Activation of estrogen receptor induces differential proteomic responses mainly involving migration, invasion, and tumor development pathways in human testicular embryonal carcinoma NT2/D1 cells.

The aims of the present study were to investigate the global changes on proteome of human testicular embryonal carcinoma NT2/D1 cells treated with 17ß-estradiol (E2), and the effects of this hormone on migration, invasion, and colony formation of these cells. A quantitative proteomic analysis identified the presence of 1230 proteins in both E2-treated and control cells. The analysis revealed 75 differentially abundant proteins (DAPs), out of which 43 proteins displayed a higher abundance and, 30 proteins showed a lower abundance in E2-treated NT2/D1 cancer cells. Functional analysis using IPA highlighted some activation processes such as migration, invasion, metastasis, and tumor growth. Interestingly, the treatment with E2 and ERß-selective agonist DPN increased the migration of NT2/D1 cells. On the other hand, ERα-selective agonist PPT did not modify cell migration, indicating that ERß is the upstream receptor involved in this process. The activation of ERß increased the invasion and anchorage­independent growth of NT2/D1 cells more intensely than ERα. ERα and ERß may play overlapping roles on invasion and colony formation of these cells. Further studies are required to clarify the mechanism underlying these effects. The molecular mechanisms revealed by proteomic and functional studies might also guide the development of potential targets for a better understanding of the biology of these cells and novel treatments for non-seminoma in the future.

Molecular regulation of prostate cancer by Galectin-3 and estrogen receptor.

Prostate cancer remains the most prevalent cancer among men worldwide. This cancer is hormone-dependent; therefore, androgen, estrogen, and their receptors play an important role in development and progression of this disease, and in emergence of the castration-resistant prostate cancer (CRPC). Galectins are a family of ß-galactoside-binding proteins which are frequently altered (upregulated or downregulated) in a wide range of tumors, participating in different stages of tumor development and progression, but the molecular mechanisms which regulate its expression are still poorly understood. This review provides an overview of the current and emerging knowledge on Galectin-3 in cancer biology with focus on prostate cancer and the interplay with estrogen receptor (ER) signaling pathways, present in androgen-independent prostate cancer cells. We suggest a molecular mechanism where ER, Galectin-3 and ß-catenin can modulate nuclear transcriptional events, such as, proliferation, migration, invasion, and anchorage-independent growth of androgen-independent prostate cancer cells. Despite a number of achievements in targeted therapy for prostate cancer, CRPC may eventually develop, therefore new effective drug targets need urgently to be found. Further understanding of the role of Galectin-3 and ER in prostate cancer will enhance our understanding of the molecular mechanisms of prostate cancer development and the future treatment of this disease.

Membrane estrogen receptor ERα activation improves tau clearance via autophagy induction in a tauopathy cell model.

Alzheimer's disease (AD) is the most prevalent aging-associated neurodegenerative disease, with a higher incidence in women than men. There is evidence that sex hormone replacement therapy, particularly estrogen, reduces memory loss in menopausal women. Neurofibrillary tangles are associated with tau protein aggregation, a characteristic of AD and other tauopathies. In this sense, autophagy is a promising cellular process to remove these protein aggregates. This study evaluated the autophagy mechanisms involved in neuroprotection induced by 17ß-estradiol (E2) in a Tet-On inducible expression tauopathy cell model (EGFP-tau WT or with the P301L mutation, 0N4R isoform). The results indicated that 17ß-estradiol induces autophagy by activating AMPK in a concentration-dependent manner, independent of mTOR signals. The estrogen receptor α (ERα) agonist, PPT, also induced autophagy, while the ERα antagonist, MPP, substantially attenuated the 17ß-estradiol-mediated autophagy induction. Notably, 17ß-estradiol increased LC3-II levels and phosphorylated and total tau protein clearance in the EGFP-tau WT cell line but not in EGPF-tau P301L. Similar results were observed with E2-BSA, a plasma membrane-impermeable estrogen, suggesting membrane ERα involvement in non-genomic estrogenic pathway activation. Furthermore, 17ß-estradiol-induced autophagy led to EGFP-tau protein clearance. These results demonstrate that modulating autophagy via the estrogenic pathway may represent a new therapeutic target for treating AD.

