Action of estrogens in the aging brain: Dementia and cognitive aging

Background

Menopause is associated with sharp declines in concentrations of circulating estrogens. This change in hormone milieu has the potential to affect brain functions relevant to dementia and cognitive aging.

Scope of review

Focused review of published results of randomized clinical trials of estrogen-containing hormone therapy for Alzheimer's disease treatment and dementia prevention, observational research on cognition across the menopause transition, and observational research on the association of hormone therapy and Alzheimer's disease risk.

Major conclusions

Clinical trial evidence supports conclusions that estrogen therapy does not improve dementia symptoms in women with Alzheimer's disease and that estrogen-containing hormone therapy initiated after about age 65 years increases dementia risk. Hormone therapy begun in this older postmenopausal group does not ameliorate cognitive aging. Cognitive outcomes of midlife hormone exposures are less well studied. There is no strong indication of short-term cognitive benefit of hormone use after natural menopause, but clinical trial data are sparse. Little research addresses midlife estrogen use after surgical menopause; limited clinical trial data imply short-term benefit of prompt initiation at the time of oophorectomy. Whether exogenous estrogen exposures in the early postmenopause affect Alzheimer risk or cognitive aging much later in life is unanswered by available data. Observational results raise the possibility of long-term cognitive benefit, but bias is a concern in interpreting these findings.

General significance

Estrogen-containing hormone therapy should not be initiated after age 65 to prevent dementia or remediate cognitive aging. Further research is needed to understand short-term and long-term cognitive effects of estrogen exposures closer to the age of menopause.     

Debate: The potential role of estrogen in the prevention of heart disease in women after menopause

The observational studies of hormone users are compromised by systematic biases that lead to an overestimation of benefit and an underestimation of risk. Studies of mechanism could support either benefit or harm. The results of clinical trials of oral hormone therapy in women with existing coronary heart disease (CHD) have been uniformly disappointing. The largest trial found an early increased risk for CHD and for venous thromboembolism. Postmenopausal hormone therapy should not be considered for CHD prevention until methods for excluding high-risk women have been established, and until the results of the long-term trials have shown benefit. There is a need for clinical trials of nonoral estrogens.     

Bias in Observational Studies of the Association between Menopausal Hormone Therapy and Breast Cancer

BackgroundDuring the period 1985-2000 the breast cancer incidence rates increased 50% in the age group invited to mammography screening in Norway and Sweden. Simultaneously, use of hormone replacement treatment therapy (HT) increased 5 times. Several influential observational studies showed that HT was associated with 50% to 100% increased risk of breast cancer and most for those using combined (estrogen plus progestin) hormone replacement therapy (CHT). In contrast, the randomized WHI trial reported that CHT increased the risk by 10% for those not having previously used hormones and 24% when including previous users in the analyses. In another randomized trial, estrogen use only was not associated with any increased risk at all. After the WHI trial was published in 2003, use of HT dropped 70% within 5 years in Norway and Sweden while breast cancer rates were essentially unchanged. After 2008, HT use has dropped further and breast cancer incidence rates have started increasing again. The study objective is to calculate and to explain potential bias in the observational study design.ConclusionsWe suggest that the mechanism causing higher hazard ratio of breast cancer (compared to the observational studies) is the time-varying effect of CHT on the breast cancer risk and selective retrospective reporting of hormone use. Other risk factors for the increase in breast cancer risk in the age group 50-69 years should be considered, for example, overdiagnosis.     

Early initiation of statin therapy after a coronary event

PURPOSE OF REVIEW: Despite improvements in the early management of acute coronary syndromes, the risk of major cardiovascular complications remains high. Lipid-modifying treatment with statins has the potential to further improve outcomes through improved endothelial function, antithrombotic and antiinflammatory actions. Statins are of proven benefit in patients with stable coronary heart disease. There has been speculation on potential mechanisms of benefit but, until recently, little data on the efficacy and safety of statins in the acute setting. Recent observational studies and randomized trials have addressed some of the questions regarding early initiation of statins in acute coronary syndromes. RECENT FINDINGS: Recent observational and randomized trials have shown that early commencement of statins in acute coronary syndromes is safe as early as 6 hours after the event and is likely to improve longer-term compliance. The current data are not sufficient to draw conclusions about the efficacy of statins early in the course of acute coronary syndromes. SUMMARY: Current management for acute coronary syndromes should include the commencement of statin therapy during initial hospital admission. This recommendation is based on safety and compliance data. More randomized trial evidence is required to determine whether early initiation will produce better outcomes than later initiation after an acute coronary event.     

