Sex differences in endothelin-1-mediated vasoconstrictor tone in middle-aged and older adults

Endothelin-1 signaling in the kidney: recent advances and remaining gaps

The involvement of endothelin-1 (ET-1) in the maintenance of kidney function as well as its role in renal pathophysiology has been appreciated for decades; however, there still exist important gaps in knowledge in our understanding of the mechanistic pathways activated by this system in the kidney. The purpose of this article is to review recent advances in the field, as well as to underscore areas that need more investigation, with an emphasis on the interplay of ET-1 with inflammation, sex differences, circadian rhythms of renal function, the most recent clinical trials involving the ET-1 system, and the interaction between microRNAs and the ET-1 system.

Sex dimorphism in kidney health and disease: mechanistic insights and clinical implication

Sex is a key variable in the regulation of human physiology and pathology. Many diseases disproportionately affect one sex: autoimmune diseases, such as systemic lupus erythematosus, are more common in women but more severe in men, whereas the incidence of other disorders such as gouty arthritis and malignant cancers is higher in men. Besides the pathophysiology, sex may also influence the efficacy of therapeutics; participants in clinical trials are still predominately men, and the side effects of drugs are more common in women than in men. Sex dimorphism is a prominent feature of kidney physiology and function, and consequently affects the predisposition to many adult kidney diseases. These differences subsequently influence the response to immune stimuli, hormones, and therapies. It is highly likely that these responses differ between the sexes. Therefore, it becomes imperative to consider sex differences in translational science from basic science to preclinical research to clinical research and trials. Under-representation of one sex in preclinical animal studies or clinical trials remains an issue and key reported outcomes of such studies ought to be presented separately. Without this, it remains difficult to tailor the management of kidney disease appropriately and effectively. In this review, we provide mechanistic insights into sex differences in rodents and humans, both in kidney health and disease, highlight the importance of considering sex differences in the design of any preclinical animal or clinical study, and propose guidance on how to optimal design and conduct preclinical animal studies in future research.

G protein-coupled estrogen receptor activation attenuates cisplatin-induced CKD in C57BL/6 mice: An insight into sex-related differences

Gender contributes to differences in incidence and progression of chronic kidney disease (CKD) post-cisplatin therapy. This study aims at investigating the potential effect of G1 compound, a GPER agonist, on attenuating cisplatin-induced CKD. To induce CKD in male, intact female, and ovariectomized (OVX) mice, CKD was induced by injecting two cycles of 2.5 mg/kg cisplatin with a 16-day recovery period between cycles). G1 (50 or 100 μg/kg was administered daily for 6 weeks. Severity of renal damage was more pronounced in males than females. Interestingly, OVX resulted in renal damage that is non-significant compared to males and significantly higher than females. G1 improved renal function and blood flow as evidenced by reduction of serum creatinine and elevation of creatinine clearance, NO production, and reduction of ET1. This renoprotective effect could be attributed to its immunomodulatory effect regulated by TGF-β that shifted the balance to favor anti-inflammatory cytokine production (increased IL-10) rather than pro-inflammatory cytokines (decreased Th17 expression). Reduction of TGF-β activation also inhibited epithelial-to-mesenchymal transition that eventually ameliorated CKD development. Antioxidant potential of G1 has been demonstrated by upregulation of Nrf2 and subsequent antioxidant enzymes. These data suggest that G1 could be a promising therapeutic tool to attenuate CP-induced CKD.

Comprehensive analysis of the endothelin system in the kidneys of mice, rats, and humans

The intrarenal endothelin (ET) system is an established moderator of kidney physiology and mechanistic contributor to the pathophysiology and progression of chronic kidney disease in humans and rodents. The aim of the present study was to characterize ET system by combining single cell RNA sequencing (scRNA-seq) data with immunolocalization in human and rodent kidneys of both sexes. Using publicly available scRNA-seq data, we assessed sex and kidney disease status (human), age and sex (rats), and diurnal expression (mice) on the kidney ET system expression. In normal human biopsies of both sexes and in rodent kidney samples, the endothelin-converting enzyme-1 (ECE1) and ET-1 were prominent in the glomeruli and endothelium. These data agreed with the scRNA-seq data from these three species, with ECE1/Ece1 mRNA enriched in the endothelium. However, the EDN1/Edn1 gene (encodes ET-1) was rarely detected, even though it was immunolocalized within the kidneys, and plasma and urinary ET-1 excretion are easily measured. Within each species, there were some sex-specific differences. For example, in kidney biopsies from living donors, men had a greater glomerular endothelial cell endothelin receptor B (Ednrb) compared with women. In mice, females had greater kidney endothelial cell Ednrb than male mice. As commercially available antibodies did not work in all species, and RNA expression did not always correlate with protein levels, multiple approaches should be considered to maintain required rigor and reproducibility of the pre- and clinical studies evaluating the intrarenal ET system.

Sex differences in blood pressure regulation and hypertension: renal, hemodynamic, and hormonal mechanisms

The teleology of sex differences has been argued since at least as early as Aristotle's controversial Generation of Animals more than 300 years BC, which reflects the sex bias of the time to contemporary readers. Although the question "why are the sexes different" remains a topic of debate in the present day in metaphysics, the recent emphasis on sex comparison in research studies has led to the question "how are the sexes different" being addressed in health science through numerous observational studies in both health and disease susceptibility, including blood pressure regulation and hypertension. These efforts have resulted in better understanding of differences in males and females at the molecular level that partially explain their differences in vascular function and renal sodium handling and hence blood pressure and the consequential cardiovascular and kidney disease risks in hypertension. This review focuses on clinical studies comparing differences between men and women in blood pressure over the life span and response to dietary sodium and highlights experimental models investigating sexual dimorphism in the renin-angiotensin-aldosterone, vascular, sympathetic nervous, and immune systems, endothelin, the major renal sodium transporters/exchangers/channels, and the impact of sex hormones on these systems in blood pressure homeostasis. Understanding the mechanisms governing sex differences in blood pressure regulation could guide novel therapeutic approaches in a sex-specific manner to lower cardiovascular risks in hypertension and advance personalized medicine.

Antecubital venous endothelial ETB receptor protein expression is preserved with aging in men

Changes in endothelial function precede the development of cardiovascular disease (CVD). We have previously shown that age-related declines in endothelial function in women are due in part to a reduction in endothelial cell endothelin-B receptor (ETBR) protein expression. However, it is not known if ETBR protein expression changes with aging in men. The purpose of this study was to test the hypothesis that ETBR protein expression is attenuated in older men (OM) compared with younger men (YM). Primary endothelial cells were harvested from the antecubital vein of 14 OM (60 ± 6 yr; 26 ± 3 kg/m2) and 17 YM (24 ± 5 yr; 24 ± 2 kg/m2). Cells were stained with 4',6-diamidino-2-phenylindole, vascular endothelial cadherin, and ETBR. Images were quantified using immunocytochemistry. Endothelial function was assessed using brachial artery flow-mediated dilation (FMD). Systolic BP was similar (OM, 123 ± 11 vs. YM, 122 ± 10 mmHg) whereas diastolic BP was higher in OM (OM, 77 ± 7 vs. YM, 70 ± 6 mmHg; P < 0.01). Total testosterone was lower in OM (OM, 6.28 ± 4.21 vs. YM, 9.10 ± 2.68 ng/mL; P = 0.03). As expected, FMD was lower in OM (OM, 3.85 ± 1.51 vs. YM, 6.40 ± 2.68%; P < 0.01). However, ETBR protein expression was similar between OM and YM (OM, 0.39 ± 0.17 vs. YM, 0.42 ± 0.17 AU; P = 0.66). These data suggest that ETBR protein expression is not altered with age in men. These findings contrast with our previous data in women and further support sex differences in the endothelin system.NEW & NOTEWORTHY Our laboratory has previously shown that age-related declines in endothelial function are associated with a reduction in endothelial cell ETBR protein expression in women. However, it is unclear if endothelial cell ETBR protein expression is reduced with aging in men. This study demonstrates that endothelial cell ETBR protein expression is preserved with aging in men, and provides additional evidence for sex differences in the endothelin system.

