Donate Help Contact The AHA Sign In Home
American Heart Association
Circulation
Search: search_blue_button Advanced Search
« Previous Article | Table of Contents | Next Article »
Circulation. 1995;92:24-30

This Article
Right arrow Abstract Freely available
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Collins, P.
Right arrow Articles by Poole-Wilson, P. A.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Collins, P.
Right arrow Articles by Poole-Wilson, P. A.

(Circulation. 1995;92:24-30.)
© 1995 American Heart Association, Inc.

Articles

17ß-Estradiol Attenuates Acetylcholine-Induced Coronary Arterial Constriction in Women but Not Men With Coronary Heart Disease

Peter Collins, MD; Giuseppe M. C. Rosano, MD; Philip M. Sarrel, MD; Lian Ulrich, MD; Stamatis Adamopoulos, MD; Carolyn M. Beale, BSc; John G. McNeill, DCRR; Philip A. Poole-Wilson, MD

From the National Heart and Lung Institute and Royal Brompton National Heart and Lung Hospital, London, UK; Yale University School of Medicine, New Haven, Conn (P.M.S.); and Novo Nordisk, Bagsvaerd, Denmark (L.U.).

Correspondence to Dr Peter Collins, National Heart and Lung Institute, Dovehouse St, London SW3 6LY, UK.


*    Abstract
up arrowTop
 *Abstract
down arrowIntroduction
 down arrowMethods
down arrowResults
down arrowDiscussion
down arrowReferences
 
Background Women are protected from coronary artery disease until the menopause. Ovarian hormones are vasoactive substances that influence both hemodynamic parameters and atheroma formation. Intravenous ethinyl estradiol has been shown to reverse acetylcholine-induced vasoconstriction in cynomolgus monkeys and humans, and 17ß-estradiol improves exercise-induced myocardial ischemia in female patients. We investigated the effect of the naturally occurring estrogen 17ß-estradiol on the coronary circulation in postmenopausal women and men with coronary artery disease.

Methods and Results We studied nine postmenopausal women 59±3 years old, mean±SEM, and seven men 52±4 years old with proven coronary artery disease. They underwent measurement of coronary artery diameter and coronary blood flow after intracoronary infusion of acetylcholine 1.6 and 16 µg/min before and 20 minutes after intracoronary administration of 2.5 µg of 17ß-estradiol into atherosclerotic, nonstenotic coronary arteries. Changes in coronary artery diameter were measured by quantitative angiography, and changes in coronary blood flow were measured with an intracoronary Doppler catheter. In female patients, acetylcholine 1.6 and 16 µg/min caused constriction before the administration of 17ß-estradiol (-6±2% and -8±5%, respectively, compared with baseline). This constrictor response was converted to dilatation after intracoronary administration of 17ß-estradiol (+8±2% and +9±3%, respectively; P<.01 before versus after estrogen). Acetylcholine 1.6 and 16 µg/min increased coronary blood flow before and after the infusion of 17ß-estradiol. However, the mean acetylcholine-induced increases in coronary flow were significantly greater (P<.009) after (126±37% and 248±89%, respectively) than before (94±31% and 143±49% mL/min, respectively) the administration of 17ß-estradiol. 17ß-Estradiol alone had no significant effect on coronary diameter or coronary blood flow (P>.05). Isosorbide dinitrate (1 mg) caused dilatation of the coronary arteries by 11±2% (P<.005). In men, acetylcholine 1.6 and 16 µg/min caused constriction both before and after the administration of 17ß-estradiol and caused similar increases in coronary blood flow both before and after the intracoronary administration of 17ß-estradiol. Infusion of intracoronary placebo in six female control patients 55±3 years old and six male control patients 56±3 years old did not change coronary diameter responses or coronary blood flow responses to acetylcholine.

Conclusions 17ß-Estradiol modulates acetylcholine-induced coronary artery responses of female but not male atherosclerotic coronary arteries in vivo. These human data confirm reports from studies in cynomolgus monkeys that estrogen modulates the responses of atherosclerotic coronary arteries. An enhancement of endothelium-dependent relaxation by natural estrogen (as used in most hormone replacement therapy) may be important in postmenopausal women with established coronary heart disease and may contribute to the acute effect of 17ß-estradiol on blood flow and its long-term protective effect on the development of coronary artery disease.


Key Words: hormones • arteries • circulation


*    Introduction
up arrowTop
 up arrowAbstract
 *Introduction
down arrowMethods
down arrowResults
down arrowDiscussion
down arrowReferences
 
Women appear to be protected, until the menopause, from the development of coronary artery syndromes. This protective effect seems to be due to the beneficial effect of ovarian hormones, in particular 17ß-estradiol, since estrogen replacement therapy reduces the incidence of coronary artery disease and the progression of coronary artery lesions.1 2 3 4 5 6 7 A number of potential mechanisms for the protective effect of estrogens on coronary arteries have been proposed. Estrogen has a beneficial effect on plasma lipoproteins, increasing HDL cholesterol and decreasing LDL cholesterol.8 Although early studies suggested that >50% to 60% of the protective effect of estrogens on coronary artery disease was due to the favorable change in plasma lipids,9 more recent data suggest that this figure is closer to 25%.3 10 Estrogens also appear to inhibit cholesterol deposition in the arterial wall.11 Other potential protective mechanisms of estrogen action include calcium antagonism12 and hormone-induced release of endothelium-derived relaxing factor(s) and suppression of contracting factors.13 14 15 16

Acute hemodynamic effects of estrogens reported in both animal and human studies include increases in cardiac output and uterine and peripheral blood flow.17 18 17ß-Estradiol has been shown to induce relaxation of precontracted coronary artery rings and to inhibit calcium influx in isolated cardiac myocytes.19 20 21 Intravenous ethinyl estradiol reverses acetylcholine-induced vasoconstriction in cynomolgus monkeys22 and in humans.23 A recent study showed that 17ß-estradiol improves exercise-induced myocardial ischemia in postmenopausal women with angiographically proven coronary artery disease.24

Therefore, it is plausible that the increase in incidence of coronary artery events after the menopause is due not only to the progression of coronary atherosclerosis but also to abnormalities of coronary vasodilator reactivity as a consequence of the decreased plasma levels of ovarian hormones.

The aim of the present study was to assess the effect of intracoronary administration of 17ß-estradiol and to evaluate its mechanism of action in female and male patients with angiographically proven coronary artery disease.


