Objective:To investigate the mechanism by which indomethacin inhibits the expression of
matrix metalloproteinase-9 in abdominal
aortic aneurysm(AAA) in rats. Methods: Male Wistar rats underwent intraluminal perfusion of the abdominal aorta with 50 units of porcine pancreatic elastase followed by treatment with indomethacin (1.6 mg/d) subcutaneously (n=8) for 7 d or with normal saline(NS,n=8).Aortic wall elastin and collagen concentrations were measured with an imaging analysis system, and fixed aortic tissues were examined by light microscopy for inflammation. The expression of MMP-9 in aortic tissues was observed with immunohistochemistry technique. Results: AAAs developed in all NS treated rats and in none of indomethacin treated rats on d 7(P<0.01). The expression of MMP-9 protein in indomethacin treated aortic tissues was much less than that in control rats. Conclusion: Indomethacin can inhibit the development of experimental abdominal aortic aneurysm in vivo. This inhibition may be due to a selective blockade of elastolytic MMP-9 expression, leading to degradation of abdominal aortic elastin.