Estrogen inhibits the vascular injury response in estrogen receptor β-deficient female mice

The protective effects of estrogen in the cardiovascular system result from both systemic effects and direct actions of the hormone on the vasculature. Two estrogen receptors have been identified, ER alpha and ER beta. We demonstrated previously that estrogen inhibits the response to vascular injury in both wild-type and ER alpha-deficient mice, and that ER beta is expressed in the blood vessels of each, suggesting a role for ER beta in the vascular protective effects of estrogen. In the present study, we examined the effect of estrogen administration on mouse carotid arterial injury in ER beta-deficient mice. Surprisingly, in ovariectomized female wild-type and ER beta knockout mice, 17 beta-estradiol markedly and equally inhibited the increase in vascular medial area and the proliferation of vascular smooth muscle cells after vascular injury, These data demonstrate that ER beta is not required for estrogen-mediated inhibition of the response to vascular injury, and suggest that either of the two known estrogen receptors is sufficient to protect against vascular injury, or that another unidentified estrogen receptor mediates the vascular protective effects of estrogen.