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(Circulation. 2000;102:445.)
© 2000 American Heart Association, Inc.

Basic Science Reports

Chronic 17ß-Estradiol Replacement Increases Nitric Oxide–Mediated Vasodilation of Guinea Pig Coronary Microcirculation

Loren P. Thompson, PhD; Gerard Pinkas, BS; Carl P. Weiner, MD

From the Department of Obstetrics/Gynecology and Reproductive Sciences, University of Maryland School of Medicine, Baltimore.

Correspondence to Loren P. Thompson, PhD, Department of Obstetrics/Gynecology and Reproductive Sciences, University of Maryland School of Medicine, Baltimore, MD 21201. E-mail lthompso{at}ummc001.ummc.umaryland.edu

Background—Estrogen is cardioprotective of the coronary circulation by mechanisms incompletely understood. This study determined the effect of chronic 17ß-estradiol replacement on dilator responses to acetylcholine and sodium nitroprusside of the isolated coronary microcirculation.

Methods and Results—Adult female guinea pigs were ovariectomized, and a 21-day-release pellet containing 0.0, 0.1, 0.25, 0.5, or 1.0 mg 17ß-estradiol was implanted subcutaneously. Serum estradiol concentrations ranged from 3.9 to 74.9 pg/mL, increasing with the dose of estradiol. After 19 to 20 days, the animals were euthanized, and their hearts were removed and perfused with buffer at constant flow on an isolated heart apparatus. Both perfusion pressure and contractile force were measured in prostaglandin F₂–constricted hearts. Vasodilation to the cumulative addition of the endothelium-dependent agonist acetylcholine (10^-9 to 10^-5 mol/L) and the nitric oxide (NO) donor sodium nitroprusside (10^-9 to 10^-5 mol/L) was measured before and after NO synthesis inhibition by nitro-L-arginine (LNA, 10^-4 mol/L). Baseline coronary resistance was unaltered by estradiol, although LNA increased resistance in estradiol-treated hearts more than in ovariectomized controls. Chronic 17ß-estradiol increased sensitivity (measured by -log EC₅₀ values) but not maximal response to acetylcholine compared with ovariectomized controls. Differences were abolished by LNA at all doses of estradiol. Sodium nitroprusside–induced dilation was unaffected by estradiol replacement.

Conclusions—Chronic 17ß-estradiol replacement, at doses producing hormone levels within the physiological range, enhances dilator sensitivity of the coronary microcirculation through enhanced NO production by the endothelium, independent of changes in NO sensitivity of the vascular smooth muscle. Thus, estradiol enhances NO production as a protective mechanism of the coronary microcirculation.

Key Words: acetylcholine • hormones • nitric oxide • vasodilation • endothelium

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