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Hypertension. 2007;49:1364-1370
Published online before print April 30, 2007, doi: 10.1161/HYPERTENSIONAHA.106.081554
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(Hypertension. 2007;49:1364.)
© 2007 American Heart Association, Inc.

Original Articles

Distinct Roles of Estrogen Receptors {alpha} and ß Mediating Acute Vasodilation of Epicardial Coronary Arteries

Tobias Traupe; Christoph D. Stettler; Huige Li; Elvira Haas; Indranil Bhattacharya; Roberta Minotti; Matthias Barton

From the Department of Internal Medicine (T.T., C.D.S., E.H., I.B., R.M., M.B.), Internal Medicine I, Medical Policlinic, University Hospital Zürich, Zürich, Switzerland; and the Department of Pharmacology (H.L.), Johannes Gutenberg University, Mainz, Germany. Current address: Internal Medicine (T.T.), City Hospital Triemli, Zürich, Switzerland.

Correspondence to Matthias Barton, Department of Internal Medicine, Internal Medicine I, Medical Policlinic, University Hospital Zürich, Rämistrasse 100, CH-8091 Zürich, Switzerland. E-mail barton{at}usz.ch


*    Abstract
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 *Abstract
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This study investigated the contribution of estrogen receptors (ERs) {alpha} and ß for epicardial coronary artery function, vascular NO bioactivity, and superoxide (O2–) formation. Porcine coronary rings were suspended in organ chambers and precontracted with prostaglandin F2{alpha} to determine direct effects of the selective ER agonists 4,4',4''-(4-propyl-[1H]pyrazole-1,3,5-triyl)tris-phenol (PPT) or 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN) or the nonselective ER agonist 17ß-estradiol. Indirect effects on contractility to U46619 and relaxation to bradykinin were assessed and effects on NO, nitrite, and O2– formation were measured in cultured cells. Within 5 minutes, selective ER{alpha} activation by PPT, but not 17ß-estradiol or the ERß agonist DPN, caused rapid, NO-dependent, and endothelium-dependent relaxation (49±5%; P<0.001 versus ethanol). PPT also caused sustained endothelium- and NO-independent vasodilation similar to 17ß-estradiol after 60 minutes (72±3%; P<0.001 versus ethanol). DPN induced endothelium-dependent NO-independent relaxation via endothelium-dependent hyperpolarization (40±4%; P<0.01 versus ethanol). 17ß-Estradiol and PPT, but not DPN, attenuated the responses to U46619 and bradykinin. All of the ER agonists increased NO and nitrite formation in vascular endothelial but not smooth muscle cells and attenuated vascular smooth muscle cell O2– formation (P<0.001). ER{alpha} activation had the most potent effects on both nitrite formation and inhibiting O2– (P<0.05). These data demonstrate novel and differential mechanisms by which ER{alpha} and ERß activation control coronary artery vasoreactivity in males and females and regulate vascular NO and O2– formation. The findings indicate that coronary vascular effects of sex hormones differ with regard to affinity to ER{alpha} and ERß, which will contribute to beneficial and adverse effects of hormone replacement therapy.


Key Words: atherosclerosis • endothelium • gender • hormone replacement therapy • nitric oxide • vascular smooth muscle


*    Introduction
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 *Introduction
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Vascular effects of estrogens (reviewed in References 1 and 2) can be divided in acute (nongenomic) and chronic (genomic) effects. 17ß-Estradiol and selective estrogen receptor (ER) modulators directly induce relaxation in different vascular beds; however, whether vasodilatory effects occur dependent or independent of the endothelium remains controversial.3 Moreover, the natural estrogen 17ß-estradiol may indirectly affect both vascular tone and vasoreactivity to different contractile or relaxant agonists, including U46619 or bradykinin.4–6 Endothelium-dependent effects of 17ß-estradiol involve endothelial factors, including effects on reactive oxygen species, NO, and superoxide anion (O2–).1

Two distinct subtypes of ERs have been cloned, ER{alpha}7 and ERß.8 Both are located intracellularly and on the cell membrane9,10 and are present in vascular smooth muscle11 and endothelial cells.12 Nongenomic vascular effects of 17ß-estradiol on endothelial cells are thought to be mediated by plasma membrane–bound and caveolar ERs, involving activation of protein kinases and endothelial NO synthase.13 17ß-Estradiol and other estrogenic compounds, including those found in conjugated equine estrogens used for hormone replacement therapy,14 bind to ERs.7,8 The contribution of ER{alpha} and ERß to regulation of vascular tone in the coronary circulation is still obscure and only recently have suitable pharmacological tools become available, including 4,4',4''-(4-propyl-[1H]pyrazole-1,3,5-triyl)tris-phenol (PPT), a selective ER{alpha} receptor agonist, and 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN), a selective agonist for ERß.15–18

