Effect of 17 beta-oestradiol on contraction, Ca2+ current and intracellular free Ca2+ in guinea-pig isolated cardiac myocytes

Estrogen supplement prevents the calcium hypersensitivity of cardiac myofilaments in ovariectomized rats

Our previous biochemical and mechanical studies have demonstrated an increase in Ca2+ sensitivity of cardiac myofilaments in ovariectomized rats. To test whether the body weight gain associated with ovariectomy contributed some effects to the changes in myofibrillar functions, the relations of pCa (-log Ca2+ molar concentration) to actomyosin adenosine triphosphatase (ATPase) activity of isolated myofibrillar preparations from 10-week pair-fed ovariectomized rats were compared with those from sham-operated controls. Despite similar body weights, the maximum myofibrillar ATPase activity was significantly lower in pair-fed ovariectomized rats as compared to that of sham-operated controls. In addition, the pCa-actomyosin ATPase relationship of pair-fed ovariectomized hearts still demonstrated a significant leftward shift in pCa50 (-log half-maximally Ca2+ activation) from that of sham-operated controls. To find out which hormone was responsible for the observed increase in myofibrillar Ca2+ sensitivity, different sex hormone supplemental regimens were administered to ovariectomized rats. Subcutaneous injection of estrogen (5 microg/rat) or estrogen plus progesterone (1 mg/rat) three times a week could effectively prevent the changes in body weight, heart weight, and uterine weight of the ovariectomized animals. Moreover, supplements of either estrogen or progesterone could prevent a decrease in maximum ATPase activity. In contrast, only the estrogen replacement could abolish the Ca2+ hypersensitivity of the myofilaments in these ovariectomized rats. These results suggest differential cardio-regulatory effects of ovarian sex hormones on the Ca2+ activation of the myofilaments.

Myocardial ischemia-reperfusion injury in estrogen receptor-alpha knockout and wild-type mice

We investigated the function of estrogen receptor-alpha in global myocardial ischemia and reperfusion injury in male estrogen receptor-alpha knockout (ERKO) and wild-type mice. Mouse hearts were subjected to 45 min of global ischemia followed by 180 min of reperfusion. The hearts were excised, cannulated, and maintained in a chilled (4 degrees C) cardioplegia solution until warm (37 degrees C) oxygenated Krebs-Henseleit bicarbonate buffer was perfused through the coronary arteries. ERKO hearts started beating later and had a higher incidence of ventricular fibrillation and/or tachycardia than control hearts. Coronary flow rate was significantly lower in ERKO hearts during the 90- and 120-min periods of reperfusion. Ca(2+) accumulation was significantly greater following 30, 90, 120, 150, and 180 min of reperfusion in ERKO hearts. Nitrite production was significantly less in ERKO hearts following 90, 120, and 150 min of reperfusion. Myocardial reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide was significantly lower in experimental ERKO hearts. Marked interstitial edema and contraction bands were seen in hematoxylin-eosin-stained sections of ischemia-reperfused ERKO hearts but not in control tissues. Hematoxylin-basic fuchsin-picric acid-stained sections from experimental ERKO hearts had fewer viable myocytes compared with controls. Transmission electron microscopy revealed swollen and fragmented mitochondria with amorphous and granular bodies, loss of matrix, and rupture of cristae in experimental ERKO hearts. This is the first demonstration that estrogen receptor-alpha plays a cardioprotective role in ischemia-reperfusion injury in males.

Acute modulation of Ca2+ influx on rat heart by 17beta-estradiol

Estrogens initiate their action by binding to specific intracellular receptors and then acting on gene expression. In addition, there is growing evidence of a direct membrane effect via interaction with a cell surphase receptor. The aim of the present study was to investigate the acute effects of 17beta-estradiol on Ca2+ fluxes through second messenger pathways in rat cardiac muscle. Exposure of rat ventricle to low levels of 17beta-estradiol (10(-12)-10(-8) M) increased 45Ca2+ influx within 1 min (+38%); the response was biphasic, peaking at 2 and 5 min (+60 and +55%, respectively). The effect of the hormone on rat heart seems to be specific since 17alpha-estradiol, dihydrotestosterone, and progesterone were devoid of activity. The effect of 17beta-estradiol (5 min, 10(-10) M) was suppressed by nitrendipine (1 microM) and LaCl3 (10 microM), involving the activation of voltage-dependent Ca2+ channels in the acute increase of rat heart calcium influx by the hormone. 17Beta-estradiol rapidly increased cAMP content and PKA activity of rat cardiac muscle in parallel to the changes in Ca2+ uptake. In addition the cAMP antagonist Rp-cAMPS suppressed 17beta-estradiol-dependent Ca2+ influx. Altogether, the data suggest the involvement of the cAMP/PKA messenger system in the nongenomic modulation of Ca2+ influx in rat cardiac muscle by physiological levels of 17beta-estradiol.

Effects of transdermal 17beta-estradiol on left ventricular anatomy and performance in hypertensive women

To reduce cardiovascular complications, antihypertensive therapy should not only normalize blood pressure but also induce a regression of structural abnormalities, which are the expression of end-organ damage. We investigated the effects of transdermal 17beta-estradiol, combined with standard antihypertensive therapy, on the modification of left ventricular anatomy and systolic performance in hypertensive postmenopausal women. In a randomized, double-blind, placebo-controlled study, we enrolled 169 postmenopausal women with mild or moderate hypertension. Eighty-six patients (group 1) received transdermal 17beta-estradiol (50 microg/d) and norethisterone acetate (2.5 mg/d, orally), and 83 patients (group 2) received placebo. At baseline, all women underwent M-mode and 2-D echocardiogram, which was repeated after 6, 12, and 18 months of follow-up. After 18 months of treatment, we observed a significant decrease in left ventricular diastolic septal and posterior wall thickness and mass in both groups. Furthermore, after 18 months, left ventricular mass was significantly less than in the estrogen-treated group. No significant modifications were observed in left ventricular systolic and diastolic dimensions or in systolic performance, as expressed by left ventricular fractional shortening. In conclusion, transdermal 17beta-estradiol, which is associated with antihypertensive therapy, may contribute in the reduction of left ventricular mass in hypertensive postmenopausal women.

Gender differences in the presentation of adult obstructive hypertrophic cardiomyopathy with resting gradient: a study of 122 patients

The present study investigated gender differences among adult patients with obstructive hypertrophic cardiomyopathy (OHCM) and resting gradient. Using outflow gradients >10 mmHg and the presence of asymmetrical septal hypertrophy of the left ventricle as inclusion criteria, 122 patients were identified among patients referred for echocardiographic examinations between May 1990 and October 1996. Clinical, echocardiographical and follow-up data were compared between male and female patients. The female patients were significantly older than male patients (mean age +/-SD 66.7+/-10.5 vs 54.8+/-12.5 years). The female patients had a smaller interventricular septal wall thickness, less frequent systolic anterior movement of the mitral valve, more frequent association with hypertension, and less frequent association with ischemic heart disease (IHD) and giant T wave inversion. In this study population, adult female patients presented with OHCM 12 years later than males. Whether this represents female patients' reluctance to seek medical attention early, a different disease process that affects predominantly elderly females, or a gender-specific end organ response to aging, hypertension, IHD and other processes, or the protective effects of estrogen remains to be determined.

Raloxifene acutely relaxes rabbit coronary arteries in vitro by an estrogen receptor-dependent and nitric oxide-dependent mechanism

BACKGROUND

Selective estrogen receptor modulators (SERMs) have been defined as compounds that display tissue specificity with regard to estrogenic effects. They appear to share the beneficial effects of estrogen on bone and lipids but are not associated with an increased risk of breast or uterine carcinoma. Estrogen relaxes coronary arteries and has long-term protective effects on the vascular system. The effect of SERMs on the coronary vasculature is unknown. We therefore investigated the effects of the SERM raloxifene on isolated rabbit coronary arteries.

METHODS AND RESULTS

Rings of coronary artery from adult male and nonpregnant female New Zealand White rabbits were suspended in organ baths containing Krebs solution; isometric tension was then measured. Raloxifene induced coronary arterial relaxation in male and female coronary arteries by an endothelium-dependent and estrogen receptor-dependent mechanism involving nitric oxide. Raloxifene also had a direct calcium antagonistic effect on the coronary myocyte. Estrogen, however, induced only endothelium-independent coronary arterial relaxation. The endothelium-dependent component of relaxation induced by raloxifene 10(-6) mol/L resulted in almost 100% (79+/-7% versus 43+/-3%, P<0.001) more relaxation than that induced by estrogen 10(-6) mol/L.

CONCLUSIONS

These data demonstrate that raloxifene has vascular relaxing properties. The surprising finding is that the receptor-dependent effects via the endothelium are observed in coronary arteries from both male and female animals.

