Cell-surface estrogen receptors mediate calcium-dependent nitric oxide release in human endothelia

Peripheral estradiol induces temporomandibular joint antinociception in rats by activating the nitric oxide/cyclic guanosine monophosphate signaling pathway

Recently, we have reported that high physiological estradiol level during the proestrus phase of the estrous cycle or systemic estradiol administration in ovariectomized rats decreases formalin-induced temporomandibular joint nociception. However, the mechanisms underlying the antinociceptive effect of estradiol are presently unknown. In this study, we used the temporomandibular joint formalin model in rats to investigate whether estradiol decreases nociception by a peripheral non-genomic mechanism, and if so, whether this mechanism is mediated by the activation of the nitric oxide-cyclic guanosine monophosphate signaling pathway and of opioid receptors. The administration of estradiol into the ipsilateral, but not into the contralateral temporomandibular joint significantly reduced formalin-induced temporomandibular joint nociception in ovariectomized and diestrus but not in proestrus females. However, the administration of the estrogen receptor antagonist ICI 182780 into the ipsilateral, but not into the contralateral temporomandibular joint blocked the antinociceptive effect of serum estradiol in proestrus females, suggesting that the physiological effect of estradiol in nociception is mediated, at least in part, by a peripheral mechanism. The administration of estradiol into the ipisilateral temporomandibular joint did not affect formalin-induced nociception in male rats. The antinociceptive effect of temporomandibular joint estradiol administration in ovariectomized and diestrus females was mimicked by estradiol conjugated with bovine serum albumin, which does not diffuse through the plasma membrane, and was blocked by the estrogen receptor antagonist ICI 182780. The administration of the nitric oxide synthase inhibitor (nitro-l-arginine) or of a guanylate cyclase inhibitor (1H-(1,2,4)-oxadiasolo (4,2-a) quinoxalin-1-one) into the ipsilateral, but not into the contralateral temporomandibular joint blocked the antinociceptive effect of estradiol and of estradiol conjugated with bovine serum albumin, while the opioid receptor antagonist naloxone had no effect. These findings suggest that estradiol decreases temporomandibular joint nociception in female rats through a peripheral non-genomic activation of the nitric oxide-cyclic guanosine monophosphate signaling pathway.

Enhancement of vascular relaxation in rat aorta by phytoestrogens from Curcuma comosa Roxb

The present study aims to examine the effects and mechanisms of Curcuma comosa Roxb., an indigenous medicinal plant containing phytoestrogens, on vascular relaxation. Using an organ bath system, acute exposure of intact or endothelium-denuded aortic rings to the hexane extract of C. comosa or an isolated diarylheptanoid compound, D3, did not induce relaxation. However, pre-incubation of aortic rings for 20 min with hexane extract of C. comosa (10 microg/ml) or the isolated diarylheptanoid compound, D3, (0.1, 1 and 10 microg/ml) markedly enhanced endothelial-dependent relaxation in response to ACh. The hexane extract did not modulate the relaxation of denuded aortic rings in response to SNP, which suggested a predominant effect on endothelial cells rather than on vascular smooth muscle cells. Co-incubation with ICI 182,780 (estrogen receptor antagonist), L-NAME (nitric oxide synthase inhibitor) or ODQ (guanylase cyclase inhibitor) inhibited the enhancing effects of C. comosa on ACh-induced relaxation. These findings suggest that the actions of C. comosa are mediated through estrogen receptor (ER) and NO-cGMP-dependent mechanisms. In addition, C. comosa also increased the phosphorylation of serine 1177 eNOS and serine 473 Akt proteins, and these effects were abolished by ICI 182,780. The results suggest that C. comosa acutely increases endothelium-dependent relaxation of aortic rings through the ER-Akt-eNOS pathway. This is the first evidence indicating non-genomic action of a novel phytoestrogen from C. comosa, on vascular relaxation.

Oxidative stress and compartment of gene expression determine proatherosclerotic effects of inducible nitric oxide synthase

Genetic and pharmacological inhibition of inducible nitric oxide synthase (iNOS) decreases atherosclerosis development. Potential proatherogenic effects of iNOS include iNOS mediated oxidative stress and iNOS expression in different cellular compartments. Lesional iNOS can potentially produce nitric oxide radicals (NO), superoxide radicals (O2(-)), or both; these radicals may then react to form peroxynitrite. Alternatively, O2(-) radicals from oxidases co-expressed with iNOS could react with NO to produce peroxynitrite. Therefore, the expression profiles of the genes that modulate the redox system in different iNOS-expressing cell compartments may determine the role of iNOS in atherosclerosis. We used apoE (apoE(-/-)) and apoE/iNOS double knockout (apoE(-/-)/ iNOS(-/-)) mice to assess vascular NO, O2(-), and peroxynitrite formation by electron spin resonance spectroscopy, high performance liquid chromatography, and 3-nitrotyrosine staining. The relevance of the iNOS expressing cell compartment was tested by bone marrow transplantation. We show that iNOS significantly contributes to vascular NO production and itself produces O2(-), leading to peroxynitrite formation in atherosclerotic lesions. Our bone marrow transplantation experiments show that bone marrow derived cells exclusively mediate the proatherosclerotic effects of iNOS in males, while both parenchymal and bone marrow derived iNOS equally contribute to atherosclerosis in females. Moreover, iNOS expression affects vascular remodeling. These findings establish for the first time that the proatherosclerotic effects of iNOS vary with sex in addition to the compartment of its expression.

Estrogen and the Ca2+-mobilizing agonist ATP evoke acute NO synthesis via distinct pathways in an individual human vascular endothelium-derived cell

In this study, we have systematically evaluated the signaling mechanisms underlying stimulated nitric oxide (NO) synthesis by estrogen (E2) and other vasoactive agents at the level of a single endothelium-derived cell. To do so, we have characterized and contrasted rapid E2-evoked NO synthesis with that of ATP using single-cell microfluorimetry and patch-clamp recordings to monitor stimulated changes in cellular NO synthesis (via 4-amino-5-methylamino-2',7'-difluorofluorescein), Ca2+ transients (via Fluo-3), and membrane hyperpolarization in cultured human EA.hy926 cells. E2-evoked NO synthesis in single cells (EC50 approximately 0.3 nM) was blocked by the E2 receptor antagonist ICI 182,780 and the NO synthase inhibitor N(omega)-nitro-l-arginine methyl ester. Although both E2 and ATP stimulated comparable Ca2+ transients, E2-induced NO synthesis was insensitive to intracellular BAPTA-AM or removal of external Ca2+. In contrast, ATP-evoked NO production was abolished by either one of these treatments. ATP-evoked hyperpolarizations ( approximately 20 mV) and NO production were both inhibited by the respective small-conductance and intermediate-conductance calcium- activated K+ channel blockers apamin and charybdotoxin. E2 minimally affected membrane potential, and stimulated NO synthesis was insensitive to calcium-activated K+ channel blockers. Exposure to either the phosphatidylinositol 3-kinase inhibitor LY-294002 or the MAP kinase inhibitor PD-98059 abolished the NO response to E2, but not that to ATP. Finally, the NO response evoked by a combined stimulus of E2 plus ATP was similar to that of ATP alone. In conclusion, our data directly demonstrate that an individual human EA.hy926 cell contains at least two distinct mechanisms for stimulated NO synthesis that depend on either calcium or protein kinase signaling events.

Nitric oxide selective electrodes

Since nitric oxide (NO) was identified as the endothelial-derived relaxing factor in the late 1980s, many approaches have attempted to provide an adequate means for measuring physiological levels of NO. Although several techniques have been successful in achieving this aim, the electrochemical method has proved the only technique that can reliably measure physiological levels of NO in vitro, in vivo, and in real time. We describe here the development of electrochemical sensors for NO, including the fabrication of sensors, the detection principle, calibration, detection limits, selectivity, and response time. Furthermore, we look at the many experimental applications where NO selective electrodes have been successfully used.

The non-genomic crosstalk between PPAR-gamma ligands and ERK1/2 in cancer cell lines

Peroxisome proliferator activated receptors (PPARs) are members of the nuclear receptor superfamily acting as transcription factors. PPAR-gamma, one of the three PPAR subtypes, is expressed in many malignant and non-malignant cells and tissues. PPAR-gamma ligands influence cancer biology via both genomic as well as non-genomic events. The non-genomic action of PPAR-gamma ligands, including the activation of MAPK signaling pathways, is under intense investigation. In the presence of PPAR-gamma ligands, a rapid phosphorylation of ERK1/2 is observed in many cancer cell lines. Activated ERK1/2 elicits rapid, non-genomic cellular effects and can directly repress PPAR-gamma transcriptional activity by phosphorylation. This paper reviews the interrelation of PPAR-gamma ligands and activated ERK1/2, in relation to their antineoplastic actions in cancer cell lines, which may offer the potential for improved anticancer therapies.

