Full text of DOI:10.1002/clc.4960250407

Clin. Cardiol. 25, 167–172 (2002)
Conjugated Estrogen Administration Improves Common Carotid Artery Elastic
Properties in Normotensive Postmenopausal Women
IOANNIS KALLIKAZAROS, M.D., FESC, COSTAS TSIOUFIS, M.D., FESC, PANAGIOTIS ZAMBARAS, M.D., CHRISTODOULOS STEFANADIS, M.D., FACC,
PAVLOS TOUTOUZAS, M.D., FACC
Department of Cardiology, Hippokration Hospital, University of Athens, Athens, Greece
Summary
Background: Various vascular effects of estrogens have
been proposed to explain further the beneficial effect of re-
placement therapy in cardiovascular events.
Conclusions: Acute conjugated estrogen administration in-
duced an improvement in CCA elasticity and a reduction in
brain impedance in normotensive, postmenopausal women.
As the age of women and the time since menopause increased,
the improvement in carotid distensibility decreased in such se-
lected subjects.
Hypothesis: The study was undertaken to assess the effect
of conjugated estrogen on the elastic properties of the large ar-
teries in normotensive, healthy, postmenopausal women.
Methods: Toward this end, we investigated the acute effect
of conjugated estrogen on the elastic properties of the common
carotid artery (CCA) in 20 normotensive, healthy, postmeno-
pausal women (age 54 ± 3 years) at baseline and 20 min after
the intravenous administration of 1.25 mg conjugated estro-
gens. The CCA distensibility was derived by a combination of
surface ultrasonographic data and simultaneous blood pres-
sure measurements at the brachial artery. The carotid pulsatil-
ity index, a measure of brain impedance, was determined elec-
tronically by tracing the CCA Doppler waveform.
Key words: conjugated estrogen, carotid artery distensibility,
postmenopausal women
Introduction
Menopause is associated with structural and functional car-
diovascular adaptations regardless of the presence or absence
1, 2
of high blood pressure. The reduced arterial elasticity which
accompanies menopause contributes to increased pulse pres-
sure which has been shown to be an independent predictor of
2–5
Results: At baseline, CCA distensibility had a negative
correlation with both patients’ age and time since menopause
future cardiovascular events. Although stroke is an impor-
tant cause of morbidity and mortality in women, there is little
information about the risk of stroke in current postmenopausal
(r = ꢀ0.57 and r = ꢀ0.48, p<0.05 for both cases). After estro-
6, 7
gen administration, estradiol and estrone plasma levels were
restored to the range of usual premenopausal values. Estrogen
induced a significant increase in CCA distensibility by 0.92 ±
hormone users, and these results are still conflicting. Fur-
thermore, since only 25–50% of the replacement therapy ben-
eficial effect in cardiovascular events is attributable to lipid
lowering, a variety of vascular effects of estrogens is suggest-
ꢀ1
2
ꢀ6
ꢀ1
2
ꢀ6
0
.005dyne ·cm ·10 (from2.03to2.95dyne ·cm ·10 )
and a significant reduction in CCA pulsatility index by 0.24 ±
.06, (from 2.17 to 1.93) (p<0.001 for both cases). The im-
8–10
ed.
Estrogen may inhibit atherosclerosis and also play an
0
integral role in the maintenance of arterial hemodynamics that
11, 12
provement in CCA distensibility had a negative correlation
with both patients’ age and time since menopause (r = ꢀ0.46
and r = ꢀ0.44, respectively, p<0.05 for both cases).
prevent ischemia.
In this study, we report the acute effect
of conjugated estrogens on the elastic properties of common
carotid artery (CCA) in normotensive, postmenopausal wom-
en in an attempt to clarify the possible mechanisms by which
hormone replacement therapy exerts its favorable effect on the
risk of stroke.
Subjects and Methods
Study Population
Address for reprints:
Ioannis Kallikazaros, M.D.
