Basal release of nitric oxide from aortic rings is greater in female rabbits than in male rabbits: implications for atherosclerosis

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.

Connecting Aortic Stiffness to Vascular Contraction: Does Sex Matter?

This study was designed to connect aortic stiffness to vascular contraction in young male and female Wistar rats. We hypothesized that female animals display reduced intrinsic media-layer stiffness, which associates with improved vascular function. Atomic force microscopy (AFM)-based nanoindentation analysis was used to derive stiffness (Young’s modulus) in biaxially (i.e., longitudinal and circumferential) unloaded aortic rings. Reactivity studies compatible with uniaxial loading (i.e., circumferential) were used to assess vascular responses to a selective α1 adrenergic receptor agonist in the presence or absence of extracellular calcium. Elastin and collagen levels were indirectly evaluated with fluorescence microscopy and a picrosirius red staining kit, respectively. We report that male and female Wistar rats display similar AFM-derived aortic media-layer stiffness, even though female animals withstand higher aortic intima-media thickness-to-diameter ratio than males. Female animals also present reduced phenylephrine-induced aortic force development in concentration-response and time-force curves. Specifically, we observed impaired force displacement in both parts of the contraction curve (Aphasic and Atonic) in experiments conducted with and without extracellular calcium. Additionally, collagen levels were lower in female animals without significant elastin content and fragmentation changes. In summary, sex-related functional differences in isolated aortas appear to be related to dissimilarities in the dynamics of vascular reactivity and extracellular matrix composition rather than a direct response to a shift in intrinsic media-layer stiffness.

Estrogen Receptor and Vascular Aging

Cardiovascular diseases remain an age-related pathology in both men and women. These pathologies are 3-fold more frequent in men than in women before menopause, although this difference progressively decreases after menopause. The vasculoprotective role of estrogens are well established before menopause, but the consequences of their abrupt decline on the cardiovascular risk at menopause remain debated. In this review, we will attempt to summarize the main clinical and experimental studies reporting the protective effects of estrogens against cardiovascular diseases, with a particular focus on atherosclerosis, and the impact of aging and estrogen deprivation on their endothelial actions. The arterial actions of estrogens, but also part of that of androgens through their aromatization into estrogens, are mediated by the estrogen receptor (ER)α and ERβ. ERs belong to the nuclear receptor family and act by transcriptional regulation in the nucleus, but also exert non-genomic/extranuclear actions. Beside the decline of estrogens at menopause, abnormalities in the expression and/or function of ERs in the tissues, and particularly in arteries, could contribute to the failure of classic estrogens to protect arteries during aging. Finally, we will discuss how recent insights in the mechanisms of action of ERα could contribute to optimize the hormonal treatment of the menopause.

Sex-Specific Impacts of Exercise on Cardiovascular Remodeling

Cardiovascular diseases (CVD) remain the leading cause of death in men and women. Biological sex plays a major role in cardiovascular physiology and pathological cardiovascular remodeling. Traditionally, pathological remodeling of cardiovascular system refers to the molecular, cellular, and morphological changes that result from insults, such as myocardial infarction or hypertension. Regular exercise training is known to induce physiological cardiovascular remodeling and beneficial functional adaptation of the cardiovascular apparatus. However, impact of exercise-induced cardiovascular remodeling and functional adaptation varies between males and females. This review aims to compare and contrast sex-specific manifestations of exercise-induced cardiovascular remodeling and functional adaptation. Specifically, we review (1) sex disparities in cardiovascular function, (2) influence of biological sex on exercise-induced cardiovascular remodeling and functional adaptation, and (3) sex-specific impacts of various types, intensities, and durations of exercise training on cardiovascular apparatus. The review highlights both animal and human studies in order to give an all-encompassing view of the exercise-induced sex differences in cardiovascular system and addresses the gaps in knowledge in the field.

Potentiation of Acetylcholine-Induced Relaxation of Aorta in Male UC Davis Type 2 Diabetes Mellitus (UCD-T2DM) Rats: Sex-Specific Responses

Previous reports suggest that diabetes may differentially affect the vascular beds of females and males. The objectives of this study were to examine whether there were (1) sex differences in aortic function and (2) alterations in the relative contribution of endothelium-derived relaxing factors in modulating aortic reactivity in UC Davis Type 2 Diabetes Mellitus (UCD-T2DM) rats. Endothelium-dependent vasorelaxation (EDV) in response to acetylcholine (ACh) was measured in aortic rings before and after exposure to pharmacological inhibitors. Relaxation responses to sodium nitroprusside were assessed in endothelium-denuded rings. Moreover, contractile responses to phenylephrine (PE) were measured before and after incubation of aortic rings with a nitric oxide synthase (NOS) inhibitor in the presence of indomethacin. Metabolic parameters and expression of molecules associated with vascular and insulin signaling as well as reactive oxygen species generation were determined. Diabetes slightly but significantly impaired EDV in response to ACh in aortas from females but potentiated the relaxation response in males. The potentiation of EDV in diabetic male aortas was accompanied by a traces of nitric oxide (NO)- and prostanoid-independent relaxation and elevated aortic expression of small- and intermediate conductance Ca2+-activated K+ channels in this group. The smooth muscle sensitivity to NO was not altered, whereas the responsiveness to PE was significantly enhanced in aortas of diabetic groups in both sexes. Endothelium-derived NO during smooth muscle contraction, as assessed by the potentiation of the response to PE after NOS inhibition, was reduced in aortas of diabetic rats regardless of sex. Accordingly, decreases in pAkt and peNOS were observed in aortas from diabetic rats in both sexes compared with controls. Our data suggest that a decrease in insulin sensitivity via pAkt-peNOS-dependent signaling and an increase in oxidative stress may contribute to the elevated contractile responses observed in diabetic aortas in both sexes. This study demonstrates that aortic function in UCD-T2DM rats is altered in both sexes. Here, we provide the first evidence of sexual dimorphism in aortic relaxation in UCD-T2DM rats.

Sex Differences in the Inflammatory Response: Pharmacological Opportunities for Therapeutics for Coronary Artery Disease

Coordinated molecular responses are key to effective initiation and resolution of both acute and chronic inflammation. Vascular inflammation plays an important role in initiating and perpetuating atherosclerotic disease, specifically at the site of plaque and subsequent fibrous cap rupture. Both men and women succumb to this disease process, and although management strategies have focused on revascularization and pharmacological therapies in the acute situation to reverse vessel closure and prevent thrombogenesis, data now suggest that regulation of host inflammation may improve both morbidity and mortality, thus supporting the notion that prevention is better than cure. There is a clear sex difference in the incidence of vascular disease, and data confirm biological differences in inflammatory initiation and resolution between men and women. This article reviews contemporary opinions describing the sex difference in the initiation and resolution of inflammatory responses, with a view to explore potential targets for pharmacological intervention.

Influence of Sex, Menstrual Cycle, and Menopause Status on the Exercise Pressor Reflex

In this review, we highlight the underlying mechanisms responsible for the sex differences in the exercise pressor reflex (EPR), and, importantly, the impact of sex hormones and menopausal status. The EPR is attenuated in premenopausal women compared with age-matched men. Specifically, activation of the metaboreflex (a component of the EPR) results in attenuated increases in blood pressure and sympathetic vasomotor outflow compared with age-matched men. In addition, premenopausal women exhibit less transduction of sympathetic outflow to the peripheral vasculature than men. In stark contrast, postmenopausal women exhibit an augmented EPR arising from exaggerated metaboreflex-induced autonomic and cardiovascular reflexes. We propose that metaboreflex-induced autonomic and cardiovascular changes associated with menopause majorly contribute to the elevated blood pressure response during dynamic exercise in postmenopausal women. In addition, we discuss the potential mechanisms by which sex hormones in premenopausal women may impact the EPR as well as metaboreflex.