Aerobic exercise training reduces ET-1-mediated vasoconstriction and improves endothelium-dependent vasodilation in postmenopausal women

Endothelin-1 (ET-1) contributes to vascular dysfunction in postmenopausal women (PMW). Although aerobic exercise is beneficial in reducing ET-1-mediated vasoconstrictor tone in men, it is unknown whether this favorable vascular effect occurs in women. We tested the hypothesis that aerobic exercise training reduces ET-1-mediated vasoconstriction in PMW. We further hypothesized that reductions in ET-1 vasoconstrictor tone underly exercise-induced improvements in endothelium-dependent vasodilatation in PMW. Forearm blood flow (FBF) responses to intra-arterial infusion of selective ETA receptor blockade (BQ-123, 100 nmol/min for 60 min) and acetylcholine (4.0, 8.0, and 16.0 μg/100 mL tissue/min) in the absence and presence of ETA receptor blockade were determined before and after a 12-wk aerobic exercise training intervention in 18 healthy, sedentary PMW (58 ± 4 yr). Women exercised an average of 4.9 ± 0.7 day/wk for 51 ± 7 min/day at 71 ± 3% of maximal heart rate. Before exercise, BQ-123 significantly increased FBF (∼25%) in sedentary PMW; however, this effect was abolished following the exercise intervention. FBF responses to acetylcholine were also significantly higher after exercise training (from 4.2 ± 1.2 to 14.0 ± 3.8 mL/100 mL tissue/min) versus before (from 4.1 ± 1.0 to 11.4 ± 3.3 mL/100 mL tissue/min; ∼25% increase; P < 0.05). Before exercise training, coinfusion of BQ-123 with acetylcholine enhanced (∼25%; P < 0.05) the vasodilator response (from 4.4 ± 1.1 to 13.9 ± 4.2 mL/100 mL tissue/min) compared with acetylcholine alone; after exercise training, the presence of BQ-123 did not significantly affect the vasodilator response to acetylcholine. Aerobic exercise training reduces ET-1-mediated vasoconstriction in PMW. Furthermore, decreased ET-1-mediated vasoconstriction is an important mechanism underlying aerobic exercise-induced improvement in endothelium-dependent vasodilation in PMW.NEW & NOTEWORTHY Endothelin-1 (ET-1) contributes to declines in endothelial function in postmenopausal women. To our knowledge, we show for the first time that aerobic exercise reduces ET-1-mediated vasoconstriction in previously sedentary postmenopausal women. Moreover, aerobic exercise improved endothelial-dependent dilation due in part to the reductions in ET-1-mediated vasoconstriction.

ET-1 as a Sex-Specific Mechanism Impacting Age-Related Changes in Vascular Function

Aging is a primary risk factor for cardiovascular disease (CVD), which is the leading cause of death in developed countries. Globally, the population of adults over the age of 60 is expected to double by the year 2050. CVD prevalence and mortality rates differ between men and women as they age in part due to sex-specific mechanisms impacting the biological processes of aging. Measures of vascular function offer key insights into cardiovascular health. Changes in vascular function precede changes in CVD prevalence rates in men and women and with aging. A key mechanism underlying these changes in vascular function is the endothelin (ET) system. Studies have demonstrated sex and sex hormone effects on endothelin-1 (ET-1), and its receptors ETA and ETB. However, with aging there is a dysregulation of this system resulting in an imbalance between vasodilation and vasoconstriction. Thus, ET-1 may play a role in the sex differences observed with vascular aging. While most research has been conducted in pre-clinical animal models, we describe more recent translational data in humans showing that the ET system is an important regulator of vascular dysfunction with aging and acts through sex-specific ET receptor mechanisms. In this review, we present translational evidence (cell, tissue, animal, and human) that the ET system is a key mechanism regulating sex-specific changes in vascular function with aging, along with therapeutic interventions to reduce ET-mediated vascular dysfunction associated with aging. More knowledge on the factors responsible for the sex differences with vascular aging allow for optimized therapeutic strategies to attenuate CVD risk in the expanding aging population.

Activation of G protein-coupled estrogen receptor fine-tunes age-related decreased vascular activities in the aortae of female and male rats

BACKGROUND

Hormone replacement therapy was found to be effective in cardiovascular protection only in younger women, not in older women. In this study, we tested whether G protein-coupled estrogen receptor 1 (GPER) activation improves vascular activities in response to ET-1 and ACh in aging rats.

METHODS

Isometric tension study was applied on aortic rings isolated from young adult (5-7 months) and reproductive senescent middle-aged (10-12 months) female Sprague Dawley rats and age matched males.

RESULTS

The aortic contractile response to ET-1 and the relaxation response to ACh were reduced in the female middle-aged rats compared to the female young adult rats. The presence of G-1, the GPER agonist, normalized the reduced vascular activities. Cyclooxygenase inhibitor, meclofenamate, blocked the increased constriction effect of G-1, but further enhanced relaxation effect of G-1. There was no significant difference in aortic reactivity to either ET-1 or ACh between the male middle-aged and young adult rats. The contractile response to ET-1 was not different within the same age of the two sex groups, but there was a remarkable difference in relaxation response to ACh between young adult females and males with better response in females. GPER activation greatly improved the aortic relaxation of both young adult and middle-aged females, but not the males.

CONCLUSIONS

Endothelial dysfunction occurs earlier in males, but in females, dysfunction delays until middle age. GPER activation improves the vascular activities in females, but not males. It is promising to employ GPER as a potential drug target in cardiovascular disease in women.

Sex Differences in Peripheral Artery Disease

Peripheral artery disease (PAD) is a prevalent condition that confers substantial morbidity and mortality and remains underdiagnosed as well as undertreated in the overall population. Although PAD prevalence is similar or higher in women compared with men, associations of traditional and nontraditional risk factors with PAD and clinical manifestations of PAD differ by sex and may contribute to delayed or lack of diagnosis in women. Such sex-based differences in the manifestation of PAD may arise from sexual dimorphism in the vascular substrate in health as well as sex variation in the responses to vascular stressors. Despite the availability of proven therapies for improving symptoms and reducing risk of ischemic cardiovascular and limb events among patients with diagnosed PAD, important sex differences in treatment and outcomes have been observed. We provide an overview of current knowledge regarding sex differences in the epidemiology, pathophysiology, clinical presentation, and management of PAD.

Sex and gender in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare disease characterised by pulmonary vascular remodelling and elevated pulmonary pressure, which eventually leads to right heart failure and death. Registries worldwide have noted a female predominance of the disease, spurring particular interest in hormonal involvement in the disease pathobiology. Several experimental models have shown both protective and deleterious effects of oestrogens, suggesting that complex mechanisms participate in PAH pathogenesis. In fact, oestrogen metabolites as well as receptors and enzymes implicated in oestrogen signalling pathways and associated conditions such as BMPR2 mutation contribute to PAH penetrance more specifically in women. Conversely, females have better right ventricular function, translating to a better prognosis. Along with right ventricular adaptation, women tend to respond to PAH treatment differently from men. As some young women suffer from PAH, contraception is of particular importance, considering that pregnancy in patients with PAH is strongly discouraged due to high risk of death. When contraception measures fail, pregnant women need a multidisciplinary team-based approach. This article aims to review epidemiology, mechanisms underlying the higher female predominance, but better prognosis and the intricacies in management of women affected by PAH.

Circulating endothelin-1 levels are positively associated with chronic kidney disease in women but not in men: a longitudinal study in the Vara-Skövde cohort

Background

The vasoconstricting peptide endothelin-1 (ET-1) is associated with endothelial dysfunction. The aim of this paper was to investigate whether circulating ET-1 levels predicts chronic kidney disease (CKD) in a prospective population study.

Methods

In 2002–2005, 2816 participants (30–74 years) were randomly selected from two municipalities in South-Western Sweden and followed up in a representative sample of 1327 individuals after 10 years. Endothelin-1 levels were assessed at baseline. Outcome was defined as CKD stage 3 or above based on eGFR < 60 mL/min/1.73m². Those 1314 participants with successful analysis of ET-1 were further analyzed using binary logistic regression.

Results

At follow-up, 51 (8%) men and 47 (7,8%) women had CKD stage 3 and above. Based on levels of ET-1 the population was divided into quintiles showing that women in the highest quintile (n = 132) had a significantly increased risk of developing CKD during the follow up period (OR = 2.54, 95% CI:1.19–5.45, p = 0.02) compared with the other quintiles (1–4). The association was borderline significant after adjusted for age, current smoking, alcohol consumption, hypertension, diabetes, BMI, high- sensitive CRP and LDL-cholesterol (OR = 2.25, 95% CI:0.97–5.24, p = 0.06). No significant differences were observed between quintiles of ET-1 and development of CKD in men (NS).

Conclusions

High levels of ET-1 are associated with development of CKD in women.

Endothelin-1 axes in the framework of predictive, preventive and personalised (3P) medicine

Endothelin-1 (ET-1) is involved in the regulation of a myriad of processes highly relevant for physical and mental well-being; female and male health; in the modulation of senses, pain, stress reactions and drug sensitivity as well as healing processes, amongst others. Shifted ET-1 homeostasis may influence and predict the development and progression of suboptimal health conditions, metabolic impairments with cascading complications, ageing and related pathologies, cardiovascular diseases, neurodegenerative pathologies, aggressive malignancies, modulating, therefore, individual outcomes of both non-communicable and infectious diseases such as COVID-19. This article provides an in-depth analysis of the involvement of ET-1 and related regulatory pathways in physiological and pathophysiological processes and estimates its capacity as a predictor of ageing and related pathologies,a sensor of lifestyle quality and progression of suboptimal health conditions to diseases for their targeted preventionand as a potent target for cost-effective treatments tailored to the person.