1
1
2, Anapauseos Street
5126 Marousi
Women were eligible if menopause had occurred at least 1
year previously, without their undergoing any hormone re-
placement therapy, and whose plasma estradiol concentration
was within the appropriate range of postmenopausal values
for our laboratory. All participants were free of vasomotor
Athens, Greece
Received: January 9, 2001
Accepted with revision: August 7, 2001

168
Clin. Cardiol. Vol. 25, April 2002
symptoms associated with the effect of menopause. Women
with a history or clinical evidence of coronary artery disease,
cerebrovascular disease, valvular disease, myocardiopathy,
congestive heart failure, hypertension, diabetes mellitus, liver
or renal or any systemic disease were excluded, as were wom-
en with a history of thromboembolism, smoking, familiar hy-
percholestorelemia, and alcohol or drug abuse. We looked
carefully for evidence of plaques (defined as a thickening of
the wall ≥50% of the surrounding wall) bilateral on the com-
mon, internal, and external carotid artery in order to exclude
such women with presence of plaques. Finally, 20 healthy, un-
medicated postmenopausal women, aged 54 ± 3 years with
BP variation of <5 mmHg over two consecutive measure-
ments. Pulse pressure was calculated as the difference be-
tween systolic and diastolic BP values. The CCA measure-
ments were combined with the simultaneous oscillometric
BP readings to calculate the carotid artery distensibility by
means of the formula: Carotid artery distensibility = 2ꢁ
[CCA systolic diameter ꢀCCA diastolic diameter]/[CCA di-
ꢀ1
2
ꢀ6 13–16
astolic diameter ꢁpulse pressure] [dyne ·cm ·10 ]).
When the CCA diameter measurements were completed,
the pulsed Doppler range gate was placed across the right ca-
rotid artery 1.5 cm proximal to the carotid bifurcation, which
was the measurement site, to obtain flow velocity waveforms.
We made certain that the sample volume was placed in exactly
the same position for all repeated measurements and that at
least five consecutive Doppler waveforms of adequate quality
(representing 5 cardiac cycles) were recorded. Common carot-
id artery pulsatility index was determined electronically by
tracing the CCA Doppler waveform and defined as the dif-
ference between the peak systolic shifted frequency and end-
diastolic shifted frequency divided by the mean frequency
4.8 ± 2.5 years since menopause fulfilling the above criteria
were selected.
All subjects underwent physical examination, 12-lead
electrocardiogram, chest x-ray, and standard laboratory ex-
aminations. The study protocol included duplex ultrasound
scanning of carotid arteries and assay of plasma estradiol (E2)
and estrone (E1) concentrations before as well as 20 min after
intravenous administration of 1.25 mg conjugated estrogens
®
13, 17, 18
(
Premarin , Wyeth-Ayerst). The study protocol was approved
shift over the cardiac cycle given.
by the ethics committee of the Institutional Review Board of
our hospital. After description of the procedure, written in-
formed consent was obtained from all women participating in
the study.
After the above baseline CCA measurements, conjugated
estrogens were administered intravenously through a periph-
eral vein in a bolus dose of 1.25 mg over a 2 min period.
19
Electrocardiogram, BP, and carotid artery duplex scanning pa-
rameters were continuously monitored and recorded repeated-
ly at 20 min after the end of conjugated estrogen administra-
tion. At the same time, blood was drawn for determination of
E1 and E2 concentrations. All images were recorded on super
VHS videotapes for subsequent off-line analysis. Five consec-
utive cycles were measured blindly by two observers and the
mean value was used in the analysis.
Carotid Artery Duplex Ultrasonography
Carotid arteries duplex ultrasound studies were performed
in the echocardiography department of our clinic by an experi-
enced investigator, using a Hewlett Packard Sonos 2500
(Hewlett Packard [Philips Medical Systems/Agilent Technol-
ogies, Andover, Mass., USA]), equipped with a 7.5/5.5 MHz
phased linear-array transducer. The ultrasonographic studies
were scheduled to start at 11.00 A.M. under a controlled room
temperature of 22˚C, with constant noise and light intensity,
during a day’s hospitalization. All subjects had had a similar
meal at least 3 h prior to the study and rested in a supine posi-
tion for 15–20 min. Patients were studied in the supine posi-
tion with slight neck hyperextension. Long axis B-mode im-
ages of the right CCA were obtained in three projections
Repeatability of Arterial Measurements
Repeatability of our measurements was investigated in five
subjects through calculation of the repeatability coefficient
(
RC) as defined by the British Standard Institution, according
2
2
to the formula RC = (ꢂDi )/N, where N is the sample size
and Di the relative difference between each pair of measure-
20
ments. Repeatability coefficient values for the intraobserv-
er repeatability (comparison of two determinations obtained
at 24 h intervals by the same observer) concerning CCA sys-
tolic and diastolic diameter and pulsatility index at baseline
were 0.031 and 0.035 mm, and 0.09, respectively. Also, RC
values for the interobserver repeatability (comparison of two
determinations obtained at the same time by two observers)
concerning CCA systolic and diastolic diameter and pulsatil-
ity index at baseline were 0.041 and 0.039 mm, and 0.08, re-
spectively. These values were small compared with the mean
values of CCA systolic and diastolic diameter and its pulsatil-
ity index in the sample.