Vascular phenotype of amyloid precursor protein-deficient mice

The amyloid precursor protein (APP) is expressed in the blood vessel wall, but the physiological function of APP is not completely understood. Previous studies established that APP has amine oxidase activity responsible for degradation of catecholamines. In the present study, we characterized the vascular phenotype of APP-knockout (APP-/-) mice. We demonstrate that circulating levels of catecholamines are significantly increased in male as compared with female APP-/- mice. Studies of vasomotor function in isolated aortas revealed that contractions to the α1-receptor agonist phenylephrine were significantly reduced in male APP-/- mice but not in females. In addition, contractions to G protein activation with sodium fluoride were reduced exclusively in male APP-/- mice aortas. The endothelium-dependent relaxations to acetylcholine were not affected by the loss of APP in mice of both sexes. Further analysis of the mechanisms underlying endothelium-dependent relaxations revealed that inhibition of cyclooxygenase by indomethacin significantly impaired relaxations to acetylcholine exclusively in male APP-/- mice. Furthermore, acetylcholine-induced production of cyclic guanosine monophosphate (cGMP) was significantly reduced in male APP-/- mice aortas while acetylcholine-induced production of cyclic adenosine monophosphate (cAMP) was enhanced. We concluded that altered vascular reactivity to phenylephrine appears to be in part the result of chronic exposure of male APP-/- aorta to high circulating levels of catecholamines. The mechanisms responsible for the impairment of endothelium-dependent cGMP signaling and adaptive enhancement of endothelium-dependent production of cAMP remain to be defined. NEW & NOTEWORTHY Male amyloid precursor protein (APP)-deficient mice have higher circulating levels of catecholamines as compared with female APP-deficient mice. As a consequence, endothelium-dependent and endothelium-independent vasomotor functions of male APP-deficient mice are significantly altered. Under physiological conditions, expression of APP appears to play an important role in vascular function.

Sex-specific eNOS activity and function in human endothelial cells

Clinical and epidemiological data show that biological sex is one of the major determinants for the development and progression of cardiovascular disease (CVD). Impaired endothelial function, characterized by an imbalance in endothelial Nitric Oxide Synthase (eNOS) activity, precedes and accelerates the development of CVD. However, whether there is any sexual dimorphism in eNOS activity and function in endothelial cells (ECs) is still unknown. Here, by independently studying human male and female ECs, we found that female ECs expressed higher eNOS mRNA and protein levels both in vitro and ex vivo. The increased eNOS expression was associated to higher enzymatic activity and nitric oxide production. Pharmacological and genetic inhibition of eNOS affected migratory properties only in female ECs. In vitro angiogenesis experiments confirmed that sprouting mostly relied on eNOS-dependent migration in female ECs. At variance, capillary outgrowth from male ECs was independent of eNOS activity but required cell proliferation. In this study, we found sex-specific differences in the EC expression, activity, and function of eNOS. This intrinsic sexual dimorphism of ECs should be further evaluated to achieve more effective and precise strategies for the prevention and therapy of diseases associated to an impaired endothelial function such as CVD and pathological angiogenesis.

Respiratory muscle blood flow during exercise: Effects of sex and ovarian cycle

Sex and ovarian cycle have been speculated to modify respiratory muscle blood flow control during exercise, but the findings are inconclusive. We tested the hypotheses that females would have higher respiratory muscle blood flow and vascular conductance (VC) compared with males during exercise and that this difference would be accentuated in proestrus vs. ovariectomized (OVA) females. Mean arterial pressure (carotid artery catheter) and respiratory muscle blood flow (radiolabeled microspheres) were measured during moderate-intensity (24 m/min, 10% grade) exercise in male (n = 9), female (n = 9), and OVA female (n = 7) rats and near-maximal (60 m/min, 5% grade) exercise in male (n = 5) and female (n = 7) rats. At rest, diaphragm, intercostal, and transversus abdominis blood flow were not different (P = 0.33) among groups. During moderate-intensity exercise, diaphragm (M: 124 ± 16; F: 140 ± 14; OVA: 140 ± 20 ml·min^-1·100 g^-1), intercostal (M: 33 ± 5; F: 34 ± 5; OVA: 30 ± 5 ml·min^-1·100 g^-1), and transversus abdominis blood flow (M: 24 ± 4; F: 35 ± 7; OVA: 35 ± 9 ml·min^-1·100 g^-1) significantly increased in all groups compared with rest but were not different (P = 0.12) among groups. From rest to moderate-intensity exercise, diaphragm (P < 0.03) and transversus abdominis (P < 0.04) VC increased in all groups, whereas intercostal VC increased only for males and females (P = 0.01). No differences (P > 0.13) existed in VC among groups. During near-maximal exercise, diaphragm (M: 304 ± 62; F: 283 ± 17 ml·min^-1·100 g^-1), intercostal (M: 29 ± 8; F: 40 ± 6 ml·min^-1·100 g^-1), and transversus abdominis (M: 85 ± 14; F: 86 ± 9 ml·min^-1·100 g^-1) blood flow and VC were not different (P > 0.27) between males and females. These data demonstrate that respiratory muscle blood flow and vascular conductance at rest and during exercise are not affected by sex or ovarian cycle in rats.NEW & NOTEWORTHY It has been proposed that sex and ovarian cycle modulate respiratory muscle blood flow control during exercise. We demonstrate herein that neither sex nor ovarian cycle influences respiratory muscle blood flow or vascular conductance at rest or during exercise in rats.

Type of supplemented simple sugar, not merely calorie intake, determines adverse effects on metabolism and aortic function in female rats

High consumption of simple sugars causes adverse cardiometabolic effects. We investigated the mechanisms underlying the metabolic and vascular effects of glucose or fructose intake and determined whether these effects are exclusively related to increased calorie consumption. Female Sprague-Dawley rats were supplemented with 20% wt/vol glucose or fructose for 2 mo, and plasma analytes and aortic response to vasodilator and vasoconstrictor agents were determined. Expression of molecules associated with lipid metabolism, insulin signaling, and vascular response were evaluated in hepatic and/or aortic tissues. Caloric intake was increased in both sugar-supplemented groups vs. control and in glucose- vs. fructose-supplemented rats. Hepatic lipogenesis was induced in both groups. Plasma triglycerides were increased only in the fructose group, together with decreased expression of carnitine palmitoyltransferase-1A and increased microsomal triglyceride transfer protein expression in the liver. Plasma adiponectin and peroxisome proliferator-activated receptor (PPAR)-α expression was increased only by glucose supplementation. Insulin signaling in liver and aorta was impaired in both sugar-supplemented groups, but the effect was more pronounced in the fructose group. Fructose supplementation attenuated aortic relaxation response to a nitric oxide (NO) donor, whereas glucose potentiated it. Phenylephrine-induced maximal contractions were reduced in the glucose group, which could be related to increased endothelial NO synthase (eNOS) phosphorylation and subsequent elevated basal NO in the glucose group. In conclusion, despite higher caloric intake in glucose-supplemented rats, fructose caused worse metabolic and vascular responses. This may be because of the elevated adiponectin level and the subsequent enhancement of PPARα and eNOS phosphorylation in glucose-supplemented rats.

