Showing papers by "Bruce S. McEwen published in 2002"

The Neuroendocrinology of Stress and Aging: The Glucocorticoid Cascade Hypothesis

Abstract: Over the past 5 yr, we have examined some of the sharpest edges of the pathology of aging. We have studied the capacity of aged organisms to respond appropriately to stress and the capacity of stre...

Estrogen Actions Throughout the Brain

Abstract: Besides affecting the hypothalamus and other brain areas related to reproduction, ovarian steroids have widespread effects throughout the brain, on serotonin pathways, catecholaminergic neurons, and the basal forebrain cholinergic system as well as the hippocampal formation, a brain region involved in spatial and declarative memory. Thus, ovarian steroids have measurable effects on affective state as well as cognition, with implications for dementia. Two actions are discussed in this review; both appear to involve a combination of genomic and nongenomic actions of ovarian hormones. First, regulation of the serotonergic system appears to be linked to the presence of estrogen- and progestin-sensitive neurons in the midbrain raphe as well as possibly nongenomic actions in brain areas to which serotonin neurons project their axons. Second, ovarian hormones regulate synapse turnover in the CA1 region of the hippocampus during the 4- to 5-day estrous cycle of the female rat. Formation of new excitatory synapses is induced by estradiol and involves N-methyl-D-aspartate (NMDA) receptors, whereas downregulation of these synapses involves intracellular progestin receptors. A new, rapid method of radioimmunocytochemistry has made possible the demonstration of synapse formation by labeling and quantifying the specific synaptic and dendritic molecules involved. Although NMDA receptor activation is required for synapse formation, inhibitory interneurons may play a pivotal role as they express nuclear estrogen receptor-alpha (ERa). It is also likely that estrogens may locally regulate events at the sites of synaptic contact in the excitatory pyramidal neurons where the synapses form. Indeed, recent ultrastructural data reveal extranuclear ERalpha immunoreactivity within select dendritic spines on hippocampal principal cells, axons, axon terminals, and glial processes. In particular, the presence of ER in dendrites is consistent with a model for synapse formation in which filopodia from dendrites grow out to find new synaptic contacts and estrogens regulate local, post-transcriptional events via second messenger systems.

The end of stress as we know it

Abstract: Modern life throws a variety of stressful situations at us. This book aims to show stress in a different light - as a natural bodily reaction to help us through certain situations. Although our bodies produce the "fight or flight" reaction when subjected to stress, it often seems inappropriate - our increased heart and lung rate and the chemicals injected into system by the brain can cause illnesses such as asthma and diabetes. This text invites us to improve our brain-body connections in an approach to healthy living based on science. It aims to encourage us to use our natural abilities to cope with stress, rather than falling victim to it.

Effects of chronic stress on hippocampal long-term potentiation.

Abstract: Chronic stress causes atrophy of the apical dendrites of CA3 pyramidal neurons and deficits in spatial memory. We investigated the effects of chronic stress on hippocampal physiology and long-term potentiation (LTP) in the CA3 and dentate gyrus (DG). Rats were subjected to chronic (21 days, 6 h/day) restraint stress and tested for LTP 48 h following the last stress episode. Control animals were briefly handled each day, similar to the experimental group but without restraint. To eliminate acute stress effects, a second control group of rats was subjected to a single acute (6 h) restraint stress and tested for LTP 48 h later. Field potential recordings were made, under chloropent anesthesia, from the stratum lucidum of CA3, with stimulation of either the mossy fiber or commissural/associational pathways, or in the DG granule-cell layer, with stimulation of the medial perforant pathway. Chronic stress produced a suppression of LTP at 48 h compared to controls in a site-specific manner, namely, significantly lower LTP in the medial perforant input to the DG and also in the commissural/associational input to the CA3, but not in the mossy fiber input to CA3. The animals subjected to acute stress and tested 48 h later did not show a suppression in LTP. High-frequency stimulation (HFS) of the commissural/associational and mossy fiber inputs to CA3 produced epileptic afterdischarges in 56% of acutely stressed animals and in 29% of chronically stressed animals, whereas HFS caused afterdischarges in only 9% of nonstressed controls. No afterdischarges were seen in the medial perforant path input to DG. In order to explore the basis for these changes, we performed paired-pulse inhibition/facilitation (PPI/F) and current-source-density (CSD) analysis in stressed and control animals. For PPI/F, acute stress caused an overall significant enhancement of excitation in the commissural/associational input to CA3 and medial perforant path input to DG. In contrast, chronic stress did not produce significant changes in PPI/F. The CSD analysis revealed significant chronic stress-induced shifts in the current sources and sinks in the apical dendrites and pyramidal cell layers of the CA3 field but not in the DG. These results are consistent with the morphological findings for stress effects upon dendrites of CA3 neurons. Furthermore, they suggest that chronic stress produces changes in the input-output relationship in the hippocampal trisynaptic circuit which could affect information flow through this structure.