Cardiovascular pharmacology of hormone replacement therapy

The incidence of cardiovascular disease in women is negligible before natural or surgically-induced menopause, and increases after menopause. Epidemiological data suggest that estrogen replacement therapy reduces the occurrence of coronary artery, and possibly cerebrovascular, disease by 25 to 50% in treated women compared with non-users. These findings are supported by the evidence that estrogens have a beneficial effect on cholesterol metabolism and deposition, contributing to the inhibition of atherosclerotic plaque formation in arterial walls. Early reports suggested that up to 60% of the protective effect of estrogens on coronary artery disease was attributable to favourable changes in plasma lipids. Reanalysis of the data indicated that the lipid changes probably account for approximately 25% of the cardioprotective effect of estrogens and that other effects are, therefore, likely to be important. The influence of estrogens on carbohydrate metabolism, atheroma formation and cardiovascular haemodynamics may also play an integral role in the overall beneficial effect of the hormones. Animal and human studies have shown that the administration of estrogens leads to a restoration of endothelial function, an increase in cardiac output, an increase in arterial flow velocity, a decrease in vascular resistance, and a decrease in systolic and diastolic blood pressure. Recent studies on hormone replacement regimens have shown that estrogens may favourably affect fibrinolysis and reduce plasma fibrinogen to premenopausal levels. Despite these effects of estrogens the recent Heart and Estrogen/Progestin Replacement Study (HERS) failed to show a cardioprotective effect of hormone replacement therapy (HRT) in elderly women with coronary artery disease. However, the HERS study has several limitations and stands alone against the large body of evidence that suggest that HRT may reduce cardiovascular mortality and morbidity.

Effects of estrogen on action potential and membrane currents in guinea pig ventricular myocytes

To explore a possible ionic basis for the prolonged Q-T interval in women compared with that in men, we investigated the electrophysiological effects of estrogen in isolated guinea pig ventricular myocytes. Action potentials and membrane currents were recorded using the whole cell configuration of the patch-clamp technique. Application of 17beta-estradiol (10-30 microM) significantly prolonged the action potential duration (APD) at 20% (APD(20)) and 90% repolarization (APD(90)) at stimulation rates of 0. 1-2.0 Hz. In the presence of 30 microM 17beta-estradiol, APD(20) and APD(90) at 0.1 Hz were prolonged by 46.2 +/- 17.1 and 63.4 +/- 11.7% of the control (n = 5), respectively. In the presence of 30 microM 17beta-estradiol the peak inward Ca(2+) current (I(CaL)) was decreased to 80.1 +/- 2.5% of the control (n = 4) without a shift in its voltage dependence. Application of 30 microM 17beta-estradiol decreased the rapidly activating component of the delayed outward K(+) current (I(Kr)) to 63.4 +/- 8% and the slowly activating component (I(Ks)) to 65.8 +/- 8.7% with respect to the control; the inward rectifier K(+) current was barely affected. The results suggest that 17beta-estradiol prolonged APD mainly by inhibiting the I(K) components I(Kr) and I(Ks).

Differential effects of 17beta-estradiol on mitogen-activated protein kinase pathways in rat cardiomyocytes

Cardiac myocytes contain functional estrogen receptors, however, the effect of estrogen on growth-related signaling pathways such as mitogen-activated protein kinases (MAPK) in the pathogenesis of cardiac disease is unclear. MAPKs are critically involved in regulatory signaling pathways which ultimately lead to cardiac hypertrophy. Here we show that 17beta-estradiol (E2) activates extracellular signal-regulated kinase (ERK1/2), c-Jun-NH2-terminal protein kinase (JNK) and p38 in rat cardiomyocytes in a distinctive pattern. As shown by immunoblot analysis and phosphorylation assays, E2 (10(-9) M) induced a rapid and transient activation of ERK1/2 and a rapid but sustained increase of JNK phosphorylation. In contrast, E2 had only a marginal effect on p38 activation. Furthermore, MAPK phosphatase expression was induced by E2 and E2-stimulated expression of endothelial and inducible NO synthase was inhibited by PD 98059, an inhibitor of the ERK pathway. These novel observations may help to explain the role of estrogen in gender-based differences found in cardiac disease.

Estradiol inhibits Ca2+ and K+ channels in smooth muscle cells from pregnant rat myometrium

The purpose of this study was to investigate the actions of 17beta-estradiol on the electrical activity of pregnant rat myometrium. The longitudinal layer of the myometrium was dissected from pregnant rats (17 to 19 days of gestation), and single cells were isolated by enzymatic digestion. Calcium currents and potassium currents were recorded by the whole-cell voltage-clamp method, and the single calcium-dependent potassium current was recorded by the outside-out patch-clamp method. The effects of 17beta-estradiol on these currents were investigated. When a myometrial cell was held at -50 mV, depolarization to a potential more positive than -30 mV produced an inward current followed by a slowly developing outward current. Application of tetraethylammonium inhibited the outward current while the inward current was completely abolished in a calcium-free solution. Estradiol at high concentrations (> 3 microM) inhibited both inward and outward currents in a voltage-dependent manner. Removal of estradiol restored the amplitude of the outward but not of the inward current. Estradiol (30 microM) also inhibited the activity of single calcium-dependent potassium channels without changing single channel conductance. In conclusion, estradiol at high concentrations inhibited: (1) voltage-dependent calcium, (2) calcium-dependent potassium and (3) voltage-dependent potassium currents. These actions of estradiol would prevent action potential generation and after-hyperpolarizations. Suppression of the after-hyperpolarization might further prevent spike generation due to slowing of the calcium channel's recovery from the inactivated state.

Augmentation and suppression of action potentials by estradiol in the myometrium of pregnant rat

The purpose of this study was to investigate the actions of estradiol on spontaneous and evoked action potentials in the isolated longitudinal smooth muscle cells of the pregnant rat. Single cells were obtained by enzymatic digestion from pregnant rat longitudinal myometrium. Action potentials and currents were recorded by whole-cell current-clamp and voltage-clamp methods, respectively. The acute effects of 17β-estradiol on action potentials and inward and outward currents were investigated. The following results were obtained. The average resting membrane potential of single myometrial cells was -54 mV (n = 40). In many cells, an electrical stimulation evoked a membrane depolarization, and action potentials were superimposed on the depolarization. In some cells, spontaneous action potentials were observed. Estradiol (30 µM) slightly depolarized the membrane (ca. 5 mV) and attenuated the generation of action potentials by reducing the frequency and amplitude of the spikes. Afterhyperpolarization was also attenuated by estradiol (30 µM). On the other hand, in 5 of 35 cells, estradiol increased the first spike amplitude and action potential duration, while frequency of the spike generation and afterhyperpolarization were inhibited. In voltage-clamped muscle cells, estradiol inhibited both inward and outward currents. Acute inhibition or augmentation of spike generation by estradiol is due to the balance of inhibition of inward and outward currents. Inhibition of both currents also prevented afterhyperpolarization, causing potential-dependent block of Ca spikes.Key words: estradiol, progesterone, rat myometrium, action potential, channel current.

Study of myocardial contractility by pulsed wave Doppler tissue imaging does not reveal an inotropic effect of estrogen at physiologic dose

We studied myocardial contractility by pulsed wave Doppler tissue imaging in 6 postmenopausal healthy women. According to a crossover, double-blind protocol, we randomized patients to treatment with transdermal patches of estradiol-17beta or matched placebo. Estradiol-17beta did not modify local systolic and diastolic functions. Thus, at least when acutely administered, estrogen seems to be unable to determine hemodynamic changes at the myocardial level, in opposition to what occurs in the peripheral vascular system.

Antiarrhythmic effect and its underlying ionic mechanism of 17beta-estradiol in cardiac myocytes

1. The effects of oestrogens on action potential and membrane currents were examined in single guinea-pig atrial myocytes. 2. 17Beta-estradiol (3-10 microM) shortened the action potential duration without significant changes in the resting membrane potential. E-4031 (1 microM) markedly prolonged the action potential duration and induced early afterdepolarization, and 17beta-estradiol (10 microM) abolished it. 3. When cells were perfused in isoproterenol-containing solution, action potentials due to abnormal automaticity caused by membrane depolarization developed, and were also inhibited by 17beta-estradiol. 4. Under voltage clamp conditions, the voltage-dependent Ca2+ currents consisted of both T-(I(Ca,T)) and L-type (I(Ca,L)). 17Beta-estradiol reduced I(Ca,L) concentration-dependently, while it (10 microM) suppressed I(Ca,T) only by approximately 10%. 17Beta-estradiol did not affect time courses of I(Ca,L) inactivation, but it shifted the steady-state inactivation curve to more negative potentials. 5. 17Beta-estradiol (10 microM) did not affect the time-dependent K+ current (I(K)), referred to as I(Kr) and I(Ks) and inwardly rectifying K+ current. However, 17beta-estradiol (30 microM) or diethylstilbestrol (10 microM) inhibited K+ currents. 6. DES and ethinylestradiol (EES) also suppressed I(Ca,L), but testosterone and progesterone failed to inhibit I(Ca,L) The potency of the inhibitory effect on I(Ca,L) was DES> EES> 17beta-estradiol. 7. 17Beta-estradiol and DES also inhibited the cyclic AMP-enhanced I(Ca,L), but cyclic GMP in the pipette or pretreatment of L-NAME could not block the effects of oestrogen on I(Ca,L). 8 These results suggest that oestrogen specifically has antiarrhythmic effects, possibly by acting the L-type Ca2+ channels. The antiarrhythmic effects of oestrogens may contribute to the cardioprotective actions of oestrogens.

