Both ERα and ERβ have been identified
in various components of the vascular wall of experimental
animals and humans; however, estrogen modulates vascular
function mainly through ERα in both nongenomic and
genomic pathways. Estrogen directly regulates the expression
of endothelial nitric oxide synthase (eNOS) in cerebral
microvessels4 and the aorta.5 In addition, estrogen can
indirectly regulate eNOS expression through inhibition of the
pro-inflammatory cytokine tumor necrosis factor-α (TNF-α),
which down-regulates expression of eNOS by destabilizing its
mRNA.6 The role of estrogen in regulating eNOS production is
also supported by the observation of elevated TNF-α serum
levels in postmenopausal women and ovariectomized (OVX)
rats.7