Reperfusion injury salvage kinase signalling: taking a RISK for cardioprotection

Following an acute myocardial infarction (AMI), early coronary artery reperfusion remains the most effective means of limiting the eventual infarct size. The resultant left ventricular systolic function is a critical determinant of the patient's clinical outcome. Despite current myocardial reperfusion strategies and ancillary antithrombotic and antiplatelet therapies, the morbidity and mortality of an AMI remain significant, with the number of patients developing cardiac failure increasing, necessitating the development of novel strategies for cardioprotection which can be applied at the time of myocardial reperfusion to reduce myocardial infarct size. In this regard, the Reperfusion Injury Salvage Kinase (RISK) Pathway, the term given to a group of pro-survival protein kinases (including Akt and Erk1/2), which confer powerful cardioprotection, when activated specifically at the time of myocardial reperfusion, provides an amenable pharmacological target for cardioprotection. Preclinical studies have demonstrated that an increasing number of agents including insulin, erythropoietin, adipocytokines, adenosine, volatile anesthetics natriuretic peptides and 'statins', when administered specifically at the time of myocardial reperfusion, reduce myocardial infarct size through the activation of the RISK pathway. This recruits various survival pathways that include the inhibition of mitochondrial permeability transition pore opening. Interestingly, the RISK pathway is also recruited by the cardioprotective phenomena of ischemic preconditioning (IPC) and postconditioning (IPost), enabling the use of pharmacological agents which target the RISK pathway, to be used at the time of myocardial reperfusion, as pharmacological mimetics of IPC and IPost. This article reviews the origins and evolution of the RISK pathway, as part of a potential common cardioprotective pathway, which can be activated by an ever-expanding list of agents administered at the time of myocardial reperfusion, as well as by IPC and IPost. Preliminary clinical studies have demonstrated myocardial protection with several of these pharmacological activators of the RISK pathway in AMI patients undergoing PCI. Through the use of appropriately designed clinical trials, guided by the wealth of existing preclinical data, the administration of pharmacological agents which are known to activate the RISK pathway, when applied as adjuvant therapy to current myocardial reperfusion strategies for patients presenting with an AMI, should lead to improved clinical outcomes in this patient group.

Minireview: estrogen receptor-mediated rapid signaling

In addition to nuclear-initiated (genomic) responses, estrogen receptors (ERs) have the ability to facilitate rapid, membrane-initiated, estrogen-triggered signaling cascades via a plasma membrane-associated form of the receptor. These rapid responses are dependent on assembly of membrane ER-centered multimolecular complexes, which can transduce ligand-activated signals to affect a variety of enzymatic pathways, often occurring in a cell-type-specific fashion with tissue-specific physiological outcomes. In some instances, cross-talk occurs between these membrane-initiated and nuclear responses, ultimately regulating transcriptional activation. The role of splice variants in membrane-initiated estrogen responses has been described, notably those within the vascular endothelium. In this review, we describe the evidence for membrane ERs, the molecular components of the aforementioned signaling complexes and pathways, the relevance of ER splice variants, and ER-mediated responses in specific tissues. Our growing understanding of ER-mediated actions at a molecular level will provide insight into the controversies surrounding hormone replacement therapy in postmenopausal women.

Nongenomic responses to 17beta-estradiol in male rat mesenteric arteries abolish intrinsic gender differences in vascular responses

The aim of the present study was to investigate the gender differences in the acute effects of 17beta-estradiol on the rat superior mesenteric artery. Isometric tension was measured in rings of mesenteric arteries from both male and female Sprague-Dawley rats. Relaxation to acetylcholine was not significantly different between arteries (with endothelium) from male and female rats in the absence or presence of 17beta-estradiol. After blockade of endothelium-dependent hyperpolarizations with apamin (0.3 microM) plus charybdotoxin (0.1 microM), acute exposure to 17beta-estradiol (1 nM) for 30 min resulted in enhancement of relaxation to acetylcholine in arteries from male but not female rats. After acute exposure to 17beta-estradiol, mesenteric arteries from male rats were more sensitive to sodium nitroprusside than arteries from female rats. Contractions of mesenteric arteries to phenylephrine and 9,11-dideoxy-11alpha,9alpha-epoxymethanoprostaglandin F(2alpha) (U46619) were greater in arteries from male rats than female rats. This difference was not detected after acute exposure to 17beta-estradiol. In preparations without endothelium, the enhancement of relaxation and reduction in contraction in arteries from male rats were preserved. These results suggest that there exists a gender difference in the response to the acute nongenomic modulatory effect of 17beta-estradiol in rat mesenteric arteries. Arteries from male rats seem to be more sensitive to the modulatory effects of 17beta-estradiol than arteries from female rats. The effect appears to be mainly at the level of the vascular smooth muscles.

The Isoflavone Equol Mediates Rapid Vascular Relaxation

We recently reported that soy isoflavones increase gene expression of endothelial nitric-oxide synthase (eNOS) and antioxidant defense enzymes, resulting in improved endothelial function and lower blood pressure in vivo. In this study, we establish that equol (1-100 nM) causes acute endothelium- and nitric oxide (NO)-dependent relaxation of aortic rings and rapidly (2 min) activates eNOS in human aortic and umbilical vein endothelial cells. Intracellular Ca2+ and cyclic AMP levels were unaffected by treatment (100 nM, 2 min) with equol, daidzein, or genistein. Rapid phosphorylation of ERK1/2, protein kinase B/Akt, and eNOS serine 1177 by equol was paralleled by association of eNOS with heat shock protein 90 (Hsp90) and NO synthesis in human umbilical vein endothelial cells, expressing estrogen receptors (ER)alpha and ERbeta. Inhibition of phosphatidylinositol 3-kinase and ERK1/2 inhibited eNOS activity, whereas pertussis toxin and the ER antagonists ICI 182,750 and tamoxifen had negligible effects. Our findings provide the first evidence that nutritionally relevant plasma concentrations of equol (and other soy protein isoflavones) rapidly stimulate phosphorylation of ERK1/2 and phosphatidylinositol 3-kinase/Akt, leading to the activation of NOS and increased NO production at resting cytosolic Ca2+ levels. Identification of the nongenomic mechanisms by which equol mediates vascular relaxation provides a basis for evaluating potential benefits of equol in the treatment of postmenopausal women and patients at risk of cardiovascular disease.

Genetic polymorphisms of eNOS, hormone receptor status, and survival of breast cancer

The endothelial cell-specific form of nitric oxide synthase (eNOS) may play an important role in tumor progression via angiogenesis or apoptosis. We studied eNOS -786T > C and 894G > T (Glu298Asp), two functionally significant SNPs, in relation to hazard of breast cancer recurrence or death in 873 women with incident, non-metastatic breast cancer, recruited from two teaching hospitals in Seoul, Korea, 1995-2002. Hazards were estimated by Cox proportional hazard models, in relation to genotype, adjusting for hormone receptor status, lymph node involvement, and tumor size. Women carriers of the eNOS -786C allele had significantly increased hazards of breast cancer recurrence or death, compared with women having the TT genotype (HR = 2.1, 95% CI = 1.03-4.33); risks increased up to 3-fold in ER positive cases (HR = 3.2, 95% CI = 0.95-10.50). The hazard was also increased in eNOS 894T carriers, however, it did not reach statistical significance (HR = 1.8, 95% CI = 0.85-3.93). The combined genotypes containing -786C or 894T was associated with a 2.5-fold risk, compared to the TT-GG genotypes, the most dominant genotype combination (95% CI = 1.29-4.68), with the greatest risks in ER positive cases (HR = 4.9, 95% CI = 1.31-18.36). These results indicate that the eNOS -786C polymorphism, and possibly the 894T polymorphism, are associated with breast cancer recurrence and death, particularly in women with ER positive tumors.