*    Methods
up arrowTop
 up arrowAbstract
 up arrowIntroduction
 *Methods
down arrowResults
down arrowDiscussion
down arrowReferences
 
Population of Patients
The study population consisted of nine female patients 59±3 years old and seven male patients 52±4 years old with angiographically proven coronary artery disease. The female patients were all postmenopausal (11±3 years), three had had a hysterectomy, and none were receiving or had ever received hormone therapy. Patients with primary valvar heart disease, complete heart block, or uncorrected hypokalemia and female patients on chronic hormone replacement therapy were excluded. A group of six female patients 55±3 years old with angiographically proven coronary artery disease served as female control patients. The female control patients were all postmenopausal (7±3 years), one had had a hysterectomy, and none were receiving or had ever received hormone therapy. Six male patients 56±3 years old with angiographically proven coronary artery disease served as male control patients.

Study Design
Patients were studied off antianginal therapy for at least 24 hours. Caffeine-containing beverages and nicotine were avoided on the day of study. Patients arrived in the catheterization laboratory in the fasting state and underwent diagnostic left heart catheterization and coronary angiography using a standard percutaneous femoral approach. The coronary angiograms were reviewed, and those patients with documented coronary atheroma were included in the study. The study vessel was atheromatous but not stenotic (no lesion >50% occlusive), and suitable angiographic views were determined.

Full anticoagulation was maintained with intravenous heparin. A bipolar temporary pacing wire was positioned in the right ventricle, and the pacemaker was set on demand at 10 beats per minute less than the patient's resting heart rate. An 8F guiding catheter (Medtronic) was positioned in the left or right coronary ostium, and a 3F 20-MHz Doppler flow probe (Schneider) was passed over a 0.014-in guide wire into the proximal coronary artery. The Doppler catheter was connected to a Millar velocimeter (Millar Instruments Inc) for continuous recordings of mean and phasic coronary artery blood flow velocities onto a chart recorder (Lectromed). The catheter was calibrated on a 0- to 40-cm/s scale, and the position and range gating were adjusted to optimize the audio velocity signal and the phasic flow velocity waveform. The Doppler position was maintained throughout the study protocol and checked at regular intervals. The ECG, heart rate, and mean and phasic arterial blood pressures were measured continuously.

Intracoronary Infusion Protocols
All solutions were infused through the Doppler probe by use of an infusion pump (Becton Dickinson UK Ltd) at a rate of 1 mL/min. A 2-minute control infusion of 5% dextrose in sterile water was given. Two-minute infusions of acetylcholine (1.6 and 16 µg/min) in 5% dextrose were then selectively administered into the coronary artery through the lumen of the Doppler flow probe. Next, 2.5 µg of 17ß-estradiol (dissolved in ethanol; final concentration of ethanol, 0.04%; Novo Nordisk A/S) was infused into the coronary artery over a period of 1 minute. The acetylcholine infusion procedure was then repeated 20 minutes after the administration of 17ß-estradiol. Finally, 1 mg of isosorbide dinitrate was infused into the coronary artery. An identical protocol was used in the control patients with estradiol vehicle (0.04% ethanol) instead of estradiol.

Quantitative Coronary Angiography
Coronary angiograms were taken at the start of the protocol and at peak mean velocity response during each infusion or at the end of the infusion if no change in velocity was detected. A resting period was observed between infusions until all measured parameters had returned to baseline. Coronary angiograms were performed before and at 10 and 20 minutes after the estradiol infusion. All angiograms were performed with nonionic contrast media (Omnipaque, Nycomed AS; iodine content, 350 mg/mL) at an injection rate of 7 mL/s. The view that best displayed the coronary artery segment for analysis in the isocenter was selected, and the x-ray gantry position was maintained throughout the study. A 4- to 5-mm length of vessel was measured in up to three consecutive end-diastolic frames at the tip of the Doppler probe and at a fixed anatomic point from the Doppler probe, and the results were then averaged. The quantitative analyses were performed independently and in a blinded fashion by an observer who was unaware of the infusion protocols.

Angiographic image data were acquired digitally in a 512x512 matrix with 10-bit depth per pixel on a real-time digital image acquisition and analysis system (Digitron III VACI, Siemens AG) at 25 frames per second (dose rate, 25 µR per frame) with gap filling, using a 12-cm nominal input field and 0.8-mm2 focal spot. A low-lag, 1249-line progressive-scan video camera (Videomed C) was directly coupled to the image intensifier. The analog output of the video camera was digitized in real time with a linear lockup table relating radiographic density to gray level, with parallel transfer via a solid-state buffer, to be stored on 4x690-megabyte Fujitsu hard disks. To correct for geometric magnification, calibration was determined from the diameter of the guiding catheter, which was measured with hand-held micrometer calipers after each study. Both algorithms for automatic edge-detection of digital data (directly acquired or from the digitized cinefilm image) used the weighted sum of the first and second derivatives to detect the vessel edge. The methods of acquisition and analysis were validated by use of contrast-filled polymethyl methacrylate phantoms of cylindrical wells ranging from 1.5 to 4.0 mm in diameter.

Area, Velocity, and Flow Measurements
Area measurements were calculated from the mean luminal diameter. Measurements were made before infusion and at peak velocity change. Coronary blood flow in milliliters per minute was estimated from the product of the mean coronary blood flow velocity and the cross-sectional area of the arterial segment under investigation.

Statistical Analysis
Patient and control data were compared by unpaired Student's t tests. Serial changes in coronary artery diameter and coronary blood flow were compared by means of the Wilcoxon test for paired data.25 A two-tailed probability level of P<.05 was considered to be significant. Values are expressed as mean±SEM.

Informed Consent
Written informed consent was obtained from every patient by the senior investigator (P.C.) in accordance with institutional guidelines, and the studies were performed by the same person. The protocol had the approval of the Royal Brompton National Heart and Lung Hospital Ethics Committee.


*    Results
up arrowTop
 up arrowAbstract
 up arrowIntroduction
 up arrowMethods
*Results
down arrowDiscussion
down arrowReferences
 
Characteristics of the Patients
All patients had coronary atherosclerosis. Eight female patients had stenoses of >50% in one or more major coronary arteries. One patient had irregular coronary arteries, four patients had one-vessel disease, and four patients had two-vessel disease. In three patients the left anterior descending coronary artery was studied, in three patients the left circumflex coronary artery was studied, and in three patients the right coronary artery was studied.