An Analytic Framework for Aligning Observational and Randomized Trial Data: Application to Postmenopausal Hormone Therapy and Coronary Heart Disease

We describe a conceptual analytic framework for aligning observational and randomized controlled trial (RCT) data. The framework allows one to (1) use observational data to estimate treatment effects comparable to their RCT counterparts, (2) properly include early events that occur soon after treatment initiation in the analysis of observational data, (3) estimate various treatment effects that are of clinical and scientific relevance while appropriately adjusting for time-varying confounders in both the RCT and observational analyses, (4) assess the generalizability of RCT findings in the more diverse populations generally found in the observational data, and (5) combine both types of data to study associations that cannot be addressed by one study or a single data set. We describe the theoretical application of this framework to the Women’s Health Initiative data to examine the relation between postmenopausal hormone therapy and coronary heart disease. The analytic framework can be tailored to specific exposure-outcome associations and data sources, and may be refined as more is learned about its strengths and limitations.     

Observation versus intervention in the evaluation of drugs: the story of hormone replacement therapy

Hormone replacement therapy, which was approved for menopausal symptoms, offers an opportunity to compare clinical trials and observational studies when evaluating the risks and benefits of drugs. The differences between randomized and observational evidence relate mainly to the risks of coronary heart diseases and dementia, higher or not elevated in users in trials, and decreased in observational studies. The most likely explanation for these discrepancies is bad accounting for confounders, in particular, time-dependent confounders in classical multivariate analyses and use of prevalent user design. Marginal structural models and new user design should help to diminish strongly indication bias in future observational studies aiming at the evaluation of the risks and benefits of drugs.     

Sex hormones and coronary disease: a review of the clinical studies

A male to female ration of coronary disease of 2:1 has been a consistent finding. This differential persists event when the classic risk factors for coronary disease--hypertension, smoking, obesity, diabetes, and hyperlipidemia--are controlled for gender. The most likely ultimate cause of this phenomenon is male-female differences in sex hormone patterns. Clinical studies in this area have either compared the sex hormone profiles of men and women with and without coronary disease or computed the relative prevalence of disease in populations that differ in their sex hormone patterns. In general, research findings have disputed the hypothesis that persons with coronary disease have low levels of a protective factor such as estrogen or progesterone and high levels of testosterone. Coronary disease patients actually have elevated estrogen levels and low testosterone levels; endogenous progesterone levels are normal before infarction but show a stress-mediated increase in the immediate postinfarction period. Findings of a low prevalence of coronary disease in premenopausal women, a loss of protection after menopause, and a low prevalence of coronary disease in men with cirrhosis-related hyperestrogenemia suggest that natural estrogens are antiatherogenic. The protective effect of pregnancy against myocardial infarction, despite concomitant potentially thrombogenic levels of estrogen at the time, seems to indicate that progesterone, whose levels are also extremely high during pregnancy, plays a major anti-infarction protective effect distinct from that of estrogen. Studies of women oral contraceptive (OC) users and men taking estrogens for brief periods have found that these exogenous hormones produce coronary thrombosis but not atherosclerosis. Finally, the finding of increased coronary disease risk in long-term OC users indicates that synthetic estrogens favor coronary atherosclerosis by suppressing natural estrogen and progesterone production.     

Postmenopausal hormone therapy and cognition

This article is part of a Special Issue "Estradiol and cognition".Prior to the publication of findings from the Women's Health Initiative (WHI) in 2002, estrogen-containing hormone therapy (HT) was used to prevent age-related disease, especially cardiovascular disease, and to treat menopausal symptoms such as hot flushes and sleep disruptions. Some observational studies of HT in midlife and aging women suggested that HT might also benefit cognitive function, but randomized clinical trials have produced mixed findings in terms of health and cognitive outcomes. This review focuses on hormone effects on cognition and risk for dementia in naturally menopausal women as well as surgically induced menopause, and highlights findings from the large-scale WHI Memory Study (WHIMS) which, contrary to expectation, showed increased dementia risk and poorer cognitive outcomes in older postmenopausal women randomized to HT versus placebo. We consider the ‘critical window hypothesis’, which suggests that a window of opportunity may exist shortly after menopause during which estrogen treatments are most effective. In addition, we highlight emerging evidence that potential adverse effects of HT on cognition are most pronounced in women who have other health risks, such as lower global cognition or diabetes. Lastly, we point towards implications for future research and clinical treatments.     

