Cardiovascular protection by oestrogen--a calcium antagonist effect?

Does melatonin affect calcium influx in human aortic smooth muscle cells and estradiol-mediated calcium antagonism?

The pineal hormone melatonin showed no effect on voltage-gated calcium channels in cultured human aortic smooth muscle cells. In combination with estradiol, which blocked calcium channels, melatonin did not antagonize the effect of estradiol. It is concluded that melatonin seems to have different effects on voltage-gated calcium channels of divergent cell types since the positive action of melatonin previously observed on rat cardiac membranes by other authors could not be seen in the present investigations with human vascular smooth muscle cells.

Estrogen induction and contact phase activation of human factor XII

This paper reviews data reported in the literature and results of our experiments on the transcriptional control of Factor XII by estrogens and on the activation of Factor XII in the plasma. Coagulation Factor XII (Hageman factor, FXII) is a serine protease secreted by the liver and activated by negative charged surfaces to play roles in fibrinolysis, coagulation, and inflammation. Multiple effects on hemostasis involving these processes via Hageman factor have been reported in relation to estrogen therapy. The nucleotide sequence of 3,174 base pair (bp) DNA at the 5' end of the Factor XII gene indicates that the Factor XII promoter is typical of TATA-less, liver-specific, and serine protease-type eukaryotic genes involved in clotting. In addition the Factor XII promoter contains at position -44/-31 a palindrome similar, but not identical, to an estrogen-responsive element (ERE) together with four hemisite EREs between positions -1314 and -608. These promoter regions may underlie the mechanism by which estrogens enhance Factor XII concentrations in plasma. In vivo, a 6-fold stimulation of FXII gene transcription by 17 beta-estradiol was observed in ovariectomized rats. In vitro a 230-bp promoter fragment of Factor XII (-181/+49) confers a strong 17 beta-estradiol responsiveness onto a chlorampenicol acetyltransferase reporter when transiently co-transfected with the human estrogen receptor. The domain structure of Factor XII allows identification of those parts of the protein with particular functions. cDNA constructs, in which sequences coding for selected domains were deleted, were used to produce recombinant deleted Factor XII proteins in a vacinia virus expression system. To identify the domain(s) responsible for contact phase activation, these recombinant proteins were tested for their capacity to bind to negatively charged substrates, to become activated by kallikrein, and to sustain blood clotting and amidolytic activity. In addition to the N-terminal domain, the growth factor and kringle domains and, to a lesser extent, the polyproline region also interact with negatively charged surfaces and presumably thus contribute to activation.

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.

Inhibition of the protective effect of estrogen by progesterone in experimental atherosclerosis

The aim of the present study was to determine the effect of progesterone on the action of estrogen in the development of atherosclerosis. A total of 48 female New Zealand white (NZW) rabbits were ovariectomized. The animals were separated into 6 groups of 8 animals each and received subsequently a 0.5% cholesterol diet for 12 weeks. During this cholesterol feeding period, either estradiol (1 mg/kg body weight (BW)/week), progesterone (25 mg/kg BW/week), or combined estradiol/progesterone (in above dosages) was administered intramuscularly in each group (n = 8 each) of ovariectomized rabbits. One additional group of 8 animals received a combined estrogen/ progesterone regimen, but with progesterone at one third of the above mentioned dosage. In another 8 rabbits, progesterone was reduced to one ninth of the maximum dosage above, whereas estrogen was kept the same, at 1 mg/kg BW/week. Eight ovariectomized animals served as the control group and received no hormone treatment. After 12 weeks, the animals were sacrificed and the proximal aortic arch was removed for further histological examination. An inhibitory effect of estrogen of intimal thickening was found, in comparison to the control group (intimal area: 0.7 +/- 0.5 mm2 vs. 3.7 +/- 2.5 mm2, P < 0.01), whereas progesterone alone did not show a significant effect on intimal plaque size (intimal area: 4.0 +/- 2.3 mm2). In combination with progesterone (high dose), estrogen was not able to reduce intimal atherosclerosis (intimal area: 3.4 +/- 2.4 mm2). However, the beneficial effect of estrogen was not affected by progesterone, when this was reduced respectively to one third (intimal area: 0.8 +/- 0.7 mm2), or to one ninth of the highest dosage (intimal area: 0.6 +/- 0.4 mm2). Interestingly, these differences in atherosclerotic plaque development were observed without significant changes in plasma cholesterol concentrations by the administered hormones. In conclusion, progesterone was dose-dependently able to completely inhibit the beneficial effect of estrogen in experimental atherosclerosis, suggesting that progesterone exerts a direct inhibitory effect on the athero-protective action of estrogen. In the context of recently published data, the present work confirms the importance of the 'non-lipid-mediated', anti-atherosclerotic effect of estrogen, probably due to an interaction with six hormone receptors in vascular smooth muscle cells (VSMC).

