Limb ischemic preconditioning mitigates lung injury induced by haemorrhagic shock/resuscitation in rats

Aim of the study: Haemorrhagic shock and subsequent resuscitation induce acute lung injury. We elucidated whether bilateral lower limb ischemic pre-conditioning (IP) could mitigate lung injury in haemorrhagic shock/resuscitation rats. The role of heme oxygenase-1 (HO-1) was also elucidated. Method: Adult male rats were randomized to receive haemorrhagic shock/resuscitation (HS), HS plus IP, or HS plus IP plus the HO-1 inhibitor tin protoporphyrin (SnPP) (n=12 in each group). Sham groups were employed simultaneously. For pre-conditioning, 3 cycles of limb IP (10min ischemia followed by 10min reperfusion) were performed immediately before haemorrhagic shock. Haemorrhagic shock (mean arterial pressure: 40-45mmHg) was induced by blood drawing and maintained for 120min. SnPP was injected 5min before resuscitation. Shed blood/saline mixtures were re-infused to achieve resuscitation. After monitoring for another 8h, rats were sacrificed. Arterial blood gas and alveolar-arterial oxygen difference (lung function index), histology, polymorphonuclear leukocytes/alveoli ratio (leukocyte infiltration index), wet/dry weight ratio (water content index), inflammatory molecules (e.g., chemokine, cytokine, prostaglandin E₂), and malondialdehyde (lipid peroxidation index) assays were preformed. Results: Haemorrhagic shock/resuscitation induced significant lung function alterations and significant increases in leukocyte infiltration, water content, inflammation, and lipid peroxidation in lungs. Histological analysis confirmed that haemorrhagic shock/resuscitation caused marked lung injury. Limb IP significantly mitigated the adverse effects of haemorrhagic shock/resuscitation. Moreover, the protective effects of limb IP were reversed by SnPP. Conclusions: Limb IP mitigates lung injury in haemorrhagic shock/resuscitation rats. The mechanisms may involve HO-1.