Alternative hormone replacement regimens: is there a need for further clinical trials?

PURPOSE OF REVIEW: To review the randomized trials of hormone replacement therapy. RECENT FINDINGS: Studies have shown that conjugated equine estrogen 0.625 mg a day plus medroxyprogesterone acetate 2.5 mg a day increased the risk of cardiovascular events during the first year of treatment in women both with and without coronary heart disease. Conjugated equine estrogen plus medroxyprogesterone acetate also increased the overall risk of myocardial infarction and stroke in women without coronary heart disease, and myocardial infarction or death in women with coronary heart disease, and also increased the risk of breast cancer, cognitive decline and dementia. Unopposed, oral 17B-estradiol increased the risk of stroke during the first 6 months of treatment in women with a previous stroke. Oral 17B-estradiol with or without cyclic progestin had no effect on the progression of atherosclerosis or reinfarction. Transdermal 17B-estradiol plus cyclic progestin was associated with a non-significant increase in coronary heart disease events in women with coronary heart disease. Compared with placebo, cardiovascular events increased in the ongoing estrogen-only arm of the Women's Health Initiative, indicating that unopposed conjugated equine estrogen is unlikely to be cardioprotective. However, oral 17B-estradiol retarded the progression of subclinical atherosclerosis in younger women without coronary heart disease. SUMMARY: Hormone replacement therapy should not be initiated for the primary or secondary prevention of coronary heart disease in women. A trial of 17B-estradiol started at menopause in women without coronary heart disease should be considered.     

Positive and negative affect and risk of coronary heart disease: Whitehall II prospective cohort study

Objective To examine the associations between positive and negative affect and subsequent coronary heart disease events independently of established risk factors.Design Prospective cohort study with follow-up over 12 years.Setting 20 civil service departments originally located in London.Participants 10 308 civil servants aged 35-55 years at entry into Whitehall II study in 1985.Main outcome measures Fatal coronary heart disease, clinically verified incident non-fatal myocardial infarction, and definite angina (n=619, mean follow-up 12.5 years).Results In Cox regression analysis adjusted for age, sex, ethnicity, and socioeconomic position, positive affect (hazard ratio=1.01, 95% confidence interval 0.82 to 1.24) and the balance between positive and negative affect, referred to as the affect balance score (hazard ratio=0.89, 0.73 to 1.09), were not associated with coronary heart disease. Further adjustment for behaviour related risk factors (smoking, alcohol consumption, daily fruit and vegetable intake, exercise, body mass index), biological risk factors (hypertension, blood cholesterol, diabetes), and psychological stress at work did not change these results. However, participants in the highest third of negative affect had an increased incidence of coronary events (hazard ratio=1.32, 1.09 to 1.60), and this association remained unchanged after adjustment for multiple confounders.Conclusions Positive affect and affect balance did not seem to be predictive of future coronary heart disease in men and women who were free of diagnosed coronary heart disease at recruitment to the study. A weak positive association between negative affect and coronary heart disease was found and needs to be confirmed in further studies.     

How can we best prolong life? Benefits of coronary risk factor reduction in non-diabetic and diabetic subjects.

OBJECTIVE--To compare the theoretical benefits of different approaches to reduce risk factors for coronary heart disease in subjects at risk. DESIGN--The results of findings from meta-analyses of intervention studies on cause specific mortality and of observational studies on smokers and ex-smokers were applied to observational data on 10 year cause specific mortality derived from the multiple risk factor intervention trial. Lifetable analyses were used to estimate gains in life expectancy. SUBJECTS--Diabetic and non-diabetic men initially 35-57 years of age. MAIN OUTCOME MEASURES--10 year mortality from coronary heart disease, 10 year total mortality, man years of intervention to prevent one death and one death from coronary heart disease, gain in life expectancy, and drug costs per year of additional life in diabetic and non-diabetic men of 45. RESULTS--In non-diabetic men a 10 year mortality from coronary heart disease of 14.4 per 1000 would be reduced by a mean of 0.58, 0.82, 2.64, and 2.74 per 1000 by antihypertensive treatment, lowering cholesterol concentration, taking aspirin, and stopping smoking respectively; a 10 year total mortality of 44.1 per 1000 would fall by a mean of 1.06, 5.16, and 8.65 per 1000 with antihypertensive and aspirin treatment and stopping smoking respectively and increased by a mean of 0.07 per 1000 with the lowering of cholesterol concentration. In diabetic men the reductions in mortality from coronary heart disease would be between three and five times greater, and total mortality would show mean reductions of 5.81, 0.56, 16.17, and 20.84 per 1000 respectively, with all interventions of significant benefit except the lowering of cholesterol concentration. Between 2400 and 3800 man years of pharmacological intervention were calculated as being necessary to prevent one death from coronary heart disease in a non-diabetic man, and between 800 and 1200 man years in a diabetic man. The loss of life expectancy associated with smoking and hypertension is greater than that accruing from hypercholesterolaemia, but stopping smoking would prolong life by a mean of around four years in a 45 year old non-diabetic man and three years in a diabetic man, whereas aspirin and antihypertensive treatment would provide approximately one year of additional life expectancy in both categories. CONCLUSIONS--Studies to date have shown little impact of drugs that lower cholesterol concentration and blood pressure on either coronary heart disease or total mortality. Although new treatments for hypercholesterolaemia and hypertension might help prevent coronary heart disease, other approaches to reduce the burden of premature death are required.     