Estrogen down-regulates nicotine-induced adhesion molecule expression via nongenomic signal pathway in endothelial cells

Although gonadal hormone mostly causes genotropic actions through the members of nuclear receptor family, it also can regulate these actions via membrane receptor. To explore the possibility of plasma membrane estrogen receptors (mER) mediating genotropic events, we have investigated estrogen's effect on nicotine-stimulated adhesion molecule expression and evaluated whether this effect depends on calcium, MAPK signal pathway. Fluorescence Spectroscopy analysis of Ca2+ from human umbilical vein endothelial cells (HUVECs) showed through mER, estrogen induced a rapid rise of intracellular free Ca2+ concentration and this rise could not be inhibited by tamoxifen (classic ER inhibitor). In the context of nicotine stimulating, however, estrogen attenuated phosphorylation of mitogen-activated protein kinase (MAPK) family members, extracellular signal regulated kinase 1/2 (ERK1/2), p38 but not c-Jun-N-terminal kinase (JNK) in HUVECs and this effect could not still be prevented by tamoxifen. In the meantime, estrogen also down-regulated surface/soluble vascular cell adhesion molecule (VCAM-1, sVCAM-1) and endothelial selectin (E-selectin, sE-selectin) levels, which was not abolished by tamoxifen either. Moreover, calcium chelator BAPTA, ERK1/2 inhibitor PD98059, p38 inhibitor SB203580 significantly reduced the production of nicotine-activated surface/soluble VCAM-1 and E-selectin and both of the remained levels were no longer regulated by estrogen. Our study here provides the information of decrease effect of mER-mediated estrogen through Ca2+ and ERK1/2, p38 MAPK signaling pathway on nicotine-stimulated expression of surface/soluble VCAM-1 and E-selectin in HUVECs.

Membrane estrogen receptors: genomic actions and post transcriptional regulation

The primary cellular location of the nuclear estrogen receptor II (nER II) is the plasma membrane. A number of reports that have appeared in the recent past indicate that plasma membrane localized estrogen receptor alpha (ERalpha) also exists. Whether the membrane localized ERalpha represents the receptor that binds to the estrogen responsive element (ERE) remains to be known. The mechanisms that underlie the internalization of nER II (non-activated estrogen receptor, deglycosylated) have been identified to a certain extent. The question remains: is the primary location of the ERalpha also the plasma membrane? If that is the case, it will be a challenging task to identify the molecular events that underlie the plasma membrane-to-nucleus movement of ERalpha. The internalization mechanisms for the two 66kDa plasma membrane ERs, following hormone binding, appear to be distinct and without any overlaps. Interestingly, while the major gene regulatory role for ERalpha appears to be at the level of transcription, the nER II has its major functional role in post transcriptional mechanisms. The endoplasmic reticulum associated anchor protein-55 (ap55) that was recently reported from the author's laboratory needs a closer look. It is a high affinity estrogen binding protein that anchors the estrogen receptor activation factor (E-RAF) in an estrogen-mediated event. It will be interesting to examine whether ap55 bears any structural similarity with either ERalpha or ERbeta.

Central and peripheral interactions between endocannabinoids and steroids, and implications for drug dependence

Endocannabinoids are biologically active amides, esters and ether of long chain polyunsaturated fatty acids. They interact with several neurotransmitters in the central nervous system (CNS), and with various signaling molecules (including cytokines) in the periphery. Critical interactions have emerged also with steroids, another group of well-known bioactive lipids, both centrally and peripherally. Here, I briefly review the targets of the combined action of endocannabinoids and steroids, and the available evidence concerning the direct regulation by the latter compounds of the proteins of the endocannabinoid system (ES). In addition, I discuss recent examples of endocannabinoids and steroids working together in the central nervous system and in the periphery, which allowed to disclose some molecular details of the interactions between these two groups of lipids. Taken together, available data suggest that steroids can modulate the endocannabinoid tone, through genomic or nongenomic regulation, and that endocannabinoids can complement the biological activity of steroids. In this line, the issues concerning the tissue- and species-specificity of the endocannabinoid-steroid interface, and the possibility that also endocannabinoids may modulate steroid metabolism, are addressed. Finally, I present the hypothesis that retrograde endocannabinoid signaling, by reducing striatal glutamate release, may be part of the molecular events responsible for the influence of steroids on drug abuse.

Regulation of nitric oxide synthase isoforms by estrogen in the human endometrium

OBJECTIVE

To examine the influence of estrogen on the expression of nitric oxide synthase (NOS) isoforms in human endometrial surface epithelial cell line (HES) and primary endometrial cells.

DESIGN

Laboratory-based investigation.

SETTING

Academic center.

INTERVENTION(S)

The expression of NOS isoform protein levels and mRNA was determined following estrogen/progesterone stimulation.

MAIN OUTCOME MEASURE(S)

NOS protein and mRNA levels in HES and primary endometrial cells.

RESULT(S)

Estradiol 17-beta (E2) induced a dose- and time-dependent increase in the expression of eNOS mRNA and protein and iNOS protein in HES cells which could be blocked by the estrogen receptor antagonist ICI 182,780. Estradiol increased the expression of eNOS mRNA and protein in primary endometrial cells. Estrogen also induced phosphorylation of eNOS which could not be blocked by ICI 182,780. Progesterone in physiologic concentrations augmented the effect of estrogen on the expression of both eNOS and peNOS but not of iNOS. ICI 182,780 in high concentrations stimulated the expression of iNOS protein while inhibiting eNOS.

CONCLUSION(S)

Estradiol through a genomic mechanism stimulates the expression of NOS isoforms in endometrial derived primary and HES cells. This effect is potentiated by progesterone.

Estrogen modulates endothelial and neuronal nitric oxide synthase expression via an estrogen receptor beta-dependent mechanism in hypothalamic slice cultures

Although it is evident that estrogen has important physiological effects in the brain, the signaling mechanisms mediating these effects remain unclear. We recently showed that estrogen mediates attenuated blood pressure responses to psychological stress in ovariectomized female rats through brain nitric oxide (NO). An area likely to mediate these effects is the hypothalamic paraventricular nucleus (PVN), because here NO exerts inhibitory effects on autonomic output to the periphery. Because little is known about how estrogen acts on the NO system in the PVN, our aim was to study the effects of estrogen on the NO system in the PVN of hypothalamic slices cultures. We show that 17beta-estradiol (E2; 1 nm) increases endothelial NO synthase (eNOS) protein expression and decreases the numbers of neuronal NOS (nNOS)-positive neurons in the PVN after 8 and 24 h, respectively. Using the nonselective estrogen receptor (ER) antagonist, ICI 182,780 (10 nm), we determined that E2-induced changes in NOS expression in the PVN are ER dependent. Using the ERbeta agonist, genistein (0.1 microm), we determined that activation of ERbeta induces increased eNOS expression and a decreased number of nNOS-positive neurons. We used the selective ERalpha agonist, propyl-pyrazole-triol (10 nm), and antagonist, methyl-piperidino-pyrazole (1 microm), to exclude the possibility that ERalpha is involved in the E2-induced increase in eNOS and nNOS in the PVN. These results demonstrate that E2 induces changes in NOS expression in the PVN and that these effects are ERbeta dependent.

Acute impairment of contractile responses by 17beta-estradiol is cAMP and protein kinase G dependent in vascular smooth muscle cells of the porcine coronary arteries

The aim of the present study was to investigate the involvement of adenosine 3',5'-cyclic monophosphate (cAMP) cascade in the acute impairment of contraction by 17beta-estradiol in porcine coronary arteries, and to elucidate the signaling pathway leading to the activation of this cascade by the hormone. Isometric tension was recorded in isolated rings of porcine coronary arteries. The contraction to U46619 was reduced significantly following 30 min incubation with 1 nM 17beta-estradiol or 1 nM isoproterenol. There was no additive effect when 17beta-estradiol and isoproterenol were administered together. The effect of 17beta-estradiol was mimicked by both the cyclic AMP analogue 8-Br-cAMP and the guanosine 3',5'-cyclic monophosphate (cyclic GMP) analogue 8-Br-cGMP. In rings with and without endothelium, the modulatory effect of 17beta-estradiol was abolished by the adenylyl cyclase inhibitor, SQ 22536, but was unaffected by the guanylyl cyclase inhibitor, ODQ. Both the cAMP antagonist Rp-8-Br-cAMPS and the cGMP antagonist inhibitor Rp-8-Br-cGMPS inhibited the effect of 17beta-estradiol. The effect of 17beta-estradiol was unaffected by the protein kinase A inhibitor, KT5720, but was abolished by the protein kinase G (PKG) inhibitor, KT5823, which also abolished the effect of isoproterenol. These data support our earlier findings that 17beta-estradiol (1 nM) acutely impairs contractile responses of porcine coronary arteries in vitro. This acute effect of 17beta-estradiol involves cAMP in vascular smooth muscles and the activation of PKG.