NEW & NOTEWORTHY

This is the first study comparing the effects of glucose and fructose consumption on metabolic factors and aortic function in female rats. Our results show that, although total caloric consumption was higher in glucose-supplemented rats, fructose ingestion had a greater impact in inducing metabolic and aortic dysfunction.

Sex-specific vascular responses of the rat aorta: effects of moderate term (intermediate stage) streptozotocin-induced diabetes

Hyperglycemia affects male and female vascular beds differently. We have previously shown that 1 week after the induction of diabetes with streptozotocin (STZ), male and female rats exhibit differences in aortic endothelial function. To examine this phenomenon further, aortic responses were studied in male and female rats 8 weeks after the induction of diabetes (intermediate stage). Endothelium-dependent vasodilation (EDV) to acetylcholine (ACh) was measured in phenylephrine (PE) pre-contracted rat aortic rings. Concentration response curves to PE were generated before and after L-NAME, a nitric oxide synthase (NOS) inhibitor. Furthermore, mRNA expression of endothelial nitric oxide synthase (eNOS) and NADPH oxidase subunit (Nox1) were determined. At 8 weeks, diabetes impaired EDV to a greater extent in female than male aortae. Furthermore, the responsiveness to PE was significantly enhanced only in female diabetic rats, and basal NO, as indicated by the potentiation of the response to PE after L-NAME, was reduced in female diabetic rat aortae to the same levels as in males. In addition, eNOS mRNA expression was decreased, while the Nox1 expression was significantly enhanced in diabetic female rats. These results suggest that aortic function in female diabetic rats after 8 weeks exhibits a more prominent impairment and that NO may be involved.

Low-dose estrogen is as effective as high-dose treatment in rats with postmenopausal hypertension

: This study was conducted to test the hypothesis that 17β-estradiol therapy improves redox balance by decreasing reactive oxygen species production and increasing nitric oxide (NO) bioavailability, favoring Akt pathway activation and resulting in a better autonomic vascular control. Ovariectomized female Wistar rats were divided into 4 groups: (1) vehicle (VL) and animals treated with a pellet of 17β-estradiol for 21 days; (2) low dose (LE; 0.05 mg); (3) medium dose (ME; 0.2 mg); and (4) high dose (HE; 0.5 mg). Arterial pressure and its sympathetic nervous system modulation were evaluated by spectral analysis. Nitric oxide synthase and NADPH oxidase (Nox) activities, H2O2 concentration, redox status (GSH/GSSG), protein expression of Trx-1 and p-Akt/Akt were evaluated in the aorta, whereas NO metabolites were measured in the serum. Estrogen-treated groups showed a significant decrease in arterial pressure and sympathetic vascular drive. Redox status was significantly improved and NADPH oxidase and H2O2 were decreased in all estrogen-treated groups. Estrogen also induced an enhancement in NO metabolites, nitric oxide synthase activity, and Akt phosphorylation. This study demonstrated that estrogen treatment to ovariectomized rats induced cardioprotection, which was evidenced by reduced blood pressure variability and vascular sympathetic drive. These effects were associated with an improved redox balance and Akt activation, resulting in an enhanced NO bioavailability.

Sexual dimorphism in autonomic changes and in the renin-angiotensin system in the hearts of mice subjected to thyroid hormone-induced cardiac hypertrophy

Based on the relevance of the renin-angiotensin system and the ongoing controversy regarding the role of the sympathetic nervous system in thyroid hormone-induced cardiac hypertrophy, the aim of the present study was to establish whether the putative difference in the degree of cardiac hypertrophy exhibited by males and females might be related to differences in the sympathetic-vagal balance and/or in the cardiac renin-angiotensin system in mice of different genders. Male and female mice (n = 117) were given 0.1 mg kg(-1) of triiodothyronine or normal saline each day for 10 days consecutively. At the end of that period, study of the heart rate variability, spectral analysis and histopathological examination were performed to assess the sympathetic-vagal balance and the diameter of cardiomyocytes. The cardiac levels of angiotensin I and II were also measured. Treatment with triiodothyronine induced a greater degree of cardiac hypertrophy in male (~73%) than in female mice (~42%). This difference was attributed to greater modulation of the sympathetic nervous system and higher levels of angiotensin I and II in male than in female mice. Our data indicate that thyroid hormone-induced cardiac hypertrophy was more intense in male mice due to the synergic effect of the sympathetic nervous system and the cardiac renin-angiotensin system.

Regulation of endothelial nitric oxide synthase and high-density lipoprotein quality by estradiol in cardiovascular pathology

Estrogens have been recognized, in the last 3 decades, as important hormones in direct and indirect modulation of vascular health. In addition to their direct benefit on cardiovascular health, the presence of esterified estrogen in the lipid core of high-density lipoprotein (HDL) particles indirectly contributes to atheroprotection by significantly improving HDL quality and functionality. Estrogens modulate their physiological activity via genomic and nongenomic mechanisms. Genomic mechanisms are thought to be mediated directly by interaction of the hormone receptor complex with the hormone response elements that regulate gene expression. Nongenomic mechanisms are thought to occur via interaction of the estrogen with membrane-bound receptors, which rapidly activate intracellular signaling without binding of the hormone receptor complex to its hormone response elements. Estradiol in particular mediates early and late endothelial nitric oxide synthase (eNOS) activation via interaction with estrogen receptors through both nongenomic and genomic mechanisms. In the vascular system, the primary endogenous source of nitric oxide (NO) generation is eNOS. Nitric oxide primarily influences blood vessel relaxation, the heart rate, and myocyte contractility. The abnormalities in expression and/or functions of eNOS lead to the development of cardiovascular diseases, both in animals and in humans. Although considerable research efforts have been dedicated to understanding the mechanisms of action of estradiol in regulating cardiac eNOS, more research is needed to fully understand the details of such mechanisms. This review focuses on recent findings from animal and human studies on the regulation of eNOS and HDL quality by estradiol in cardiovascular pathology.

Antiatherosclerotic potential of clopidogrel: antioxidant and anti-inflammatory approaches

Background. Atherosclerosis is characterized by endothelial dysfunction, vascular inflammation, and the buildup of lipids, cholesterol, calcium, and cellular debris within the intima of the walls of large and medium size arteries. Objective. To evaluate the effect of clopidogrel on atherosclerosis progression. Materials and Methods. A total of 28 local domestic rabbits were assigned to four groups: normal control, atherogenic control, vehicle control, and clopidogrel treated. Serum triglycerides, total cholesterol, HDL-C, plasma high sensitive C-reactive protein (hsCRP), plasma malondialdehyde (MDA), and plasma reduced glutathione (GSH) were measured at the end of the experiment. Immunohistochemical of aortic atherosclerotic changes were also performed. Results. There was no statistically significant difference between atherogenic control group and vehicle group. Levels of lipid profile, atherogenic index, hsCRP, and MDA are increased while GSH levels were decreased in animals on atherogenic diet. Immunohistochemical analysis showed that aortic expressions of VCAM-1, MCP-1, TNF-α, and IL-17A were significantly increased in atherogenic control group. Histopathologic finding showed that animals on atherogenic diet have significant atherosclerotic lesion. Compared to atherogenic control group clopidogrel do not have significant effect on lipid profile. Clopidogrel significantly reduces hsCRP and MDA levels and increases GSH level. Furthermore, clopidogrel treatment significantly reduced aortic expressions parameters and the histopathologic examination of the aortic arch showed a significant reduction of atherosclerotic lesion. Conclusions. This study outlines how clopidogrel reduces lipid peroxidation, systemic inflammation, and aortic expression of inflammatory markers and hence reduces the progression of atherosclerosis.