All the male patients had coronary atherosclerosis and stenoses of >50% in one or more major coronary arteries. Three patients had one-vessel disease, and four patients had two-vessel disease. In one patient the left anterior descending coronary artery was studied, in three patients the left circumflex coronary artery was studied, and in three patients the right coronary artery was studied.

All the female control patients had coronary atherosclerosis. Four patients had stenoses of >50% in one or more major coronary arteries. Two patients had irregular coronary arteries, two had one-vessel disease, and two had two-vessel disease. In three control patients the left anterior descending coronary artery was studied, and in three control patients the right coronary artery was studied.

All the male control patients had coronary atherosclerosis and stenoses of >50% in one or more major coronary arteries. Three patients had one-vessel disease, and two had two-vessel disease. In three control patients the left anterior descending coronary artery was studied, and in three control patients the right coronary artery was studied.

There were no significant differences between the groups with respect to factors that might influence the coronary response to acetylcholine (TableDown). These include age, levels of total and LDL cholesterol, triglycerides, blood glucose, blood pressure, heart rate, and coronary atherosclerosis. Blood pressure and heart rate did not change during any of the intracoronary infusions.


View this table:
[in this window]
[in a new window]
  		Table 1. Patient Characteristics

Plasma 17ß-estradiol levels were the same before versus after intracoronary infusion of 2.5 µg 17ß-estradiol. The 17ß-estradiol level in women was 52±8 pmol/L before intracoronary estrogen and 67±7 pmol/L after intracoronary estrogen (P=NS) (postmenopausal 17ß-estradiol level <200 pmol/L). In men it was 123±3 pmol/L before intracoronary estrogen and 197±54 pmol/L after intracoronary estrogen (P=NS).

Changes in Coronary Artery Diameter
Female Patients
There was no difference in coronary artery diameter between baseline and at 10 or 20 minutes after the infusion of 2.5 µg 17ß-estradiol (2.91±0.15, 2.88±0.18, and 2.82±0.15 mm, respectively, P=NS). Before intracoronary infusion of estrogen, coronary artery diameter decreased from baseline after infusion of acetylcholine (1.6 and 16 µg/min) from 2.91±0.3 to 2.73±0.26 and 2.69±0.3 mm, respectively. Twenty minutes after the intracoronary infusion of 2.5 µg 17ß-estradiol, the same concentrations of acetylcholine induced an increase in coronary artery diameters from 2.82±0.15 to 3.08±0.26 and 3.11±0.3 mm, respectively (P<.01 compared with acetylcholine response before versus after estradiol, Fig 1Down). A 1-mg dose of isosorbide dinitrate caused dilatation of the coronary arteries studied to 3.31±0.26 mm (P<.001 compared with baseline).



View larger version (28K):
[in this window]
[in a new window]
  		Figure 1. Bar graphs showing change in the diameter of female coronary arteries (left) produced by an intracoronary infusion of acetylcholine (1.6 µmol/min, open bars; 16 µmol/min, stippled bars) before and after 2.5 µmol of intracoronary 17ß-estradiol. Net constriction before estrogen was converted to dilatation after estrogen (* indicates P<.01 before vs after estrogen). Change in the diameter of male coronary arteries (right) produced by an intracoronary infusion of acetylcholine (1.6 µmol/min, open bars; 16 µmol/min, stippled bars) before and after 2.5 µmol of intracoronary 17ß-estradiol (P=NS before vs after estrogen).

Male Patients
There was no difference in coronary artery diameter between baseline and at 10 or 20 minutes after the infusion of 2.5 µg 17ß-estradiol (2.85±0.24, 2.90±0.26, and 2.85±0.26 mm, respectively, P=NS). The effect of acetylcholine (1.6 and 16 µg/min) on coronary artery diameter was no different before (from 2.91±0.24 [baseline] to 2.66±0.2 and 2.63±0.3 mm, respectively) and 20 minutes after the intracoronary infusion of 2.5 µg 17ß-estradiol (from 2.85±0.24 [baseline] to 2.73±0.26 and 2.65±0.3 mm, respectively, P=NS compared with acetylcholine response before versus after estradiol). A 1-mg dose of isosorbide dinitrate caused dilatation of the coronary arteries studied to 3.30±0.24 mm (P<.01 compared with baseline).

Female Control Patients
Placebo administration did not change coronary artery diameter from baseline at 10 and 20 minutes after the infusion (2.65±0.15, 2.59±0.19, and 2.66±0.17 mm, respectively, P=NS). The effect of acetylcholine (1.6 and 16 µg/min) on coronary artery diameter was no different before (from 2.65±0.15 [baseline] to 2.40±0.13 and 2.54±0.14 mm, respectively) and 20 minutes after placebo (from 2.66±0.17 [baseline] to 2.46±0.17 and 2.46±0.12 mm, respectively, P=NS compared with acetylcholine response before versus after placebo). A 1-mg dose of isosorbide dinitrate caused dilatation of the coronary arteries studied to 3.05±0.16 mm (P<.005 compared with baseline).

Male Control Patients
Placebo administration did not change coronary artery diameter from baseline at 10 and 20 minutes after the infusion (2.85±0.18, 2.92±0.24, and 2.79±0.19 mm, respectively, P=NS). The effect of acetylcholine (1.6 and 16 µg/min) on coronary artery diameter was no different before (from [baseline] 2.84±0.18 to 2.54±0.14 and 2.63±0.14 mm, respectively) and 20 minutes after placebo (from [baseline] 2.79±0.19 to 2.64±0.16 and 2.66±0.12 mm, respectively, P=NS compared with acetylcholine response before versus after placebo). A 1-mg dose of isosorbide dinitrate caused dilatation of the coronary arteries studied to 3.20±0.11 mm (P<.005 compared with baseline).

Changes in Coronary Blood Flow
Female Patients
There were no significant correlations between coronary blood flow and changes in blood pressure, heart rate, or the blood pressure–heart rate product. There was no difference in coronary blood flow from baseline at 10 or 20 minutes after the infusion of 17ß-estradiol (63±12, 71±16, and 68±31 mL/min, respectively, P=NS). Acetylcholine (1.6 and 16 µg/min) increased coronary blood flow both before (94±31 and 143±49 mL/min, respectively) and after (126±37 and 248±89 mL/min, respectively) the administration of 17ß-estradiol. However, there were significant differences in the increases in flow response to acetylcholine after intracoronary 17ß-estradiol (P<.009 compared with acetylcholine response before versus after estradiol, Fig 2Down). A 1-mg dose of isosorbide dinitrate caused a significant increase in coronary blood flow to 219±53 mL/min (P<.01 compared with baseline).



