Endogenous estrogen and acetylcholine-induced vasodilation in normotensive women

Acute exogenous oestradiol augments endothelial and smooth muscle vasodilatory responsiveness in premenopausal but not postmenopausal females

Menopause is associated with vascular dysfunction. During the menopausal transition, endogenous oestradiol concentrations diminish. Oestradiol is vasoprotective because it has direct and indirect effects on the vasculature. The present study aimed to determine the effect of acute exogenous oestradiol on endothelium-dependent, endothelium independent and β2-adrenergic receptor-induced vasodilatation in females. Forearm blood flow (venous occlusion plethysmography) was measured during brachial intraarterial infusions of ACh (endothelium-dependent agonist), sodium nitroprusside (endothelium independent agonist) and terbutaline (β2-adrenergic receptor agonist) with and without concurrent infusion of 17β-oestradiol. Nine young premenopausal (age: 26 ± 4 years) and nine postmenopausal (PM, age: 58 ± 4 years, 8 ± 1 years post-menopause) females completed the study. Concurrent oestradiol infusion augmented the vasodilatory response to ACh, sodium nitroprusside and terbutaline in young premenopausal (all P < 0.05) but not older postmenopausal (all P > 0.05), females. Local infusion of exogenous 17β-oestradiol augmented endothelial and smooth muscle microvascular vasodilatation in premenopausal but not postmenopausal, females. KEY POINTS: Menopause is associated with vascular dysfunction. Because oestradiol has vasoprotective effects, the menopause-associated drop in oestradiol concentrations is hypothesized to contribute to vascular dysfunction during the menopause transition. The present study shows that local infusion of exogenous oestradiol augmented microvascular vasodilatation in premenopausal but not postmenopausal females.

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.

Gender Differences in Cardiac Chronotropic Control: Implications for Heart Rate Variability Research

There is a continuing debate concerning “adjustments” to heart period variability [i.e., heart rate variability (HRV)] for the heart period [i.e., increases inter-beat-intervals (IBI)]. To date, such arguments have not seriously considered the impact a demographic variable, such as gender, can have on the association between HRV and the heart period. A prior meta-analysis showed women to have greater HRV compared to men despite having shorter IBI and higher heart rate (HR). Thus, it is plausible that men and women differ in the association between HRV and HR/IBI. Thus, the present study investigates the potential moderating effect of gender on the association between HRV and indices of cardiac chronotropy, including both HR and IBI. Data from 633 participants (339 women) were available for analysis. Cardiac measures were assessed during a 5-min baseline-resting period. HRV measures included the standard deviation of inter-beat-intervals, root mean square of successive differences, and autoregressive high frequency power. Moderation analyses showed gender significantly moderated the association between all HRV variables and both HR and IBI (each p < 0.05). However, results were not consistent when using recently recommended HRV variables “adjusted” for IBI. Overall, the current investigation provides data illustrating a differential association between HRV and the heart period based on gender. Substantial neurophysiological evidence support the current findings; women show greater sensitivity to acetylcholine compared to men. If women show greater sensitivity to acetylcholine, and acetylcholine increases HRV and the heart period, then the association between HRV and the heart period indeed should be stronger in women compared to men. Taken together, these data suggest that routine “adjustments” to HRV for the heart period are unjustified and problematic at best. As it relates to the application of future HRV research, it is imperative that researchers continue to consider the potential impact of gender.

Systemic NOS inhibition reduces contracting muscle oxygenation more in intact female than male rats

Females respond to baroreceptor stimulation with enhanced modulation of heart rate (HR) to regulate blood pressure and also express greater reliance on nitric oxide (NO) for vascular control compared to males. Sex differences in muscle oxygenation consequent to central hemodynamic challenge induced by systemic NO synthase (NOS) inhibition are unknown. We tested the hypotheses that systemic NOS inhibition would induce lower contracting skeletal muscle oxygenation in females compared to males. The spinotrapezius of Sprague-Dawley rats (females (♀) = 9, males (♂) = 9) was surgically exposed and contracted by electrical stimulation (180s, 1 Hz, ~6 V) under pentobarbital sodium anesthesia. Oxyphor G4 was injected into the muscle and phosphorescence quenching was used to measure the interstitial PO₂ (PO₂is, determined by O₂ delivery-to-utilization matching) under control (Krebs-Henseleit solution) and after intra-arterial infusion of nitro-l-arginine methyl ester (l-NAME; NOS blockade; 10 mg kg^-1). At rest, females showed a greater PO₂is increase (ΔPO₂is/ΔMAP) and HR (ΔHR/ΔMAP) reduction than males in response to the elevated MAP induced by systemic NOS inhibition (both p < 0.05). Following l-NAME, during the contracting steady-state, females exhibited lower PO₂is than males (♂: 17.1 ± 1.4 vs ♀: 10.8 ± 1.4 mmHg, p < 0.05). The rate pressure product was lower in females than males (♂: 482 ± 14 vs ♀: 392 ± 29, p < 0.05) and correlated with the steady-state PO₂is (r = 0.66, p < 0.05). These results support that females express greater reductions in HR than males in response to l-NAME-induced elevation of MAP via the baroreceptor reflex and provide new insights on how central hemodynamics affect skeletal muscle oxygenation in a sex-specific manner.

Endothelial Vascular Function as a Surrogate of Vascular Risk and Aging in Women

Cardiovascular disease is the leading cause of morbidity and mortality in women. We suggest the need to develop a paradigm that connects sex- and age-specific nontraditional risk factors that serve as a common mechanism ultimately leading to an increased risk of cardiovascular events. Vascular injury with abnormal repair leading to functional, rather than structural, abnormalities can be regarded as accelerated vascular aging. It emerges as a common feature that can trigger the early diagnosis and risk stratification for cardiovascular disease in women. We discuss sex-specific risk factors that can contribute to vascular injury with age, and these might not always be considered by cardiovascular physicians. It is important for the primary physician to be aware of these risk factors to enable more intensified management of this at-risk population. Novel technologies that allow the assessment of vascular function noninvasively can serve as key diagnostic and therapeutic tools with which we can identify such individuals and target therapy to manage this important patient population appropriately and effectively. We hope that this article will stimulate interest in this field and encourage further research in these important areas.

Aging women and their endothelium: probing the relative role of estrogen on vasodilator function

Despite significant decreases in cardiovascular disease (CVD) mortality in the past three decades, it still remains the leading cause of death in women. Following menopause and the accompanying loss of estrogen, women experience a unique, accelerated rise in CVD risk factors. Dysfunction of the endothelium represents an important antecedent to CVD development, with rapid declines in endothelial vasodilator function reportedly taking place across the menopause transition. Importantly, the decline in endothelial function is independent of chronological age and is associated with estrogen deficiency. Estrogen-mediated effects, including increasing nitric oxide bioavailability and attenuating oxidative stress and inflammation, contribute to preserving endothelial health. This review will discuss studies that have probed the role of estrogen on endothelial vasodilator function in women at discrete stages of the menopause transition and the effects of estradiol supplementation in postmenopausal women. Estrogen receptor signaling is also an important aspect of endothelial function in women, and studies suggest that expression is reduced with both acute and prolonged estrogen deficiency. Changes in regulatory mechanisms of estrogen receptor-α expression as well as sensitivity to estrogen may underlie the differential effects of estrogen therapy in early (≤5 yr past final menstrual period) and late postmenopausal women (>5 yr past final menstrual period). Lastly, this review presents potential therapeutic targets that include increasing l-arginine bioavailability and estrogen receptor activation to prevent endothelial dysfunction in postmenopausal women as a strategy for decreasing CVD mortality in this high-risk population.

Endothelial dysfunction and menopause: is exercise an effective countermeasure?

