Evidence that oestradiol attenuates beta-adrenoceptor function in the hypothalamus of female rats by altering receptor phosphorylation and sequestration

Treat more than heat-New therapeutic implications of Cimicifuga racemosa through AMPK-dependent metabolic effects

BACKGROUND

Cimicifuga racemosa extracts (CRE) have obtained a "well-established use status" in the treatment of postmenopausal (i.e., climacteric) complaints, which predominantly include vasomotor symptoms such as hot flushes and sweating, as well as nervousness, irritability, and metabolic changes. Although characteristic postmenopausal complaints are known for a very long time and the beneficial effects of CRE on climacteric symptoms are well accepted, both the pathophysiology of postmenopausal symptoms and the mechanism of action of CREs are not yet fully understood. In particular, current hypotheses suggest that changes in the α-adrenergic and serotonergic signaling pathways secondary to estrogen depletion are responsible for the development of hot flushes.

PURPOSE

Some of the symptoms associated with menopause cannot be explained by these hypotheses. Therefore, we attempted to extend our classic understanding of menopause by integrating of partly age-related metabolic impairments.

METHODS

A comprehensive literature survey was performed using the PubMed database for articles published through September 2021. The following search terms were used: (cimicifuga OR AMPK) AND (hot flush* OR hot flash* OR menopaus* OR osteoporos* OR cancer OR antioxida* OR cardiovasc*). No limits were set with respect to language, and the references cited in the articles retrieved were used to identify additional publications.

RESULTS

We found that menopause is a manifestation of the general aging process, with specific metabolic changes that aggravate menopausal symptoms, which are accelerated by estrogen depletion and associated neurotransmitter dysregulation. Cimicifuga extracts with their metabolic effects mitigate climacteric symptoms but may also modulate the aging process itself. Central to these effects are effects of CRE on the metabolic key regulator, the AMP-activated protein kinase (AMPK).

CONCLUSIONS

As an extension of this effect dimension, other off-label indications may appear attractive in the sense of repurposing of this herbal treatment.

Estradiol regulates responsiveness of the dorsal premammillary nucleus of the hypothalamus and affects fear- and anxiety-like behaviors in female rats

Research suggests a causal link between estrogens and mood. Here, we began by examining the effects of estradiol (E2 ) on rat innate and conditioned defensive behaviors in response to cat odor. Second, we utilized whole-cell patch clamp electrophysiological techniques to assess noradrenergic effects on neurons within the dorsal premammillary nucleus of the hypothalamus (PMd), a nucleus implicated in fear reactivity, and their regulation by E2 . Our results show that E2 increased general arousal and modified innate defensive reactivity to cat odor. When ovariectomized females treated with E2 as opposed to oil were exposed to cat odor, they showed elevations in risk assessment and reductions in freezing, indicating a shift from passive to active coping. In addition, animals previously exposed to cat odor showed clear cue + context conditioning 24 h later. However, although E2 persisted in its effects on general arousal in the conditioning task, its effects on fear disappeared. In the patch clamp experiments noradrenergic compounds that typically induce fear clearly excited PMd neurons, producing depolarizations and action potentials. E2 treatment shifted some excitatory effects of noradrenergic agonists to inhibitory, possibly by differentially affecting α- and β-adrenoreceptors. In summary, our results implicate E2 in general arousal and fear reactivity, and suggest these may be governed by changes in noradrenergic responsivity in the PMd. These effects of E2 may have ethological relevance, serving to promote mate seeking even in contexts of ambiguous threat and shed light on the involvement of estrogen in mood and its associated disorders.

Physiological and nutritional aspects of post-exercise recovery: specific recommendations for female athletes

