Cardiovascular responses of perimenopausal women to hormonal replacement therapy

Aerobic training abolishes ambulatory blood pressure increase induced by estrogen therapy: a double blind randomized clinical trial

Emerging data reveal that oral estrogen therapy can increase clinic blood pressure (BP) in post-menopausal women; however, it is important to establish its effects on ambulatory BP, which is a better predictor for target-organ damage. Besides estrogen therapy, aerobic training is widely recommended for post-menopausal women, and it can decrease ambulatory BP levels. This study was designed to evaluate the effect of aerobic training and estrogen therapy on the ambulatory BP of post-menopausal women. Forty seven healthy hysterectomized women were randomly divided (in a double-blind manner) into 4 groups: placebo-control (PLA-CO=12), estrogen therapy-control (ET-CO=14), placebo-aerobic training (PLA-AT=12), and estrogen therapy-aerobic training (ET-AT=09). The ET groups received estradiol valerate (1 mg/day) and the AT groups performed cycle ergometer, 3×/week at moderate intensity. Hormonal status (blood analysis), maximal cardiopulmonary exercise test (VO(2) peak) and ambulatory BP (24-h, daytime and nighttime) was evaluated before and 6 months after interventions. A significant increase in VO(2) peak was observed only in women who participated in aerobic training groups (+4.6±1.0 ml kg(-1) min(-1), P=0.00). Follicle-stimulating hormone was a significant decreased in the ET groups (-18.65±5.19 pg/ml, P=0.00), and it was accompanied by an increase in circulating estrogen (56.1±6.6 pg/ml). A significant increase was observed in the ET groups for daytime (P=0.01) and nighttime systolic BP (P=0.01), as well as nighttime diastolic BP (P=0.02). However, daytime diastolic BP was increased only in the ET-CO group (+3.4±1.2 mmHg, P=0.04), and did not change in any other groups. No significant effect was found in ambulatory heart rate. In conclusion, aerobic training abolished the increase of daytime ambulatory BP induced by estrogen therapy in hysterectomized, healthy, normotensive and postmenopausal women.

Cardiovascular hemodynamics during stress in premenopausal versus postmenopausal women

OBJECTIVE

After menopause, women are at an increased risk of cardiovascular disease. The present study assessed cardiovascular hemodynamics in premenopausal versus postmenopausal women, with a focus on systemic vascular resistance (SVR) at rest and during stress. Sympathetic nervous system activity and cardiovascular adrenergic receptor (AR) function were also examined.

METHODS

A total of 90 women (45 premenopausal and 45 postmenopausal) completed a laboratory protocol composed of a resting baseline and four mental stress tasks. Measurements included blood pressure, cardiac output, SVR, and plasma catecholamine level. In addition, alpha- and beta-AR responsiveness to the infusion of selective pharmacological agonists was assessed.

RESULTS

Compared with premenopausal women, postmenopausal women were characterized by similar blood pressure but lower cardiac output and higher SVR, both at rest and during stress (Ps < 0.05). Postmenopausal women also had higher baseline plasma norepinephrine levels (P = 0.007) and reduced beta-AR responsiveness (P = 0.02), although differences in beta-AR responsiveness may have been confounded by aging effects.

CONCLUSIONS

After menopause, women exhibit altered sympathetic nervous system activity and a sustained increase in hemodynamic load that may contribute to pathological structural and functional changes in the heart and blood vessels.

Effect of lifestyle factors and hormone therapy on heart function by serial echocardiography in postmenopausal women

BACKGROUND

There is conflicting information on the effects of oestrogen on the heart in women, especially those using postmenopausal hormone therapy. Whilst some studies reported a beneficial effect, others showed adverse outcomes. The interplay of lifestyle factors and type/timing of therapy remains to be clarified.

AIM

The aim of this study was to determine the effects of lifestyle and hormone therapy on heart function and structure in postmenopausal women.

