Effect of lung ischemic preconditioning on expression of aquaporin-1 during lung ischemia-reperfusion induced by cardiopulmonary bypass in dogs

Objective To investigate the effect of lung ischemic preconditioning (IP) on the expression of aquaporin-1 (AQP1) during lung ischemia-reperfusion (I/R) induced by cardiopulmonary bypass (CPB) in dogs.Methods Twelve adult mongrel dogs,weighing 15-20 kg,were randomly divided into 2 groups (n =6 each):lung I/R (group I/R) and ischemic preconditioning group (group IP).The left pulmonary artery was occluded at 10 min of off-pump CPB and mechanical ventilation was stopped in the left lung,60 min later occlusion was released,and mechanical ventilation was recovered to establish the model of left lung ischemia-reperfusion injury induced by CPB.In group IP,lung ischemic preconditioning was induced by 2 cycles of 5 min ischemia followed by 5 min reperfusion before occlusion of the left pulmonary artery.Before CPB (T1),immediately after occlusion of the left pulmonary artery (T2),at the end of CPB (T3),and at 2 h after the end of CPB (T4),pulmonary specimens were collected for determination of wet to dry lung weight ratio (W/D ratio) and expression of AQP1 and for examination of the pathological changes of lungs which were scored.Respiration index (RI),oxygenation index (OI),and alveolar-arterial oxygen tension difference (P(A-a)O2) were calculated at T1,T3 and T4,and the left pulmonary alveolar fluid clearance (AFC) was calculated at T4.Results Compared with group I/R,P(A-a) O2 and RI were significantly decreased,OI was increased,W/D ratio and pathological scores were decreased,the expression of AQP1 was up-regulated,and the AFC was increased at T3 and T4 in group IP.The pathological changes of the lung were significantly attenuated in group IP as compared with group I/R.Conclusion The mechanism by which lung ischemic preconditioning mitigates lung I/R injury induced by CPB is related to upregulation of the expression of AQP1 in dog lung tissues. Key words: Ischemic preconditioning;  Cardiopulmonary bypass ;  Reperfusion injury ;  Lung ;  Aquaporin 1