Circulating neutrophil priming and systemic inflammation in limb ischaemia-reperfusion injury

Background. Recruitment and activation of neutrophils is a key step in the development of local and systemic injury in lower limb ischaemia-reperfusio n. We hypothesise that increased circulating neutrophil priming is responsi ble for systemic inflammation. Methods. Anaesthetised ventilated swine (n=6 per group) underwent mid-line laparotomy and were randomised to control group or bilateral external iliac artery occlusion for two hours followed by two and a half hours reperfusio n (IIR group). Using luminol, respiratory bust activity was assayed with a BioOrbit Luminometer to detect whole blood chemiluminescence (CL) by stimul ation with phorbol 1,2-myristate 1,3-acetate (PMA) in the absence or presen ce of tumour necrosis factor (TNF) respectively. PMN priming is expressed a s the ratio of whole blood CL in the presence of TNF to that without. We me asured plasma interleukin(IL)-6 and tumour necrosis factor alpha by bioassa y as a measure of systemic inflammation. The alveolar-arterial (A-a) gradie nt was measured using the formula [(A-a)gradient=fraction inspired O(2)x710 -(arterial pCO(2)/0.8)-arterial pO(2)], it is a measure of lung function, a large gradient being indicative of impaired oxygen transport and hence lun g injury. Results. Lower limb I/R caused significanlly greater PMN priming, 0.83 +/-0 .14, compared to control group, 0.22 +/-0.04, (p <0.001). Plasma IL-6, a re liable indicator of systemic inflammation, was significantly increased in I /R group after two and a half hours of reperfusion, 1295.0 (833.9-2073.0) p g/L, compared to control, 382.9 (367.4-568.3) pg/L, (p <0.005). Plasma tumo ur necrosis factor alpha was significantly elevated after one hour of reper fusion in the I/R group, 86.8 (48.7-106.6) pg/ml, compared to the control g roup, 32.7 (0.9-42.8) pg/ml, (p <0.01). (A-a) gradient was significantly in creased after IRI, 407.97 +/- 53.13, compared to the control, 183.19 +/- 45 .75, (p <0.005). Mean pulmonary artery pressure was significantly greater a fter IRI, 38.80 +/-4.87 mmHg, compared to control, 27.86 +/-1.92 mmHg, (p < 0.005). Data represents mean +/- standard error mean or median (interquarti le range), statistical comparisons using one-way Anova with Student's "t"-t est and Kruskall-Wallis Anova with the Mann-Whitney U test. Conclusions. Priming of neutrophils increases their circulating respiratory burst activity and ability to induce tissue injury. Systemic PMN priming d uring hind Limb ischaemia-reperfusion injury is associated with the systemi c inflammatory response syndrome.