(
anterior, posterior, and lateral) in order to obtain simultane-
13–17
ously a fine image of the near and far wall.
The CCA sys-
tolic and diastolic diameter was determined in frames corre-
sponding to the maximal and minimal diameters, respectively.
Both CCA systolic and diastolic diameters were measured as
the distance between the intima-lumen interface of the near
13–16
and far walls.
Values were measured over five consecutive
cardiac cycles and averaged.
For the calculation of CCA distensibility, pulse rate and
blood pressure were measured at the brachial artery simulta-
neously with the performance of CCA ultrasonographic stud-
ies, with the use of an automatic oscillometric device (Dina-
map XL, Johnson & Johnson, Inc.). Blood pressure (BP)
values were obtained for measurements after the achievement
of a steady hemodynamic state, manifested by a pulse rate
variation of less than five beats/min and systolic and diastolic
Plasma Estradiol and Estrone Assay
Blood samples were drawn and centrifuged immediately
and plasma was frozen at ꢀ20˚C for estimation of E1 and E2
concentration by radioimmunoassay.

I. Kallikazaros et al.: Estrogen and carotid elasticity
169
TABLE I Clinical characteristics of the study subjects
ultrasonographic measurements and the oscillometric blood
pressure data, at baseline as well as after the acute administra-
tion of conjugated estrogen, are presented in Table II.
The CCA systolic and diastolic diameter was significantly
increased by 0.035 and 0.02 cm, respectively (p< 0.001 for
both cases), after estrogen administration. Similarly, the pul-
satile changes of CCA diameter increased significantly by
Age (years)
Time since menopause (years)
Body surface area (kg/m )
Total cholesterol (mg/dl)
Plasma estradiol (pg/ml)
Plasma estrone (pg/ml)
54.2 ± 3
4.8 ± 2.5
1.72 ± 0.8
215 ± 45
45 ± 23
32 ± 16
124/82
2
0
.015 cm (p< 0.001). Estrogen induced a significant increase
Clinic blood pressure (mmHg)
ꢀ1
2
ꢀ6
in CCA distensibility by 0.92 ± 0.005 dyne · cm ·10
ꢀ1
2
ꢀ6
(
from 2.03 to 2.95 dyne ·cm ·10 ) (p<0.001) and a sig-
nificant reduction in CCA pulsatility index by 0.24 ± 0.06
from 2.17 to 1.93) (p < 0.001).
(
Statistical Analysis
Correlations
Data are expressed as mean ± standard deviation (SD).
A value of p≤0.05 was accepted as statistically significant.
The variables compared before and after conjugated estrogen
administration intervals included BP, heart rate, E1 and E2
plasma levels, CCA systolic and diastolic diameter, CCA dis-
tensibility, and CCA pulsatility index. Significant differences
of the parameters studied at baseline and after estrogen ad-
ministration were determined by use of the paired t-test. Mul-
tiple linear regression analysis, with inclusion criteria at the
Before estrogen administration, pulsatility index had a pos-
itive correlation with age (r = 0.90, p<0.0001) and with time
since menopause (r = 0.94, p< 0.001), while CCA distensibil-
ity had a negative correlation with age (r = ꢀ0.57, p< 0.001)
and with time after menopause (r = ꢀ0.48, p< 0.05).