Activation of estrogen receptor ESR1 and ESR2 induces proliferation of the human testicular embryonal carcinoma NT2/D1 cells.

The aims of the present study were to investigate the expression of the classic estrogen receptors ESR1 and ESR2, the splicing variant ESR1-36 and GPER in human testicular embryonal carcinoma NT2/D1 cells, and the effects of the activation of the ESR1 and ESR2 on cell proliferation. Immunostaining of ESR1, ESR2, and GPER were predominantly found in the nuclei, and less abundant in the cytoplasm. ESR1-36 isoform was predominantly expressed in the perinuclear region and cytoplasm, and some weakly immunostained in the nuclei. In nonstimulated NT2/D1 cells (control), proteins of the cell cycle CCND1, CCND2, CCNE1 and CDKN1B are present. Activation of ESR1 and ESR2 increases, respectively, CCND2 and CCNE1 expression, but not CCND1. Activation of ESR2 also mediates upregulation of the cell cycle inhibitor CDKN1B. This protein co-immunoprecipitated with CCND2. Also, E2 induces an increase in the number and viability of the NT2/D1 cells. These effects are blocked by simultaneous pretreatment with ESR1-and ESR2-selective antagonists, confirming that both estrogen receptors regulate NT2/D1 cell proliferation. In addition, E2 increases SRC phosphorylation, and SRC mediates cell proliferation. Our study provides novel insights into the signatures and molecular mechanisms of estrogen receptor in NT2/D1 cells.

The role of estrogen receptors in rat Sertoli cells at different stages of development.

The aim of the study was to investigate the effects of estrogen receptors (ESR1 and ESR2) on the expression of the proteins involved with proliferation (CCND1) and differentiation (CDKN1B and CTNNB) of Sertoli cells from rat in different stages of development. ESR1-selective agonist PPT, but not ESR2-selective agonist DPN, increased CCND1 expression in Sertoli cells from 5- and 15-day old rats. PPT did not have any effect on CCND1 expression in Sertoli cells from 20- and 30-day-old rats. DPN, but not PPT, increased CDKN1B expression in Sertoli cells from 15-, 20-, 30-day-old rats. DPN did not have any effect on Sertoli cells from 5-day-old rats. 17ß-estradiol (E2) and PPT enhanced the [Methyl-3H] thymidine incorporation in Sertoli cells from 15-day-old rats, whereas the treatment did not have any effect in 20-day-old rats. E2 and DPN, but not PPT, increased non-phosphorylated CTNNB expression in Sertoli cells from 20-day-old rats. This upregulation was blocked by ESR2-selective antagonist PHTPP. The activation of ESR1 and ESR2, respectively, plays a role in the proliferation and differentiation of Sertoli cells in a critical period of testicular development. Furthermore, in Sertoli cells from 20-day-old rats, upregulation of non-phosphorylated CTNNB by E2/ESR2, via c-SRC/ERK1/2 and PI3K/AKT, may play a role in the interaction between Sertoli cells and/or in cell-germ cell adhesion and/or in the stabilization and accumulation of CTNNB in the cytosol. CTNNB could be translocated to the nucleus and modulate the transcriptional activity of specific target genes. The present study reinforces the important role of estrogen in normal testis development.

Ovariectomy and 17ß-estradiol replacement play a role on the expression of Endonuclease-G and phosphorylated cyclic AMP response element-binding (CREB) protein in hippocampus.