Both male gender and estrogen deficiency after menopause are independent cardiovascular risk factors (reviewed in References 1 and 2). The incidence of coronary artery disease is low in premenopausal women14,19 but increases after menopause and with aging,20 indicating protective effects of endogenous estrogens on the cardiovascular system. Importantly, the administration of exogenous nonhuman hormones, such as conjugated equine estrogens and methoxyprogesteroneacetate in postmenopausal women, increases clinical complications, such as thrombosis in veins and coronary arteries.14,21 In humans, atherosclerosis typically develops in large conduit arteries, such as the epicardial coronaries. Porcine coronary arteries are widely used as a suitable experimental model of human coronary arteries because of the high anatomic and physiological similarities.22 Therefore, using selective agonists for both ERs as well as the nonselective ER agonist 17ß-estradiol, the objective of the present study was to investigate whether and through which mechanisms combined or selective activation of ER{alpha} and ERß affects epicardial coronary artery tone, vascular reactive oxygen species, and bioactivity.


*    Methods
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 *Methods
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Tissue Preparations
Experiments were in accordance with the institutional guidelines and the Guide for the Care and Use of Laboratory Animals, published by the National Institutes of Health. Porcine hearts of either sex were obtained from a local abattoir and immediately immersed in cold physiological Krebs–Ringer bicarbonate solution (in millimoles per liter): 118.6 NaCl, 4.7 KCl, 2.5 CaCl2, 1.2 MgSO4, 25.1 NaHCO3, 1.2 KH2PO4, 0.026 Na2Ca-EDTA, and 10.1 glucose. The left anterior descending coronary artery was dissected free from surrounding myocardium, cleaned of adherent fat and connective tissue, and cut into rings 4 to 5 mm in length. Six rings were prepared from each coronary artery. In a subset of rings, the endothelium was removed by gently rubbing the intimal surface with a wooden probe.

Vascular Function Experiments
Vascular rings were mounted onto stainless steel hooks and placed in organ chambers containing Krebs–Ringer solution (25 mL [pH 7.4], 37°C, 95% O2, and 5% CO2) as described.23 Rings were progressively stretched until optimal tension for generating force during isometric contraction was reached (4.0 g) and repeatedly exposed to KCl (60 mmol/L; iso-osmotically replaced) to determine a maximal contraction. Before the experiments, all rings were preincubated with the nonselective cyclooxygenase-inhibitor meclofenamate (1 µmol/L) for 30 minutes. A subset of rings was additionally incubated with NG-nitro-L-arginine methyl ester (L-NAME; 300 µmol/L) for 30 minutes to inhibit endothelial NO synthesis.

The integrity of vascular smooth muscle was determined by precontracting with acetylcholine (1 µmol/L), and the absence or presence of the endothelium was determined by the relaxant response to bradykinin (0.1 nmol/L to 1 µmol/L; data not shown); endothelium-independent relaxation was determined using sodium nitroprusside (300 µmol/L; data not shown). In rings precontracted with prostaglandin F2{alpha}, direct vascular effects of 17ß-estradiol, PPT, or DPN (10 µmol/L each)16–18 were recorded for 60 minutes. Ethanol at a final concentration of 0.2% (vol/vol) served as solvent control. A subset of rings exposed to DPN was preincubated with inhibitors of endothelium-dependent hyperpolarization factors, charybdotoxin in combination with apamin (0.1 µmol/L each).24 After repeated washings, rings were incubated again with 17ß-estradiol, PPT, or DPN (10 µmol/L) and precontracted with U46619 (1 nmol/L to 0.3 µmol/L). Endothelium-dependent relaxation was determined using bradykinin (0.01 nmol/L to 1 µmol/L), and endothelium-independent relaxation was determined using sodium nitroprusside.