METHOD

As part of a large longitudinal study of women randomly recruited from an urban population, the study assessed 410 suitable women by echocardiography in Year 1 and Year 5 of the study by two independent cardiologists.

RESULTS

In lifestyle characteristics, the difference in age and body mass (as markers of cardiovascular risk) was in favour of never-users versus hormone therapy-users. Using an arbitrary cut-off > or =15% change for an effect, we found lifestyle factors had minimal effect on the two measured parameters - ejection fraction, left ventricular mass. Effects of hormone therapy were variable and mixed; greatest effect was found for an 'early start' of hormone therapy with oestrogen-only preparation - the risk of reduced ejection fraction was decreased [hazard ratio (HR) 0.42, confidence interval = 0.17-1.03, P = 0.06] and risk of increased left ventricular mass was increased (HR 2.21, 1.09-4.49, P = 0.03).

CONCLUSION

Our findings add to the evidence that oestrogen given to postmenopausal women has a mixed effect on the heart, with effect best shown when started early.

Hemodynamic effects of acute and repeated exposure to raloxifene in ovariectomized sheep

We hypothesize that administration of acute and daily doses of raloxifene will have significant effects on ovine coronary and uterine hemodynamics and that these changes are estrogen receptor dependent. Eleven ovariectomized sheep were instrumented to measure mean arterial pressure, heart rate (HR), cardiac output (CO), and coronary (CBF) and uterine artery blood flows (UBF). A dose-response curve was generated for raloxifene (1, 3, and 10 microg/kg) and compared with a standard dose of estradiol-17beta (1 microg/kg) given intravenously. In a second group of animals, raloxifene (10 microg.kg-1.day-1) was administered intravenously for 14 consecutive days, and cardiovascular responses were compared with a group of animals administered estradiol-17beta (10 microg/kg) daily for the same period. To determine whether raloxifene-related vascular responses were estrogen receptor (ER) mediated, the animals were pretreated with estrogen antagonist ICI-182,780 given intravenously. Finally, RT-PCR was preformed to determine the presence of ERalpha and ERbeta mRNA in ovine coronary and uterine vessels. Raloxifene increased CBF and UBF dose dependently with a parallel decrease in the associated vascular resistances. Acute cardiovascular responses to daily doses of raloxifene and estradiol-17beta were sustainable. In contrast to estradiol-17beta, which significantly increases CO by increasing HR but not stroke volume, raloxifene significantly increased stroke volume without a significant parallel increase in HR. ICI-182,780 abolished raloxifene-induced hemodynamic responses, and ERalpha and ERbeta mRNA are present in both ovine coronary and uterine vessels. Hence, the hemodynamic effects of raloxifene are dose dependent, sustainable, and estrogen receptor mediated.

Emerging Selective Estrogen Receptor Modulators

Menopause, regardless of age at onset, is associated with a marked increase in coronary heart disease (CHD) risk. On the basis of epidemiological studies that demonstrated mainly positive effects of postmenopausal hormone therapy on CHD as well as on risk markers of CHD, it has been suggested that CHD could be prevented in postmenopausal women with long-term hormone therapy. However, since the publications of the Heart and Estrogen/progestin Replacement Study and the Women's Health Initiative trial, prescription of hormone therapy for the prevention of CHD has become controversial. Major efforts have been made to identify alternatives for hormone therapy. Compounds suggested have included selective estrogen receptor modulators (SERMs), which represent a class with a growing number of compounds that act as either estrogen receptor agonists or antagonists in a tissue-specific manner. This pharmacological profile may offer the opportunity to dissociate favourable estrogenic effects on the bone and cardiovascular system from unfavourable stimulatory effects on the breast and endometrium. Two SERMs presently on the market are tamoxifen and raloxifene. The only data available regarding the effects of tamoxifen on cardiovascular events in postmenopausal women are from breast cancer trials. These trials found fewer fatal myocardial events in women randomly assigned to tamoxifen compared with women assigned to placebo. Raloxifene is a second-generation SERM that has been shown to prevent osteoporotic fractures, is safe for the endometrium and holds high promise for the prevention of breast cancer. The effect of raloxifene on CHD is still uncertain. On the basis of the MORE (Multiple Outcomes of Raloxifene Evaluation) trial, raloxifene may offer some protection to women with CHD or to those who are at high risk of CHD. Proof that raloxifene reduces the risk of CHD requires a clinical trial with hard clinical endpoints. Such a study is currently underway. Next-generation SERMs taken into clinical development include idoxifene, droloxifene, ospemifene, arzoxifene, acolbifene/EM-800, levormeloxifene, lasofoxifene, bazedoxifene and HMR 3339. The aim is to find a compound with the ideal profile, that is, alleviation of climacteric symptoms and prevention of osteoporotic fractures, but without an adverse effect on the breast and endometrium, and no negative effect or even a beneficial effect on the cardiovascular system and the brain. Currently, limited data are available with regard to these next-generation SERMs and CHD. Nevertheless, some of these novel agents provide arguments for continuing the search for an ideal SERM.