Endothelium-dependent dilatory effects of 3α-OH-tibolone in gracilis muscle arterioles of the female Wistar rat

OBJECTIVE

Tibolone is a synthetic steroid used for the treatment of the symptoms of menopause that, once metabolized, has estrogenic, progestogenic, and androgenic properties. We investigated the direct vasodilatory effects of the major active tibolone metabolite 3alpha-OH-tibolone and its sulfated form on female rat skeletal muscle arterioles, which play an important role in the control of blood pressure.

DESIGN

In isolated, pressurized spontaneously constricted arterioles (mean passive diameter 83 +/- 3 microm), we investigated the vasodilatory effect of 3alpha-OH-tibolone and its sulfated form. To study the role of the endothelium and in particular that of nitric oxide, we repeated the experiments with 3alpha-OH-tibolone after removal of the endothelium and on vessels pretreated with the nitric oxide synthesis inhibitor, Nomega-nitro-L-arginine (L-Na). Finally we compared the vasodilatory effect of 3alpha-OH-tibolone with 17beta-estradiol.

RESULTS

A dose-dependent dilatation to 3alpha-OH-tibolone was observed starting at a concentration of 10 M. With the sulfated form of 3alpha-OH-tibolone, dilatation was only present at the highest concentration (10 M). In the denuded vessels, the vasodilatory effect was absent at concentrations from 10 to 10 M. The dilatation induced by 3alpha-OH-tibolone was not significantly reduced by L-Na. The vasodilatory effect of 3alpha-OH-tibolone did not differ from that of 17beta-estradiol.

CONCLUSIONS

3alpha-OH-tibolone has a dose-dependent vasodilatory effect on isolated skeletal muscle arterioles from the rat. The sulfated form has no vasodilatory effect in this setup. This finding suggests that during this short incubation time there was no conversion of the sulfated metabolite into its active form by the vascular endothelium. The vasodilatory effect of 3alpha-OH-tibolone is endothelium dependent at physiologic concentrations and comparable to that of 17beta-estradiol.

Adaptive hypersensitivity to estrogen: mechanisms and clinical relevance to aromatase inhibitor therapy in breast cancer treatment

Breast tumors in women can adapt to endocrine deprivation therapy by developing hypersensitivity to estradiol. For this reason, aromatase inhibitors can be effective in women relapsing after treatment with tamoxifen or following oophorectomy. To understand the mechanisms responsible, we examined estrogenic stimulation of cell proliferation in a model system and provided in vitro and in vivo evidence that long-term estradiol deprivation (LTED) causes "adaptive hypersensitivity". The primary mechanisms responsible involve up-regulation of ER alpha as well as the MAP kinase, PI-3 kinase, and mTOR growth factor pathways. ER alpha is 4-10-fold up-regulated and co-opts a classical growth factor pathway using Shc, Grb2, and Sos. This induces rapid non-genomic effects which are enhanced in LTED cells. Estradiol binds to cell membrane associated ER alpha, physically associates with the adaptor protein Shc, and induces its phosphorylation. In turn, Shc binds Grb2 and Sos which result in the rapid activation of MAP kinase. These non-genomic effects of estradiol produce biologic effects as evidenced by Elk activation and by morphologic changes in cell membranes. Additional effects include activation of PI-3 kinase and mTOR pathways through estradiol induced binding of ER alpha to the IGF-1 and EGF receptors. Further proof of the non-genomic effects of estradiol involved use of "designer" cells which selectively express ER alpha in nucleus, cytosol, and cell membrane. We have used a new downstream inhibitor of these pathways, farnesyl-thio-salicylic acid (FTS), to block proliferation in hypersensitive cells as a model for a potentially effective strategy for treatment of patients.

Estrogen receptor activation of phosphoinositide-3 kinase, akt, and nitric oxide signaling in cerebral blood vessels: rapid and long-term effects

Estrogen receptor regulation of nitric oxide production by vascular endothelium may involve rapid, membrane-initiated signaling pathways in addition to classic genomic mechanisms. In this study, we demonstrate using intact cerebral blood vessels that 17beta-estradiol rapidly activates endothelial nitric-oxide synthase (eNOS) via a phosphoinositide-3 (PI-3) kinase-dependent pathway. The effect is mediated by estrogen receptors (ERs), consistent with colocalization of ERalpha and caveolin-1 immunoreactivity at the plasma membrane of endothelial cells lining cerebral arteries. Treatment with 10 nM 17beta-estradiol for 30 min increased NO production, as measured by total nitrite assay, in cerebral vessels isolated from ovariectomized rats. This effect was significantly decreased by membrane cholesterol depletion with beta-methyl-cyclodextrin, the ER antagonist ICI 182,780 [fulvestrant (Faslodex)], and two inhibitors of PI-3 kinase: wortmannin and LY294002 [2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride]. In parallel with NO production, 17beta-estradiol treatment rapidly increased phosphorylation of both eNOS (p-eNOS) and Akt (p-Akt). PI-3 kinase inhibitors also blocked the latter effects; together, these data are consistent with ER activation of the PI-3 kinase-p-Akt-p-eNOS pathway. ERalpha protein (66 and 50 kDa) coimmunoprecipitated with eNOS as well as with the p85alpha regulatory subunit of PI-3 kinase, further implicating ERalpha in kinase activation of eNOS. Little is known regarding the effects of estrogen on cellular kinase pathways in vivo; therefore, we compared cerebral blood vessels isolated from ovariectomized rats that were either untreated or given estrogen replacement for 4 weeks. Long-term estrogen exposure increased levels of cerebrovascular p-Akt and p-eNOS as well as basal NO production. Thus, in addition to the rapid activation of PI-3 kinase, p-Akt, and p-eNOS, estrogen signaling via nontranscriptional, kinase mechanisms has long-term consequences for vascular function.

Estrogen therapy increases plasma concentrations of nitric oxide metabolites in postmenopausal women but increases flow-mediated vasodilation only in younger women

OBJECTIVE

To evaluate the effect of estrogen therapy (ET) on endothelial nitric oxide (NO) production and in flow-mediated vasodilation (FMV).

DESIGN

Randomized, crossover, double-blind, placebo-controlled study.

SETTING

Healthy postmenopausal women in an academic research environment.

PATIENT(S)

Forty postmenopausal women between 45 and 72 years of age.

INTERVENTION(S)

Women received ET or placebo during two periods of 12 weeks that were separated by 2 weeks of washout.

MAIN OUTCOME MEASURE(S)

Flow-mediated vasodilation, nitrite and nitrate, lipid profile, creatinine, and glucose were measured at weeks 12 and 24. Student's t or Wilcoxon tests were used for comparative analyses, and kappa test and limit analysis determined variability.

RESULT(S)

After placebo treatment, nitrate and nitrite mean concentration was 8.28 +/- 1.17 mmol/L; it increased to 62.6 +/- 12.82 mmol/L after ET. Percentage FMV was 18.8 +/- 2.58 after the placebo period and did not change after ET (20.1 +/- 1.92) in the whole sample, but in the subgroup (n = 15) of younger women (45-50 years of age), percentage FMV increased from 13.6 +/- 3.6 after the placebo period to 22.2 +/- 3.5 after ET.

CONCLUSION(S)

An increase in plasma concentrations of nitrite and nitrate after ET was observed in all the women studied, but the improvement in FMV was observed only in the younger ones. These age-related differences in FMV in response to ET must be further investigated.

Expression of estrogen receptors-alpha and -beta in the pregnant ovine uterine artery endothelial cells in vivo and in vitro

Estrogen is recognized to be one of the driving forces in increases in uterine blood flow through both rapid and delayed actions via binding to its receptors, ER alpha and ER beta at the uterine artery (UA) wall, and especially in UA endothelium (UAE). However, information regarding estrogen receptor (ER) expression in UAE is limited. This study was designed to test whether ERs are expressed in UAE in vivo, and if they are, whether these receptors are maintained in cultured UA endothelial cells (UAECs) in vitro. By using immunohistochemical and Western blot analyses, we clearly demonstrated ER alpha and ER beta protein expression in pregnant (Days 120-130) sheep UA and UAE in vivo and as well as cultured UAECs in vitro. Reverse transcription-polymerase chain reaction (RT-PCR) amplified both ER alpha and ER beta mRNAs in UA, UAE, and UAECs. Of interest, a truncated ER beta (ER beta2) variant due to a splicing deletion of exon 5 of the ER beta gene was detected in these cells. Quantitative RT-PCR analysis revealed that ER alpha mRNA levels are approximately 8-fold (P < 0.01) higher than that of ER beta in UAECs, indicating that ER alpha may play a more important role than ER beta in the UAEC responses to estrogen. Fluorescence immunolabeling analysis showed that ER alpha is present in both nuclei and plasma membranes in UAECs, and the latter is also colocalized with caveolin-1. The membrane and nuclear ER alpha presumably participate in rapid and delayed responses, respectively, to estrogen on UAE. Taken together, our data demonstrated that UAE is a direct target of estrogen actions and that the UAEC culture model we established is suitable for dissecting estrogen actions on UAE.

