Synthetic gestagens exert differential effects on arterial thrombosis and aortic gene expression in ovariectomized apolipoprotein E ‐deficient mice

Background and Purpose Combined hormone replacement therapy with oestrogens plus the synthetic progestin medroxyprogesterone acetate ( MPA ) is associated with an increased risk of thrombosis. However, the mechanisms of this pro‐thrombotic effect are largely unknown. The purpose of this study was to: (i) compare the pro‐thrombotic effect of MPA with another synthetic progestin, norethisterone acetate ( NET ‐ A ), (ii) determine if MPA's pro‐thrombotic effect can be antagonized by the progesterone and glucocorticoid receptor antagonist mifepristone and (iii) elucidate underlying mechanisms by comparing aortic gene expression after chronic MPA with that after NET ‐ A treatment. Experimental Approach Female apolipoprotein E‐deficient mice were ovariectomized and treated with placebo, MPA , a combination of MPA + mifepristone or NET ‐ A for 90 days on a Western‐type diet. Arterial thrombosis was measured in vivo in a photothrombosis model. Aortic gene expression was analysed using microarrays; GeneOntology and KEGG pathway analyses were conducted. Key Results MPA's pro‐thrombotic effects were prevented by mifepristone, while NET ‐ A did not affect arterial thrombosis. Aortic gene expression analysis showed, for the first time, that gestagens induce similar effects on a set of genes potentially promoting thrombosis. However, in NET ‐ A ‐treated mice other genes with potentially anti‐thrombotic effects were also affected, which might counterbalance the effects of the pro‐thrombotic genes. Conclusions and Implications The pro‐thrombotic effects of synthetic progestins appear to be compound‐specific, rather than representing a class effect of gestagens. Furthermore, the different thrombotic responses elicited by MPA and NET ‐ A might be attributed to a more balanced, ‘homeostatic’ gene expression induced in NET ‐ A ‐ as compared with MPA ‐treated mice.