View larger version (21K):
[in this window]
[in a new window]
  		Figure 2. Graphs showing increase in female coronary artery blood flow evoked by acetylcholine (left) before ({circ}) and after ({bullet}) estrogen. The dose-dependent increases in coronary blood flow induced by acetylcholine were significantly greater after estrogen (* indicates P<.009 before vs after estrogen, Wilcoxon test). Increase in male coronary blood flow evoked by acetylcholine (right) before ({circ}) and after ({bullet}) estrogen. The dose-dependent increases in coronary blood flow induced by acetylcholine were the same before and after estrogen (P=NS, Wilcoxon test).

Male Patients
In male patients there was no change in coronary blood flow from baseline at 10 or 20 minutes after the infusion of 17ß-estradiol (75±10, 74±8, and 77±11 mL/min, respectively, P=NS). The effect of acetylcholine (1.6 and 16 µg/min) on coronary artery blood flow was no different before (from [baseline] 75±8 to 90±22 and 137±39 mL/min, respectively) and 20 minutes after the infusion of 17ß-estradiol (from [baseline] 77±11 to 95±19 and 142±27 mL/min, respectively, P=NS compared with acetylcholine response before versus after placebo). A 1-mg dose of isosorbide dinitrate caused an increase in coronary blood flow to 237±41 mL/min (P<.005 compared with baseline).

Female Control Patients
Placebo administration did not change coronary blood flow from baseline at 10 or 20 minutes after the infusion (76±17, 75±19, and 79±20 mL/min, respectively, P=NS). The effect of acetylcholine (1.6 and 16 µg/min) on coronary artery blood flow was no different before (from [baseline] 76±17 to 103±27 and 146±48 mL/min, respectively) and 20 minutes after placebo infusion (from [baseline] 88±24 to 104±39 and 154±49 mL/min, respectively, P=NS compared with acetylcholine response before versus after placebo). A 1-mg dose of isosorbide dinitrate caused an increase in coronary blood flow to 184±44 mL/min (P<.005 compared with baseline).

Male Control Patients
Placebo administration did not change coronary blood flow from baseline at 10 or 20 minutes after the infusion (84±15, 78±12, and 77±12 mL/min, respectively, P=NS). The effect of acetylcholine (1.6 and 16 µg/min) on coronary artery blood flow was no different before (from 84±15 [baseline] to 102±13 and 133±17 mL/min, respectively) and 20 minutes after placebo infusion (from 84±17 [baseline] to 94±18 and 118±11 mL/min, respectively, P=NS compared with acetylcholine response before versus after placebo). A 1-mg dose of isosorbide dinitrate caused an increase in coronary blood flow to 200±46 mL/min (P<.001 compared with baseline).


*    Discussion
up arrowTop
 up arrowAbstract
 up arrowIntroduction
 up arrowMethods
up arrowResults
*Discussion
down arrowReferences
 
This study demonstrates that in postmenopausal female patients with documented coronary artery disease, the vascular responses of atherosclerotic coronary arteries to acetylcholine were converted from net constriction to net dilatation within 20 minutes of exposure of the coronary arteries to 17ß-estradiol. This effect was not apparent in men of a similar age with coronary heart disease. 17ß-Estradiol also enhances the coronary flow response to acetylcholine, suggesting an additional effect on the coronary resistance vessels. Acetylcholine causes a release of endothelium-derived relaxing factor (now known to be nitric oxide or a closely related substance)26 27 28 29 and has both an indirect dilator action via the release of endothelium-derived nitric oxide and a direct constrictor effect via muscarinic receptors on vascular smooth muscle. Acetylcholine accounts for the endothelium-dependent vasodilation in human epicardial coronary arteries with normally functioning endothelium.28 In coronary arteries that have been damaged or in which the endothelium has been removed, the constrictor smooth muscle response to acetylcholine predominates, resulting in vasoconstriction.30 Acetylcholine causes paradoxical constriction of atherosclerotic and dilatation of angiographically normal coronary arteries, suggesting that atherosclerosis impairs endothelium-mediated dilatation of coronary arteries in vivo. However, it has not yet been definitively established to what extent the constrictor response of atherosclerotic coronary arteries to acetylcholine is due to an abnormality of nitric oxide release from the endothelium. In human atherosclerotic coronary arteries, endothelial dysfunction may result in an increased sensitivity to the constrictor effects of catecholamines.31 Atherosclerosis appears to disturb the normal vasomotor response of large coronary arteries to mental stress; paradoxical coronary constriction occurs during mental stress, particularly at points of stenosis.32 This vasomotor response correlates with the extent of atherosclerosis in the artery and with the response to an infusion of acetylcholine. In this study, acetylcholine had a preferential dilator effect on the microvascular coronary arterial bed, since despite a small degree of constriction of the epicardial coronary arteries (except after intracoronary 17ß-estradiol in the female patients), increases in coronary flow occurred in the absence of systemic hemodynamic changes. This is in accord with similar results for intracoronary infusions of acetylcholine published by other workers.32 33 34 35 The increase in flow induced by isosorbide dinitrate involved both epicardial coronary arterial and microvascular coronary arterial dilation, which may suggest that mechanisms other than nitric oxide are involved in the response to acetylcholine. The fact that estrogen reversed the epicardial constriction induced by acetylcholine in the female patients would suggest enhancement of nitric oxide effects or the inhibition of acetylcholine-induced epicardial coronary constriction either at the smooth muscle muscarinic receptor or by the inhibition of the release of or response to acetylcholine-induced vasoconstrictor signals.