Cardiovascular disease is the leading cause of death in women. There is a dramatic rise in risk factors for cardiovascular disease during the menopausal transition that is independent of aging. Endothelial dysfunction is an early hallmark of developing cardiovascular disease and has been shown to increase across the stages of menopause. Exercise is considered one of the most effective lifestyle therapies to maintain and improve endothelial function. However, accumulating evidence suggests that exercise does not have the same benefit on endothelial function in menopausal women as it does in other populations, and factors associated with menopause likely influence the endothelial responsiveness to exercise. This review will detail the current available evidence on endothelial dysfunction, exercise, and menopause, including mechanisms that may mediate the accumulating endothelial dysfunction in women with menopause, the impact of exercise on endothelial function in women, and whether regular exercise is an effective therapeutic and prevention strategy to maintain endothelial function with menopause. We conclude that the effect of exercise on endothelial function differs according to menopausal stage and cardiovascular disease risk burden. Finally, we will address critical gaps in the literature with the goal of identifying future research directions to improve healthy aging in women.

Treatment with Standard and Low Dose of Conjugated Equine Estrogen Differentially Modulates Estrogen Receptor Expression and Response to Angiotensin II in Mesenteric Venular Bed of Surgically Postmenopausal Hypertensive Rats

Standard hormone therapy for menopausal women [conjugated equine estrogen (CEE) 0.625 mg] has been associated with increased risk of venous thrombosis. Regimens containing a lower CEE dose (0.30 mg) have been used clinically to decrease side effects of supraphysiologic doses of estrogen. In this study, we determined the effects of standard (SD) and low dose (LD) of CEE on venular function in ovariectomized (OVX) spontaneously hypertensive rats (SHR). Contractions by angiotensin-II (Ang-II 10 μM) in perfused mesenteric venular bed were markedly increased in OVX (21.5 ± 1.3 mmHg) compared with Sham (14.7 ± 1.1 mm Hg, P < 0.05). CEE-SD did not modify Ang-II responses in OVX, whereas CEE-LD restored Ang-II contraction to Sham levels. Endothelial nitric oxide synthase (eNOS) inhibition by L-NAME increased Ang-II contractions in Sham and CEE-LD and was without effect in venules of OVX SHR and CEE-SD. In OVX there was decreased NO generation in association with diminished eNOS phosphorylation and increased O2- generation in the venular wall. CEE-LD reverted the deleterious effects of ovariectomy. Although CEE-SD augmented eNOS phosphorylation in OVX, it was unable to increase NO levels, probably owing to its inability to reduce O2- Distinct effects by CEE-SD and CEE-LD parallel the differential modulation of Ang-II and estrogen receptors. Compared with Sham, CEE-LD increases Ang II receptor type 2, whereas CEE-SD modified ERβ expression in the venous bed. Interestingly, both CEE doses increased G protein-coupled estrogen receptor in OVX. Our data suggest that estrogen dose is an important factor for venous function. Although CEE-LD reversed deleterious effects of OVX, CEE-SD showed null effects despite its ability to increase eNOS activity.

Alzheimer's Disease, Acetylcholine and Oestrogen

Common types of dementia occurring in old age are associated with the loss of cholinergic activity from basal forebrain neurons projecting to the cerebral cortex. In Alzheimer's disease this loss correlates with cognitive decline, and in dementia with Lewy bodies with neuropsychiatric features such a hallucinations. New therapies aimed at restoring the levels of acetylcholine, such as the cholinesterase inhibitors tacrine or donepezil, provide some symptomatic benefit and may also be protective. Similar symptomatic and protective effects of oestrogen may operate through stimulation of the affected cholinergic neurons. These neurons have oestrogen receptors and, in animal models, oestrogen elevates cortical cholinergic activity. Cholinergic control of vasodilation is also affected by oestrogen. Declining oestrogen in postmenopausal women is thus likely to contribute to age-related cognitive decline and increased risk of Alzheimer's via cholinergic mechanisms. In addition to accumulating evidence of the protective effect of oestrogen in Alzheimer's, there is already a report that oestrogen replacement therapy enhances the response of female patients to cholinergic medication (eg, tacrine).

Estrogens and Coronary Artery Disease: New Clinical Perspectives

In premenopausal women, endogenous estrogens are associated with reduced prevalence of arterial hypertension, coronary artery disease, myocardial infarction, and stroke. Clinical trials conducted in the 1990s such as HERS, WHI, and WISDOM have shown that postmenopausal treatment with horse hormone mixtures (so-called conjugated equine estrogens) and synthetic progestins adversely affects female cardiovascular health. Our understanding of rapid (nongenomic) and chronic (genomic) estrogen signaling has since advanced considerably, including identification of a new G protein-coupled estrogen receptor (GPER), which like the "classical" receptors ERα and ERβ is highly abundant in the cardiovascular system. Here, we discuss the role of estrogen receptors in the pathogenesis of coronary artery disease and review natural and synthetic ligands of estrogen receptors as well as their effects in physiology, on cardiovascular risk factors, and atherosclerotic vascular disease. Data from preclinical and clinical studies using nonselective compounds activating GPER, which include selective estrogen receptor modulators such as tamoxifen or raloxifene, selective estrogen receptor downregulators such as Faslodex™ (fulvestrant/ICI 182,780), vitamin B3 (niacin), green tea catechins, and soy flavonoids such as genistein or resveratrol, strongly suggest that activation of GPER may afford therapeutic benefit for primary and secondary prevention in patients with or at risk for coronary artery disease. Evidence from preclinical studies suggest similar efficacy profiles for selective small molecule GPER agonists such as G-1 which are devoid of uterotrophic activity. Further clinical research in this area is warranted to provide opportunities for future cardiovascular drug development.

Interaction of central Angiotensin II and estrogen on systolic blood pressure in female DOCA-salt treated rats

Background:

There is a probable interaction of central angiotensin II (Ang II) and estrogen (Est) on blood pressure in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Therefore, in the present study, the interaction between Ang II and Est in ovariectomized (Ovx) and Sham rats that were treated with DOCA- salt was evaluated.

Materials and Methods:

The female rats were divided into 10 groups as follows: Sham, Ovx, Sham-DOCA, Ovx-DOCA, Sham-DOCA-estrogen (E), Ovx DOCA-E, Sham-DOCA-losartan (L), Ovx-DOCA-L, Sham–DOCA-L-E, and Ovx-DOCA-L-E. The Est groups received estradiol valerate (2 mg/kg; daily; subcutaneously (s.c)) for four weeks. Following that, several doses of Ang II (0.5, 5, 50, 500, 5000 ng/5 μl) were injected via the intracerebroventricular (i.c.v) route and the changes in systolic blood pressure (SBP) were evaluated. In the losartan groups, 200 μg losartan was injected (i.c.v) 15 minutes after the Ang II injection and the blood pressure was recorded. Treatment by DOCA was performed by removal of one kidney, injection of DOCA (45 mg/kg i.p), and adding of sodium chloride (NaCl) (1%) and potassium chloride (KCl) (0.1%) in the drinking water.

Results:

The SBP was increased by Ang II and this effect in DOCA-salt treated rat was higher than in the untreated groups. The effect of Ang II on SBP in groups that were treated with Est and L was lower than that in the DOCA-salt groups. Increase in SBP was strongly attenuated by Ang II in groups that were co-treated with both Est and L compared to the DOCA-treated rats. These results showed that Est significantly attenuated the effect of central Ang II on SBP in the DOCA-salt treated rats.

Conclusion:

We suggest that there are interactions between E and Ang II in the control of blood pressure in DOCA-salt treated rats.

