Progesterone receptor-Src kinase signaling pathway mediates neuroprogesterone induction of the luteinizing hormone surge in female rats.

Neural circuits in female rats are exposed to sequential estradiol and progesterone to regulate the release of luteinizing hormone (LH) and ultimately ovulation. Estradiol induces progesterone receptors (PGRs) in anteroventral periventricular nucleus (AVPV) kisspeptin neurons, and as estradiol reaches peak concentrations, neuroprogesterone (neuroP) synthesis is induced in hypothalamic astrocytes. This local neuroP signals to PGRs expressed in kisspeptin neurons to trigger the LH surge. We tested the hypothesis that neuroP-PGR signaling through Src family kinase (Src) underlies the LH surge. As observed in vitro, PGR and Src are co-expressed in AVPV neurons. Estradiol treatment increased the number of PGR immunopositive cells and PGR and Src colocalization. Furthermore, estradiol treatment increased the number of AVPV cells that had extranuclear PGR and Src in close proximity (< 40 nm). Infusion of the Src inhibitor (PP2) into the AVPV region of ovariectomized/adrenalectomized (ovx/adx) rats attenuated the LH surge in trunk blood collected 53 h post-estradiol (50 µg) injection that induced neuroP synthesis. Although PP2 reduced the LH surge in estradiol benzoate treated ovx/adx rats, activation of either AVPV PGR or Src in 2 µg estradiol-primed animals significantly elevated LH concentrations compared to dimethyl sulfoxide infused rats. Finally, antagonism of either AVPV PGR or Src blocked the ability of PGR or Src activation to induce an LH surge in estradiol-primed ovx/adx rats. These results indicate that neuroP, which triggers the LH surge, signals through an extranuclear PGR-Src signaling pathway.

An antiprogestin, CDB4124, blocks progesterone's attenuation of the negative effects of a mild stress on sexual behavior.

These experiments were designed to test the hypothesis that a progesterone receptor antagonist would block progesterone's ability to reduce the negative effects of a 5 min restraint on female rat sexual behavior. Ovariectomized Fischer rats were injected with 10 µg estradiol benzoate. Two days later, rats were injected subcutaneously (sc) with the progesterone receptor antagonist, CDB4124 (17α-acetoxy-21-methoxy-11ß-[4-N,N-dimethyaminopheny]-19-norpregna-4,9-dione-3,20-dione) (60 mg/kg), or vehicle (20% DMSO+propylene glycol). One hour later, rats were injected sc with 500 µg progesterone or vehicle (sesame seed oil). Rats were assigned to one of three different treatment conditions: (1) (ECV) estradiol benzoate, CDB4124, sesame seed oil vehicle, (2) (ECP) estradiol benzoate, CDB4124, progesterone, and (3) (EVP) estradiol benzoate, DMSO/propylene glycol vehicle, progesterone. That afternoon sexual behavior was examined before and after a 5 min restraint experience. Before restraint, lordosis behavior was comparable across treatment conditions but only progesterone-treated rats exhibited proceptive behavior. CDB4124 did not block progesterone's induction of proceptivity. However, after restraint, CDB4124 attenuated the positive effects of progesterone on all sexual behaviors examined. The restraint experience inhibited sexual behavior in rats treated with estradiol benzoate and CDB4124 and in rats treated with estradiol benzoate, CDB4124, and progesterone but not in rats given estradiol benzoate and progesterone without CDB4124. These findings are consistent with the hypothesis that progesterone receptors mediate progesterone's ability to reduce the negative sexual behavioral effects of a mild stressor.

A phase plane graph based model of the ovulatory cycle lacking the "positive feedback" phenomenon.