Previous studies in estrogen-deficient female monkeys show that atherosclerosis impairs acetylcholine-mediated vascular responses.22 36 Long-term (2 years)36 estrogen replacement therapy protects against impaired vascular responses of atherosclerotic coronary arteries in postmenopausal female monkeys. However, even animal models have yet to provide any information with regard to mechanisms of action of estrogen. Suggested possible mechanisms are long-term effects on plasma lipids and atherogenesis or direct short-term effects on the endothelium. In a short-term study, coronary angiography in monkeys with coronary atherosclerosis demonstrated that arteries constricted in response to intracoronary infusion of acetylcholine before estrogen treatment but dilated 20 minutes after intravenous infusion of ethinyl estradiol.22 The vascular responses were not associated with variations in plasma lipid concentrations, blood pressure, heart rate, or plaque size. Our study shows almost identical responses in human atherosclerotic coronary arteries. An acute effect would argue against an effect on plasma lipid and lipoprotein concentrations. Long-term estrogen replacement therapy in surgically induced menopausal female monkeys inhibits the progression of atherosclerosis, reducing plaque size11 ; however, the effects of long-term estrogen therapy on vascular responses were not directly associated with the effect of estrogen on plaque content.36 A 20-minute exposure of the arteries to 17ß-estradiol would be very unlikely to change plaque size. Plasma lipids can modulate endothelium-dependent dilatation of coronary arteries,37 38 but it is unlikely that an acute change in plasma lipoprotein levels would occur in such a short period of time, as confirmed in an animal study.22 Recent evidence suggests that cells or cell breakdown products in atherosclerotic arteries may increase the breakdown of nitric oxide.39 Estrogen has been shown to be a potent antioxidant of lipids,40 and oxidized lipids inhibit nitric oxide.37 41 A reduction in lipid peroxidation in the atherosclerotic arterial wall may be one of the mechanisms whereby estrogen protects against the breakdown of endothelium-derived nitric oxide.

Estrogen may modulate the function of muscarinic receptors on endothelial or smooth muscle cells. It may facilitate the release or response of endothelium-derived relaxing factor(s) or inhibit the release of constricting factors,16 or there may be a combination of these effects. Estrogen can inhibit constrictor responses to endothelin-1 in rabbit coronary and basilar arteries.20 42 It is therefore possible that the rapid effects of estrogen on vascular responses could be explained by an inhibitory effect on endothelin-1 constrictor responses in the coronary artery. Increases in plasma endothelin-1 levels after intracoronary acetylcholine infusions in pigs with coronary artery atherosclerosis have been reported.43 An inhibition of endothelin-1 by estrogen may contribute to the reversal of the constrictor effect of acetylcholine in human atherosclerotic coronary arteries.

We previously showed a direct relaxing effect of estrogen on the vascular smooth muscle of rabbit coronary arteries.19 20 Concentrations of estrogen used in these experiments were above physiological concentrations (10-6 and 10-5 mol/L). Physiological concentrations of estrogen do not appear to have direct coronary vasodilator effects in vivo in monkeys,22 although a physiological long-term calcium antagonistic effect of estrogen on the coronary artery may explain some of its beneficial effect on atherosclerotic disease.12 Our study was designed to expose the artery to estrogen acutely in an attempt to avoid any direct continuous effect on the vessel at the time of the acetylcholine infusion. The concentration of estrogen used was the same as that used in a short-term study in the uterine circulation of ewes.17

The objective of the present study was to determine the effect of acute 17ß-estradiol on acetylcholine responses in human female and male atherosclerotic coronary arteries. The coronary arteries constricted in response to the infusion of acetylcholine before estrogen treatment, but in women they dilated 20 minutes after the intracoronary administration of 2.5 µg of 17ß-estradiol. 17ß-Estradiol also enhanced the flow-dependent responses to acetylcholine at concentrations of 1.6 and 16 µg/min in these women. These data confirm reports of a similar effect in the coronary arteries of atherosclerotic female monkeys. This is the first report of such an effect of naturally occurring estrogen (17ß-estradiol) in human female and male coronary arteries in vivo, and it confirms a similar beneficial effect of synthetic and natural estrogen in women.23 44 Short-term estrogen administration, therefore, may affect coronary endothelium-mediated dilatation in women in vivo, and rapid effects can occur. Such rapid effects may be of clinical benefit in the short- and long-term treatment of atherosclerotic coronary heart disease in postmenopausal women.

The lack of effect in male coronary arteries would argue against a nonspecific effect of estrogen. It may indicate that estrogen is working via a mechanism that is more sensitive in female coronary arteries than in those of men. Recent data show that acutely estrogen-withdrawn female rabbits demonstrate coronary arterial relaxation to estrogen that is endothelium- and nitric oxide–dependent.45 The acute exposure of estrogen-deficient women to estrogen may enhance the release of or response to nitric oxide synthase by acetylcholine. Animal data support this hypothesis. Femoral arteries from rabbits treated with 17ß-estradiol show an enhanced endothelium-dependent relaxation to acetylcholine at small concentrations (3x10-9 to 3x10-8 mol/L).13 An increased basal release of nitric oxide in endothelium-intact aortic rings from female rabbits compared with those from males has been reported.14 It has also been demonstrated that estrogen-induced increases in blood flow in the uterine artery can be antagonized by nitric oxide synthase inhibition.15 Recent work shows that estrogen can stimulate constitutive nitric oxide synthase in cultured bovine endothelial cells.46 This effect in vitro, however, is not acute and takes 16 to 24 hours. There are also conflicting data showing no effect on nitric oxide synthase in cultured bovine aortic endothelial cells.47 An acute effect on the constitutive enzyme in vivo cannot be ruled out, and an acute effect on the inducible enzyme is possible. An in vivo study in guinea pigs examined the effects of estrogen on nitric oxide synthase activity in heart, kidney, and skeletal muscle. Estradiol increased nitric oxide in female guinea pigs after 5 days of treatment; however, this occurred in males only after 10 days of estrogen exposure.48 It was suggested that the number or availability of estrogen receptors in male tissues is initially too low, requiring a period of estrogen priming.

In this study, single-plane angiograms were used, assuming that at the site measured, the coronary artery was circular. Minor errors could result from this; however, the coronary artery diameter was assessed at more than one site, which would decrease potential errors.

We recently showed a beneficial effect of sublingual estrogen on myocardial ischemia in women with established coronary artery disease.24 The mechanism of this effect is unknown, but an improvement in blood supply to the myocardium is likely, since the beneficial effect of estrogen was associated with an increased heart rate at 1-mm ST-segment depression compared with placebo. The results of the present study support the hypothesis that an acetylcholine-induced increase in coronary blood flow by estrogen may be due, in part, to a facilitation of endothelium-dependent relaxation, which may be gender specific.