Evaluation and management of chronic pelvic pain

Evaluating patients with chronic pelvic pain is complex. A detailed medical history should be ideally supplemented by psychologic evaluation and assessment of the woman's social background. At the time of physical examination, the location and intensity of the pain should be mapped. Assessment of pain relief with the administration of a local anesthetic to trigger points or selected nerves may be useful in predicting the potential efficacy of surgical interventions such as uterosacral nerve ablation. Appropriate tests include pelvic ultrasound and magnetic resonance imaging. Ultimately, laparoscopy may provide the final diagnosis. Management should address the underlying cause(s) of pain; when this cannot be done, it should focus on treating the pain itself. When appropriate, empiric administration of antidepressants may be considered. In selected women, therapeutic goals may be achieved by electrical stimulation of nerves.

Oestradiol-induced relaxation of rabbit basilar artery by inhibition of voltage-dependent Ca channels through GTP-binding protein

1. Effects of oestradiol on the electrical and mechanical properties of the rabbit basilar artery were investigated by use of microelectrode, patch-clamp and isometric tension recording methods. 2. Oestradiol (10 nM-100 microM) relaxed arterial tissue pre-contracted by excess [K]o solution (30 mM) in a concentration-dependent manner. In Ca-free solution, histamine (10 microM) and caffeine (20 mM) each produced a phasic contraction, but oestradiol (10 microM) did not significantly affect their amplitude. 3. Oestradiol (< or = 100 microM) did not change the resting membrane potential of the artery whether in the presence or absence of TEA (10 mM). Action potentials observed in the presence of 10 mM TEA were abolished by oestradiol (100 microM). 4. Oestradiol (1 microM-100 microM) inhibited the voltage-dependent Ba current in a concentration-dependent manner. Oestradiol (100 microM) inhibited the Ba current observed in the presence of nicardipine (1 microM) more than that in the absence of nicardipine (to 31.0% vs 62.0% of control). 5. GTP gamma S (30 microM) in the pipette enhanced the inhibitory actions of oestradiol on the Ba current. On the other hand, with GDP beta S (1 mM) in the pipette, oestradiol failed to inhibit the Ba current. Pertussis toxin (PTX 3 micrograms ml-1) in the pipette totally prevented the inhibitory action of oestradiol on the Ba current. 6. Oestradiol (< or = 100 microM) had no significant effect on the outward K currents evoked by a membrane depolarization. 7. These results strongly suggest that oestradiol relaxes arterial tissue by inhibition of voltage-dependent Ca channels and that it inhibits both nicardipine-sensitive and -resistant Ca currents via a PTX-sensitive GTP-binding protein. The main target of oestradiol among the arterial Ca channels seems to be the nicardipine-resistant Ca channel, rather than the nicardipine-sensitive one.

17beta-Estradiol inhibits the voltage-dependent L-type Ca2+ currents in aortic smooth muscle cells

To elucidate the mechanisms of estrogens-induced relaxation effects on vascular smooth muscle cells, the effects of estrogens and the related hormones were examined in cultured rat thoracic aortic smooth muscle cell lines (A7r5), using the whole-cell voltage clamp technique. The patch pipette was filled with 140 mM CsCl- or KCl-containing internal solution. With CsCl-internal solution, 17beta-estradiol and synthetic estrogens, ethynylestradiol and diethylstilbestrol (0.1-30 mu M) inhibited the Ba2+ inward current (IBa) through the voltage-dependent L-type Ca2+ channel in a concentration-dependent and reversible manner. The potency of the inhibitory effects on IBa was 17beta-estradiol < ethynylestradiol < diethylstilbestrol. 17beta-Estradiol (10 mu M) appeared to reduce the maximal conductance of IBa with only a slight shift of voltage-dependency of inactivation and to affect IBa in a use-independent fashion. On the other hand, testosterone and progesterone (30 mu M) failed to affect IBa. At a holding potential of -40 mV, both vasopressin and endothelin-1 (100 nM) activated a long-lasting inward current. After endothelin-1 (100 nM) activated the current, the additional application of vasopressin (100 nM) could not induce it furthermore, suggesting that each agonist activates the same population of the channels. The reversal potential of the current was about 0 mV and was not significantly altered by replacement of [Cl-]i or [Cl-]0 and the inward current was also observed even when extracellular cations are Ca2+, proposing that it was a Ca2+-permeable non-selective cation channel (IN.S.). La3+ or Cd2+ (1 nM) completely abolished IN.S., however, nifedipine (10 mu M) failed to inhibit it at all. Diethylstilbestrol (1-30 mu M) suppressed the IN.S. evoked by both endothelin-1 and vasopressin in a concentration-dependent manner, while 17beta-estradiol, ethynylestradiol, progesterone and testosterone (30 mu M) failed to inhibit it significantly. In addition, at a holding potential of +0 mV, 17beta-estradiol by itself did not affect the holding currents, and did not inhibit K+ currents evoked by endothelin-1 or vasopressin, possibly due to the Ca2+ release from the storage sites. These results suggest that 17beta-estradiol may play a role in regulating vascular tone, selectively by inhibiting the voltage-dependent L-type Ca2+ current in vascular smooth muscle cells.

