Estrogen modulates alpha(1)/beta-adrenoceptor- induced signaling and melatonin production in female rat pinealocytes

Estrogenic endocrine disruptors: Molecular mechanisms of action

A comprehensive summary of more than 450 estrogenic chemicals including estrogenic endocrine disruptors is provided here to understand the complex and profound impact of estrogen action. First, estrogenic chemicals are categorized by structure as well as their applications, usage and effects. Second, estrogenic signaling is examined by the molecular mechanism based on the receptors, signaling pathways, crosstalk/bypassing and autocrine/paracrine/homeostatic networks involved in the signaling. Third, evaluation of estrogen action is discussed by focusing on the technologies and protocols of the assays for assessing estrogenicity. Understanding the molecular mechanisms of estrogen action is important to assess the action of endocrine disruptors and will be used for risk management based on pathway-based toxicity testing.

Melatonin in perimenopausal and postmenopausal women: associations with mood, sleep, climacteric symptoms, and quality of life

OBJECTIVE

Melatonin synthesis and secretion are partly modulated by estrogen and progesterone. Changes in melatonin concentrations, possibly related to the menopausal transition, may be associated with climacteric mood, sleep, and vasomotor symptoms. The aims of this study were to compare the serum concentrations of melatonin in perimenopausal and postmenopausal women and to evaluate melatonin's influence on mood, sleep, vasomotor symptoms, and quality of life.

METHODS

We analyzed the data of 17 healthy perimenopausal women (aged 43-51 y) and 18 healthy postmenopausal women (aged 58-71 y) who participated in a prospective study. On study night (9:00 pm-9:00 am), serum melatonin was sampled at 20-minute (9:00 pm-12:00 midnight; 6:00-9:00 am) and 1-hour (12:00 midnight-6:00 am) intervals. Questionnaires were used to assess depression (Beck Depression Inventory), anxiety (State-Trait Anxiety Inventory), insomnia and sleepiness (Basic Nordic Sleep Questionnaire [BNSQ]), subjective sleep quality, vasomotor symptoms, and quality of life (EuroQoL).

RESULTS

Postmenopausal women had lower nighttime serum melatonin concentrations than perimenopausal women. The duration of melatonin secretion tended to be shorter in postmenopause, whereas melatonin peak time did not differ. Mean melatonin concentrations and exposure levels did not correlate with follicle-stimulating hormone level, estradiol level, body mass index, Beck Depression Inventory score, State-Trait Anxiety Inventory score, BNSQ insomnia score, BNSQ sleepiness score, subjective sleep score, climacteric vasomotor score, or quality of life. In perimenopause, the later is the melatonin peak, the higher is the level of anxiety (P = 0.022), and the longer is the melatonin secretion, the better is the quality of life (P < 0.001).

CONCLUSIONS

Longitudinal research is needed to better understand the possible contributory role of menopause in lower melatonin levels.

The effect of hormone therapy on serum melatonin concentrations in premenopausal and postmenopausal women: a randomized, double-blind, placebo-controlled study

OBJECTIVES

Melatonin levels decrease physiologically with age, and possibly with the transition to menopause. The plausible influence of hormone therapy (HT) on melatonin is poorly understood. The aim of this randomized, placebo-controlled, double-blind trial was to investigate the effect of HT administration on serum melatonin concentrations in late premenopausal and postmenopausal women.

STUDY DESIGN

Analyses were carried out among 17 late premenopausal and 18 postmenopausal healthy women who participated in a prospective HT study in Finland. Serum melatonin was sampled at 20-min (21:00-24:00 h; 06:00-09:00 h) and 1-h (24:00-06:00 h) intervals at baseline and after 6 months with HT or placebo.

MAIN OUTCOME MEASURES

Melatonin levels and secretion profile after 6 months of HT compared to placebo.

RESULTS

Mean melatonin levels, mean melatonin exposure level (area under curve, AUC) and mean duration of melatonin secretion did not differ after 6 months with HT vs. placebo, irrespectively of the reproductive state. However, in postmenopausal women the melatonin peak time (acrophase) was delayed by 2.4h (2 h 21 min) on average after 6 months with HT vs. placebo (p<0.05). No interaction between time and group was detected when melatonin level was modelled before or after treatment.

CONCLUSIONS

Administration of HT to postmenopausal women alters melatonin peak time, but not melatonin levels. Further research on larger clinical samples is needed to better understand the effects of HT on melatonin profile.

Sleep, Hormones, and Circadian Rhythms throughout the Menstrual Cycle in Healthy Women and Women with Premenstrual Dysphoric Disorder

A relationship exists between the sleep-wake cycle and hormone secretion, which, in women, is further modulated by the menstrual cycle. This interaction can influence sleep across the menstrual cycle in healthy women and in women with premenstrual dysphoric disorder (PMDD), who experience specific alterations of circadian rhythms during their symptomatic luteal phase along with sleep disturbances during this time. This review will address the variation of sleep at different menstrual phases in healthy and PMDD women, as well as changes in circadian rhythms, with an emphasis on their relationship with female sex hormones. It will conclude with a brief discussion on nonpharmacological treatments of PMDD which use chronotherapeutic methods to realign circadian rhythms as a means of improving sleep and mood in these women.