*    Acknowledgments
 
This study was supported by a grant from the British Heart Foundation. We are indebted to the patients who participated in this study; to D. Clarke, Sister G. Maketo and the catheter laboratory staff, P. Allibone, S. Pearson, L. Haskell, and the staff on the Paul Wood and York wards at the Royal Brompton Hospital. Without their help and cooperation this study would not have been possible.

Received October 3, 1994; revision received December 27, 1994; accepted January 2, 1995.


*    References
up arrowTop
 up arrowAbstract
 up arrowIntroduction
 up arrowMethods
up arrowResults
up arrowDiscussion
*References
 

  1. Colditz GA, Willett WC, Stampfer MJ, Rosner B, Speizer FE, Hennekens CH. Menopause and the risk of coronary heart disease in women. N Engl J Med. 1987;316:1105-1110. [Abstract]
  2. Godsland IF, Wynn V, Crook D, Miller NE. Sex, plasma lipoproteins, and atherosclerosis: prevailing assumptions and outstanding questions. Am Heart J. 1987;114:1467-1503. [Medline] [Order article via Infotrieve]
  3. Bush TL, Barrett-Connor E, Cowan LD, Criqui MH, Wallace RB, Suchindran CM, Tyroler HA, Rifkind BM. Cardiovascular mortality and noncontraceptive use of estrogen in women: results from the Lipid Research Clinics Program Follow-up Study. Circulation. 1987;75:1102-1109.[Abstract/Free Full Text]
  4. Gruchow HW, Anderson AJ, Barboriak JJ, Sobocinski KA. Postmenopausal use of estrogen and occlusion of coronary arteries. Am Heart J. 1988;115:954-963. [Medline] [Order article via Infotrieve]
  5. Sullivan JM, Vander Zwaag R, Lemp GF, Hughes JP, Maddock V, Kroetz FW, Ramanathan KB, Mirvis DM. Postmenopausal estrogen use and coronary atherosclerosis. Ann Intern Med. 1988;108:358-363.
  6. Stampfer MJ, Colditz GA, Willett WC, Manson JE, Rosner B, Speizer FE, Hennekens CH. Postmenopausal estrogen therapy and cardiovascular disease. N Engl J Med. 1991;325:756-762. [Abstract]
  7. Sarrel PM. Ovarian hormones and the circulation. Maturitas. 1990;12:287-298. [Medline] [Order article via Infotrieve]
  8. Knopp RH. The effects of postmenopausal estrogen therapy on the incidence of arteriosclerotic vascular disease. Obstet Gynecol. 1988;72:23S-30S.
  9. Bush TL, Fried LP, Barrett-Connor E. Cholesterol, lipoproteins, and coronary heart disease in women. Clin Chem. 1988;34:B60-B70.
  10. Barrett-Connor E, Bush TL. Estrogen and coronary heart disease in women. JAMA. 1991;265:1861-1867. [Abstract]
  11. Adams MR, Kaplan JR, Manuck SB, Koritnik DR, Parks JS, Wolfe MS, Clarkson TB. Inhibition of coronary artery atherosclerosis by 17-beta estradiol in ovariectomized monkeys: lack of an effect of added progesterone. Arteriosclerosis. 1990;10:1051-1057. [Abstract/Free Full Text]
  12. Collins P, Rosano GMC, Jiang C, Lindsay D, Sarrel PM, Poole-Wilson PA. Hypothesis: cardiovascular protection by oestrogen: a calcium antagonist effect? Lancet. 1993;341:1264-1265. [Medline] [Order article via Infotrieve]
  13. Gisclard V, Miller VM, Vanhoutte PM. Effect of 17ß-estradiol on endothelium-dependent responses in the rabbit. J Pharmacol Exp Ther. 1988;244:19-22. [Abstract/Free Full Text]
  14. Hayashi T, Fukuto JM, Ignarro LJ, Chaudhuri G. Basal release of nitric oxide from aortic rings is greater in female rabbits than in male rabbits: implications for atherosclerosis. Proc Natl Acad Sci U S A. 1992;89:11259-11263. [Abstract/Free Full Text]
  15. Van Buren G, Yang D, Clark KE. Estrogen-induced uterine vasodilatation is antagonized by L-nitroarginine methyl ester, an inhibitor of nitric oxide synthesis. Am J Obstet Gynecol. 1992;16:828-833.
  16. Polderman KH, Stehouwer CDA, van Kamp GJ, Dekker GA, Verheugt FWA, Gooren LJG. Influence of sex hormones on plasma endothelin levels. Ann Intern Med. 1993;118:429-432. [Abstract/Free Full Text]
  17. Magness RR, Rosenfeld CR. Local and systemic estradiol-17 beta: effects on uterine and systemic vasodilation. Am J Physiol. 1989;256:E536-E542. [Abstract/Free Full Text]
  18. Volterrani M, Rosano GMC, Coats A, Beale C, Collins P. Estrogen acutely increases peripheral blood flow in postmenopausal women. Am J Med. In press.
  19. Jiang C, Sarrel PM, Lindsay DC, Poole-Wilson PA, Collins P. Endothelium-independent relaxation of rabbit coronary artery by 17ß-oestradiol in vitro. Br J Pharmacol. 1991;104:1033-1037. [Medline] [Order article via Infotrieve]
  20. Jiang C, Sarrel PM, Poole-Wilson PA, Collins P. Acute effect of 17ß-estradiol on rabbit coronary artery contractile responses to endothelin-1. Am J Physiol. 1992;263:H271-H275. [Abstract/Free Full Text]
  21. Jiang C, Poole-Wilson PA, Sarrel PM, Mochizuki S, Collins P, MacLeod KT. Effect of 17ß-oestradiol on contraction, Ca2+ current and intracellular free Ca2+ in guinea-pig isolated cardiac myocytes. Br J Pharmacol. 1992;106:739-745. [Medline] [Order article via Infotrieve]
  22. Williams JK, Adams MR, Herrington DM, Clarkson TB. Short-term administration of estrogen and vascular responses of atherosclerotic coronary arteries. J Am Coll Cardiol. 1992;20:452-457. [Abstract]
  23. Reis SE, Gloth ST, Blumenthal RS, Resar JR, Zacur HA, Gerstenblith G, Brinker JA. Ethinyl estradiol acutely attenuates abnormal coronary vasomotor responses to acetylcholine in postmenopausal women. Circulation. 1994;89:52-60. [Abstract/Free Full Text]