ETB receptor-mediated vasodilation is regulated by estradiol in young women

The endothelin-B (ET_B) receptor is a key regulator of vascular endothelial function in women. We have previously shown that the ET_B receptor mediates vasodilation in young women, an effect that is lost after menopause. However, the direct impact of changes in estradiol (E₂) on ET_B receptor function in women remains unclear. Therefore, the purpose of this study was to test the hypothesis that E₂ exposure modulates ET_B receptor-mediated dilation in young women. Fifteen young women (24 ± 4 yr, 24 ± 3 kg/m²) completed the study. Endogenous sex hormone production was suppressed with daily administration of a gonadotropin-releasing hormone antagonist (GnRHant; Ganirelix) for 10 days; E₂ (0.1 mg/day, Vivelle-Dot patch) was added back on days 4-10. We measured vasodilation in the cutaneous microcirculation (microvascular endothelial function) via local heating (42°C) on day 4 (GnRHant) and day 10 (GnRHant + E₂) using laser Doppler flowmetry coupled with intradermal microdialysis during perfusions of lactated Ringer's (control) and ET_B receptor antagonist (BQ-788, 300 nM). During GnRHant, vasodilatory responses to local heating were enhanced with ET_B receptor blockade (control: 83 ± 9 vs. BQ-788: 90 ± 5%CVC_max, P = 0.004). E₂ administration improved vasodilation in the control site (GnRHant: 83 ± 9 vs. GnRHant + E₂: 89 ± 8%CVC_max, P = 0.036). Furthermore, cutaneous vasodilatory responses during ET_B receptor blockade were blunted after E₂ administration (control: 89 ± 8 vs. BQ-788: 84 ± 8%CVC_max, P = 0.047). These data demonstrate that ovarian hormones, specifically E₂, modulate ET_B receptor function and contribute to the regulation of microvascular endothelial function in young women.NEW & NOTEWORTHY The endothelin-B (ETB) receptor mediates vasodilation in young women, an effect lost following menopause. It is unclear whether these alterations are due to aging or changes in estradiol (E2). During endogenous hormone suppression (GnRH antagonist), blockade of ETB receptors enhanced cutaneous microvascular vasodilation. However, during E2 administration, blockade of ETB receptors attenuated vasodilation, indicating that the ETB receptor mediates dilation in the presence of E2. In young women, ETB receptors mediate vasodilation in the presence of E2, an effect that is lost when E2 is suppressed.

Experimental design of the Effects of Dehydroepiandrosterone in Pulmonary Hypertension (EDIPHY) trial

Pulmonary arterial hypertension (PAH) remains life-limiting despite numerous approved vasodilator therapies. Right ventricular (RV) function determines outcome in PAH but no treatments directly target RV adaptation. PAH is more common in women, yet women have better RV function and survival as compared to men with PAH. Lower levels of the adrenal steroid dehydroepiandrosterone (DHEA) and its sulfate ester are associated with more severe pulmonary vascular disease, worse RV function, and mortality independent of other sex hormones in men and women with PAH. DHEA has direct effects on nitric oxide (NO) and endothelin-1 (ET-1) synthesis and signaling, direct antihypertrophic effects on cardiomyocytes, and mitigates oxidative stress. Effects of Dehydroepiandrosterone in Pulmonary Hypertension (EDIPHY) is an on-going randomized double-blind placebo-controlled crossover trial of DHEA in men (n = 13) and pre- and post-menopausal women (n = 13) with Group 1 PAH funded by the National Heart, Lung and Blood Institute. We will determine whether orally administered DHEA 50 mg daily for 18 weeks affects RV longitudinal strain measured by cardiac magnetic resonance imaging, markers of RV remodeling and oxidative stress, NO and ET-1 signaling, sex hormone levels, other PAH intermediate end points, side effects, and safety. The crossover design will elucidate sex-based phenotypes in PAH and whether active treatment with DHEA impacts NO and ET-1 biosynthesis. EDIPHY is the first clinical trial of an endogenous sex hormone in PAH. Herein we present the study’s rationale and experimental design.

Newer insights into the pathobiological and pharmacological basis of the sex disparity in patients with pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) affects more women than men, although affected females tend to survive longer than affected males. This sex disparity in PAH is postulated to stem from the diverse roles of sex hormones in disease etiology. In animal models, estrogens appear to be implicated not only in pathologic remodeling of pulmonary arteries, but also in protection against right ventricular (RV) hypertrophy. In contrast, the male sex hormone testosterone is associated with reduced survival in male animals, where it is associated with increased RV mass, volume, and fibrosis. However, it also has a vasodilatory effect on pulmonary arteries. Furthermore, patients of both sexes show varying degrees of response to current therapies for PAH. As such, there are many gaps and contradictions regarding PAH development, progression, and therapeutic interventions in male versus female patients. Many of these questions remain unanswered, which may be due in part to lack of effective experimental models that can consistently reproduce PAH pulmonary microenvironments in their sex-specific forms. This review article summarizes the roles of estrogens and related sex hormones, immunological and genetical differences, and the benefits and limitations of existing experimental tools to fill in gaps in our understanding of the sex-based variation in PAH development and progression. Finally, we highlight the potential of a new tissue chip-based model mimicking PAH-afflicted male and female pulmonary arteries to study the sex-based differences in PAH and to develop personalized therapies based on patient sex and responsiveness to existing and new drugs.

Influence of sex on heightened vasoconstrictor mechanisms in the non-Hispanic black population

Cardiovascular disease (CVD) affects individuals of all races and ethnicities; however, its prevalence is highest in non-Hispanic black individuals (BL) relative to other populations. While previous research has provided valuable insight into elevated CVD risk in the BL population, this work has been almost exclusively conducted in men. This is alarming given that BL women suffer from CVD at an equivalent rate to BL men and each has a greater prevalence when compared to all other ethnicities, regardless of sex. The importance of investigating sex differences in mechanisms of cardiovascular function is highlighted by the National Institute of Health requiring sex to be considered as a biological variable in research studies to better our "understanding of key sex influences on health processes and outcomes." The mechanism(s) responsible for the elevated CVD risk in BL women remains unclear and is likely multifactorial. Limited studies in BL women suggest that, while impaired vasodilator capacity is involved, heightened vasoconstrictor tone and/or responsiveness may also contribute. Within this mini-review, we will discuss potential mechanisms of elevated rates of hypertension and other CVDs in BL individuals with a particular focus on young, otherwise healthy, college-aged women. To stimulate academic thought and future research, we will also discuss potential mechanisms for impaired vascular function in BL women, as well as possible divergent mechanisms between BL men and women based on either preliminary data or plausible speculation extending from findings in the existing literature. Last, we will conclude with potential future research directions aimed at better understanding the elevated risk for hypertension and CVD in BL women.

Diabetes-related sex differences in the brain endothelin system following ischemia in vivo and in human brain endothelial cells in vitro

The endothelin (ET) system has been implicated to contribute to the pathophysiology of cognitive impairment and stroke in experimental diabetes. Our goals were to test the hypotheses that (1) circulating and (or) periinfarct ET-1 levels are elevated after stroke in both sexes and this increase is greater in diabetes, (2) ET receptors are differentially regulated in the diabetic brain, (3) brain microvascular endothelial cells (BMVEC) of female and male origin express the ETA receptor subtype, and (4) diabetes- and stroke-mimicking conditions increase ET-1 levels in BMVECs of both sexes. Control and diabetic rats were randomized to sham or stroke surgery. BMVECs of male (hBEC5i) and female (hCMEC/D3) origin, cultured under normal and diabetes-mimicking conditions, were exposed to normoxia or hypoxia. Circulating ET-1 levels were higher in diabetic animals and this was more pronounced in the male cohort. Stroke did not further increase plasma ET-1. Tissue ET-1 levels were increased after stroke only in males, whereas periinfarct ET-1 increased in both control and diabetic females. Male BMVECs secreted more ET-1 than female cells and hypoxia increased ET-1 levels in both cell types. There was sexually dimorphic regulation of ET receptors in both tissue and cell culture samples. There are sex differences in the stroke- and diabetes-mediated changes in the brain ET system at the endothelial and tissue levels.