The aim of the present study was to investigate the effects of different periods of ovariectomy and 17ß-estradiol (E2) replacement on the expression of Cytochrome C, apoptosis inducing factor (AIF) and Endonuclease-G (Endo-G) in mitochondrial and cytosolic fractions obtained from hippocampus of the adult female rats. In addition, the expression of phosphorylated CREB (phospho-CREB) was also analyzed in hippocampus. Ovariectomy or E2 treatment did not change the expression of Cytochrome C and AIF. Ovariectomy (15, 21 and 36 days) decreased the expression of Endo-G in the mitochondrial fractions and increased it in the cytosolic fractions obtained from hippocampus. The treatment with E2 after 15 days of ovariectomy for 7 days or 21 days, and throughout the post-ovariectomy period prevented the effects of ovariectomy on Endo-G expression. Our results suggest that ovariectomy-induced apoptotic cell death in hippocampal tissue could be mediated by Endo-G, but not by AIF, via a caspase-independent apoptotic pathway. Furthermore, ovariectomy decreased the expression of phospho-CREB and the treatment with E2 prevented these effects. In conclusion, E2 may help maintain long-term neuronal viability by regulating the expression of members of the Bcl-2 family. Regulation of Endo-G released from mitochondria, but not of Cytochrome C and AIF, is also involved in the neuroprotective actions of E2. Furthermore, CREB may be involved in the expression of Bcl-2. These data provide new understanding into the mechanisms involved in the neuroprotective role of estrogen.

Intracellular signaling pathways involved in the relaxin-induced proliferation of rat Sertoli cells.

Regulation of Sertoli cell number is a key event to determine normal spermatogenesis. We have previously shown that relaxin and its G-protein coupled receptor RXFP1 are expressed in rat Sertoli cells, and that relaxin stimulates Sertoli cell proliferation. This study examined the mechanisms underlying the mitogenic effect of relaxin in a primary culture of Sertoli cells removed from testes of immature rats. Stimulation with exogenous relaxin increased Sertoli cell number and the expression of the proliferating cell nuclear antigen (PCNA), but did not affect the mRNA level of the differentiation markers cadherins 1 and 2. Relaxin-induced Sertoli cell proliferation was blocked by inhibition of MEK/ERK1/2 or PI3K/AKT pathways, but not by inhibition of PKC or EGFR activity. Relaxin induced a rapid and transient activation of ERK1/2 phosphorylation, which was MEK and SRC-dependent, and involved upstream activation of G(i). AKT activation could be detected 5 min after relaxin stimulation, and was still detected after 24h of stimulation with relaxin. Relaxin-induced AKT phosphorylation was G(i)- but not PKA-dependent, and it was blocked by both PI3K and MEK inhibitors. In conclusion, the mitogenic effect of relaxin in Sertoli cell involves coupling to G(i) and activation of both MEK/ERK1/2 and PI3K/AKT pathways.

In vivo treatments with fulvestrant and anastrozole differentially affect gene expression in the rat efferent ductules.

Estrogen plays a key role in maintaining the morphology and function of the efferent ductules. We previously demonstrated that the antiestrogen fulvestrant markedly affected gene expression in the rat efferent ductules. The mechanism of fulvestrant action to modulate gene expression may involve not only the blockade of ESR1 and ESR2 estrogen receptors, but also the activation of ESR1 and ESR2 when the receptors are tethered to AP-1 or SP1 transcription factors, or the activation of the G protein-coupled estrogen receptor 1. We therefore compared the effects of two strategies to interfere with estrogen action in the rat efferent ductules: treatment with fulvestrant or with the aromatase inhibitor anastrozole. Whereas fulvestrant markedly increased Mmp7 and Spp1, and reduced Nptx1 mRNA levels, no changes were observed with anastrozole. Fulvestrant caused changes in epithelial morphology that were not seen with anastrozole. Fulvestrant shifted MMP7 immunolocalization in the epithelial cells from the supranuclear to the apical region; this effect was less pronounced with anastrozole. In vitro studies of (35)S-methionine incorporation showed that protein release was increased, whereas tissue protein content in the efferent ductules of fulvestrant-treated rats was decreased. Although fulvestrant markedly affected gene expression, no changes were observed on AP-1 and SP1 DNA-binding activity. The blockade of ESRs seems to be the major reason explaining the differences between both treatments. At least some of the effects of fulvestrant appear to result from compensatory mechanisms activated by the dramatic changes caused by ESR1 blockade.

Effects of 17beta-estradiol replacement on the apoptotic effects caused by ovariectomy in the rat hippocampus.