Hormone replacement therapy and cardiovascular disease: lessons from a monkey model of postmenopausal women

Concerns exist about the cardiovascular effects of hormone replacement therapy (HRT) in postmenopausal women because results from the Women's Health Initiative (WHI) and the Heart and Estrogen/Progestin Replacement Study (HERS) are contradictory. In both of these studies, postmenopausal conjugated equine estrogens + medroxyprogesterone acetate did not reduce risk, and somewhat increased the risk of myocardial infarction in both primary (WHI) and secondary (HERS) prevention. These results appear to contradict numerous observational clinical trials and animal studies, which reported profound beneficial effects of HRT on cardiovascular disease risk. Results of both human and monkey studies indicate that estrogen replacement therapy (ERT)/HRT is effective in inhibiting progression of early stage (fatty streak) atherosclerosis but that ERT/HRT is much less effective in inhibiting progression of more advanced (established plaque) atherosclerosis. Results of these monkey studies are consistent with those of studies in women wherein ERT/HRT was initiated in postmenopausal women with different initial amounts of atherosclerosis. Based on these findings, it is speculated that ERT/HRT may be more cardioprotective in younger postmenopausal women with less coronary artery disease, and less effective in women with established coronary artery disease. Researchers are challenged to define the relative cardiovascular risk/benefit in different populations of postmenopausal women based on differences in age, amounts of pre-existing atherosclerosis, and risk factors.     

n-3 Fatty acids, cardiac arrhythmia and fatal coronary heart disease

n-3 Polyunsaturated fatty acids (n-3 PUFA) are suggested to prevent cardiac death via inhibition of cardiac arrhythmia. In this review we discuss the results of human studies on intake of n-3 PUFAs and heart disease and, more specifically, on cardiac arrhythmia. Observational studies indicate that intake of fish is associated with a lower incidence of fatal coronary heart disease in several populations. These studies are fairly consistent, but people that have a high intake of fatty fish might have a healthier lifestyle in general, and such confounding is difficult to remove completely with statistical adjustments and corrections. Evidence from trials is less clear. In two open label trials in patients with a previous myocardial infarction intake of fish or fish oil prevented fatal coronary heart disease. In contrast, a trial in patients with angina suggested a higher risk of sudden cardiac death in patients taking fish oil. Furthermore, results of trials in patients with an implantable cardioverter defibrillator (ICD) that investigated effects of fish oil on arrhythmia in patients already suffering from ventricular tachycardia are not consistent. Also, studies on relationships between intake of n-3 PUFA from fish and less life-threatening forms of arrhythmia, such as atrial fibrillation and premature ventricular complexes (PVCs) are equivocal. Thus, after 35 years of research the question whether fish prevents heart disease remains unanswered, and an anti-arrhythmic effect of fish oil remains unproven although the idea is still viable and is being actively tested in further trials.     

Menopausal Hormone Therapy and Chronic Disease Risk in the Women’S Health Initiative: is Timing Everything?