Postmenopausal oestrogens and arteries

Postmenopausal oestrogen use is associated with a significant reduction in cardiovascular morbidity and mortality. The fact that a large scale controlled trial has not been conducted is a valid criticism, but the epidemiological data are compelling and there is evidence of biologically plausible mechanisms which may mediate this effect. Postmenopausal HRT also abolishes climacteric symptoms and conserves bone. For the postmenopausal woman who has had a hysterectomy, unless there are compelling reasons to the contrary, we believe that unopposed oestrogen therapy should be offered routinely. Women who still have a uterus (and these form the majority of potential HRT users) require oestrogens with cyclical progestogens. Whether such opposed therapy results in any reduction in cardiovascular protection needs to be addressed urgently. Meanwhile, it could be argued that these women should also be offered HRT routinely. Indeed, a recent consensus conference (Lobo & Speroff 1994) concluded that because of the magnitude of cardiovascular disease as a cause of morbidity and mortality, the beneficial role of estrogen in the primary prevention of cardiovascular disease in most women outweighs its potential risk. At the present time, there are insufficient data to indicate whether there are any groups of women for whom the risks may be too great to prescribe some form of estrogen therapy. As life expectancy increases in developed countries, such reductions in the leading cause of mortality are likely to benefit not only the individual woman, but the society in which she lives.

The menopause revisited

The continuing growth of female life expectancy has resulted in a marked increase of women in years beyond the menopause. Women can nowadays expect to live one-third of their lives in a potential hormonal deficiency state. Women over 50 comprise 17% of the total population of any country in the modern western world. Any decision regarding their health issues will have a great impact on our limited health care resources. There is no doubt that estrogen replacement therapy effectively mitigates hot flushes and other vasomotor symptoms and more effectively so than other treatment modalities. Vasomotor symptoms affect more than half of the female population around the menopause with a mean duration of 2-3 years. When used to treat vasomotor symptoms hormone replacement therapy has repeatedly been shown to be cost effective. It is also well documented that hormone replacement therapy effectively prevents bone loss and osteoporotic fractures as well as heart disease. The majority of cases of both fractures and heart disease occur at ages over 75 and concern has been expressed if treatment from the menopausal age to the onset of fractures or heart disease is cost effective with regard to the perceived increase in risk of side effects, especially breast cancer. One important aspect in this scenario is the control system that we impose on women on HRT. Given our present preparations women are recommended an annual check-up. If the number of office procedures and visits to the clinic cannot be substantially reduced long-term therapy with HRT is not cost effective. An exception from this rule is the treatment of urogenital estrogen deficiency using low dose vaginal estrogens. Systemic concentrations of estrogens following such administration are negligible. Hence, low dose estrogen topical applications can be made an OTC preparation. As no control system is needed this therapy seems to be highly cost effective. The pharmaceutical industry is urged to produce better products so that side effects such as bleeding problems leading to a number of visits to the clinic and fear of cancer among women can be avoided. Recent data also imply that estrogen treatment may confer protection against Alzheimer's disease. Breast cancer is the remaining controversy even if recent data imply that estrogens could be given to women operated on for breast cancer without increasing the risk of a relapse.

Influence of two hormone replacement therapy regimens, oral oestradiol valerate and cyproterone acetate versus transdermal oestradiol and oral dydrogesterone, on lipid metabolism

OBJECTIVE

To compare the influence on lipid metabolism of two discontinuous, sequentially combined hormone replacement therapy (HRT) regimens.

STUDY DESIGN

In an open, randomized study in 60 women, a full lipid profile including Lp(a) and liver function tests were assessed in a fasting state at the end of treatment cycles 6 and 12. Group A was treated with 2 mg oestradiol valerate (days 1-21) sequentially combined with 1 mg cyproterone acetate (days 12-21); group B was treated with a patch releasing 50 micrograms oestradiol daily, twice a week (3 weeks), sequentially combined with 20 mg dydrogesterone (days 12-21) orally. Statistical analysis by two-sided one-way analysis of covariance (covariable is baseline) for adjusted means of lipid parameters and rank transformation analysis for lipoprotein(a) (Lp(a)) was performed.

