Ischemic postconditioning alleviates lung injury and maintains a better expression of aquaporin-1 during cardiopulmonary bypass

Background It has found that ischemic postconditioning (IPO) might decrease pulmonary ischemia/reperfusion (I/R) injury, which is one of the main reasons of lung injury caused by cardiopulmonary bypass (CPB). It was found that aquaporins (AQPs) play a role in the maintenance of fluid homeostasis. But it is still unclear whether IPO influences the expression of aquaporin-1 (AQP1). This study was designed to investigate whether IPO can reduce CPB-related lung injury and affect the expression of AQP1 of lungs.

Methods Twelve healthy dogs were divided into control group (C group) and ischemia postconditioning group (IPO group). CPB procedures were implemented. Ten minutes later, the left pulmonary artery was separated and blocked. Postconditioning consisted of two cycles of 5-minute pulmonary artery reperfusion/5-minute reocclusion starting at the beginning of reperfusion. The 2×4 cm tissues of both sides of pulmonary apex, superior, middle and inferior lobe were taken before CPB (T1), before occlusion and reopening of left pulmonary artery (T2, T3), and 2 hours after CPB (T4). Samples were used to evaluate lung injury degrees and to detect the expression of AQP1. At T1 and T4, blood was collected from femoral artery to calculate pulmonary function.

Results At T4, each pulmonary function showed significant deterioration compared with T1. Lung injury could be found at the onset of CPB. However, the expression of AQP1 decreased and wet to dry weight ratio (W/D) increased after T2. In the left lung of C group, the worst pulmonary function and structures were detected. The slightest changes were discovered in the right lung of C group. A close relationship between W/D and lung injury score was found. The lung injury score was negatively related with the expression of AQP1. It was found that the expression of AQP1 was negatively connected with W/D.

Conclusions In dog CPB models, lung injury induced by CPB was related with down regulated expression of AQP1. AQP1 is believed to be involved in the mechanisms of lung ischemia/reperfusion (I/R) injury caused by CPB. IPO increases the expression of AQP1, provides a protective effect on lung suffering from CPB, and alleviates CPB-related lung injury.