Chronic estrogen treatment increases levels of endothelial nitric oxide synthase protein in rat cerebral microvessels

Background and Purpose-A number of studies indicate that the female gonadal hormone, estrogen, confers protection against cerebrovascular disorders su ch as stroke. One postulated mechanism for these effects of estrogen is an action on the enzyme endothelial nitric oxide synthase (eNOS), which produc es the vasodilatory molecule NO. We have investigated the hypothesis that e strogen increases expression of eNOS in cerebral microvessels of male and f emale rats. Methods-We measured levels of eNOS protein by Western blot in cerebral micr ovessels isolated from 7 groups of animals: females, ovariectomized females , ovariectomized females treated with estrogen, males, castrated males, cas trated males heated with estrogen, and castrated males treated with testost erone. Results-Ovariectomized female rats treated with estrogen bad 17.4-fold grea ter levels of eNOS protein in cerebral microvessels than ovariectomized fem ales, and intact females had 16.6-fold greater levels than ovariectomized F emales (P<0.01). In intact females, cerebral microvessel eNOS protein level s were 9.2-fold higher than those of intact males (P<0.05). Levels of eNOS protein in castrated males, castrated males treated with testosterone, and males were not different from each other. Estrogen treatment of castrated a nimals resulted in an 18.8-fold increase in cerebral microvessel eNOS prote in (P<0.05). Conclusions-Chronic estrogen treatment, increases levels of eNOS protein in cerebral microvessels of male and female rats. This increase in eNOS prote in correlates with our previous functional findings indicating that estroge n exposure increases NO modulation of cerebrovascular reactivity in both ma le and female animals. Upregulation of eNOS expression may contribute to th e neuroprotective effect of estrogen.