RESULTS

Both groups were statistically comparable. The trial was completed by 45 subjects. Protocol violations occurred in 3 cases. Twelve subjects, equally divided between the groups, dropped out mainly because of adverse reactions. Both treatments were equally effective in the treatment of climacteric complaints. Liver function tests during the treatment period were normal in both groups. In group A, a statistically significant (P < 0.05) decrease versus baseline was observed in the serum levels (adjusted means) of the following parameters after 6 and 12 treatment cycles: total cholesterol (TC)-5% and -7%, respectively; low-density lipoprotein cholesterol (LDL-C) -13% and -14%, respectively; low-density lipoprotein cholesterol/high-density lipoprotein cholesterol ratio (LDL-C/HDL-C ratio) -16% and -18%, respectively. Triglycerides (TG) levels were significantly increased by 28% and nearly significantly (P = 0.07) by 25% after 6 and 12 treatment cycles, respectively. In group B, all lipid parameters (with the exception of apolipoprotein A-II which was significantly decreased after 12 treatment cycles) remained unchanged during therapy. Statistically significant differences for all aforementioned variables were found between the groups after 6 and 12 treatment cycles, respectively, with the exception of TC after 12 treatment cycles. After 6 treatment cycles, Lp(a) was decreased significantly (-18%) in group A as compared with baseline; after 12 months the decrease was -17% without reaching statistical significance. In group B, Lp(a) showed a slight but not statistically significant tendency to increase by 2% and 12% after 6 and 12 treatment cycles, respectively. Differences between both groups did not reach the level of significance.

CONCLUSION

In this randomized, comparative study, a sequentially combined oral HRT regimen consisting of oestradiol valerate (2 mg daily on days 1-21) and cyproterone acetate (1 mg daily on days 12-21), induced a lipid pattern and probably also a change in Lp(a) levels, which is generally viewed to be more beneficial with regard to the prevention of cardiovascular disease than the lipid pattern induced by a sequentially combined regimen of transdermal 17 beta-oestradiol (50 micrograms twice weekly during three weeks) and oral dydrogesterone (20 mg daily on days 12-21).

Estrogen acutely increases peripheral blood flow in postmenopausal women

PURPOSE

To test the acute effect of estrogen on peripheral blood flow and vascular resistance in postmenopausal women.

PATIENTS AND METHODS

Eleven normotensive, post-menopausal female volunteers (mean age 53 +/- 6 years) were studied. Six women were in natural menopause and 5 had had a hysterectomy (mean age of the menopause 49 +/- 3 years). We used a double-blind, randomized protocol to assess the acute response to sublingual estradiol-17 beta (1 mg) on the forearm resistance vessels, compared with sublingual placebo. Blood flow was measured by strain-gauge plethysmography, and mean peripheral vascular resistance was then calculated. Mean blood pressure was also measured.

RESULTS

The mean blood flow induced by estradiol-17 beta after 40 minutes was significantly greater than that induced by placebo (3.9 +/- 0.5 mL/100 mL per minute versus 2.4 +/- 0.4 mL/100 mL per minute, respectively, P < 0.05). The forearm resistance was significantly reduced at 40 minutes after estradiol-17 beta compared with placebo (25.7 +/- 4.4 resistance units (RU) to 44.4 +/- 6.4 RU, respectively, P < 0.05). Mean blood pressure 40 minutes after the administration of estradiol-17 beta was no different when compared with placebo (91 +/- 1.5 mm Hg versus 90 +/- 2.5 mm Hg, respectively, P = NS).

CONCLUSIONS

These results indicate that the acute administration of estradiol-17 beta affects blood flow in the peripheral vasculature in human subjects. The mechanism of this effect has not been determined, but it may explain some of the beneficial effects of estrogen on the vascular system and have future therapeutic potential in postmenopausal women.

17 beta-Estradiol attenuates acetylcholine-induced coronary arterial constriction in women but not men with coronary heart disease

BACKGROUND

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Microscopic findings of the nail-fold capillaries--dependence on menopausal status and hormone replacement therapy

The aim of our controlled study was to evaluate peripheral microcirculation at the level of the nail-fold capillaries in relation to menopause status and postmenopausal hormone replacement therapy (HRT). A total of 105 postmenopausal women were randomly allocated to three different HRT groups of equal size. A fourth group of 35 similar healthy volunteers served as controls. HRT was either peroral or transdermal 17-beta-oestradiol with cyclic addition of dydrogesterone or 2.5 mg Tibolone (Org OD 14) in a daily peroral dose. Morphological parameters such as capillary diameters, loop width, papillary width and capillary density, measured by video-capillaroscopy at the nail-fold, were unaffected in early menopause and also under HRT. A significant decrease of capillary blood flow velocity (P < 0.001) could be demonstrated in postmenopausal (n = 41, v = 0.53 +/- 0.16 mm/s) as compared to premenopausal women (n = 37, v = 0.65 +/- 0.15 mm/s). HRT resulted in an increase of capillary blood flow velocity in the nail-fold after 6 and 12 months leading to an increase in capillary blood flow in the order of 20%-30% of the initial values, and was independent of the type of HRT.

