The Effects Of Acidic Reperfusion On Ischemia Reperfusion Myocardial Endoplasmic Reticulum Stress And Apoptosis Undergoing Cardiopulmonary Bypass In Rabbits

Objective: To determine the effects of acidic reperfusion on myocardial ischemia/reperfusion (I/R) injury undergoing cardiopulmonary bypass (CPB) and choose the optimum pH of perfusion fluid.Methods: Thirty-six adult New Zealand white rabbits of both sexes weighing 2.5-3.0 kg were randomly divided into 6 groups (n=6 each). In control group (C), CPB was executed for 3 h without aortic clamping. Hearts were subjected to ischemia for 40 min followed by 2 h of reperfusion in ischemia/reperfusion group (I/R). In the other groups, hearts were also subjected to ischemia for 40 min followed by 2 h of reperfusion, and were respectively perfused with Krebs-Henseleit bicarbonate buffer (KHB) at pH 7.4, 7.1, 6.9 and 6.7 in the first 2 min of reperfusion. After 2 h reperfusion, the lactate dehydrogenase (LDH) activity was tested with colorimetric method, cardiac troponin I (cTnI) concentration was determined with enzyme linked immunosorbent assay (ELISA) and myocardial tissues were observed by light microscopy and transmission electron microscope.Results: In the other groups, the LDH activity and cTnI concentration were significantly increased as compared with in the control group (P<0.05). Compared with I/R group, the LDH activity and cTnI concentration were not significantly different in pH7.4 group, and were significantly lower in acidic reperfusion groups (P<0.05), and were lowest in pH6.9 group. The I/R group and pH7.4 group showed the most serious injury while the pH6.9 group showed the least damage in the acidic reperfusion groups by pathological examination.Conclusion: Acidic reperfusion can attenuate the myocardial I/R injury by CPB in rabbits and the KHB at pH6.9 reperfusion provides best protective effect. Objective: To determine the effects of acidic reperfusion during CPB on the myocardial endoplasmic reticulum stress (ERS) and apoptosis after I/R in rabbits.Methods: Thirty adult New Zealand white rabbits of both sexes weighing 2.5-3.0 kg were randomly divided into 5 groups (n=6 each). Control group (C): CPB for 3 h without aortic clamping; ischemia/reperfusion group (I/R): hearts were subjected to ischemia for 40 min followed by 2 h of reperfusion; pH7.4 group and pH6.9 group: hearts were subjected to ischemia for 40 min followed by 2 h of reperfusion, and perfused with KHB respectively at pH 7.4 and 6.9 in the first 2 min of reperfusion; ischemic postconditioning group (I-postC): 40 min after aortic clamping, 6 cycles of 10-second reperfusion/10-second occlusion were given in the first 2 min of 2-hour reperfusion. After the experments, the LDH activity was tested with colorimetric method, cTnI concentration was determined with ELISA, apoptosis of cardiac myocyte was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL), the expressions of glucose-regulated protein 78 (GRP78) and calreticulin (CRT) mRNA were detected by reverse transcription polymerase chain reation (RT-PCR), the expressions of caspase-12 and C/EBP homologous protein (CHOP) were assayed by immunohistochemistry and western blot, and transmission electron microscope was used to abserve the change of ultrastructure in cardiac myocyte.Results: Compared with the C group, the LDH activity, cTnI concentration, apoptotic rate, expressions of GRP78 and CRT mRNA and expressions of caspase-12 and CHOP of the other groups increased significantly (P<0.05). Compared with the I/R group, all the indexes were not significantly different in pH7.4 group and were significantly lower in pH6.9 group and I-postC group (P<0.05), but no significantly difference was found between the latter two groups (P>0.05). The ultrastructure of cardiac myocyte was no obvious abnormality in control group, in I/R group and pH7.4 group showed the most serious injury, and the endoplasmic reticulum edema was obvious, in pH6.9 group and I-postC group, the endoplasmic reticulum edema was less than in I/R group.Conclusion: Acidic reperfusion could protect the heart against I/R injury, and may through regulating ERS response, inhibiting the excessive ERS, and relieving ERS-induced apoptosis during I/R.