Allostasis, homeostats, and the nature of stress.

Abstract: This essay continues discussion of a new formulation of homeostasis that uses the concepts of allostasis and homeostats. The new formulation moves beyond Cannon's concept of "homeostasis," which posits an ideal set of conditions for maintenance of the internal environment. The notion of allostasis recognizes that there is no single ideal set of steady-state conditions in life, and different stressors elicit different patterns of activation of the sympathetic nervous and adrenomedullary hormonal systems. Allostasis reflects active, adaptive processes that maintain apparent steady states, via multiple, interacting effectors regulated by homeostatic comparators--"homeostats." "Allostatic load" refers to the consequences of sustained or repeated activation of mediators of allostasis. From the analogy of a home temperature control system, the temperature can be maintained at any of a variety of levels (allostatic states) by multiple means (effectors), regulated by the thermostat (homeostat). Allostatic load and risks of system breakdown increase when, for example, the front door is left open in the winter. Applying these notions can aid in understanding how acute and chronic stress can exert adverse health consequences via allostatic load.

Estrogen and Aging Affect the Subcellular Distribution of Estrogen Receptor-α in the Hippocampus of Female Rats

Abstract: Estrogen replacement increases both the number of dendritic spines and the density of axospinous synapses in the hippocampal CA1 region in young rats, yet this is attenuated in aged rats. The estrogen receptor-α (ER-α) is localized within select spines of CA1 pyramidal cells in young animals and thus may be involved locally in this process. The present study investigated the effects of estrogen on the ultrastructural distribution of ER-α in the CA1 of young (3–4 months) and aged (22–23 months) Sprague Dawley rats using postembedding immunogold electron microscopy. Within dendritic spines, most ER-α immunoreactivity (IR) was seen in plasmalemmal and cytoplasmic regions of spine heads, with a smaller proportion within 60 nm of the postsynaptic density. In presynaptic terminals, ER-α-IR was clustered and often associated with synaptic vesicles. Significant effects of both aging and estrogen were observed. Quantitative analysis revealed that nonsynaptic pools of ER-α-IR within the presynaptic and postsynaptic compartments were decreased (35 and 27%, respectively) in the young estrogen-replaced animals compared with those that received vehicle. Such localized regulation of ER-α in response to circulating estrogen levels might directly affect synaptic signaling in CA1 pyramidal cells. No estrogen treatment-related differences were observed in the aged animals. However, 50% fewer spines contained ER-α in the aged compared with young hippocampus. These data suggest that the decreased responsiveness of hippocampal synapses to estrogen in aged animals may result from age-related decrements in ER-α levels and its subcellular localization vis-a-vis the synapse. Such a role for spinous ER-α has important implications for age-related attenuation of estrogen-induced hippocampal plasticity.

Sexually dimorphic expression of estrogen receptor β in the anteroventral periventricular nucleus of the rat preoptic area: Implication in luteinizing hormone surge

Abstract: Striking sex difference was detected in the expression of estrogen receptor (ER) β mRNA and protein by nonisotopic in situ hybridization and immunohistochemistry in the anteroventral periventricular nucleus (AVPV) of the rat preoptic area. In females more than in males, a significantly larger number of ERβ mRNA-positive cells were visualized in the medial-most portion of the AVPV within 50 μm from the ependymal lining of the third ventricle. Rats of 7, 14, 21, 35, and 60 days of age (d 1 = day of birth) showed the sex difference. Orchidectomy of male neonates or estrogen treatment of female pups reversed the brain phenotype when examined on d 14. In the AVPV of adult females, ERα immunoreactivity colocalized in 83% of ERβ mRNA-positive cells. Tyrosine hydroxylase immunoreactivity colocalized in 18% of ERβ immunoreactive cells in d 21 females. Infusion of an ERβ antisense oligonucleotide into the third ventricle in the vicinity of the AVPV resulted in significantly longer days of successive estrus and a 50% reduction in the number of ERβ-immunoreactive cells in the AVPV. These findings provide support for the hypothesis that activation of ERβ in the AVPV is an important regulatory event in the female-typical induction of luteinizing hormone surge by estrogen.