Expression of melatonin receptor (MT1) and interaction between melatonin and estrogen in endometrial cancer cell line

AIM

To determine the receptor subtypes of melatonin in estrogen receptor-positive endometrial cancer cell line, Ishikawa, and the influence of melatonin on chemosensitivity.

METHODS

To confirm the subtype of melatonin on Ishikawa cells, cells were treated with melatonin alone and with antagonists against melatonin receptor luzindole and 4-phenyl-2-propionamidotetralin (4-P-PDOT). Expression of MT1/MT2 mRNA was analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR). Immunocytochemistry of MT1/MT2 was also performed. The effect of melatonin against expression of MT1, MT2, and ERalpha-receptors mRNA was compared with RT-PCR. To determine whether melatonin enhances the effect of anticancer agents, chemosensitivity test was performed with or without melatonin.

RESULTS

Our study revealed that Ishikawa cells express MT1 by both RT-PCR and immunocytochemistry. In contrast, expression of MT2 mRNA was not found. Furthermore, ERalpha mRNA expression was attenuated at melatonin level of 1 x 10(-9) M. Chemosensitivity test revealed that melatonin enhanced anti-tumor effects of paclitaxel among anticancer drugs tested.

CONCLUSION

Based on the above results, MT1 receptor, but not MT2, is expressed in Ishikawa cells. It was also revealed that the cytostatic effect of melatonin is partly an action mediated by MT1 receptor, and attenuation of ERalpha expression was predicted as the mechanism of action. Clinical application of melatonin to biochemotherapy might be also expected.

Estrogen, cognition and female ageing

Starting from fetal life, estrogens are crucial in determining central gender dimorphism, and an estrogen-induced synaptic plasticity is well evident during puberty and seasonal changes as well as during the ovarian cycle. Estrogens act on the central nervous system (CNS) both through genomic mechanisms, modulating synthesis, release and metabolism of neurotransmitters, neuropeptides and neurosteroids, and through non-genomic mechanisms, influencing electrical excitability, synaptic function and morphological features. Therefore, estrogen's neuroactive effects are multifaceted and encompass a system that ranges from the chemical to the biochemical to the genomic mechanisms, protecting against a wide range of neurotoxic insults. Clinical evidences show that, during the climacteric period, estrogen withdrawal in the limbic system gives rise to modifications in mood, behaviour and cognition and that estrogen administration is able to improve mood and cognitive efficiency in post-menopause. Many biological mechanisms support the hypothesis that estrogens might protect against Alzheimer's disease (AD) by influencing neurotransmission, increasing cerebral blood flow, modulating growth proteins associated with axonal elongation and blunting the neurotoxic effects of beta-amyloid. On the contrary, clinical studies of estrogen replacement therapy (ERT) and cognitive function have reported controversial results, indicating a lack of efficacy of estrogens on cognition in post-menopausal women aged >or=65 years. These findings suggest the presence of a critical period for HRT-related neuroprotection and underlie the potential importance of early initiation of therapy for cognitive benefit. In this review, we shall first describe the multiple effects of steroids in the nervous system, which may be significant in the ageing process. A critical update of HRT use in women and a discussion of possible prospectives for steroid use are subsequently proposed.

Estrogens Cross-Talk to α1b-Adrenergic Receptors

beta-Estradiol induced alpha1b-adrenergic receptor desensitization in U373 MG cells stably expressing alpha1b-adrenoceptors, as evidenced by a reduction in the adrenergic-mediated Ca2+ mobilization; desensitization was associated with receptor phosphorylation and internalization. These effects of beta-estradiol were rapid (taking place during 15 min) and were blocked by the estrogen receptor antagonist ICI 182,780 (faslodex). Likewise, inhibitors of phosphoinositide 3-kinase [wortmannin and 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002)] and of protein kinase C [staurosporine, 3-[1-[3-(amidinothio)propyl-1H-indol-3-yl]-3-(1-methyl-1H-indol-3-yl) maleimide (Ro31-8220), and rottlerin] blocked the desensitization and phosphorylation of alpha1b-adrenoceptors induced by estradiol. The formation of a complex was suggested by coimmunoprecipitation assays. The regulatory and catalytic subunits of phosphoinositide 3-kinase (p85 and p110) and protein kinase C delta were associated with alpha1b-adrenoceptors in the absence of stimulus, and such association further increased in a dynamic fashion in response to beta-estradiol. In cells cotransfected with the estrogen receptor alpha and alpha1b-adrenoceptors, beta-estradiol induced phosphorylation, desensitization and internalization of the adrenergic receptors; pretreatment with ICI 182,780 inhibited these effects. Our data support the idea that estrogens modulate alpha1b-adrenergic action through estrogen receptor alpha.