Membrane associated estrogen receptors and related proteins: localization at the plasma membrane and the endoplasmic reticulum

The female sex steroid, estradiol 17beta, mediates its effect through its association with estrogen receptor present in the target cell. So far the major emphasis has been given to the genomic actions of the hormone mediated by the nuclear estrogen receptors. Recent years have seen a shift in the ideas revealing the existence of estradiol binding entities both in the plasma membrane and the endoplasmic reticulum. Though the true identity of this membrane associated receptors is far from being known, a functional role for the same have been implicated both at the genomic as well as the non-genomic level. The major focus of the review is to highlight the existence of membrane associated estrogen receptors and receptor-related proteins and the functional roles played by some of them. The signalling events exerted by this class of membrane associated estrogen receptor could partly explain the physiological significance of estrogen in cardiovascular disease, osteoporosis and breast cancer as well as the molecular mechanism associated with xenoestrogen action.

Lipids: potential regulators of nitric oxide generation

The endothelium is a dynamic organ that secretes several biologically active substances and plays a major functional role in the health of an organism in both physiological and pathological conditions. For instance, the endothelium is involved in control of the exchange of plasma and tissue biomolecules, regulation of vessel tone, inflammation, lipid metabolism, vessel growth and remodeling, and modulation of coagulation and fibrinolysis. The endothelium generates nitric oxide, which is a key regulator of vasodilation and plays important roles in preventing, or in some cases promoting, numerous cardiovascular diseases. Several recent studies have examined the interplay between lipids and nitric oxide generation, especially in relation to atherosclerosis. The endothelium is continuously exposed to circulating lipids in the form of lipoproteins and protein carriers that may have a direct impact on nitric oxide synthesis and function. The purpose of this review is to illustrate some of the recent findings that link lipids (plasma and cellular) to nitric oxide generation (see Fig. 1).

Vasomodulating potential of mediterranean wild plant extracts

The incidence of cardiovascular disease and endothelial dysfunction is low in the Mediterranean area, where the major proportion of daily calories comes from plant food, high in antioxidant polyphenols. It has been shown that a reduced production or enhanced inactivation of endothelium-derived nitric oxide (NO) is involved in the onset of endothelial dysfunction. We investigated the effects of Mediterranean wild plant, that is, wild artichoke and thyme, phenolic-rich extracts on NO release by porcine aortic endothelial cells (PAECs; by using indirect methods) and by cerebral cell membrane homogenates (by using direct NO detection). NO release by PAECs was significantly potentiated by 234% and 135% by wild artichoke and thyme extracts (10(-6) mol/L), respectively. Direct detection of NO release by brain membranes also showed significantly increased NO production after wild artichoke addition (+35.4%). Further, the release of another vasorelaxant factor by PAECs, that is, prostacyclin, was significantly increased by wild artichoke and thyme (10(-6) mol/L) (+269% and +190%, respectively). Investigation of the mechanism(s) of action of wild artichoke and thyme suggests maintenance of an intracellular reduced environment, as previously shown for ascorbate. Even though these data require in vivo confirmation, they suggest that regular intake of bioactive compounds from Mediterranean wild plants contributes to maintenance of proper vasomotion and to the low incidence of atherosclerosis and endothelial dysfunction recorded in the Mediterranean area.

Estradiol-stimulated nitric oxide release in nervous tissue, vasculature, and gonads of the giant cockroach Blaberus craniifer

The vertebrate system of steroid hormones appears to have been conserved widely throughout the animal kingdom. The sex hormone estrogen, 17-beta-estradiol (E2), long considered to be exclusively a vertebrate hormone, is found also in invertebrates related to reproductive and developmental processes such as spawning, vitellogenesis and molting. These processes are affected by estrogen induced changes at the genomic level and take place at a large time scale. The discovery of surface membrane receptors for E2 has opened new possibilities for the involvement of estrogen in biological functions other than reproductive. These processes take place within a few seconds to minutes and involve sudden cytosolic calcium transients, activation of adenylate cyclase or activation of phospholipase C (PLC). E2 can modulate the production of nitric oxide (NO) in endotheliar and other cells. A similar mechanism linking estrogen to cNOS catalized nitric oxide (NO) release is reported herein for the first time in several tissues of the giant cockroach Blaberus craniifer. This process has been identified in the brain, nerve cord, vasculature and ovaries. This effect is concentration dependent and is inhibited by tamoxifen an estrogen receptor blocker.

Estrogen up-regulates cyclooxygenase-2 via estrogen receptor in human uterine microvascular endothelial cells

OBJECTIVE

To investigate the effects of 17beta-estradiol (E(2)) on cyclooxygenase-2 (COX-2) expression and prostaglandin E(2) (PGE(2)) synthesis in primary human uterine microvascular endothelial cells (HUMEC).

DESIGN

Prospective study.

SETTING

Basic research laboratory at an academic medical center.

PATIENT(S)

Primary HUMEC of three women donors and primary human dermal microvascular endothelial cells of three women donors (as control), purchased from a third-party source.

INTERVENTION(S)

The HUMEC were cultured in specific media in a humidified atmosphere with 5% CO(2) at 37 degrees C.

MAIN OUTCOME MEASURE(S)

Measures of COX-2 mRNA and protein, PGE(2) production, and estrogen receptor alpha and beta mRNA and protein.

RESULT(S)

Treatment with E(2) (10(-10) to 10(-6) M) increased COX-2 mRNA levels by 2.3-fold to 2.4-fold in HUMEC. Treatment of HUMEC with E(2) (10(-8) M) resulted in a time-dependent increase of COX-2 mRNA levels. This was accompanied by a 2.8-fold increase in COX-2 protein level and a 1.5-fold increase in PGE(2) synthesis. Pretreatment of HUMEC with a selective COX-2 inhibitor, NS-398, abolished E(2)-induced PGE(2) synthesis, suggesting that E(2) specifically up-regulates COX-2 activity. The estrogen receptor antagonist ICI 182,780 fully reversed the stimulation of COX-2 mRNA and protein levels and PGE(2) synthesis by E(2). Interestingly, estrogen receptor beta mRNA and protein were abundant in HUMEC, whereas estrogen receptor alpha mRNA or protein was barely detectable.

CONCLUSION(S)

We conclude that various levels of E(2) can significantly increase COX-2 expression and PGE(2) synthesis in HUMEC via the estrogen receptor.

Expression of estrogen receptors in human corpus cavernosum and male urethra

Estrogen, largely produced in testis and adrenal gland, may play important roles in male reproduction. Most of the effects of estrogens are mediated by binding of estrogen to one or both of the two estrogen receptor (ER) subtypes alpha and beta. Recently, they have been described in testis, prostate, and efferent ducts, mostly in rodents. The goal of this study was to prove the evidence of ERs in human corpus cavernosum and male urethra, exploring the protein expression of these receptors by immunohistochemistry. Corpus cavernosum and corpus spongiosum smooth muscle was immunoreactive for the androgen receptor (AR), ER alpha, and strongly for ER beta. Endothelial cells were negative for AR, sporadically positive for ER alpha, and positive for ER beta. Urethral epithelium showed strong nuclear expression of AR, predominantly in the basal cell layer, and nuclear expression of ER alpha in the intermediate cells. ER beta was highly expressed in almost all urethral nuclei and, much more weakly, in cytoplasm. Progesterone receptor (PGR) was negative in all cases and all tissues. These results represent the first report that ER alpha and particularly ER beta are regularly expressed in human penile tissue.