Protective and damaging effects of stress mediators: the good and bad sides of the response to stress.

Abstract: TRESS IS A CONDITION of human existence and a factor in the expression of disease. A broader view of stress is that it is not just the dramatic stressful events that exact their toll but rather the many events of daily life that elevate activities of physiological systems so as to cause some measure of wear and tear. This wear and tear is called “allostatic load,” and it reflects the impact not only of life experiences that are stressful, but also of genetic constitution; individual habits reflecting items such as diet, exercise, and substance abuse; and developmental experiences that set life-long patterns of behavior and physiological reactivity. 1 Thus, lifestyle is as important a factor in allostatic load as are the experiences that we classify as stressful, and the effects of allostatic load on body shape, size and function are often gradual and almost imperceptible as they develop over months and years. In many cases, the physiological and behavioral aspects of lifestyle and stress interact with each other, such as when we grab a bag of potato chips or smoke a cigarette while experiencing psychological stress due to an important event or deadline. Allostasis, a term coined by Sterling and Eyer 2 means literally “achieving stability, ie, homeostasis, through change.” It reflects the active process of coping physiologically and behaviorally with challenges to the individual. Hormones associated with allostasis and allostatic load protect the body in the shortrun and promote adaptation, but in the long run allostatic load causes changes in the body that lead to disease. These hormones include the so-called “stress hormones” of the adrenal medulla and adrenal cortex, the catecholamines, and glucocorticoids. However, many other cellular mediators in tissues, such as excitatory amino acid neurotransmitters, as well as other circulating hormones, show similar patterns of promoting short-term adaptation but promoting pathophysiology if they are overproduced or not properly regulated. This general principle can be illustrated for the immune system and brain. Acute stress actually enhances the ability of the immune system to respond to pathogens and it does so by facilitating the “trafficking” of immune cells to tissue where they are needed. Adrenal steroids and catecholamines act as mediators of this trafficking, in addition to their role in enhancing the delayed-type hypersensitivity (DTH) response.3-5 In

Regulation of Neurotransmitter Release by Synapsin III

Abstract: Synapsin III is the most recently identified member of the synapsin family, a group of synaptic vesicle proteins that play essential roles in neurotransmitter release and neurite outgrowth. Here, through the generation and analysis of synapsin III knock-out mice, we demonstrate that synapsin III regulates neurotransmitter release in a manner that is distinct from that of synapsin I or synapsin II. In mice lacking synapsin III, the size of the recycling pool of synaptic vesicles was increased, and synaptic depression was reduced. The number of vesicles that fuse per action potential was similar between synapsin III knock-out and wild-type mice, and there was no change in the quantal content of EPSCs; however, IPSCs were greatly reduced in synapsin III-deficient neurons. The density and distribution of synaptic vesicles in presynaptic terminals did not appear to be different in synapsin III knock-out mice in comparison to wild-type littermates. In addition to the changes in neurotransmitter release, we observed a specific delay in axon outgrowth in cultured hippocampal neurons from synapsin III knock-out mice. Our data indicate that synapsin III plays unique roles both in early axon outgrowth and in the regulation of synaptic vesicle trafficking.

Trends of Reproductive Hormones in Male Rats During Psychosocial Stress: Role of Glucocorticoid Metabolism in Behavioral Dominance