Altered endothelial ETB receptor expression in postmenopausal women

The endothelin system plays an important role in mediating vascular function. The endothelin-B receptor (ET_BR) on endothelial cells mediates vasodilation via nitric oxide production. The vasodilatory effect of the ET_BR is lost following menopause and may contribute to impaired vascular endothelial function in postmenopausal women (PMW). However, it is unclear if these functional changes are due to changes in ET_BR expression on the endothelium. Therefore, the purpose of this study was to test the hypothesis that endothelial cell ET_BR expression is lower in PMW compared with young women (YW). Primary endothelial cells were harvested from the antecubital vein of healthy PMW (n = 15, 60 ± 6 yr) and YW (n = 15, 22 ± 2 yr). Cells were identified as endothelial cells by staining for vascular endothelial cadherin, and nuclear integrity was assessed using 4',6-diamidino-2-phenylindole (DAPI). Within those cells, ET_BR was quantified using immunocytochemistry; fluorescence intensity was measured in 30 cells and averaged for each participant. Endothelial function was assessed using brachial artery flow-mediated dilation (FMD). Endothelial cell ET_BR expression was lower in PMW [0.46 ± 0.11 arbitrary units (AU)] compared with YW (0.58 ± 0.14 AU; P = 0.02). Furthermore, significant correlations between ET_BR expression and FMD (r = 0.47, P < 0.01), total cholesterol (r = -0.38, P = 0.04), and LDL cholesterol (r = -0.39, P = 0.03) were observed. These data demonstrate that endothelial cell ET_BR expression is attenuated in PMW. These novel findings provide additional insight into the mechanisms underlying vascular endothelial dysfunction in PMW.NEW & NOTEWORTHY Our study provides novel data demonstrating attenuated endothelial ET_BR expression in postmenopausal women. Furthermore, our data extend current knowledge by demonstrating a positive relation between ET_BR expression and brachial artery flow-mediated dilation. These findings provide additional mechanistic insight into vascular endothelial dysfunction in postmenopausal women.

Afferent arteriole responsiveness to endothelin receptor activation: does sex matter?

BACKGROUND

The pathogenesis of hypertension is distinct between men and women. Endothelin-1 (ET-1) is a potential contributor to sex differences in the pathophysiology of hypertension. ET-1 participates in blood pressure regulation through activation of endothelin A (ET_A) and endothelin B (ET_B) receptors including those in the vasculature. Previous studies demonstrated that sex and sex hormones evoke discrepancies in ET-1-mediated control of vascular tone in different vascular beds. However, little is known about sex- and sex hormone-related differences in ET-1-dependent renal microvascular reactivity. Accordingly, we hypothesized that loss of sex hormones impairs afferent arteriole reactivity to ET-1.

METHODS

Male and female Sprague Dawley rats were subjected to gonadectomy or sham surgery (n = 6/group). After 3 weeks, kidneys from those rats were prepared for assessment of renal microvascular responses to ET-1 (ET_A and ET_B agonist, 10^-12 to 10^-8 M) and sarafotoxin 6c (S6c, ET_B agonist, 10^-12 to 10^-8 M) using the blood-perfused juxtamedullary nephron preparation.

RESULTS

Control afferent arteriole diameters at 100 mmHg were similar between sham male and female rats averaging 14.6 ± 0.3 and 15.3 ± 0.3 μm, respectively. Gonadectomy had no significant effect on control arteriole diameter. In sham males, ET-1 produced significant concentration-dependent decreases in afferent arteriole diameter, with 10^-8 M ET-1 decreasing diameter by 84 ± 1%. ET-1 induced similar concentration-dependent vasoconstrictor responses in sham female rats, with 10^-8 M ET-1 decreasing the diameter by 82 ± 1%. The afferent arteriolar vasoconstrictor responses to ET-1 were unchanged by ovariectomy or orchiectomy. Selective ET_B receptor activation by S6c induced a concentration-dependent decline in afferent arteriole diameter, with 10^-8 M S6c decreasing diameter by 77 ± 3 and 76 ± 3% in sham male and female rats, respectively. Notably, ovariectomy augmented the vasoconstrictor response to S6c (10^-12 to 10^-9 M), whereas orchiectomy had no significant impact on the responsiveness to ET_B receptor activation.

CONCLUSION

These data demonstrate that sex does not significantly influence afferent arteriole reactivity to ET receptor activation. Gonadectomy potentiated the responsiveness of the afferent arteriole to ET_B-induced vasoconstriction in females, but not males, suggesting that female sex hormones influence ET_B-mediated vasoconstriction in the renal microcirculation.

Sex differences in endothelial function important to vascular health and overall cardiovascular disease risk across the lifespan

Diseases of the cardiovascular system are the leading cause of morbidity and mortality in men and women in developed countries, and cardiovascular disease (CVD) is becoming more prevalent in developing countries. The prevalence of atherosclerotic CVD in men is greater than in women until menopause, when the prevalence of CVD increases in women until it exceeds that of men. Endothelial function is a barometer of vascular health and a predictor of atherosclerosis that may provide insights into sex differences in CVD as well as how and why the CVD risk drastically changes with menopause. Studies of sex differences in endothelial function are conflicting, with some studies showing earlier decrements in endothelial function in men compared with women, whereas others show similar age-related declines between the sexes. Because the increase in CVD risk coincides with menopause, it is generally thought that female hormones, estrogens in particular, are cardioprotective. Moreover, it is often proposed that androgens are detrimental. In truth, the relationships are more complex. This review first addresses female and male sex hormones and their receptors and how these interact with the cardiovascular system, particularly the endothelium, in healthy young women and men. Second, we address sex differences in sex steroid receptor-independent mechanisms controlling endothelial function, focusing on vascular endothelin and the renin-angiotensin systems, in healthy young women and men. Finally, we discuss sex differences in age-associated endothelial dysfunction, focusing on the role of attenuated circulating sex hormones in these effects.

Ovarian hormones modulate endothelin-1 receptor responses in young women

OBJECTIVE

We recently demonstrated ETB_R mediate vasodilation in young but not postmenopausal women; it is unclear if this is related to age or a decline in ovarian hormones. The purpose of this study was to test the hypothesis that ETB_R responses are modulated by ovarian hormones.

METHODS

We measured cutaneous vasodilatory responses in 12 young women (22 ± 1 years, 23 ± 1 kg/m² ) during the ML (days 20-25) and EF (days 2-5) phases of the menstrual cycle. Cutaneous microdialysis perfusions of lactated Ringer (control), ETB_R antagonist (BQ-788, 300 nmol/L), and ETA_R antagonist (BQ-123, 500 nmol/L) were performed, followed by local heating to 42°C.

RESULTS

Serum estradiol (ML: 118 ± 16 vs EF: 44 ± 9 pg/mL, P < 0.05) and progesterone (ML: 8.3 ± 1.0 vs EF: 0.7 ± 0.2 ng/mL, P < 0.05) were higher during ML vs EF phase. ETB_R blockade decreased vasodilation during ML (control: 91 ± 2 vs BQ-788: 83 ± 2%CVCmax, P < 0.05) but not EF (control: 89 ± 2 vs BQ-788: 89 ± 1%CVCmax). ETA_R blockade also decreased vasodilation during ML (control: 91 ± 2 vs BQ-123: 87 ± 2%CVCmax, P < 0.05) but not EF (control: 89 ± 2 vs BQ-123: 92 ± 2%CVCmax).

CONCLUSIONS

These data suggest that fluctuations in ovarian hormones modulate ETB_R and ETA_R responses in young women.

GPCRs in context: sexual dimorphism in the cardiovascular system

Cardiovascular disease (CVD) remains the largest cause of mortality worldwide, and there is a clear gender gap in disease occurrence, with men being predisposed to earlier onset of CVD, including atherosclerosis and hypertension, relative to women. Oestrogen may be a driving factor for female-specific cardioprotection, though androgens and sex chromosomes are also likely to contribute to sexual dimorphism in the cardiovascular system (CVS). Many GPCR-mediated processes are involved in cardiovascular homeostasis, and some exhibit clear sex divergence. Here, we focus on the G protein-coupled oestrogen receptor, endothelin receptors ET_A and ET_B and the eicosanoid G protein-coupled receptors (GPCRs), discussing the evidence and potential mechanisms leading to gender dimorphic responses in the vasculature. The use of animal models and pharmacological tools has been essential to understanding the role of these receptors in the CVS and will be key to further delineating their sex-specific effects. Ultimately, this may illuminate wider sex differences in cardiovascular pathology and physiology.

LINKED ARTICLES

This article is part of a themed section on Molecular Pharmacology of GPCRs. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.21/issuetoc.

Pulmonary Arterial Hypertension and the Sex Hormone Paradox

PURPOSE OF REVIEW

Prevalence and outcome differences between women and men with pulmonary arterial hypertension (PAH) raise questions about the role of sex hormones in disease pathobiology. This review will summarize the current understanding of sex and sex hormone pathways and their influence on heart-lung function in health and in disease.

RECENT FINDINGS

Female sex has been shown to be a risk factor for the development of PAH, but women have improved survival compared to men with PAH. These paradoxical observations are likely driven in part by complex sex hormone signaling and processing pathways and their interaction with the pulmonary vasculature and the right ventricle. These relationships may vary depending on an individual's underlying sex, age, and/or genetic substrate. The study of the connections between sex, sex hormones, the pulmonary circulation, and the right ventricle may improve our understanding of disease epidemiology and outcomes and lead to new treatment strategies for PAH.

