Ceiling effect of Postconditioning and Atrial Natriuretic Peptide in Cardioprotection against Ischemia Reperfusion Injury in Ovariectomized rat hearts

Abstract Ischemic postconditioning (IPTC) brings cardioprotection endogenously, Atrial natriuretic peptide (ANP) produces the same effect. It happens due to down expression of endothelial nitric oxide synthase (eNOS). Thus, experimental protocol associating IPTC has been formulated to find the role of ANP in the cardioprotection of heart in OVX rats. For this experiment, heart was isolated from OVX rat and held tightly on Langendorff’s apparatus in a manner that ischemia of 30 min and reperfusion of 120 min were also given. Simultaneously, IPTC with four cycles of 5 min ischemia and 5 min reperfusion of each was applied. Parameters like size of myocardial infarct, levels of lactate dehydrogenase (LDH) and release of creatine kinase- MB (CK-MB) in coronary effluent were noted after each stage of experiment for ensuring the extent of myocardial injury. Some significant changes were also seen in the histopathology of cardiovascular tissues. The cardio-protection has been made by four cycles of IPTC. It was confirmed by decline in the size of myocardial infarct. It diminishes the release of LDH and CK-MB in heart of OVX rat. Thus, IPTC induces cardio-protection in the isolated heart from OVX rat. Perfusion of ANP associating with IPTC favors the cardioprotection which is further confirmed by rise in the NO release and heart rate. The level of myocardial damage changes using IPTC, IPTC+OVX, IPTC+OVX+ANP, IPTC+ OVX+ANP+L-NAME and other groups were observed significantly and were found to be less than those in I/R control group. Thus, it is recommended that ANP involving IPTC restores attenuated cardio-protection in OVX rat heart. Therefore, Post-conditioning is useful in various clinical aspects.

摘要 缺血后处理（Ischemic postconditioning，IPTC）可内源性发挥心脏保护作用，心房利钠肽（Atrial natriuretic peptide，ANP）亦具备相同效应。既往研究认为其作用机制与内皮型一氧化氮合酶（endothelial nitric oxide synthase，eNOS）的表达下调相关。本研究构建了联合IPTC的实验方案，旨在明确ANP在去卵巢（OVX）大鼠心脏缺血后处理保护中的作用。实验过程中，我们从OVX大鼠体内分离心脏，并将其固定于兰根多夫（Langendorff）灌流装置中，建立30分钟缺血、120分钟再灌注的模型；同时施加由4个周期组成的IPTC干预，每个周期包含5分钟缺血与5分钟再灌注。于实验各阶段记录多项指标，包括心肌梗死面积、冠脉灌流液中乳酸脱氢酶（lactate dehydrogenase，LDH）及肌酸激酶同工酶MB（creatine kinase-MB，CK-MB）的释放水平，以评估心肌损伤程度；同时观察心血管组织的病理学特征变化。结果显示，4周期IPTC干预可产生心脏保护作用，表现为心肌梗死面积缩小、OVX大鼠心脏中LDH与CK-MB的释放量降低，该效应得到了验证。由此证实，IPTC可在OVX大鼠离体心脏中诱导心脏保护效应。将ANP与IPTC联合灌注可进一步增强心脏保护作用，该效应可通过一氧化氮（NO）释放量与心率的升高得到进一步确认。本研究对IPTC组、IPTC+OVX组、IPTC+OVX+ANP组、IPTC+OVX+ANP+L-NAME组及其他实验组的心肌损伤程度进行了比较，结果显示各组损伤程度均显著低于缺血再灌注（I/R）对照组。综上，ANP联合IPTC可恢复OVX大鼠心脏受损的缺血后处理保护作用，提示后处理技术在诸多临床场景中具有应用价值。