Modification of blood pressure in postmenopausal women: role of hormone replacement therapy

The rate of hypertension increases after menopause. Whether estrogen and progesterone deficiency associated with menopause play a role in determining a worst blood pressure (BP) control is still controversial. Also, studies dealing with the administration of estrogens or hormone therapy (HT) have reported conflicting evidence. In general it seems that, despite some negative data on subgroups of later postmenopausal women obtained with oral estrogens, in particular conjugated equine estrogens (CEE), most of the data indicate neutral or beneficial effects of estrogen or HT administration on BP control of both normotensive and hypertensive women. Data obtained with ambulatory BP monitoring and with transdermal estrogens are more convincing and concordant in defining positive effect on BP control of both normotensive and hypertensive postmenopausal women. Overall progestin adjunct does not hamper the effect of estrogens. Among progestins, drospirenone, a spironolactone-derived molecule, appears to be the molecule with the best antihypertensive properties.

Combination of Echocardiography and Pulse Wave Velocity Provides Clues for the Differentiation between White Coat Hypertension and Hypertension in Postmenopausal Women

OBJECTIVE

To determine whether or not noninvasive assessment of the cardiovascular system can discriminate white coat hypertension and hypertension in postmenopausal women. The major reason is the high prevalence of white coat hypertension in these subjects and the uncertain associations of white coat hypertension with cardiovascular risk.

PATIENTS AND METHODS

Selected women were required to be naturally or surgically menopausal for at least 1 year but not more than 5 years past their menstrual period. White coat hypertension patients were defined as subjects who had office blood pressures >150/90 mm Hg but who had both systolic and diastolic ambulatory pressures <120/80 mm Hg. In total, 44 subjects with a mean age of 52 years were recruited from the outpatient clinic and examined. Office and home blood pressures were measured using the HEM 401C (Omron Life Science Co. Ltd., Tokyo, Japan), a semi-automatic device that operates on the cuff-oscillometric principle and generates a digital display of the systolic (SBP) and diastolic blood pressure as well as the pulse rate. The pulse wave velocity (PWV) was recorded, and the left ventricular (LV) diameter, septal wall thickness, and left posterior wall thickness were assessed by M-mode echocardiography after selecting the measurement section by B-mode echocardiography.

RESULTS

Twenty patients were diagnosed as having white coat hypertension based on the criteria in the trial. Pulse wave patterns were different between subjects with white coat hypertension and those with hypertension. PWV of subjects with white coat hypertension was 1.32 ± 0.33 m/s and that of patients with hypertension was 1.46 ± 0.37 m/s (p < 0.01). In addition to these findings, there was a significant association between the values of home SBP and PWV and the LV mass index. However, this association was not seen for office SBP. When the data of the LV mass index and PWV were combined, white coat hypertension could be easily differentiated from hypertension.

CONCLUSIONS

The combination of blood pressure self-monitoring, echocardiographic data, and PWV can be a powerful indicator for the treatment of hypertension in postmenopausal women.

The effect of endogenous estrogen on Doppler-estimated right ventricular systolic pressure during exercise

We evaluated the effect of endogenous estrogen levels on exercise-related changes in right ventricular systolic pressure (RVSP) of healthy, eumenorrheic, sedentary women. Volunteers were studied at two separates phases of the menstrual cycle (LO and HI estrogen phases), exercised on a semi-supine ergometer with escalating workload and monitored continuously by 12-lead ECG and automated blood pressure cuff. At each exercise stage, Doppler echocardiography measurements were obtained and analyzed to determine RVSP. Fourteen subjects (age 24 ± 5) were studied. Exercise duration was significantly higher on the HI estrogen day, but no significant differences in hemodynamic response to exercise were found between the two study days. There were also no significant differences with respect to heart rate (HR) acceleration during early exercise, as well as resting and peak RVSP, HR, blood pressure, and rate pressure product. Doppler-estimated RVSP demonstrated a linear relationship to HR at a ratio of 1 mm Hg (1 mm Hg = 133.3224 Pa) for every 5 bpm (beats per minute) increase in HR. There were no differences in the slope of this relationship between HI and LO estrogen phases of the menstrual cycle. Our findings did not demonstrate any effect of endogenous estrogen levels on the modulation of the pulmonary vascular response to exercise in healthy women.

Modern combined hormonal therapy in early postmenopause women

Aim.To study the effects of hormone replacement therapy (HRT) with a combination of estradiol and drospirenone on cardiometabolic risk levels and subclinical vascular pathology among women in early postmenopause.Material and methods.In total, 84 women in early postmenopause, who had given informed consent and underwent a standard examination, were divided into two groups: Group I (with gynaecologist-confirmed indications for HRT with Angeliq (1 mg 17 β-estradiol and 2 mg drospirenone)) and Group II (no HRT). All participants underwent the assessment of metabolic parameters, visceral obesity, intima-media thickness (IMT) of common carotid arteries (CCA), arterial stiffness, and microcirculation (MC) status at baseline and 12 months later.Results.HRT demonstrated beneficial effects on autonomic regulation, lipid metabolism, CCA IMT, and arterial stiffness. It was also associated with a reduction in visceral obesity, some antihypertensive effect, and an increase in the MC dilatation reserve in postmenopausal women.Conclusion.Low-dose combined hormone therapy with drospirenone and estradiol could be recommended to a specific clinical group of women in early postmenopause.

Exercise-induced vasodilation is associated with menopause stage in healthy middle-aged women

Leg exercise hemodynamics during single-leg knee extensions were compared among healthy groups of early perimenopausal (n = 15), late perimenopausal (n = 12), and early postmenopausal (n = 11) women. Femoral blood flow (FBF) and vascular conductance (FVC) at rest and during very light work rates (0 and 5 W) were similar among all three menopause stage groups. Vascular responses at 10 W (FBF) and 20 W (FBF and FVC) were significantly higher (P < 0.05) in early perimenopausal compared with late perimenopausal women. At 15 and 25 W, FBF and FVC were similar between late perimenopausal and early postmenopausal groups but higher (P < 0.05) in early perimenopausal women as compared with the other two menopausal groups. In the combined sample of all three menopause stage groups, follicle-stimulating hormone was significantly correlated with vascular conductance during submaximal (15 W) exercise (R = -0.56, P < 0.001), even after adjustment for age, fitness, LDL cholesterol, and abdominal fat (R = -0.46, P = 0.005). Collectively, these findings suggest that in middle-aged women, there is an association between menopause stage and leg vascular responsiveness during exercise.

Endothelial aging and gender

The endothelium plays a pivotal role in maintaining vascular homeostasis, mainly by the production of the relaxing factor nitric oxide, which protects the vessel wall from the development of atherosclerosis. Aging is a powerful cardiovascular risk factor, associated with endothelial dysfunction both in normotensive subjects and in hypertensive patients. Premenopausal normotensive women are protected against the deleterious effect of aging on endothelial function, and age-related impairment of endothelial function is attenuated in premenopausal hypertensive women. This protective effect on endothelium seems to be mediated by endogenous estrogen, which preserves nitric oxide availability by activating the l-arginine-NO pathway in normotensive women and by inhibiting reactive oxygen species generation. Whether endogenous androgen may modulate endothelial function and the mechanisms involved are still unsolved issues, since data concerning the effect of testosterone on endothelium are scanty and contradictory.