Acute and nongenomic effects of testosterone on isolated and perfused rat heart

Gonadal steroid hormones influence vascular tone and the development of hypertension. There are sex differences in the incidence of cardiovascular diseases, and great attention has been placed on the study of estrogen cardiovascular effects. However, there are only a few reports on the effects of testosterone on the vasculature. It is commonly accepted that the mechanism of the action of steroid hormones on target tissues is mediated through the binding of hormones to cytoplasmic or nuclear receptors. However, some studies indicate that steroid action can be extremely rapid and therefore unlikely to be through a genomic mechanism. The purpose of this study was to assess the effect of intravascularly confined testosterone on an isolated rat heart to demonstrate acute and possibly nongenomic effects of the steroid. Our results show that testosterone blocked the adenosine vasodilator effect and increased vascular resistance, even when its presence was restricted to the coronary vascular lumen. These effects were exerted rapidly and possibly through nongenomic mechanisms.

Estrogen improves abnormal norepinephrine-induced vasoconstriction in postmenopausal women

OBJECTIVE

An exaggerated blood pressure response to mental stress in postmenopausal women has been reported but the underlying mechanism is not clear. In the present study, we examined the role of estrogen in the blood pressure response to mental stress.

SUBJECTS AND METHODS

Hemodynamic responses to mental stress and constrictor responses to norepinephrine were compared in 18 premenopausal (mean +/- SD age 33 +/- 5 years), 22 postmenopausal women (62 +/- 7 years) and 13 postmenopausal women with estrogen replacement therapy (58 +/- 8 years). Premarin was infused in 10 postmenopausal women to determine whether estrogen attenuates norepinephrine-induced vasoconstriction. The hemodynamic responses to a standard mental arithmetic test were measured. Norepinephrine (12.5, 25, 50, 100 ng/min) was infused at 0.5 ml/min for 5 min via the dorsal hand vein. Norepinephrine (100 ng/min) combined with premarin (200 microg/min) was infused into the dorsal hand vein of postmenopausal women. Changes in venous diameter were measured by ultrasonography using a 7.5 MHz transducer.

RESULTS

All study subjects were healthy, normotensive and had normal lipid profiles. The postmenopausal women showed a significantly greater blood pressure response to the mental arithmetic test than the premenopausal women or those taking estrogen replacement therapy (P < 0.01). Norepinephrine induced significant dose-dependent vasoconstriction in all three groups (P < 0.001). The postmenopausal women showed significantly greater constriction in response to norepinephrine than the premenopausal women and those taking estrogen replacement therapy (P = 0.02). Premarin significantly attenuated the norepinephrine-induced vasoconstriction in the postmenopausal women (P< 0.001).

CONCLUSION

Healthy, normotensive postmenopausal women showed an exaggerated blood pressure response to mental stress. An increased vasoconstriction in response to norepinephrine and loss of estrogen-mediated vasodilation may contribute to the increased blood pressure response to stress in postmenopausal women without estrogen replacement therapy.

Effects of 17beta-estradiol on tachycardia-induced changes of atrial refractoriness and cisapride-induced ventricular arrhythmia

INTRODUCTION

Gender difference is known to be associated with the occurrence of arrhythmia. However, the effects of female sex hormone on atrial electrophysiology, and on the occurrence of torsades de pointes (TdP) induced by cisapride have been unclear.

METHODS AND RESULTS

Two experiments were included in this study. In experiment 1, effective refractory periods (ERPs) from five epicardial atrial sites were measured before and after rapid atrial pacing at 800 beats/min for 30 minutes in dogs with pretreatment of verapamil (n = 10), 17beta-estradiol (n = 10), or without pretreatment (n = 10, control group). In experiment 2, limb-lead ECG and monophasic action potentials in the left and right ventricles were recorded before and after each dose of cisapride (2 to 6 mg/kg) during different ventricular rates in dogs with (n = 9) and without (n = 14) concomitant administration of 17beta-estradiol (0.3 microg/kg). After 17beta-estradiol administration, there were greater atrial ERPs in the study dogs than in the control group. The atrial ERPs were shortened significantly after rapid atrial pacing, but the degree was greater in the control group than in the dogs pretreated with verapamil or 17beta-estradiol. Moreover, the recovery of atrial ERPs was faster in dogs pretreated with verapamil or 17beta-estradiol than in the control group. In experiment 2, cisapride prolonged the QT interval and biventricular APD90 and induced early afterdepolarizations (EADs) in a dose-dependent manner. However, dogs receiving cisapride combined with 17beta-estradiol had a greater increase of ventricular repolarization and a higher incidence of EADs than those receiving cisapride only. Moreover, dogs receiving cisapride combined with 17beta-estradiol (3/9, 33%) had a greater incidence of TdP than those receiving cisapride only (0/14, 0%, P < 0.05).

CONCLUSIONS

17beta-estradiol has a significant effect on atrial electrophysiology, which may be related to the prevention of atrial fibrillation. However, the high incidence of TdP in dogs receiving cisapride combined with 17beta-estradiol suggests that the female sex hormone is an important risk factor of cisapride-induced proarrhythmia.

Cycling of inducibility of paroxysmal supraventricular tachycardia in women and its implications for timing of electrophysiologic procedures

Arrhythmias in women may be affected by phases of the menstrual cycle. This study was designed to determine the prevalence of perimenstrual clustering of spontaneous episodes of paroxysmal supraventricular tachycardia (SVT) in women. It also tested the hypothesis that women with this temporal pattern of events have an altered probability of induction of paroxysmal SVT during electrophysiologic testing at higher estrogen states (midcycle or with estrogen replacement therapy) than at low estrogen states (perimenstrual or without estrogen replacement). A structured history of the relation of spontaneous paroxysmal SVTs to phases of the menstrual cycle was obtained prospectively among 42 women referred during a 3-year period. Patients with cyclical patterns of spontaneous tachycardias, who had had negative electrophysiologic studies at midcycle or while receiving estrogen replacement therapy, had repeat procedures (1) when premenstrual or at the onset of menses, or (2) after stopping estrogen replacement therapy. Seventeen of 42 consecutive female patients (40%) had histories of perimenstrual clustering of arrhythmias. Six women (4 with normal menstrual cycles, 2 on estrogen replacement therapy), who qualified for paired electrophysiologic studies because of a negative initial electrophysiologic study that included provocation with isoproterenol, had inducibility into SVTs during the second study. All 6 had dual atrioventricular (AV) nodal pathway physiology, 4 had AV nodal reentrant tachycardia (AVNRT) induced, 1 had both AVNRT and reciprocating AV tachycardias, and 1 had nonsustained AVNRT and an atrial tachycardia induced. Successful ablation procedures were performed in 5 of the 6 patients. Thus, among women with a history of perimenstrual clustering of paroxysmal SVT and among those receiving estrogen replacement therapy, scheduling of elective electrophysiologic procedures at times of low estrogen levels (premenstrual or off estrogen replacement therapy) may facilitate the probability of a successful procedure.

Estrogen increases Ca2+ efflux from female porcine coronary arterial smooth muscle

Acute estrogen administration relaxes vascular smooth muscle by decreasing intracellular Ca2+ concentration ([Ca2+]i). In the present study, we examined the hypothesis that this reduction in [Ca2+]i is mediated in part by enhanced Ca2+ efflux. Coronary artery smooth muscle cells were isolated from gonad-intact, sexually mature female pigs. The [Ca2+]i response to endothelin-1 was measured using fluo 3 and confocal microscopy. 17beta-Estradiol (E2beta), but not 17alpha-estradiol or triamcinolone acetonide, caused a concentration-dependent (IC50 = 10 nM) decrease in the [Ca2+]i response to endothelin-1. This decrease was blocked by the specific estrogen receptor antagonist ICI-182780. Under conditions in which Ca2+ influx and sarcoplasmic reticulum Ca2+ reuptake were blocked, E2beta still decreased [Ca2+]i. The response was blocked by extracellular lanthanum. These data indicate that E2beta decreases [Ca2+]i in coronary artery smooth muscle by affecting Ca2+ efflux via a receptor-mediated mechanism.

