Differential effects of medroxyprogesterone acetate on thrombosis and atherosclerosis in mice

Background and purpose:  The risk for cardiovascular events including venous and arterial disease and stroke is elevated after treatment with estrogen and medroxyprogesterone acetate (MPA) in postmenopausal women. Here, we have investigated the effect of MPA on arterial thrombosis and atherosclerosis in a murine model of atherosclerosis. Experimental approach:  Apolipoprotein E (ApoE) −/− mice were bilaterally ovariectomized and treated with placebo, MPA (27.7 µg·day −1 ) and MPA + 17‐β‐oestradiol (E 2 ; 1.1 µg·day −1 ) for 90 days, on a Western‐type diet. Thrombotic response was measured in a photothrombosis model, platelet activation by fluorescence activated cell sorting (FACS) analysis (CD62P) and thrombin generation by the endogenous thrombin potential (ETP). Furthermore, aortic plaque burden and aortic root plaque composition were determined. Key results:  MPA and MPA + E 2 ‐treated animals showed an aggravated thrombotic response shown by significantly reduced time to stable occlusion. The pro‐thrombotic effect of MPA was paralleled by increased ETP whereas platelet activation was not affected. Furthermore, MPA + E 2 reduced the number of cells positive for α‐smooth muscle actin and increased hyaluronan in the plaque matrix. Interestingly, total plaque burden was reduced by MPA but unchanged by MPA + E 2 . Conclusion and implications:  Long‐term treatment with MPA and MPA + E 2 increased arterial thrombosis despite inhibitory effects of MPA on atherosclerosis in ApoE‐deficient mice. Increased thrombin formation, reduced smooth muscle content and remodelling of non‐collagenous plaque matrix may be involved in the pro‐thrombotic effects. Thus, MPA exhibits differential effects on arterial thrombosis and on atherosclerosis.