The Protective Effect Of Dexmedetomidine In A Rat Ex Vivo Lung Model Of Ischemia-reperfusion Injury

Objective:This study was designed to establish an ideal rat ex vivo model of lung ischemia-reperfusion injury?LIRI?and to to investigate the effect of dexmedetomidine?Dex?on LIRI and relationships between LIRI and endoplasmic reticulum stress?ERS?and oxidative stress.Methods:Part I.A total of 40 male Sprague-Dawley?SD?rats were divided randomly into 4 groups,with 10 rats in each group:sham group?S group?,ischemia-reperfusion 45min group?IR45 group?,ischemia-reperfusion 60min group?IR60 group?,ischemia-reperfusion 75min group?IR75 group?.An IL-2 rat ex vivo lung perfusion system was used.S group kept perfusion and ventilation for 75 minutes.After perfusion for 15 minutes to reach steady state,IR45 group,IR60 group and IR75 group separately stopped ventilation and perfusion for 45,60 and 75 minutes,following by reperfusion and reventilation for 90 minutes.At15 minutes after the initial perfusion?T0?and 15?T1?,45?T2?,75?T3?and 90?T4?minutes after the reperfusion,the airway pressure?Res?,lung compliance?Compl?,perfusion flow?Flow?,and pulmonary venous oxygen partial pressure?PaO2?were recorded.After perfusion,the pulmonary edema of each group was observed,the lung wet/dry weight ratio?W/D?was determined,and pathological changes of the lung tissue were evaluated to rate the lung injury.Part?.A total of 70 male SD rats were divided randomly into seven groups,with10 rats in each group:sham group?S group?,ischemia-reperfusion group?IR group?,low-dose Dex group?D1 group?,intermediate-dose Dex group?D5 group?,high-dose Dex group?D10 group?,Dex+yohimbine group?DY group?,and yohimbine group?Y group?.By using IL-2 system,S group kept perfusion and ventilation for 150 minutes,and other groups took perfusion for 15 minutes to reach steady state,then stopped lung ventilation and perfusion for 60 minutes,following by reperfusion and reventilation for 75 minutes.For the D1,D5,D10and IR groups,1 nM,5 nM,10 nM Dex or equivalent volume of normal saline?NS?was added to the ex vivo perfusion solution at the beginning of reperfusion;for the DY group,10 nM Dex and 1?M yohimbine were added to the perfusion solution at the beginning of reperfusion;for the Y group,1?M yohimbine was added to the perfusion solution at the beginning of reperfusion.For the S group,equivalent volume of NS was added to the perfusion solution after 75 minutes of perfusion.At 15 minutes after the initial perfusion?T0?,and at 15?T1?,45?T2?,and 75?T3?minutes after reperfusion,the Res,Compl,Flow and PaO2 were recorded.After perfusion,the pulmonary edema of each group was observed,the W/D was determined,and pathological changes of the lung tissue were evaluated to rate the lung injury.Part?.Lung tissue of each group was fixed to do paraffin sections,with TUNEL kit to detect apoptosis index?AI?;the activity of Orgotein Superoxide Dismutase?SOD?and the content of Malondialdehyde?MDA?were evaluated by the kit method;the levels of mRNA of Glucose-regulated protein 78?GRP78?and C/EBP homologous protein?CHOP?in the lung tissue were determined by RT-PCR method;the levels of protein of GRP78 and CHOP in the lung tissue were determined by Western Blot methodResults:Part?.Compared with S group,at T1,T2 and T3 time point,IR45 group had no significant difference on Res,Compl and Flow,only PaO₂ was significantly reduced?P<0.05?,while at T4,each data was significant different?P<0.05?.At T1,T2 and T3,each data of IR60 group was significant different with S group?P<0.05?,but each data of IR60 group was close to 0 or unable to be shown at T4.Although pulmonary function parameters of IR75 group were all significantly reduced at T1 and T2 comparing with S group?P<0.05?,each data was close to 0 or unable to be shown at T3 or T4.Compared with S group,other three groups had obvious pulmonary edema,significant higher W/D and lung injury score?P<0.05?.Of the four groups,W/D and lung injury score increased successively?P<0.05?.Part?.Compared with S group,the other six groups had significant higher Res and lower Compl,Flow and PaO₂?P<0.05?.Compared with IR group,Res reduced obviously and Compl,Flow and PaO₂ increased obviously in D1,D5 and D10 groups?P<0.05?,but there was no significant difference among IR,DY and Y groups?P>0.05?.In D1,D5 and D10 groups,Res successively reduced and Compl,Flow and PaO₂ successively increased?P<0.05?.Compared with S group,the other six groups had significant higher W/D and lung injury score?P<0.05?.Compared with IR group,W/D and lung injury score obviously reduced in D1,D5and D10 groups?P<0.05?,but there was no significant difference among IR,DY and Y groups?P>0.05?.In D1,D5 and D10 groups,W/D and lung injury score reduced successively?P<0.05?.Part?.Compared with S group,the other six groups had significant higher AI,content of MDA,mRNA and protein level of GRP78 and CHOP,and significant lower activity of SOD?P<0.05?.AI,content of MDA,mRNA and protein level of GRP78 and CHOP reduced obviously and activity of SOD increased obviously in D1,D5 and D10 groups compared with IR group?P<0.05?,but there was no significant difference among IR,DY and Y groups?P>0.05?.In D1,D5 and D10groups,AI,content of MDA,mRNA and protein level of GRP78 and CHOP reduced successively?P<0.05?while the activity of SOD increased successively?P<0.05?.Conclusions:?1?The model of rat ex vivo LIRI was successfully established,which wasobtained by 60 minnutes ischemia and 75 minutes reperfusion.?2?In LIRI,Dex had protective effect.Dex could improve Compl,Flow and PaO₂,reduce Res,pulmonary edema and lung injury score.?3?The lung protective effect of Dex positively related to the dosage.Among the1nM,5nM and 10nM content,10nM of Dex had the strongest lung protectiveeffect.?4?The mechanism of lung protective effect by Dex may be related to theactivation ofa2 receptor which leads to anti-oxidative stress effect andinhibition of ERS in LIRI,so as to inhibits the apoptosis of alveolar cells.