The Protective Effect Of Ischemic Postconditioning On Ischemia Reperfusion Injury Of Rat Lung

ObjectiveIschemia reperfusion injury of the lung (LIRI) is still a challenge for the thoracic and cardiovascular surgeon, which occurs in many clinical conditions, such as cardiopulmonary bypass, lung transplantation, lung embolism, shock, ans so on, especially during lung transplantation. The characteristics of ischemia reperfusion injury in lung transplantation are nonspecific alveoli pulmonum injury, lung edema and hypoxemia. The morbidity and mortality of lung ischemia reperfusion injury are still higher which takes place in lung transplantation, though the achievement ratio increases to some extent by improving lung conservation method, upgrading surgical technic and strengthening guardianship in perioperation. Ischemic postconditioning(I postC), a new method which is practiced by interrupted pre-irritating in the initial stage of reperfusion, has been certificated to decrease the reperfusion injury of myocardium and liver. This experiment was carried out, establishing an in situ hilar occlusion, in vivo rat lung ischemia reperfusion injury model. The 125I-BSA leakage, the expression level of TNF-αand IL-1βof the lung tissue were measured. The histopathological changes of the lung tissue were observed to explore the effects of ischemic post-conditioning on ischemia reperfusion injury of rat lung in vivo.Materials and MethodsEighty male Sprague-Dawley rats were anesthetized with an intraperitoneal injection of sodium pentobarbital (30mg/kg). The animals were shaved, endotracheal intubated with a 14 gauge tube, and ventilated with a rodent respirator ventilator at a respiratory rate of 60 breaths/min, a 1:1.5 of I/E ratio and a mean peak pressure of 0.02 MPa. All animals received 0.04 mg/kg of intramuscular atropine after being anesthetized. The chest was opened via a left thoracotomy through the fifth intercostal space. After the left pulmonary hilum including neural, vascular, lymphatic, and connective tissue was stripped, a ligature was placed through, and the ends of the tie were threaded through a small plastic tube to form a snare for reversible left pulmonary hilar occlusion. Heparinization was maintained during the experimental period with a bolus injection of 100U/kg sodium heparin via the dorsal penile vein.All animals were randomized into five gro ups with 8 animals in each group:①sham operation group (C group) ;②IR 30mins group( IR30 ) ;③IR 120mins group(IR120) ;④postconditioning 30mins group(P30).⑤postconditioning 120mins group(P120). IR injury consisted of 30 minutes of lung cross-clamping followed by 30/120mins of reperfusion, sham operation animals had a thoracotomy only. postconditioning was given by 30s reperfusion/30s ischemia for 5 circle before the persistent reperfusion.At the end of the experiment, all operated rats were killed by blood letting through carotid artery. The left lung tissue were retrieved, and then saved in 4% Polyoxymethylene for determining. The expression level of TNF-αand IL-1βof lung tissue were detected by immunohistochemical stain technically. The pathological changes of the lung tissue were observed under microscopy. Another forty male Sprague-Dawley rats were randomized into five groups with 8 animals in each group to determine the 125I-BSA leakage in lung tissue to detecte permeability of pulmonary capillary.Results(1) The 125I-BSA leakage in lung tissue After reperfusion 30mins/120mins, the 125I-BSA leakage increased markedly in IR group and had significantly change compared with group C (p <0.05). Treatment with postconditioning alleviated the 125I-BSA leakage. Moreover, the 125I-BSA leakage in P group were lower than IR group (p <0.01).(2) The level of TNF-αin lung tissue Immunohistochemical stain analysis of lung TNF-α: The cell which express TNF-αshowed brown immunostaining in cytoplasm. In contrast, significant increase of TNF-αexpression was found in IR group (p <0.01). In the rats treated with postconditioning, the positive cell ratio is lower compared with IR group (p <0.01).(3) The level of IL-1βin lung tissue Using immunohistochemical stain analysis, expression of IL-1βin the cell of lung tissue showed brown immunostaining in cytoplasm. In contrast, significant increase of IL-1βexpression was found in IR group (p <0.01). In the rats treated with postconditioning, the positive cell ratio is lower compared with IR group (p <0.01).(4) Histological evaluation In the process of ischemia-reperfusion, the lung injury was aggravating progressively in the IR group. Marked pulmonary capillary congestion, edema in pulmonary stroma, neutrophils infiltration, inflammatory exudation, thickening of alveolar wall and intra-alveolar hemorrhage could be observed. These changes in morphology were less pronounced in rats that had been pretreated with postconditioning. Conclusions(1) Ischemic Postconditioning can restrain the expression of TNF-αand IL-1βon the lung;(2) Ischemic Postconditioning can attenuate pulmonary capillary permeability and inhibit the exudation of inflammatory factors and cells; (3) Ischemic Postconditioning can attenuate the BSA leakage in lung. In a word, ischemic Postconditioning can attenuate the lung ischemia reperfusion injury in rats through restraining the inflammation by the mechanisms above .