Estrogen receptors do not influence angiogenesis after myocardial infarction

Background. There is controversy on whether estrogen receptors are present and functioning in the myocardium. Aims. To explore if after myocardial infarction (MI) estrogen receptors α (ERα) and β (ERβ) are upregulated in myocardial tissue and to explore if the presence/ absence of ERα or ERβ influences angiogenesis after MI. Methods. MI was induced by ligation of the left anterior descending artery in knockout (KO) mice, ERαKO and ERβKO, respectively, and non-KO littermate-controls, C57Bl/6 mice. The hearts were harvested after 12 days. A part of the periinfarct tissue was collected for ERα and ERβ mRNA expression determination by real-time polymerase chain reaction. Using immunohistochemistry, ERα and ERβ protein expression and capillary and arteriolar densities were blindly determined in the periinfarct area. Results. In myocardium disrupted mRNA was upregulated in both ERαKO and ERβKO, (p < 0.005) and did not change after MI. There was no change in mRNA expression of ERα or ERβ in wild type mice after MI. Expression of ERβ in ERαKO and of ERα in ERβKO did not change. Following MI ERα or ERβ could not be demonstrated by immunohistochemistry in either wild type or ERαKO or ERβKO. The capillary and arteriolar densities after MI did not differ between the groups in the periinfarct area. Conclusions. Although disrupted ER mRNA is upregulated in myocardium of ER knockout mice, no change in these or native receptors occurs following MI. At least in this model ER therefore seems not to have a role in myocardial arteriogenesis and angiogenesis after MI.