Rapid inhibition of rat brain mitochondrial proton F0F1-ATPase activity by estrogens: comparison with Na+, K+ -ATPase of porcine cortex

Our earlier studies have identified oligomycin sensitivity-conferring protein (OSCP), a subunit of proton F0F1-ATPase/ATP synthase in the mitochondrial inner membranes, as a new estradiol binding protein. This finding suggests that mitochondrial ATPase/ATP synthase could be a potential target for estradiol or compounds with similar structures. Here, we report that estradiol and several other compounds inhibited F0F1-ATPase activity of detergent-solubilized rat brain mitochondrial preparations in a following decreasing order: diethylstilbestrol (half-inhibition concentration, IC50 of 10-25 microM) > alpha-zearalenol, 4-hydroxyestradiol (1C50 of 55 microM) >2-hydroxyestradiol (IC50 of 110 microM), 17beta-estradiol, 17alpha-estradiol > beta-zearalanol > estriol, testosterone, 16alpha-hydroxyestrone > corticosterone, progesterone, dehydroepiandrosterone, dehydroepiandrosterone 3-sulfate, cholesterol (less than 10% inhibition at 140 microM). On the other hand, Na+, K+ -ATPase of porcine cortex showed different sensitivity to the compounds tested above. At 70 microM, the rank of inhibitory potency in decreasing order was as follows: 2-hydroxyestradiol (IC50 of 70 microM) > diethylstilbestrol> 4-hydroxyestradiol > progesterone > alpha-zearalenol, while other compounds had little effect (less than 5%). The data indicate that the ubiquitous mitochondrial F0F1-ATPase is a specific target site for estradiol and related estrogenic compounds; however, under this in vitro condition, the effect seems to require pharmacological concentrations.

Effect of estrogen on aortic function in postmenopausal women

We hypothesized that estrogen may alter aortic elastic properties. The aortic pressure-diameter relation was obtained in 20 postmenopausal women, 10 without (group 1) and 10 with (group 2) proven coronary artery disease, before and after intravenous administration of 10 micrograms of 17beta-estradiol. Instantaneous aortic diameter was measured by an intravascular catheter developed in our institution simultaneously with aortic pressure at the same aortic level with a catheter-tipped micromanometer. At baseline, elastic properties of the aorta were decreased in group 2 compared with group 1. Compared with baseline, aortic distensibility was increased in both groups (P < 0.01 and P < 0.05 for groups 1 and 2, respectively) after estrogen administration, whereas the pressure-diameter loop was shifted downward along a different hypothetical line of elasticity, suggesting active changes in the aortic elastic properties. Furthermore, a significant reduction in wave reflection was found in both groups (P < 0.001). This action may contribute to the beneficial effects of estrogen on the cardiovascular system and may have future therapeutic implications in postmenopausal women.

The effect of 17beta-oestradiol on regional blood flow in anaesthetized pigs

1. The present study was designed to investigate the effects of 17beta-oestradiol on the mesenteric, renal, iliac and coronary circulations and to determine the mechanisms involved. 2. In pigs anaesthetized with sodium pentobarbitone, changes in blood flow in the superior mesenteric, left renal, left external iliac and left circumflex coronary arteries caused by intravenous infusion of 17beta-oestradiol at constant heart rate and arterial pressure were assessed using electromagnetic flowmeters. 3. In eight pigs, infusion of 2 microg h-1 of the hormone caused an increase in renal, iliac and coronary blood flow without affecting mesenteric blood flow, left ventricular dP/dtmax (rate of change of left ventricular systolic pressure) and filling pressures of the heart. In four pigs, these vasodilator effects were enhanced by graded increases in the dose of the hormone between 1, 2 and 3 microg h-1; the highest dose also caused an increase in mesenteric blood flow. 4. In five pigs, blockade of muscarinic cholinoceptors and adrenoceptors with the intravenous administration of atropine, propranolol and phentolamine did not affect the vasodilator responses caused by infusion of 2 microg h-1 of 17beta-oestradiol. 5. The increases in renal, iliac and coronary blood flow caused by infusion of 2 microg h-1 of 17beta-oestradiol were prevented, respectively, by the injection of Nomega-nitro-L-arginine methyl ester (L-NAME) into the renal artery (five pigs), the iliac artery (five pigs) or the coronary artery (five pigs). In five pigs, all responses were prevented by injection of L-NAME into all three arteries. In two pigs, injection of L-NAME into the mesenteric, renal, iliac and coronary arteries abolished the vasodilator responses to the infusion of 3 microg h-1 of 17beta-oestradiol. 6. The present study shows that intravenous infusion of 2 microg h-1 of 17beta-oestradiol primarily dilated renal, iliac and coronary circulations and that a higher dose of the hormone also caused vasodilatation in the mesenteric vascular bed. The mechanism of these responses was shown to be nitric oxide dependent.

Protective action of 17beta-estradiol in cardiac cells: implications for hyperkalemic cardioplegia

BACKGROUND

Hyperkalemic cardioplegic solutions effectively arrest the heart, but may also induce intracellular Ca2+ loading and cellular hypercontracture, which could contribute to ventricular dysfunction associated with global surgical ischemia. Recently, it has been proposed that 17beta-estradiol may possess protective properties in the ischemic myocardium. The purpose of the present study was to examine the action of 17beta-estradiol on cardiac cells exposed to hyperkalemic stress.

METHODS

Single ventricular cardiomyocytes, a preparation devoid of vascular and neuronal elements, were isolated from guinea pig hearts, loaded with a Ca2+-sensitive fluorescent probe, and imaged by digital epifluorescent microscopy. The emitted fluorescence of the probe, a measure of intracellular Ca2+ concentration, and cell length were simultaneously recorded during hyperkalemic challenge, in the absence or presence of 17beta-estradiol.

RESULTS

In control cardiomyocytes, the cytosolic concentration of Ca2+ was 138+/-11 nmol/L and cell length 93+/-11 microm. Exposure to high K+ (+16 mmol/L KCl) significantly increased cytosolic Ca2+ to 2,191+/-87 nmol/L (p < 0.001), and produced cell shortening (length at 39+/-5 microm; p < 0.001). 17beta-Estradiol (10 micromol/L) acutely prevented high K+ to induce either intracellular Ca2+ loading (144+/-13 nmol/L, p < 0.001) or hypercontracture (91+/-10 microm, p < 0.001). Tamoxifen (10 micromol/L), an antiestrogen, abolished the protective effect of 17beta-estradiol.

CONCLUSIONS

We conclude that 17beta-estradiol prevents hyperkalemia-induced Ca2+ loading and hypercontracture through a direct and tamoxifen-sensitive action in cardiomyocytes. This study raises the possibility that 17beta-estradiol should be considered as a cardioprotective adjunct toward a safer hyperkalemic cardioplegia.

Various actions of oestrogens on the vascular system

Epidemiological studies show a reduction in cardiovascular disease with postmenopausal oestrogen use. Oestrogens have been shown to have both metabolic effects and direct effects on the vasculature, both of which may improve arterial function and reduce or reverse atheroma formation. The metabolic effects include changes in lipids and lipoproteins, glucose and insulin metabolism, coagulation and fibrinolysis. The direct arterial effects include changes in endothelium-dependent processes, ion channels, renin-angiotensin system and remodelling processes. The various actions of oestrogens on the vascular system are reviewed. It is clearly important to understand the biological basis of these effects of oestrogen on the cardiovascular system in order to optimize current and future hormone-replacement therapy in women after natural or surgical menopause.

Focal atrial tachycardia: reanalysis of the clinical and electrophysiologic characteristics and prediction of successful radiofrequency ablation

INTRODUCTION

Reports about the clinical and electrophysiologic characteristics of focal atrial tachycardia vary widely. Furthermore, the impact of age, gender, associated cardiac diseases, mechanism, location of atrial tachycardia, and the prediction of results of radiofrequency catheter ablation was not clear. The purpose of this study was to further understand the clinical and electrophysiologic characteristics of focal atrial tachycardia and the prediction of results of radiofrequency ablation.

METHODS AND RESULTS

We searched the literature published between January 1969 and July 1997 using the key word "atrial tachycardia" from the MEDLINE and National Library of Medicine systems. The items analyzed were age, sex, cardiac disease, mechanism, attack pattern, cycle length, location, number of atrial tachycardias, results of ablation, and recurrence after ablation. Multivariate analysis showed that age and paroxysmal type of tachycardia were independent predictors of nonautomatic mechanism; age and presence of other cardiac diseases were independent predictors of multiple atrial tachycardias, and age also was the independent predictor of right-sided atrial tachycardia. Atrial tachycardia located in the right atrium was the only significant predictor of successful radiofrequency catheter ablation. Other cardiac diseases and multiple atrial tachycardias were the significant predictors of recurrence after initial successful radiofrequency catheter ablation.

