Key Role of Estrogens and Endothelial Estrogen Receptor α in Blood Flow-Mediated Remodeling of Resistance Arteries

Objective-Flow-(shear stress-)mediated outward remodeling of resistance arteries is involved in collateral growth during postischemic revascularization. As this remodeling is especially important during pregnancy, we hypothesized that estrogens may be involved. A surgical model eliciting a local increase in blood flow in 1 mesenteric resistance artery was used in 3-month-old ovariectomized female rats either treated with 17-beta-estradiol (E2) or left untreated. Methods and Results-After 14 days, arterial diameter was greater in high-flow arteries than in normal-flow vessels. An ovariectomy suppressed high-flow remodeling, while E2 restored it. High-flow remodeling was absent in mice lacking the estrogen receptor a but not estrogen receptor beta. The kinetics of inflammatory marker expression, macrophage infiltration, oxidative stress, and metaloproteinases expression were not altered by the absence of E2 after 2 and 4 days, that is, during remodeling. Nevertheless, E2 was required for the increase in endothelial nitric oxide synthase expression and activation at day 4 when diameter expansion occurs. Finally, the impact of E2 on the endothelium appeared crucial for high-flow remodeling, as this E2 action was abrogated in mice lacking endothelial NOS, as well as in Tie2-Cre(+) ER alpha(f/f) mice. Conclusion-We demonstrate the essential role of E2 and endothelial estrogen receptor a in flow-mediated remodeling of resistance arteries in vivo. (Arterioscler Thromb Vasc Biol. 2013;33:605-611.)