Association between increased estrogen status and increased fibrinolytic potential in the Framingham Offspring Study

BACKGROUND

Although extensive evidence indicates that estrogen is responsible for the markedly decreased cardiovascular risk of premenopausal women, the mechanism through which estrogen might exert its protective effect has not been adequately explained. Since thrombosis is now recognized to play an important role in the onset of cardiovascular disease, we investigated the relation between estrogen status and fibrinolytic potential, a determinant of thrombotic risk.

METHODS AND RESULTS

We determined levels of plasminogen activator inhibitor (PAI-1) antigen and tissue plasminogen activator (TPA) antigen in 1431 subjects from the Framingham Offspring Study. Fibrinolytic potential was compared between subjects with high estrogen status (premenopausal women and postmenopausal women receiving hormone replacement therapy) and low estrogen status (men and postmenopausal women not receiving hormone replacement therapy). In all comparisons, subjects with high estrogen status had greater fibrinolytic potential (lower PAI-1 levels) than subjects with low estrogen status. First, postmenopausal women receiving estrogen replacement therapy had lower levels of PAI-1 than those not receiving therapy (13.0 +/- 0.5 versus 19.5 +/- 1.0 ng/mL, P < .001). Second, premenopausal women had lower levels of PAI-1 than men of a similar age (14.8 +/- 0.6 versus 20.3 +/- 0.8 ng/mL, P < .001); this sex difference diminished when postmenopausal women not receiving hormone replacement therapy were compared with men of a similar age (19.6 +/- 0.7 versus 21.1 +/- 0.7 ng/mL, P = .089). Third, premenopausal women had markedly lower levels of PAI-1 antigen than postmenopausal women not receiving estrogen therapy (14.8 +/- 0.6 versus 19.5 +/- 1.0 ng/mL, P < .001). The between-group differences observed for TPA antigen were similar to those for PAI-1 antigen.

CONCLUSIONS

Each of these comparisons indicates that the cardioprotective effect of estrogen may be mediated, in part, by an increase in fibrinolytic potential. These findings might provide at least a partial explanation for the protection against cardiovascular disease experienced by premenopausal women, and the loss of that protection following menopause.

Influence of hormones on platelet intracellular calcium

The pathophysiology of thromboembolic disease associated with estrogen therapy is poorly understood. There are innumerable calcium-dependent activities involved in platelet function. To determine whether platelet calcium levels are affected by exogenous hormones, intracellular calcium and release were studied in platelets in various hormonal environments and findings were correlated with platelet adhesion and aggregation. Platelet intracellular calcium concentration and release was significantly decreased in women ingesting tamoxifen compared to controls and significantly increased, as was platelet adhesion, in oral contraceptive users. Platelets incubated ex vivo with estradiol had increased intracellular calcium and release but there was decreased adhesion to fibronectin. Intracellular calcium concentration and release were not affected when platelets were incubated with tamoxifen. Adhesion to collagen III was increased in tamoxifen-incubated platelets. Only oral contraceptive users had increased sensitivity to aggregating agents. This data suggests that 17 beta estradiol, progesterone, and tamoxifen likely have a nongenomic effect on platelet intracellular calcium and calcium release and that platelet calcium levels are closely related to the degree of platelet adhesion and aggregation in vivo.

Testosterone relaxes rabbit coronary arteries and aorta

BACKGROUND

Until menopause, women appear to be protected from coronary heart disease. Evidence suggests that estrogen may play a role in the protection of the cardiovascular system by exerting a beneficial effect on risk factors such as cholesterol metabolism and by a direct effect on the coronary arteries. To date there has been no evidence linking testosterone with the occurrence of coronary heart disease. Testosterone may affect the cardiovascular system directly, thus partially explaining the difference in the incidence of coronary artery disease in men and premenopausal women. The purpose of this study was to assess the direct effect of testosterone and a number of testosterone analogues on rabbit coronary arteries and aorta in vitro.