Effects of estrogen on cardiovascular injury in ovariectomized female DahlS.Z-Lepr(fa)/Lepr(fa) rats as a new animal model of metabolic syndrome

Although recent clinical trials have found an increased incidence of cardiovascular disease in women on estrogen replacement therapy, the underlying mechanism remains unclear. We have recently characterized DahlS.Z-Lepr(fa)/Lepr(fa) (DS/obese) rats, derived from a cross between Dahl salt-sensitive and Zucker rats, as a new animal model of metabolic syndrome. We have now examined the effects of estrogen replacement on cardiac pathophysiology in ovariectomized female DS/obese (Ovx-DS/obese) rats. Animals subjected to ovariectomy at 7 weeks of age were implanted subcutaneously with a 60-day release pellet containing 0.5 mg of 17β-estradiol (E(2)) or placebo at 8 weeks. Age-matched female homozygous lean littermates (DahlS.Z-Lepr(+)/Lepr(+) or DS/lean rats) of DS/obese rats served as controls. Animals were maintained on a normal diet and were subjected to echocardiography followed by various pathological analyses at 13 weeks of age. Ovx-DS/obese rats manifested hypertension at 7 weeks of age and thereafter and showed left ventricular (LV) fibrosis and diastolic dysfunction at 13 weeks. Treatment with E(2) attenuated hypertension in Ovx-DS/obese rats but had no effect on blood pressure in ovariectomized female DS/lean (Ovx-DS/lean) rats. E(2) treatment exacerbated LV fibrosis and diastolic dysfunction, as well as further increased cardiac oxidative stress and inflammation in Ovx-DS/obese rats, and it elicited similar effects in Ovx-DS/lean rats. E(2) reduced food intake, body weight, and visceral fat content in both Ovx-DS/obese and Ovx-DS/lean rats. E(2) treatment attenuated hypertension and obesity but exacerbated LV fibrosis and diastolic dysfunction in Ovx-DS/obese rats, with these latter effects being associated with increased cardiac oxidative stress and inflammation.

Aging and vascular endothelial function in humans

Advancing age is the major risk factor for the development of CVD (cardiovascular diseases). This is attributable, in part, to the development of vascular endothelial dysfunction, as indicated by reduced peripheral artery EDD (endothelium-dependent dilation) in response to chemical [typically ACh (acetylcholine)] or mechanical (intravascular shear) stimuli. Reduced bioavailability of the endothelium-synthesized dilating molecule NO (nitric oxide) as a result of oxidative stress is the key mechanism mediating reduced EDD with aging. Vascular oxidative stress increases with age as a consequence of greater production of reactive oxygen species (e.g. superoxide) without a compensatory increase in antioxidant defences. Sources of increased superoxide production include up-regulation of the oxidant enzyme NADPH oxidase, uncoupling of the normally NO-producing enzyme, eNOS (endothelial NO synthase) (due to reduced availability of the cofactor tetrahydrobiopterin) and increased mitochondrial synthesis during oxidative phosphorylation. Increased bioactivity of the potent endothelial-derived constricting factor ET-1 (endothelin-1), reduced endothelial production of/responsiveness to dilatory prostaglandins, the development of vascular inflammation, formation of AGEs (advanced glycation end-products), an increased rate of endothelial apoptosis and reduced expression of oestrogen receptor α (in postmenopausal females) also probably contribute to impaired EDD with aging. Several lifestyle and biological factors modulate vascular endothelial function with aging, including regular aerobic exercise, dietary factors (e.g. processed compared with non-processed foods), body weight/fatness, vitamin D status, menopause/oestrogen deficiency and a number of conventional and non-conventional risk factors for CVD. Given the number of older adults now and in the future, more information is needed on effective strategies for the prevention and treatment of vascular endothelial aging.

The thromboxane/endoperoxide receptor (TP): the common villain

The stimulation of thromboxane/endoperoxide receptors (TP) elicits diverse physiological/pathophysiological reactions, including platelet aggregation and contraction of vascular smooth muscle. Furthermore, the activation of endothelial TP promotes the expression of adhesion molecules and favors adhesion and infiltration of monocytes/macrophages. In various cardiovascular diseases, endothelial dysfunction is predominantly the result of the release of endothelium-derived contracting factors that counteract the vasodilator effect of nitric oxide produced by the endothelial nitric oxide synthase. Endothelium-dependent contractions involve the activation of cyclooxygenases, the production of reactive oxygen species along with that of endothelium-derived contracting factors, which diffuse toward the vascular smooth muscle cells and activate their TP. TP antagonists curtail the endothelial dysfunction in diseases such as hypertension and diabetes, are potent antithrombotic agents, and reduce vascular inflammation. Therefore, TP antagonists, because of this triple activity, may have a unique potential for the treatment of cardiovascular disorders.

Human endothelial dysfunction: EDCFs

Human studies, conducted in the presence of clinical conditions characterized by endothelial dysfunction, evidenced that endothelial cells, in response to different agonists and physical stimuli, become a source of endothelium-derived contracting factors (EDCFs), mainly cyclooxygenase (COX)-derived prostanoids. Their production has been documented in several human diseases, mostly in essential hypertension and aging. The EDCF production was at first identified as responsible for impaired endothelium-dependent vasodilation in the forearm microcirculation of patients with essential hypertension. Subsequent studies demonstrated that COX-dependent EDCF products are also a characteristic of the aging process, and essential hypertension seems to only anticipate the phenomenon. Of note, in aging and hypertension, both indomethacin, a COX inhibitor, and vitamin C, an antioxidant, totally reverse the blunted vasodilation to acetylcholine by restoring NO availability, thus suggesting that EDCFs could be one of the major sources of oxygen free radicals. The presence of EDCFs was documented also in other clinical setting, such as coronary artery disease and estrogen deprivation. In conclusion, many human pathological conditions characterized by a decline in endothelial function are associated with a progressive decrease in NO bioavailability and increase in the production of EDCFs. The mechanisms that regulate the balance between NO and EDCFs and the processes transforming the endothelium from a protective organ to a source of vasoconstrictor, proaggregatory and promitogenic mediators, remain to be determined.

Nitric oxide and coronary vascular endothelium adaptations in hypertension

This review highlights a number of nitric oxide (NO)-related mechanisms that contribute to coronary vascular function and that are likely affected by hypertension and thus become important clinically as potential considerations in prevention, diagnosis, and treatment of coronary complications of hypertension. Coronary vascular resistance is elevated in hypertension in part due to impaired endothelium-dependent function of coronary arteries. Several lines of evidence suggest that other NO synthase isoforms and dilators other than NO may compensate for impairments in endothelial NO synthase (eNOS) to protect coronary artery function, and that NO-dependent function of coronary blood vessels depends on the position of the vessel in the vascular tree. Adaptations in NOS isoforms in the coronary circulation to hypertension are not well described so the compensatory relationship between these and eNOS in hypertensive vessels is not clear. It is important to understand potential functional consequences of these adaptations as they will impact the efficacy of treatments designed to control hypertension and coronary vascular disease. Polymorphisms of the eNOS gene result in significant associations with incidence of hypertension, although mechanistic details linking the polymorphisms with alterations in coronary vasomotor responses and adaptations to hypertension are not established. This understanding should be developed in order to better predict those individuals at the highest risk for coronary vascular complications of hypertension. Greater endothelium-dependent dilation observed in female coronary arteries is likely related to endothelial Ca(2+) control and eNOS expression and activity. In hypertension models, the coronary vasculature has not been studied extensively to establish mechanisms for sex differences in NO-dependent function. Genomic and nongenomic effects of estrogen on eNOS and direct and indirect antioxidant activities of estrogen are discussed as potential mechanisms of interest in coronary circulation that could have implications for sex- and estrogen status-dependent therapy for hypertension and coronary dysfunction. The current review identifies some important basic knowledge gaps and speculates on the potential clinical relevance of hypertension adaptations in factors regulating coronary NO function.

