Vascular Dysfunction in Hypertensive Postmenopausal Women

Study Overview
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Brief Summary
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The purpose of this study is to investigate the role of ET-1 in mediating vasoconstrictor tone in hypertensive postmenopausal women (PMW) alone and in combination with a commonly prescribed Angiotensin II (ANG II) antagonist. The long term goal is to understand the mechanisms contributing to hypertension (HTN) in PMW. This study is the first step in reaching our goal.

Detailed Description
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Cardiovascular disease (CVD) is the leading cause of death in women, and mortality from CVD is higher in PMW compared to age-matched men. PMW are at a greater risk for developing HTN, a major risk factor for CVD. They are also more likely to have uncontrolled or resistant HTN despite medication. ANG II is a common therapeutic target for the treatment HTN. ANG II blockade is highly effective in normalizing blood pressure (BP) in hypertensive male rats, but does not reduce BP to the same degree in hypertensive post menopausal female rats. Endothelin-1 (ET-1) receptor antagonists reduce BP in hypertensive postmenopausal female rats, but have no effect on males. Thus the mechanisms contributing to HTN in female rats and likely women, particularly after menopause, are complex, multifactorial and not completely understood. After menopause, the vasoconstrictor effects of both ANG II and ET-1 are amplified in animal models. As such, these two predominant pathways may contribute to the high incidence of HTN in PMW. ET-1 is a potent vasoconstrictor produced and released by endothelial cells that binds to two receptor subtypes, ET-A and ET-B. While both receptors are located on vascular smooth muscle (VSM) and mediate vasoconstriction, ET-B receptors are also located on the endothelium and mediate vasodilation via nitric oxide. Importantly, the production of ET-1 and expression of ET-A and B receptors can be modulated by hormones such as estradiol and ANG II. Estradiol attenuates ET-1 production, and reduces ET-1 mediated vasoconstriction via an ET-B receptor mechanism in vitro. Thus, decline in estradiol after menopause may enhance vasoconstrictor tone via ET-1 and lead to HTN. ET-1 also potentiates the vasoconstrictor effects of ANG II since the vasoconstrictor and hypertensive effects of ANG II are ameliorated by ET-1 receptor blockade. Additionally, ANG II stimulates the synthesis of ET-1 and upregulates ET-A and ET-B receptor expression on VSM. The ANG II receptor antagonist Losartan reduces ET-A and ET-B receptor expression and attenuates the constrictor effects of ET-1 in a diabetic rat model. Therefore, ET-1 is an important independent factor contributing to HTN in PMW, but therapeutic agents targeting both ANG II and ET-1 may have greater efficacy given their interactions. The investigators propose a comprehensive assessment of vascular function by measuring blood flow responses in the cutaneous circulation during perfusion of ET-1 receptor antagonists via microdialysis, combined with measures of intracellular protein and receptor expression of endothelial cells and skin punch biopsies collected from normotensive and hypertensive PMW. Investigators central hypothesis is that hypertensive PMW have greater ET-1 mediated vasoconstrictor tone due to increased ET-1 expression, down-regulation of ET-B receptors on endothelial cells and up-regulation of both ET-A and ET-B receptors on VSM leading to increased vasoconstriction and HTN. Investigators further hypothesize that ANG II exacerbates the increase in ET-1, and ET-A and ET-B receptor expression contributing to exaggerated constriction with HTN in PMW.

Official Title
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Losartan and ET-1 Mediated Constriction in Postmenopausal Women With High Blood Pressure

Conditions
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Cardiovascular Diseases, Hypertension

Intervention / Treatment
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* Other: Normotensive
* Drug: Hypertensives


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: - Women. > 1year post menopausal. Age range 50-70 years Resting ECG in normal limits Standard blood chemistry within normal limits Systolic blood pressure: <130mm Hg for normotensives; >130mm Hg for hypertensives. Diastolic blood pressure: < 80mm Hg for normotensives; > 80mm Hg for hypertensives. Exclusion Criteria: History of cardiovascular disease Blood clots or stroke Cancer Diabetes Kidney or Liver disease Obesity (BMI>35kg/m2) Pregnant/Breast feeding Current use of hormone therapy Current use of tobacco products High cholesterol Current use of anti-hypertensive meds