Gender differences in microcirculation: observation using the hamster cheek pouch

OBJECTIVES

Estrogen has been shown to play an important protective role in non-reproductive systems, such as the cardiovascular system. Our aim was to observe gender differences in vivo with regard to the increase in macromolecular permeability and leukocyte-endothelium interaction induced by ischemia/reperfusion as well as in microvascular reactivity to vasoactive substances using the hamster cheek pouch preparation.

METHODS

Thirty-six male and 36 female hamsters, 21 weeks old, were selected for this study, and their cheek pouches were prepared for intravital microscopy. An increase in the macromolecular permeability of post-capillary venules was quantified as a leakage of intravenously injected fluorescein-labeled dextran, and the leukocyte-endothelium interaction was measured as the number of fluorescent rolling leukocytes or leukocytes adherent to the venular wall, labeled with rhodamin G, during reperfusion after 30 min of local ischemia. For microvascular reactivity, the mean internal diameter of arterioles was evaluated after the topical application of different concentrations of two vasoconstrictors, phenylephrine (α1-agonist) and endothelin-1, and two vasodilators, acetylcholine (endothelial-dependent) and sodium nitroprusside (endothelial-independent).

RESULTS

The increase in macromolecular permeability induced by ischemia/reperfusion was significantly lower in females compared with males [19 (17-22) leaks/cm2 vs. 124 (123-128) leaks/cm2, respectively, p<0.001), but the number of rolling or adherent leukocytes was not different between the groups. Phenylephrine-induced arteriolar constriction was significantly lower in females compared with males [77 (73-102)% vs. 64 (55-69)%, p<0.04], but there were no detectable differences in endothelin-1-dependent vasoreactivity. Additionally, arteriolar vasodilatation elicited by acetylcholine or sodium nitroprusside did not differ between the groups.

CONCLUSION

The female gender could have a direct protective role in microvascular reactivity and the increase in macromolecular permeability induced by ischemia/reperfusion.

Sexual dimorphism in rat aortic endothelial function of streptozotocin-induced diabetes: possible involvement of superoxide and nitric oxide production

Little is known of the interactions between diabetes and sex hormones on vascular function. The objectives of this study were to investigate whether there were sex differences in rat aortic endothelial function one week after the induction of streptozotocin (STZ)-diabetes, and to examine the potential roles of superoxide and nitric oxide (NO) in this sex-specific effect. Endothelium-dependent vasodilatation to acetylcholine (ACh) was measured in rat aortic rings before and after treatment with MnTMPyP (25µM), a superoxide dismutase. Contractile responses to phenylephrine (PE) were generated before and after treatment with l-NAME (200μM), a nitric oxide synthase (NOS) inhibitor. The mRNA expression of NADPH oxidase (Nox) and endothelial nitric oxide synthase (eNOS) were also determined. We demonstrated that (1) STZ-diabetes impaired endothelium-dependent vasodilatation to ACh to a greater extent in female than male aortae, (2) inhibition of superoxide enhanced sensitivity to ACh only in diabetic females, and (3) Nox1 and Nox4 mRNA expression were significantly elevated only in aortic tissue of diabetic females. Furthermore, incubation of aortic rings with l-NAME potentiated PE responses in all groups, but aortae from control females showed a greater potentiation of the PE response after NOS inhibition compared with others. STZ-diabetes reduced the extent of PE potentiation after l-NAME and the aortic eNOS mRNA expression in females to the same levels as seen in males. These data suggest that a decrease in NO, resulting from either decreased eNOS or elevated superoxide, may partially contribute to the predisposition of the female aorta to injury early in diabetes.

Ovariectomy reinstates the infarct size-limiting effect of postconditioning in female rabbits

Gender seems to interfere with the cardioprotective effect of ischemic preconditioning (PreC) and postconditioning (PostC); PreC-conferred protection is weaker or lost in female animals after ovariectomy (Ov), while the role of PostC is still in dispute. We sought to investigate the effect of PostC in female rabbits, its interaction with Ov, and the potential implicated intracellular pathways. Intact or Ov adult female rabbits (n = 46) were subjected to 30 min ischemia and reperfusion with PostC (PostC or OvPostC), which consisted of six cycles of 30-s ischemia/30-s reperfusion at the end of ischemia, or without PostC (Fem or OvFem). Infarct size (I) and area at risk (R) were determined by TTC staining and fluorescent particles, respectively, after 3-h reperfusion in 30 out of 46 animals. Plasma levels of estradiol and nitrite/nitrate (NO x ) were evaluated. ERKs, p38-MAPK, and Akt assessment was performed in excised hearts 1-min after starting the final reperfusion period in the remaining 16 animals. Infarct size was significantly reduced only in OvPostC group (I/R ratio, 25.3 ± 2.7, vs 48.1 ± 2.0, 43.6 ± 4.2 and 55.1 ± 5.6 % in Fem, OvFem, and PostC groups, p < 0.05). In ovariectomized rabbits, plasma estradiol and NO x levels were lower than in the normal ones. Akt phosphorylation in ischemic regions was significantly higher in OvPostC group, whereas ERK1/2 and p38-MAPK activation was observed in all ovariectomized animals irrespective of PostC. PostC is not effective in female rabbits, but the protection is reinstated after Ov potentially via the RISK pathway.

Increased estrogen receptor alpha in experimental aortic aneurysms in females compared with males

BACKGROUND

Estrogen receptor alpha (ERα) has been identified in the vessel wall, offering vasoprotective effects when upregulated. Estrogens are known to mediate the inflammatory milieu, and inflammation has long been associated with abdominal aortic aneurysm (AAA) formation. Therefore, it is theorized that increased estrogen receptor in females contributes to their relative resistance to AAAs. The objective of this study was to determine gender differences in ERα levels during experimental AAA formation.

METHODS

Infrarenal aortas of male and female C57 mice (n = 18 and n = 16, respectively) were infused with 0.4% elastase. Diameters were measured at days 0 and 14. Aortic messenger RNA expression of ERα was determined on day 3 by reverse transcription-polymerase chain reaction, whereas ERα protein levels were measured via Western blot. Immunohistochemistry using rabbit antibody for ERα was performed on day 14 samples and quantified. Zymography was done for matrix metalloproteinases (MMP)2 and 9 activity levels. Samples of human AAAs were collected and Western blot performed. Data were compared for significance using a student t-test.

RESULTS

Infrarenal aortic diameter increased in elastase-perfused males (ME) by 80% at 14 days after perfusion, whereas females (FE) increased by only 35% (P = 0.0012). FE had ×10 greater ERα messenger RNA expression compared with ME at day 3 (P = 0.003). Similarly, ERα protein levels were 100% higher in FE compared with those in ME on day 14 (P = 0.035). ERα protein levels were 80% higher in female human patients with AAA than those in their male counterparts (P = 0.029). ERα visualized via immunohistochemistry was 1.5 fold higher in FE than ME (P = 0.029). MMP2 and 9 activity levels were decreased in female compared with male aortas.

CONCLUSIONS

This study demonstrates an increase in aortic wall ERα in females compared with males that correlates inversely with MMP activity and AAA formation. These findings, coupled with observations that exogenous estrogen inhibits AAA formation in males, further suggest that estrogen supplementation may be important to prevent AAA formation and growth.