Abstract: Stress in socially subordinate male rats, associated with aggressive attacks by dominant males, was studied in a group-housing context called the visible burrow system (VBS). It has been established that subordinate males have reduced serum testosterone (T) and higher corticosterone (CORT) relative to dominant and singly housed control males. The relationship of the decreased circulating T levels in subordinate males to changes in serum LH concentrations has not been evaluated previously. Since decreases in LH during stress may cause reductions in Leydig cell steroidogenic activity, the present study defined the temporal profiles of serum LH, T, and CORT in dominant and subordinate males on Days 4, 7, and 14 of a 14-day housing period in the VBS. The same parameters were followed in serum samples from single-housed control males. Leydig cells express glucocorticoid receptors and may also be targeted for direct inhibition of steroidogenesis by glucocorticoid. We hypothesize that Leydig cells are protected from inhibition by CORT at basal concentrations through oxidative inactivation of glucocorticoid by 11β-hydroxysteroid dehydrogenase (11βHSD). However, Leydig cell steroidogenesis is inhibited when 11βHSD metabolizing capacity is exceeded. Therefore, 11βHSD enzyme activity levels were measured in Leydig cells of VBS-housed males at the same time points. Significant increases in LH and T relative to control were observed in the dominant animals on Day 4, which were associated with the overt establishment of behavioral dominance as evidenced by victorious agonistic encounters. Serum LH and T were lower in subordinate males on Day 7, but T alone was lower on Day 14, suggesting that lowered LH secretion in subordinates may gradually be reversed by declines in androgen-negative feedback. Serum CORT levels were higher in subordinate males compared to control at all three time points. In contrast, oxidative 11βHSD activity in Leydig cells of dominant males was higher relative to control and unchanged in subordinates. These results suggest the following: 1) failure of Leydig cells of subordinate males to compensate for increased glucocorticoid action during stress, by increasing 11βHSD oxidative activity, potentiates stress-mediated reductions in T secretion; and 2) an inhibition of the reproductive axis in subordinate males at the level of the pituitary.

Depression and anxiety symptoms in relation to anthropometry and metabolism in men

Abstract: Depression is associated with an increased risk of developing cardiovascular disease and type 2 diabetes mellitus. Abdominal obesity is also a high risk factor for these diseases. Therefore, symptoms of depression and anxiety were examined in relation to abdominal obesity. A total of 59 middle-aged men volunteered for measurements with the Hamilton Depression Scale (HDS), the Montgomery–Asberg Depression Rating Scale (MADRS), the Beck Depression Inventory (BDI) and the Hamilton Anxiety Scale (HAS). These results were examined in relation to body mass index (BMI), waist/hip ratio (WHR) and sagittal abdominal diameter, a measurement of intra-abdominal fat mass, and metabolic variables. Men with WHR>1.0 ( n =26) in comparison with men with normal WHR ( n =33) showed significantly higher sum scores in all the scales used. There were positive correlations between the sum scores of all the depression scales and the WHR or the sagittal abdominal diameter. BMI correlated comparatively weakly only with the HDS. The correlations with the WHR remained when the influence of BMI was eliminated, suggesting that obesity is less involved than centralization of body fat. Insulin and glucose were significantly related to the HDS. Morning cortisol levels were negatively related to the BDI and (borderline) to the MADRS, suggesting perturbations of the regulation of the hypothalamic–pituitary–adrenal axis. We conclude that men with abdominal obesity have symptoms of depression and anxiety.

Peripheral glucose administration stimulates the translocation of GLUT8 glucose transporter to the endoplasmic reticulum in the rat hippocampus.

Abstract: The expression and localization of glucose transporter isoforms play essential roles in the glucoregulatory activities of the hippocampus and ultimately contribute to cognitive status in physiological and pathophysiological settings. The recently identified glucose transporter GLUT8 is uniquely expressed in neuronal cell bodies in the rat hippocampus and therefore may contribute to hippocampal glucoregulatory activities. We show here that GLUT8 has a novel intracellular distribution in hippocampal neurons and is translocated to intracellular membranes following glucose challenge. Immunoblot analysis revealed that GLUT8 is expressed in high-density microsomes (HDM), suggesting that GLUT8 is associated with intracellular organelles under basal conditions. Immunogold electron microscopic analysis confirmed this observation, in that GLUT8 immunogold particles were associated with the rough endoplasmic reticulum (ER) and cytoplasm. Peripheral glucose administration produced a rapid twofold increase in GLUT8 levels in the HDM fraction while decreasing GLUT8 levels in low-density microsomes. Similarly, peripheral glucose administration significantly increased GLUT8 association with the rough ER in the hippocampus. Conversely, under hyperglycemic/insulinopenic conditions, namely, in streptozotocin (STZ) diabetes, hippocampal GLUT8 protein levels were decreased in the HDM fraction. These results demonstrate that GLUT8 undergoes rapid translocation to the rough ER in the rat hippocampus following peripheral glucose administration, trafficking that is impaired in STZ diabetes, suggesting that insulin serves as a stimulus for GLUT8 translocation in hippocampal neurons. Because glucose is liberated from oligosaccharides during N-linked glycosylation events in the rough ER, we propose that GLUT8 may serve to transport glucose out of the rough ER into the cytosol and in this manner contribute to glucose homeostasis in hippocampal neurons.