Gender-based differences in the physiological response to exercise have been studied extensively for the last four decades, and yet the study of post-exercise, gender-specific recovery has only been developing in more recent years. This review of the literature aims to present the current state of knowledge in this field, focusing on some of the most pertinent aspects of physiological recovery in female athletes and how metabolic, thermoregulatory, or inflammation and repair processes may differ from those observed in male athletes. Scientific investigations on the effect of gender on substrate utilization during exercise have yielded conflicting results. Factors contributing to the lack of agreement between studies include differences in subject dietary or training status, exercise intensity or duration, as well as the variations in ovarian hormone concentrations between different menstrual cycle phases in female subjects, as all are known to affect substrate metabolism during sub-maximal exercise. If greater fatty acid mobilization occurs in females during prolonged exercise compared with males, the inverse is observed during the recovery phase. This could explain why, despite mobilizing lipids to a greater extent than males during exercise, females lose less fat mass than their male counterparts over the course of a physical training programme. Where nutritional strategies are concerned, no difference appears between males and females in their capacity to replenish glycogen stores; optimal timing for carbohydrate intake does not differ between genders, and athletes must consume carbohydrates as soon as possible after exercise in order to maximize glycogen store repletion. While lipid intake should be limited in the immediate post-exercise period in order to favour carbohydrate and protein intake, in the scope of the athlete's general diet, lipid intake should be maintained at an adequate level (30%). This is particularly important for females specializing in long-duration events. With protein balance, it has been shown that a negative nitrogen balance is more often observed in female athletes than in male athletes. It is therefore especially important to ensure that this remains the case during periods of caloric restriction, especially when working with female athletes showing a tendency to limit their caloric intake on a daily basis. In the post-exercise period, females display lower thermolytic capacities than males. Therefore, the use of cooling recovery methods following exercise, such as cold water immersion or the use of a cooling vest, appear particularly beneficial for female athletes. In addition, a greater decrease in arterial blood pressure is observed after exercise in females than in males. Given that the return to homeostasis after a brief intense exercise appears linked to maintaining good venous return, it is conceivable that female athletes would find a greater advantage to active recovery modes than males. This article reviews some of the major gender differences in the metabolic, inflammatory and thermoregulatory response to exercise and its subsequent recovery. Particular attention is given to the identification of which recovery strategies may be the most pertinent to the design of training programmes for athletic females, in order to optimize the physiological adaptations sought for improving performance and maintaining health.

Reduction in the latency of action of antidepressants by 17 beta-estradiol in the forced swimming test

RATIONALE

Antidepressants (ADs) are slow to produce their therapeutic effect. This long latency promotes the development of new strategies to short their onset of action. Previous reports indicated that 17beta-estradiol (E(2)) promotes the antidepressant-like activity of fluoxetine (FLX) and desipramine (DMI) in the forced swimming test (FST).

OBJECTIVE

The aim of the present work was to analyze if E(2) reduces the antidepressant-like onset of action of venlafaxine (VLX), FLX, and DMI.

MATERIALS AND METHODS

Independent groups of ovariectomized female Wistar rats were tested in the FST and in the open field after chronic (1 to 14 days) treatment with VLX (20 mg/kg/day), FLX (1.25 mg/kg/day), or DMI (1.25 mg/kg/day) alone or in combination with a single injection of E(2) (2.5 microg/rat sc, 8 h before FST).

RESULTS

VLX, FLX, or DMI by themselves at these doses did not induce changes in the FST at short intervals after their injection (from 1 to 7 days). The addition of E(2) promoted the antidepressant-like effect of VLX and DMI as early as day 1. Such action was also evident after 3, for FLX, and 14 days for both FLX and DMI, but not for VLX. The behavioral actions of these ADs combined with E(2) were not accompanied by increases in general activity in the open-field test.

CONCLUSION

E(2) clearly reduced the latency to the onset of action for these ADs in the FST. These results represent an interesting therapeutic strategy for the treatment of depression in perimenopausal women.

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.

Mepartricin long-term administration regulates steroid hormone and adrenergic receptor concentrations in the prostate of aged rats

Mepartricin is a semi-synthetic macrolide antibiotic developed as a drug for the treatment of benign prostatic hyperplasia (BPH) in human patients. In the present study, aged rats are used as an experimental model to evaluate the effects of mepartricin on circulating hormone concentrations and prostate receptor concentrations, to compare these possible effects with clinical findings observed in long-term treated dogs. Fifty-six aged male rats were randomly divided into four experimental groups treated orally with 0 (group 1), 2 mg (group 2), 5 mg (group 3) and 20 mg (group 4) mepartricin/kg of body weight. for 28 days respectively. Serum oestradiol and testosterone concentrations were measured by radio-immune-assays methods. Binding assays were used to measure the prostate concentrations of oestrogen receptors (ER), androgen receptors (AnR), alpha(1)-adrenergic receptor (alpha(1)-AR), and beta-adrenerergic receptor (beta-AR) subtypes. Mepartricin induced a significant reduction of prostate weight and serum oestradiol concentrations. Serum testosterone concentrations were unaffected. The treatment induced a significant down-regulation of ER concentrations (P < 0.05) and a significant up-regulation of AnR (P < 0.05) in rat prostate. Mepartricin induced a significant (P < 0.05) dose-dependent up-regulation of alpha(1)-AR and beta(2)-AR. In contrast, the concentration of beta(3)-ARs was significantly decreased (P < 0.05) in treated animals. The increase in prostate beta(2)-AR concentrations observed in subjects treated with mepartricin may be a favourable element in the evolution of BPH, because of the role exerted by these receptors in the control of prostatic smooth muscle relaxation. Curiously, beta(3)-AR concentrations were significantly reduced in treated animals. Data collected suggest that the prostatic beta-AR expression might be strongly influenced by oestrogen deprivation (mepartricin treatment); therefore, the combination of oestrogen suppression (mepartricin) and adrenergic suppression (alpha(1)-AR blockers) may be proposed as a possible nonhormonal therapeutic strategy for the treatment of benign prostatic hyperplasia in dogs.