CONCLUSION

Patient age is closely related to the clinical and electrophysiologic characteristics of atrial tachycardia based on our reanalysis, which found that patient age is an independent predictor of nonautomatic mechanism, right atrial location, existence of multiple atrial tachycardias, and recurrence of atrial tachycardia after initial successful ablation.

Familial hypertrophic cardiomyopathy mice display gender differences in electrophysiological abnormalities

Genetically-manipulated mice harboring an alpha-myosin heavy chain Arg403Gln missense mutation (alpha-MHC403/+) display a phenotype characteristic of familial hypertrophic cardiomyopathy (FHC). Male and female (30 +/- 8 week old) heterozygous alpha-MHC403/+ mice and litter-mate controls were evaluated using a surface electrocardiogram (ECG) and an in vivo cardiac electrophysiology study (EPS). Wild type animals had normal intracardiac electrophysiology, with no significant differences between male and female control mice during EPS. The female wild-type mice did have slower heart rates and longer ECG intervals than their male wild-type counterparts. The female alpha-MHC403/+ mice had similar ECG's, cardiac conduction times, and refractory periods compared with female wild-type mice. In contrast, male FHC mice had distinctive ECG and electrophysiologic abnormalities including right axis deviation, prolonged ventricular repolarization and prolonged sinus node recovery times. During programmed ventricular stimulation, 62% of male alpha-MHC403/+ mice and 28% of female alpha-MHC403/+ mice had inducible ventricular tachycardia. These studies identify gender-specific electrophysiologic abnormalities in alpha-MHC403/+ FHC mice, concordant with the histological and hemodynamic derangements previously reported.

17Beta-oestradiol enhances nitric oxide synthase activity in endothelium-denuded rat aorta

1. It has been suggested that oestrogen-produced vasodilatation is due to induction of endothelial nitric oxide synthase (NOS), but there are many reports of direct effects on vascular smooth muscle. In the present study, these processes were investigated in rat aorta isolated from ovariectomized rats. 2. Short-term treatment (10 min) with 17beta-oestradiol (10 micromol/L) produced a small attenuation of the phenylephrine (PE)-induced constriction, which was unaffected by the nitric oxide synthase inhibitor L-N5(-1-iminoethyl)ornithine (NIO; 100 micromol/L). Long-term treatment (6 h) with 17beta-oestradiol (10 micromol/L) did not affect acetylcholine-mediated vasorelaxation in endothelium-intact aortic rings, but did attenuate PE-induced constriction. This attenuation was also observed in endothelium-denuded preparations after 17beta-oestradiol (10 micromol/L for 6 h) and was far greater than the acute effect of 17beta-oestradiol (10 micromol/L). 3. The attenuation produced by 17beta-oestradiol (10 micromol/L for 6 h) was significantly inhibited by concomitant treatment with cycloheximide (1 micromol/L), suggesting that protein synthesis was involved. NIO (100 micromol/L) also attenuated the effect, which suggests that the anti-constrictor effect of 17beta-oestradiol occurs through the increased production of nitric oxide (NO). 17Beta-oestradiol increased NO production, as assessed by the conversion of [3H]-arginine to [3H]-citrulline in rat aorta. These effects were prevented by cycloheximide and NIO. The anti-constrictor effect of oestrogen was blocked by the oestrogen receptor antagonist ICI 182 780 (100 nmol/L). 4. Western blotting using an antibody specific for inducible nitric oxide synthase (NOS) revealed that 17beta-oestradiol (10 micromol/L for 24 h) treatment induced the formation of inducible NOS protein in the aorta, an effect blocked by cycloheximide. The results indicate that 17beta-oestradiol can attenuate the vasoconstrictor effect of PE by a specific receptor-mediated process that involves induction of inducible NOS.

The effect of progestagens on the carotid artery pulsatility index in postmenopausal women on oestrogen replacement therapy

Part of the cardioprotective effect of postmenopausal oestrogen replacement therapy has been attributed to arterial vasodilation. This effect is partially reversed in the uterine artery by the addition of a progestagen. This study was designed to compare the effects of the C21 progestagen, dydrogesterone and the C19 testosterone derivative, norethisterone on the carotid artery pulsatility index (PI) (thought to represent distal impedance to flow) using a randomized double blind cross-over trial. The addition of progestagen resulted in a significant increase in the carotid artery PI from a median value of 1.67 during the oestrogen only phase to 1.77 (P = 0.02) during the combined phase. This trend was seen with both dydrogesterone and norethisterone, but there was no significant difference in the size of the effect caused by either progestagen. The addition of cyclical progestagen to ERT partially antagonizes the reduction in the carotid artery PI.

Modulation of cardiac hypertrophy by estrogens

Gender-specific differences in heart disease have long been known but it has only been since the advent of molecular biology that it has become possible to investigate the molecular mechanisms. Most biochemical work in the last 50 years has focused on the characterization of the steroid hormones involved in gender specificity. More recently, the cloning of the steroid receptors and characterization of the signaling pathways through these proteins has given new insights into the mechanisms underlying the mode of action of steroid hormones. It has also become clear that the steroid receptors can be classified into families (receptors for thyroid hormone, glucocorticoids, estrogens, androgens, retinoic acid, and so called orphan receptors of mostly unknown function). The structures of these receptors show very close resemblance and all are DNA-binding proteins acting as transcription factors. Some (if not all) act as repressors of transcription of some genes in the native state and are converted to activators (or perhaps repressors of other genes) upon binding of the cognate hormone. Naturally, classical target tissues for estrogens and androgens have been studied first and only in very recent years has it been recognized that estrogens and androgens act on a much wider spectrum of tissues. In the cardiovascular field, the beneficial effect of estrogen replacement therapy in postmenopausal women which reduces the incidence of cardiovascular disease by some 40% and the lower incidence of cardiovascular disease in premenopausal women have mostly been explained by the beneficial action of estrogens on the lipid profile (increase in HDL and decrease in LDL cholesterol). Recently, functional estrogen receptors have also been shown in vascular smooth muscle cells and in the endothelium. Our own group has characterized the presence of estrogen receptors in the myocardium and in cardiac fibroblasts. We have also shown that these receptors are transcriptionally active because they are able to drive a minigene composed of a triple estrogen responsive DNA regulatory element (promoter) coupled to the firefly luciferase gene which serves as a reporter by way of its ability to drive a light-emitting reaction. We are in the process of characterizing the target genes for estrogen in the myocardium. A specific series of immediate-early genes is induced by estradiol (the major premenopausal estrogen) and we have also characterized a number of tissue-specific genes whose expression is driven by estrogens in the myocardium. The ultimate goal of these investigations is to explore the use of estrogens in the treatment of cardiac hypertrophy (and failure) by way of their properties to counteract (at least some of) the pathological switches in gene expression in these disease entities.

Physiological concentrations of estradiol attenuate endothelin 1-induced coronary vasoconstriction in vivo

BACKGROUND

Estrogens are cardioprotective hormones and are reported to have antianginal properties. We examined the effect of physiological concentrations of 17beta-estradiol on coronary reactivity in anesthetized female farm pigs.

METHODS AND RESULTS

Epicardial coronary cross-sectional area (CSA) was assessed by two-dimensional intravascular ultrasound, average coronary peak flow velocity (APV) by intravascular Doppler velocimetry, and coronary blood flow (CBF) was calculated. Dose-response curves to intracoronary endothelin-1 (ET-1, 1 pmol/L to 10 nmol/L), the selective ET(B) receptor agonist sarafotoxin (1 pmol/L to 10 nmol/L), and serotonin (0.1 nmol/L to 1 micromol/L) were assessed before and after a 10-minute infusion of intracoronary estradiol (1 nmol/L). Before estradiol administration, ET-1 induced significant dose-dependent decreases in CSA, APV, and CBF. Estradiol attenuated ET-1-induced epicardial vasoconstriction (P<.001) as well as ET-1-induced decreases in APV (P=.05) and CBF (P=.012). In an additional five pigs, vehicle (DMSO) had no effect on ET-1-induced coronary vasoconstriction. Before estradiol administration, sarafotoxin induced no net change in CSA but induced increases in APV and CBF, the extent of which did not change significantly after estradiol. Serotonin induced small decreases in CSA but increased APV and CBF. Estradiol did not influence serotonin-induced changes in CSA, APV, or CBF.

CONCLUSIONS

We conclude that estradiol attenuates ET-1-induced vasoconstriction, possibly through effects on the ET(A) receptor, because selective ET(B) receptor-induced stimulation with sarafotoxin remained unchanged. Such an effect on the ET(A) receptor may relate to the antianginal properties of estrogens.