Cell Culture Experiments
Human umbilical vein endothelial cells (HUVECs) were isolated by collagen digestion and cultured in endothelial cell growth medium (PromoCell). HUVEC-derived EA.hy 926 endothelial cells (a kind gift of Dr C J Edgell, University of North Carolina at Chapel Hill, Chapell Hill, NC)25 were grown as described.26

Human vascular smooth muscle cells (VSMC) were isolated using the explant technique and cultured as described.27 Cells of passages 3 to 6 were used for all of the experiments.

Determination of Endothelial NO Synthesis
To determine the effects of ER agonists, NO release by HUVECs was bioassayed using guanylyl cyclase–containing RFL-6 rat lung fibroblasts as reporter cells.26 HUVECs were treated with ER agonists (all 10 µmol/L) for 5 minutes. Thereafter, NO-containing conditioned media from the HUVECs were transferred to RFL-6 cells to stimulate guanylyl cyclase. The cGMP content of the RFL-6 samples was determined by radioimmunoassay.26

In additional experiments, HUVECs, EA.hy 926 cells, or VSMCs were treated with ER agonists for 60 minutes, and nitrite accumulation in the cell culture supernatant was measured as an indicator of NO production by chemiluminescence using an NOA 280 nitric oxide analyzer (Sievers) or by the Griess reaction according to the instructions of the manufacturer (Caymann). Total protein content was determined (Bradford), and nitrite levels were normalized for protein.26 The nitrite concentration in control cells was set 100%.

Vascular O2– Formation
Subconfluent VSMCs were starved for 24 hours and exposed to 17ß-estradiol, PPT, DPN (all 10 µmol/L), or ethanol for 30 minutes. Three independent experiments were performed, with measurements being performed in triplicate. Cells were suspended in Krebs-HEPES buffer, and O2– generation was monitored using a chemiluminescence probe (L-012; 500 µmol/L, Wako Chemicals) in a luminometer (Lumat LB 9507) as described previously.28

Drugs
Acetylcholine chloride, apamin, bradykinin, charybdotoxin, 17ß-estradiol, L-NAME, prostaglandin F2{alpha}, sodium nitroprusside dihydrate, and U46619 were from Sigma-Aldrich. DPN and PPT were from Tocris (Anawa). DPN, PPT, and 17ß-estradiol were dissolved in 100% ethanol. All of the other substances were dissolved in water; stock solutions were diluted in Krebs solution to the required final concentration before use.

Calculations and Statistical Analysis
Data are expressed as mean±SEM, and n equals the number of animals. Contraction was expressed as the percentage of contraction to KCl 60 mmol/L, and relaxation was expressed as the percentage of precontraction. EC50 values (as negative logarithm: pD2), area under the curve, and maximal responses were calculated by nonlinear regression analysis.29 One-way ANOVA, ANOVA for repeated measurements (followed by Bonferroni–Dunn posthoc test), or unpaired Student’s t test was used when appropriate. A P<0.05 was considered significant.


*    Results
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 *Results
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Selective ER{alpha} Activation Induces Rapid Endothelium- and NO-Dependent Relaxation
The selective ER{alpha} agonist PPT induced a rapid relaxation (49±5% within 5 minutes; P<0.001 versus ethanol [ETOH]) that was not seen with either 17ß-estradiol or the selective ERß agonist DPN (Figure 1, original tracings, and Figure 2A). As shown in Figure 3A, the rapid response induced by PPT was abolished in rings without endothelium (5±1% versus 49±5%; P<0.001 versus PPT) or after pretreatment with the NO synthase inhibitor L-NAME (6±1% versus 49±5%; P<0.001 versus PPT). Data for males and females are presented separately in Table 1.


Figure 1
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  		Figure 1. Original recordings of acute and sustained relaxant responses of ER agonists in epicardial coronary arteries. 17ß-Estradiol (E2), PPT, and DPN induced a sustained time-dependent relaxant effect in precontracted arteries (10 µmol/L; original experiments recorded for 60 minutes) compared with solvent-control ETOH. Only activation of ER{alpha} by PPT showed a rapid dilator component within <1 minute that was completely inhibited by NO inhibition (L-NAME) or endothelial denudation. Arrows indicate administration of increasing concentrations of prostaglandin F2{alpha} (PGF2{alpha}), ER agonists, or sodium nitroprusside (SNP).


Figure 2
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  		Figure 2. Maximal relaxant effects of ER agonists in epicardial coronary arteries after 5 minutes (A) and 60 minutes (B). The ER{alpha} agonist PPT induced potent relaxation after 5 minutes, whereas after 60 minutes, relaxations caused by PPT and 17ß-estradiol were comparable. In contrast, the response to DPN was significantly less. Data are mean±SEM; n=8 to 20. *P<0.01 vs ETOH; {dagger}P<0.01 vs PPT.


