Menopause Effects on Vascular Function

The purpose of the study is to identify the independent effect of estradiol (E2) on endothelin-1 (ET-1) mediated vasomotor function in women. The study is the first step in recognizing the impact of ovarian hormones on the mechanisms that regulate vascular function in women to provide a better understanding of the cardiovascular efficacy of hormone therapy.

Cardiovascular disease (CVD) is the leading cause of death in women (Roger, Go, Lloyd, Adams, Berry, Brown, et al, 2011). Functional changes in the microvasculature occur with aging and precede atherosclerosis, contributing to CVD (Seals, Jablonski, \& Donato, 2011). Furthermore, because of the decline in ovarian hormones during menopause, age-related impairments in endothelial function are exacerbated in postmenopausal women (PMW). However, the safety and efficacy of currently available hormone-based therapies remains controversial (Devi, Sugiguchi, Pederson, Abrassart Glodowski, \& Nachtigall, 2013: Miller, Black, Brinton, Budoff, Cedars, Hodis, et al, 2009). Endothelin-1 (ET-1) is a potent vasoconstrictor produced and released by endothelial cells and implicated in the development of atherosclerosis (Best, McKenna, Holmes, \& Lerman, 1999; Donato, Gano, Eskurza, Silver, Gates, Jablonski, et al, 2009; Ihling, Szombathy, Bohrmann, Brockhaus, Schaefer, \& Loeffler, 2009). ET-1 binds to two receptor subtypes, ET-A and ET-B (Yanagisawa, Kurihara, Kimura, Tomobe, Kobayashi, Mitsui, et al, 1988). While both receptors are located on vascular smooth muscle (VSM) and cause vasoconstriction, ET-B receptors are also located on the endothelium and cause vasodilation (Gomez-Sanchez, Cozza, Foecking, Chiou, \& Ferris, 1990; Haynes, 1995; Ishikawa, Ihara, Noguchi, Mase, Mino Saeki, et al, 1994). In women, ET-1 preferentially binds to ET-B receptors compared to ET-A receptors, supporting findings of sex differences in ET-1 receptor responses and suggesting ET-B receptors are under hormonal control (Ergul, Shoemaker, Puett, \& Tackett, 1998; Kellogg, Liu, \& Pergola, 2001; Stauffer, Westby, Greiner, Van Guilder, \& Desouza, 2010). In animal models, estradiol (E2) reduces ET-1 mediated vasoconstriction and increases ET-B receptor mRNA (Pederson, Nielsen, Mortensen, Nilas, \& Ottesen, 2008). Thus, low levels of E2 in PMW may contribute to impaired vascular function through an ET-B receptor mechanism. However, the interaction between E2 and ET-1 receptor responses on regulating vascular function in women is currently unknown.

The long-term goal of the laboratory is to understand the impact of ovarian hormones on the mechanisms that regulate vascular function in women to provide a better understanding of the cardiovascular efficacy of hormone therapy. The study is the first step in reaching our goal; the objective of the study is to identify the independent effect of E2 on ET-1 mediated vasomotor function in women. The investigators will measure blood flow responses to local heating in the cutaneous circulation during perfusion of ET-1 receptor antagonists via microdialysis, coupled with measures of intracellular protein and receptor expression on endothelial cells and skin punch biopsies (to assess VSM cells) collected from young and PMW while controlling ovarian hormone exposure. Young women will be tested after suppressing ovarian production of E2 and progesterone with a gonadotropin-releasing hormone antagonist (GnRHant), and again after E2 administration; PMW, who are not using hormone therapy, will be tested before and after E2 admin. The central hypothesis is that declines in E2 impair microvascular vasodilatory function due to cellular changes in ET-B receptor expression on endothelial and VSM cells, and that E2 administration reverses these responses.

Eligibility Criteria:
Inclusion Criteria:

* Young women between 18-35 years of age with regular menstrual cycles
* Postmenopausal women between 50-65 years of age and no more than 10 years past menopause
* Non-smoking
* BMI \< 30 kg/m2
* Free from known disease (heart disease, cancer, diabetes)

Exclusion Criteria:

* Current use of hormone therapy or within the past year
* Women using Depo-provera or an intra-uterine device (IUD)
* Pregnant, are planning on becoming pregnant, or are breast- feeding.
* History of stable or unstable angina
* Diabetes
* Neurological disease
* Lung disease
* Kidney or liver disease
* Cancer
* Hysterectomy
* Peripheral vascular disease
* History of blood clots
* Heart disease
* Fibroids
* High blood pressure
* Stroke