Short-term anti-ischemic effect of 17beta-estradiol in postmenopausal women with coronary artery disease

BACKGROUND

Short-term administration of 17beta-estradiol improves effort-induced myocardial ischemia in female patients with coronary artery disease. 17Beta-estradiol also has direct and indirect coronary vascular smooth muscle relaxing properties. The aim of the present study was to evaluate the effect of short-term administration of 17beta-estradiol on pacing-induced myocardial ischemia by means of continuous monitoring of coronary sinus pH in 16 postmenopausal female patients with coronary artery disease.

METHODS AND RESULTS

Patients underwent incremental atrial pacing starting at a rate of 100 bpm and increments of 20 bpm every 2 minutes up to 160 bpm before and 20 minutes after either 17beta-estradiol (1 mg sublingual, 9 patients) or placebo (sublingual, 7 patients). The time to the onset of myocardial ischemia during pacing was significantly increased by 17beta-estradiol (mean+/-SD, 254+/-36 versus 298+/-23 seconds; P<.02) but not by placebo (262+/-45 versus 256+/-34 seconds; P=NS) The pH shift was significantly reduced by 17beta-estradiol but not by placebo at every step of the pacing protocol. The maximum pH shift at peak pacing was significantly reduced by the administration of 17beta-estradiol by 0.022 pH units (95% CI, 0.001, 0.043; P<.04) but not by sublingual placebo (-0.002 pH units; 95% CI, -0.0073, 0.0021; P=NS). The maximum pH shift at maximum comparable pacing was also reduced by 17beta-estradiol by 0.015 pH units (95% CI, 0.012, 0.017; P<.001) but not by placebo (-0.0022 pH units; 95% CI, -0.006, 0.0015; P=NS).

CONCLUSIONS

17Beta-estradiol reduces the degree of pacing-induced myocardial ischemia in postmenopausal patients with coronary artery disease. The reduction of pacing-induced coronary sinus pH shift is consistent with an anti-ischemic effect of the hormone and is not due to preconditioning, as evidenced by the absence of improvement after placebo.

Effects of a pure antiestrogen and progesterone on estrogen-mediated alterations of blood flow and progesterone receptor expression in the aorta of ovariectomized rabbits

There is ample evidence from epidemiological studies that estrogen-replacement therapy protects postmenopausal women against cardiovascular disease. One explanation for this beneficial effect could be the improvement of blood flow under estrogen therapy. By using ultrasound and Doppler color flow mapping we demonstrated in the aorta of ovariectomized rabbits a significant dose-dependent increase in blood flow after treatment with 17beta-estradiol. An increase in blood flow was already observed within 1 h of estradiol treatment and lasted until the end of a 14-day treatment phase. Progesterone did not attenuate the effects of 17beta-estradiol on aortic blood flow. The pure estrogen receptor antagonist ZM 182780, however, dose-dependently reversed the effect of 17beta-estradiol on blood flow after the 14-day treatment phase, but was not able to antagonize the rapid 17beta-estradiol effect on blood flow after 1 h. After killing the animals mRNA and protein expression of the progesterone receptor (PR), a known estrogen-responsive gene in classic target organs, were examined. Analogous to the blood flow results the PR mRNA level increased dose-dependently after 17beta-estradiol treatment, whereas ZM 182780 was able to reverse this effect. Immunohistochemical localization of PR in the aortic wall revealed an increase in immunoreactivity in fibroblasts of the adventitia after 17beta-estradiol treatment. ZM 182780, and to a lesser degree progesterone, reversed the 17beta-estradiol-induced increase in PR immunoreactivity. PR immunoreactivity was further detected in endothelial and smooth muscle cells, but the various hormonal treatments had no discernible effect on the PR mRNA level in these cellular compartments. Our findings in the aorta of OVX rabbits suggest that (a) 17beta-estradiol exhibits a rapid effect on arterial tone, (b) the pure estrogen receptor antagonist ZM 182780 inhibits the 17beta-estradiol effect on blood flow and PR mRNA and (c) progesterone does not attenuate the beneficial effect of estrogens on arterial tone.

Estrogen regulates myogenic tone in pressurized cerebral arteries by enhanced basal release of nitric oxide

Second-order middle cerebral arteries (135.0 +/- 4.6 microns ID) from male, female, ovariectomized female (no endogenous estrogen), and estrogen-treated ovariectomized female Sprague-Dawley rats were harvested and mounted in a pressure myograph. Myogenic response was recorded over a pressure range of 10-100 mmHg and was repeated in the presence of N omega-nitro-L-arginine methyl ester (L-NAME; 2 x 10(-4) M, an inhibitor of nitric oxide (NO) synthase, and after endothelium removal, to examine the contribution of NO to net myogenic tone. With intact endothelium, there were no differences in myogenic tone between the groups, but in the presence of L-NAME and after endothelium removal, estrogen-exposed vessels developed significantly greater tone at-high transmural pressure. There were no differences in sensitivity to sodium nitroprusside, an NO donor, or A-23187, a calcium ionophore. These results suggest an increase in basal release of NO in cerebral arteries exposed to estrogen, without change in NO sensitivity or maximally stimulated NO release.

In vitro administration of 17 beta-estradiol inhibits drug-induced contractions of the rat isolated seminal vesicle

1. The rat isolated seminal vesicle responded to noradrenaline (NA), acetylcholine (ACh), potassium chloride (KCl) and barium chloride (BaCl2) with reproducible contractions. 2. 17 beta-estradiol (17 beta E) cumulatively added in the isolated organ bath reduced the number of contractions with all agonists used in the rank order of potency: BaCl2 > or = KCl > ACh > NA. The dose-response curves constructed in the presence of 17 beta E (2 x 10(-5) mol/l) produced a rightward shift and a reduction in the maximum response showing inhibitory activity. 3. When the calcium content in the normal Krebs medium (2.5 mmol/l) was reduced to half, the inhibitory activity of 17 beta E was potentiated. The maximum inhibition rates to KCl (phasic and tonic), BaCl2 and ACh were significantly (P < 0.05) different from each other. 4. The inhibitory effects of 17 beta E against all agonists tested were found to be similar in their responses to verapamil, but were much lower in potency. 5. The inhibitory effects of 17 beta E was seen only when the hormone was present in the tissue environment and was readily reversible as soon as the tissue was washed with the Krebs medium, suggesting that the effect of 17 beta E is localized. 6. It is suggested that the in vitro application of 17 beta E on the rat isolated seminal vesicle interferes with the process of translocation of calcium ions from the extracellular medium.

Amelioration of ischemia- and reperfusion-induced myocardial injury by 17beta-estradiol: role of nitric oxide and calcium-activated potassium channels

BACKGROUND

17Beta-estradiol increases the production of nitric oxide (NO) and prostacyclin and opens Ca2+-activated K+ (K(Ca)) channels. Whether these effects of 17beta-estradiol reduce infarct size and the incidence of ventricular arrhythmia was investigated in dogs subjected to myocardial ischemia and reperfusion.

METHODS AND RESULTS

Infarct size was measured in open-chest dogs after 90 minutes' occlusion of the left anterior descending coronary artery and a subsequent 6 hours of reperfusion. Infusion of 17beta-estradiol into the coronary artery was initiated 10 minutes before coronary occlusion and continued until after 1 hour of reperfusion, with the exception of the occlusion period. The difference in NO concentration between coronary venous and arterial blood 10 minutes after the onset of reperfusion was significantly greater in dogs treated with 17beta-estradiol (10 ng x kg(-1) x min(-1)) than in control animals. Infarct size (13.1+/-3.0% versus 43.7+/-5.4% of the area at risk) and the incidence of ventricular arrhythmia during ischemia and reperfusion periods were significantly reduced in the 17beta-estradiol group. Both N(G)-nitro-L-arginine methyl ester (an inhibitor of NO synthase) and iberiotoxin (a blocker of K(Ca) channels) reduced both the infarct size-limiting effect (infarct size, 29.3+/-3.0% and 31.7+/-2.1%, respectively) and the antiarrhythmic effect of 17beta-estradiol; indomethacin (an inhibitor of cyclooxygenase) did not attenuate the beneficial effects of 17beta-estradiol.

CONCLUSIONS

17Beta-estradiol reduced both myocardial infarct size and the occurrence of ischemia- and reperfusion-induced ventricular arrhythmias, which appear to be mediated by NO and the opening of K(Ca) channels in canine hearts.

Effect of acute administration of estradiol 17 beta on aortic blood flow in menopausal women

Acute administration of estradiol 17beta increases aortic blood flow velocity in menopausal women. This suggests that the effect of the ovarian hormone on cardiac dynamics is mainly dependent on a reduction in peripheral vascular resistances.

