Activation of Akt and cardioprotection against reperfusion injury are maximal with only five minutes of sevoflurane postconditioning in isolated rat hearts

It had been proved that administration of sevoflurane for the first two minutes of reperfusion effectively protects the heart against reperfusion injury in rats in vivo.Our aim was to investigate the duration of effective sevoflurane administration and its underlying mechanism in isolated rat hearts exposed to global ischemia/reperfusion(I/R) injury.Adult male Sprague-Dawley rats were randomly divided into six groups(n=12):a sham-operation group,an I/R group,and four sevoflurane postconditioning groups(S2,S5,S10,and S15).In the S2,S5,S10,and S15 groups,the duration times of sevoflurane administration were 2,5,10,and 15 min after the onset of reperfusion,respectively.The isolated rat hearts were mounted on the Langendorff system,and after a period of equilibrium were subjected to 40 min global ischemia and 120 min reperfusion.Left ventricular(LV) hemodynamic parameters were monitored throughout each experiment and the data at 30 min of equilibrium and 30,60,90,and 120 min of reperfusion were analyzed.Myocardial infarct size at the end of reperfusion(n=7 in each group) and the expression of myocardial phosphorylated Akt(p-Akt) after 15-min reperfusion were determined in a duplicate set of six groups of rat hearts(n=5 in each group).Compared with the I/R group,the S5,S10,and S15 groups had significantly improved left ventricular end-diastolic pressure(LVEDP),left ventricular developed pressure(LVDP),and the maximal rate of rise or fall of the LV pressure(±dP/dtmax),and decreased myocardial infarct size(P<0.05),but not the S2 group.After 15 min of reperfusion,the expression of p-Akt was markedly up-regulated in the S5,S10,and S15 groups compared with that in the I/R group(P<0.05),but not in the S2 group.Sevoflurane postconditioning for 5 min was sufficient to activate Akt and exert maximal cardioprotection against I/R injury in isolated rat hearts.

Downregulation of Na^＋/Ca^2＋ Exchanger Isoform 1 Protects Isolated Hearts by Sevoflurane Postconditioning but Not by Delayed Remote Ischemic Preconditioning in Rats

Background：Calcium regulatory proteins-L-type Ca^2＋ channels （LTCCs）,ryanodine receptor 2 （RyR2）,and Na^＋/Ca^2＋ exchanger isoform 1 （NCX1） have been recognized as important protective mechanisms during myocardial ischemia-reperfusion injury （I/RI）.Both sevofturane postconditioning （SevoPoC） and delayed remote ischemic preconditioning （DRIPC） have been shown to protect the heart against I/RI.In this study,we aimed to compare the effects of SevoPoC and DRIPC on the expression of the three calcium regulatory proteins in an isolated rat heart model.Methods：After 30-min balanced perfusion,isolated hearts from rats were subjected to 30-min ischemia followed by 60-min reperfusion.Totally 40 isolated hearts were randomly assigned to four groups （n =10/group）：time control group,I/RI group,SevoPoC group,and DRIPC group.The effect of SevoPoC （3% v/v） and DRIPC were observed.Myocardial infarct size （IS）,cardiac troponin I level,and heart function were measured.The protein and messenger RNA levels of LTCCs,RyR2,and NCX1 were determined.Results：Both SevoPoC and DRIPC improved the recovery of myocardial function,and reduced cardiac troponin Ⅰ release after I/RI.The decrease in IS was more significant in the SevoPoC group than that in the DRIPC group （16.50% ± 4.54% in the SevoPoC group [P =0.0006],and 22.34% ± 4.02% in the DRIPC group [P =0.0007] vs.35.00% ± 5.24% in the I/RI group,respectively）.SevoPoC,but not DRIPC significantly inhibited the activity of NCX 1 （0.59 ＋ 0.09 in the I/RI group vs.0.32 ± 0.16 in the SevoPoC group,P =0.006;vs.0.57 ± 0.14 in the DRIPC group,P =0.072）.No statistical significant differences were observed in the expression of LTCCs and RyR2 between SevoPoC and DRIPC.In addition,subsequent correlation analysis showed a significantly positive relationship between the cardiac troponin Ⅰ level and the protein expression ofNCX1 （r =0.505,P =0.023）.Conclusion：SevoPoC may be more effective in the cardioprotection than DRIPC partly due to the deactivation of NCX1.