Figure 3
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  		Figure 3. Acute relaxant effects of ER agonists PPT (A), DPN (B), and 17ß-estradiol ([E2] C) in epicardial coronary arteries. Selective ER{alpha} activation using PPT induced a rapid relaxation not noted with either 17ß-estradiol or ERß-agonist DPN; the rapid response was inhibited by L-NAME or denudation. DPN-induced relaxation was inhibited by endothelial denudation or inhibition of endothelium-dependent hyperpolarization (CHAP). LN indicates L-NAME; E-, denuded; CHAP, charybdotoxin+apamin. Data are mean±SEM; n=8 to 20. *P<0.01 vs ETOH; {dagger}P<0.05 vs agonist alone.


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  		TABLE 1. Maximal Effects of Acute Relaxant Responses to ER Agonists in Porcine Coronary Arteries

Sustained Relaxation to PPT and 17ß-Estradiol Are Endothelium- and NO-Independent
After 60 minutes of recording time, relaxation caused by PPT was increased further and became comparable to 17ß-estradiol (72±3%; P<0.001 versus ETOH), whereas DPN induced a smaller but significant response (40±4%; P<0.01 versus ETOH; Figure 1, original tracings and Figure 2B). Data for males and females are presented separately in Table 1. Denudation or inhibition of NO synthesis did not affect relaxation to PPT measured after 60 minutes (67±3% and 63±2%, respectively; P value not significant versus PPT). 17ß-Estradiol induced a time-dependent relaxation (77±4% after 60 minutes; P<0.001 versus ETOH; Figure 1, original tracing and Figure 2B). Inhibition of NO synthesis with L-NAME did not affect this response (Figure 3C). Calculated values for area under the curve and maximal response are given in Table 2.


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  		TABLE 2. Acute Relaxant Effects of ER Agonists in Porcine Coronary Arteries

Sustained Relaxation Following ERß Activation Involves Endothelium-Dependent Hyperpolarization
The sustained response of DPN recorded after 60 minutes was unaffected by L-NAME (33±4% versus 40±4%; P value not significant; Figure 3B) and comparable to solvent control after removal of the endothelium (24±2% versus 40±4%; P=0.01 versus DPN alone). After pretreatment with L-NAME, charybdotoxin, and apamin, relaxation was completely inhibited (17±2% versus 33±3%; P=0.01 versus L-NAME alone). Calculated values for area under the curve and maximal response are given in Table 2.

Thromboxane-Mediated Contraction Is ER{alpha}-Sensitive
Contractions to the thromboxane receptor agonist U46619 were attenuated in rings pretreated with either the unselective agonist 17ß-estradiol or the ER{alpha}-selective agonist PPT (P<0.05 and P<0.001 versus ETOH; Figure 4A), whereas DPN had no effect. Maximal relaxations and sensitivity of endothelium-dependent relaxations to bradykinin were reduced after PPT and 17ß-estradiol in rings precontracted with U46619 (P<0.05 versus ETOH; Figure 4B and Tables 3 and 4Down). Pretreatment with DPN had no effect.


Figure 4
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  		Figure 4. Acute effects of ER agonists on contractions to the thromboxane A2 receptor agonist U46619 and bradykinin in epicardial coronary arteries. 17ß-Estradiol and PPT attenuated the contractile and relaxant response, whereas DPN had no effect. Data are mean±SEM; n=8 to 18. *P<0.05 vs ETOH; {dagger}P<0.05 vs ETOH for PPT and 17ß-estradiol (E2).


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  		TABLE 3. Acute Effects of ER Agonists on Contractions to U46619 in Porcine Coronary Arteries


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  		TABLE 4. Acute Effects of ER Agonists on Relaxant Responses to Bradykinin in Porcine Coronary Arteries

Effects of ER Agonists on NO Synthesis in Human Vascular Cells
Incubation with PPT, DPN, or 17ß-estradiol (10 µmol/L each) increased NO production in HUVECs (cGMP generation in RFL-6 reporter cells) after 5 minutes of treatment (P<0.05 versus ETOH; Figure 5A). Nitrite concentration also significantly increased after treatment with PPT, DPN, or 17ß-estradiol after 60 minutes (P<0.05 versus ETOH), the strongest effect being observed after ER{alpha} activation with PPT (P<0.05 versus DPN and 17ß-estradiol; Figure 5B). In HUVEC-derived EA.hy 926 hybridoma cells, nitrite synthesis after 60 minutes was increased only by 17ß-estradiol (+147±20%; P<0.05 versus ETOH). In contrast, PPT, DPN, and 17ß-estradiol did not induce nitrite formation in VSMCs (data not shown).


