| Backgroud: Tremendous people experience sudden cardiac death inworld wide. Despite various techniques applied for resuscitation of thosepatients survival rates are lower. The low survival rate seems to be aresult of severe cardiac injury and reperfusion (I/R) injury. Ischemicapreconditioning (IPC) is known to attenuate myocardial injury induced byI/R. However, because of the inability to predict the onset of ischemia,the clinical setting is rarely an option. Study showed that pharmacologicalpreconditioning (PP) had similar cardiac protection effect as IPC, but it'smore under the clinician's control. Previous studies suggested that PKCinvolved in IPC-derived cardioprotection. On the other hand, some agentswere PKC independently increase the cAMP expression and protects themyocardium as well. cAMP-PKA signal passway was suggested toparticipated in preconditioning induced myocardium protection. Theresults of upregulated proinflammatory genes in I/R heart demonstratedthat those genes might involved in I/R induced cardiac dysfunction.NF-κB could regulate the gene transcription of IκB-dependentinflammatory cytokines that play an important role in myocardial injury.The aims of this study were to use a well-characterized model of multiple-episode-induced ischemic preconditioning to evaluate whetherthe preconditioning induced myocardium protection is relay oncAMP-PKA signal passway to inhibit NF-κB activation andNF-κB-depended inflammatory cytokines transcription during thereperfusion.Methods:Fifty male Sprague-Dawley rats (300-350 g) were randomized intofive groups (n=10): I/R group,IPC group,H89 (PKA inhibitor) group,PDTC (NF-κB inhibitor) group and db-cAMP group. Using rat isolatedhearts Langendorff model, hemodynamic and cardiodynamic parameterswere recorded at baseline, post-reperfusion 10 min, 20min, 30min. Theparameters included heart rate (HR), left ventricular developed pressure(LVDP: difference between left ventricular end systolic pressure and enddiastolic pressure), the velocity of contraction and relaxation (±dP/dtmax).Coronary flow (CF) was measured, LDH activity and CK in the coronaryeffluent was analyzed. The heart tissues were sampled at 30min ofreperfusion and rapidly stored in liquid nitrogen to analysis NF-κB-DNAactivition (EMSA),TNF-amRNA (Real-timePCR),phospho-CREB(Ser133),phospho-IκBa (Ser32/36),phospho-NF-κB p65 (Ser276)(Western Blotting)Results:1,In the myocardial nucleus, compared to the group pretreated with 3 cycles of I/R and db-cAMP, the phospho-NF-κBp65 (Ser276), NF-kBactivity and TNFa mRNA expression are significantly higher in the I/Rgroup (P＜0.01), the difference among the I/R,H89 and PDTC groupsdid not reach statistical significance. Compare to the I/R and H89 groups,the phospho-CREB(Ser133) in the IPC, PDTC, and the db-cAMP groupswere significantly increased (p＜0.01). The level of phospho-IκBa(Ser32/36) in the I/R group and PDTC group was higher than that in theother groups (P＜0.01).2,Compared to the baseline data, the cardiac function duringreperfusion in the I/R group, H89 group and PDTC group wassignificantly decreased. However, the cardiac function in the IPC anddb-cAMP groups during reperfusion was significantly better than that ofthe I/R group (P＜0.05)Conclusion:We demonstrated that the db-cAMP preconditioning is an effectivemethod as IPC in protection against I/R induced myocardial injury. Themechanism is relayed on inhibiting the NF-κB activity and attenuatinginflammatory cytokines upregulation. The protection may be attributableto cAMP-PKA signal transduction passway.
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