Dose Dependent Effect Of Angiotensin Ⅱ On The Incidence And Mortality Of Aortic Dissection In Mouse And Its Underlying Mechanism

Aortic dissection is a life-threatening disease.It can be induced by using AngiotensinⅡin mice.Presently,it is still unclear whether different doses of angiotensinⅡadministration in mice will affect the formation of aortic dissection.Therefore,we explored the morbidity and mortality of aortic dissection mice by giving different doses of angiotensinⅡtreatments.Methods:33 6-weeks-old male ApoE^-/-mice randomly divided into four groups:Control group（n=6）,1000 ng/kg/min angiotensinⅡgroup（n=9）,1500 ng/kg/min angiotensinⅡgroup（n=9）and 2000 ng/kg/min angiotensinⅡgroup（n=9）.First,BAPN（β-aminopropionitrile monofumarate）at concentration of 0.1%was orally given to all four groups for 21 days.Then,osmotic minipump infilled with different doses of angiotensinⅡwere planted subcutaneously in mice from different groups respectively.0.9%Na Cl contained osmotic minipumps were painted in mice from control group.These minipumps were reserved for 28 days.At the 29^th day.All mice were euthanized and aortic tissue were collected.Mice who died before the end time of experiment were autopsied immediately,and aortic tissue were conserved.Results:Systolic blood pressure and diastolic blood pressure were increased after angiotensinⅡadministration.Both blood pressure was increased continuously after angiotensinⅡinjection.But there was no significant difference between those three angiotensinⅡinjected group.Heart rate growth faster compared to control group after angiotensinⅡadministration.Body weight did not change significantly after giving angiotensinⅡ.No aortic dissection formed in control group.The morbidity of aortic dissection was 22%in the 1000 ng/kg/min angiotensinⅡgroup,55%in the1500 ng/kg/min group and 55%in the 2000 ng/kg/min group（P=0.322）.No mouse died in 1000 ng/kg/min angiotensinⅡgroup.The morbidity of group 1500 and 2000were 33%and 44%（P=0.351）.Compared with the 1000 ng/kg/min group,the survival curves were significantly different in 1500 ng/kg/min angiotensinⅡgroup and 2000 ng/kg/min angiotensinⅡgroup（P=0.037 and P=0.014,Log-Rank test）.However,there was no significance between 1500 ng/kg/min angiotensinⅡgroup and 2000 ng/kg/min angiotensinⅡgroup（P=0.442）.The incidence of death was appeared at the second week and first week in group 1500 ng/kg/min and 2000ng/kg/min.Hemothorax or hemoperitoneum could be seen after autopsy at those died mice.Hematoxylin Eosin stain of aortic tissue from aortic dissection mice showed the false lumen formation.Broken of aortic elastin layer can be seen by using Elastin Van Gieson stain at those aortic dissection happened mice.Collagen deposition at false lumen can be seen by Masson stain at those without aortic dissection ruptured mice.The Mac-2 positive macrophage and matrix metalloproteinase 9（MMP9）were obviously stained at the adventitia of aortic tissue who had ruptured aortic dissection by using immunohistochemistry technique.The MMP9 co-stained with macrophage were confirmed by using immunofluoresence technique.The expression of MMP9 by macrophage can be stimulated by adding interleukin-6（IL-6）is confirmed by in vitro experiments.Conclusion:When the concentration of angiotensinⅡvaried from 1000 to 2000ng/kg/min.The morbidity and mortality of aortic dissection has an increasing tendency as the doses of angiotensinⅡgo up,but statistic not significant.The death incidence due to ruptured aortic dissection appeared at the first or second week after angiotensinⅡadministration.Mice were more likely to die of ruptured aortic dissection in those higher concentration of angiotensinⅡadministration.Ruptured aortic dissection was relevant to IL-6 dependent adventitial macrophage MMP9expression.