Aim To approach the effects of mast cell degranulation on plaque stabilization in apolipoprotein E-knock out(ApoE-/-) mice with perivascular common carotid collar placement. Methods 40 male ApoE-/-mice were fed a western-type diet and operated with perivascular right common carotid collar placement.4 weeks after surgery,mice were divided into 2 groups and treated for 7 days as follows(n=20): experimental mice were intraperitoneally injected with mast cell degranulator-Compound 48/80,0.5 mg/kg;control mice were intraperitoneally injected with an equal volume of dissolvent(D-Hank's).Thirty minutes after the 4th injection,animals were sacrificed to obtain blood and carotid.Serum was collected to quantify the activity of tryptase by colorimetric assay.Sections were routinely stained with hematoxylin and eosin.Corresponding sections on separate slides were stained with toluidine blue to detect mast cell degranulation and immunohistochemically with antibodies against a von Willebrand factor(vWF),interleukin-1β(IL-1β) and VE-cadherin. Results There were more foam cells,pericellular lipids and inflammatory cells in plaque in com mon carotids with collarplacement of experimental group.The percentage of degranulated mast cells(P<0.01),the activity of tryptase in serum(P<0.05),the density of neovessel in plaque(P<0.05),intraplaque hemorrhage(P<0.05),the expressions of IL-1β(P<0.05) and VE-cadherin(P<0.05) in plaque were significantly increased in experimental group than in control group. Conclusions Mast cell degranulation increases foam cells,pericellular lipids and inflammatory cells in plaque,and promotes angiogenesis in plaque,intraplaque hemorrhage,the expressions of IL-1β and VE-cadherin in plaque,accordingly weakens plaque stabilization.