NOS inhibition enhances myogenic tone by increasing rho-kinase mediated Ca2+ sensitivity in the male but not the female gerbil spiral modiolar artery

Cochlear blood flow regulation is important to prevent hearing loss caused by ischemia and oxidative stress. Cochlear blood supply is provided by the spiral modiolar artery (SMA). The myogenic tone of the SMA is enhanced by the nitric oxide synthase (NOS) blocker L-N^G-Nitro-Arginine (LNNA) in males, but not in females. Here, we investigated whether this gender difference is based on differences in the cytosolic Ca²⁺ concentration and/or the Ca²⁺ sensitivity of the myofilaments. Vascular diameter, myogenic tone, cytosolic Ca²⁺, and Ca²⁺ sensitivity were evaluated in pressurized SMA segments isolated from male and female gerbils using laser-scanning microscopy and microfluorometry. The gender difference of the LNNA-induced tone was compared, in the same vessel segments, to tone induced by 150 mM K⁺ and endothelin-1, neither of which showed an apparent gender-difference. Interestingly, LNNA-induced tone in male SMAs was observed in protocols that included changes in intramural pressure, but not when the intramural pressure was held constant. LNNA in male SMAs did not increase the global Ca²⁺ concentration in smooth muscle cells but increased the Ca²⁺ sensitivity. This increase in the Ca²⁺ sensitivity was abolished in the presence of the guanylyl cyclase inhibitor ODQ or by extrinsic application of either the nitric oxide (NO)-donor DEA-NONOate or the cGMP analog 8-pCPT-cGMP. The rho-kinase blocker Y27632 decreased the basal Ca²⁺ sensitivity and abolished the LNNA-induced increase in Ca²⁺ sensitivity in male SMAs. Neither LNNA nor Y27632 changed the Ca²⁺ sensitivity in female SMAs. The data suggest that the gender difference in LNNA-induced tone is based on a gender difference in the regulation of rho-kinase mediated Ca²⁺ sensitivity. Rho-kinase and NO thus emerge as critical factors in the regulation of cochlear blood flow. The larger role of NO-dependent mechanisms in male SMAs predicts greater restrictions on cochlear blood flow under conditions of impaired endothelial cell function.

Nitric oxide function in atherosclerosis

Atherosclerosis is a chronic inflammatory process in the intima of conduit arteries, which disturbs the endothelium-dependent regulation of the vascular tone by the labile liposoluble radical nitric oxide (NO) formed by the constitutive endothelial nitric oxide synthase (eNOS). This defect predisposes to coronary vasospasm and cardiac ischaemia, with anginal pain as the typical clinical manifestation. It is now appreciated that endothelial dysfunction is an early event in atherogenesis and that it may also involve the microcirculation, in which atherosclerotic lesions do not develop. On the other hand, the inflammatory environment in atherosclerotic plaques may result in the expression of the inducible NO synthase (iNOS) isozyme. Whether the dysfunction in endothelial NO production is causal to, or the result of, atherosclerotic lesion formation is still highly debated. Most evidence supports the hypothesis that constitutive endothelial NO release protects against atherogenesis e.g. by preventing smooth muscle cell proliferation and leukocyte adhesion. Nitric oxide generated by the inducible isozyme may be beneficial by replacing the failing endothelial production but excessive release may damage the vascular wall cells, especially in combination with reactive oxygen intermediates.

Migraine in women: the role of hormones and their impact on vascular diseases

Migraine is a predominantly female disorder. Menarche, menstruation, pregnancy, and menopause, and also the use of hormonal contraceptives and hormone replacement treatment may influence migraine occurrence. Migraine usually starts after menarche, occurs more frequently in the days just before or during menstruation, and ameliorates during pregnancy and menopause. Those variations are mediated by fluctuation of estrogen levels through their influence on cellular excitability or cerebral vasculature. Moreover, administration of exogenous hormones may cause worsening of migraine as may expose migrainous women to an increased risk of vascular disease. In fact, migraine with aura represents a risk factor for stroke, cardiac disease, and vascular mortality. Studies have shown that administration of combined oral contraceptives to migraineurs may further increase the risk for ischemic stroke. Consequently, in women suffering from migraine with aura caution should be deserved when prescribing combined oral contraceptives.

Protection of estrogen in portal hypertension gastropathy: an experimental model

CONTEXT

Portal hypertension is a complication secondary to cirrhosis that is characterized by increased blood flow and/or vascular resistance in the portal system, causing the appearance of a hyperdynamic collateral circulation. Partial portal vein ligation is an experimental model used in rats to study the pathophysiological mechanisms involved in pre-hepatic portal hypertension. Estrogen E2 is an antioxidant molecule with various physiological actions.

OBJECTIVES

To evaluate the antioxidant activity of endogenous estrogen in an experimental model of partial portal vein ligation by comparing intact with castrated rats.

METHODS

Twenty Wistar rats, weighing on average 250 g were used and divided into four groups: sham-operated (SO); intact (I) with partial portal vein ligation (I + PPVL), castrated (C) and castrated with partial ligation of the vein (C + PPVL). Day 1: castration or sham-operation; day 7, PPVL surgery; on day 15 post-PPVL, portal pressure in the mesenteric vein of rats was measured on polygraph Letica. Lipid peroxidation in the stomach was assessed using the technique of thiobarbituric acid reactive substances and activity of antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase. Statistical analysis was done with ANOVA - Student-Newman-Keuls (mean ± SE), and P<0.05 was considered as significant.

RESULTS

Portal pressure was significantly increased in C + PPVL as compared to the other groups. There was no significant difference in the group of intact rats. TBARS showed significant damage in C and C + PPVL in relation to others. Antioxidant enzymes were significantly increased in the castrated rats with subsequent PPVL as compared to the other groups.

CONCLUSION

We suggest that estrogen E2 plays a protective role in intact compared with castrated rats because it presents hydrophenolic radicals in its molecule, thus acting as an antioxidant in this experimental model.

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.

Mechanisms underlining gender differences in Phenylephrine contraction of normoglycaemic and short-term Streptozotocin-induced diabetic WKY rat aorta

The female gender reduces the risk, but succumbs more to cardiovascular disease. The hypothesis that short-term (8weeks) Streptozotocin-induced diabetes could produce greater female than male vascular tissue reactivity and the mechanistic basis were explored. Aortic ring responses to Phenylephrine were examined in age- and sex-matched normoglycaemic/diabetic rats. The normoglycaemic male tissue contracted significantly more than the normoglycaemic female and the male/female diabetic tissues. Endothelial-denudation, l-NAME or MB reversed these differences suggesting an EDNO-cGMP dependence. 17β-oestradiol exerted relaxant effect on all endothelium-denuded (and normoglycaemic endothelium-intact male) tissues, but not endothelium-intact normoglycaemic female. The greater male tissue contraction is attributable to absent 17β-oestradiol-modulated relaxation. Indomethacin blockade of COX attenuated male normoglycaemic and female diabetic tissue contraction (both reversed by l-NAME), but augmented diabetic male tissue contraction. These data are consistent with the raised contractile TXA(2) and PGE(2) in normoglycaemic male and diabetic female tissues, and the relaxant PGI(2) in diabetic male (and female). The higher levels of PGI(2) in the normoglycaemic and diabetic female perhaps explain their greater relaxant response to Acetylcholine compared to the respective male. In conclusion, there is an endothelium-dependent gender difference in the effect of short term diabetes on vascular tissue reactivity which is COX mediated.

Gender difference and change of α(1)-adrenoceptors in the distal mesenteric arteries of streptozotocin-induced diabetic rats

BACKGROUND

The purpose of this study was to evaluate the gender-related changes in the function and distribution of α(1)-adrenoceptors in the distal mesenteric artery of streptozotocin (STZ)-induced diabetic rats at the level of α(1)-adrenoceptor subtypes.