Endothelium-dependent contractions and endothelial dysfunction in human hypertension

The endothelium is a crucial regulator of vascular physiology, producing in healthy conditions several substances with a potent antiatherosclerotic properties. Accordingly, the presence of endothelial dysfunction is associated with subclinical atherosclerosis and with an increased future risk of cardiovascular events. A large body of evidence supports the fundamental role of nitric oxide (NO) as the main endothelium-derived relaxing factor. However, in the presence of pathological conditions, such as hypertension, endothelial cells, in response to a number of agents and physical stimuli, become also a source of endothelium-derived contracting factors (EDCFs), including endothelins and angiotensin II and particularly cyclooxygenase-derived prostanoids and superoxide anions. These latter were at first identified as responsible for impaired endothelium-dependent vasodilation in patients with essential hypertension. However, cyclooxygenase-dependent EDCFs production is characteristic of the aging process, and essential hypertension seems to only anticipate the phenomenon. It is worth noting that both in aging and hypertension EDCF production is associated with a parallel decrease in NO availability, suggesting that this substance could be oxygen free radicals themselves. Accordingly, in hypertension both indomethacin, a cyclooxygenase inhibitor, and vitamin C, an antioxidant, increase the vasodilation to acetylcholine by restoring NO availability. In conclusion, hypertension is characterized by a decline in endothelial function, associated with a progressive decrease in NO bioavailability and increase in the production of EDCF. The mechanisms that regulate the balance between NO and EDCF, and the processes transforming the endothelium from a protective organ to a source of vasoconstrictor, proaggregatory and promitogenic mediators remain to be determined.

Estradiol increases angiotensin II type 1 receptor in hearts of ovariectomized rats

We tested the hypothesis that 17beta-estradiol (E(2)) has dual effects on the heart, increasing levels of proteins thought to have beneficial cardiovascular effects (e.g. endothelial nitric oxide (NO) synthase (eNOS)) as well as those thought to have detrimental cardiovascular effects (e.g. type 1 angiotensin II (AngII) receptor (AT(1)R)). Ovariectomized Wistar rats consuming a high-sodium diet received one of four treatments (n=7 per group): group 1, placebo pellets; group 2, E(2) (0 x 5 mg/pellet, 21-day release); group 3, NOS inhibitor, N(omega)-nitro-L-arginine-methyl-ester (L-NAME; 40 mg/kg per day for 14 days) plus Ang II (0 x 225 mg/kg per day on days 11-14); group 4, E(2) plus L-NAME/Ang II. E(2) increased cardiac levels of estrogen receptors ESR1 and ESR2, an ESR-associated membrane protein caveolin-3, eNOS, and phosphorylated (p)eNOS, thus, exerting potentially beneficial cardiovascular effects on NO. However, E(2) also increased cardiac levels of proteins associated with cardiovascular injury and inflammation including, AT(1)R, protein kinase C delta (PRKCD), phosphorylated PRKC, and phosphorylated extracellular signal regulated kinase (pMAPK)3/1, plasminogen activator inhibitor-1 (PAI-1), osteopontin and ED-1, a monocyte/macrophage-specific protein. E(2) treatment led to similar protein changes in the hearts of L-NAME/Ang II-treated rats except that the increase in peNOS was prevented, and L-NAME/Ang II and E(2) had additive effects in increasing cardiac PRKCD and PAI-1. Thus, the highest levels of cardiac PAI-1 and PRKCD occurred in L-NAME/Ang II-treated rats receiving E(2). In summary, E(2) treatment increased cardiac expression of AT(1)R as well as the expression of pro-inflammatory and prothrombotic factors.

Nitric oxide inhibits cutaneous vasoconstriction to exogenous norepinephrine

Previously, we found that nitric oxide (NO) inhibits cutaneous vasoconstrictor responsiveness evoked by whole body cooling, as well as an orthostatic stress in the heat-stressed human (Shibasaki M, Durand S, Davis SL, Cui J, Low DA, Keller DM, Crandall CG. J Physiol 585: 627-634, 2007). However, it remains unknown whether this response occurs via NO acting through presynaptic or postsynaptic mechanisms. The aim of this study was to test the hypothesis that NO is capable of impairing cutaneous vasoconstriction via postsynaptic mechanisms. Skin blood flow was monitored over two forearm sites where intradermal microdialysis membranes were previously placed. Skin blood flow was elevated four- to fivefold through perfusion of the NO donor sodium nitroprusside at one site and through perfusion of adenosine (primarily non-NO mechanisms) at a second site. Once a plateau in vasodilation was evident, increasing concentrations of norepinephrine (1 x 10(-8) to 1 x 10(-2) M) were administrated through both microdialysis probes, while the aforementioned vasodilator agents continued to be perfused. Cutaneous vascular conductance was calculated by dividing skin blood flow by mean arterial blood pressure. The administration of norepinephrine decreased cutaneous vascular conductance at both sites. However, the dose of norepinephrine at the onset of vasoconstriction (-5.9 +/- 1.3 vs. -7.2 +/- 0.7 log M norepinephrine, P = 0.021) and the concentration of norepinephrine resulting in 50% of the maximal vasoconstrictor response (-4.9 +/- 1.2 vs. -6.1 +/- 0.2 log M norepinephrine dose; P = 0.012) occurred at significantly higher norepinephrine concentrations for the sodium nitroprusside site relative to the adenosine site, respectively. These results suggested that NO is capable of attenuating cutaneous vasoconstrictor responsiveness to norepinephrine via postsynaptic mechanisms.

Long-term effects of low-dose 17beta-estradiol plus dydrogesterone on 24-h ambulatory blood pressure in healthy postmenopausal women: a 1-year, randomized, prospective study

The aim of the present 12-month, randomized, prospective controlled study was to investigate the long-term effects of low-dose oral hormone replacement therapy (HRT) on 24-h blood pressure in healthy, normotensive postmenopausal women. A total of 80 postmenopausal women received either 1 mg micronized 17beta-estradiol daily, sequentially combined with 10 mg dydrogesterone for 14 days of each 28-day cycle (n = 44), or no treatment (n = 36). Ambulatory blood pressure was recorded for a 24-h period at baseline and after 12 months. After 12 months, mean 24-h systolic ambulatory blood pressure fell significantly in the HRT group (-5.4 mmHg; p < 0.01). The difference between the values in the HRT and control groups after 12 months was significant (p < 0.01). Mean 24-h heart rate also fell significantly with HRT (-4.9 beats/min; p < 0.05), and the value was significantly lower than in the control group (p < 0.05). Mean daytime systolic blood pressure fell significantly in the HRT group (-6.6 mmHg; p < 0.001), and the value was significantly lower than in the control group (p < 0.05). There were no significant changes in blood pressure in the control group. In conclusion, sequential low-dose oral HRT with 17beta-estradiol/dydrogesterone caused a significant decrease in 24-h and daytime systolic ambulatory blood pressure in normotensive postmenopausal women.

Effects of ACE inhibition and beta-blockade on female genital structures in spontaneously hypertensive rats

INTRODUCTION AND AIM

This study evaluated the possible differences between an angiotensin converting enzyme (ACE) inhibitor and a beta-blocker concerning their potential protective role on female external genitalia in spontaneously hypertensive rats (SHR).

MAIN OUTCOME MEASURES

Morphological changes in the clitoris after antihypertensive treatments.

METHODS

For 6 months, SHR received no treatment; SHR + ramipril (RAM), SHR + atenolol (AT), and control Wistar Kyoto (WKY) rats received no treatment. Clitorises were processed for immunohistochemistry using anti-alpha-smooth muscle actin (alpha-SMA), anti-collagen I and III, anti-transforming growth factor beta(1) (TGFbeta(1)), and anti-endothelial nitric oxide synthase (eNOS) antibodies.

