Published Online
on May 24, 2004

A more recent version of this article appeared on July 1, 2004

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Submitted on March 26, 2004
Revised on April 13, 2004

Estrogen and Tamoxifen Modulate Cerebrovascular Tone in Ovariectomized Female Rats

Suk-Ying Tsang; Xiaoqiang Yao; Franky L. Chan; Chi-Ming Wong; Zhen-Yu Chen; Ismail Laher; and Yu Huang^*

From the Departments of Physiology (S.-Y.T., X.Y., C.-M.W., Y.H.), Anatomy (F.L.C.), and Biochemistry (Z.-Y.C.), Chinese University of Hong Kong, Hong Kong, China; and Department of Pharmacology and Therapeutics (I.L.), University of British Columbia, Canada.

^* To whom correspondence should be addressed. E-mail: yu-huang{at}cuhk.edu.hk.

Abstract--Postmenopausal estrogen deficiency increases the incidence of cerebrovascular disease. However, hormone replacement therapy is associated with an increased cardiovascular risk. Tamoxifen is a selective estrogen receptor modulator with estrogenic effects on cardiovascular risk factors, but its long-term impacts on cerebral vasculature are unknown. We hypothesized that chronic 17-estradiol or tamoxifen treatment exerted similar effects in reducing cerebrovascular tension in ovariectomized rats. We therefore determine whether (1) chronic 17-estradiol treatment could influence vasomotor activities, (2) chronic tamoxifen therapy could exert an estrogen-like or estrogen-antagonistic effect, and (3) acute exposure to estrogen could mimic the effect of 17-estradiol. Isometric tension was measured in cerebral arteries from female rat groups: control, ovariectomy, ovariectomy plus 17-estradiol treatment, ovariectomy plus tamoxifen treatment, and ovariectomized rats treated with tamoxifen and 17-estradiol. Ovariectomy enhanced cerebrovascular contractions to endothelin-1 or CaCl₂, but not to U46619 or phenylephrine. 17-Estradiol therapy reversed these effects. Chronic tamoxifen treatment exerted estrogen-like actions by reversing ovariectomy-induced enhancement of vessel tone without antagonizing the effect of chronic 17-estradiol treatment. Ovariectomy enhanced the relaxing potency of nicardipine, and 17-estradiol treatment prevented this effect. Acute exposure to 10^-9 mol/L 17-estradiol or 10^-8 mol/L tamoxifen did not modulate contractions in rings from nonoperated female rats. In conclusion, ovariectomy differentially enhances agonist-induced cerebrovascular tone, an effect that was reversed by estrogen therapy. Tamoxifen does not act as an estrogen antagonist; instead, it functions as an estrogen agonist during estrogen deficiency. Thus, tamoxifen may confer beneficial effects similar to estrogen in cerebrovascular vessels.

Key words: cerebral arteries • estrogen • vasoconstriction • rats

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