METHODS

Diabetes was induced by intravenous injection of STZ in a dose of 60 mg/kg through the tail vein in 8 week-old male or female Sprague-Dawley rats (n = 13/group). Age-matched normal rats (n = 15) were used as a control group. Four weeks after STZ injection, the change in mean arterial pressure caused by a 45° tilting was recorded. The α(1)-adrenoceptor subtypes mediating contractions of the distal mesenteric artery were investigated using the agonist, phenylephrine as well as subtype-selective antagonists including prazocin, 5-methylurapidil, and BMY 7378. The expression of α(1)-adrenoceptor subtypes of each artery was examined by immunofluorescence staining and western blotting using subtype selective antibodies.

RESULTS

Compared with normal male rats, the contractile response to phenylephrine was decreased in the distal mesenteric artery in normal female rats. Moreover, a decrease in contractile force was observed in STZ-induced diabetic rats compared with age-matched controls. Western blotting revealed that there was the difference between normal male and female rats in manifestation of the α(1D)-adrenoceptor. In STZ-induced male and female diabetic rats, all α(1)-adrenoceptor subtypes were decreased in distal mesenteric arteries, compared with normal rats.

CONCLUSIONS

There was the gender-related functional difference of α(1)-adrenoceptors in normal rats. In both male and female rats, diabetes decreased the contractile response in mesenteric arteries, which might be caused by the overall change in α(1)-adrenoceptor.

Akt/eNOS pathway activation in endothelium-dependent relaxation is preserved in aortas from female, but not from male, type 2 diabetic mice

Cardiovascular problems are major causes of morbidity and mortality, the main problems being coronary artery disease and atherosclerosis, in type 2 diabetes mellitus. However, female gender is a protective factor in the development of, for example, atherosclerosis and hypertension. Our aim was to investigate possible gender differences in the activation of Akt/eNOS signaling in aortas from a mouse type 2 diabetic model. Nonfasting plasma glucose was significantly above control in the diabetic mice (both males and females). Plasma insulin was not different between the age-matched controls and the diabetic mice (of either gender). In diabetic males (vs male controls and/or diabetic females): (a) systemic blood pressure was elevated, (b) the clonidine- and insulin-induced Akt-dependent aortic relaxations were impaired, but the ACh-induced Akt-independent and SNP-induced endothelium-independent aortic relaxations were not, (c) Akt and eNOS expression levels were lower, (d) both Akt phosphorylation at Ser(473) and eNOS phosphorylation at Ser(1177) in the aorta were lower under clonidine- or insulin-stimulation, but not under ACh-stimulation. These results suggest that in mice: (i) endothelial functions mediated via the Akt/eNOS pathway are abrogated in type 2 diabetes only in males and (ii) in females (vs males), eNOS expression is elevated and the endothelium resists dysfunction.

Aging and estrogen alter endothelial reactivity to reactive oxygen species in coronary arterioles

Endothelium-dependent, nitric oxide (NO)-mediated vasodilation can be impaired by reactive oxygen species (ROS), and this deleterious effect of ROS on NO availability may increase with aging. Endothelial function declines rapidly after menopause, possibly because of loss of circulating estrogen and its antioxidant effects. The purpose of the current study was to determine the role of O(2)(-) and H(2)O(2) in regulating flow-induced dilation in coronary arterioles of young (6-mo) and aged (24-mo) intact, ovariectomized (OVX), or OVX + estrogen-treated (OVE) female Fischer 344 rats. Both aging and OVX reduced flow-induced NO production, whereas flow-induced H(2)O(2) production was not altered by age or estrogen status. Flow-induced vasodilation was evaluated before and after treatment with the superoxide dismutase (SOD) mimetic Tempol (100 μM) or the H(2)O(2) scavenger catalase (100 U/ml). Removal of H(2)O(2) with catalase reduced flow-induced dilation in all groups, whereas Tempol diminished vasodilation in intact and OVE, but not OVX, rats. Immunoblot analysis revealed elevated nitrotyrosine with aging and OVX. In young rats, OVX reduced SOD protein while OVE increased SOD in aged rats; catalase protein did not differ in any group. Collectively, these studies suggest that O(2)(-) and H(2)O(2) are critical components of flow-induced vasodilation in coronary arterioles from female rats; however, a chronic deficiency of O(2)(-) buffering by SOD contributes to impaired flow-induced dilation with aging and loss of estrogen. Furthermore, these data indicate that estrogen replacement restores O(2)(-) homeostasis and flow-induced dilation of coronary arterioles, even at an advanced age.

The role of insulin growth factor on atherosclerosis and endothelial function: the effect on hyperlipidemia and aging

AIMS

Insulin/insulin-like growth factor (IGF-1) signaling is important for a variety of age-related processes. However, whether or not it affects atherosclerosis is unknown.

MAIN METHODS

Six groups of 6 male New Zealand white rabbits were treated for 12 weeks under the following conditions: Groups YC and YIGF: Young rabbits (10 weeks old) were fed regular chow w/wo IGF-1(Somazon 0.1 mg/kg/day, s.c.). Groups HC and HIGF: young rabbits were fed HCD (0.5% cholesterol plus regular chow) w/wo IGF-1. Groups OC and OIGF: old rabbits (120 weeks old) were fed regular chow w/wo IGF-1.

KEY FINDINGS

Plasma lipid levels, endothelial responses and morphological findings did not differ between groups YIGF and YC. Animals in group HC had increased plasma lipid levels and atheromas. In group HIGF, IGF led to atheromas with increased plasma insulin growth factor binding protein 3 (IBP3), inducible nitric oxide synthase(iNOS) expression and nitrotyrosine staining, macrophage staining, SM1 staining and SM embryo staining compared to HC. Basal nitric oxide (NO) release evaluated by plasma NO metabolites (NOx) and cGMP levels were lowest in the HIGF group.

SIGNIFICANCE

Overall, IGF-1 promoted atherosclerosis by affecting endothelial function and aging. These findings indicate that Insulin/IGF1 may contribute to atherogenesis in the elderly.

Estrogen and oxidative stress: A novel mechanism that may increase the risk for cardiovascular disease in women

Although early studies demonstrated that exogenous estrogen lowered a woman's risk of cardiovascular disease, recent trials indicate that HRT actually increases the risk of coronary heart disease or stroke. However, there is no clear explanation for this discrepancy. Is estrogen a helpful or a harmful hormone in terms of cardiovascular function? This review discusses some recent findings that propose a novel mechanism which may shed significant light upon this controversy. We propose that nitric oxide synthase (NOS) expressed within the vascular wall is a target of estrogen action. Under normal conditions in younger women, the primary product of estrogen action is NO, which produces a number of beneficial effects on vascular biology. As a woman ages, however, there is evidence for loss of important molecules essential for NO production (e.g., tetrahydrobiopterin, l-arginine). As these molecules are depleted, NOS becomes increasingly "uncoupled" from NO production, and instead produces superoxide, a dangerous reactive oxygen species. We propose that a similar uncoupling and reversal of estrogen response occurs in diabetes. Therefore, we propose that estrogen is neither "good" nor "bad", but simply stimulates NOS activity. It is the biochemical environment around NOS that will determine whether estrogen produces a beneficial (NO) or deleterious (superoxide) product, and can account for this dual and opposite nature of estrogen pharmacology. Further, this molecular mechanism is consistent with recent analyses revealing that HRT produces salutary effects in younger women, but mainly increases the risk of cardiovascular dysfunction in older postmenopausal women.