Gender, sex hormones, and vascular tone

The greater incidence of hypertension and coronary artery disease in men and postmenopausal women compared with premenopausal women has been related, in part, to gender differences in vascular tone and possible vascular protective effects of the female sex hormones estrogen and progesterone. However, vascular effects of the male sex hormone testosterone have also been suggested. Estrogen, progesterone, and testosterone receptors have been identified in blood vessels of human and other mammals and have been localized in the plasmalemma, cytosol, and nuclear compartments of various vascular cells, including the endothelium and the smooth muscle. The interaction of sex hormones with cytosolic/nuclear receptors triggers long-term genomic effects that could stimulate endothelial cell growth while inhibiting smooth muscle proliferation. Activation of plasmalemmal sex hormone receptors may trigger acute nongenomic responses that could stimulate endothelium-dependent mechanisms of vascular relaxation such as the nitric oxide-cGMP, prostacyclin-cAMP, and hyperpolarization pathways. Additional endothelium-independent effects of sex hormones may involve inhibition of the signaling mechanisms of vascular smooth muscle contraction such as intracellular Ca2+ concentration and protein kinase C. The sex hormone-induced stimulation of the endothelium-dependent mechanisms of vascular relaxation and inhibition of the mechanisms of vascular smooth muscle contraction may contribute to the gender differences in vascular tone and may represent potential beneficial vascular effects of hormone replacement therapy during natural and surgically induced deficiencies of gonadal hormones.

Estradiol-induced expression of N(+)-K(+)-ATPase catalytic isoforms in rat arteries: gender differences in activity mediated by nitric oxide donors

We tested the hypothesis that previously demonstrated gender differences in ACh-induced vascular relaxation could involve diverse Na(+)-K(+)-ATPase functions. We determined Na(+)-K(+)-ATPase by measuring arterial ouabain-sensitive 86Rb uptake in response to ACh. We found a significant increase of Na+ pump activity only in aortic rings from female rats (control 206 +/- 11 vs. 367 +/- 29 nmol 86Rb/K.min(-1).g wt tissue(-1); P < 0.01). Ovariectomy eliminated sex differences in Na(+)-K(+)-ATPase function, and chronic in vivo hormone replacement with 17beta-estradiol restored the ACh effect on Na(+)-K(+)-ATPase. Because ACh acts by enhancing production of NO, we examined whether the NO donor sodium nitroprusside (SNP) mimics the action of ACh on Na(+)-K(+)-ATPase activity. SNP increased ouabain-sensitive 86Rb uptake in denuded female arteries (control 123 +/- 7 vs. 197 +/- 12 nmol 86Rb/K.min(-1).g wt tissue(-1); P < 0.05). Methylene blue (an inhibitor of guanylate cyclase) and KT-5823 (a cGMP-dependent kinase inhibitor) blocked the stimulatory action of SNP. Exposure of female thoracic aorta to the Na+/K+ pump inhibitor ouabain significantly decreased SNP-induced and ACh-mediated relaxation of aortic rings. At the molecular level, Western blot analysis of arterial tissue revealed significant gender differences in the relative abundance of catalytic isoforms of Na(+)-K(+)-ATPase. Female-derived aortas exhibited a greater proportion of alpha2-isoform (44%) compared with male-derived aortas. Furthermore, estradiol upregulated the expression of alpha2 mRNA in male arterial explants. Our results demonstrate that enhancement of ACh-induced relaxation observed in female rats may be in part explained by 1) NO-dependent increased Na(+)-K(+)-ATPase activity in female vascular tissue and 2) greater abundance of Na(+)-K(+)-ATPase alpha2-isoform in females.

Homocysteine impairs estrogen-induced vasodilation in isolated rat arterioles

OBJECTIVE

Clinical and basic studies have provided evidence that the cardiovascular protective effects of estrogens are partly due to effects on vasoreactivity and changes in homocysteine metabolism. Moreover, homocysteine has also been shown to influence vasoreactivity. We investigated the influence of homocysteine on the rapid vasodilatory effects of estradiol in an isolated vessel setup.

DESIGN

Isolated, spontaneously constricted, gracilis muscle arterioles (diameter approximately 50 micromol/L) from female Wistar rats were cumulatively exposed to 10-10 to 10-4 mol/L 17beta-estradiol in the presence of 50 micromol/L homocysteine or N-nitro-L-arginine (L-NA) (a blocker of nitric oxide synthesis), or both. Control experiments were done without L-NA or homocysteine (n = 6 for each series).

RESULTS

The dose-dependent dilation during short-term exposure to 17beta-estradiol was significantly less or absent in arterioles where L-NA, homocysteine, or both were present. The addition of 50 micromol/L homocysteine significantly increased the spontaneous constriction by 6% to 10%.

CONCLUSIONS

We showed that a pathophysiological concentration of homocysteine increases the spontaneous arteriolar constriction and inhibits the 17beta-estradiol-induced, endothelium-mediated, rapid vasodilatory effect on muscle arterioles from the female rat. The endothelium-independent vasodilation remained unchanged.

Membrane estrogen receptor-dependent extracellular signal-regulated kinase pathway mediates acute activation of endothelial nitric oxide synthase by estrogen in uterine artery endothelial cells

Rapid uterine vasodilatation after estrogen administration is believed to be mediated by endothelial production of nitric oxide (NO) via endothelial NO synthase (eNOS). However, the mechanism(s) by which estrogen activates eNOS in uterine artery endothelial cells (UAEC) is unknown. In this study, we observed that estradiol-17beta (E2) and E2-BSA rapidly (<2 min) increased total NOx production in UAEC in vitro. This was associated with rapid eNOS phosphorylation and activation but was unaltered by pretreatment with actinomycin-D. Estrogen receptor-alpha protein was detectable in isolated plasma membrane proteins by immunoblotting, and E2-BSA-fluorescein isothiocyanate binding was evident on the plasma membrane of UAEC. E2 did not mobilize intracellular Ca2+, but E2 and ionomycin in combination induced greater eNOS phosphorylation than either E2 or ionomycin alone. E2 did not stimulate rapid Akt phosphorylation. E2 stimulated rapid ERK2/1 activation in a time- and dose-dependent manner, with maximal responses observed at 5-10 min with E2 (10 nm to 1 microm) treatment. Acute activation of eNOS and NOx production by E2 could be inhibited by PD98059 but not by LY294002. When E2-BSA was applied, similar responses in NOx production, eNOS, and ERK2/1 activation to those of E2 were achieved. In addition, E2 and E2-BSA-induced ERK2/1 activation and ICI 182,780 could inhibit NOx production by E2. Thus, acute activation of eNOS to produce NO in UAEC by estrogen is at least partially through an ERK pathway, possibly via estrogen receptor localized on the plasma membrane. This pathway may provide a novel mechanism for NO-mediated rapid uterine vasodilatation by estrogen.

High glucose blocks the effects of estradiol on human vascular cell growth: differential interaction with estradiol and raloxifene

Because diabetic women appear not to be protected by estrogen in terms of propensity to cardiovascular disease, we tested the possibility that chronic hyperglycemia modulates the effects of E(2) on vascular cell growth in vitro. Human endothelial cells (E304) and vascular smooth muscle cells (VSMC) were grown in normal glucose (5.5 mmol/l), high glucose (22 mmol/l) or high manitol (22 nmol/l; an osmotic control) for 7 days. In endothelial cells glucose per se stimulated DNA synthesis. However E(2)- (but not RAL-) stimulated [3H] thymidine incorporation was attenuated in the presence of high glucose. In parallel, E(2)-dependent MAP-kinase-kinase activity was blocked in the presence of high glucose. High glucose increased basal creatine kinase (CK) specific activity, but E(2)-stimulated CK was not significantly impaired in the presence of high glucose. In VSMC, high glucose prevented the inhibitory effect of high E(2) (but not of high RAL) concentrations on DNA synthesis. High glucose also prevented E(2)-induced MAP-kinase-kinase activity. In contrast, while high glucose augmented basal CK, the relative E(2)-induced changes were roughly equal in normal and high high glucose media. Hence, high glucose blocks several effects of E(2) on vascular cell growth, which are mediated, in part, via the MAP-kinase system and are likely contributors to E(2)'s anti-atherosclerotic properties. Since RAL's estrogen-mimetic effects on human vascular cell growth were independent of MAP-kinase activation and were not affected by hyperglycemia, the potential use of RAL to circumvent the loss of estrogen function induced by hyperglycemia and diabetes in the human vasculature should be further explored.

Subcellular localization of estrogen receptor β in mouse hippocampus

While estrogen receptors have been known to represent estrogen-dependent transcription factors as part of the nuclear receptor family, a putative membrane-bound form of estrogen receptors has been suggested. Since estrogen receptor beta (ERbeta) is reportedly abundant in the hippocampus and other regions of the central nervous system, subcellular localization of ERbeta in mouse hippocampus was investigated. ERbeta was predominantly found in nuclear, synaptosomal and synaptic membrane fractions, particularly this last fraction. Immunocytochemical investigation using the NG108-15 neuroblastoma-glioma hybridoma cell line indicated that ERbeta is predominantly localized in cell membranes and nuclei. These results suggest that ERbeta localizes on synaptic membranes and may represent an important regulator of intracellular signal transduction from membrane to cytosol in hippocampal neurons.