After estrogen administration, the reduction of pulsatility
index had no significant correlation with age or the time since
menopause, while the improvement of CCA distensibility had
a negative correlation with age and with time since menopause
0.01 level and exclusion criteria at the 0.05 level, was used to
evaluate the relation of clinical, demographic, and laboratory
parameters with CCA elasticity indices. Pearson correlation
coefficient was employed to detect possible significant corre-
lation between CCA elasticity indices and demographic and
clinical parameters.
(r = ꢀ0.46 and r = ꢀ0.44, respectively, p <0.05 for both cases)
(Figs. 1 and 2, respectively).
Furthermore, CCA distensibility at baseline and the change
of CCA distensibility after estrogen administration was en-
tered in multiple regression models to identify significant rela-
tions with age, time since menopause, body mass index, arteri-
al pressure, total serum cholesterol levels, and E1 and E2 levels.
It was revealed that both CCA distensibility at baseline and the
change of CCA distensibility after estrogen administration
were significantly related with age (p = 0.004 and p = 0.002,
respectively) and time since menopause (p = 0.002 and p =
Results
All women underwent the study without reporting any ad-
verse symptoms after conjugated estrogen administration. The
clinical and demographic characteristics are presented in
Table I. After estrogen administration, E1 and E2 concentration
increased substantially, peaking to 308 ± 52 pg/ml and 341 ±
0.02, respectively).
1
33 pg/ml, respectively, at 15 min (p < 0.001) and remaining at
Discussion
typical premenopausal levels throughout the study. Heart rate
and systolic and diastolic BP as well as pulse pressure did not
change significantly after estrogen administration. The CCA
In the present study, we investigated the acute effect of conju-
gated estrogen on CCA mechanics in normotensive, postmen-
TABLE II Carotid artery and oscillometric blood pressure measurements
CCA parameters
Baseline
20 min
p Value
Systolic diameter (cm)
Diastolic diameter (cm)
Pulsatile change of diameter (cm)
Heart rate (beats/min)
0.690 ± 0.03
0.660 ± 0.02
0.03 ± 0.01
76 ± 5
0.725 ± 0.02
0.680 ± 0.02
0.045 ± 0.01
77 ± 5
0.001
0.001
0.001
NS
Systolic blood pressure (mmHg)
Diastolic blood pressure (mmHg)
Pulse pressure (mmHg)
128.7 ± 6
84.1 ± 3
44.6 ± 4
2.03 ± 0.4
2.17 ± 0.13
128.4 ± 6
83.7 ± 3
44.7 ± 4
2.95 ± 0.7
1.93 ± 1.15
NS
NS
NS
0.001
0.001
Distensibility (dyne · cm ·10ꢀ6)
ꢀ
1
2
Pulsatility index
Abbreviations: CCA = common carotid artery, NS = not significant.

170
Clin. Cardiol. Vol. 25, April 2002
0
0
.2
.1
menopause on the elastic properties of the aortic root is abrupt
and devastating in hypertensive women. In agreement with
this study, we found that CCA distensibility decreased as pa-
tients age, and as the time since menopause increased in nor-
motensive postmenopausal women.
2
r =ꢀ0.46, p < 0.05
Pulsatility index represents the impedance to blood flow
downstream from the point of measurement; the higher the
17, 18
value the greater the impedance.
In our postmenopausal
0
.0
women, the pulsatility index was found to have a positive cor-
relation with age and time since menopause, and these find-
ings are in agreement with a previous study by Gangar et al.
17
Epidemiologic studies have shown that the rates of cardio-
vascular and cerebrovascular mortality in women who receive
estrogen replacement therapy are a third to a half of those in
ꢀ
0.1
4
8
50
52
54
56
58
60
Age (years)
3, 4
untreated women; however, in the Nurses’ Health Study,
there was no significant association between stroke and use of
FIG. 1 Relation between changes in common carotid artery (CCA)
distensibility induced by estrogen and age of postmenopausal women.