When hormones during the ovulatory cycle are shown in phase plane graphs, reported FSH and estrogen values form a specific pattern that resembles the leaning "&" symbol, while LH and progesterone (Pg) values form a "boomerang" shape. Graphs in this paper were made using data reported by Stricker et al. [Clin Chem Lab Med 2006;44:883-887]. These patterns were used to construct a simplistic model of the ovulatory cycle without the conventional "positive feedback" phenomenon. The model is based on few well-established relations:hypothalamic GnRH secretion is increased under estrogen exposure during two weeks that start before the ovulatory surge and lasts till lutheolysis.the pituitary GnRH receptors are so prone to downregulation through ligand binding that this must be important for their function.in several estrogen target tissue progesterone receptor (PgR) expression depends on previous estrogen binding to functional estrogen receptors (ER), while Pg binding to the expressed PgRs reduces both ER and PgR expression.Some key features of the presented model are here listed:High GnRH secretion induced by the recovered estrogen exposure starts in the late follicular phase and lasts till lutheolysis. The LH and FSH surges start due to combination of accumulated pituitary GnRH receptors and increased GnRH secretion. The surges quickly end due to partial downregulation of the pituitary GnRH receptors (64% reduction of the follicular phase pituitary GnRH receptors is needed to explain the reported LH drop after the surge). A strong increase in the lutheal Pg blood level, despite modest decline in LH levels, is explained as delayed expression of pituitary PgRs. Postponed pituitary PgRs expression enforces a negative feedback loop between Pg levels and LH secretions not before the mid lutheal phase.Lutheolysis is explained as a consequence of Pg binding to hypothalamic and pituitary PgRs that reduces local ER expression. When hypothalamic sensitivity to estrogen is diminished due to lack of local ERs, hypothalamus switches back to the low GnRH secretion rate, leading to low secretion of gonadotropins and to lutheolysis. During low GnRH secretion rates, previously downregulated pituitary GnRH receptors recover to normal levels and thus allow the next cycle.Possible implications of the presented model on several topics related to reproductive physiology are shortly discussed with some evolutionary aspects including the emergence of menopause.

Comparison of 7α-methyl-19-nortestosterone effectiveness alone or combined with progestins on androgen receptor mediated-transactivation.

7α-methyl-19-nortestosterone (MENT) is an androgen with potent gonadotropin inhibitory activity and prostate-sparing effects. These attributes give MENT advantages over testosterone as a male contraceptive, but, as in the case of testosterone, a partial dose-dependent suppression of spermatogenesis has been observed. Combination of testosterone or MENT with synthetic progestins improves the rate of azoospermia; however, it is unknown whether these combinations affect hormone androgenicity or exert synergistic effects via progestational or androgenic interaction. Herein, using transactivation assays, we examined the ability of MENT alone or combined with several 19-nor-derived synthetic progestins to activate androgen receptor (AR)-dependent gene transcription. In addition, the capability of 7α-methyl-estradiol (7α-methyl-E(2)), an aromatized metabolite of MENT, to transactivate gene transcription via estrogen receptor α (ERα; ESR1) or ERß (ESR2) was also investigated. As expected, MENT induced gene transactivation through either the progesterone receptor (PGR) or the AR. MENT was as efficient as progesterone in activating PGR-mediated reporter gene expression, but it was ten times more potent than testosterone and dihydrotestoterone in activating of AR-driven gene expression. The addition of increasing concentrations of other 19-nortestosterone derivatives (norethisterone or levonorgestrel) did not affect, in a significant manner, the ability of MENT to activate AR-dependent reporter gene transcription. The same results were obtained with different cell lines. 7α-Methyl-E(2) resulted in potent estrogen activity via both ER subtypes with efficiency similar to natural E(2). These results suggest that the addition of 19-nortestosterone-derived progestins, as a hormonal adjuvant in male fertility strategies for effective spermatogenic suppression, does not display any detrimental effect that would interfere with MENT androgenic transcriptional activity.

In vitro characterization of ZK 230211--A type III progesterone receptor antagonist with enhanced antiproliferative properties.

The progesterone receptor (PR) is a key regulator of female reproductive functions. Compounds with progesterone inhibiting effects (PR antagonists) have found numerous utilities in female reproductive health, ranging from contraception to potential treatment of progesterone-dependent diseases like uterine leiomyomas. Based on in vitro characteristics such as DNA binding activity and partial agonistic transcriptional behavior in the presence of protein kinase A activators (cyclic-AMP), three types of PR modulators with antagonistic properties have been defined. In this study, we analyzed the in vitro characteristics of the PR antagonist ZK 230211 in comparison to the classical antagonists onapristone and mifepristone. We focused on PR actions in genomic signaling pathways, including DNA binding activity, nuclear localization and association with the nuclear receptor corepressor (NCoR) as well as actions in non-genomic signaling, such as the activation of c-Src kinase signaling and cyclin D1 gene promoter activity. ZK 230211 represents a type of PR antagonist with increased inhibitory properties in comparison to mifepristone and onapristone. When liganded to the progesterone receptor, ZK 230211 induces a strong and persistent binding to its target response element (PRE) and increases NCoR recruitment in CV-1 cells. Furthermore, ZK 230211 displays less agonistic properties with regard to the association of PR isoform B and the cytoplasmic c-Src kinase in HeLa cells. It represses T47D cell cycle progression, in particular estradiol-induced S phase entry. In summary, our studies demonstrate ZK 230211 to be a type III progesterone receptor antagonist which is characterized by very strong DNA binding activity and strong antiproliferative effects in the cancer cell lines HeLa and T47D.