AIMS: The aim of the present study was to investigate the effects of different periods of ovariectomy and 17beta-estradiol replacement on apoptotic cell death and expression of members of the Bcl-2 family in the rat hippocampus. MAIN METHODS: Hippocampi were obtained from rats in proestrus, ovariectomized (15 days, 21 days and 36 days), ovariectomized for 15 days and then treated with 17beta-estradiol for 7 or 21 days, and rats ovariectomized and immediately treated with 17beta-estradiol for 21 days. The expression of Bcl-2 and Bax and the number of apoptotic cells were determined. KEY FINDINGS: Ovariectomy decreased Bcl-2 expression and increased Bax expression and the number of apoptotic cells. Replacement with 17beta-estradiol (21 days) throughout the post-ovariectomy period reduced the number of apoptotic cells to the control levels, and prevented the effects of ovariectomy on Bax expression, but only partially restored the Bcl-2 expression. After 15 days of ovariectomy, the replacement with 17beta-estradiol for 21 days, but not for 7 days, restored the Bcl-2 and Bax expression and the percentage of apoptotic cells to the levels found in the proestrus control. SIGNIFICANCE: The present results show that a physiological concentration of 17beta-estradiol may help maintain long-term neuronal viability by regulating the expression of members of the Bcl-2 family. Even after a period of hormonal deprivation, treatment with 17beta-estradiol is able to restore the expression of Bax and Bcl-2 to control levels, but the duration of the treatment is a key factor to obtain the desired effect. These data provide new understanding into the mechanisms contributing to the neuroprotective action of estrogen.

Effects of 17ß-estradiol on expression of muscarinic acetylcholine receptor subtypes and estrogen receptor alpha in rat hippocampus.

The aim of the present study was to investigate the effects of 17beta-estradiol on expression of muscarinic acetylcholine receptor subtypes (M1 to M5) and estrogen receptor alpha, in the rat hippocampus. Hippocampi were obtained from rats in proestrus, rats ovariectomized for 15 days, rats ovariectomized for 15 days and then treated with 17beta-estradiol for 7 days, and rats ovariectomized and immediately treated with 17beta-estradiol for 21 days. Expression of M1 to M5 was increased in hippocampi of rats ovariectomized for 15 days compared to rats in proestrus. Although this effect was abolished when replacement with 17beta-estradiol started immediately after ovariectomy, the increased expression of M1, M3 and M5 receptor subtypes was unchanged when replacement with 17beta-estradiol started only 15 days after ovariectomy. The expression of estrogen receptor alpha in the hippocampus was also upregulated after ovariectomy when compared to rats in proestrus. This effect was abolished when 17beta-estradiol was replaced immediately after ovariectomy, and slightly reduced when the replacement started 15 days after ovariectomy. The replacement with estrogen also had beneficial effects on cognitive function, as suggested by data obtained in the plus-maze discriminative avoidance task. In conclusion, the present results provide evidence that 17beta-estradiol regulates the expression of muscarinic acetylcholine receptor subtypes and estrogen receptor alpha. The immediate replacement with estrogen seems critical to restore the expression of these receptors after hormonal deprivation. The understanding of the regulation of expression and intracellular signaling of the muscarinic acetylcholine receptor subtype M1 and the estrogen receptor alpha may be helpful to elucidate the mechanisms involved in changes of cognitive function in postmenopausal women and in neurodegenerative diseases.

Locally produced relaxin may affect testis and vas deferens function in rats.