Diabetes, but not stress, reduces neuronal nitric oxide synthase expression in rat hippocampus: implications for hippocampal synaptic plasticity

Abstract: Neuronal nitric oxide synthase (nNOS) plays an important role in synaptic plasticity and learning and memory. Since deficits in long-term potentiation (LTP) and learning are observed in diabetic rats and following stress, we examined the expression of nNOS mRNA and protein in the hippocampus of streptozotocin (STZ) diabetic rats and rats subjected to restraint stress. Stress did not modulate nNOS expression, while nNOS mRNA and protein levels were significantly decreased in the hippocampus of STZ diabetic rats. These results suggest that: (1) decreased expression of nNOS mRNA and protein may contribute to deficits in hippocampal dependent learning and LTP in diabetic rats; and (2) other mechanisms may be involved in stress mediated decreases in hippocampal synaptic plasticity.

Serotonin mediates CA1 spine density but is not crucial for ovarian steroid regulation of synaptic plasticity in the adult rat dorsal hippocampus.

Abstract: The activity of the serotonin (5-hydroxytryptamine, 5-HT) system is sensitive to estradiol and progesterone. During the ovarian cycle, dendritic spines on CA1 pyramidal neurons of the dorsal hippocampus are increased by estradiol and later decreased by progesterone. We sought to determine whether 5-HT is involved in maintaining CA1 spine density and/or in steroid regulation of synaptic plasticity in dorsal hippocampus. Ovariectomized rats were treated (sc) over 10 days with the tryptophan hydroxylase inhibitor parachlorophenylalanine (pCPA) to deplete 5-HT, followed by estradiol benzoate on days 10 and 11. A subset of animals received progesterone on day 12. The day after the last treatment, rats were perfused and brains were processed for Golgi impregnation. Separate groups were processed for radioimmunocytochemistry (RICC) for the spine-associated protein, spinophilin, or high-performance liquid chromatography (HPLC) for monoamine analysis. Golgi and RICC data indicate that CA1 apical spine density was significantly decreased by pCPA (17-20%). Estradiol increased spine density in both saline- and pCPA-treated rats compared to respective controls (30%); however, pCPA animals maintained significantly fewer spines. No differences in spine densities were observed between saline- and pCPA-treated rats given estradiol and progesterone. Depletion of 5-HT by pCPA was confirmed in the CA1 (-90%) and dorsal raphe (-80%) by HPLC analysis. While 5-HT depletion was associated with a 57% decrease in CA1 norepinephrine (NE), there was no difference in dorsal raphe NE. Thus, whereas 5-HT is involved in maintaining spine density in the adult female rat CA1, it is not crucial for steroid-mediated plasticity. 5-HT-regulated spines/synapses may represent distinct populations from those modulated by estradiol and progesterone in dorsal hippocampus.

Effects of adrenal steroids on basal ganglia neuropeptide mRNA and tyrosine hydroxylase radioimmunoreactive levels in the adrenalectomized rat.

Abstract: To investigate the effects of type I (mineralocorticoid) and type II (glucocorticoid) receptor activation on striatal neuropeptide [preproenkephalin (PPE), preprotachykinin (PPT), and preprodynorphin (DYN)] mRNA and midbrain cholecystokinin (CCK) mRNA as well as striatal tyrosine hydroxylase radioimmunoreactivity (TH-RIC) levels, we administered either replacement levels of corticosterone (CORT; 0.5 mg/kg/day, s.c.) or pharmacological levels of deoxycorticosterone acetate (DOCA; a mineralocorticoid steroid with ability to bind to type I and type II receptors; 5 mg/kg, s.c.) to adrenalectomized adult male rats. After 1 week of recovery from adrenalectomy surgery, animals were injected daily with sesame oil or CORT for 1, 3, or 7 days or DOCA for 3 or 7 days and killed 16 h after the last injection. Adrenalectomy resulted in a decrease in all three striatal neuropeptide mRNA levels, compared with sham-operated rats. CORT replacement resulted in recovered PPE and PPT mRNA levels after 1 day and elevated PPE mRNA levels over those in sham-operated controls after 3 days. In contrast, DYN mRNA levels showed recovery after 7 days of CORT replacement. Results after DOCA treatment largely paralleled those after CORT replacement. There were no significant treatment effects on indirect markers of midbrain dopaminergic activity, i.e., CCK mRNA and TH-RIC. From these results we conclude that compared with striatal tachykinin and dynorphinergic neurons, enkephalinergic cells show greater sensitivity, whereas the dopaminergic system, including mesencephalic CCK, demonstrates an insensitivity to physiological CORT and to pharmacological DOCA treatment.