Interactions between melatonin and estrogen may regulate cerebrovascular function in women: clinical implications for the effective use of HRT during menopause and aging

A number of clinical trials associated with the Women's Health Initiative (WHI) have assessed the potential benefits of hormone replacement therapy (HRT) for protection against the development of cardiovascular disease and memory loss in menopausal women. The results of the WHI Memory Study suggest that HRT increases the risk of stroke and dementia in menopausal women. This finding has called into question the results of hundreds of basic science studies that have suggested that estrogen could protect brain cells from damage and improve cognition. A number of researchers have argued that inappropriate formulation, improper dosing, a limited study population, and poor timing of administration likely contributed to the reported findings from the clinical trial. Regarding appropriate formulation, it has been suggested that interactions between estrogen and other hormones should be considered for further investigation. A review of the literature has led us to conclude that a thorough investigation into such hormonal interactions is warranted. We hypothesize that the increased risk of cerebrovascular disease observed in menopausal women may, in part, be due to changes in the circulating levels of melatonin and estrogen and their modulatory affects on many relevant endothelial cell biological activities, such as regulation of vascular tone, adhesion to leukocytes, and angiogenesis, among others. Our hypothesis is supported by numerous studies demonstrating the reciprocal inhibitory effects of melatonin and estrogen on vascular tone, neuroprotection, and receptor expression. We believe that a thorough analysis of the distribution, localization, expression, quantification, and characterization of hormonal receptor subtypes, as well as changes in structural morphology in diseased and normal, healthy cerebrovascular tissue, will substantially aid in our understanding of the effects of HRT on the cerebrovascular circulation. The application of new molecular biological techniques such as tissue microarray analysis, gene and protein arrays, and multi-photon confocal microscopy may be of tremendous benefit in this regard.

Estrogen mediates sex differences in stress-induced prefrontal cortex dysfunction

Many anxiety disorders, as well as major depressive disorder (MDD), are at least twice as prevalent in women as in men, but the neurobiological basis of this discrepancy has not been well studied. MDD is often precipitated by exposure to uncontrollable stress, and is frequently characterized by abnormal or disrupted prefrontal cortex (PFC) function. In animals, exposure to stress has been shown to cause PFC dysfunction, but sex differences in this effect have not been investigated. The present study tested male and female rats on a PFC-dependent working memory task after administration of FG7142, a benzodiazepine inverse agonist that activates stress systems in the brain. Female rats were impaired by lower doses than males during proestrus (high estrogen), but not during estrus (low estrogen). Similarly, ovariectomized females showed increased stress sensitivity only after estrogen replacement. These results suggest that estrogen amplifies the stress response in PFC, which may increase susceptibility to stress-related disorders.

Generation of the melatonin endocrine message in mammals: a review of the complex regulation of melatonin synthesis by norepinephrine, peptides, and other pineal transmitters

Melatonin, the major hormone produced by the pineal gland, displays characteristic daily and seasonal patterns of secretion. These robust and predictable rhythms in circulating melatonin are strong synchronizers for the expression of numerous physiological processes in photoperiodic species. In mammals, the nighttime production of melatonin is mainly driven by the circadian clock, situated in the suprachiasmatic nucleus of the hypothalamus, which controls the release of norepinephrine from the dense pineal sympathetic afferents. The pivotal role of norepinephrine in the nocturnal stimulation of melatonin synthesis has been extensively dissected at the cellular and molecular levels. Besides the noradrenergic input, the presence of numerous other transmitters originating from various sources has been reported in the pineal gland. Many of these are neuropeptides and appear to contribute to the regulation of melatonin synthesis by modulating the effects of norepinephrine on pineal biochemistry. The aim of this review is firstly to update our knowledge of the cellular and molecular events underlying the noradrenergic control of melatonin synthesis; and secondly to gather together early and recent data on the effects of the nonadrenergic transmitters on modulation of melatonin synthesis. This information reveals the variety of inputs that can be integrated by the pineal gland; what elements are crucial to deliver the very precise timing information to the organism. This also clarifies the role of these various inputs in the seasonal variation of melatonin synthesis and their subsequent physiological function.

Pineal melatonin synthesis and release are not altered throughout the estrous cycle in female rats

Melatonin times reproduction with seasons in many photoperiodic mammalian species. Whether sexual hormones reflect on melatonin synthesis is still debated. The aim of this work was to study, using a large panel of technical approaches, whether the daily profile of pineal melatonin synthesis and release varies with the estrous cycle in the female rat. The mRNA levels and enzyme activities of the melatonin synthesizing enzymes, arylalkylamine N-acetyltransferase and hydroxyindole-O-methyltransferase were similar at the four stages of the rat estrous cycle. The endogenous release of melatonin, followed by transpineal microdialysis during six consecutive days in cycling female rats, displayed no significant variation during this interval. Taken together, the present results demonstrate that there is no regular fluctuation in the pineal metabolism leading to melatonin synthesis and release throughout the estrous cycle in female rats.