Figure 5
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  		Figure 5. Effects of ER agonists on cGMP formation and NO bioactivity in cultured human endothelial cells. Conditioned media from HUVECs exposed to ER agonists for 5 minutes increased cGMP formation in RFL-6 reporter cells (A). Each ER agonist increased HUVEC nitrite formation, the ER{alpha} agonist PPT having the most potent effect (B). Data are mean±SEM; n=3 independent experiments. *P<0.05 vs ETOH; {dagger}P<0.05 vs DPN and 17ß-estradiol (E2).

Inhibition of Smooth Muscle Cell O2– Formation by ER Agonists
Treatment of VSMCs with 17ß-estradiol or DPN reduced O2– generation by –39±5% and –38±2%, respectively (P<0.001 versus ETOH). Interestingly, the ER{alpha}-selective agonist PPT had a much stronger inhibitory effect on O2– generation than the other agonists (–62±0.5%; P<0.001 versus ETOH and P<0.01 versus DPN).


*    Discussion
up arrowTop
 up arrowAbstract
 up arrowIntroduction
 up arrowMethods
 up arrowResults
 *Discussion
down arrowReferences
 
This study demonstrates that, in epicardial porcine coronary arteries of males and females, selective activation of ER{alpha} by PPT involves a rapid, NO-dependent component, as well as sustained relaxant response, whereas selective ERß activation causes sustained relaxation only. The sustained relaxing effect of combined ER activation by 17ß-estradiol was similar to that of PPT; however, 17ß-estradiol lacked rapid dilator effects. Rapid relaxation after ER{alpha} activation was NO-dependent, whereas sustained responses after activation of ERß or both ERs were not. Activation of ER{alpha}, but not of ERß, also reduced thromboxane A2-receptor–mediated vasoconstriction. Finally, differential effects of selective ER agonists on endothelial NO bioactivity and on VSMC O2– formation were observed.

This study is the first to demonstrate that, in epicardial coronary arteries, the dilator response after selective ER{alpha} activation involves 2 independent components. On the one hand, rapid, endothelium- and NO-dependent vasodilation occurs within the first minutes, which is followed by a sustained endothelium-independent dilator component reaching a maximum after {approx}1 hour similar to that of the unselective ER agonist 17ß-estradiol. Importantly, 17ß-estradiol, which also activates ERß,3 lacked the rapid NO-dependent dilator response, suggesting a possible inhibitory effect of ERß on ER{alpha}-mediated NO-dependent activity. Endothelium- and NO-dependent relaxant effects have been demonstrated for both the ER{alpha} agonist PPT15,17,30 and combined ER agonist 17ß-estradiol,31–35 yet none of these previous studies reported a rapid or NO-dependent dilator component to PPT, even at concentrations higher than those used in the present study.17,30 It has been shown previously that NO is released after short-term treatment with 17ß-estradiol from HUVECs.12 Although there is evidence that NO release from endothelial cells is mediated by ER{alpha},36,37 more recent data suggest that both ER{alpha} and ERß can activate endothelial NO synthase and mitogen-activated protein kinases.38 In line with these observations, we show here that selective activation of either ER increases bioactive NO in HUVECs and also rapidly stimulates endothelial cell cGMP formation. It is noteworthy that again the strongest effect was seen after selective activation of ER{alpha}. Increased cGMP after 17ß-estradiol was also detected in HUVEC-derived EA.hy 926 hybridoma cells,25 which, unlike in HUVECs,38 express only a truncated form of ER{alpha}.39 Thus, either selective or unselective activation of ERs appears to stimulate endothelial cell NO formation of most species. In the present study, the rapid NO-mediated dilator response in porcine coronary arteries was only seen after selective activation ER{alpha}, suggesting possible species differences in ER expression and/or function. Increased NO bioactivity may also be affected by antioxidant effects of estrogen agonists because of their phenolic structure.40 Our experiments using human VSMCs show that all of the ER agonists used inhibit vascular O2– generation. Because the most potent effect was again seen with the ER{alpha} agonist PPT, it appears reasonable to speculate that scavenging of O2– by PPT also indirectly contributes to the observed NO bioavailability and the rapid vasodilator component observed in the present study.

