| Objective: By observing the effects of dexmedetomidine（Dex）on the apoptosis of lung tissue in rats in cardiopulmonary bypass（CPB）to explore its protective effects and mechanisms.Methods: 40 healthy male Sprague-Dawley rats were randomly divided into 5 groups（n=8,each）: left lung ischemia-reperfusion injury of CPB group（group IR）,Dex group（group D）,Dimethyl sulfoxide（DMSO）group（group DM）,Wortmannin group（group W）and Wortmannin+ Dex group（group WD）.5 groups separately received open chest operation after 10 mins of pre-parallel bypass,and blocked the left hilus pulmonis,then the left lung ischemia-reperfusion injury of CPB model were established.In group D,Dex(3μg×kg-1 i.v)were given 10 minutes before blocking the left hilus pulmonis,then continued to pump the Dex at a rate of 1.5μg×kg-1×h-1 till the end of CPB.In group IR,equal volume of normal saline were given at the same time.In group DM,equal volume of DMSO were given at the same time.In group W,wortmannin(15μg×kg-1 i.v)were given at the same time,then continued to pump the wortmannin at a rate of 2.0μg×kg-1×min-1 till the end of CPB.In group WD,wortmannin(15μg×kg-1i.v)and Dex(3μg×kg-1 i.v)were given at the same time,then continued to pump the wortmannin at a rate of 2.0μg×kg-1×min-1 and the Dex at a rate of 1.5μg×kg-1×h-1 respectively till the end of CPB.Arterial blood were taken before CPB（T1）,at the onset of opening the left hilus pulmonis（T2）,and at the end of this experiment（T3）.Arterial blood gas analysis was used to calculate the respiratory index（RI）and oxygenation index（OI）.At the time of T3,the left lung tissue were divided into 3parts.The superior part of lung tissue was fixed by 4% paraformaldehyde to observe the degree of lung injury and pathological score of lung tissue with optical microscope;The middle part of lung tissuewas digested into single cell suspension to measure the apoptosis rate of lung tissue by flow-cytometry;The inferior part of lung tissue was saved in liquid nitrogenat-196°C to measure the expression of Akt,p-Akt,caspase-3,caspase-9 by Western-blot.Recorded the vital signs of rats at the time of T1、T2、T3.Results:（1）The changes of heart rate（HR）and mean arterial pressure（MAP）of each group.The changes within each group in different time: HR and MAP at at T2 and T3 were obviously lower than T1 in each group（P<0.05）;compared with T2,HR at T3 decreased in group IR、DM、W、WD（P<0.05）,HR at T3 increased in group D（P<0.05）,MAP at T3 increased in group IR、D、DM、WD（P<0.05）.The changes at the same time in each group: There were no obvious changes of HR and MAP among five groups at T1（P>0.05）;At T2,there were no obvious changes of HR in each group（P>0.05）,MAP increased obviously in group D compared with group IR、DM、W and WD（P<0.05）;At T3,HR and MAP increased obviously in group D compared with group IR、W and WD（P<0.05）;There were no obvious changes of HR and MAP in group IR、DM、W and WD.（2）The changes of lung function parameters.The changes within each group in different time: OI at T2 and T3 were obviously lower than T1 in 5 groups（P<0.05）,RI showed the contrary trend;compared with T2,OI at T3 decreased and RI increased in 5 groups（P<0.05）.The changes at the same time in the each group: At T3,OI in group D increased obviously compared with group IR、DM、W and WD（P<0.05）.RI showed the contrary trend,this difference was statistically significant（P<0.05）（3）Pathological change and Lung injury score.In group IR,the lung tissue structure were disordered,alveolar walls were broken,there was abundant fluids、exudation of erythrocytes and inflammatory infiltration in alveolar space;in group D,the lung tissue structure and alveolar walls were relatively clear and complete,there was a small amount of inflammatory exudation;in group DM,the lung tissue structure was relatively clear,a few alveolar walls were broken and moderate amount of inflammatory cells appeared;in group W,the most serious change could be found,the lung tissue structure were remarkably disordered,alveolar walls were brokenseverely,there was abundant fluids、a great quantity of exudation of erythrocytes and inflammatory infiltration in alveolar space,the lung injury was more severe than group D;in group WD,the lung tissue structure were disordered,exudation of erythrocytes and inflammatory infiltration could be found in alveolar space,the lung injury was obviously severe compared with group D.The lung injury scores of group D were obviously lower compared with group IR、W and WD（P<0.05）,the lung injury scores of group W and WD were obviously higher than group IR（P<0.05）;There were no significant difference in group IR and DM（P>0.05）;There were no significant difference in group W and WD（P>0.05）.（4）Apoptosis rate of lung tissue.The apoptosis rate of lung tissue of group D was obviously lower compared with group IR、DM、W and WD（P<0.05）;The apoptosis rate of lung tissue of group DM were obviously lower compared with group W and WD（P<0.05）;There were no obvious changes in group IR、W and WD（P>0.05）.（5）Expression of Akt、p-Akt of lung tissue.The expression of Akt、p-Akt of group D were obviously higher compared with group IR 、DM、W and WD（P<0.05）,The expression of Akt、p-Akt of group DM were obviously higher compared with group IR、W and WD（P<0.05）.There were no obvious changes in group IR、W and WD（P>0.05）.（6）Expression of caspase-3、caspase-9 of lung tissue.Compared with group IR,the expression of caspase-3、caspase-9 of group D and DM were obviously lower（P<0.05）,the expression of caspase-3、caspase-9 of group W were obviously higher（P<0.05）,there were no obvious changes in group WD（P>0.05）;compared with group D,the expression of caspase-3、caspase-9 of group DM、W and WD were obviously higher（P<0.05）;compared with group DM,the expression of caspase-3、caspase-9 of group W were obviously higher（P<0.05）,there were no obvious changes in group WD（P>0.05）;compared with group W,the expression of caspase-3、caspase-9 of group WD were obviously lower（P<0.05）.Conclusion:Dex can reduce CPB related lung injury in rats,thus it has a certain protective effect on lung,its protective mechanism may be associated with inducing the apoptosis by activating PI3K/Akt pathway to inhibit the expression of caspase-3、caspase-9 of lung tissue. |
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