RESULTS

SHR + RAM and SHR + AT presented significantly lower blood pressure in both groups vs. untreated SHR. Compared with WKY, alpha-SMA was increased in the arteries and in the cavernous spaces of the clitoris together with a marked increase in wall/lumen ratio in clitoral vessels in untreated SHR. All these alterations were diminished in SHR + AT (P < 0.01). SHR + RAM presented differences with respect to SHR + AT in the reduction of these variables. TGFbeta(1) expression in the vessel wall from the clitoris and collagen I and III deposition in the interstitium from the clitoris in untreated SHR were significantly more (P < 0.01) than in WKY. While SHR + AT showed a mild decrease in these variables, SHR + RAM presented a significant reduction (P < 0.01) in TGFbeta(1) expression interstitial fibrosis and in both types of collagens. Positive immunostaining of eNOS in the sinusoidal endothelium from the clitoris was less (P < 0.01) in untreated SHR (3.4 +/- 1.3%) and SHR + AT (5.1 +/- 1.2%) than in SHR + RAM (17.2 +/- 1.6%) and WKY (15.9 +/- 1.7%). Untreated SHR and SHR + AT presented more surrounding connective tissue at the perineurium in the clitoris (P < 0.01) than SHR + RAM.

CONCLUSION

ACE inhibition provided a considerable protective role on the female external genitalia structures in SHR by a mechanism that may be, at least in part, independent of the degree of blood pressure lowering.

Endothelial function across an oral contraceptive cycle in women using levonorgestrel and ethinyl estradiol

Oral contraceptive pills (OCPs) are a popular contraception method. Currently, lower-dose ethinyl estradiol formulations are most commonly prescribed, although they have been linked to increased arterial vascular risk. The aim of this study was to investigate endothelial function in healthy young women using lower-dose ethinyl estradiol OCPs. We examined flow-mediated, endothelium-dependent and nitroglycerin-mediated, endothelium-independent vasodilation of the brachial artery, comparing two doses of ethinyl estradiol/levonorgestrel OCPs in 15 healthy young women on two study days: once during the active phase and once during the placebo phase of an OCP cycle. Group low dose (LD) ( n = 7) active pills contained 150 μg levonorgestrel/30 μg ethinyl estradiol versus Group very low dose (VLD) ( n = 8) with 100 μg levonorgestrel/20 μg ethinyl estradiol. Endothelium-dependent vasodilation was lower during the active phase in Group VLD (5.33 ± 1.77% vs. 7.23 ± 2.60%; P = 0.024). This phase difference was not observed in Group LD (8.00 ± 0.970% vs. 7.61 ± 1.07%; P = 0.647). Endothelium-independent vasodilation did not differ between phases in either group. Finally, we measured endothelium-dependent vasodilation in two additional women who received 10 μg of unopposed ethinyl estradiol. Endothelium-dependent vasodilation was increased by unopposed ethinyl estradiol compared with the placebo phase (10.88 ± 2.34% vs. 6.97 ± 1.83%). These results suggest that levonorgestrel may antagonize the activity of ethinyl estradiol. Thus both the progestin type and estradiol dose need to be considered when assessing arterial vascular risk of OCP use in women.

Novel aspects of endothelium-dependent regulation of vascular tone

The vascular endothelium plays a crucial role in the regulation of vascular homeostasis and in preventing the initiation and progress of cardiovascular disease by controlling mechanical functions of the underlying vascular smooth muscle. Three vasodilators: nitric oxide (NO), prostacyclin, and endothelium-derived hyperpolarizing factor, produced by the endothelium, underlie this activity. These substances act in a co-ordinated interactive manner to maintain normal endothelial function and operate as support mechanisms when one pathway malfunctions. In this review, we discuss recent advances in our understanding of how gender influences the interaction of these factors resulting in the vascular protective effects seen in pre-menopausal women. We also discuss how endothelial NO synthase (NOS) can act in both a pro- and anti-inflammatory action and therefore is likely to be pivotal in the initiation and time course of an inflammatory response, particularly with respect to inflammatory cardiovascular disorders. Finally, we review recent evidence demonstrating that it is not solely NOS-derived NO that mediates many of the beneficial effects of the endothelium, in particular, nitrite acts as a store of NO released during pathological episodes associated with NOS inactivity (ischemia/hypoxia). Each of these more recent findings has emphasized new pathways involved in endothelial biology, and following further research and understanding of the significance and mechanisms of these systems, it is likely that new and improved treatments for cardiovascular disease will result.

17β-Oestradiol enhances the acute hypotensive effect of captopril in female ovariectomized spontaneously hypertensive rats

The objective of this study was to investigate whether the acute haemodynamic effects of angiotensin-converting enzyme inhibition with captopril could be enhanced by oestrogen administration, and then to evaluate the mechanisms involved in this enhancement. All experiments were performed in 18-week-old female spontaneously hypertensive rats arranged in three experimental groups: intact; ovariectomized (OVX); and ovariectomized plus treatment with 17beta-oestradiol (OVX + E2). These groups were used to evaluate the effects of captopril administration alone, or following bradykinin B2 receptor blockade or nitric oxide synthase inhibition, on a number of haemodynamic parameters (mean arterial pressure, cardiac index, vascular resistance and heart rate). The drop in mean arterial pressure and vascular resistance index in response to captopril was more pronounced in intact and ovariectomized rats treated with 17beta-oestradiol than in ovariectomized animals. Blockade of bradykinin B2 receptors or inhibition of nitric oxide synthesis attenuated the synergy between 17beta-oestradiol and captopril. It is concluded that ovariectomy blunted the blood pressure and vascular resistance index drop observed in intact rats in response to captopril. Treatment with 17beta-oestradiol prevented the blunted response to captopril in ovariectomized rats. Kinins and nitric oxide may be involved in the mechanisms of 17beta-oestradiol potentiation of the haemodynamic effects of captopril.

Premature ovarian failure, endothelial dysfunction and estrogen-progestogen replacement

Cardiovascular disease, including coronary artery disease, stroke and peripheral vascular disease, is the leading cause of death among women. Vascular endothelial dysfunction is an early marker of atherosclerosis. Women with premature ovarian failure (or premature menopause) present an increased risk for cardiovascular disease, which might be attributed to the early onset of vascular endothelial dysfunction, associated with sex steroid deficiency. Cyclical estrogen and progestogen therapy has been shown to restore endothelial function in these young women. Further research is required to assess primarily the long-term effects of hormone replacement therapy on cardiovascular and overall prognosis in young women with premature ovarian failure, as well as the effects of different doses, duration and routes of hormone administration in these women.

Contribution of prostanoids to endothelium-dependent vasodilatation in the digital circulation of women with primary Raynaud's disease

In 15 women with PR (primary Raynaud's) disease and in 15 matched control women, ACh (acetylcholine) was delivered by iontophoresis to the dorsum of the finger (seven 20 s pulses of 0.1 mA, followed by one 20 s pulse of 0.2 mA, applied at 60 s intervals). Cutaneous RCF (red cell flux) was recorded from the same site by the laser Doppler technique. ACh evoked progressive increases in RCF that were comparable in pre- and post-menopausal women with PR [maxima of 294±113 and 259±59 pu (perfusion units) respectively, n=7 and 8 respectively], and in pre-menopausal controls (225±92 pu, n=7), but smaller in post-menopausal controls (140±63 pu, n=8; P<0.05). Aspirin (600 mg, orally), a COX (cyclo-oxygenase) inhibitor, potentiated the ACh-evoked dilator responses in pre- and post-menopausal women with PR (343±129 and 311±48 pu respectively) and post-menopausal controls (277±124 pu; P<0.05), but had no effect in pre-menopausal controls (225±92 pu). These results suggest that vasoconstrictor COX products limit ACh-evoked endothelium-dependent cutaneous dilatation in the digits in pre- and post-menopausal women with PR and in post-menopausal, but not pre-menopausal, control women. We propose that PR disease is associated with abnormality in the ability of oestrogen to modulate the synthesis of endothelium-dependent vasodilator and/or vasoconstrictor COX products.

