| The myocardial protection of ischemic preconditioning (IPC) haswell been documented; it has been conformed on in situ heart,langendorffed heart, and cultured mycardiocyte as well. The majormechanism is the trigger of intrinsic protection chain in cell itself by thefirst messagers, which proceed to trigger the huge reaction net ofmolecular chain around protein kinase C (PKC). However, the effect ofensued stress reaction triggered by ischemic is still to be studied, even notbeen noticed to date. In fact, it proves to be limited of the mycardiocyteprotection on their own without modulation as a whole, whether thenonspecific anti-injury stress affects IPC, and the possible mechanisms, isto be studied. Our designs include four parts.Part one: Modeling of de-stressed ischemic and reperfusionanimalObjective: To study the depression on adrenal cortex while maintainthe stability of circulation system of etomidate, methods: 24 Japaneserabbits were randomized into 4 group (n=6), an IPC group, a one-dose ofetomidate group, a two-dose of etomidate group and a sham operationgroup. Heart rates and mean arterial pressure as well as plasmas cortisolconcentration of several time points were measured. Results: thetwo-dose group markedly impairs the cortisol reaction while maintain thestabilities of heart rates and mean blood pressure.Part two: Stress affects myocardial protection of ischemicpreconditioningObjective: To determine the effects of reacting cortisol on ischemicpreconditioning (IPC). Methods: Thirty rabbits were randomized into anischemic preconditioning group (IPC), an etomidate (Etom), anischemic/reperfusion (IR), a methylprednisolone group (MP) and a control group. The ratios of infarction size versus risk area (Infarct/Risk)were calculated, the elevations of serum CK activity and cTnIconcentrations as well as serum cortisol concentrations were measured.Results: the ratios of Infarct/Risk were 5.9%±2.8% of IPC, 11.3%±3.6%of Etom, 26.8%±4.5% of IR and 18.2%±3.7% of MP, the elevations ofserum CK activity(U/L) were 255±89 of IPC, 314±160 of MP, 855±371of IR, 768±404 of Etom and 120±41 of control group; the elevations ofserum cTnI concentrations(μg/l) were 3.6±0.6 of IPC, 6.4±1.6 of Etom,8.1±3.6 of IR, 6.1±2.2 of MP and 1.8±0.2 of control group. Differencesof those indicator between Etom and IPC group are all significant(P＜0.05). The cortisol reacting is markedly diminished in Etom group.Conclusion: a blunted cortisol reaction of stress can markedly impair thebenefit of ischemic preconditioning, methylprednisolone show a certainmyocardial protection.Part three: stress affects myocardial apoptosis in ischemicpreconditioningObjective: To study the contribution of a depressed stress responseon IPC-triggered myocardial apoptosis. Methods: protocols are samewith that of Part three. Myocardial apoptosis mere examined usingDNA-laddering, In Situ Nick-End Labeling (TUNEL) and Hoechstdyeing as well. Results: Etom group fred an increase of DNA ladder thanthat of IPC group, and the percentages of apoptosis by TUNEL were1.7%±0.2% of IPC group, 2.3%±0.8% of MP group, 3.8%±1.3% of IRgroup and 3.0%±0.4% of Etom group, and by Hoechst dyeing were3.5%±0.4% of IPC group, 4.1%±0.9% of MP group, 7.6%±0.4% of IRgroup and 6.2%±1.6% of Etom group, the difference between Etomgroup and IPC group is significant, and the difference between MP groupand IR group is also significant. The bcl-2/bax ratio by integrated optical control group. The ratios of infarction size versus risk area (Infarct/Risk)were calculated, the elevations of serum CK activity and cTnIconcentrations as well as serum cortisol concentrations were measured.Results: the ratios of Infarct/Risk were 5.9%±2.8% of IPC, 11.3%±3.6%of Etom, 26.8%±4.5% of IR and 18.2%±3.7% of MP, the elevations ofserum