ObjectiveThis review provides a comprehensive overview of the most recent findings from the Women’s Health Initiative (WHI) hormone therapy (HT) trials and highlights the role of age and other clinical risk factors in risk stratification.MethodsWe review the findings on cardiovascular disease, cancer outcomes, all-cause mortality, and other major endpoints in the two WHI HT trials (conjugated equine estrogens [CEEs, 0.625 mg/day] with or without medroxyprogesterone acetate [MPA, 2.5 mg/day]).ResultsThe hazard ratio (HR) for coronary heart disease (CHD) was 1.18 (95% confidence interval [CI], 0.95 to 1.45) in the CEE + MPA trial and 0.94 (95% CI, 0.78 to 1.14) in the CEE-alone trial. In both HT trials, there was an increased risk of stroke and deep vein thrombosis and a lower risk of hip fractures and diabetes. The HT regimens had divergent effects on breast cancer. CEE + MPA increased breast cancer risk (cumulative HR, 1.28; 95% CI, 1.11 to 1.48), whereas CEE alone had a protective effect (cumulative HR, 0.79; 95% CI, 0.65 to 0.97). The absolute risks of HT were low in younger women (ages 50 to 59 years) and those who were within 10 years of menopause onset. Furthermore, for CHD, the risks were elevated for women with metabolic syndrome or high low-densitylipoprotein cholesterol concentrations but not in women without these risk factors. Factor V Leiden genotype was associated with elevated risk of venous thromboembolism on HT.ConclusionHT has a complex pattern of benefits and risks. Women in early menopause have low absolute risks of chronic disease outcomes on HT. Use of HT for management of menopausal symptoms remains appropriate, and risk stratification will help to identify women in whom benefits would be expected to outweigh risks. (Endocr Pract. 2014;20:1201-1213)     

Dairy products and cardiovascular disease

PURPOSE OF REVIEW: Although it has often been postulated that the consumption of dairy products is associated with a high risk of coronary heart disease, study results have been conflicting. This review summarizes recent observational and human intervention trial findings on dairy products and cardiovascular disease. RECENT FINDINGS: Results from more recent observational studies on dairy products and milk disagree. This may be because of the very different methods used combined with several methodological problems. A somewhat surprising beneficial association between the intake of dairy products and the metabolic syndrome was observed in some studies, although not in a single study of elderly women. Milk may have the same cholesterol-raising properties as butter, whereas cheese does not seem to increase plasma cholesterol. Some milk products fermented by specific bacterial strains have been shown to have rather moderate cholesterol-reducing properties. There is also good evidence that certain fermented products (especially by Lactobacillus helveticus) have a mildly decreasing effect on hypertension, probably because of bioactive peptides. SUMMARY: When guiding principles such as balance, variety and moderation are stressed, there is no strong evidence that dairy products increase the risk of coronary heart disease in healthy men of all ages or young and middle-aged healthy women. Human studies should investigate the role of dairy products with respect to sex and age by including classic and novel risk markers of coronary heart disease. Specific fermented milks may be beneficial in the future prevention of hypertension. The beneficially neutral effect of cheese on coronary heart disease risk factors should be elucidated further.     

Estrogen and oxidative stress: A novel mechanism that may increase the risk for cardiovascular disease in women

Although early studies demonstrated that exogenous estrogen lowered a woman's risk of cardiovascular disease, recent trials indicate that HRT actually increases the risk of coronary heart disease or stroke. However, there is no clear explanation for this discrepancy. Is estrogen a helpful or a harmful hormone in terms of cardiovascular function? This review discusses some recent findings that propose a novel mechanism which may shed significant light upon this controversy. We propose that nitric oxide synthase (NOS) expressed within the vascular wall is a target of estrogen action. Under normal conditions in younger women, the primary product of estrogen action is NO, which produces a number of beneficial effects on vascular biology. As a woman ages, however, there is evidence for loss of important molecules essential for NO production (e.g., tetrahydrobiopterin, l-arginine). As these molecules are depleted, NOS becomes increasingly “uncoupled” from NO production, and instead produces superoxide, a dangerous reactive oxygen species. We propose that a similar uncoupling and reversal of estrogen response occurs in diabetes. Therefore, we propose that estrogen is neither “good” nor “bad”, but simply stimulates NOS activity. It is the biochemical environment around NOS that will determine whether estrogen produces a beneficial (NO) or deleterious (superoxide) product, and can account for this dual and opposite nature of estrogen pharmacology. Further, this molecular mechanism is consistent with recent analyses revealing that HRT produces salutary effects in younger women, but mainly increases the risk of cardiovascular dysfunction in older postmenopausal women.     

Estrogens in vascular biology and disease: where do we stand today?