The maximum effect of the sustained vasodilator response to the ER{alpha} agonist PPT was equally potent but somewhat delayed compared with that induced by 17ß-estradiol. In contrast, the maximum response to the ERß agonist DPN was less pronounced. This is in agreement with a study using aortic rings of female rats, in which the ER{alpha} agonist PPT acutely and concentration-dependently induced relaxations similar to those by 17ß-estradiol,15 whereas the ERß agonist DPN had no effect.15 We found that the sustained dilator component to all 3 of the ER agonists was NO independent, which is in line with earlier studies using 17ß-estradiol in coronary arteries of humans,41,42 dogs,43 or adult pigs of either sex.44,45 Therefore, the sustained dilator response must involve mechanisms distinct from NO, possibly inhibition of VSMC Ca2+ influx.3

We surprisingly found that selective ERß-mediated epicardial coronary vasodilation was in part endothelium-dependent. Because combined cyclooxygenase and NO inhibition had no effect on the endothelium-dependent portion of the relaxant response to DPN, the results suggested a role for other vasodilator mechanisms, such as endothelium-mediated hyperpolarization. Indeed, experiments using inhibitors of endothelium-dependent hyperpolarization showed an attenuation of the relaxant responses after ERß activation, confirming this hypothesis. This mechanism may be particularly relevant to epicardial coronary arteries, which are known to produce high levels of endothelium-dependent hyperpolarizing factor,46 and to conditions when NO bioactivity is low, such as atherosclerosis or aging.

We finally investigated whether ER agonists indirectly affect vasoreactivity to contracting and relaxing substances. The vasoconstrictor thromboxane A2 is released in high concentrations from aggregating platelets at sites of coronary plaque rupture and is a key event in the pathogenesis of acute coronary syndromes. We found that contractions to the thromboxane A2 receptor agonist U46619 were markedly attenuated after ER{alpha} activation only but unaffected by ERß activation, indicating another indirect and NO-independent vasodilator function of ER{alpha}. The effect of unselective ER activation in response to 17ß-estradiol was less pronounced than that of selective ER{alpha} activation and comparable to previous studies.5 This suggests that (1) activation of ER{alpha} alone is sufficient and (2) that ERß possibly regulates vascular ER{alpha} function. Indeed, our results suggest that ERß activation appears to attenuate the ER{alpha}-mediated effects during combined ER activation with 17ß-estradiol, which would be compatible with a functional cross-talk between both ERs. Whether selective ER agonists also affect function of vasoconstrictors such as endothelin-1 in epicardial coronary arteries47,48 remains to be determined in future studies.

Perspectives
The observed NO-dependent coronary dilator response and attenuation of O2– anion formation after selective ER{alpha} activation may have therapeutic implications for human vascular disease, including acute coronary syndromes and restenosis,30,49,50 and possibly also for hormone therapy in postmenopausal women.14,15 Our results also show that the effects of ER activation were similar in coronary arteries from male and female pigs. Finally, because endogenous 17ß-estradiol also contributes to vascular homeostasis in males,51,52 effects of endogenous estrogens on the epicardial coronary arterial circulation, a vascular bed that is highly susceptible to atherosclerosis in humans,20 may be possibly also of similar relevance for vascular disease in men and women.


*    Acknowledgments
 
We thank Giochen Bearth and coworkers at Schlachthof Zürich for their help and Wilhelm Vetter for support.

Sources of Funding

This work was supported by the Swiss National Science Foundation (SCORE 32.58421.99, 32-58426.99/1, and 3200-108258/1), the Hanne Liebermann Stiftung Zürich, and the University of Zürich.

Disclosures

None.

Received October 5, 2006; first decision October 30, 2006; accepted April 3, 2007.


*    References
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 *References
 

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Choreographing the Rapid Vascular Effects of Estrogen: Sorting Out the Partners and the Steps
Ross D. Feldman and Robert Gros
Hypertension 2007 49: 1222-1224. [Full Text] [PDF]



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R. D. Feldman and R. Gros
Choreographing the Rapid Vascular Effects of Estrogen: Sorting Out the Partners and the Steps
Hypertension, June 1, 2007; 49(6): 1222 - 1224.
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