Comparison of the effects of tibolone and estrogen replacement therapy on echocardiographic basic cardiac functions in post-menopausal women: a randomized placebo controlled study

OBJECTIVES

This study is designed to investigate and compare the effects of synthetic steroid tibolone and HRT on systolic and diastolic heart functions in post-menopausal women.

METHODS

This prospective, randomized placebo controlled double blind study was conducted in a university clinic. Fifty-eight non-smoking, otherwise healthy post-menopausal women who did not receive any kind of HRT at least for 3 years within the onset of menopause were included in the study. The patients were randomly allocated to either 2.5 mg per day tibolone (OD, n = 18), daily combined 0.625 mg of conjugated estrogens 2.5 mg-1 of medroxy progesterone acetate pill (EP, n = 20) or a vitamin pill (n= 20) in a double blinded fashion. Their basic systolic and diastolic functions were investigated with HP Sonos-1000 echocardiography using standard positions and windows before and 6 months after the initiation of HRT.

RESULTS

Mean age, weight, length of post-menopausal period, heart rate, systolic and diastolic pressures were similar between the groups. At the initiation of the study all groups had similar echocardiographic measurements. However, at the end of 6 months, left ventricular end-systolic and -diastolic volumes were decreased significantly compared to pretreatment and placebo in both EP and OD treated groups. (55.5 +/- 18.4 and 53.7 +/- 19.1.8 ml; 109.9 +/-19.9 and 110.7 +/- 20.8 ml versus 74.5 +/- 14.9 and 142.7 +/- 19.1 ml, respectively; P < 0.05). Improvement in diastolic functions was significant in EP/OD groups compared to pre-treatment period and the placebo groups (E/A 1.34 +/- 0.1 and 1.38 +/- 0.1 versus 1.18 +/-.09, deceleration time 204 +/- 11.1 and 202.8 +/- 27.1 ms versus 237.6 +/- 26.9 ms, respectively). Besides increase in left ventricular mass adjusted for height, decrease in left ventricular relative wall thickness, and systemic vascular resistance were significant in EP and OD treated groups than placebo and the pre-treatment measurements. Although improved in both OD and EP groups, the changes in systolic and diastolic functions were significantly higher in the OD treated group. Based on our preliminary results, we may conclude that both EP and OD regimens may improve cardiac performance and age related dysfunctions.

CONCLUSION

The present results may further support that both OD and EP exert many direct effects on cardiovascular system other than metabolic changes regarding lipoproteins. The greater improvement in the OD group may be explained by its weak androgenic activity which is consistent with the in vitro data that androgens are potent relaxing agents on coronary arteries and restores cardiac myosin isoenzyme and ATPase patterns which mandates further clinical studies.