PURPOSE OF REVIEW: Whereas hormone therapy may increase the risk of coronary heart disease and stroke in menopausal women, epidemiological studies (protection in premenopausal women) suggest and experimental studies (prevention of fatty streak development in animals) demonstrate a major atheroprotective action of estradiol. There is also evidence for a thrombogenic effect of oral estrogens. An understanding of the deleterious and beneficial effects of estrogens is thus required. RECENT FINDINGS: The immuno-inflammatory system plays a key role in the development of fatty streak deposit as well as in the rupture of the atherosclerotic plaque. Whereas estradiol favors an anti-inflammatory effect in vitro (cultured cells), it rather elicits a pro-inflammatory response in vivo involving several subpopulations of the immuno-inflammatory system, which could contribute to plaque destabilization. Endothelium is another important target for estrogens, since estradiol potentiates endothelial nitric oxide and prostacyclin production. The respective actions of estrogens on these cell populations may be influenced by the timing of hormonal therapy initiation, hormone regimens, status of the vessel wall and expression of isoforms of estrogen receptors alpha and beta. SUMMARY: A better understanding of the balance between the deleterious and beneficial effects of estrogens is required and should help to improve hormonal therapy safety and to optimize the prevention of cardiovascular disease after menopause.     

Statistical issues arising in the Women's Health Initiative

A brief overview of the design of the Women's Health Initiative (WHI) clinical trial and observational study is provided along with a summary of results from the postmenopausal hormone therapy clinical trial components. Since its inception in 1992, the WHI has encountered a number of statistical issues where further methodology developments are needed. These include measurement error modeling and analysis procedures for dietary and physical activity assessment; clinical trial monitoring methods when treatments may affect multiple clinical outcomes, either beneficially or adversely; study design and analysis procedures for high-dimensional genomic and proteomic data; and failure time data analysis procedures when treatment group hazard ratios are time dependent. This final topic seems important in resolving the discrepancy between WHI clinical trial and observational study results on postmenopausal hormone therapy and cardiovascular disease.     

Gender difference in oxidative stress: a new look at the mechanisms for cardiovascular diseases

Gender differences are present in many diseases and are especially prevalent in cardiovascular disease. Males tend to suffer from myocardial infarctions earlier than females, and a woman's risk of cardiovascular disease increases after menopause, suggesting a cardio‐protective role of estrogen. However, hormone replacement therapy did not decrease the risk of cardiovascular disease in post‐menopausal women; thus, other mechanisms may be involved besides estrogen. Oxidative stress plays an important role in the development of cardiovascular diseases such as coronary artery disease. Gender is also associated with differences in oxidative stress. Under physiological conditions, females appear to be less susceptible to oxidative stress. This may be due to the antioxidant properties of estrogen, gender differences in NADPH‐oxidase activity or other mechanism(s) yet to be defined. This review strives to discuss gender differences in general terms followed by a more detailed examination of gender differences with oxidative stress and various associated diseases and the possible mechanisms underlying these differences.     

Estrogen-induced contraction of coronary arteries is mediated by superoxide generated in vascular smooth muscle

Although previous studies demonstrated beneficial effects of estrogen on cardiovascular function, the Women's Health Initiative has reported an increased incidence of coronary heart disease and stroke in postmenopausal women taking hormone replacement therapy. The objective of the present study was to identify a molecular mechanism whereby estrogen, a vasodilatory hormone, could possibly increase the risk of cardiovascular disease. Isometric contractile force recordings were performed on endothelium-denuded porcine coronary arteries, whereas molecular and fluorescence studies identified estrogen signaling molecules in coronary smooth muscle. Estrogen (1-1,000 nM) relaxed arteries in an endothelium-independent fashion; however, when arteries were pretreated with agents to uncouple nitric oxide (NO) production from NO synthase (NOS), estrogen contracted coronary arteries with an EC(50) of 7.3 +/- 4 nM. Estrogen-induced contraction was attenuated by reducing superoxide (O(2)(-)). Estrogen-stimulated O(2)(-) production was detected in NOS-uncoupled coronary myocytes. Interestingly, only the type 1 neuronal NOS isoform (nNOS) was detected in myocytes, making this protein a likely target mediating both estrogen-induced relaxation and contraction of endothelium-denuded coronary arteries. Estrogen-induced contraction was completely inhibited by 1 muM nifedipine or 10 muM indomethacin, indicating involvement of dihydropyridine-sensitive calcium channels and contractile prostaglandins. We propose that a single molecular mechanism can mediate the dual and opposite effect of estrogen on coronary arteries: by stimulating type 1 nNOS in coronary arteries, estrogen produces either vasodilation via NO or vasoconstriction via O(2)(-).