Effect of acute transdermal estrogen administration on basal, mental stress and cold pressor-induced sympathetic responses in postmenopausal women

Administration of estrogen has vascular effects through poorly defined mechanisms that may include sympathetic withdrawal. To define the effects of acute estrogen administration on sympathetic responses, nineteen healthy postmenopausal women (age 54+/-2 years) were studied after application of a placebo or estrogen patch for 36 hours, in random order. A p-value, adjusted for multiple comparisons, of <0.017 was used to determine statistical significance. Heart rate, blood pressure, and norepinephrine spillover were measured at rest, during mental stress (Stroop test), and during a cold pressor test. Estrogen did not attenuate basal or stimulated hemodynamic responses significantly. The increase in mean arterial pressure after the Stroop test (5.9+/-1.2mm/ Hg on placebo vs 6.1+/-1.6mm/Hg on estrogen, p=0.9) and after the cold pressor test (12.6+/-2.4mm/Hg on placebo vs 13.0+/-2.2 mm/Hg on estrogen, p=0.8) did not differ. Basal, mental stress and cold pressor-stimulated norepinephrine spillover were not significantly affected by short-term estrogen administration. Norepinephrine spillover tended to be higher after estrogen (1296.2+/-238 ng/min) than placebo (832.5+/-129 ng/min) (p=0.02) at baseline and after the Stroop test (1881.1+/-330 ng/min vs 1014.6+/-249 ng/min) (p=0.02). Acute transdermal estrogen administration did not attenuate norepinephrine spillover or sympathetically mediated hemodynamic responses.

Weight changes and obesity predict impaired resting and endothelium-dependent myocardial blood flow in postmenopausal women

BACKGROUND

Obesity has been associated with impaired endothelial function, but the influence of lifetime weight patterns on endothelial function has not been studied.

HYPOTHESIS

We hypothesized that coronary vascular reactivity would be diminished in postmenopausal women with a history of obesity and frequent weight swings.

METHODS

We performed dynamic N-13 ammonia positron emission tomography in 18 postmenopausal women with cardiac risk factors. Myocardial blood flow (MBF) was measured at rest, after the cold pressor test (CPT), and after adenosine infusion in order to determine baseline and endothelium-dependent and -independent flows, respectively. Myocardial blood flow was corrected for cardiac work by normalizing to the rate-pressure product. Weight history was obtained by standardized questionnaire.

RESULTS

Normalized rest (n-rest) MBF correlated negatively with current weight (r = -0.52, p = 0.026) and weight at age 18 (r = -0.47, p = 0.047). Normalized CPT (n-CPT) MBF correlated inversely with current weight (r = -0.55, p = 0.018), weight at age 18 (r = -0.605, p = 0.008), and highest weight (r = -0.62, p = 0.006). Higher waist circumference predicted lower n-rest MBF (r = -0.52, p = 0.028) and n-CPT MBF (r = -0.48, p = 0.04). The same association was found with hip circumference (r = -0.52, p = 0.028; r = -0.49, p = 0.038, respectively), whereas higher body mass index (BMI) predicted lower n-CPT MBF (r = -0.53, p = 0.02). Women with at least four significant weight swings had lower MBF during rest, CPT, and n-CPT (0.88 vs. 1.19 ml/g/min, p = 0.008; 0.76 vs. 1.23 ml/g/min, p < 0.001; 0.74 vs. 1.10 ml/g/min, p = 0.009, respectively).

CONCLUSIONS

Increased waist and hip circumference, weight, and frequent weight swings are associated with impaired resting and endothelium-dependent MBF in postmenopausal women. These data suggest that lifetime weight patterns may influence cardiovascular risk in women.

Role of estrogen in nitric oxide- and prostaglandin-dependent modulation of vascular conductance during treadmill locomotion in rats

Endothelial production of nitric oxide (NO) and prostaglandins (PG) may be greater in females than in males, increasing vasodilatory responses in females. Does sex influence the cardiovascular responses to dynamic exercise through estrogen-dependent modulation of NO and PG vasodilatory pathways? After the administration of hexamethonium, we assessed terminal aortic blood flow (TAQ), mean arterial pressure (MAP), and hindlimb vascular conductance (VC) in four groups of rats (6 males, 5 females, 5 ovariectomized females, and 6 ovariectomized females with chronic estrogen supplementation) during graded mild-intensity treadmill locomotion (5-15 m/min, 0 degrees grade, 2 min). All rats repeated exercise after cyclooxygenase inhibition (indomethacin) and then again after NO synthase inhibition (nitro-l-arginine methyl ester) to examine the roles of NO and PG. Regression analysis was used to determine the influence of sex and plasma 17beta-estradiol on TAQ, MAP, and VC. The analysis revealed that female sex did not influence TAQ but reduced MAP and increased VC at rest and during exercise conditions. Plasma 17beta-estradiol (measured by immunoassay) significantly decreased MAP and increased TAQ and VC, irrespective of sex. Cyclooxygenase inhibition eliminated the significant association between MAP and estrogen, suggesting that estrogenic modulation occurred through PG-dependent processes. In contrast, the significant influence of estrogen on TAQ and VC was eliminated after NO synthase inhibition. On the basis of the overall findings of this study, estrogen influenced the vascular responses to dynamic exercise through PG- and NO-dependent pathways, but this occurred independent of sex.

Estrogen modulation of endothelial nitric oxide synthase

Over the past decade, clinical and basic research has demonstrated that estrogen has a dramatic impact on the response to vascular injury and the development of atherosclerosis. Further work has indicated that this is at least partially mediated by an enhancement in nitric oxide (NO) production by the endothelial isoform of NO synthase (eNOS) due to increases in both eNOS expression and level of activation. The effects on eNOS abundance are primarily mediated at the level of gene transcription, and they are dependent on estrogen receptors (ERs), which classically serve as transcription factors, but they are independent of estrogen response element action. Estrogen also has potent nongenomic effects on eNOS activity mediated by a subpopulation of ERalpha localized to caveolae in endothelial cells, where they are coupled to eNOS in a functional signaling module. These observations, which emphasize dependence on cell surface-associated receptors, provide evidence for the existence of a steroid receptor fast-action complex, or SRFC, in caveolae. Estrogen binding to ERalpha on the SRFC in caveolae leads to G(alphai) activation, which mediates downstream events. The downstream signaling includes activation of tyrosine kinase-MAPK and Akt/protein kinase B signaling, stimulation of heat shock protein 90 binding to eNOS, and perturbation of the local calcium environment, leading to eNOS phosphorylation and calmodulin-mediated eNOS stimulation. These unique genomic and nongenomic processes are critical to the vasoprotective and atheroprotective characteristics of estrogen. In addition, they serve as excellent paradigms for further elucidation of novel mechanisms of steroid hormone action.

Flow-mediated dilatation of the brachial artery in pregnancy at high altitude

OBJECTIVE

Pregnancy at high altitude has been associated with increased prevalence of pre-eclampsia and reduced maternal oestrogen levels, factors that have been associated with endothelial dysfunction. The aim of this study was to examine the effect of high altitude (4370 m above sea level) on endothelial function during pregnancy as assessed by a non-invasive method.

DESIGN

Cross-sectional study.

SETTING

Two maternity units providing routine antenatal care: one at high altitude (District General Hospital--IPSS in Cerro de Pasco, Peru) and one at sea level (Instituto Materno-Perinatal in Lima, Peru).