Neurosteroids are excitatory in supraoptic neurons but inhibitory in the peripheral nervous system: it is all about oxytocin and progesterone receptors.

Neuroactive steroids synthesized from the brain or peripheral sources are called neurosteroids. Beside their common nuclear effects, they are considered to be potent neuromodulators, acting rapidly mainly in a non-genomic manner, either through allosteric regulation of ionic channels, or through membrane-bound steroid receptors. In contrast to the situation in the adult, the neurotransmitter GABA is excitatory during development and plays a trophic role, in particular inducing calcium signals necessary for the regulation of excitability and neuronal maturation. We demonstrated that the primary metabolite of progesterone (Proges), allopregnanolone (Allo), evoked a robust Ca(2+) influx in foetal hypothalamic neurons and in postnatal supraoptic nucleus (SON) neurons. In the latter, this led to oxytocin and arginine vasopressin release. Interestingly, these responses were GABA(A) and oxytocin-receptor-dependent. Allo is a well-known positive allosteric modulator of GABA(A) receptors. It is noteworthy that two other steroids, Proges and 17-beta-estradiol, displayed the same effect on Ca(2+) and oxytocin release but to a lesser extent. Importantly, no effect was observed in adult neurons from the SON, or in neurohypophysial axon terminals, regardless of the stage. The molecular mechanisms of the neurosteroid actions are multifaceted and depend on the type of cells, and are thus extremely interesting and challenging. In the peripheral nervous system, Allo and Proges surprisingly inhibited the GABA-induced Ca(2+) increases in embryonic dorsal root ganglion neurons. We propose that this rapid, reversible and dose-dependent phenomenon (at very low concentrations) was mediated by membrane Proges receptors, since transcripts for a newly discovered receptor protein, 25-Dx, were detected in our model. Recently, novel families of membrane steroid receptors, activating intracellular-signalling pathways such as MAP kinases, have been identified and described. This opens new perspectives to understand the intracellular machinery involved in the interaction between neuropeptides and neurosteroids, two major regulators of hypothalamo-neurohypophysial system development.

Antiproliferative actions of the synthetic androgen, mibolerone, in breast cancer cells are mediated by both androgen and progesterone receptors.

Androgen signaling, mediated by the androgen receptor (AR), is a critical factor influencing growth of normal and malignant breast cells. Given the increasing use of exogenous androgens in women, a better understanding of androgen action in the breast is essential. This study compared the effects of 5alpha-dihydrotestosterone (DHT) and a synthetic androgen, mibolerone, on estradiol (E(2))-induced proliferation of breast cancer cells. DHT modestly inhibited E(2)-induced proliferation and mibolerone significantly inhibited proliferation in T-47D cells. The effects of both androgens could be reversed by an AR antagonist, suggesting that their actions were mediated, in part, by AR. Whereas high physiological doses (10-100nM) of DHT reduced E(2)-mediated induction of the estrogen-regulated gene progesterone receptor (PR) to basal levels, mibolerone at lower doses (1nM) eliminated PR expression, suggesting that mibolerone may also act via the PR. In the AR positive, PR-negative MCF-7 cells, mibolerone had modest effects on E(2)-induced proliferation, but was a potent inhibitor of proliferation in the AR positive, PR positive MCF-7M11 PRA cells. The effects of mibolerone in breast cancer cells were similar to those of the progestin, medroxyprogesterone acetate. Our results demonstrate that mibolerone can have both androgenic and progestagenic actions in breast cancer cells.

Synthesis and function of hypothalamic neuroprogesterone in reproduction.