METHODS AND RESULTS

Rings of coronary artery and aorta of adult male or nonpregnant female New Zealand White rabbits were suspended in organ baths containing Krebs solution; isometric tension then was measured. The response to testosterone was investigated in prostaglandin F2 alpha (PGF 2 alpha)- and KCl-contracted rings. The effects of endothelium and nitric oxide synthase, prostaglandin synthetase, and guanylate cyclase inhibition on testosterone-induced relaxation were investigated. The effects of ATP-sensitive potassium channels and potassium conductance were also assessed. Relaxing responses in the presence of aromatase inhibition and testosterone receptor blockade were performed. The relaxing responses to the testosterone analogues etiocholan-3 beta-ol-17-one, epiandrosterone, 17 beta-hydroxy-5 alpha-androst-1-en-3-one, androst-16-en-3-ol, and testosterone enanthanate were measured. Testosterone relaxed rabbit coronary arteries and aorta. There was no significant difference between the relaxation effect of testosterone with or without endothelium. Similar results were obtained from male and nonpregnant female rabbits. The relaxing response of testosterone in the coronary artery was significantly greater than in the aorta. The relaxing response of testosterone in the coronary artery was significantly reduced by the potassium channel inhibitor barium chloride but not by the ATP-sensitive potassium channel inhibitor glibenclamide. The relaxing response to testosterone was greater in PGF 2 alpha-contracted rings compared with KCl-contracted rings. Inhibitors of nitric oxide synthase, prostaglandin synthetase, and guanylate cyclase did not affect relaxation induced by testosterone. Inhibition of aromatase and testosterone receptors did not affect relaxation. Testosterone did not shift the rabbit coronary arterial calcium concentration-dependent contraction curves, whereas verapamil did. There were, however, significant differences in the relaxing response to testosterone compared with testosterone analogues. Testosterone was the most potent relaxing agent, suggesting that there may be a structure-function relation in the relaxing response.

CONCLUSIONS

Testosterone induces endothelium-independent relaxation in isolated rabbit coronary artery and aorta, which is neither mediated by prostaglandin I2 or cyclic GMP. Potassium conductance and potassium channels but not ATP-sensitive potassium channels may be involved partially in the mechanism of testosterone-induced relaxation. The in vitro relaxation is independent of sex and of a classic receptor. The coronary artery is significantly more sensitive to relaxation by testosterone than the aorta. Testosterone is a more potent relaxing agent of rabbit coronary artery than other testosterone analogues.

Vascular responses to 17 beta-oestradiol in postmenopausal women

The vascular responses to 17 beta-oestradiol were examined in 23 postmenopausal women (59 +/- 7 years [mean +/- SD]) using a placebo-controlled double-blind crossover design. All women received 1 mg 17 beta-oestradiol or placebo (P) sublingually on consecutive days in random order. Axial diameters and blood flow rates of the left common femoral arteries were determined before and 60-80 min after application of verum or placebo as well as 10-30 min after 10 mg isosorbide dinitrate (ISDN) with a quantitative duplex ultrasound technique. Oestradiol induced a vasodilation of femoral arteries (+6.4 +/- 4.1% of basal, P < 0.001 vs. basal and P), the vessel diameter was unchanged with placebo (+0.7 +/- 2.1%). The blood flow rate increased significantly after oestradiol application (+30 +/- 28%, P < 0.05 vs. basal and P), but not after placebo (+11 +/- 21%). Mean blood pressure and heart rate remained constant with both drugs. Despite its vasodilatory effect, ISDN significantly reduced the arterial blood flow after pretreatment with oestradiol and placebo, probably through cardiac preload reduction. In conclusion, 17 beta-oestradiol alters the vascular tone of systemic arteries resulting in a vasodilation and increase of blood flow. We suggest that these direct vascular actions may contribute to the preventive properties of oestrogens on cardiovascular diseases in postmenopausal women.

Postmenopausal hormone therapy and atherosclerotic disease

Several lines of evidence suggest that estrogen is an important determinant of cardiovascular risk in women. Epidemiologic data document low rates of coronary heart disease (CHD) in premenopausal women, a narrowing of the gender gap in CHD mortality after menopause, and elevated risk of CHD among young women with bilateral oophorectomy not treated with estrogen. Nearly all of the more than 30 observational studies of exogenous estrogen replacement therapy have indicated a reduced risk of CHD among women receiving estrogen therapy. In a meta-analysis comparing estrogen users and nonusers, the estimated reduction of CHD among users was 44%. In angiographic studies, women taking estrogen were less likely to have coronary artery stenosis. Estrogen is known to affect a wide range of physiologic processes that may have an impact on CHD risk. Use of oral estrogen has favorable effects on serum lipid profiles; it increases high-density lipoprotein cholesterol levels by 10% to 15% and decreases low-density lipoprotein cholesterol levels by a similar magnitude. Other proposed mechanisms include inhibition of endothelial hyperplasia, reduced arterial impedance, enhanced production of prostacyclin, increased insulin sensitivity, and inhibition of oxidation of low-density lipoprotein. Nevertheless, the role of hormone replacement therapy in preventing clinical atherosclerotic events in women remains inconclusive because of the absence of randomized trial data. The benefit-to-risk ratio must be reliably assessed, because estrogen has complex actions, including postulated benefits (CHD, osteoporosis, and menopausal symptoms) and postulated risks (endometrial cancer, breast cancer, and gallstones.(ABSTRACT TRUNCATED AT 250 WORDS)