Lack of effect of estrogen on rest and treadmill exercise in postmenopausal women without known cardiac disease

To assess the peripheral vascular effects of estrogen in women without coronary disease, normal postmenopausal women (mean age 56 +/- 8 years) participated in a randomized, crossover trial using treadmill exercise echocardiography, and received oral conjugated estrogen, 0.625 mg/day or underwent a drug-free period. There was no significant effect on heart rate, blood pressure, double product, left ventricular end-systolic and end-diastolic diameters, or electrocardiographic measures after estrogen. In contrast to the profound effects reported in patients with cardiac disease, oral estrogen in normal women does not bestow significant benefit on treadmill exercise echocardiographic variables at rest or during modest levels of exercise.

Acute hemodynamic effects of estrogen administration in postmenopausal women

The hemodynamic effects of estrogens in replacement doses have not been fully clarified; therefore, we studied the acute hemodynamic changes after 0.625 and 1.25 mg of conjugated estrogens, administered intravenously, using a thermodilution catheter, in postmenopausal women without structural heart disease. Pulmonary and systemic pressures and resistances and stroke volume did not change compared with baseline, but heart rate and cardiac output decreased significantly, which may be associated with estrogen's previously described calcium-blocking effect or with a more recently contemplated beta-blocking action.

Increased expression of the cardiac L-type calcium channel in estrogen receptor-deficient mice

Steroid hormones control the expression of many cellular regulators, and a role for estrogen in cardiovascular function and disease has been well documented. To address whether the activity of the L-type Ca2+ channel, a critical element in cardiac excitability and contractility, is altered by estrogen and its nuclear receptor, we examined cardiac myocytes from male mice in which the estrogen receptor gene had been disrupted (ERKO mice). Binding of dihydropyridine Ca2+ channel antagonist isradipine (PN200-110) was increased 45.6% in cardiac membranes from the ERKO mice compared to controls, suggesting that a lack of estrogen receptors in the heart increased the number of Ca2+ channels. Whole-cell patch clamp of acutely dissociated adult cardiac ventricular myocytes indicated that Ca2+ channel current was increased by 49% and action potential duration was increased by 75%. Examination of electrocardiogram parameters in ERKO mice showed a 70% increase in the QT interval without significant changes in PQ or QRS intervals. These results show that the membrane density of the cardiac L-type Ca2+ channel is regulated by the estrogen receptor and suggest that decreased estrogen may lead to an increase in the number of cardiac L-type Ca2+ channels, abnormalities in cardiac excitability, and increased risk of arrhythmia and cardiovascular disease.

Sex hormones and vascular reactivity

It is increasingly recognized that sex steroids have, among many other effects, the ability to cause vasodilation. The vasodilatory effects of estradiol have been the best documented and described. At low concentrations, estradiol has the ability to improve impaired endothelium dependent (nitric oxide mediated) relaxation in estrogen deficient subjects. At high concentrations, estradiol causes vasodilation principally by endothelium independent mechanisms, in a gender independent fashion, which appear to involve a number of pathways such as ATP-dependent K+ channels. Testosterone also has ability, at higher doses, to cause vasodilation of the coronary circulation, in a gender independent fashion. The mechanisms of sex steroid-induced vasodilation are reviewed in this article.

Long-term estrogen therapy improves vascular function in male to female transsexuals

OBJECTIVES

This study sought to examine the effects of long-term estrogen therapy on vascular function in male to female transsexuals and to compare the findings with those observed in men and premenopausal women.

BACKGROUND

Gender differences in coronary artery disease have largely been attributed to the beneficial effects of estrogen on vascular function and plasma lipids in women. However, the effects of estrogen on the male vasculature have not been widely studied.

METHODS

We compared the effects of estrogen on vascular function in 14 male to female transsexuals, 14 age-matched men and 15 premenopausal women. Flow-mediated vasodilation and response to nitroglycerin were assessed in the brachial artery using noninvasive ultrasound.

RESULTS

Flow-mediated vasodilation was similar in transsexuals and women but greater than that in men ([mean +/- SE] 11.5 +/- 1.3% and 9.4 +/- 1.1% vs. 5.2 +/- 1.0% respectively, p < 0.005). Responses to nitroglycerin were also greater in transsexuals and women than in men (21.6 +/- 1.7% and 21.0 +/- 0.9% vs. 14.5 +/- 1.2%, respectively, p = 0.0005). These differences persisted even after adjusting for vessel size. Despite similar total cholesterol levels, transsexuals had high density lipoprotein cholesterol levels similar to those in women and greater than those observed in men (1.76 +/- 0.12 and 1.82 +/- 0.11 mmol/liter vs. 1.35 +/- 0.07 mmol/liter, respectively, p < 0.005). Moreover, triglyceride levels were greater in transsexuals than in men and women, and low density lipoprotein cholesterol (LDL-C) particle size was smaller (25.7 +/- 0.2 nm vs. 26.2 +/- 0.1 and 26.6 +/- 0.1 nm, respectively, p = 0.0001). Serum testosterone (an index of estrogen therapy in transsexuals) was markedly suppressed in transsexuals and similar to that in women. Univariate analysis revealed that there was a strong inverse correlation between serum testosterone and flow-mediated vasodilation (r(s) = -0.48, p < 0.005). Multivariate analysis revealed that the best combination of predictors of flow-mediated vasodilation was serum testosterone, vessel size and LDL-C (R2 = 0.3, p < 0.005).

CONCLUSIONS

Long-term estrogen therapy appears to improve vascular function in male to female transsexuals and occurs despite higher triglyceride levels and the presence of small, dense LDL-C. The beneficial effects of estrogen are not gender specific or solely mediated through endothelium-derived nitric oxide.

Estradiol, Administered Acutely, Protects Ischemic Myocardium in Both Female and Male Rabbits

BACKGROUND: The benefits of chronic administration of estrogen to postmenopausal women are well documented; however, the acute effects of exogenous estradiol on myocardium after coronary artery occlusion and reperfusion in male and female animal models are unknown. We tested the influence of acute pretreatment with estradiol on the development of myocardial necrosis in two protocols, studying intact anesthetized female and male rabbits. METHODS AND RESULTS: 17beta-estradiol (1 mg) was given 15 minutes before coronary artery occlusion in the treated groups (n = 10 females, 10 males); control rabbits (n = 11 females, 10 males) received water. All rabbits underwent 30 minutes of coronary artery occlusion and 4 hours of reperfusion. Myocardial blood flow was similar between groups at 10 minutes after treatment and during coronary artery occlusion and reperfusion. Thus estradiol did not increase blood flow. Heart rate and systemic pressure were also similar between groups. Estradiol levels during coronary artery occlusion were 1-8 pg/mL in untreated female and male rabbits and 66 +/- 28 (male) and 352 +/- 273 (female) in treated rabbits. Although the size of the ischemic risk zones was similar in both groups in both protocols, estradiol-treated rabbits of both sexes developed significantly less necrosis. Infarct size as a percent of the risk region was 10 +/- 1% in female estradiol-treated rabbits compared with 23 +/- 5% in controls (P <.03) and 16 +/- 4% in estradiol-treated male rabbits compared with 31 +/- 5% in control males (P =.03). Although male rabbits had larger infarcts than female rabbits, sex was not a significant covariate for infarct size. CONCLUSIONS: Estradiol exerts a protective effect on ischemic myocardium that is not associated with an increase in myocardial blood flow or alteration in hemodynamics. This study shows that acute administration of estrogen before coronary artery occlusion reduces infarct size in both male and female rabbits.

Effect of 17 alpha-ethinylestradiol, levonorgestrel, 3-keto-desogestrel, and gestodene on calcium influx via voltage-gated calcium channels in human aortic smooth muscles

The effect of the synthetic estradiol, 17 alpha-ethinylestradiol, and three progestogens on calcium influx was investigated in cell cultures of human aortic smooth muscle. Neither the synthetic estrogen nor the progestogens levonorgestrel, 3-keto-desogestrel, and gestodene showed, in the concentration range of 10(-9) to 10(-6) M, a significant effect on calcium influx both alone or in equimolar estrogen-gestagen combinations. The results indicate that these substances, commonly used in contraceptive pills, do not change vasotonus interfering with calcium homeostasis.

The menopause and the cardiovascular system

Combining the wealth of epidemiological, metabolic and recent mechanistic data, it would appear biologically plausible that HRT, either oestrogen alone or in combination with progestogen, is cardioprotective. Further research is required, as information is lacking on cardiovascular effects of HRT instigated at an older age. There is a need to identify cardiovascular benefit, indirect and/or direct, of combined oestrogen/progestogen therapy using randomized trials. The various progestogen types and doses also need to be investigated. Studies are also required to investigate the effect of HRT use in higher risk patients with established CVD. There is scant information on the effect of HRT on blood pressure of patients with hypertension. Cardiovascular risk factor profiles and incidence surveys need to be conducted in developing countries to characterize their female population and to identify the prevalence of CVD; this needs to be undertaken before widespread recommendations on CVD prevention and the role of HRT can be made. If HRT is to be used effectively in the future treatment of heart disease in women these questions need to be addressed. At present HRT is indicated for the relief of menopausal symptoms and the prevention of osteoporosis. In women without these indications, ORT may be recommended in those who have had a premature menopause, and possibly in those who have established CHD or who are at high risk of developing CHD. It is too early to suggest a blanket recommendation for the use of HRT in the treatment of the symptoms of women with established CVD, but HRT after the menopause may at least be safely used in the secondary prevention of CHD.