CK activity(U/L) were 255±89 of IPC, 314±160 of MP, 855±371of IR, 768±404 of Etom and 120±41 of control group; the elevations ofserum cTnI concentrations(μg/l) were 3.6±0.6 of IPC, 6.4±1.6 of Etom,8.1±3.6 of IR, 6.1±2.2 of MP and 1.8±0.2 of control group. Differencesof those indicator between Etom and IPC group are all significant(P＜0.05). The cortisol reacting is markedly diminished in Etom group.Conclusion: a blunted cortisol reaction of stress can markedly impair thebenefit of ischemic preconditioning, methylprednisolone show a certainmyocardial protection.Part three: stress affects myocardial apoptosis in ischemicpreconditioningObjective: To study the contribution of a depressed stress responseon IPC-triggered myocardial apoptosis. Methods: protocols are samewith that of Part three. Myocardial apoptosis mere examined usingDNA-laddering, In Situ Nick-End Labeling (TUNEL) and Hoechstdyeing as well. Results: Etom group find an increase of DNA ladder thanthat of IPC group, and the percentages of apoptosis by TUNEL were1.7%±0.2% of IPC group, 2.3%±0.8% of MP group, 3.8%±1.3% of IRgroup and 3.0%±0.4% of Etom group, and by Hoechst dyeing were3.5%±0.4% of IPC group, 4.1%±0.9% of MP group, 7.6%±0.4% of IRgroup and 6.2%±1.6% of Etom group, the difference between Etomgroup and IPC group is significant, and the difference between MP groupand IR group is also significant. The bcl-2/bax ratio by integrated optical density(IOD) were 0.597±0.047 of IPC group, 0.178±0.030 of Etomgroup, 0.146±0.181 of IR group, 0.168±0.021 of MP group; and bypercentage of positive area(PPA) were 0.740±0.102 of IPC group,0.251±0.055 of Etom group, 0.197±0.048 of IR group, 0.213±0.023 ofMP group, the difference between Etom group and IPC group issignificant, and the difference between MP group and IR group isinsignificant. Conclusion: a depressed stress response impair theinhibition on myocardial apoptosis of ischemic preconditioning,depressing the upregulation of bcl-2/bax by a blunted stress may be themolecular basis, methylprednisolone can inhibit the apoptosis but not bybcl-2/bax upregulation.Part four: stress affects the IPC-triggered PKC transiocationObjective: To study the contribution of a depressed stress responseon IPC-triggered PKC translocation. Methods: 24 rabbits wererandomized into 4 groups, an ischemic preconditioning group (IPC), anetomidate (Etom), an ischemic/reperfusion (IR) and a methylprednisolonegroup (MP). hearts were harvested at 10min of the sustained ischemia,membrane protein were separate from cytoplasm, PKC translocation wereassessed by PKC activity and Western-blotting, Results: by PKC activity,the PKC translocation were 0.32±0.06 of Etom group, 0.38±0.04 of IPCgroup, 0.25±0.03 of IR group and 0.29±0.03 of MP group; and byWestern-blotting, the PKCεtranslocation percentages were 0.49±0.08 ofEtom group, 0.58±0.06 of IPC group, 0.47±0.06 of IR group and0.50±0.04 of MP group, the difference between Etom group and IPCgroup is significant, and the difference between MP group and IR groupis insignificant. Conclusion: a depressed stress response impair theIPC-triggered PKC translocation, methylprednisolone have myocardialprotection but may not by promoting PKCεtranslocation. sympathoadrenal axis for the sake of circulation stable, thoughetomidate suppress but cortisol axis, the most important essence of stress,which is only part of the stress hormone network, we still consider that itplay a de-stress role, for etomidate break the balance of the stresshomeostasis thus impact it greatly, and the core of our research is impactof stress on IPC, so we preferably designate the cortisol axis to stresstopic, and this preference can emphasize the brand new recognition ofIPC in respect of stress.
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