Sex differences in hemodynamic responses and long-term survival to optimal medical therapy in patients with pulmonary arterial hypertension

It is widely known that the incidence of pulmonary arterial hypertension (PAH) is higher in female, whereas prognosis is poorer in male patients. However, sex differences in hemodynamic response to and long-term prognosis with PAH-targeted treatment in the modern era remain to be fully elucidated. We examined the long-term prognosis of 129 consecutive PAH patients (34 males and 95 females) diagnosed in our hospital from April 1999 to October 2014, and assessed hemodynamic changes in response to PAH-targeted therapy. Female patients had better 5-year survival compared with male patients (74.0 vs. 53.4%, P = 0.003); however, higher age quartiles in females were associated with poor outcome. Follow-up examination after medical treatment showed significant decreases in mean pulmonary arterial pressure (mPAP), pulmonary vascular resistance (PVR), and pulmonary arterial capacitance (PAC) in both sexes (both P < 0.05), whereas only females had a significant improvement in right ventricular end-diastolic pressure (RVEDP), right atrial pressure (RAP), cardiac index, and mixed venous oxygen saturation (SvO₂) (all P < 0.05). Baseline age significantly correlated with the hemodynamic changes only in female patients; particularly, there were significant sex interactions in RVEDP and RAP (both P < 0.10). The multivariable analysis showed that SvO₂ at baseline and mPAP and SvO₂ at follow-up were significant prognostic factors in males, whereas the changes in mPAP, PVR, and PAC and use of endothelin-receptor antagonist in females. These results indicate that female PAH patients have better long-term prognosis than males, for which better improvements of right ventricular functions and hemodynamics may be involved.

Physiological role of endothelin-1 in flow-mediated vasodilatation in humans and impact of cardiovascular risk factors

OBJECTIVES

The current study addressed the hypothesis that the local decrease in endothelin-1 (ET-1) bioavailability during sustained flow increases contributes to endothelium-dependent, flow-mediated dilatation (FMD) of conduit arteries and is altered in presence of cardiovascular risk factors.

METHODS AND RESULTS

In nine young healthy individuals, the decrease in local ET-1 plasma levels and radial artery FMD in response to hand skin heating (from 34 to 44 °C) was not affected by endothelin type A (ETA) receptor blockade, achieved using the brachial infusion of BQ-123 (100 nmol/min per l of forearm), as compared with physiological saline (0.9% NaCl) infusion. In contrast, endothelin type B (ETB) receptor blockade with BQ-788 (10 nmol/min per l) suppressed the decrease in plasma ET-1 during heating and reduced FMD, without altering nitric oxide release. The coinfusion of BQ-123 did not affect the inhibitory effect of ETB receptor blockade on the decrease in ET-1 plasma levels during heating but prevented the reduction in FMD. Basal radial artery parameters, systemic hemodynamics, and endothelium-independent dilatation to glyceryl trinitrate were not modified by ETA and/or ETB blockade. In a general population of 40 participants without treatment or major cardiovascular diseases, including the nine healthy individuals, the reduction in endothelin-1 level during heating was correlated with FMD (r = -0.55, P < 0.001) and decreased with increased age (r = 0.49, P = 0.001), mean arterial blood pressure (r = 0.48, P = 0.002), and total cholesterol level (r = 0.37, P = 0.024).

CONCLUSION

The uptake of endothelin-1 by ETB receptors contributes to conduit artery FMD, preventing its vasoconstrictor action mediated by ETA receptors. The alteration of this mechanism by cardiovascular risk factors may contribute to endothelial dysfunction.

Effects of endothelin-related gene polymorphisms and aerobic exercise habit on age-related arterial stiffening: a 10-yr longitudinal study

Increased arterial stiffness has emerged as a strong predictor of future cardiovascular events and all-cause mortality. The aim of this study was to elucidate influences of endothelin (ET)-related genetic polymorphisms and regular physical activity on age-related arterial stiffening through a 10-yr longitudinal study. A decadal change in brachial-ankle pulse wave velocity (baPWV), an index of arterial stiffness, was evaluated retrospectively among 92 volunteers (63 ± 14 yr, 51 men). The targeted single-nucleotide polymorphisms were ET-A receptor SNP rs5333 (ET-A) and ET-B receptor SNP rs5351 (ET-B). Subjects with either ET-A TC or CC genotypes exhibited significantly greater increases in baPWV (+15.3 ± 11.7 and +16.6 ± 15.7%/dec, respectively) than ET-A TT genotype holders (+9.2 ± 9.0%/dec), whereas subjects with the ET-B GG genotype showed a significantly greater increase in baPWV (+17.7 ± 14.1%/dec) than other ET-B genotype holders (AA: +9.5 ± 10.0%/dec; AG: +11.2 ± 9.6%/dec). The combination of these ET-related genetic risks was associated with a 2.4 times greater decadal increase in baPWV compared with no genetic risk (+8.1 ± 8.4 vs. 19.5 ± 16.0%/dec). In contrast, individuals engaging in >15 METs·h/wk of aerobic exercise showed substantially smaller increases in baPWV (+5.0 ± 9.7%/dec) compared with their physically inactive peers (approximately +13%/dec). These differences remained significant after adjusting for confounding factors, including baseline baPWV and ET-related genotype risk. Our current longitudinal study found that ET-related gene polymorphisms contribute to diverse age-related changes in arterial stiffness, and that regular sufficient aerobic exercise attenuates the age-related arterial stiffening independently of ET-related gene polymorphisms. NEW & NOTEWORTHY This 10-yr longitudinal study suggests that endothelin-related gene polymorphisms contribute to divergent increases in arterial stiffness with advancing age, whereas regular sufficient aerobic exercise attenuates age-related arterial stiffening independently of ET-related gene polymorphisms. This notion partly supports prevailing evidence that regular aerobic exercise contributes to a lower incidence of cardiovascular disease.

Influence of sex on the number of circulating endothelial microparticles and microRNA expression in middle-aged adults

NEW FINDINGS

What is the central question of this study? Are there sex-related differences in the number of circulating endothelial microparticles (EMPs) and microparticle microRNA expression in middle-aged adult humans? What is the main finding and its importance? Although the numbers of circulating endothelial microparticles do not differ between middle-aged men and women, there are sex-related differences in the expression of miR-125a in activation-derived EMPs and miR-34a in apoptosis-derived EMPs. Differences in circulating endothelial microparticle microRNA content may provide new insight into the sex-related disparity in the risk and prevalence of vascular disease in middle-aged adults. The aims of this study were to determine: (i) whether circulating concentrations of endothelial microparticles (EMPs) differ in middle-aged men compared with women; and (ii) whether there are sex-related differences in microRNA expression in EMPs. Peripheral blood was collected from 30 sedentary adults: 15 men (56 ± 6 years old) and 15 women (56 ± 5 years old). Endothelial microparticles were defined by markers of activation (CD62e⁺ ) or apoptosis (CD31⁺ /CD42b^- ) by flow cytometry. Expression of microRNA (miR-34a, 92a, 125a and 126) in activation- and apoptosis-derived EMPs was measured by RT-PCR. Circulating activation- (33 ± 31 versus 39 ± 35 microparticles μl^-1 ) and apoptosis-derived EMPs (49 ± 54 versus 42 ± 43 microparticles μl^-1 ) were not significantly different between men and women. Expression of miR-125a (2.23 ± 2.01 versus 6.95 ± 3.99 a.u.) was lower (∼215%; P < 0.05) in activation-derived EMPs, whereas expression of miR-34a (1.17 ± 1.43 versus 0.38 ± 0.35 a.u.) was higher (∼210%; P < 0.05) in apoptosis-derived EMPs from men compared with women. Expression of microRNA in circulating EMPs may provide new insight into sex-related differences in cardiovascular disease.

ETB receptor contribution to vascular dysfunction in postmenopausal women

Endothelin-1 (ET-1) contributes to age-related endothelial dysfunction in men via the ET_A receptor. However, there are sex differences in the ET-1 system, and ET_B receptors are modulated by sex hormones. The purpose of this study was to test the hypothesis that ET_B receptors contribute to impaired vasodilatory function in postmenopausal women (PMW). We measured flow-mediated dilation (FMD) using ultrasound, and cutaneous nitric oxide-mediated vasodilation during local heating (42°C) via laser Doppler flowmetry in 18 young women (YW; 22 ± 1 yr) and 16 PMW (56 ± 1 yr). Cutaneous microdialysis perfusions of lactated Ringer (control), an ET_B receptor antagonist (BQ-788, 300 nM), and an ET_A receptor antagonist (BQ-123, 500 nM), were done through separate fibers, followed by perfusions of sodium nitroprusside (28 mM) and local heating to 43°C (max). Cutaneous vascular conductance (CVC) was calculated as cutaneous blood flow/mean arterial pressure and expressed as a percent of maximal dilation. FMD (YW: 7.5 ± 0.5 vs. PMW: 5.6 ± 0.6%) and cutaneous vasodilation (YW: 93 ± 2 vs. PMW: 83 ± 4%CVC_max) were lower in PMW (both P < 0.05). Blockade of ET_B receptors decreased cutaneous vasodilation in YW (87 ± 2%CVC_max; P < 0.05 vs. control) but increased vasodilation in PMW (93 ± 1%CVC_max; P < 0.05 vs. control). ET_A receptor blockade had minimal effect in YW (92 ± 1%CVC_max) but increased cutaneous vasodilation in PMW (91 ± 2%CVC_max; P < 0.05 vs. control). In conclusion, ET_B receptors mediate vasodilation in YW, but this effect is lost after menopause. Impaired vasodilatory function in PMW is due in part to a loss of ET_B-mediated dilation.