Effects of combined use of sildenafil citrate (Viagra) and 17beta-estradiol on ovine coronary and uterine hemodynamics

OBJECTIVE

This study was undertaken to determine whether Viagra (Pfizer, New York, NY), a type 5 phosphodiesterase (PDE-5) inhibitor, increases baseline coronary and uterine blood flow or potentiates estrogen-induced increases in blood flow.

STUDY DESIGN

Seven nonpregnant ovariectomized ewes were chronically instrumented to measure blood pressure, heart rate, cardiac output, and coronary and uterine blood flow. Estradiol-17beta (E2, 0.3 microg/kg) (Sigma Chemical Co, St Louis, Mo) and Viagra (50 mg) were intravenously administered separately or together and hemodynamic responses monitored.

RESULTS

Viagra alone rapidly decreased mean arterial pressure and cardiac output while increasing heart rate and uterine blood flow. Viagra tended to decrease coronary blood flow but not significantly. E2 by itself increased coronary and uterine blood flow over a 2-hour time course, whereas mean arterial pressure, cardiac output, and heart rate remained unchanged. Administration of E2 to animals pretreated with Viagra reversed Viagra-related decrease in cardiac output and coronary blood flow, resulting in a time-related increase in both parameters over baseline values. Viagra significantly augmented estradiol-related increases in uterine blood flow.

CONCLUSION

In our surgically menopausal ovine model, Viagra alone has a tendency to decrease baseline coronary blood flow, but the reduction does not reach statistical significance. The presence of estradiol reverses this Viagra-related negative trend and results in a net increase in coronary blood flow and cardiac output. Furthermore, Viagra significantly augments baseline and estrogen-induced increases in uterine blood flow suggesting the presence of PDE-5 in the ovine uterine vasculature.

[Impact of HRT on the arterial carotid vascular tree]

Hormone replacement therapy (HRT) and arterial impact, this is a controversial subject since it is a large field that needs weeding, a theme in which new questions are raised by the cross-results of various studies conducted, and in which doubt is perhaps one of, or even the only, certitude that all the various specialists agree on. In this controversial climate, we feel that three important points should be underlined: the American studies, however reliable they may be, have been conducted with conjugated estrogens and the generalisation to the results of other types of hormones such as those prescribed in Europe is perhaps a little hasty; other factors of risk should be taken into consideration in the eventual potentialisation of the risk induced by such treatment; the venous and arterial vascular risks are not based on the same physiopathological mechanisms. Hence the increased risk in one or the other network system should perhaps not be amalgamated either.

CEU:Managing menopausal symptoms after the women's health initiative

Until the results of the Women's Health Initiative (WHI) were released in July 2002, hormone replacement therapy (HRT) had been thought to be the most effective way to manage unwanted menopausal symptoms and to prevent long-term health problems associated with aging. The results of the WHI, showing that HRT is less beneficial and associated with more risks than previously thought, has complicated the management of unwanted menopausal symptoms. This article discusses the effectiveness of HRT and other modalities used to relieve menopausal symptoms and discusses how to choose an HRT product to match specific menopausal complaints and provide maximum safety.

Effect of postmenopausal hormone replacement therapy on cardiovascular performance

Postmenopausal hormone replacement therapy (HRT) has usually been evaluated the relationship with atherosclerotic disease, whereas its effect on direct cardiac functions hasn't been investigated in detail. This study was planned to investigate the long-term effects of HRT on cardiac functions and exercise performance.

METHODS

Thirty-six postmenopausal women (mean age: 51 +/- 4 years, 39-60 years) were prospectively analyzed with pulsed wave Doppler echocardiography and symptom-limited exercise stress test before HRT (oral 0.625 mg conjugated estrogen and 2.5 mg medroxyprogesteron acetate/day), and at the third and the sixth months. The effect of HRT on left ventricular ejection fraction (EF), early filling velocity (E wave) and late filling velocity (A wave), E wave deceleration time (EDT), E/A ratio, myocardial performance index (MPI), exercise duration and METS changes were examined.