Resveratrol modulates the phosphoinositide 3-kinase pathway through an estrogen receptor α-dependent mechanism: Relevance in cell proliferation

Resveratrol (RES), a natural phytoalexin, has antiproliferative activity in human-derived cancer cells and in rodent models of tumor development. We have previously shown that RES induced apoptotic death in estrogen-responsive MCF-7 human breast cancer cells. Recent data have indicated that the estrogen receptor-alpha (ERalpha), through interaction with p85, regulates phosphoinositide 3-kinase (PI3K) activity, revealing a physiologic, nonnuclear function of the ERalpha potentially relevant in cell proliferation and apoptosis. In our study, using MCF-7, we have analyzed the ability of RES to modulate the ERalpha-dependent PI3K pathway. Immunoprecipitation and kinase activity assays showed that RES increased the ERalpha-associated PI3K activity with a maximum stimulatory effect at concentrations close to 10 microM; concentrations >50 microM decreased PI3K activity. Stimulation of PI3K activity by RES was ERalpha-dependent since it could be blocked by the antiestrogen ICI 182,780. RES did not affect p85 protein expression but induced the proteasome-dependent degradation of the ERalpha. Nevertheless, the amount of PI3K immunoprecipitated by the ERalpha remained unchanged in presence of RES, indicating that ERalpha availability was not limiting PI3K activity. Phosphoprotein kinase B (pPKB/AKT) followed the pattern of PI3K activity, whereas RES did not affect total PKB/AKT expression. PKB/AKT downstream target glycogen synthase kinase 3 (GSK3) also showed a phosphorylation pattern that followed PI3K activity. We propose a mechanism through which RES could inhibit survival and proliferation of estrogen-responsive cells by interfering with an ERalpha-associated PI3K pathway, following a process that could be independent of the nuclear functions of the ERalpha.

17 beta-Estradiol inhibits angiotensin II activation of area postrema neurons

It is well established that the area postrema, as a circumventricular organ, is susceptible to modulation by circulating hormones and peptides. Furthermore, activation of the area postrema has been shown to modulate central neurons involved in the regulation of cardiovascular function and blood pressure. In particular, the vasoactive peptide angiotensin II (ANG II) has been shown to inhibit baroreflex regulation of heart rate and increase sympathetic outflow and blood pressure via activation of area postrema neurons. Estrogen is thought to protect against hypertension in both humans and animal models and has been shown in a number of systems to alter the effects of ANG II. The purpose of the present study was to determine the effects of estrogen on ANG II activation of area postrema neurons. In this study, the effects of ANG II and KCl on fura 2-measured cytosolic Ca2+ concentration ([Ca2+]i) responses in cultured area postrema neurons in the presence and absence of 12-h exposure to 100 nM 17 beta-estradiol (E2) were evaluated. In neurons incubated in control vehicle media, 50 nM ANG II increased [Ca2+]i by 92 +/- 12%. In neurons preincubated with 100 nM E2, ANG II increased [Ca2+]i by only 68 +/- 11%, for a total inhibition of the ANG II-evoked response of 24%. Coapplication of the estrogen receptor antagonist ICI-182,780 did not inhibit the effects of E2. In the same cells in which the effects of E2 on ANG II-evoked responses were tested, the effects of incubation in E on the depolarization-induced increased [Ca2+2]i due to 60 mM KCl were also tested. Incubation of the cells with 100 nM E increased the KCl-evoked [Ca2+2]i response, and this response was blocked by ICI-182,780. These results suggest that in the area postrema, estrogen may utilize multiple pathways to modulate neural activity and responses to ANG II.

Acute and chronic effects of oestrogen on endothelial tissue-type plasminogen activator release in postmenopausal women

The capacity of vascular endothelium to locally release tissue-type plasminogen activator (t-PA) represents an important endogenous defence mechanism against intravascular fibrin deposition and thrombosis. We determined the influence of chronic and acute oestrogen administration on endothelial t-PA release in postmenopausal women. Sixty-three healthy postmenopausal women were studied: 31 non-users (age 58 +/- 1 years) and 32 users of hormone replacement therapy, including oestrogen alone (ORT: 62 +/- 2 years; n = 15) and in combination with progesterone (HRT: 57 +/- 1 years; n = 17). Net endothelial t-PA release was determined in vivo, in response to intrabrachial infusions of bradykinin and sodium nitroprusside. To examine the acute effects of oestrogen on endothelial t-PA release, bradykinin and sodium nitroprusside dose-response curves were repeated in the presence of 17 beta-oestradiol in 20 of the 31 non-users. Net endothelial release of t-PA was ~30 % higher (P < 0.01) in women taking ORT (from 2.0 +/- 1.0 to 83.6 +/- 9.2 ng (100 ml tissue)-1 min-1) compared with those taking HRT (from 1.4 +/- 0.4 to 63.5 +/- 5.6 ng (100 ml tissue)-1 min-1) and those not taking supplementation (1.0 +/- 0.7 to 63.0 +/- 4.7 ng (100 ml tissue)-1 min-1). Intra-arterial infusion of 17 beta-oestradiol significantly potentiated bradykinin-induced t-PA release. Net endothelial release of t-PA was approximately 45 % higher (P < 0.01) after (from 1.0 +/- 0.8 to 87.4 +/- 9.9 ng (100 ml tissue)-1 min-1) versus before (1.2 +/- 0.6 to 60.8 +/- 5.6 ng (100 ml tissue)-1 min-1) acute 17 beta-oestradiol administration. Our results suggest that oestrogen has a direct modulatory effect on the capacity of the endothelium to release t-PA in healthy postmenopausal women. However, progesterone appears to oppose the favourable influence of oestrogen on endothelial fibrinolytic capacity.

Mechanisms of vasorelaxation to 17beta-oestradiol in rat arteries

We have investigated the involvement of the endothelium, K+ channels, oestradiol receptors, and Ca2+ influx in 17beta-oestradiol-induced vasorelaxation in rat mesenteric arterial beds and aortae. 17beta-Oestradiol (10 pM-1 mM) caused acute vasorelaxations in mesenteric arterial beds and aortae from male and female rats. In male rat mesenteric vessels and aortae, the vasorelaxations were mostly independent of the endothelium and nitric oxide (NO). However, indomethacin (10 microM) enhanced the relaxant responses to 17beta-oestradiol. In male rat mesenteric beds, 60 mM KCl, tetrabutylammonium chloride (300 microM), 4-aminopyridine (1 mM), and barium chloride (30 microM), charybdotoxin (100 nM), but not glibenclamide (10 microM) and tamoxifen (10 microM), inhibited vasorelaxation to 17beta-oestradiol. In male rat aortae, 60 mM KCl did not affect vasorelaxation to 17beta-oestradiol. However, in the presence of indomethacin, vasorelaxation to 17beta-oestradiol was enhanced but this was sensitive to 60 mM KCl. Pre-treatment with 17beta-oestradiol (100 microM) inhibited CaCl2-induced contraction. The present findings indicate that, in rat mesenteric beds and aortae, 17beta-oestradiol causes acute and potent vasorelaxation which may be enhanced in the presence of a cyclooxygenase inhibitor. In mesenteric arterial bed, 17beta-oestradiol-induced vasorelaxation occurs primarily via activation of K+ channels. In the aorta, vasorelaxations involved activation of K+ efflux when the cyclooxygenase pathway was inhibited, and also inhibition of Ca2+ influx.

Estrogens, homocysteine, vasodilatation and menopause: basic mechanisms, interactions and clinical implications

Estrogens influence the independent cardiovascular risk factor homocysteine as well as vasodilatation. Homocysteine alone also influences vasodilatation, indicating a relational triangle that seems important in interpreting the isolated effects of estrogens on homocysteine metabolism and vasoreactivity. This paper gives an overview of the current understanding regarding vasoreactivity, homocysteine metabolism and the role of estrogens. This is placed against the background of the clinical trials on the effect of postmenopausal hormone replacement therapy on homocysteine levels and addresses the importance of the interaction between homocysteine, estrogens and vasoreactivity.