Lewis A. Conner Memorial Lecture. Mechanisms leading to myocardial infarction: insights from studies of vascular biology

Myocardial infarction is the most frequent cause of mortality in the United States as well as in most western countries. In this review, the processes leading to myocardial infarction are described based on the most recent studies of vascular biology; in addition, evolving strategies for prevention are outlined. The following was specifically discussed. (1) Five phases of the progression of coronary atherosclerosis (phases 1 to 5) and eight morphologically different lesions (types I, II, III, IV, Va, Vb, Vc, and VI) in the various phases are defined. (2) The present understanding of the pathogenesis of each of the phases of progression and of the various lesion types preceding myocardial infarction is described; particular emphasis is placed on the physical, structural, cellular, and chemical characteristics of the "vulnerable or unstable plaques" prone to disruption (types IV and Va lesions). (3) The fate of plaque disruption (type VI lesion) in the genesis of the various coronary syndromes and especially acute myocardial infarction is defined; particular emphasis is placed on the combination of plaque disruption and a high thrombogenic risk profile--local factors (ie, degree of plaque disruption, exposure of lipid-macrophage-rich plaque, etc) and systemic factors (ie, catecholamines, RAS, fibrinogen, etc)--in the genesis of myocardial infarction. (4) Strategies of regression or stabilization of "vulnerable or unstable plaques" for prevention of myocardial infarction are presented within the context of recent favorable experience with risk factor modification and lipid-modifying angiographic trials, beta-blockade and angiotensin-converting enzyme inhibition, antithrombotic strategies, and the possible role of estrogens. The recent past has been very fruitful in yielding a better understanding of the processes leading to myocardial infarction, and the near future appears very promising in terms of preventing the number 1 killer in the western world.

Nitric oxide accounts for dose-dependent estrogen-mediated coronary relaxation after acute estrogen withdrawal

BACKGROUND

Estrogen replacement therapy reduces the risk of coronary heart disease in postmenopausal women, and estrogen treatment modulates endothelium-dependent vasodilation in ovariectomized, atherosclerotic monkeys. Estradiol-17 beta also induces relaxation in isolated rabbit coronary arteries as well as cerebral basilar arteries. The estrogen concentrations required to induce such relaxation are in the pharmacological range (10(-6) to 10(-5) mol/L).

METHODS AND RESULTS

The present study was designed to test whether the sensitivity and specificity of the relaxing response of coronary vascular smooth muscle to exogenous estradiol-17 beta is dependent on the sex hormone status of the animal. In coronary artery rings contracted with PGF2 alpha (3 x 10(-5) mol/L), estradiol-17 beta caused significant relaxation at a physiological estrogen concentration (10(-9) mol/L), in coronary artery rings from oophorectomized, estrogen-treated and acutely estrogen-withdrawn rabbits only. Relaxation induced by estradiol-17 beta at lower concentrations (10(-9) to 10(-6) mol/L) in these rings was 20 +/- 6%, 42 +/- 8%, 54 +/- 9%, and 75 +/- 8%, respectively, compared with 4 +/- 2%, 12 +/- 5%, 16 +/- 7%, and 25 +/- 12% and 5 +/- 2%, 12 +/- 5%, 18 +/- 8%, and 23 +/- 10% in rings from estrogen-maintained and oophorectomized rabbits, respectively (P < .01). The relaxation in coronary artery rings from estrogen-treated and acutely estrogen-withdrawn rabbits was endothelium and nitric oxide dependent since it was abolished by endothelium removal and the nitric oxide synthase inhibitor N omega-nitro-L-arginine.

CONCLUSIONS

This study demonstrates that estrogen-induced, endothelium-dependent relaxation of coronary arteries may, in some species, depend on the sex hormone status of the animal. These findings may help to better understand the effects of ovarian steroids in the coronary circulation of females.

Endothelium-independent relaxation by 17-alpha-estradiol of pig coronary arteries