  24. Rosano GMC, Sarrel PM, Poole-Wilson PA, Collins P. Beneficial effect of oestrogen on exercise-induced myocardial ischaemia in women with coronary artery disease. Lancet. 1993;342:133-136. [Medline] [Order article via Infotrieve]
  25. Wallenstein S, Zucker CL, Fleiss JL. Some statistical methods useful in circulation research. Circ Res. 1980;47:1-9. [Abstract/Free Full Text]
  26. Furchgott RF, Zawadzki JV. The obligatory role of endothelial cells in the relaxation of arterial smooth muscle by acetylcholine. Nature. 1980;288:373-376. [Medline] [Order article via Infotrieve]
  27. Palmer RM, Ferrige AG, Moncada S. Nitric oxide release accounts for the biological activity of endothelium-derived relaxing factor. Nature. 1987;327:524-526. [Medline] [Order article via Infotrieve]
  28. Collins P, Burman J, Chung H, Fox KM. Hemoglobin inhibits endothelium-dependent relaxation to acetylcholine in human coronary arteries in vivo. Circulation. 1993;87:80-85. [Abstract/Free Full Text]
  29. Myers PR, Minor RL Jr, Guerra R Jr, Bates JN, Harrison DG. Vasorelaxant properties of the endothelium-derived relaxing factor more closely resemble S-nitrosocysteine than nitric oxide. Nature. 1990;345:161-163. [Medline] [Order article via Infotrieve]
  30. Ludmer PL, Selwyn AP, Shook TL, Wayne RR, Mudge GH, Alexander RW, Ganz P. Paradoxical vasoconstriction induced by acetylcholine in atherosclerotic coronary arteries. N Engl J Med. 1986;315:1046-1051. [Abstract]
  31. Vita JA, Treasure CB, Yeung AC, Vekshtein VI, Fantasia GM, Fish RD, Ganz P, Selwyn AP. Patients with evidence of coronary endothelial dysfunction as assessed by acetylcholine infusion demonstrate marked increase in sensitivity to constrictor effects of catecholamines. Circulation. 1992;85:1390-1397. [Abstract/Free Full Text]
  32. Yeung AC, Vekshtein VI, Krantz DS, Vita JA, Ryan TJ Jr, Ganz P, Selwyn AP. The effect of atherosclerosis on the vasomotor response of coronary arteries to mental stress. N Engl J Med. 1991;325:1551-1556. [Abstract]
  33. Horio Y, Yasue H, Okumura K, Takaoka K, Matsuyama K, Goto K, Minoda K. Effects of intracoronary injection of acetylcholine on coronary arterial hemodynamics and diameter. Am J Cardiol. 1988;62:887-891. [Medline] [Order article via Infotrieve]
  34. Egashira K, Inou T, Hirooka Y, Yamada A, Urabe Y, Takeshita A. Evidence of impaired endothelium-dependent coronary vasodilatation in patients with angina pectoris and normal coronary angiograms. N Engl J Med. 1993;328:1659-1664. [Abstract/Free Full Text]
  35. Egashira K, Inou T, Hirooka Y, Kai H, Sugimachi M, Suzuki S, Kuga T, Urabe Y, Takeshita A. Effects of age on endothelium-dependent vasodilation of resistance coronary artery by acetylcholine in humans. Circulation. 1993;88:77-81. [Abstract/Free Full Text]
  36. Williams JK, Adams MR, Klopfenstein HS. Estrogen modulates responses of atherosclerotic coronary arteries. Circulation. 1990;81:1680-1687. [Abstract/Free Full Text]
  37. Simon BC, Cunningham LD, Cohen RA. Oxidized low density lipoproteins cause contraction and inhibit endothelium-dependent relaxation in the pig coronary artery. J Clin Invest. 1990;86:75-79.
  38. Jiang C, Jacobs M, Kerr P, Collins P. Oxidised low density lipoproteins (OxLDL) inhibit endothelium-dependent relaxation to acetylcholine (ACh) in isolated rabbit coronary arteries. J Am Coll Cardiol. 1993;21:430A. Abstract.
  39. Minor RL Jr, Myers PR, Guerra R Jr, Bates JN, Harrison DG. Diet-induced atherosclerosis increases the release of nitrogen oxides from rabbit aorta. J Clin Invest. 1990;86:2109-2116.
  40. Yagi K, Komura S. Inhibitory effect of female hormones on lipid peroxidation. Biochem Int. 1986;13:1051-1055. [Medline] [Order article via Infotrieve]
  41. Creager MA, Cooke JP, Mendelsohn ME, Gallagher SJ, Coleman SM, Loscalzo J, Dzau VJ. Impaired vasodilation of forearm resistance vessels in hypercholesterolemic humans. J Clin Invest. 1990;86:228-234.
  42. Shay J, Badrov N, Attele A, Levinson M, Moss J. Estrogen antagonises endothelin-1 vasoconstriction in rabbit basilar artery. Anesth Analg. 1993;A561. Abstract.
  43. Lerman A, Webster MWI, Chesebro JH, Edwards WD, Wei C-M, Fuster V, Burnett JC Jr. Circulating and tissue endothelin immunoreactivity in hypercholesterolemic pigs. Circulation. 1993;88:2923-2928. [Abstract/Free Full Text]
  44. Gilligan DM, Quyyumi AA, Cannon RO III. Effects of physiological levels of estrogen on coronary vasomotor function in postmenopausal women. Circulation. 1994;89:2545-2551. [Abstract/Free Full Text]
  45. Collins P, Shay J, Jiang C, Moss J. Nitric oxide accounts for dose-dependent estrogen-mediated coronary relaxation following acute estrogen withdrawal. Circulation. 1994;90:1964-1968. [Abstract/Free Full Text]
  46. Schray-Utz B, Zeiher AM, Busse R. Expression of constitutive NO synthase in cultured endothelial cells is enhanced by 17ß-estradiol. Circulation. 1993;88(suppl I):I-80. Abstract.
  47. Sayegh HS, Ohara Y, Navas JP, Peterson TE, Dockery S, Harrison DG. Endothelial nitric oxide synthase regulation by estrogens. Circulation. 1993;88(suppl I):I-80. Abstract.
  48. Weiner CP, Lizasoain I, Baylis SA, Knowles RG, Charles IG, Moncada S. Induction of calcium-dependent nitric oxide synthases by sex hormones. Proc Natl Acad Sci U S A. 1994;91:5212-5216.[Abstract/Free Full Text]