Gender-related differences in pulmonary arterial hypertension targeted drugs administration

During the last 15 years, a real "paradigm-shift" occurred, due to the development of PAH-targeted drugs, leading to crucial improvements in symptoms, exercise capacity, hemodynamics and outcome of PAH patients. In order to describe differences regarding epidemiology and therapy in PAH according to gender, we performed a review of the available literature in "PubMed" and "Web of Science" databases. In order to find relevant articles, we combined each of the following the keywords "pulmonary arterial hypertension", "gender", "sex", "men", "woman", "male", "female", "phosphodiesterase inhibitors", "endothelin receptor antagonists", "prostanoids". While there is a substantial agreement among epidemiological studies in reporting an increased prevalence of pulmonary arterial hypertension (PAH) among women, male PAH patients are affected by a higher impairment of the right ventricular function and consequently experience poorer outcomes. With regards to PAH-targeted drug administration, endothelin receptor antagonists (ERAs) and prostacyclin analogues (PC) show better treatment results in female PAH patients, while phosphodiesterase-5 inhibitors (PD5-I) seem to exert a more beneficial effect on male patients. However, to date no clear consensus could be formed by the available literature, which is constituted mainly by retrospective studies. Females with PAH are more prone to develop PAH, while males experience poorer outcomes. Females PAH might benefit more from ERAs and PC, while males seem to have more beneficial effects from PD5-I administration. However, more research is warranted in order to assess the most effective treatment for PAH patients according to gender.

Sex-Specific Association of Obstructive Sleep Apnea With Retinal Microvascular Signs: The Multi-Ethnic Study of Atherosclerosis

BACKGROUND

Obstructive sleep apnea (OSA) is a common condition affecting more men than women. The relationship of OSA with microvascular disease is unclear, complicated by possible sex difference. Assessment of the relationship of OSA with retinal microvascular signs in men and women may provide insights into such a relationship.

METHODS AND RESULTS

We examined the sex-specific cross-sectional association of OSA severity with retinal vascular calibers in 1808 participants, and with specific retinopathy signs in 1831 participants from a sample of 2060 participants aged 54 to 93 years who underwent successful polysomnography in the Multi-Ethnic Study of Atherosclerosis, 2010-2012. OSA severity was defined by the apnea-hypopnea index (events/h) as none (<5), mild (5-14.9), moderate (15-29.9), and severe (≥30). As compared to no OSA, moderate/severe OSA in men was associated with retinal arteriolar narrowing (odds ratio [OR] and 95% CI for the narrowest quartile: 1.65 [1.00-2.71]) and retinal venular widening (1.80 [1.07-3.04] for the widest quartile), but not in women (odds ratio: 1.10 [0.67-1.81] and 0.91 [0.58-1.43], respectively) after adjusting for age, race/ethnicity, body mass index, pack-years of cigarette smoking, alcohol intake, hypertension duration, diabetes mellitus duration, HbA1c levels, lipid profile, micro-/macroalbuminuria, estimated glomerular filtration rate, β-blockers use, antihypertensive therapy, and lipid-lowering therapy. In contrast, severe OSA was associated with retinal microaneurysms in women, but not in men (odds ratio: 3.22 [1.16-8.97] and 0.59 [0.27-1.30], respectively).

CONCLUSIONS

The associations of OSA severity with retinal microvascular signs may differ by sex. Whether these findings were related to sex differences in OSA exposure needs further investigation.

Sex and Gender Differences in Risk, Pathophysiology and Complications of Type 2 Diabetes Mellitus

The steep rise of type 2 diabetes mellitus (T2DM) and associated complications go along with mounting evidence of clinically important sex and gender differences. T2DM is more frequently diagnosed at lower age and body mass index in men; however, the most prominent risk factor, which is obesity, is more common in women. Generally, large sex-ratio differences across countries are observed. Diversities in biology, culture, lifestyle, environment, and socioeconomic status impact differences between males and females in predisposition, development, and clinical presentation. Genetic effects and epigenetic mechanisms, nutritional factors and sedentary lifestyle affect risk and complications differently in both sexes. Furthermore, sex hormones have a great impact on energy metabolism, body composition, vascular function, and inflammatory responses. Thus, endocrine imbalances relate to unfavorable cardiometabolic traits, observable in women with androgen excess or men with hypogonadism. Both biological and psychosocial factors are responsible for sex and gender differences in diabetes risk and outcome. Overall, psychosocial stress appears to have greater impact on women rather than on men. In addition, women have greater increases of cardiovascular risk, myocardial infarction, and stroke mortality than men, compared with nondiabetic subjects. However, when dialysis therapy is initiated, mortality is comparable in both males and females. Diabetes appears to attenuate the protective effect of the female sex in the development of cardiac diseases and nephropathy. Endocrine and behavioral factors are involved in gender inequalities and affect the outcome. More research regarding sex-dimorphic pathophysiological mechanisms of T2DM and its complications could contribute to more personalized diabetes care in the future and would thus promote more awareness in terms of sex- and gender-specific risk factors.

Role of the endothelin system in sexual dimorphism in cardiovascular and renal diseases

Epidemiological studies of blood pressure in men and women and in experimental animal models point to substantial sex differences in the occurrence of arterial hypertension as well as in the various manifestations of arterial hypertension, including myocardial infarction, stroke, retinopathy, chronic kidney failure, as well as hypertension-associated diseases (e.g. diabetes mellitus). Increasing evidence demonstrates that the endothelin (ET) system is a major player in the genesis of sex differences in cardiovascular and renal physiology and diseases. Sex differences in the ET system have been described in the vasculature, heart and kidney of humans and experimental animals. In the current review, we briefly describe the role of the ET system in the cardiovascular and renal systems. We also update information on sex differences at different levels of the ET system including synthesis, circulating and tissue levels, receptors, signaling pathways, ET actions, and responses to antagonists in different organs that contribute to blood pressure regulation. Knowledge of the mechanisms underlying sex differences in arterial hypertension can impact therapeutic strategies. Sex-targeted and/or sex-tailored approaches may improve treatment of cardiovascular and renal diseases.

Endothelin, sex, and pregnancy: unique considerations for blood pressure control in females

Endothelin-1 (ET-1) is a potent vasoconstrictor, and dysregulation of the endothelin (ET) system has been implicated in the development of hypertension. Sex differences in the ET system have been identified in ET receptor expression and activation, levels of ET-1, and downstream mediators of the ET system. More specifically, males have greater ET-1/ETA receptor activation, whereas females exhibit greater ETB receptor activation. These differences have been suggested to contribute to the sex differences observed in blood pressure control, with greater ETB receptor activation in females potentially acting as an important pathway contributing to the lower prevalence of hypertension in young females compared with age-matched males. This hypothesis is further supported by studies in pregnancy; the role of the ET system is enhanced during pregnancy, with dysregulation of the ET system resulting in preeclampsia. Further research is necessary to elucidate the relative roles of the ET system in blood pressure control in both sexes and to further explore the potential benefits of pharmacological ET blockade in women.

Ovarian hormones modulate endothelin A and B receptor expression

AIMS

The study aims to determine the modulatory roles of ovarian hormones, estrogen (E2) and progesterone (P), on the expression of endothelin A (ETA) and B (ETB) receptors in lung, liver and kidney tissues.

MAIN METHODS

Female Sprague-Dawley rats were subjected to bilateral ovariectomy and divided into four groups ovariectomized (OVX), OVX+E2, OVX+P, and OVX+E2+P. A separate group of rats underwent sham surgery and served as a control. Three weeks after OVX or sham surgery, tissues from lungs, liver, renal cortex, and inner medulla were collected, snap-frozen, and kept at -80°C for assessment of ETA and ETB receptor expression using real-time PCR.

KEY FINDINGS

E2-treated OVX animals had significantly lower expression of ETA receptors in the lungs, compared to OVX rats. Pulmonary ETB receptor mRNA was not measurably affected by any of the interventions. Hepatic ETA and ETB were significantly increased in OVX+E2+P rats, compared to sham rats. Renal inner medullary ETA and ETB receptor expressions were significantly elevated in OVX compared to sham, an effect that was prevented by co-supplementation of OVX with E2 and P. Additionally, both ETA and ETB receptor expression in the renal cortex were significantly attenuated by ovariectomy, and this reduction was not evident in OVX+E2 rats.

SIGNIFICANCE

These data suggest that ovarian hormones regulate ET receptor expression and may contribute to sex differences in cardiovascular and renal health.