22
23
combined hormones or estrogen alone. Graby et al. using
meta-analytic statistical methods, concluded that there is no
convincing evidence that estrogens decrease stroke risk sig-
nificantly. Even nowadays, the data on stroke are unclear, and
this issue will be addressed more directly in the next decade,
when the results of clinical trials, such as the Women’s Health
0
0
.2
.1
r =ꢀ0.44, p < 0.05
24
Initiative, will be known. The apparent benefit of estrogen
replacement therapy on cardiovascular events cannot be ac-
counted for only by its favorable effect on lipids profile. Our
findings that conjugated estrogen improves CCA elasticity
and decreases brain impedance are in agreement with previ-
ous studies suggesting a variety of vascular effects of estrogen
on both peripheral and coronary vessels and may contribute to
the better understanding of the rationale for the estrogen-in-
0
.0
5–8, 13, 19, 25, 26
duced protection from stroke.
Although the present study was not designed to assess the
mechanism of estrogen vasomotor effects, we may suggest
that conjugated estrogen actions on the CCA function could be
interpreted, at least partly, by an endothelium-independent
mechanism. We may support this, since we excluded women
with atherosclerotic plaques in the carotid arteries, as well as
women with other conditions which are associated with
endothelium dysfunction such as hypertension, smoking, or
hypercholesterolemia. Thus, it is possible that conjugated es-
trogen improves the distensibility through a calcium-channel
antagonist effect. Toward this direction, Stefanadis et al. have
proved that estrogen improves aortic distensibility by an active
ꢀ
0.1
1
2
3
4
5
6
7
8
9
Time from menopause (years)
FIG. 2 Relation between changes in common carotid artery (CCA)
distensibility induced by estrogen and time since menopause in post-
menopausal women.
opausal women. We found that estrogens induce an improve-
ment in CCA distensibility apart from the reduction of brain
impedance in this setting. Furthermore, we found that the older
the women and the longer the time since menopause, the less
improvement in CCA elasticity after estrogen administration.
Large arteries, such as aorta and carotid, function both as a
conduit delivering blood to the tissues and as an important
modulator of the cardiovascular system, buffering the inter-
mittent pulsatile output from the heart to provide steady flow
27
mechanism, suggesting a calcium-antagonist effect. In addi-
tion, Collins et al. have supported the view that if estrogens
have a calcium-channel antagonist effect on human beings,
then this mechanism may contribute significantly to its protec-
tive effect on the development and progression or regression of
28
atherosclerosis in coronary and other arteries in women. It is
obvious that we cannot rule out the possibility that conjugated
estrogen may enhance endothelium-dependent vasodilatation
by facilitating nitric oxide release. Our finding that the estro-
gen-induced improvement on CCA elasticity is inversely re-
lated with patients’ age and the time since menopause may
suggest that replacement therapy should be started early after
menopause. However, it is unclear to what extent the benefits
and risks of replacement therapy apply to older women. Only
3–5
to capillary beds. Aging, along with or without hyperten-
sion, exerts further ill effects through structural and function-
al modifications of the arterial wall. Recently, it has been
5
reported that CCA stiffness is an independent predictor of all-
21
cause mortality in end-stage renal disease. Furthermore,
menopause is associated with early structural and functional
manifestations of heart disease in both hypertensive and nor-
1
motensive women. Similarly, it is supported that the effect of

I. Kallikazaros et al.: Estrogen and carotid elasticity
171
randomized trials with clinical outcomes that are of sufficient
References
size and duration can answer this question.
1
.
Schillaci G, Verdecchia P, Borgioni C, Ciucci A, Porcellati C: Early
cardiac changes after menopause. Hypertension 1998;32:764–769
Karpanou E, Vyssoulis G, Papakyriakou S, Toutouza M, Toutouzas
P: Effects of menopause on aortic root distensibility in hypertensive
women. J Am Coll Cardiol 1996;28:1562–1566
2.
Limitations
In the present study, the distensibility of CCA was deter-
mined by pulse pressure obtained at the site of brachial artery.
Given that amplification of pulse pressure from central arteries
to a more distal one is a well known phenomenon attributable
to pulse-wave reflection, the difference between CCA BP and
brachial artery BP may affect the accuracy of CCA distensibil-
3. Darne B, Girerd X, Safar M, Cambien F, Guize L: Pulsatile versus
steady component of blood pressure: A cross-sectional analysis and
a prospective analysis on cardiovascular mortality. Hypertension
1989;13:392–400
4.