This article has been cited by other articles:


Home page
 J Am Coll Cardiol ImgHome page
L. R. Peterson, P. F. Soto, P. Herrero, B. S. Mohammed, M. S. Avidan, K. B. Schechtman, C. Dence, and R. J. Gropler
Impact of Gender on the Myocardial Metabolic Response to Obesity
J. Am. Coll. Cardiol. Img., July 1, 2008; 1(4): 424 - 433.
[Abstract] [Full Text] [PDF]

Home page
 Eur Heart JHome page
S. H. Han, J. H. Bae, D. R. Holmes Jr, R. J. Lennon, E. Eeckhout, G. W. Barsness, C. S. Rihal, and A. Lerman
Sex differences in atheroma burden and endothelial function in patients with early coronary atherosclerosis
Eur. Heart J., June 1, 2008; 29(11): 1359 - 1369.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Heart Circ. Physiol.Home page
A. Goel, D. Thor, L. Anderson, and R. Rahimian
Sexual dimorphism in rabbit aortic endothelial function under acute hyperglycemic conditions and gender-specific responses to acute 17{beta}-estradiol
Am J Physiol Heart Circ Physiol, June 1, 2008; 294(6): H2411 - H2420.
[Abstract] [Full Text] [PDF]

Home page
 Menopause IntHome page
M. Rees, J. Stevenson, and on behalf of the British Menopause Society Council
Primary prevention of coronary heart disease in women
Menopause Int, March 1, 2008; 14(1): 40 - 45.
[Abstract] [Full Text] [PDF]

Home page
 Eur Heart JHome page
P. Collins, M. Flather, B. Lees, R. Mister, A. J. Proudler, J. C. Stevenson, and on behalf of the WHISP (Women's Hormone Interventi
Randomized trial of effects of continuous combined HRT on markers of lipids and coagulation in women with acute coronary syndromes: WHISP Pilot Study
Eur. Heart J., September 1, 2006; 27(17): 2046 - 2053.
[Abstract] [Full Text] [PDF]

Home page
 HeartHome page
J C Kaski
Cardiac syndrome X in women: the role of oestrogen deficiency
Heart, May 1, 2006; 92(suppl_3): iii5 - iii9.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Heart Circ. Physiol.Home page
M. N. Cruz, G. Douglas, J.-A Gustafsson, L. Poston, and K. Kublickiene
Dilatory responses to estrogenic compounds in small femoral arteries of male and female estrogen receptor-{beta} knockout mice
Am J Physiol Heart Circ Physiol, February 1, 2006; 290(2): H823 - H829.
[Abstract] [Full Text] [PDF]

Home page
 HypertensionHome page
R. A. Khalil
Sex Hormones as Potential Modulators of Vascular Function in Hypertension
Hypertension, August 1, 2005; 46(2): 249 - 254.
[Abstract] [Full Text] [PDF]

Home page
 Eur Heart JHome page
Y. T. van der Schouw and D. E. Grobbee
Menopausal complaints, oestrogens, and heart disease risk: an explanation for discrepant findings on the benefits of post-menopausal hormone therapy
Eur. Heart J., July 2, 2005; 26(14): 1358 - 1361.
[Abstract] [Full Text] [PDF]

Home page
 J. Biol. Chem.Home page
X. Guo, M. Razandi, A. Pedram, G. Kassab, and E. R. Levin
Estrogen Induces Vascular Wall Dilation: MEDIATION THROUGH KINASE SIGNALING TO NITRIC OXIDE AND ESTROGEN RECEPTORS {alpha} AND {beta}
J. Biol. Chem., May 20, 2005; 280(20): 19704 - 19710.
[Abstract] [Full Text] [PDF]

Home page
 JNMHome page
P. A. Kaufmann and P. G. Camici
Myocardial Blood Flow Measurement by PET: Technical Aspects and Clinical Applications
J. Nucl. Med., January 1, 2005; 46(1): 75 - 88.
[Full Text] [PDF]

Home page
 ScienceHome page
K. M. Egan, J. A. Lawson, S. Fries, B. Koller, D. J. Rader, E. M. Smyth, and G. A. FitzGerald
COX-2-Derived Prostacyclin Confers Atheroprotection on Female Mice
Science, December 10, 2004; 306(5703): 1954 - 1957.
[Abstract] [Full Text] [PDF]

Home page
 Proc. Natl. Acad. Sci. USAHome page
Q. Lu, D. C. Pallas, H. K. Surks, W. E. Baur, M. E. Mendelsohn, and R. H. Karas
Striatin assembles a membrane signaling complex necessary for rapid, nongenomic activation of endothelial NO synthase by estrogen receptor {alpha}
PNAS, December 7, 2004; 101(49): 17126 - 17131.
[Abstract] [Full Text] [PDF]

Home page
 EndocrinologyHome page
G. A. Head, V. R. Obeyesekere, M. E. Jones, E. R. Simpson, and Z. S. Krozowski
Aromatase-Deficient (ArKO) Mice Have Reduced Blood Pressure and Baroreflex Sensitivity
Endocrinology, September 1, 2004; 145(9): 4286 - 4291.
[Abstract] [Full Text] [PDF]

Home page
 CirculationHome page
D. D. Waters, D. Gordon, J. E. Rossouw, R. O. Cannon III, P. Collins, D. M. Herrington, J. Hsia, R. Langer, L. Mosca, P. Ouyang, et al.
Women's Ischemic Syndrome Evaluation: Current Status and Future Research Directions Report of the National Heart, Lung and Blood Institute Workshop : October 2-4, 2002 : Section 4: Lessons From Hormone Replacement Trials
Circulation, February 17, 2004; 109 (6): e53 - e55.
[Full Text] [PDF]

Home page
 Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
J. M. Orshal and R. A. Khalil
Gender, sex hormones, and vascular tone
Am J Physiol Regulatory Integrative Comp Physiol, February 1, 2004; 286(2): R233 - R249.
[Abstract] [Full Text] [PDF]

Home page
 Circ. Res.Home page
M. E. Mendelsohn and G. M.C. Rosano
Hormonal Regulation of Normal Vascular Tone in Males
Circ. Res., December 12, 2003; 93(12): 1142 - 1145.
[Full Text] [PDF]

Home page
 Circ. Res.Home page