Protective effect of controlled oxygen reperfusion on heart with cardiopulmonary bypass in dogs

Objective To observe the protective effects of controlled oxygen reperfusion (COR) on the hearts with cardiopulmonary bypass (CPB) and its possible mechanism. Methods Twelve canines were randomized into two groups: control group and test group. The CPB model was established. The animals in the control group received 80% fraction of inspired oxygen (FiO2) throughout the whole procedure. The animals in the test group received 40% FiO2 immediately at the declamping of aorta, and an additional 10% every 5 min later until 80% FiO2 was reached, and other procedures were the same as those in the control group. Arterial oxygen partial pressure (PaO2) was analyzed after anesthesia, before aortic declamping, 5, 10, 15, 20 and 25 min after aortic declamping, and at the end of the experiment. The blood samples were obtained after anesthesia (T1) and at the end of the experiment (T2), respectively. The animals were then sacrificed to obtain the left ventricle samples. The levels of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in plasma were measured by enzyme-linked-immunosorbent assay. The level of plasma cardiac troponin T (cTnT) was measured by ECL immunoassay system. The expression of high mobility group protein B1 (HMGB1) mRNA and protein in myocardial tissue was detected by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting. Results PaO2 was significantly lower in the test group than that in the control group at 5, 10, 15 and 20 min after aortic declamping (P=0.032, 0.021, 0.046, 0.013). The levels of IL-6, TNF-α and cTnT in plasma were low and there was no significant difference between the two groups at T1 (168.51±21.47 vs. 168.93±22.87; 72.19±2.11 vs. 76.21±6.50; 0.01 vs. 0.01). The levels of IL-6, TNF-α and cTnT in plasma increased from T1 to T2. The levels of IL-6, TNF-α and cTnT in the test group were lower than those in the control group (609.36±52.37 vs. 408.65±43.45; 255.09±10.15 vs. 174.09±8.65; 3.18±1.64 vs. 1.54±0.92). The difference was statistically significant (P=0.028, 0.034, 0.039). As compared with the control group, the expression of HMGB1 mRNA and HMGB1 protein was significantly down-regulated in the test group (P=0.026, 0.033). Conclusion The COR has the protective effects on the hearts with CPB, probably by down-regulating the HMGBI expression. Key words: Controlled oxygen reperfusion; Cardiopulmonary bypass; Interleukin-6; Tumor necrosis factor-α; High mobility group box 1