Transient Limb Ischemia In Different Periods Protects Rabbit Myocardium From Ischemia-reperfusion Injury

Acute coronary syndrome (ACS) is a kind of disease, which seriously threats to the human health. Early reperfusion therapy can make the occluded coronary artery reflow, retrieve the dying cardiac myocyte, reduce the scope of necrosis. Therefore, the reperfusion as soon as possible is an important kind of treatment methods. But the reperfusion of the coronary artery leads to reperfusion injury inevitably, which largely affected the beneficial therapeutic effect. So how to reduce the ischemia-reperfusion (IR) injury is an important issue to be resolved.Since 1986, Murry and colleagues defined the concept that ischemic preconditioning (IP). A number of studies were followed, which showed the protective effects from ischemic postconditioning (IPO), remote preconditioning (RPrecon) and remote postconditioning (RPostcon), and scholars also found that the effects existed in different species of animals, such as rabbits, sheep, dogs, pigs, mice and human, and different tissues and organs, such as small intestine, lung, kidney, brain, liver and skeletal muscle. But the classical ischemic preconditioning and postconditioning have some limitations when they are practiced in the clinic: preconditioning requires advanced warning of ischemic events, postconditioning can be performed after an ischemic event has occurred, but it is possible to make the lesion vessel injured when postconditioning is performed. So, the scientists transfer their attention to the heart protection of remote postcondition.Remote preconditioning or postconditioning applied to an organ that is relatively resistant to ischemia (such as the limb) might protect tissues that are more sensitive to ischemia (such as the heart and brain) from IR injury. Studies have reported that the intestine, kidney, or limb can induce the RPrecon or RPostcon successfully. Recently, scientists paid more attention to the less invasive remote preconditioning or postconditioning induced by skeletal muscle which is relatively resistant to ischemia. But there is no report about whether transient limb ischemic at different periods, that is, remote ischemic preconditioning and remote postconditioning induced by skeletal muscle, produces similar protection between each other and whether the additive effects could be achieved by performing both RPrecon and RPostcon.Objective: To determine whether the degree of protection by RPostcon against myocardium IR injury is similar to that achieved by RPrecon, and, whether the degree of protection could be enhanced by performing both of them.Methods: 30 healthy New Zealand rabbits were randomly divided into 5 groups: sham operation group (Sham), ischemic control group (CONT), remote preconditioning group (RPrecon), remote postconditioning group (RPostcon), remote preconditioning plus remote postconditioning group (RPrecon + RPostcon). Acute ischemia reperfusion model was induced by 45 minutes occlusion on left circumflex coronary artery (LCX) and 2 hours reperfusion in all anesthetized open-chest rabbits except the Sham, the coronary occlusion and reperfusion was assessed by changes of ECG and cardiac muscle color. Skeletal muscle ischemia was induced by external iliac artery occlusion and reperfusion through artery clamp (RPrecon: 3 cycles of 5 minutes of ischemia and 5 minutes of reperfusion before the LCX occlusion, RPostcon: 2 cycles of 5 minutes of ischemia and 1 minute of reperfusion at the 33min of LCX occlusion). The distal arterial pulse disappearance was the sign for external iliac artery occlusion. Blood serum creatine kinase (CK) activity and lactate dehydrogenase (LDH) activity were measured at baseline, the end of ischemia, after 1 hour and 2 hours of reperfusion respectively. The extent of myocardial infarction was assessed by triphenyltetrazolium (TTC) staining and expressed by area ratio (area of necrotic zone/area of ischemic zone, NZ/IZs) and weight ratio (weight of necrotic zone/weight of ischemic zone, NZ/IZg).Results: Compared with the CONT, myocardial infarct size was significantly reduced by RPrecon and RPostcon (RPrecon: NZ/IZs 15.6%±7.7%, NZ/IZg 18.9%±7.8%; RPostcon: NZ/IZs 17.1%±7.7%, NZ/IZg 18.6%±6.2% CONT: NZ/IZs 33.5%±8.0 %, NZ/IZg 36.1%±5.7%, P<0.01). But there was no significant difference between RPrecon and RPostcon. Combined RPrecon and RPostcon did not enhance myocardial protection markedly (NZ/IZs 12.2%±5.6%, NZ/IZg 15.4%±5.5%, P>0.05). The reduction of CK was similar to the trend of myocardial infarct size. CK activity at the end of 2 hours reperfusion: CONT 6885±1202 U/L,RPrecon 3860±1274 U/L,RPostcon 3858±613 U/L,RPrecon+RPostcon 3997±865 U/L. There was no significant reduction of LDH activity.Conclusion: Both remote ischemic preconditioning and postconditioning induced by skeletal muscle protected the myocardium from ischemia-reperfusion injury. There was no significant difference between RPrecon and RPostcon. Combined RPrecon and RPostcon did not induce significant additive effect on myocardial protection.