Gender discrimination in the influence of hyperglycemia and hyperosmolarity on rat aortic tissue responses to insulin

Hyperglycaemia initiates endothelial dysfunction causing diabetic macro- and micro-vasculopathy, the main causes of morbidity and mortality in diabetes mellitus. The vasculopathy exhibits gender peculiarities. We therefore explored gender differences in comparing the effects of hyperglycaemia (50 mM) per se with its hyperosmolar (50 mM) effects on vascular tissue responses to insulin. Endothelium-intact or denuded thoracic aortic rings from age-matched male and female Sprague-Dawley rats were incubated for 10 min or 6 h (acute versus chronic exposure) in normal, hyperglycaemic or hyperosmolar Krebs solution. Relaxant responses to insulin (6.9x10(-7)-6.9x10(-5) M) of the phenylephrine-contracted tissues were recorded. Endothelium denudation in both genders inhibited relaxation to insulin in all conditions, more significantly in female than in male tissues, suggesting the female response to insulin is more endothelium-dependent than the male. Acutely and chronically exposed normoglycemic endothelium-intact or -denuded tissues responded similarly to insulin. Chronic hyperglycemic or hyperosmolar exposure did not alter the endothelium-denuded tissue responses to insulin, whereas the responses of the endothelium-intact male and female hyperosmolar, and male hyperglycemic tissues were enhanced. The results show that insulin exerts an endothelium-dependent and independent relaxation with the female tissue responses more endothelium-dependent than the male. The data also suggest that hyperosmolarity per se enhances aortic tissue relaxant responses to insulin whereas hyperglycemia per se inhibits the same and more so in female than male tissues. These effects are endothelium-dependent.

Gender-specific effects of caloric restriction on the balance of vascular nitric oxide and superoxide radical

AIMS

Caloric restriction (CR) and female gender attenuate oxidative damage and improve vascular endothelium-dependent relaxation (EDR). Multiple mechanisms that ameliorate vascular O(2)(*-) could enhance the NO(*)/O(2)(*-) balance and thus improve EDR. The aim of this study is to compare the effects of short-term (2 weeks) CR and gender on molecular mechanisms involved in NO(*)/O(2)(*-) balance and EDR.

METHODS AND RESULTS

Wistar rats (8 weeks old) of both genders were fed ad libitum (control) or were subjected to CR (60% of food intake of controls) for 2 weeks. Plasma levels of NO(*), insulin, and ghrelin, EDR, vascular NO(*) and O(2)(*-) production, as well as endothelial NO(*) synthase (eNOS) and NADPH oxidase (Nox) expression were examined and analysed. CR improved EDR and vascular NO(*) levels and ameliorated NADPH-sensitive O(2)(*-) production in male rats more than in females. Both CR and female gender reduced mRNA expression of Nox1 and Nox p22phox (p22phox); however, CR reduced Nox4 and p47phox only in males. Protein expression studies showed that CR enhanced eNOS and reduced Nox4 only in males.

CONCLUSION

Short-term CR improved the NO(*)/O(2)(*-) balance by lowering vascular O(2)(*-) production through decreased expression of Nox in males, thus enhancing bioactive NO(*) levels and EDR. In this regard, CR shifted the state of vascular NO(*)/O(2)(*-) balance in males to a state similar to that in females.

Possibility of the regression of atherosclerosis through the prevention of endothelial senescence by the regulation of nitric oxide and free radical scavengers

In the elderly, atherosclerotic diseases such as stroke and myocardial infarction occupy a major part of their causes of death and care. The elderly always have atherosclerosis in their aorta and other arteries and are exposed to risk of attacks. It is the elderly who should receive its safe, harmless and advanced treatment. Advanced stage of atherosclerosis in the elderly is progressed by complicated risk factors such as dyslipidemia and diabetes mellitus and specific risk factors for the elderly, aging (and menopause). Treatment of atherosclerotic disease may need special ones targeted for the elderly. Recent studies reported that frequencies of dyslipidemia were not decreased in the older oldest. In the elderly, impaired glucose tolerance occurs and it progresses atherosclerosis. Endothelial dysfunction like impairment of nitric oxide (NO) bioavailability also progresses atherosclerosis. Although we tried to regress the high cholesterol diet-induced atherosclerosis in rabbit aorta with a normal diet with or without statin, regression could not be achieved. NO targeting gene therapy (adenovirus endothelial nitric oxide synthase [eNOS] gene vector) regressed 20% of atherosclerotic lesions through reduction of lipid contents, however, a more integrated strategy is important for complete regression. We paid attention to NO bioavailability and developed two ways of increasing it in atherosclerosis: citrulline therapy and arginase II inhibition by estrogen. Further, we found a close relation between atherosclerosis and endothelial senescence and that NO can prevent it, especially in a diabetic model. Taken together, regression of atherosclerosis can be achieved by not only regulation of various risk factors but regulation of the cross-talk of NO and free radicals.

The effect of 17 beta-estradiol on intracellular calcium homeostasis in human endothelial cells

The cardiovascular effects of estrogen are mediated in part by augmenting the function of endothelial nitric oxide synthase. Endothelial nitric oxide synthase activity is dependent on many cofactors including Ca(2+). Hence, we investigated the effect of chronic 17 beta-estradiol treatment on the intracellular Ca(2+) concentration and endothelial nitric oxide synthase protein expression in the human endothelial cell line, EA.hy926, using spectrofluorometry and Western blot, respectively. Inhibiting the sarco(endo)plasmic reticulum Ca(2+) ATPase with thapsigargin caused an increase in the intracellular Ca(2+) concentration, which was higher in chronically 17 beta-estradiol-treated (1muM, 24h) cells loaded with Fura-2-acetoxymethyl ester compared to vehicle-treated cells, suggesting a higher endoplasmic reticulum Ca(2+) content in 17 beta-estradiol-treated cells. An enhanced Ca(2+) influx pathway in chronically 17 beta-estradiol-treated cells was also observed. In addition, 17 beta-estradiol-treated cells expressed higher levels of endothelial nitric oxide synthase protein in comparison to vehicle-treated cells. The chronic effect of 17 beta-estradiol on Ca(2+) homeostasis and endothelial nitric oxide synthase expression was attenuated with the nonselective estrogen receptor inhibitor, ICI 182,780 (10muM, 7alpha, 17beta-[9-[(4,4,5,5,5-Pentafluoropentyl)sulfinyl]nonyl] estra-1,3,5(10)-triene-3,17-diol). Furthermore, analysis of the thapsigargin-evoked Ca(2+) response in chronically 17 beta-estradiol-treated estrogen receptor alpha-knockdown cells showed no significant difference in Ca(2+) response compared to vehicle-treated estrogen receptor alpha-knockdown cells, indicating that the regulation of Ca(2+) homeostasis by 17 beta-estradiol is mediated through an estrogen receptor alpha-dependent pathway. These data revealed an estrogen receptor alpha-dependent modulation of Ca(2+) homeostasis accompanying the enhancement of endothelial nitric oxide synthase expression in 17 beta-estradiol-treated human endothelial cells.