Sex-specific effects of cardiovascular risk factors on endothelium-dependent dilation and endothelin activity in middle-aged women and men

Background

Healthy middle-aged postmenopausal women have higher endothelium-dependent dilation and lower vasoconstrictor activity of endothelin-1 than men. Whether these sex-specific differences extend to patients with cardiovascular risk factors has not been investigated. The current study aimed to determine whether, in patients with cardiovascular risk factors, sex-specific differences exist in endothelium-dependent dilation and endothelin-1 activity.

Methods

Forearm blood flow responses were measured by strain-gauge plethysmography during the intra-arterial infusion of acetylcholine, sodium nitroprusside, and the selective endothelin type A receptor blocker BQ-123 in 50 women and 64 men with cardiovascular risk factors.

Results

Acetylcholine and sodium nitroprusside induced a significant vasodilation in women and men alike (p < 0.01 for both). Also BQ-123 caused a significant vasodilation (p < 0.001) in both groups. The vasodilator response to acetylcholine was greater in women compared to men; however there were no differences in the response to sodium nitroprusside and BQ-123 (p = NS for both) between the two sex groups.

Conclusions

Middle-aged women with cardiovascular risk factors have significantly higher endothelium-dependent dilation than middle-aged men; however, vascular endothelin 1 activity is similar in the two groups. These findings suggest that the presence of cardiovascular risk factors is associated with sex-specific effects on endothelium-dependent dilation but not on endothelin 1 activity. Further study is needed to confirm our findings and to characterize the mechanisms underlying this sex-specific regulation of endothelial function.

Sex differences in response to tadalafil in pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is a progressive disease with high rates of morbidity and mortality. Current therapies improve symptoms, functional capacity, and, in select cases, survival. Little is known about patient factors that may predict the likelihood of patient-important, clinically relevant responses to therapy such as the 6-min walk distance (6MWD) and health-related quality of life (HRQoL).

METHODS

Data from the randomized clinical trial of tadalafil in PAH were used. Adjusted logistic regression models were created to examine the relationship between baseline characteristics and odds of achieving the minimal important difference (MID) in three parameters, defined as either a > 33-m increase in 6MWD, a > 5-unit increase in physical component summary score of the Medical Outcomes Study Short Form-36 (SF-36), or a > 5-unit increase in mental component summary score of the SF-36.

RESULTS

The study included 405 subjects. Younger age, male sex, lower baseline 6MWD, and disease etiology were associated with greater odds of achieving the MID for the 6-min walk test. Active treatment, younger age, and male sex were associated with greater odds of achieving the MID for the physical component summary score. Male sex was associated with greater odds of achieving the MID for the mental component summary score.

CONCLUSIONS

Age, sex, baseline functional capacity, and disease etiology are variably associated with the likelihood of achieving clinically relevant responses in patient-important outcomes to PAH-specific therapy such as 6MWD and HRQoL. The increased likelihood of response in men compared with women is a novel finding and may reflect pathophysiologic differences between sexes.

Sympathetic neural activity to the cardiovascular system: integrator of systemic physiology and interindividual characteristics

The sympathetic nervous system is a ubiquitous, integrating controller of myriad physiological functions. In the present article, we review the physiology of sympathetic neural control of cardiovascular function with a focus on integrative mechanisms in humans. Direct measurement of sympathetic neural activity (SNA) in humans can be accomplished using microneurography, most commonly performed in the peroneal (fibular) nerve. In humans, muscle SNA (MSNA) is composed of vasoconstrictor fibers; its best-recognized characteristic is its participation in transient, moment-to-moment control of arterial blood pressure via the arterial baroreflex. This property of MSNA contributes to its typical "bursting" pattern which is strongly linked to the cardiac cycle. Recent evidence suggests that sympathetic neural mechanisms and the baroreflex have important roles in the long term control of blood pressure as well. One of the striking characteristics of MSNA is its large interindividual variability. However, in young, normotensive humans, higher MSNA is not linked to higher blood pressure due to balancing influences of other cardiovascular variables. In men, an inverse relationship between MSNA and cardiac output is a major factor in this balance, whereas in women, beta-adrenergic vasodilation offsets the vasoconstrictor/pressor effects of higher MSNA. As people get older (and in people with hypertension) higher MSNA is more likely to be linked to higher blood pressure. Skin SNA (SSNA) can also be measured in humans, although interpretation of SSNA signals is complicated by multiple types of neurons involved (vasoconstrictor, vasodilator, sudomotor and pilomotor). In addition to blood pressure regulation, the sympathetic nervous system contributes to cardiovascular regulation during numerous other reflexes, including those involved in exercise, thermoregulation, chemoreflex regulation, and responses to mental stress.

Metabolic syndrome and endothelin-1 mediated vasoconstrictor tone in overweight/obese adults

OBJECTIVE

To determine whether endothelin (ET)-1 vasoconstrictor tone is greater in overweight and obese adults with the metabolic syndrome (MetS).

MATERIALS/METHODS

Forty overweight/obese middle-aged and older adults (age: 43-71 years; BMI: 25.1-36.9 kg/m²) were studied: 20 without MetS (13 M/7 F) and 20 with MetS (13 M/7 F). MetS was established according to NCEP ATP III guidelines. Forearm blood flow (FBF; plethysmography) responses to intra-arterial infusion of selective ET(A) receptor blockade (BQ-123; 100 nmol/min; for 60 min) and non-selective ET(A/B) receptor blockade (BQ-123 + BQ-788 [50 nmol/min for 60 min]) were determined.

RESULTS

In response to the selective ET(A) antagonism, there was a significant increase in forearm blood flow from baseline in both groups. However, the increase in forearm blood flow was significantly higher (P=0.03; ~45%) in the overweight/obese group with MetS than the group without MetS. In contrast, there were no significant group differences in FBF responses to non-selective ET(A/B) receptor blockade. Peak vasodilator responses to nonselective ET(A/B) blockade were ~50% higher than baseline blood flow in the overweight/obese groups without and with MetS.

CONCLUSION

MetS is associated with higher ET-1 vasoconstrictor tone in overweight/obese adults. The enhanced ET-1 vasoconstrictor activity with MetS is mediated by the ET(A) receptor subtype.

Effects of sex on coronary microvascular dysfunction and cardiac outcomes

BACKGROUND

Coronary microvascular dysfunction (CMD) is a prevalent and prognostically important finding in patients with symptoms suggestive of coronary artery disease. The relative extent to which CMD affects both sexes is largely unknown.

METHODS AND RESULTS

We investigated 405 men and 813 women who were referred for evaluation of suspected coronary artery disease with no previous history of coronary artery disease and no visual evidence of coronary artery disease on rest/stress positron emission tomography myocardial perfusion imaging. Coronary flow reserve was quantified, and coronary flow reserve <2.0 was used to define the presence of CMD. Major adverse cardiac events, including cardiac death, nonfatal myocardial infarction, late revascularization, and hospitalization for heart failure, were assessed in a blinded fashion over a median follow-up of 1.3 years (interquartile range, 0.5-2.3 years). CMD was highly prevalent both in men and women (51% and 54%, respectively; Fisher exact test =0.39; equivalence P=0.0002). Regardless of sex, coronary flow reserve was a powerful incremental predictor of major adverse cardiac events (hazard ratio, 0.80 [95% confidence interval, 0.75-086] per 10% increase in coronary flow reserve; P<0.0001) and resulted in favorable net reclassification improvement (0.280 [95% confidence interval, 0.049-0.512]), after adjustment for clinical risk and ventricular function. In a subgroup (n=404; 307 women/97 men) without evidence of coronary artery calcification on gated computed tomography imaging, CMD was common in both sexes, despite normal stress perfusion imaging and no coronary artery calcification (44% of men versus 48% of women; Fisher exact test P=0.56; equivalence P=0.041).

CONCLUSIONS

CMD is highly prevalent among at-risk individuals and is associated with adverse outcomes regardless of sex. The high prevalence of CMD in both sexes suggests that it may be a useful target for future therapeutic interventions.

End o' the line revisited: moving on from nitric oxide to CGRP

When endothelin-1(ET-1) was discovered it was hailed as the prototypical endothelium-derived contracting factor (EDCF). However, over the years little evidence emerged convincingly demonstrating that the peptide actually contributes to moment-to-moment changes in vascular tone elicited by endothelial cells. This has been attributed to the profound inhibitory effect of nitric oxide (NO) on both the production (by the endothelium) and the action (on vascular smooth muscle) of ET-1. Hence, the peptide is likely to initiate acute changes in vascular diameter only under extreme conditions of endothelial dysfunction when the NO bioavailability is considerably reduced if not absent. The present essay discusses whether or not this concept should be revised, in particular in view of the potent inhibitory effect exerted by calcitonin gene related peptide (CGRP) released from sensorimotor nerves on vasoconstrictor responses to ET-1.