We have previously shown that the rat testis and vas deferens contain high levels of the relaxin receptor, RXFP1. The present study was undertaken to determine the expression of relaxin in these tissues, and the effect of exogenous relaxin on Sertoli cell proliferation and on the mRNA levels of some proteins that may contribute to epithelial secretion and tissue reorganization in the vas deferens. Relaxin mRNA levels in testis and vas deferens were much lower than in the prostate. Sertoli cells seem to be an important source of relaxin mRNA in testis. Relaxin immunoreactivity was detected in the seminiferous epithelium but not in the interstitial compartment. The relaxin precursor was expressed in the vas deferens, and relaxin immunoreactivity was detected in apical cells of the vas deferens. Castration, but not treatment with the anti-estrogen ICI 182,780, dramatically reduced relaxin mRNA levels in the prostate and vas deferens, and this effect was prevented by testosterone. Rxfp1 mRNA levels in the vas deferens and prostate were not affected by castration or treatment with ICI 182,780. Exogenous relaxin increased the incorporation of (3)H-thymidine in cultured Sertoli cells, and treatment of the vas deferens with 100 ng/ml relaxin increased the mRNA levels for the cystic fibrosis chloride channel (cystic fibrosis transmembrane regulator) about three times, and doubled mRNA levels for the inducible form of nitric oxide synthase and metalloproteinase 7. These results suggest that locally produced relaxin acts as an autocrine or paracrine agent in the testis and vas deferens to affect spermatogenesis and seminal fluid composition.

Effects of 17â-estradiol replacement on the apoptotic effects caused by ovariectomy in the rat hippocampus

The aim of the present study was to investigate the effects of different periods of ovariectomy and 17â- estradiol replacement on apoptotic cell death and expression of members of the Bcl-2 family in the rat hippocampus. Hippocampi were obtained from rats in proestrus, ovariectomized (15 days, 21 days and 36 days), ovariectomized for 15 days and then treated with 17â-estradiol for 7 or 21 days, and rats ovariectomized and immediately treated with 17â-estradiol for 21 days. The expression of Bcl-2 and Bax and the number of apoptotic cells were determined. Ovariectomy decreased Bcl-2 expression and increased Bax expression and the number of apoptotic cells. Replacement with 17â-estradiol (21 days) throughout the post-ovariectomy period reduced the number of apoptotic cells to the control levels, and prevented the effects of ovariectomy on Baxexpression, but only partially restored the Bcl-2 expression. After 15 days of ovariectomy, the replacementwith 17â-estradiol for 21 days, but not for 7 days, restored the Bcl-2 and Bax expression and the percentageof apoptotic cells to the levels found in the proestrus control.The present results show that a physiological concentration of 17â-estradiol my help maintainlong-term neuronal viability by regulating the expression of members of the Bcl-2 family. Even after a period of hormonal deprivation, treatment with 17â-estradiol is able to restore the expression of Bax and Bcl-2 to control levels, but the duration of the treatment is a key factor to obtain the desired effect. These dataprovide new understanding into the mechanisms contributing to the neuroprotective action of estrogen.

Estrogen receptors and function in the male reproductive system: [review] / Receptores e função do estrógeno no sistema reprodutor masculino: [revisão]

A substantial advance in our understanding on the estrogen signaling occurred in the last decade. Estrogens interact with two receptors, ESR1 and ESR2, also known as ERα and ERβ, respectively. ESR1 and ESR2 belong to the nuclear receptor family of transcription factors. In addition to the well established transcriptional effects, estrogens can mediate rapid signaling, triggered within seconds or minutes. These rapid effects can be mediated by ESRs or the G protein-coupled estrogen receptor GPER, also known as GPR30. The effects of estrogen on cell proliferation, differentiation and apoptosis are often mediated by growth factors. The understanding of the cross-talk between androgen, estrogen and growth factors signaling pathways is therefore essential to understand the physiopathological mechanisms of estrogen action. In this review we focused on recent discoveries about the nature of the estrogen receptors, and on the signaling and function of estrogen in the male reproductive system.

Durante a última década, ocorreu um avanço substancial no conhecimento da sinalização do estrógeno. Estrógenos interagem com dois receptores, ESR1 e ESR2, também conhecidos como ERα e ERβ, respectivamente. ESR1 e ESR2 pertencem à família de receptores nucleares, que funcionam como fatores de transcrição. Além dos bem estabelecidos efeitos transcricionais, os estrógenos medeiam a sinalização rápida, desencadeada dentro de segundos ou minutos. Esses efeitos rápidos podem ser mediados por ESRs ou pelo receptor de estrógeno acoplado à proteína G, GPER, também conhecido como GPR30. Os efeitos de estrógenos sobre a proliferação celular, diferenciação e apoptose são, muitas vezes, mediados por fatores de crescimento. Portanto, a compreensão da interação entre as vias de sinalização de andrógeno, estrógeno e fatores de crescimento é essencial para entender os mecanismos fisiopatológicos envolvidos na ação estrogênica. Nesta revisão, foram abordadas descobertas recentes sobre a estrutura dos receptores, a sinalização e a função do estrógeno no sistema reprodutor masculino.