Benetos A, Rudnichi A, Safar M, Guize L: Pulse pressure and car-
diovascular mortality in normotensive and hypertensive subjects.
Hypertension 1998;32:560–564
5
5. O’Rourke M: Mechanical principles in arterial disease.
ity. However, the pulse pressure, which was estimated nonin-
Hypertension 1995;26:1–9
vasively at the brachial artery, correlates well with that mea-
sured directly from the aorta and has been extensively used for
6.
Stampfer MJ, Coldritz GA, Willet WC, Ronser B, Speizer E,
Hennekens CH: Postmenopausal estrogen therapy and cardiovas-
cular disease: Ten year follow-up from the Nurses Health Study.
N Engl J Med 1991;325:756–762
15, 16, 29
determination of the aortic and CCA elastic properties.
Furthermore, we used a video imaging analysis for estimation
of CCA systolic and diastolic diameter. Although the video
imaging analysis has much less reproducibility than does the
7.
Paganini-Hill A, Ross RK, Henderson BE: Postmenopausal estro-
gen treatment and stroke: A prospective study. Br Med J 1988;295:
519–522
30
echo-tracking method, our method has been used previous-
8.
Bourne T, Hillard TC, Whitehead MI, Crook D, Campbell S: Estro-
gens, arterial status, and postmenopausal women. Lancet 1990;
335:1470–1471
15, 16, 30
ly
and is preferred in clinical practice due to our good
repeatability in arterial measurements.
We chose to administer conjugated equine estrogens since
they are the most commonly prescribed medications for the
amelioration of menopausal symptoms, and their effect on
the function of peripheral circulation has not been well in-
vestigated. However, it is known that estrogen may have
class-specific and dose-dependent vasomotor properties. In
our case, a dose of 1.25 mg conjugated equine estrogen giv-
en intravenously increased plasma E1 levels to approximate-
ly 300 pg/ml, typical mid-cycle premenopausal values pro-
viding precise physiologic replacement without producing
any potential harmful side effect. In addition, the conjugat-
ed estrogen used in this study contains several vasoactive
estrogenic compounds, which may account for some of the
effects observed.
9. Lieberman EH, Gerhard MD, Uehata A, Walsh B, Selwyn A, Ganz
P, Yeung A, Creager M: Estrogen improves endothelium-depen-
dent flow mediated vasodilatation in postmenopausal women. Ann
Intern Med 1994;121:936–941
1
0. Gilligan DM, Badar DM, Panza JA, Quyyumi AA, Canon RO:
Acute vascular effect of estrogen in postmenopausal women.
Circulation 1994;90:786–791
1
1. Holm P, Korsgaard N, Shalmi M, Andersen l, Hougaard P, Skouby
O, Stender S: Significant reduction of the antiatherogenic effect of
estrogen by long term inhibition of nitric oxide synthesis in choles-
terol-clamped rabbits. J Clin Invest 1997;100:821–828
12. Vogel R, Corretti M: Estrogens, progestin and heart disease.
Can endothelial function divine the benefit? Circulation 1998;97:
1223–1226
1
3. Kallikazaros I, Tsioufis C, Sideris S, Stefanadis C: Acute adminis-
tration of conjugated estrogen improves common carotid artery
physical properties in normotensive postmenopausal women.
Circulation 1999;100(18)(suppl):I-178
Another limitation of our study may be the rather small
study population. However, this small sample may be balanced
against the strict inclusion criteria, and, consequently, our
women are part of a highly selected population.
