| Objective: To observe the protective effect of dexmedetomidine preconditioning on isolated myocardial ischemia-reperfusion injury in rat hearts,and further clarify the role of JNK pathway and its mediating ER stress-induced apoptosis.Methods: Sixty healthy adult male rats weighing 230-260 g were randomly divided into 5groups(n=12): Normal group(N group),ischemia-reperfusion group(I/R group),dexmedetomidine Pretreatment + ischemia reperfusion group(D group),JNK inhibitor SP600125 + ischemia reperfusion group(SP group),dexmedetomidine + SP600125 +ischemia reperfusion group(D + SP group).After anesthetized each experimental rat with pentobarbital sodium by intraperitoneal injection,the heart was quickly opened and the heart was removed.Gently squeeze the heart chamber to eliminate congestion,quickly lift the aortic root suspension from the tip of the infusion needle in a Langendorff isolated cardiac perfusion device,and insert the left atrial appendix into the preadjusted latex balloon and adjust its size to LVEDP at 4-7mm Hg.Each group was given different perfusion protocols,N group was continuously infused with K-H solution for 205 minutes;IR group: after K-H solution was equilibrated for 15 minutes,perfusion with K-H solution was continued for 30 minutes,then perfusion was stopped for 40 minutes,and then perfusion with K-H solution was continued for 120 minutes;D group : After 15 minutes of balanced perfusion with K-H solution,perfusion with K-H solution containing dexmedetomidine continued for 30 minutes and then treated with the same I/R group;SP group: After 15 minutes of balanced perfusion with K-H solution,continuous perfusion with KH solution containing SP600125 was continued.After 30 minutes,the same treatment was performed in the I/R group;D+SP group: K-H solution was perfused for 15 minutes,and continued for 30 minutes with K-H solution containing dexmedetomidine and SP600125,and then treated with the I/R group.Heart function indexes were collected at the end of balance(T1),before ischemia(T2),and at the end of reperfusion(T3): heart rate(HR),left ventricular maximum pressure(ądp/dtmax),left ventricular development pressure(LVDP),left ventricular end-diastolic pressure(LVEDP);The myocardial tissue of rats after reperfusion was taken.The concentration of c Tn I was measured by ELISA.The myocardial infarct size was detected by TTC staining.The apoptosis rate of cardiomyocytes was detected by TUNEL method.The ultrastructure of cardiac muscle was observed by electron microscopy.GRP78 and JNK gene was detected by RT-PCR.The expression of GRP78?JNK and p-JNK protein were detected by Western blot.Results:(1)There was no significant difference in the indexes of cardiac function between the end of balance(T1)and pre-ischemic(T2)between groups(P>0.05).Compared with the time of T1,the end of reperfusion in each group of rats(T3)HR,ądp/dtmax,and LVDP were significantly lower,and LVEDP was significantly increased(P<0.05).At T3,I/R group,D group,and SP group were compared with N group.The HR,ądp/dtmax,and LVDP in the D+SP group were significantly lower,and the LVEDP was significantly increased(P<0.05).Compared with the I/R group,the HR of the D group,SP group,and D+SP group was significantly lower.Both ądp/dtmax and LVDP increased significantly,and LVEDP decreased significantly(P<0.05).There was no significant difference in changes of cardiac function between group D,SP and D+SP(P>0.05)..(2)Compared with N group,the relative concentration of c Tn I,myocardial infarct area and cardiomyocyte apoptotic rate were significantly increased in I/R group,D group,SP group and D+SP group(P<0.05);Compared with group D,SP group,D+SP group,relative c Tn I concentration,myocardial infarct size,cardiomyocyte apoptotic rate were significantly decreased(P<0.05);c Tn I of D group,SP group,and D+SP group were relatively Concentration and myocardial infarct size did not change significantly(P>0.05);Cardiomyocyte apoptosis rate in group D and D+SP did not change significantly(P>0.05),but myocardial cell apoptosis in group D and D+SP The rate was less than SP group(P<0.05).(3)The ultrastructure of N group myocardial cells was observed under electron microscope;the ultrastructure of I/R group was severely damaged and apoptotic bodies were clearly seen;the ultrastructure of myocardial cells in group D,SP and D+SP was destroyed.Fewer,but occasionally apoptotic bodies(4)compared with N group,the expression of GRP78 gene and protein in I/R group increased significantly(P<0.05),and the expression of JNK gene and P-JNK protein decreased significantly(P<0.05);Compared with I/R group,the expression of GRP78 gene and protein in other groups was significantly decreased,and the expression of JNK gene and P-JNK protein was significantly decreased(P<0.05).Conciusions:Dexmedetomidine preconditioning can reduce the myocardial ischemia-reperfusion injury in isolated rat heart,and this protective effect may be related to the activation of JNK signaling pathway in the suppression of excessive endoplasmic reticulum stress.So as to reduce myocardial cell apoptosis. |
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