Divergent effects of aging and sex on vasoconstriction to endothelin in coronary arterioles

OBJECTIVE

The risk for cardiovascular disease increases with advancing age; however, the chronological development of heart disease differs in males and females. The purpose of this study was to determine whether age-induced alterations in responses of coronary arterioles to the endogenous vasoconstrictor, endothelin, are sex-specific.

METHODS

Coronary arterioles were isolated from young and old male and female rats to assess vasoconstrictor responses to endothelin (ET), and ETa and ETb receptor inhibitors were used to assess receptor-specific signaling.

RESULTS

In intact arterioles from males, ET-induced vasoconstriction was reduced with age, whereas age increased vasoconstrictor responses to ET in intact arterioles from female rats. In intact arterioles from both sexes, blockade of either ETa or ETb eliminated age-related differences in responses to ET; however, denudation of arterioles from both sexes revealed age-related differences in ETa-mediated vasoconstriction. In arterioles from male rats, ETa receptor protein decreased, whereas ETb receptor protein increased with age. In coronary arterioles from females, neither ETa nor ETb receptor protein changed with age, suggesting age-related changes in ET signaling occur downstream of ET receptors.

CONCLUSIONS

Thus, aging-induced alterations in responsiveness of the coronary resistance vasculature to endothelin are sex-specific, possibly contributing to sexual dimorphism in the risk of cardiovascular disease with advancing age.

Hypertension: what's sex got to do with it?

Hypertension is a complex and multifaceted disease, and there are well established sex differences in many aspects of blood pressure (BP) control. The intent of this review is to highlight recent work examining sex differences in the molecular mechanisms of BP control in hypertension to assess whether the "one-size-fits-all" approach to BP control is appropriate with regard to sex.

Sex differences in the biomechanics and contractility of intramural coronary arteries in angiotensin II-induced hypertension

BACKGROUND

It is well known that sex differences occur in both the pathogenesis and therapy of hypertension. A deeper understanding of the underlying processes may be helpful when planning a personalized therapeutic strategy.

OBJECTIVE

In laboratory animal experiments, we studied the early mechanisms of vascular adaptation of the intramural small coronary arteries that play a fundamental role in the blood supply of the heart.

METHODS

In our study, an osmotic minipump was implanted into 10 male and 10 female Sprague-Dawley rats. The pump remained in situ for 4 weeks, infusing a dose of 100 ng/kg/min angiotensin II acetate. Four weeks later, the animals were killed, and the intramural coronary arteries from the left coronary branch, which are fundamentally responsible for the blood supply of the heart, were prepared. The pharmacologic reactivity and biomechanical properties of the prepared segments were studied in a tissue bath.

RESULTS

The relative heart mass and vessel wall thickness were greater in females than males (0.387 [0.009] g/100 g vs 0.306 [0.006] g/100 g body weight; 41.9 [4.09] μm vs 33.45 [3.37] μm on 50 mm Hg). The vessel tone and vasoconstriction in response to thromboxane agonists were, however, significantly more pronounced in males. The extent of relaxation in response to bradykinin was also greater in females. Although we observed inward eutrophic remodeling in females, an increase in wall stress and elastic modulus dominated in males.

CONCLUSION

The early steps of angiotensin II-dependent hypertension evoked very different adaptation mechanisms in males and females.

Sex and gender differences in cardiovascular drug therapy

This chapter outlines sex differences in pharmacokinetics and pharmacodynamics of the most frequently used drugs in cardiovascular diseases, e.g., coronary artery disease, hypertension, heart failure. Retrospective analysis of previously published drug trials revealed marked sex differences in efficacy and adverse effects in a number of cardiovascular drugs. This includes a higher mortality among women taking digoxin for heart failure, more torsade de pointes arrhythmia in QT prolonging drugs and more cough with ACE inhibitors. Trends towards a greater benefit for women and/or female animals have been observed in some studies for endothelin receptor antagonists, the calcium channel blocker amlodipine, the ACE-inhibitor ramipril and the aldosterone antagonist eplerenone. However, reproduction of these results in independent studies and solid statistical evidence is still lacking. Some drugs require a particularly careful dose adaptation in women: the beta-blocker metoprolol, the calcium channel blocker verapamil, loop-, and thiazide diuretics. In conclusion, sex differences in pharmacokinetics and pharmacodynamics have to be taken into account for cardiovascular drug therapy in women.

Agonist-dependent modulation of arterial endothelinA receptor function

BACKGROUND AND PURPOSE Endothelin-1 (ET-1) causes long-lasting vasoconstrictions. These can be prevented by ET(A) receptor antagonists but are only poorly reversed by these drugs. We tested the hypothesis that endothelin ET(A) receptors are susceptible to allosteric modulation by endogenous agonists and exogenous ligands. EXPERIMENTAL APPROACH Rat isolated mesenteric resistance arteries were pretreated with capsaicin and studied in wire myographs, in the presence of L-NAME and indomethacin to concentrate on arterial smooth muscle responses. KEY RESULTS Endothelins caused contractions with equal maximum but differing potency (ET-1 = ET-2 > ET-3). ET-1(1-15) neither mimicked nor antagonized these effects in the absence and presence of ET(16-21). 4(Ala) ET-1 (ET(B) agonist) and BQ788 (ET(B) antagonist) were without effects. BQ123 (peptide ET(A) antagonist) reduced the sensitivity and relaxed the contractile responses to endothelins. Both effects depended on the agonist (pK(B): ET-3 = ET-1 > ET-2; % relaxation: ET-3 = ET-2 > ET-1). Also, with PD156707 (non-peptide ET(A) antagonist) agonist-dependence and a discrepancy between preventive and inhibitory effects were observed. The latter was even more marked with bulky analogues of BQ123 and PD156707. CONCLUSIONS AND IMPLICATIONS These findings indicate allosteric modulation of arterial smooth muscle ET(A) receptor function by endogenous agonists and by exogenous endothelin receptor antagonists. This may have consequences for the diagnosis and pharmacotherapy of diseases involving endothelins.

Differences in arterial stiffness at rest and after acute exercise between young men and women

There is controversy as to whether there are sex differences in arterial stiffness. Acute physical stress can elicit vascular abnormalities not present at rest. Our objective was to assess sex differences in arterial stiffness at rest and in response to acute physical stress. Healthy young men (n=67) and women (n=55) underwent pulse wave analysis and carotid-femoral pulse wave velocity measurements at rest and 2, 5, 10 and 15 min following an exercise test to exhaustion. At rest, aortic systolic, diastolic, pulse and mean pressures were all significantly higher in men as was aortic pulse pressure at 10 and 15 min post exercise and aortic systolic pressure at 15 min. Carotid-femoral pulse wave velocity was significantly higher in men (6.0±0.7 m s(-1) vs. 5.6±0.6 m s(-1), P=0.03) at rest and at all time points post exercise. Heart rate-adjusted augmentation index was significantly lower (-10.7±10.2% vs. -4.0±10.9, P<0.0001) and subendocardial viability ratio was significantly higher (176.2±43.8% vs. 163.4±40.9, P=0.04) in men at rest. To our knowledge, this is the first study to assess sex differences in the arterial stiffness response to acute physical stress in young men and women. Although we were not able to elicit differences in vascular function after adjustment, which were not present at rest, we found that young men and women exhibit differences in arterial stiffness at rest and after acute physical stress.

Influence of age and sex on the pressor response following a spontaneous burst of muscle sympathetic nerve activity

The sympathetic nervous system is critical for the beat-to-beat regulation of arterial blood pressure (BP). Although studies have examined age- and sex-related effects on BP control, findings are inconsistent and limited data are available in postmenopausal women. In addition, the majority of studies have focused on time-averaged responses without consideration for potential beat-to-beat alterations. Thus we examined whether the ability of muscle sympathetic nerve activity (MSNA) to modulate BP on a beat-to-beat basis is affected by age or sex. BP and MSNA were measured during supine rest in 40 young (20 men) and 40 older (20 men) healthy subjects. Beat-to-beat fluctuations in mean arterial pressure (MAP) were characterized for 15 cardiac cycles after each MSNA burst using signal averaging. The rise in MAP following an MSNA burst was similar between young men and women (+2.64 ± 0.3 vs. +2.57 ± 0.3 mmHg, respectively). However, the magnitude of the increase in MAP after an MSNA burst was reduced in older compared with young subjects (P < 0.05). Moreover, the attenuation of the pressor response was greater in older women (+1.20 ± 0.1 mmHg) compared with older men (+1.72 ± 0.2 mmHg; P < 0.05). Interestingly, in all groups, MAP consistently decreased after cardiac cycles without MSNA bursts (nonbursts) with the magnitude of fall greatest in older men. In summary, healthy aging is associated with an attenuated beat-to-beat increase in BP after a spontaneous MSNA burst, and this attenuation is more pronounced in postmenopausal women. Furthermore, our nonburst findings highlight the importance of sympathetic vasoconstrictor activity to maintain beat-to-beat BP, particularly in older men.