Dexamethasone increases adrenalectomy-depressed Na+,K(+)-ATPase mRNA and ouabain binding in spinal cord ventral horn.

Abstract: The Na+,K(+)-ATPase plays a key role in the regulation of ion fluxes and membrane repolarization in the CNS. We have studied glucocorticoid effects on biosynthesis of the Na+,K(+)-ATPase and on ouabain binding in the ventral horn of the spinal cord using intact rats, adrenalectomized (ADX) rats, and ADX rats receiving dexamethasone (ADX+DEX) during 4 days. Cryostat sections from spinal cords were incubated with a 35S-oligonucleotide coding for the alpha 3-subunit or a 3H-cDNA coding for the beta 1-subunit of the Na+,K(+)-ATPase using in situ hybridization techniques. In ventral horn motoneurons, grain density per cell and grain density per area of soma for both probes were slightly reduced in ADX rats but significantly increased in the ADX+DEX group, using ANOVA and the Bonferroni's test. Statistical analysis of frequency histograms of neuronal densities further indicated a significant shift to the right for intact rats compared with ADX rats for both probes. Concomitantly, [3H]ouabain binding to membrane preparations from ventral horns was reduced in ADX rats and restored to normal by DEX administration. No effect of adrenalectomy or DEX treatment was obtained in the dorsal horn. In conclusion, glucocorticoids positively modulate the mRNA for the alpha 3-subunit and the beta 1-subunit of the Na+,K(+)-ATPase and recover ouabain binding to normal values. The increments of the synthesis and activity of an enzyme affecting membrane repolarization and synaptic neurotransmission are consistent with the alleged stimulatory effect of glucocorticoids on spinal cord function.

Regulation of the Injury-Immune Response in the Central Nervous System: Allostasis and Allostatic Load in Immunity

Abstract: Publisher Summary This chapter reviews the emerging area of research after summarizing the key concepts and describing the systems that are involved. In order to understand the role of injury-immune-healing responses (IIHR) to trauma in the central nervous system (CNS), one must have a clear understanding of the mechanisms underlying regional regulation of IIHR, and the relationship between adaptive responses of the body to challenge and exacerbation of the IIHR that leads to pathophysiology. The central nervous system is not isolated from the immune system. Rather, it should be viewed as a tertiary immune tissue, and the elements of immune-system function in the CNS play an important role in the IIHR, as well as in normal adaptation and plasticity. The neuropeptide CGRP appears to be a particularly potent local-tissue mediator of the IIHR in the central nervous system. Immune-cell trafficking into brain may be one mechanism to respond to damage, and even, perhaps, to normal physiological processes.

Estrogens and the Brain

Abstract: The actions of estrogens in the brain go well beyond the regulation of reproduction and include effects upon mood, cognitive function, motor coordination, pain, and protection of the brain from certain forms of damage. Multiple receptor mechanisms are believed to be involved, including at least two types of intracellular estrogen receptors (ERα and ERβ) and nonnuclear, nongenomic actions of estrogens that may involve a form of the intracellular receptors or other as-yet-unidentified receptor types. Selective estrogen response modulators (SERMs) interact with these many mechanisms of estrogen action in different ways, acting primarily as agonists or antagonists or having no effects in some cases. For this reason, it is difficult to imagine that SERMs or any other substitute for estradiol itself will mimic all of the brain effects of 17-β estradiol itself. Rather, the challenge is to develop therapeutic strategies that emphasize particular beneficial effects of estrogens on the brain, such as neuroprotection, while minimizing the possible antagonism of other estrogen actions that are beneficial.