We have studied the effects of 17-alpha-estradiol, a non-estrogenic steroid, on pig coronary arteries contracted by K+, Ca2+ or serotonin. Experiments were performed on helicoidal strips and rings of left circumflex coronary arteries from freshly slaughtered white pigs and on helicoidal strips of rat thoracic aorta. The strips and rings were suspended inside a water-jacketed muscle chamber in an oxygenated Krebs solution at 37 degrees C. From the initial K(+)-evoked contraction, 17-alpha-estradiol caused a relaxation with an IC50 (15 microM) which was in the range of the IC50s obtained for nitroglycerin (1.3 microM) and nicorandil (50 microM). Contractions evoked by Ca2+ were inhibited by 17-alpha-estradiol, but full blockade could not be achieved. Serotonin-evoked contractions were also blocked by 17-alpha-estradiol with an IC50 of 2.1 microM; 17-beta-estradiol also inhibited the serotonin-evoked contractions. In the presence of 100 microM of the nitric oxide synthase inhibitor N-nitro-L-arginine methyl ester, the relaxing properties of 17-alpha-estradiol in pig coronary arteries and rat thoracic aorta were unaffected, suggesting that endothelial NO release was unrelated to these effects. 17-alpha-Estradiol also relaxed denuded pig coronary artery strips, suggesting that other endothelial-derived relaxing factors were not involved in its vascular effects. The results are compatible with the idea that 17-alpha-estradiol causes relaxation of coronary vessels by acting directly on the cell membrane of smooth muscle cells; these effects seem to be unrelated to the genomic physiological effects of estrogens.(ABSTRACT TRUNCATED AT 250 WORDS)

Update on the metabolic effects of steroidal contraceptives and their relationship to cardiovascular disease risk

Evaluation of metabolic disturbances has had an important role in the modification of oral contraceptive formulations toward estrogen-progestin combinations with reduced adverse metabolic impact. An increasing number of interrelationships between metabolic risk factors for cardiovascular disease are being recognized, and a metabolic syndrome of disturbances has been identified with insulin resistance as a potential underlying factor. The insulin resistance syndrome includes hyperinsulinemia and impaired glucose tolerance, hypertriglyceridemia, reduced high-density lipoprotein concentrations, and hypertension. Increased concentration of a small, dense, low-density lipoprotein subtype may also be important. Depending on steroid type and dose, combined oral contraceptives may induce all the features of the insulin resistance syndrome. Reduction in estrogen dose and modification of progestin content have resulted in formulations with no adverse effect on high-density lipoprotein and blood pressure, but insulin resistance and hypertriglyceridemia remain. These are caused primarily by the estrogen component. Therefore modification of the estrogen content of oral contraceptives might result in "metabolically transparent" formulations that could conceivably afford a degree of cardiovascular protection.

Estrogen withdrawal selectively increases serotonin reactivity in rabbit basilar artery

Clinical observations and laboratory investigations suggest that gender and menstrual status modulate cerebrovascular reactivity. We prepared 7 groups of rabbits (I) males (II) oophorectomized untreated females, (III) testosterone treated oophorectomized females, (IV) superovulated females, (V) superovulated estrogen withdrawn females, (VI) estrogen treated oophorectomized females, and (VII) estrogen withdrawn females to mimic phases of the estrous cycle and compare cerebral basilar artery reactivity to serotonin (5-HT) and norepinephrine (NE) in vitro. Basilar artery sensitivity to 5-HT vasoconstriction was increased in oophorectomized, acutely estrogen withdrawn females (Group VII) when compared to estrogen maintained and the other groups (p < 0.0001). There was a significant reduction in 5-HT sensitivity in superovulated females (Group IV) (p < 0.001). The change in 5-HT sensitivity is selective and was not observed for NE. Nitroarginine treatment and mechanical denudement resulted in higher Tmax and lower ED50 for both NE and 5-HT regardless of hormonal manipulation. We conclude that estrogen withdrawal increases 5-HT vasoreactivity by an endothelium independent mechanism.

Beneficial effect of oestrogen on exercise-induced myocardial ischaemia in women with coronary artery disease

Oestradiol-17 beta causes relaxation of isolated coronary arteries and increases blood flow in several vascular beds in human beings and animals. Oestrogen replacement therapy is associated with a lower incidence of cardiovascular disease, but the acute effects of oestradiol-17 beta on myocardial ischaemia are unknown. We have studied the acute effect of sublingual oestradiol-17 beta on exercise-induced myocardial ischaemia in eleven women (mean age 58 [SD 8] years) with coronary artery disease. The women did two treadmill exercise tests on separate days; 40 min before the test they took sublingual oestradiol-17 beta (1 mg) or placebo, in random order. Plasma oestradiol-17 beta concentrations were confirmed to be higher after sublingual oestradiol-17 beta than after placebo (2531 [1192] vs 155 [168] pmol/L, p < 0.001). Oestradiol-17 beta increased both time to 1 mm ST depression (456 [214] vs 579 [191] s, p < 0.004; difference of medians 92 [95% CI 46-254]) and total exercise time (569 [249] vs 658 [193] s, p < 0.01; difference 54 [10-212]). Acute administration of oestradiol-17 beta therefore has a beneficial effect on myocardial ischaemia in women with coronary artery disease. This effect may be due to a direct coronary-relaxing effect, to peripheral vasodilation, or to a combination of these mechanisms. Oestradiol-17 beta may prove to be a useful adjunct to the treatment of angina in postmenopausal women with coronary heart disease.