Estrogen controls PKCepsilon-dependent mechanical hyperalgesia through direct action on nociceptive neurons

Protein kinase C epsilon (PKCepsilon) is an important intracellular signaling molecule in primary afferent nociceptors, implicated in acute and chronic inflammatory as well as neuropathic pain. In behavioral experiments inflammatory mediators produce PKCepsilon-dependent hyperalgesia only in male rats. The mechanism underlying this sexual dimorphism is unknown. We show that the hormone environment of female rats changes the nociceptive signaling in the peripheral sensory neuron. This change is maintained in culture also in the absence of a gender-simulating environment. Stimulation of beta(2)-adrenergic receptors (beta(2)-AR) leads to PKCepsilon activation in cultured dorsal root ganglia (DRG) neurons derived from male but not from female rats. Addition of estrogen to male DRG neurons produces a switch to the female phenotype, namely abrogation of beta(2)-AR-initiated activation of PKCepsilon. Estrogen interferes downstream of the beta(2)-AR with the signaling pathway leading from exchange protein activated by cAMP (Epac) to PKCepsilon. The interfering action is fast indicating a transcriptional-independent mechanism. Estrogen has a dual effect on PKCepsilon. If applied before beta(2)-AR or Epac stimulation, estrogen abrogates the activation of PKCepsilon. In contrast, estrogen applied alone leads to a brief translocation of PKCepsilon. Also in vivo the activity of estrogen depends on the stimulation context. In male rats, intradermal injection of an Epac activator or estrogen alone induces mechanical hyperalgesia through a PKCepsilon-dependent mechanism. In contrast, injection of estrogen preceding the activation of Epac completely abrogates the Epac-induced mechanical hyperalgesia. Our results suggest that gender differences in nociception do not reflect the use of generally different mechanisms. Instead, a common set of signaling pathways can be modulated by hormones.

Changes in lymphocyte glucocorticoid and beta-adrenergic receptors in veal calves treated with clenbuterol and steroid hormones for growth-promoting purposes*

In order to identify possible peripheral markers of illegal treatments with growth-promoting agents in veal calves, beta-adrenergic receptor (beta-AR) and glucocorticoid receptor (GR) concentrations were measured in lymphocytes of 12 male Friesian crossbred calves (six controls and six treated). The animals received a cocktail of anabolic and re-partitioning agents [17beta-oestradiol: 3 x 10 mg intramuscular (i.m.) doses at 17-day intervals; dexamethasone sodium phosphate: 4 mg/day for 6 days and 5 mg/day for six further days dissolved in milk; and clenbuterol: 20 microg/kg/day dissolved in milk for the last 40 days before slaughter]. Blood samples were collected by venipuncture at different time points and lymphocytes were isolated by density gradient centrifugation. Lymphocyte beta-AR and GR levels were measured by binding assays. Treatment with re-partitioning agents caused a significant down-regulation of lymphocyte beta-ARs 19 days after the beginning of clenbuterol administration and at day 55 (after dexamethasone withdrawal, just before slaughter). This phenomenon was partially reversed at day 50, after dexamethasone administration, at which time a significant decrease in GR concentrations also occurred. For both types of receptors, no significant changes in the dissociation constant values were observed at any time point. Lymphocytes express measurable concentrations of beta-ARs and GRs and the measurement of receptor levels highlights the fluctuation of receptor expression due to the dynamic interaction of the drugs used in combination. Lymphocyte receptor determination could therefore be included in a battery of biological assays to detect illegal treatments with anabolic agents in veal calves in the light of a multivariate approach.

Estrogen mediated inhibition of dopamine transport in the striatum: regulation by G alpha i/o

In the current study, the interaction between estrogen priming and dopamine D2 receptor activation on dopamine uptake in the striatum of ovariectomized female rats was investigated. Basal ADP-[(32)P(i)]ribosylation of G(i/o) was examined in synaptosomal membranes prepared from ovariectomized, estrogen primed or N-p-(isothiocyanatophenethyl) spiperone (NIPS) treated rats. [(32)P(i)]-incorporation was significantly increased (141%) in tissue from NIPS treated animals but attenuated (57%) in tissue from estrogen primed animals. Dopamine uptake kinetics were measured in vivo following manipulation of the heterotrimeric G-protein by pertussis toxin (0.5 microg, 48 h). Pertussis toxin significantly inhibited dopamine uptake at all concentrations of dopamine examined. Co-treatment with estrogen and pertussis toxin resulted in a further attenuation of dopamine transport at high but not low dopamine concentrations. These data are consistent with an estrogen mediated alteration of G-protein activity and support the hypothesis that estrogen may alter transporter activity through a modulation of dopamine D2 autoreceptor/G alpha(i/o) protein coupling.

