Effects Of Dexmedetomidine Preconditioning On Myocardial Ischemia-reperfusion Injury In Isolated Rat Hearts

Objective To investigate the effects of dexmedetomidine preconditioning on myocar-dial ischemia-reperfusion injury in isolated rat hearts.Methods Thirty-two male wistar rats weighing230～260g were heparinized with heparin sodium500IU/kg inter-peritoneally and anesthetized with10%chloral hydrate400mg/kg. After thoracotomy the hearts were immediately removed and perfused retrogradely at75cmH20with Krebs-Hensleit(K-H) solution aerated with95%O2and5%CO2in a Langendorff apparatus.After10min stabilization,the thirty-two isolated hearts were randomly divided to4groups(n=8earch):①I/R group in which the hearts were perfused for30min after10min stabilization;②D1group in which the hearts were perfused with K-H solution containing dexmedetomidine (0.23ng/ml) for20min followed by10min washout before ischemia;(3)D2group in which the hearts were perfused with K-H solution containing dexmedetomidine (2.3ng/ml) for20min followed by10min washout before ischemia;④D3group in which the hearts were perfused with K-H solution containing dexmedetomidine (2.3ng/ml) and yohmbine(1μM) for20min followed by10min washout before ischemia. Hearts were subjected to30min ischemia followed by120min reperfusion with K-H solution.Hemodynamic parameters:Heart rate(HR)、Left ventricular developed pressure(LVDP)、+differential pressure timemaxium(+dp/dtmax) and-differential pressure timemaxium(-dp/dtmax) were recorded at the end of balance、 before ischemia and at60min、120min during reperfusion.The activity of creatine kinase(CK) and lactate dehydrogenase(LDH) in coronary effluent were measured at the end of balance and5min、30min、60min、120min during reperfusion. At the end of reperfusion,the activity of SOD and the content of MDA in the myocardium were measured.Results (1) Influence on hemodynamic:There were no differences of HR、LVDP、+dp/dtmax、-dp/dtmax among groups before ischemic(P>0.05).After ischemia,there were no statistical significance of HR among four groups(P>0.05) and LVDP、+dp/dtmax and-dp/dtmax tends to decrease in each group; Compared with I/R group,the LVDP、+dp/dtmax、-dp/dtmax were higher in the group of D1and D2(P<0.05), there were no statistical significance in group D3(P>0.05); Compared with D1group, the LVDP、+dp/dtmax、-dp/dtmax were higher in the group of D2and were lower in group D3(P<0.05); Compared with D2group, the LVDP、+dp/dtmax、-dp/dtmax were lower in group of D3(P<0.05).(2)Influene on the myocardical enzyme leak:There were no statistical significance of CK and LDH among four groups at the end of balance(P>0.05);Compared with I/R group, the CK and LDH release decreased in the group of D1and D2(P<0.05), there were no statistical significance in group D3(P>0.05);Compared with D1group, the CK and LDH release decreased in the group of D2(P<0.05)(P<0.05),the CK and LDH were higher in group D3(P<0.05); Compared with D2group,the CK and LDH were higher in group D3(P<0.05).(3)Influence on the content of MDA and the activity of SOD:Compared with I/R group,the content of MDA decreased and the SOD activity was higher in the group of D1and D2(P<0.05), there were no statistical significance in group D3(P>0.05); Compared with D1group, the content of MDA decreased and the SOD activity was higher in the group of D2(P<0.05), the content of MDA increased and the SOD activity was lower in the group of D3(P<0.05); Compared with D2group, the content of MDA increased and the SOD activity was lower in the group of D3(P<0.05).Conclusion Dexmedetomidine preconditioning can protect myocardial ischemia-reperfusion injury relating to concentration and the mechanism of the protection maybe concerned with α2adrenergic receptor.