Aging and estrogen alter endothelial reactivity to reactive oxygen species in coronary arterioles

Endothelium-dependent, nitric oxide (NO)-mediated vasodilation can be impaired by reactive oxygen species (ROS), and this deleterious effect of ROS on NO availability may increase with aging. Endothelial function declines rapidly after menopause, possibly because of loss of circulating estrogen and its antioxidant effects. The purpose of the current study was to determine the role of O(2)(-) and H(2)O(2) in regulating flow-induced dilation in coronary arterioles of young (6-mo) and aged (24-mo) intact, ovariectomized (OVX), or OVX + estrogen-treated (OVE) female Fischer 344 rats. Both aging and OVX reduced flow-induced NO production, whereas flow-induced H(2)O(2) production was not altered by age or estrogen status. Flow-induced vasodilation was evaluated before and after treatment with the superoxide dismutase (SOD) mimetic Tempol (100 μM) or the H(2)O(2) scavenger catalase (100 U/ml). Removal of H(2)O(2) with catalase reduced flow-induced dilation in all groups, whereas Tempol diminished vasodilation in intact and OVE, but not OVX, rats. Immunoblot analysis revealed elevated nitrotyrosine with aging and OVX. In young rats, OVX reduced SOD protein while OVE increased SOD in aged rats; catalase protein did not differ in any group. Collectively, these studies suggest that O(2)(-) and H(2)O(2) are critical components of flow-induced vasodilation in coronary arterioles from female rats; however, a chronic deficiency of O(2)(-) buffering by SOD contributes to impaired flow-induced dilation with aging and loss of estrogen. Furthermore, these data indicate that estrogen replacement restores O(2)(-) homeostasis and flow-induced dilation of coronary arterioles, even at an advanced age.