATION IN POSTISCHEMIC MYOCUTANEOUS FLAPS - ROLE OF LTB(4)

Reperfusion of ischemic tissues leads to eicosanoid- and polymorphonuc lear leukocyte (PMN)-dependent injury. The present experiments were un dertaken to examine the effect of myocutaneous flap ischemia-reperfusi on on neutrophil 5-lipoxygenase activity and to define the role of leu kotriene B-4 (LTB(4)) in postischemic PMN infiltration into such compo site tissue grafts. Anesthetized Yorkshire pigs underwent 6 h of rectu s abdominis myocutaneous flap ischemia or sham ischemia, and LTB(4) ge neration was measured in calcium ionophore-stimulated neutrophils isol ated from the circulation. At 30 min of reperfusion, neutrophil genera tion of LTB(4) increased from a baseline value of 31.0 +/- 6.8 to 98.5 +/- 5.1 ng/5 x 10(6) PMN (P < 0.01) and was significantly greater tha n those neutrophils isolated from animals subjected to sham ischemia a nd reperfusion (54.3 +/- 4.1 ng/5 x 10(6) PMN; P < 0.01). Pretreatment of animals with the LTB(4)-receptor antagonist, SC-41930 (n = 5), sig nificantly attenuated reperfusion-associated 5-lipoxygenase activation (60.3 +/- 11.6 ng LTB(4)/5 x 10(6) PMN; P < 0.01), suggesting the pre sence of a positive feedback mechanism for eicosanoid biosynthesis. Gr aft ischemia in control animals was associated with progressive PMN in filtration at 1 and 4 h of reperfusion (384 +/- 92 and 667.2 +/- 198 P MNs/25 high-powered fields, respectively; however, pretreatment with S C-41930 or the 5-lipoxygenase inhibitor, diethylcarbamazine, dramatica lly reduced PMN infiltration at 1 h of reperfusion (22 +/- 3 and 64 +/ - 36 PMNs/25 high-powered fields, respectively; P < 0.01) and at 4 h o f reperfusion (178 +/- 31 and 156 +/- 40 PMNs/25 high-powered fields; P < 0.01). These data indicate that myocutaneous flap ischemia-reperfu sion leads to activation of 5-lipoxygenase in circulating PMNs and sug gest that LTB(4) plays a critical role in the pathogenesis of reperfus ion injury by amplifying the process of neutrophil recruitment into po stischemic tissues.