RESULTS

HRT did not significantly alter the left ventricular EF. At the third month of HRT, there was an insignificant increase in E wave, EDT, and E/A ratio, whereas an insignificant decrease was noted in MPI (P > 0.05). However, at the sixth month of HRT, these changes became significant (68 +/- 12 vs. 75 +/- 13 cm/s, P < 0.01; 171 +/- 24 vs. 184 +/- 14 ms, P < 0.01; 1.01 +/- 0.23 vs. 1.11 +/- 0.27, P < 0.01, and 44 +/- 9 vs. 39 +/- 8%, P < 0.001, respectively). On the other hand, exercise duration and exercise METS values showed significant improvements at the third month of HRT (423 +/- 104 vs. 482 +/- 104 s, P < 0.001; 8.2 +/- 1.7 vs. 9.1 +/- 2 METS, P < 0.001). These improvements also continued at the sixth month of HRT. In conclusion, postmenopausal HRT leads to a progressive improvement on left ventricular function parameters, and in parallel, in exercise performance.

Effects of oral and transdermal low-dose estrogen therapy on echocardiographic parameters of cardiac function

OBJECTIVE

To investigate the effects of transdermal 17 beta-estradiol (E(2)) compared with oral unopposed as well as opposed E(2) on echocardiographic parameters of left ventricular (LV) systolic and diastolic function.

DESIGN

A prospective, randomized, double-blind, placebo-controlled, multi-center study.

SETTING

Gynecologic and cardiologic outpatient departments.

PATIENT(S)

One hundred fifty-two healthy hysterectomized postmenopausal women.

INTERVENTION(S)

Participants received daily placebo (n = 49) or transdermal E(2) (50 microg; tE(2) group, n = 33), or oral E(2) (1 mg; oE(2) group, n = 37), or oral E(2) (1 mg) combined with gestodene (25 microg; oE(2)+G group, n = 33) for thirteen 28-day treatment cycles.

MAIN OUTCOME MEASURE(S)

M-mode, quantitative two-dimensional, and Doppler echocardiographic measurements were performed at baseline and after 1 year.

RESULT(S)

Compared with placebo, tE(2) and oE(2) showed no statistically significant changes in LV function. oE(2)+G resulted in a statistically significant favorable increase in peak flow velocity, flow velocity integral, and mean acceleration. Furthermore, a favorable decrease was observed in interventricular septum thickness and ejection time.

CONCLUSION(S)

After 1 year of unopposed E(2), LV function remained unchanged. The oE(2)+G treatment showed a potential beneficial influence on LV systolic function.

Estrogen depletion increases blood pressure and hypothalamic norepinephrine in middle-aged spontaneously hypertensive rats

In male spontaneously hypertensive rats (SHR) a high NaCl diet increases arterial pressure via a reduction in anterior hypothalamic nucleus norepinephrine release. Young female SHR are relatively well protected from this NaCl-sensitive hypertension, but depletion of both endogenous and dietary estrogens greatly exacerbates NaCl-sensitive hypertension. This study tests the hypothesis that estrogen also protects late middle-aged female SHR from NaCl-sensitive hypertension and that this effect is mediated by an estrogen-related effect on hypothalamic norepinephrine release. Ten-month-old female SHR were ovariectomized and placed on a phytoestrogen-free diet containing either basal or high NaCl. Each rat was implanted with a silastic tube containing 17beta estradiol or vehicle. Three months later, arterial pressure and hypothalamic norepinephrine metabolite levels (MOPEG) were measured. On the basal NaCl diet, estrogen-depleted rats displayed increased arterial pressure (12 mm Hg) and decreased anterior hypothalamic nucleus MOPEG (20%). Both effects were reversed by estrogen treatment. In all groups, the high NaCl diet increased arterial pressure by over 35 mm Hg and reduced anterior hypothalamic nucleus MOPEG by >60%. Across all groups, there was a significant inverse correlation between arterial pressure and anterior hypothalamic nucleus MOPEG. These data suggest that both dietary NaCl excess and estrogen depletion raise arterial pressure in middle-aged female SHR by a decreasing hypothalamic norepinephrine.

