Role Of Post-hemorrhagic Shock Mesenteric Lymph On The Unbalance Of ACE And ACE2 In Myocardium

Background and objective: Cardiac contractile dysfunction associatedwith hemorrhagic shock has long been considered as an important contributorinvolved in microcirculation disturbance, multiple organ dysfunctions andeven death, meanwhile, myocardium injury induced by hemorrhagic shock isthe important structural foundation of cardiac contractile dysfunction. It hasbeen reported that the return of post-hemorrhagic shock mesenteric lymph(PHSML) is one of major factors that aggravates myocardial injury and recruitcardiac pump dysfunction. However, its mechanisms should be furtherinvestigated. The previous reports showed that renin-angiotensin-system(RAS)are closely related to the microcirculation disorders and organ hypoperfusionfollowing hemorrhagic shock. The angiotensin-converting enzyme(ACE)-angiotensin II(Ang II)- Ang II 1 receptor(AT1R) and ACE2-Ang(1-7)-Masreceptor are the key axes of RAS, which is involved in the regulation of RAS.It is reported that the unbalance of ACE and ACE2 participated the kidney andlung injury induced by hindlimb ischemia-reperfusion injury. However,whether the unbalance of ACE and ACE2 is involved in the myocardiuminjury after hemorrhagic shock, it remains unknown. Meanwhile, whether therole of PHSML drainage alleviating myocardium injury is related to theregulation of ACE and ACE2 balance needs further investigation. Hence, inthe present study, we observed the effects of PHSML drainage on the m RNAexpressions of ACE, ACE2, AT1 R and Mas1 R and the levels of Ang II andAng(1-7) in myocardium of mice with hemorrhagic shock, to discuss the roleof PHSML on the unbalance of ACE and ACE2 in myocardium.Methods: Twenty-four male BALB/c mice were randomized into control,sham, shock, shock+drainage(shock plus PHSML drainage) groups with each6 cases. All of the mice were anesthetized through intraperitoneal injection ofsodium pentobarbital for the establishment of hemorrhagic shock model withthe conventional method in the shock and shock+drainage groups. Briefly, theright femoral vein was separated and cannulated for anticoagulation withheparin sodium. A minimally heparinized polyethylene catheter wasintroduced into the right femoral artery for continuously monitoring the meanartery pressure(MAP). Another catheter was inserted into the left femoralartery for bleeding by a syringe pump. A laparotomy was carried out toseparate the mesenteric lymph duct from surrounding connective tissues. Aftera 30- min stabilization period, blood was withdrawn from the right femoralartery to a MAP of 40 mm Hg within 10 min at an even speed and wasmaintained at this level by withdrawing or reinfusing shed blood as needed.After 60 min of hypotension, the ejective blood and the equal Ringer solutionwere reperfused within 30 min through left femoral artery. At 6 h after the endof infusion, myocardial tissue was obtained and stored at-80 ℃. Part ofmyocardial tissue was prepared the homogenates for the examination of Ang IIand Ang(1-7) levels with the ELISA method; part of myocardial tissue wasprepared the RNA for the examination of ACE, ACE2, AT1 R, Mas1 R m RNAexpressions. In the shock+drainage, after infusion finished, the mesentericlymph duct was cannulated and PHSML was drained up to 6 h. In the shamgroup, the mice were anesthetized, cannulated and operated as describedabove, but no blood was withdrawn or infused. The mice in the control groupdirectly obtained the myocardial tissue after anesthesia. Data in this studywere presented as mean ± standard deviation(SD) or mean ± standard error(SE). Statistical analysis was performed using SPSS 16.0.Results: Firstly, the present results showed that there were no differencesin the ACE and AT1 R m RNA expressions and Ang II level in myocardialtissue between the control and sham groups(P>0.05); the ACE and AT1 Rm RNA expressions and Ang II level in myocardial tissue in shock group weresignificantly increased that that of the control and sham groups(P<0.05);PHSML drainage obviously reduced these indices in shocked mice(P<0.05),however, the ACE and AT1 R m RNA expressions decreased than the controland sham groups(P<0.05). Then, the ACE2 and Mas1 R m RNA expressions inmyocardial tissue in the sham group were lower than the control group(P<0.05), at the same time, the Ang(1-7) level was no difference between thecontrol and sham groups(P>0.05). Meanwhile, the ACE2 and Mas1 R m RNAexpressions in myocardial tissue in shock group were significantly decreasedthat that of the control and sham groups(P<0.05), the Ang(1-7) level wasdecreased compared with the control group(P<0.05). PHSML drainageobviously increased the ACE2 and Mas1 R m RNA expressions and Ang(1-7)level in myocardial tissue in the shocked mice(P<0.05), but the ACE2 andMas1 R m RNA expressions in the shock+drainage group were lower than thecontrol and sham groups(P<0.05). Lastly, the ratios of ACE/ACE2 and AngII/Ang(1-7) in the shock group was significantly increased than the controland sham groups(P<0.05), which was obviously reduced by PHSML drainage(P<0.05), however, the ratio in the shock+drainage group was higher that thecontrol and sham groups(P<0.05), the ratio in the sham group was higher thatthe control group(P<0.05).Conclusion: These results in this study demonstrated that hemorrhagicshock-induced upregulation of ACE-Ang II-AT1 R axis, down-regulation ofACE2-Ang(1-7)-Mas axis, and unbalance of ACE and ACE2 in myocardialtissue. PHSML drainage decreased the ACE-Ang II-AT1 R axis and increasedthe ACE2-Ang(1-7)-Mas axis, resulted in the balance of ACE and ACE2.