POPULATION

Sixty pregnant women at 6-42 weeks of gestation resident at high altitude (Cerro de Pasco, Peru, 4370 m above sea level) and 54 at sea level (Lima, Peru). Comparisons were performed also in 11 and 14 non-pregnant women at each altitude, respectively.

METHODS

Endothelial function was assessed by flow-mediated dilatation of the brachial artery using high-resolution ultrasound.

MAIN OUTCOME MEASURES

Differences in flow mediated dilatation of the brachial artery in two groups of pregnant women, one at high altitude and one at sea level.

RESULTS

Both at high altitude and sea level flow-mediated dilatation of the brachial artery increased in the first two trimesters to levels 32% higher than non-pregnant controls. However, in the third trimester, flow-mediated dilatation of the brachial artery was lower than non-pregnant levels. Resting vessel size increased during pregnancy by 15% compared with non-pregnant controls at term, with no difference between the two populations at high and low altitude. Pregnancy at high altitude, compared with sea level, was associated with 59% lower baseline blood flow and 76% higher reactive hyperaemia. Similarly, non-pregnant controls at high altitude compared with sea level demonstrated similar flow-mediated dilatation of the brachial artery and 40% lower resting blood flow of the brachial artery. However, the difference in reactive hyperaemia did not reach statistical significance.

CONCLUSION

These data suggest that, during pregnancy at high altitude, endothelial function, as assessed by flow-mediated dilatation of the brachial artery, is not impaired.

Vasomotor and vascular effects of hormone replacement therapy

Cardiovascular risk factors impair endothelium-dependent vasodilation as well as other functions of the endothelium, thereby predisposing the patient to atherosclerosis and its overt clinical manifestations. Loss of endogenous estrogen also leads to reduced bioavailability of endothelium-derived nitric oxide. In premenopausal women, the impairment of endothelial function develops within 1 month of surgical ovariectomy and is reversed by the administration of exogenous 17 beta-estradiol. Exogenous estrogen administration restores endothelial function by enhancing nitric oxide synthesis through genomic and nongenomic mechanisms and by reducing oxidative stress and nitric oxide breakdown. The effect of progesterone on endothelial function is still under investigation. In animal studies, medroxyprogesterone acetate (MPA) counteracts estrogen's beneficial effects on endothelial function and on coronary plaque size. In humans, however, the addition of progesterone to estradiol does not appreciably attenuate estrogen-associated endothelium-dependent vasodilation. Secondary prevention trials with conjugated equine estrogen plus MPA have no proven benefit in reducing coronary events, progression of angiographic coronary atherosclerosis, or incidence of cerebrovascular events. This suggests that beneficial effects of estrogen on endothelial function are counterbalanced by detrimental effects, perhaps because of proinflammatory and prothrombotic actions. The selective estrogen receptor modulators are currently under investigation as agents that might retain the favorable, without possessing the unfavorable, effects of estrogen on the vascular system.

Is estradiol cardioprotection a nitric oxide-mediated effect?

BACKGROUND

Estradiol exerts a number of biological effects that support extensive observational data suggesting a protective role for estrogen in cardiovascular disease prevention. These include effects on lipid and carbohydrate metabolism, coagulation/fibrinolysis as well as a possible effect on vascular reactivity. It has been proposed that this might be mediated by vascular endothelial nitric oxide (NO) production. Accordingly, we designed complementary in-vivo and in-vitro studies to investigate this hypothesis further.

METHODS

Firstly, in a group of 10 healthy post-menopausal women, bilateral venous occlusion plethysmography was used to examine forearm vasoconstrictor responses to intrabrachial N(G)-monomethyl-l-arginine (l-NMMA; a substrate inhibitor of nitric oxide synthase) both before and after 4 weeks of treatment with transdermal 17beta-estradiol (E(2)) (80 microg/day). Secondly, we examined the direct effects of acute (24 h) and chronic (7 days) treatment with E(2) (10 pmol/l and 10 nmol/l) on endothelial nitric oxide synthase (eNOS) gene expression in cultured human aortic endothelial cells.

RESULTS

No significant differences were observed between the vasoconstrictor responses to l-NMMA (2, 4, 8 micromol/min) before and after E(2) treatment. Comparison of E(2)-treated endothelial cells with control cells showed no significant increase in eNOS mRNA expression following either acute or chronic estradiol treatment.

CONCLUSIONS

The present studies do not provide evidence for an eNOS-mediated cardioprotective response to estrogen and therefore suggest that additional mechanisms other than the endothelial NO system may have an important role in the cardiovascular effects of estrogen.

The effects of hormone replacement therapy on endothelial function in women with Turner's syndrome

OBJECTIVES

To examine the effect of hormone replacement therapy (HRT) on endothelial function of forearm resistance vessels in women with Turner's syndrome.

DESIGN

Subjects were studied on three occasions: on their usual HRT (study 1), then after 6 weeks off HRT (study 2) and finally after a further 6 weeks on HRT (study 3).

PATIENTS

Seven young women with Turner's syndrome were studied.

MEASUREMENTS

Forearm blood flow in response to intrabrachial infusion of bradykinin, 10, 30, 100 pmol/min (endothelium-dependent vasodilator), glyceryl trinitrate, 4, 8, 16 nmol/min (GTN; endothelium-independent vasodilator), noradrenaline, 60, 120, 240 pmol/min (NA, alpha-adrenergic receptor agonist) and NG-monomethyl-l-arginine, 1, 2, 4 micromol/min (L-NMMA; NO synthase inhibitor) was assessed by bilateral venous plethysmography.

RESULTS

The vasodilator response to bradykinin, expressed as the within-subject mean difference in area under the dose-response curve between study 2 and study 1, was significantly diminished (-744.2 +/- 287.2, P = 0.04) but improved 6 weeks after HRT recommencement. However, there was no significant change in response to GTN (between study 2 and study 1, 189.5 +/- 247.8, P = 0.47). The vasoconstrictor response to L-NMMA was also diminished in study 2 when compared to study 1 (-100.4 +/- 35.4, P = 0.039) and was restored after HRT was recommenced (between study 3 and study 2, 117.5 +/- 69.3, P = 0.17) whereas there was no significant difference in response to NA between study 2 and study 1 (76.7 +/- 50.6, P = 0.18) or study 3 and study 2 (-70.8 +/- 71.1, P = 0.38).

CONCLUSIONS

HRT improves endothelial function in women with Turner's syndrome.

Assessment of endothelial function in normal twin pregnancy

OBJECTIVE

To assess the maternal endothelial function in normal twin pregnancy.

DESIGN

Cross-sectional study.

SUBJECTS

Endothelial function was investigated in 74 women with normal twin pregnancy at 11-30 weeks of gestation and the results were compared to previous reported findings in 98 women with normal singleton pregnancy and 19 non-pregnant controls.

METHODS

Endothelial function was assessed by measuring the changes of the brachial artery diameter in response to reactive hyperemia (flow-mediated dilatation) using external high resolution ultrasound.

RESULTS

Flow-mediated dilatation of the brachial artery in both twin and singleton pregnancies was significantly higher than in non-pregnant women (P = 0.002 and P = 0.02, respectively). However, there was no significant difference in flow-mediated dilatation between women with twin and singleton pregnancy (9.61 +/- 4.36 vs. 8.84 +/- 3.18, P = 0.38). Resting vessel size, baseline flow and reactive hyperemia did not change significantly with gestation in twin pregnancy and were similar to values in singleton pregnancies and controls.

CONCLUSION

Our findings indicate that although in pregnancy endothelial function is enhanced, this change may not be affected by the number of fetoplacental units present.