14. Kallikazaros I, Tsioufis C, Sideris S, Stefanadis C, Toutouzas P:
Carotid artery disease as a marker for the presence of severe coro-
nary artery disease in patients evaluated for chest pain. Stroke
1999;30:1002–1007
1
5. Pierdomenico S, Lapenna D, Guglielmi M, Costantini F, Romano
F, Schiavone C, Cuccurullo F, Mezzetti A: Arterial disease in dip-
per and non-dipper hypertensive patients. Am J Hypertens 1997;
Conclusions
10:511–518
1
6. Tsioufis C, Stefanadis C, Antoniadis D, Kallikazaros I, Zambaras P,
Pitsavos C, Tsiamis E, Toutouzas P: Absence of any significant ef-
fects of circadian blood pressure variations on carotid artery elastic
properties in essential hpertensive subjects. J Hum Hypertens 2000;
Acute conjugated estrogen administration induced an im-
provement in CCA elasticity and a reduction in brain impe-
dance in selected normotensive, postmenopausal women. As
the women’s age and the time since menopause increased, the
improvement in CCA distensibility decreased. These data pro-
vide evidence that conjugated estrogen may have a direct ef-
fect on carotid artery function and may explain some of the
protective effects of estrogen replacement therapy in post-
menopausal women. However, further investigation is re-
quired to determine whether its apparently favorable effects on
this intermediate biological outcome can be translated into the
reduction in cerebrovascular events in postmenopausal wom-
en who receive replacement therapy.
14:813–818
1
7. Gangar KF, Vyas S, Whitehead M, Crook D, Meire H, Campbell S:
Pulsatility index in internal carotid artery in relation to transdermal
oestradiol and time since menopause. Lancet 1991;338:839–842
8. Penotti M, Nencioni T, Gabrielli L, Farina M, Castiglioni E, Pol-
vani F: Blood flow variations in internal carotid and middle cerebral
arteries induced by postmenopausal hormone replacement therapy.
Am J Obstet Gynecol 1993;169:1226–1232
1
1
9. Reis S, Bhoopalam V, Zell K, Couniham P, Smith C, Pham S,
Murali S: Conjugated estrogens acutely abolish abnormal cold-
induced coronary vasoconstriction in male cardiac allografts.
Circulation 1998;97:23–25

172
Clin. Cardiol. Vol. 25, April 2002
2
0. British Standard Institution: Precision of test methods. 1: Guide for
the determination of reproducibility for a standard test method.
London, England: British Standard Institution, BS5497, part 1, 1979
1. Blacher J, Pannier B, Guerin A, Marchais S, Safar M, London G:
Carotid arterial stiffness as a predictor of cardiovascular and all
cause mortality in end stage renal disease. Hypertension 1998;32:
motor responses during atrial pacing in postmenopausal women
(abstr). Eur Heart J 1997;18:P3117
6. Williams JK, Adams MR, Herrington DM, Clarkson TB: Short
term administration of estrogens and vascular responses of ather-
osclerotic coronary arteries. J Am Coll Cardiol 1992;20:452–457
2
2
2
2
2
7. Stefanadis C, Tsiamis E, Dernellis J, Toutouzas P: Effect of estro-
570–574
gen on aortic function in postmenopausal women. Am J Physiol
2
2. Grodstein F, Stamfer M, Manson J, Colditz G, Willet W, Rosner B,
Speizer F, Hennekens C: Postmenopausal estrogen and progestin
use and the risk of cardiovascular disease. N Engl J Med 1996;
1999;276:H658–H662
8. Collins P, Rosano G, Jianc C, Lindsay D, Sarrel P, Wilson P: Car-
diovascular protection by oestrogen—a calcium antagonist effect?
Lancet 1993;341:1264–1265
9. Stefanadis C, Stratos C, Boudoulas H, Kourouklis C, Toutouzas P:
Distensibility of the ascending aorta: Comparison of invasive and
noninvasive techniques in healthy men and in men with coronary
artery disease. Eur Heart J 1990;11:990–996
30. Hoeks APG, Brands PJ, Smeets FA, Reneman RS: Assessment of
distensibility of superficial arteries. Ultrasound Med Biol 1990;
16:121–128
335:453–461
2
2
2
3. Graby D, Rubin S, Petiti D, Fox C, Black D, Ettinger B, Ernester V,
Cumming S: Hormone therapy to prevent disease and prolong life
in postmenopausal women. Ann Intern Med 1992;117:1016–1037
4. Petiti D, Sidney S, Quesenberry C, Bernestein A: Ischemic stroke
and use of estrogen and estrogen/progestin as hormone replace-
ment therapy. Stroke 1998;29:23–28
5. Kallikazaros I, Tsioufis C, Stratos C, Stefanadis C, Vavuranakis E,
Toutouzas P: Estrogen acutely modulates abnormal coronary vaso-