The value of phytoestrogens as a possible therapeutic option in postmenopausal women with coronary heart disease

Large epidemiological studies have proved that the risk of coronary heart disease in postmenopausal women can be decreased by oestrogen replacement therapy. The effect is triggered by metabolic processes in the liver (decrease of LDL-cholesterol, increase of HDL-cholesterol) as well as by direct impact on the arterial wall (anti-oxidation, relaxation, anti-proliferation). The therapeutical usage of oestrogens is limited by an increased incidence of breast and endometrial cancer. Cyclic application of progestogens virtually eliminates the risk. Unfortunately, progestogens may antagonise the atheroprotective effect of oestrogens. Structurally modified oestrogens as well as selective oestrogen receptor modulators were investigated in clinical trials. They might provide the desired atheroprotective effects of oestrogen without negative side effects on the mammary gland or the endometrium. In this respect isoflavones also known as phytoestrogens, were analysed. They are widespread and occur naturally in many plants, especially in soy products. Cell culture and animal experiments as well as clinical studies revealed that phytoestrogens such as genistein and daidzein act atheroprotectively in the same way as oestrogen. Effects on the mammary gland or the endometrium could not be detected, but positive side effects on the bone metabolism and the decrease of certain types of cancer could be observed. In total, the therapeutical application of phytoestrogens in postmenopausal women seems to be of real and great benefit. We conclude that in women the risk of death from coronary heart disease increases after the onset of menopause. Recently discovered properties of phyto-oestrogens seem to be of great benefit as they do not seem to have any side effects on the mammary gland and the endometrium which are limiting factors for oestrogen replacement therapy.

The influence of estrogen and progesterone on parasympathetic vasodilatation in the rat submandibular gland

Previous studies suggest that NO- and PGI(2)-independent pathways play a greater role in parasympathetic vasodilatation in the submandibular glands (SMG) of female than of male rats. Thus, the purpose of this study was to determine whether estrogen and progesterone influence the relative contributions of NO and PGI(2) to parasympathetic vasodilatation in the SMG. Vascular responses to chorda-lingual nerve stimulation were examined in sham-operated (SHAM) and ovariectomized (OVX) female rats and in OVX rats treated with either 17beta-estradiol alone or a combination of 17beta-estradiol and progesterone. Compared with SHAM animals, increases in vascular conductance in OVX rats were reduced at 1, 2 and 5 Hz (p<0.05). Blood flow responses in OVX+17beta-estradiol and OVX+17beta-estradiol+progesterone rats were indistinguishable from those observed in SHAM animals. Indomethacin had no effect on vasodilatation in SHAM and OVX+17beta-estradiol rats, but increased vascular responses in OVX animals (p<0.02). The addition of L-NAME resulted in a significant reduction in vasodilatation at all frequencies. In OVX rats treated with both estrogen and progesterone, indomethacin caused a reduction in vasodilatation and L-NAME further diminished the remaining responses. Under all conditions, vasodilatation was due largely, if not exclusively, to direct parasympathetic rather than antidromic sensory nerve activation. Finally, both neuronally-derived and endothelium-derived NO appeared to be responsible for the NO-dependent vasodilatation, but endothelium-derived NO became increasingly important as the frequency of stimulation increased. We conclude that estrogen and progesterone influence parasympathetic vasodilatation through combined effects on NO-, PGI(2)- and non-NO/PGI(2)-mediated pathways.

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.

The role of nitric oxide in female reproduction

The cardiovascular system undergoes profound changes during pregnancy. Maternal intravascular volume begins to increase in the first trimester rising an average of 45% by term.1Cardiac output increases similarly2and is redistributed to organs whose functions are crucial for a successful pregnancy. In the guinea pig, uterine artery (UA) blood flow increases 3500%, while mesenteric and renal artery blood flows increase only 90% and 10% respectively.3Blood flow to the trunk actually diminishes. The mechanism underlying this redistribution is unknown. Coupled with the rise in cardiac output is a decrease in the systemic pressor response to angiotensin II (AII), norepinephrine(NE), and epinephrine.4–8There is also a decrease in the contraction response among some but not all vascular beds. For example, contraction of UA to NE and thromboxane is characteristically reduced by pregnancy, whereas the response of the carotid artery is unaltered8–10Since pregnancy does not alter neuroeffector mechanisms of NE such as release, receptor sensitivity, and accumulation11, changes in sympathetic control during pregnancy must be dependent on alterations at sites other than the neuroeffector junction. We have hypothesized that the mechanisms which alter vascular reactivity during pregnancy also mediate the redistribution of maternal cardiac output.9We have further hypothesized that many of these mechanisms involve endothelium-dependent factors which are modulated by sex hormones.

Need for research on estrogen receptor function: importance for postmenopausal hormone therapy and atherosclerosis

BACKGROUND

Cardiovascular disease is the leading cause of morbidity and mortality in men and women worldwide. Although rare in premenopausal women, its incidence rises sharply after menopause, indicating atheroprotective effects of endogenous estrogens.

OBJECTIVE

This review discusses the differential effects of estrogen receptor function on atherosclerosis progression in pre- and postmenopausal women, including aspects of gender differences in vascular physiology of estrogens and androgens.

METHODS

Recent advances in the understanding of the pathogenesis of atherosclerosis, estrogen receptor function, and hormone therapy are reviewed, with particular emphasis on clinical and molecular issues.

RESULTS

Whether hormone therapy can improve cardiovascular health in postmenopausal women remains controversial. Current evidence suggests that the vascular effects of estrogen are affected by the stage of reproductive life, the time since menopause, and the extent of subclinical atherosclerosis. The mechanisms of vascular responsiveness to sex steroids during different stages of atherosclerosis development remain poorly understood in women and men.

CONCLUSION

In view of the expected increase in the prevalence of atherosclerotic vascular disease worldwide due to population aging, research is needed to determine the vascular mechanism of endogenous and exogenous sex steroids in patients with atherosclerosis. Such research may help to define new strategies to improve cardiovascular health in women and possibly also in men.

Upregulation of estrogen receptor α and mediation of 17β-estradiol vasoprotective effects via estrogen receptor α in basilar arteries in rats after experimental subarachnoid hemorrhage

Object

The authors previously demonstrated that 17β-estradiol benzoate (E2) treatment prevents subarachnoid hemorrhage (SAH)–induced cerebral vasospasm and preserves endothelial nitric oxide synthase (eNOS) in male rats. Changes in the expression of estrogen receptor (ER) subtypes ERα and -β and their roles in the E2-mediated preservation of eNOS in SAH remain unknown. In the present study the effects of SAH on the expression of ERα and -β in the cerebral arteries were clarified, and the receptor roles in the E2-mediated preservation of eNOS expression in SAH were differentiated.

Methods

A 2-hemorrhage SAH model was induced by 2 autologous blood injections into the cisterna magna of adult male rats. The effect of SAH on ERα and -β expression was evaluated. Other rats subcutaneously received implanted Silastic tubes containing corn oil with E2 and daily injections of various doses of an ERα- (methyl-piperidinopyrazole [MPP]) or ERβ-selective antagonist (R,R-tetrahydrochrysene) after the first hemorrhage. The protein levels of ERα, ERβ, eNOS, and inducible nitric oxide synthase (iNOS) from basilar arteries were examined using Western blot analysis, and their mRNAs were evaluated by reverse transcription–polymerase chain reaction.

Results

The ERα but not the ERβ was upregulated in the basilar artery after SAH. Treatment with MPP eliminated E2-mediated effects in SAH, relieved cerebral vasospasm, preserved eNOS expression, and suppressed iNOS expression.

Conclusions

Estrogen receptor α is upregulated in the basilar artery after SAH. Note that E2 exerts its protective effects through ERα-dependent pathways to relieve cerebral vasospasm and preserve eNOS expression. A selective ERα agonist may be the drug of choice for the treatment of patients with SAH.