The physiology and regulation of steroid synthesis in the brain have emerged as important for understanding brain function. Neurosteroids, those steroids synthesized de novo in nervous tissue, have been associated with numerous central nervous system functions, including myelination, mental retardation, and epilepsy. Central regulation of reproduction was thought to depend on steroids of peripheral origin. Only recently has the role of neurosteroids in reproduction been appreciated. This minireview describes our work trying to understand how circulating estradiol modulates the synthesis of neuroprogesterone. The synthesis of neuroprogesterone occurs primarily in astrocytes, and requires the interaction of membrane-associated estrogen receptor with metabotropic glutamate receptor and the release of intracellular calcium stores. The newly synthesized neuroprogesterone acts on estradiol-induced progesterone receptors in nearby neurons to initiate the LH surge.

Hypothalamic progesterone receptor-A mediates gonadotropin surges, self priming and receptivity in estrogen-primed female mice.

Ovarian progesterone (Prog) is an essential steroid hormone for the secretion of GnRH and reproductive behavior. It exerts primary effects through the progesterone receptor (PR). When analyzed separately in vitro, PR isoforms (PR-A, PR-B) display striking differences in transcriptional activity. The present study was undertaken to determine the in vivo impact of each isoform on hypothalamic function in female mice with ablation of a single isoform, either PR-A or PR-B. To this end, we used single-cell RNA analyses, reverse transcriptase real-time (q)PCR mRNA analyses of punched-out tissue, immunohistochemistry, and reproductive behavior. We provide evidence for the requirement of PR-A in individual ventrolateral ventromedial nucleus (vlVMN) neurons for Prog-facilitated proceptive and receptive behaviors in estrogen benzoate (EB)-primed females and the reciprocal male interactions. We clarify histological and molecular mechanisms of PR isoform activity by showing that (1) PR-A is predominant in individual vlVMN neurons controlling female lordosis circuitry, whilst (2) PR-B is predominant in those VMN subdivisions that provide for amplification of PR-A activity. We go on to demonstrate that PR-A is dominant in the anteroventral periventricular nucleus but not the arcuate nucleus that feed fibers into and around the VMN. In the medial preoptic area, high levels of GnRH RNA in EB-primed PR-A-expressing mice were seen coincident with increased plasma LH levels. Two consecutive GnRH pulses enhanced LH only in primed PR-A-expressing females. In all, the findings are consistent with the hypothesis that hypothalamic PR-A-mediated genomic activities result in reproductive behavior coordinated with ovulation.

Cloning and characterization of an ovine intracellular seven transmembrane receptor for progesterone that mediates calcium mobilization.

Classically, progesterone has been thought to act only through the well-known genomic pathway involving hormone binding to nuclear receptors (nPR) and subsequent modulation of gene expression. However, there is increasing evidence for rapid, nongenomic effects of progesterone in a variety of tissues in mammals, and it seems likely that a membrane PR (mPR) is causing these events. The objective of this study was to isolate and characterize an ovine mPR distinct from the nPR. A cDNA clone was isolated from ovine genomic DNA by PCR. The ovine mPR is a 350-amino acid protein that, based on computer hydrophobicity analysis, possesses seven transmembrane domains and is distinct from the nPR. Message for the ovine mPR was detected in hypothalamus, pituitary, uterus, ovary, and corpus luteum by RT-PCR. In CHO cells that overexpressed a mPR-green fluorescent protein fusion protein, the ovine mPR was localized to the endoplasmic reticulum and not the plasma membrane. Specific binding of 3H-progesterone to membrane fractions was demonstrated in CHO cells that expressed the ovine mPR but not in nontransfected cells. Furthermore, progesterone and 17 alpha-hydroxy-progesterone stimulated intracellular Ca2+ mobilization in CHO cells that expressed ovine mPR in Ca2+-free medium (P < 0.05) but not in CHO cells transfected with empty vector. This rise in intracellular Ca2+ is believed to be from the endoplasmic reticulum as intracellular Ca2+ mobilization is absent when mPR transfected cells are first treated with thapsigargin to deplete Ca2+ stores from the endoplasmic reticulum. Isolation, identification, tissue distribution, cellular localization, steroid binding, and a functional response for a unique intracellular mPR in the sheep are presented.

Differential response of progesterone receptor isoforms in hormone-dependent and -independent facilitation of female sexual receptivity.