Multiple forms of estrogen receptor-alpha in cerebral blood vessels: regulation by estrogen

The cerebral vasculature is an important target tissue for estrogen, as evidenced by significant effects of estrogen on vascular reactivity and protein levels of endothelial nitric oxide synthase and prostacyclin synthase. However, the presence, localization, and regulation of estrogen receptors in the cerebral vasculature have not been investigated. In this study, we identified the presence of estrogen receptor-alpha (ER-alpha) in female rat cerebral blood vessels and localized this receptor to both smooth muscle and endothelial cells by use of immunohistochemistry and confocal microscopy. With immunoblot analysis, multiple forms of ER-alpha were detected at 110, 93, 82, 50, and 45 kDa in addition to a relatively weak band corresponding to the 66-kDa putative unmodified receptor. The 82-kDa band was identified as Ser(118)-phosphorylated ER-alpha, whereas the 50-kDa band lacks the normal NH(2) terminus, suggestive of an ER-alpha splice variant. Lower molecular mass bands persisted after in vivo inhibition of 26S proteasome activity with lactacystin, whereas the 110- and 93-kDa bands increased. All forms of ER-alpha in cerebral vessels were decreased after ovariectomy but significantly increased after chronic estrogen exposure in vivo.

Nongenomic activity and subsequent c-fos induction by estrogen receptor ligands are not sufficient to promote deoxyribonucleic acid synthesis in human endometrial adenocarcinoma cells

Estrogen 17beta-estradiol (E2) rapidly modulates several signaling pathways related to cell growth, preservation, and differentiation. The physiological role of these nongenomic effects with regard to downstream outcomes, and the relationship with transcriptional estrogen activity are unclear. Furthermore, the ability of selective estrogen receptor modulators (SERMs) to trigger nongenomic actions is largely unknown. To determine whether estrogen receptor (ER) ligands exert nongenomic activity in endometrial adenocarcinoma cells, and whether this activity affects transcription and DNA synthesis, we challenged human Ishikawa cells with E2 or partial ER agonists 4-hydroxytamoxifen (OHT) and raloxifene (ral). Serum-starved Ishikawa cells exposed for 5 min to 0.1 nM E2 showed induced phosphorylation of MAPK (ERK1/2). Ral and 4-OHT each at 1 nM also stimulated ERK in a rapid transient manner. E2 and 4-OHT induced proto-oncogene c-fos mRNA expression in Ishikawa cells within 30 min, but ral had no effect. In contrast to nongenomic action, only E2 stimulated expression of an estrogen response element (ERE)-driven luciferase (LUC) reporter gene. To examine DNA synthesis, [(3)H]-thymidine incorporation was measured in serum-starved cultures exposed to E2 or partial agonists for 2 d. E2 at 1 nM stimulated thymidine uptake in an ERK-dependent manner, but 1 nM 4-OHT, 1 nM ral, and 0.1-nM concentrations of E2 had no significant effects. Taken together, these data indicate that both nongenomic and direct transcriptional ER effects are likely required to promote DNA synthesis.

Estrogen stimulates arachidonoylethanolamide release from human endothelial cells and platelet activation

Estrogen replacement therapy has been associated with reduction of cardiovascular events in postmenopausal women, though the mechanism for this benefit remains unclear. Here we show that at physiological concentrations estrogen activates the anandamide membrane transporter of human endothelial cells and leads to rapid elevation of calcium (apparent within 5 minutes) and release of nitric oxide (within 15 minutes). These effects are mediated by estrogen binding to a surface receptor, which shows an apparent dissociation constant (K(d)) of 9.4 +/- 1.4 nM, a maximum binding (B(max)) of 356 +/- 12 fmol x mg protein(-1), and an apparent molecular mass of approximately 60 kDa. We also show that estrogen binding to surface receptors leads to stimulation of the anandamide-synthesizing enzyme phospholipase D and to inhibition of the anandamide-hydrolyzing enzyme fatty acid amide hydrolase, the latter effect mediated by 15-lipoxygenase activity. Because the endothelial transporter is shown to move anandamide across the cell membranes bidirectionally, taken together these data suggest that the physiological activity of estrogen is to stimulate the release, rather than the uptake, of anandamide from endothelial cells. Moreover, we show that anandamide released from estrogen-stimulated endothelial cells, unlike estrogen itself, inhibits the secretion of serotonin from adenosine diphosphate (ADP)-stimulated platelets. Therefore, it is suggested that the peripheral actions of anandamide could be part of the molecular events responsible for the beneficial effects of estrogen.

Novel non-transcriptional mechanisms for estrogen receptor signaling in the cardiovascular system. Interaction of estrogen receptor alpha with phosphatidylinositol 3-OH kinase

Estrogen receptor (ER) signaling has been, for a long time, associated with transcriptional processes involving nuclear translocation and binding on specific response elements, leading to regulation of target gene expression. However, rapid, non-transcriptional mechanisms of signal transduction through steroid hormone receptors have been identified. These so-called 'non-genomic' effects are independent from gene transcription or protein synthesis and involve steroid-induced modulation of cytoplasmic or cell membrane-bound regulatory proteins. Several biological actions of estrogen have been associated with this type of signaling, and intracellular regulatory cascades such as extracellular signal-regulated kinase/mitogen-activated protein kinases (ERK/MAPK) and tyrosine kinases or the modulation of G-protein-coupled receptors have been shown to be non-transcriptionally recruited by estrogen in diverse tissues. The vascular wall is one of these sites, where estrogen triggers rapid vasodilatation mainly due to increased nitric oxide (NO) release. We have recently described a novel, non-transcriptional mechanism for ER signaling in human as well as in animal endothelial cells, showing that ER alpha can physically and functionally couple to the lipid kinase phosphatidylinositol 3-OH kinase (PI3K). This interaction leads to activation of PI3K signaling cascade to Ser/Thr kinase Akt, which mediates several PI3K-dependent intracellular effects, including endothelial isoform of NO synthase (eNOS) phosphorylation and activation. This original non-transcriptional mechanism for ER signaling may play an important role in the generation of some of the rapid 'non-genomic' effects of estrogen.

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.

17β-Estradiol rapid stimulation of rat aorta NOS activity is prevented by oestrogen deficiency

OBJECTIVES

The purpose of this study was to determine the effects of chronic oestrogen deficiency on rat aorta rapid response to 17beta-estradiol treatment.

METHODS

Rat aortic strips (RAS) were isolated from Wistar female rats of three different groups: rats 6-7-month old with normal oestrogen levels (NER); aged rats, 24-month old, with low oestrogen levels (LER); and young rats after 2 months of bilateral ovariectomy (OVX). Platelet aggregation was measured after incubation of RAS in a platelet rich plasma by addition of 10 microM ADP. NO production by RAS was measured by 3H-citrulline technique.

RESULTS

RAS obtained from NER treated with 17beta-estradiol produced an inhibition of platelet aggregation specific for ovarian hormones, since testosterone was devoid of any effect. In aortic tissue isolated from male rats no increment in nitric oxide (NO) production was found. RAS from LER and OVX treated with 1-10 nM failed to induce a significant inhibition of platelet aggregation compared with NER (5 and 17%; 6 and 20% vs. 45 and 77% inhibition of platelet aggregation respect to control, respectively). In contrast to NER, 5 min treatment of LER and OVX aortic tissue with 1 nM 17beta-estradiol did not incremented NO production (NER 1.14 vs. 2.3 (P < 0.05); LER 1.14 vs. 1.42; OVX 1.24 vs. 1.52 pmol NO per mg protein).

CONCLUSIONS

These results suggest that chronic oestrogen deprivation impairs the inhibition of platelet aggregation and suppresses the rapid stimulation of aortic NOS induced by acute 'in vitro' treatment with 17beta-estradiol.

Regional differences in the effect of oestrogen on vascular tone in isolated rabbit arteries

The aim of the study was to assess how oestrogen acutely affects the tone of isolated artery segments from different vascular beds in rabbit. Cumulative concentrations of 17beta-oestradiol were added to ring segments of thoracic aorta, pulmonary artery, ear artery and coronary arteries from adult male rabbits. Coronary arteries precontracted with potassium or the thromboxane agonist, U46619, relaxed to oestrogen (10(-7) to 10(-4) M), whereas oestrogen (10(-8) to 10(-4) M) only caused additional contraction in segments of thoracic aorta and pulmonary artery precontracted with phenylephrine. In the thoracic aorta both the phospholipase C inhibitor NCDC (10(-4) M) and the cyclooxygenase inhibitor indomethacin (10(-5) M) almost completely blocked the contractile effect of oestrogen. In segments of the ear artery, oestrogen caused relaxation only at higher concentrations of oestrogen (10(-5) to 10(-4) M). In conclusion, oestrogen may cause both relaxation and vasoconstriction in different vascular beds, and in the thoracic aorta the contractile effects of oestrogen may be mediated via inositol phosphate-dependent pathways and release of prostaglandins.