Ages Eligible for Study
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Minimum Age: 50 Years
Maximum Age: 70 Years

Sexes Eligible for Study
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Female

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Other
Allocation: Non-Randomized
Intervention Model: Parallel Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Other: Normotensive<br>Normotensive PMW will complete an experimental visit to assess vascular function. All women will wear an ambulatory BP monitor during the 24 hours preceding the experimental visit to confirm BP classification. Large blood vessel function will be assessed using two non-invasive techniques: 1. Flow Mediated Dilation (FMD) 2. Pulse Wave Analysis and Pulse Wave Velocity. ET-1 mediated vasoconstrictor tone is assessed by measuring the cutaneous blood flow during microdialysis perfusions of ET-A and ET-B receptor antagonist. ET-1 production, ET-A and ET-B receptor expression is assessed from antecubital vein endothelial cells and skin punch biopsy samples. | Other: Normotensive<br>* FMD is a measure of endothelial function by assessing the degree to which vessel dilates in response to increased flow. Pulse Wave Analysis and Pulse Wave Velocity assesses arterial stiffness and wave reflection in all women. Laser Doppler flowmetry is used in combination with cutaneous microdialysis as a minimally invasive technique to examine mechanisms of vascular function. ET-B and ET-A receptor antagonists will be perfused via intradermal microdialysis fibers while measuring cutaneous blood flow. ET-1 production and ET-B receptor expression in endothelial cells collected from an antecubital vein will also be assessed. Immunohistochemistry will be performed on skin punch biopsy samples to assess for protein expression of ET-A and ET-B receptors.<br>|
| Experimental: Hypertensives<br>Hypertensive women will be tested at baseline and then administered Losartan 50 mg once a day at night for 14 days. Vascular function is measured at baseline and again after 2 weeks of losartan. All women will wear an ambulatory BP monitor during the 24 hours preceding the experimental visits to confirm BP classification. Large blood vessel function will be assessed using two non-invasive techniques: 1. Flow Mediated Dilation (FMD) 2. Pulse Wave Analysis and Pulse Wave Velocity. ET-1 mediated vasoconstrictor tone is assessed by measuring the cutaneous blood flow during microdialysis perfusions of ET-A and ET-B receptor antagonist. ET-1 production, ET-A and ET-B receptor expression is assessed from antecubital vein endothelial cells and skin punch biopsy samples. | Drug: Hypertensives<br>* ANG II increases the synthesis of ET-1 and alters ET-A/B receptor expression, thus affecting ET-1 bioavailability. Losartan is an ANG II receptor antagonist which attenuates ET-1 production. Losartan 50 mg daily is administered for 14 days to hypertensive women. FMD is used to measure endothelial function. Pulse Wave Analysis and Pulse Wave Velocity assesses arterial stiffness and wave reflection. Laser Doppler flowmetry with cutaneous microdialysis is used to examine vascular function when ET-A and ET-B receptor antagonists is perfused via intradermal microdialysis fibers. ET-1 production and ET-B receptor expression in endothelial cells collected from an antecubital vein will be assessed. Skin punch biopsy samples will be used to assess for protein expression of ET-A and ET-B receptors.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| ET-1 Mediated Constriction | Cutaneous blood flow is measured via laser Doppler flowmetry during cutaneous microdialysis perfusions of ET-A and ET-B receptor antagonists as previously described by Wenner MM in 2017(see reference list). | Each participant was assessed at baseline and 2 weeks later. | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Endothelin Receptor A and B Expression | ET-A and ET-B receptors will be examined using immunocytochemistry from 3mm skin punch biopsy in women pre/post losartan administration. This Secondary aim was not complete due to difficulty with enrollment (no data collected in these groups). | Baseline and 2 weeks later | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Hypertension, Endothelin-1 receptor