Gut-derived leukotriene B4 following hemorrhagic shock is a pivotal mediator of neutrophil priming

Introduction: The lipid fraction of mesenteric lymph collected after hemorrhagic shock (HS) and reperfusion primes the neutrophil oxidative burst in vitro. Recently, we have identified the culprit agent to be a neutral lipid consistent with Leukotriene B4 (LTB4). We hypothesized that plasma LTB4 increases after HS and that diversion of mesenteric lymph (DML) abrogates this effect. Furthermore, we posited that administration of an LTB4 antagonist blocks the priming effect of mesenteric lymph on neutrophils (PMNs). Methods: Adult male Sprague-Dawley rats (325–375 g) underwent laparotomy with cannulation of the mesenteric lymphatics for lymph diversion (DML) or laparotomy without mesenteric cannulation (Sham). Additionally, DML rats had lymph collected both pre- and post-shock. All rats underwent cannulation of the femoral artery and vein. HS to a MAP of 30 mmHg for 45 minutes was achieved via venous exsanguination. Animals were resuscitated with shed blood and with 2x the shed blood volume of NS over two hours. After resuscitation, plasma was collected for LTB4 measurement by ELISA. Lymph collected in the resuscitation phase was added to isolated PMNs that were then measured for superoxide release in the presence and absence of the LTB4 receptor antagonist CP-105,696. Results: LTB4 concentration in the lymph collected from the DML group measured 281.25 ± 53.81 ng/ml pre-shock, increasing to 692.13 ± 176.91 ng/ml post-shock (p < 0.05). LTB4 plasma concentrations after resuscitation differed based on lymph diversion. LTB4 concentration for DML animals measured 2745 ± 214.77 pg/ml vs. Sham animals, 4012 ± 628.93 pg/ml (p < 0.05). PMN pre-treatment with the LTB4 receptor antagonist completely abrogated superoxide release in response to lymph exposure compared with the untreated control, 1.39 ± 0.23 vs. 4.22 ± 0.68 nmol O2−/3.75 x 105 cells/mL/min respectively (p < 0.05). Conclusion: These data suggest that splanchnic ischemia secondary to HS increases concentrations of the known priming agent LTB4 in mesenteric lymph and the systemic circulation. Furthermore, selective blockade of LTB4 markedly attenuates the effect of mesenteric lymph on PMN priming, indicating a potential therapeutic location for disruption of the dysfunctional PMN priming/activation sequence.