Estrogen has multiple sites of action, and estrogen deficiency
can influence both the short- and long-term regulation of
vascular dilating factors. In addition, estrogen itself provides an
anti-inflammatory action to vascular cells. Elevation of serum
pro-inflammatory cytokines has been reported in postmenopausal
women and in OVX rats.7 TNF-α is a key proinflammatory
cytokine involved in the pathogenesis of vascular
disorder, and its formation is regulated by estrogen. Therefore,
the change in the expression of TNF-α in OVX rat aorta in the
present study is consistent with previous observations in which
the decline of ovarian function in postmenopausal women is
associated with an elevation of TNF-α.7 TNF-α inhibition was
also found to enhance agonist-mediated vasorelaxation and
increase eNOS expression in the vasculature of female rats.31
Moreover, the increase in TNF-α reduced NO availability in
endothelial cells either by decreasing eNOS expression6 or by
increasing NO inactivation via enhanced superoxide anion
production from NADPH oxidases.32 Another possible reason