Neurobehavioral effects of progesterone are mediated primarily by its interaction with neural progesterone receptors (PRs), expressed as PR-A and PR-B protein isoforms. Whereas the expression of two isoforms in the neural tissues is suggestive of their selective cellular responses and modulation of distinct subsets of PR-induced target genes, the role of individual isoforms in brain and behavior is unknown. We have previously demonstrated a critical role for PRs as transcriptional mediators of progesterone (ligand-dependent), and dopamine (ligand-independent)-facilitated female reproductive behavior in female mice lacking both the isoforms of PR. To further elucidate the selective contribution of the individual PR isoforms in female sexual receptive behavior, we used the recently generated PR-A and PR-B isoform-specific null mutant mice. We present evidence for differential responses of each isoform to progesterone and dopamine agonist, SKF 81297 (SKF), and demonstrate a key role for PR-A isoform in both hormone-dependent and -independent facilitation of sexual receptive behavior. Interestingly, whereas both the isoforms were essential for SKF-facilitated sexual behavior, PR-A appeared to play a more important role in the 8-bromo-cAMP-facilitated lordosis response, raising the possibility of distinct intracellular signaling pathways mediating the responses. Finally, we also demonstrate that antiprogestin, RU38486, was an effective inhibitor of PR-A-mediated, progesterone-dependent, but not SKF or 8-bromo-cAMP-dependent sexual receptivity. The data reveal the selective contributions of individual isoforms to the signaling pathways mediating female reproductive behavior.

Diversity of ovarian steroid signaling in the hypothalamus.

It is well known that many of the actions of gonadal steroids in hypothalamic neurons are mediated via intracellular receptor/transcription factors that interact with steroid response elements on target genes. Since the cloning of the intracellular steroid receptors/transcription factors, it has been assumed that most if not all of the actions of the gonadal steroids are mediated via these intracellular receptors. However, there now exist compelling evidence for membrane (G-protein-coupled) steroid receptors for estrogen and progesterone in hypothalamic and other brain neurons. But, it is not well understood how steroids signal via membrane receptors, and how these signals impact not only membrane excitability but also gene transcription in hypothalamic neurons. Indeed, it has been known for sometime that gonadal steroids can rapidly alter hypothalamic neuronal activity within seconds, indicating that some cellular effects can occur via membrane delimited events. In addition, gonadal steroids can affect second messenger systems, including calcium and various kinases to prompt and/or alter cell signaling. Therefore, this chapter will consider our current knowledge of rapid (i.e., seconds to minutes) membrane-initiated and intracellular signaling as well as classical nuclear receptor signaling by gonadal steroids in hypothalamic neurons, the nature of these receptors and how they contribute to homeostatic functions.

Progesterone is an autocrine/paracrine regulator of human granulosa cell survival in vitro.

Ovarian follicles are composed of granulosa cells (GC), which undergo apoptosis within 24 hours of culture in serum-free medium. The present study was designed to assess the role of progesterone in regulating human GC survival. Human GC were isolated from follicular aspirates of women undergoing in vitro fertilization. GC were then cultured for 24 hours in serum-free media supplemented with progesterone and/or the progesterone antagonist RU486 and dexamethasone. Cells were then fixed and assessed for apoptosis by in situ end labeling of DNA fragments, cell cycle analysis of DNA content, and electron microscopy. When compared with controls, progesterone reduced and RU486 increased the percentage of apoptotic GC (p < 0.05), whereas dexamethasone had no effect. In addition, RU486 inhibited the protective effect of progesterone on GC survival (p < 0.05). Taken together, these data indicate that progesterone inhibits human GC apoptosis, and this effect is mediated through the progesterone receptor.

Stimulation of gonadotropin-releasing hormone surges by estrogen. I. Role of hypothalamic progesterone receptors.