Endocrinology of menopausal transition and its brain implications

The central nervous system is one of the main target tissues for sex steroid hormones, which act on both through genomic mechanisms, modulating synthesis, release, and metabolism of many neuropeptides and neurotransmitters, and through non-genomic mechanisms, influencing electrical excitability, synaptic function, morphological features, and neuron-glia interactions. During the climacteric period, sex steroid deficiency causes many neuroendocrine changes. At the hypothalamic level, estrogen withdrawal gives rise to vasomotor symptoms, to eating behavior disorders, and altered blood pressure control. On the other hand, at the limbic level, the changes in serotoninergic, noradrenergic, and opioidergic tones contribute to the modifications in mood, behavior, and nociception. Hormone replacement therapy (HRT) positively affects climateric depression throughout a direct effect on neural activity and on the modulation of adrenergic and serotoninergic tones and may modulate the decrease in cognitive efficiency observed in climaterium. The identification of the brain as a de novo source of neurosteroids, suggests that the modifications in mood and cognitive performances occurring in postmenopausal women may also be related to a change in the levels of neurosteroids. These findings open new perspectives in the study of the effects of sex steroids on the central nervous system and on the possible use of alternative and/or auxiliary HRT.

Mechanisms of ovarian steroid regulation of norepinephrine receptor-mediated signal transduction in the hypothalamus: implications for female reproductive physiology

In many mammalian species, the ovarian steroid hormones estradiol (E(2)) and progesterone (P) act in the hypothalamus and preoptic area to coordinate the timing of female sexual receptivity with ovulation. We study lordosis behavior, an important component of sexual receptivity in rats, and its regulation by E(2) and P as a model system for understanding how hormonal modulation of synaptic neurotransmission influences reproductive physiology and behavior. Our findings suggest that E(2) and P extensively regulate synaptic communication involving the catecholamine norepinephrine (NE) in the hypothalamus. Estrogen priming shifts the balance of postsynaptic NE receptor signaling in the hypothalamus and preoptic area away from beta-adrenergic activation of cAMP synthesis toward alpha(1)-adrenergic signaling pathways. Attenuation of beta-adrenergic signal transduction is achieved by receptor-G-protein uncoupling, apparently due to stable receptor phosphorylation. E(2) modification of alpha(1)-adrenergic signaling includes both increased expression of the alpha(1B)-adrenoceptor subtype and a dramatic, P-induced reconfiguration of the biochemical responses initiated by agonist activation of alpha(1)-adrenoceptors. Among these is the emergence of alpha(1)-adrenergic receptor coupling to cGMP synthesis. We also present evidence that estrogen promotes novel, functional interactions between insulin-like growth factor-1 (IGF-1) and alpha(1)-adrenergic receptor signaling in the hypothalamus and preoptic area. Thus, estrogen amplification of signaling mediated by alpha(1)-adrenoceptors is multifaceted, involving changes in gene expression (of the alpha(1B)-adrenoceptor), switching of receptor linkage to previously inactive intracellular pathways, and the promotion of cross talk between IGF-1 and NE receptors. We propose that this hormone-dependent remodeling of hypothalamic responses to NE maximizes reproductive success by coordinating the timing of the preovulatory release of gonadotropins with the period of behavioral receptivity in female rodents.

Sex hormones regulate the contribution of PKCepsilon and PKA signalling in inflammatory pain in the rat

We have evaluated the contribution of differences in second messenger signalling to sex differences in inflammatory pain and its control by sex hormones. In normal male but not female rats, epinephrine-induced mechanical hyperalgesia was antagonized by inhibitors of protein kinase Cepsilon (PKCepsilon), protein kinase A (PKA) and nitric oxide synthetase (NOS). Similarly, in PKCepsilon knockout mice, a contribution of PKCepsilon to epinephrine-dependent mechanical hyperalgesia occurred in males only. In contrast, hyperalgesia induced by prostaglandin E2, in both females and males, was dependent on PKA and NO. In both sexes, inhibitors of mitogen-activated protein kinase/extracellular-signal related kinase kinase (MEK) inhibited epinephrine hyperalgesia. In gonadectomized females, the second messenger contributions to epinephrine hyperalgesia demonstrated the pattern seen in males. Administration of oestrogen to gonadectomized females fully reconstituted the phenotype of the normal female. These data demonstrate gender differences in PKCepsilon, PKA and NO signalling in epinephrine-induced hyperalgesia which are oestrogen dependent and appear to be exerted at the level of the beta-adrenergic receptor or the G-protein to which it is coupled.