| Objective To investigate the effects of bilateral limb ischemic preconditioning on the cell apoptosis of the in situ left lung ischemia-reperfusion injury model in rabbits and the possible mechanism has been discovered according to our date.Methods Eighteen Japanese long ear white rabbits weighted 2.0-2.5kg were randomized into three groups, six rabbits in each group. The sham control group(group S) served as time controls, they remained anesthetized for the whole duration of the study without undergoing any surgical intervention. The ischemia-reperfusion group(group IR) underwent 1h left lung in situ ischemia followed by 3h reperfusion. The limb remote ischemic preconditioning group(group R), the both lower limbs of rabbits were exposed to three cycles of IP(10min of ischemia followed by 10min of reperfusion) followed by 1h left lung in situ ischemia and 3h reperfusion. The total duration of experiments in each of the groups was the same. All rabbits were fed with standard rabbits chow and water, and then received only water for 12h before the experimental procedure. After an overnight fast, the rabbits were weighted and anesthetized by intravenous infusion of 2% pentobarbital sodium (30-40) mg·kg-1 from the right ear fringe vein cannulation. The rabbits were kept in supine position for tracheal intubated from the mouth and volume-controlled ventilation with room air at a frequency of 18-25bpm, a tidal volume of 15ml·kg-1 BW, and I:E of 1:2. The tidal volume was decreased to 10ml·kg-1 when only right side of the lung was ventilated. An arterial catheter was inserted in the right carotid artery to monitor blood pressure and blood gases. During the study period, anesthesia was maintained with repeated doses of anesthetics to achieve immobility of the rabbits. Low Molecular Heparin 1mg·kg-1 BW was given before the left hilum of lung was blocked by the right ear fringe vein to prevent the thrombus formation. Lower limb remote ischemic preconditioning was produced by placement of a rubber band tourniquet across the upper thigh of the both lower extremity. The cessation of arterial blood flow was confirmed by laser flowmetry (DT-2100) placed on the extremity distal to the tourniquet. After lower limb ischemia, tourniquets were released and the extremities reperfused. Rabbits were perfused with normal saline intravenously (12ml·kg-1·h-1) and during the study period kept on a heated operating table to prevent dehydration and hypothermia. During the experiment, arterial blood samples were taken immediately after right carotid artery cannulated and at 15,30,60,120 and 180 minutes of reperfusion for blood gas analysis. Rabbits were exsanguinated by needle aspiration of the right ventricle, and the lungs and trachea were removed en bloc at the end of the study. Tissue sample were immediately frozen in liquid nitrogen for later determination of SOD, MDA, Bcl-2 and Bax. The tissue sample for pathologic detection was kept in the 10% formaldehyde.Results①PaO2, A-aDO2 and RI:There were no statistical significance in basic date of PaO2, A-aDO2 and RI among group S, group IR and group R(P>0.05). In IR group, PaO2 decreased significantly, especially within 60 min after lung reperfusion (P＜0.01). PaO2 of R group and S group were both significantly higher than those in IR group (P＜0.01). In I/R group, RI and A-aDO2 was higher progressively, especially within 60 min after reperfusion, than other groups.While RI and A-aDO2 in R group were both significantly lower than in IR group (P＜0.01).②IQA:The IQA were obviously higher in IR group than in S group (P＜0.01). Compared with IR group, IQA were lower at different degree (P＜0.01) in R group.③The content of MDA and the activity of SOD:The content of MDA in IR group significantly higher than group S and group R (P＜0.01), however, the activity of SOD was lower than the other two groups (P＜0.01).④AI and Bcl-2/Bax:Compared with sham group, the apoptosis index and Bax content in group IR increased significantly (P＜0.01), while the Bcl-2 decreased significantly (P＜0.01), and Bcl-2/Bax decreased (P＜0.01). The AI and Bax of R group decreased significantly compared with IR group (P<0.01), while the Bcl-2 and Bcl-2/Bax ratio increased in R group compared with IR group (P<0.01).There were no statistical significance between group R and group S (P>0.05).Conclusion Limb remote ischemic preconditioning has some protective effects against ischemia-reperfusion injury of lung. And the protective effects against ischemia-reperfusion injury of lung by up-regulating the Bcl-2/Bax ratio through suppressing the oxidative damage, therefore, reducing the occurrence of apoptosis in rabbit lung.
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