Acute haemodynamic effects of oestrogen administration in male patients with chronic heart failure

BACKGROUND

Although there are many studies concerning the effects of long-term oestrogen administration on systemic haemodynamics in postmenopausal women, the effects of oestrogen in patients with chronic heart failure are not defined.

AIM

The goal of this study was to evaluate the acute haemodynamic effects of oestrogen in male patients with chronic heart failure.

METHODS AND RESULTS

We studied 15 men with advanced heart failure (NYHA II-IV, EF < 35%). A Swan-Ganz thermodilution catheter was advanced in their pulmonary artery and central haemodynamics were assessed at baseline, after placebo administration, and following 0.625 and 1.25 mg of oestrogen infusion. Simultaneously, all patients underwent limb plethysmography. Analysis of variance with repeated measures was used to compare the sequential measurements. Following oestrogen administration, right atrial, pulmonary artery and pulmonary capillary wedge pressures, as well as systemic, pulmonary and forearm vascular resistance were decreased; cardiac output, cardiac index, stroke volume, stroke volume index, stroke work index and forearm blood flow were increased.

CONCLUSIONS

In male patients with chronic heart failure, acute oestrogen administration improves the indices of cardiac systolic performance and decreases pulmonary and systemic vascular resistance. These findings imply a beneficial effect of oestrogen in selected patients with chronic heart failure.

Effects of oral contraceptives on peak exercise capacity

We examined the effects of menstrual cycle phase and oral contraceptive (OC) use on peak oxygen consumption (VO(2 peak)). Six moderately active, eumenorrheic women (25.5 +/- 1.5 yr) were studied before and after 4 mo of OC. Subjects were tested during the follicular and luteal phases before OC and the inactive and high-dose phases after OC. Before OC, there were no significant differences between the follicular and luteal phases in any of the variables studied. There were also no differences between the inactive and high-dose phases. Dietary composition, exercise patterns, and peak heart rate, minute ventilation, and respiratory exchange ratio did not change with OC use. However, OC use significantly (P </= 0.05) increased body weight (59.6 +/- 2.3 to 61.2 +/- 2.6 kg) and fat mass (13.3 +/- 1.3 to 14.5 +/- 1.3 kg) and decreased VO(2 peak) (-11%, 2.53 +/- 0.21 to 2.25 +/- 0.18 l/min). In conclusion, 1) endogenous ovarian steroids have little effect on VO(2 peak), but 2) the exogenous ovarian steroids in OC decrease peak exercise capacity in moderately physically active young women.

Hormone replacement therapy to improve left ventricular diastolic functions in healthy postmenopausal women

OBJECTIVES

To investigate the effects of estrogen and estrogen plus progesterone replacement therapy on left ventricular systolic and diastolic function parameters in healthy postmenopausal women.

METHODS

Forty-six healthy consecutive postmenopausal women were prospectively enrolled. Hormone replacement therapy (HRT), which was either 0.625 mg/day conjugated equine estrogen (CEE) alone, or with 2.5 mg/day medroxyprogesterone acetate (MPA) was administered depending on the hysterectomy status. Left ventricular systolic and diastolic function parameters were evaluated with echocardiography before and after 6 months of HRT. The paired t-test was used for statistical analysis.

RESULTS

Estrogen or estrogen plus progesterone did not significantly alter the left ventricular dimensions and systolic function parameters. However, significant improvements were noted in several diastolic function parameters including late diastolic mitral flow velocity, ratio of early to late mitral flow velocity and isovolumic relaxation time (P=0.003, P=0.001 and P=0.005, respectively, for the CEE group; all P<0.001 for the CEE+MPA group).