Estrogen receptors and function in the male reproductive system.

A substantial advance in our understanding on the estrogen signaling occurred in the last decade. Estrogens interact with two receptors, ESR1 and ESR2, also known as ERalpha and ERbeta, respectively. ESR1 and ESR2 belong to the nuclear receptor family of transcription factors. In addition to the well established transcriptional effects, estrogens can mediate rapid signaling, triggered within seconds or minutes. These rapid effects can be mediated by ESRs or the G protein-coupled estrogen receptor GPER, also known as GPR30. The effects of estrogen on cell proliferation, differentiation and apoptosis are often mediated by growth factors. The understanding of the cross-talk between androgen, estrogen and growth factors signaling pathways is therefore essential to understand the physiopathological mechanisms of estrogen action. In this review we focused on recent discoveries about the nature of the estrogen receptors, and on the signaling and function of estrogen in the male reproductive system.

Effects of the antiestrogen fulvestrant (ICI 182,780) on gene expression of the rat efferent ductules.

The efferent ductules express the highest amount of estrogen receptors ESR1 (ERalpha) and ESR2 (ERbeta) within the male reproductive tract. Treatment of rats with the antiestrogen fulvestrant (ICI 182,780) causes inhibition of fluid reabsorption in the efferent ductules, leading to seminiferous tubule atrophy and infertility. To provide a more comprehensive knowledge about the molecular targets for estrogen in the rat efferent ductules, we investigated the effects of ICI 182,780 treatment on gene expression using a microarray approach. Treatment with ICI 182,780 increased or reduced at least 2-fold the expression of 263 and 98 genes, respectively. Not surprisingly, several genes that encode ion channels and macromolecule transporters were affected. Interestingly, treatment with ICI 182,780 markedly altered the expression of genes related to extracellular matrix organization. Matrix metalloproteinase 7 (Mmp7), osteopontin (Spp1), and neuronal pentraxin 1 (Nptx1) were among the most altered genes in this category. Upregulation of Mmp7 and Spp1 and downregulation of Nptx1 were validated by Northern blot. Increase in Mmp7 expression was further confirmed by immunohistochemistry and probably accounted for the decrease in collagen content observed in the efferent ductules of ICI 182,780-treated animals. Downregulation of Nptx1 probably contributed to the extracellular matrix changes and decreased amyloid deposition in the efferent ductules of ICI 182,780-treated animals. Identification of new molecular targets for estrogen action may help elucidate the regulatory role of this hormone in the male reproductive tract.

Effects of estrogen on intracellular signaling pathways linked to activation of muscarinic acetylcholine receptors and on acetylcholinesterase activity in rat hippocampus.

The aim of the present study was to investigate the effects of estrogen lack and estrogen replacement on the production of total [3H]inositol phosphate ([3H]IP) induced by the activation of muscarinic acetylcholine receptors (mAChRs) and on the mechanisms for inactivation of acetylcholine. Hippocampi were obtained from rats in proestrus (PE), ovariectomized for 15 days (C15), ovariectomized for 15 days and then treated with 17beta-estradiol for 7 days (E7) and ovariectomized and immediately treated with 17beta-estradiol for 21 days (E21). Ovariectomy did not change the basal level of total [3H]IP in the hippocampus. 17beta-Estradiol replacement (E7 and E21) reduced the basal level of total [3H]IP. In all experimental groups, carbachol (CCh) caused a concentration-dependent rise in total [3H]IP. The maximum effect was reached with 10(-4) M CCh. The response to 10(-4) M CCh in the hippocampi from C15 and E7 rats was twofold higher than in hippocampi from PE and E21 animals and was blocked by pirenzepine, but not by methoctramine. Ovariectomy or 17beta-estradiol treatment for 7 days did not change neither the total acetylcholinesterase (AChE) activity nor the relative amount of mono- and dimeric G1/G2 and tetrameric G4 globular forms. Conversely, hormonal treatment for 21 days induced an increase in AChE activity of G1/G2 and G4 forms, indicating that 17beta-estradiol stimulates both synthesis and assembly of AChE molecular forms. The present results suggest that the duration and/or a critical period with regard to the initiation of estrogen therapy are important to regulate the function of mAChRs and AChE activity in female rat hippocampus.

