Genetic and pharmacologic strategies to determine the function of estrogen receptor α and estrogen receptor β in the cardiovascular system

Background: The biological functions of estrogens extend beyond the female and male reproductive tract, affecting the cardiovascular and renal systems. Traditional views on the role of postmenopausal hormone therapy (HT) in protecting against heart disease, which were challenged by clinical end point studies that found adverse effects of combined HT, are now being replaced by more differentiated concepts suggesting a beneficial role of early and unopposed HT that does not include a progestin. Objective: We reviewed recent insights, concepts, and research results on the biology of both estrogen receptor (ER) subtypes, ER alpha and ER beta, in cardiac and vascular tissues. Knowledge of these ER subtypes is crucial to understanding gender and estrogen effects and to developing novel, exciting strategies that may have a profound clinical impact. Methods: This review focuses on in vivo studies and includes data presented at the August 2007 meeting of the American Physiological Society as well as data from a search of the MEDLINE and Ovid databases from January 1986 to November 2007. Search results were restricted to English-language publications, using the following search terms: estrogen, estrogen receptor alpha, estrogen receptor beta, estrogen receptor a agonist, estrogen receptor alpha antagonist, estrogen receptor beta agonist, estrogen receptor P antagonist, PPT, DPN, heart, vasculature, ERKO mice, BERKO mice, transgenic mice, and knockout mice. Results: Genetic mouse models and pharmacologic studies that employed selective as well as nonselective ER agonists support the concept that both ER subtypes confer protective effects in experimental models of human heart disease, including hypertension, cardiac hypertrophy, and chronic heart failure. Conclusions: Genetic models and novel ligands hold the promise of further improving our understanding of estrogen action in multiple tissues and organs. These efforts will ultimately enhance the safety and efficacy of HT and may also result in new applications for synthetic female sex hormone analogues.