Investigation of the negative inotropic effects of 17 beta-oestradiol in human isolated myocardial tissues

1. The aim of the present study was to evaluate the effects of 17 beta-oestradiol in human myocardium. The effects of 17 beta-oestradiol, progesterone and testosterone on force of contraction were investigated in electrically driven isolated atrial trabeculae and ventricular papillary muscles from human hearts in the presence and absence of Bay K 8644, a calcium channel agonist. In addition, the effects of 17 beta-oestradiol, progesterone and testosterone on binding of [3H]-PN 200 110 were assessed in membranes prepared from human ventricular myocardium. 2. 17 beta-Oestradiol elicited a negative inotropic effect in atrial (IC50: 7.1 mumol 1(-1), confidence interval 3.8 to 13.4, n = 3) and ventricular preparations (IC50: 4.6 mumol 1(-1)), confidence interval 2.2 to 9.4, n = 3) as compared with solvent controls. There was no significant difference (P > 0.05) of IC50 values in the absence and presence of isoprenaline (0.0 mumol 1(-1)) in atrial (IC50: 10.8 mumol 1(-1), confidence interval 9.1 to 12.9, n = 6) and ventricular preparations (IC50: 9.4 mumol 1(-1), confidence interval 7.3 to 11.9, n = 8). 3. 17 beta-Oestradiol at 30 mumol 1(-1) induced a significant rightward shift of the concentration-response curves for the positive inotropic effect of Bay K 8644 in atrial preparations (EC50: 0.13 mumol 1(-1), confidence interval 0.08 to 0.19, n = 6; EC50 with 17 beta-oestradiol: 0.58 mumol 1(-1), confidence interval 0.33 to 0.83, n = 6, P < 0.05) and ventricular preparations (EC50: 0.07 mumol 1(-1), confidence interval 0.04 to 0.11, n = 8; EC50 with 17 beta-oestradiol: 0.3 mumol 1(-1), confidence interval 0.18 to 0.49, n = 8, P < 0.05). Testosterone, progesterone at 30 mumol 1(-1) and the solvent control had no significant effect on the concentration-response curves to Bay K 8644. 4. In membranes prepared from human ventricular myocardium the effect of 17 beta-oestradiol on binding of [3H]-PN 200 110, an antagonist at the 1,4 dihydropyridine binding site, was not different from that observed with progesterone, testosterone or solvent controls. 5. In myocardial membranes no specific oestrogen receptors were demonstrated by [3H]-oestradiol binding studies. 6. Thus, the calcium antagonistic property of 17 beta-oestradiol cannot be attributed to a direct interaction with 1, 4 dihydropyridine binding sites.

beta-Estradiol, but not alpha-estradiol, reduced myocardial necrosis in rabbits after ischemia and reperfusion

Recent studies in several animal models have suggested that estrogen, given for the short term, may protect ischemic myocardium. Our objective was to test the effect of exogenous estradiol on the development of myocardial necrosis. Twenty minutes before coronary occlusion, rabbits were given an IV bolus of either 17 beta-estradiol, a form of the hormone that stimulates the estrogen receptor (10 micrograms) or 17 alpha-estradiol, a natural form of the hormone lacking estrogenic effects (1 mg), or vehicle. Regional myocardial blood flow (RMBF) was measured after treatment and during occlusion and reperfusion, and heart rate and blood pressure were monitored throughout. All rabbits underwent 30 minutes of coronary artery occlusion and 4 hours of reperfusion. Estradiol levels were 6 +/- 2 pg/ml in untreated rabbits, 392 +/- 78 pg/ml in rabbits given 17 beta-estradiol, and 413 +/- 68 pg/ml in rabbits given 17 alpha-estradiol. The size of the ischemic region was similar in all groups, but rabbits treated with 17 beta-estradiol developed significantly less necrosis than did control rabbits (0.33 +/- 0.04 vs 0.53 +/- 0.05 of the area at risk; p < 0.05), whereas rabbits treated with 17 alpha-estradiol did not (0.43 +/- 0.03; p = NS vs control group). Heart rate, systemic pressure, and RMBF were comparable among groups throughout the protocol. In conclusion, 17 beta-estradiol exerts a protective effect on ischemic myocardium, reducing infarct size. This beneficial effect is not associated with an increase in myocardial blood flow or alteration in hemodynamics. Because 17 alpha-estradiol did not affect infarct size, the cardioprotective effect of 17 beta-estradiol is probably receptor mediated.

Estrogen effects in the heart

Gender specific differences in cardiovascular disease are largely mediated by sex hormones. The use of estrogens significantly reduces the overall incidence of heart disease in postmenopausal women. Beneficial effects of estrogens on plasma lipoprotein levels are clearly established. However, these do not explain the magnitude of risk reduction seen in clinical studies. Thus additional and currently unknown functions of estrogens must be operative. Elucidation of the exact estrogen action in the heart will have important implications in the treatment of cardiovascular disease. It will probably enhance the therapeutic repertoire in treating heart disease, the most common cause of death in industrialized countries. We will review the current understanding of the function of estrogens in the heart and discuss potential strategies on how to apply these data to clinical practice.

Modulation of hypertensive heart disease by estrogen

Left ventricular hypertrophy is an independent risk factor for morbidity and mortality in patients with hypertensive heart disease. Cardiac hypertrophy, associated with increased cardiac fibrosis and myocardial relaxation impairment, shows gender-based differences with significantly higher mortality in men. The role of estrogen in the pathogenesis of this process is poorly understood. After our previous demonstration that cardiac myocytes and fibroblasts contain functional estrogen receptors, we therefore investigated: 1) the influence of different estrogen metabolites on cardiac fibroblast growth; 2) the influence of different estrogen metabolites on the expression of the immediate early gene c-Fos; 3) the influence of estrogen on the L-type calcium channel in cardiomyocytes.

METHODS

1) Neonatal rat cardiac fibroblasts were incubated with 17 beta-estradiol, estrone, 2-hydroxyestrone, and 2-methoxyestradiol (all 10(-9) M). Bromodeoxyuridine incorporation was measured after 24 h. 2) c-Fos expression was demonstrated by immunoblotting. 3) L-type (Ca2+) current with and without 17 beta-estradiol was assessed in adult guinea pig cardiomyocytes by whole cell patch clamp.

RESULTS

Cardiac fibroblast growth was stimulated by estrogen metabolites with 2-hydroxyestrone as the most potent activator; in addition, 10(-5) M 17 beta-estradiol reduced the L-type Ca2+ current by about 20% in cardiomyocytes.

CONCLUSIONS

Estrogen induces both short term effects (non-genomic) and long term effects (genomic) on the heart and may therefore account for gender- and age-based differences in hypertensive heart disease.

Cyclical variation in paroxysmal supraventricular tachycardia in women

BACKGROUND

Paroxysmal supraventricular tachycardia (SVT) in premenopausal women is often judged to be related to anxiety, and may be associated with the menstrual cycle. The aim of this study was to determine whether a cyclical variation of episodes of SVT exists and to correlate such variation with cyclical variation in plasma ovarian hormones.

METHODS

26 women (mean age 36 [SD 8] years; with paroxysmal SVT were screened; those with regular menses who experienced at least three episodes of paroxysmal SVT in two consecutive 48-hour ambulatory ECG recordings were included. 13 patients (aged 32 [6] years) met these criteria. Patients underwent 48-hour ambulatory ECG monitoring and determination of plasma concentrations of oestradiol-17 beta and progesterone on day 7, 14, 21, and 28 of their menstrual cycle.

FINDINGS

An increase in the number and duration of episodes of paroxysmal SVT was observed on day 28 as compared to day 7 of the menstrual cycle. A significant positive correlation was found between plasma progesterone and number of episodes and duration of SVT (5.6 [2.2] ng/mL; r=0.83, p=0.0004; and r=0.82, p=0.0005), while a significant inverse correlation was found between plasma oestradiol-17 beta and number of episodes and duration of SVT (155 [22] pg/mL; r=0.89, p<0.0001; and r=0.81, p=0.0007).

INTERPRETATION

Women with paroxysmal SVT and normal menses exhibit a cyclical variation in the occurrence of the arrhythmia with their menstrual cycle. There is a close correlation between the episodes of paroxysmal SVT and the plasma concentrations of ovarian hormones. These data suggest that changes in plasma levels of ovarian hormones (and their interaction) may be of importance in determining episodes of arrhythmia in such patients. The mechanisms of these effects are unknown.