Effects of estrogen on intracellular signaling pathways linked to activation of muscarinic acetylcholine receptors and on acetylcholinesterase activity in rat hippocampus

The aim of the present study was to investigate the effects of estrogen lack and estrogen replacement on the production of total [3H]inositol phosphate ([3H]IP) induced by the activation of muscarinic acetylcholine receptors (mAChRs) and on the mechanisms for inactivation of acetylcholine. Hippocampi were obtained from rats in proestrus (PE), ovariectomized for 15 days (C15), ovariectomized for 15 days and then treated with 17â-estradiol for 7 days (E7) and ovariectomized and immediately treated with 17â-estradiol for 21 days (E21). Ovariectomy did not change the basal level of total [3H]IP in the hippocampus. 17â-Estradiol replacement (E7 and E21) reduced the basal level of total [3H]IP. In all experimental groups, carbachol (CCh) caused a concentration-dependent rise in total [3H]IP. The maximum effect was reached with 10-4 M CCh. The response to 10-4 M CCh in the hippocampi from C15 and E7 rats was twofold higher than in hippocampi from PE and E21 animals and was blocked by pirenzepine, but not by methoctramine. Ovariectomy or 17â-estradiol treatment for 7 days did not change neither the total acetylcholinesterase (AChE) activity nor the relative amount of mono- and dimeric G1/G2 and tetrameric G4 globular forms. Conversely, hormonal treatment for 21 days induced an increase in AChE activity of G1/G2 and G4 forms, indicating that 17â-estradiol stimulates both synthesis and assembly of AChE molecular forms. The present results suggest that the duration and/or a critical period with regard to the initiation of estrogen therapy are important to regulate the function of mAChRs and AChE activity in female rat hippocampus.

Effects of rat sinoaortic denervation on the vagal responsiveness and expression of muscarinic acetylcholine receptors.

We studied heart rate (HR) responses to vagal electrical stimulation (VES) and the expression of muscarinic acetylcholine receptors (mAChRs) in the rat atria 1 day (SADa) and 20 days (SADc) after sinoaortic denervation (SAD). Arterial blood pressure (BP) was recorded in conscious, unrestrained rats and during vagal electrical stimulation of the vagus nerve. In the acute phase, SADa rats had hypertension, tachycardia, and increased blood pressure lability. In the chronic phase, heart rate and blood pressure in SADc rats returned to normal whereas blood pressure lability remained increased. VES produced a frequency-dependent bradycardia that was higher in SADa and SADc groups. Binding experiments with [H] N-methylscopolamine showed that in the chronic phase of SAD mAChRs density (SADc = 412.2 +/- 28.64, SADa = 273.38 +/- 48.37 and CTR = 241.5 +/- 25.35 fmol/mg of protein, P < 0.05) and affinity increased in SADc rats (reduced dissociation constant: SADc = 0.45 +/- 0.05, SADa = 1.01+/-0.26, and CTR = 0.98 +/- 0.12 mM, P < 0.05). Our study provides evidence that vagal hyperresponsiveness coexists with increased sympathetic activity in SADa rats without a concomitant increase in mAChRs density or affinity, suggesting that complex mechanisms might modulate the "accentuated antagonism" observed in the acute SAD phase. However, SADc rats had increased bradycardia to VES, increased affinity, and upregulation of mAChRs in the atria. Our results show that, 20 days after SAD in the rat, functional and cellular adaptations occur in the cardiac parasympathetic efferent pathway that may contribute to other regulatory mechanisms to compensate for cardiovascular changes provoked by baroreceptor arch disruption.