CONCLUSIONS

Estrogen or estrogen plus progesterone replacement therapy may significantly improve left ventricular diastolic functions in healthy postmenopausal women.

Evidence-based practice in women's health: hormone therapy for women at menopause

Women's health providers, especially midwives, must take into account the known benefits and risks, as well as the "unknown," when recommending the use of hormone therapy for menopausal women, especially as it relates to heart disease, breast cancer, impaired cognition, and osteoporosis. The most recent evidence available from various studies about the benefits and risks of estrogen and hormone therapy at menopause suggests that, although hormone therapy may be protective in some women against heart disease and osteoporosis, evidence is less certain about the benefits of hormone protection against impaired cognition and the risks of breast cancer with use. The clinical approach used by midwives in which individualizing care based on each woman's health status history as well as preferences is highly appropriate for women in the perimenopausal and menopausal period.

Transdermal estrogen reduces vascular resistance and serum cholesterol in postmenopausal women

OBJECTIVE

Our aim was to compare the effects of transdermal versus oral estrogens on vascular resistance index, mean arterial pressure, serum lipid concentrations, norepinephrine, and left ventricular structure.

STUDY DESIGN

Ten postmenopausal women received transdermal estradiol (0.05 mg/d) plus cyclic oral progesterone for 6 months. Responses were compared with those of 23 women receiving oral conjugated estrogens (0.625 mg/d) plus cyclic progesterone and with those of 9 subjects receiving placebo in a concurrent randomized trial. We assessed the vascular resistance index and the mean arterial pressure at rest and during behavioral stressors.

RESULTS

Oral and transdermal estrogen significantly decreased the vascular resistance index, mean arterial pressure, norepinephrine, and total and low-density lipoprotein cholesterol to a similar extent. Changes in the vascular resistance index and mean arterial pressure were equally evident at rest and during stress. Although both treatments reduced left ventricular mass (-4% to -6%) and relative wall thickness (-3% to -5%), these changes were not statistically significant.

CONCLUSIONS

Equivalent reductions in vascular resistance index, norepinephrine, mean arterial pressure, and cholesterol were observed with transdermal and oral estrogens. Future studies comparing novel hormone regimens with oral hormone replacement therapy should include multiple risk markers to allow better assessment of their potential impact on coronary artery health.

Hemodynamic response to tibolone in reproductive and nonreproductive tissues in the sheep

OBJECTIVE

We sought to determine the hemodynamic effects of tibolone in reproductive and nonreproductive tissues in the nonpregnant ovariectomized sheep.

STUDY DESIGN

Six ewes were chronically instrumented for measurement of mean arterial pressure, heart rate, cardiac output, and coronary and uterine blood flow. A dose response curve was generated for intravenous tibolone (1.25, 2.5, and 5 mg) and compared with intravenous 17beta-estradiol (1 microg/kg body weight). To determine whether tibolone-related cardiovascular responses were estrogen receptor mediated and produced by nitric oxide, animals were treated on separate days with either estrogen receptor antagonist ICI 182,780 or the nitric oxide synthase inhibitor, L -nitroarginine methyl ester.

RESULTS

Tibolone significantly increased coronary blood flow in a dose-related fashion by 5% +/- 3%, 9% +/- 2%, and 11% +/- 2% for the 1.25, 2.5, and 5 mg doses, respectively. Uterine blood flow was also increased significantly in a dose-dependent manner by 98 +/- 15, 216 +/- 59, and 303 +/- 56 mL/min, for the 1.25, 2.5, and 5 mg doses, respectively. L -Nitroarginine methyl ester attenuated tibolone-induced increases in uterine blood flow by 84% +/- 4% and abolished the increase in coronary blood flow. ICI 182,780 inhibited all tibolone-induced cardiovascular responses.

CONCLUSION

Tibolone significantly increases coronary and uterine blood flow in ovariectomized ewes. The coronary and uterine vascular responses are mediated via an estrogen receptor-dependent mechanism and are produced mainly by nitric oxide.