Estrogen (E2) stimulates GnRH surges by coupling a daily neural signal to neuronal circuitries governing GnRH release. We have hypothesized that E2 promotes this coupling process by inducing expression of neuronal transcription factors, which are subsequently activated by neurotransmitter-mediated mechanisms representing the daily neural signal. These experiments tested the specific hypothesis that the progesterone receptor (PR) functions in this manner, viz. as an E2-induced factor whose activation is necessary for the stimulation of GnRH surges. Two complimentary experiments were performed to determine whether activation of hypothalamic PRs is obligatory for the stimulation of GnRH surges by E2. In the first, the effects of a PR antagonist on GnRH and LH surges were assessed in ovariectomized (OVX), E2-primed rats. Rats were OVX on diestrous day 2, treated with 30 microg estradiol benzoate or oil vehicle, sc, and then administered either oil vehicle or the type I antiprogestin, ZK98299 at 0900 h on proestrus. GnRH release rates and plasma LH levels were determined in each animal by microdialysis of median eminence and atrial blood sampling, respectively. Estrogen, but not oil vehicle, treatment evoked robust and contemporaneous GnRH and LH surges in animals that received no PR antagonist on proestrus. Additional treatment with ZK98299, however, completely blocked both GnRH and LH surges. In a second experiment, specific involvement of anteroventral periventricular (AVPV) PRs in E2-induced GnRH surges was assessed. Additional groups of OVX, E2-primed rats were fitted with intracerebroventricular cannulas, and PR antisense oligonucleotides were infused into the third ventricle adjacent to the AVPV to prevent expression of PR in this periventricular region. Animals infused with PR antisense oligos did not exhibit any LH surges, whereas surges were observed in saline-, missense-, and sense oligo-treated controls. Immunohistochemistry confirmed the effectiveness of PR antisense oligonucleotides in blocking PR expression. These findings provide direct support for the hypothesis that activation of PRs, specifically those in hypothalamic regions including the AVPV, is an obligatory event in the stimulation of GnRH surges by E2.

[Progesterone receptor isoforms: function and regulation]. / Las isoformas del receptor a progesterona: función y regulación.

Progesterone participates in the regulation of several physiological processes in mammals. The biological response to progesterone is mediated by two forms of the progesterone receptor (PR) denominated PR-A and PR-B. The difference between them is that 164 amino acids of N-terminal of PR-B are absent in PR-A. Both PR isoforms are derived from a single gene but are generated from either alternative transcriptional or translational start sites, and are regulated by different estrogen-induced promoters. PR-B acts as a transcriptional activator in different cellular contexts whereas PR-A functions as a strong inhibitor of transcriptional activity. PR isoforms expression and function vary among target tissues such as the uterus, the mammary gland and the brain. The knowledge of the molecular mechanisms involved in the regulation of expression and function of PR isoforms will contribute to the understanding of fundamental biological processes such as sexual behavior and reproduction, and it will open the possibility of alternative therapies in fertility control as well as in the treatment of breast, endometrial and cerebral tumors.

Ovarian steroid action on tryptophan hydroxylase protein and serotonin compared to localization of ovarian steroid receptors in midbrain of guinea pigs.

The effect of estrogen (E) and progesterone (P) on the protein expression of the rate-limiting enzyme in serotonin synthesis, tryptophan hydroxylase (TPH), and the level of serotonin in the hypothalamic terminal field was examined in guinea pigs. In addition, we questioned whether serotonin neurons of guinea pigs contain ovarian steroid receptors (estrogen receptoralpha[ERalpha], estrogen receptor beta[ERbeta], progestin receptors [PRs]) that could directly mediate the actions of E or P. Western blot and densitometric analysis for TPH were used on raphe extracts from untreated-ovariectomized (OVX), OVX-E-treated (28 d), and OVX-E+P-treated (14 d E+14 d E+P) guinea pigs. The medial basal hypothalami from the same animals were extracted and subjected to high-performance liquid chromatography analysis for serotonin, dopamine, 5-hydroxyindole acetic acid, and homovanillic acid. The brains from other animals treated in an identical manner were perfusion fixed and examined for the colocalization of ERalpha plus serotonin and PR plus serotonin with double immunohistochemistry or for expression of ERbeta mRNA with in situ hybridization. E and E+P treatment significantly increased TPH protein levels compared to the untreated control group (p < 0.05), but TPH levels were similar in the E and E+P-treated groups. By contrast, serotonin (nanogram/milligram of protein) in the hypothalamus was significantly increased by E+P treatment, but not by E alone. Neither ERalpha nor PR proteins were detected within serotonin neurons of the guinea pig raphe nucleus. However, ERbeta mRNA was expressed in the dorsal raphe. In summary, E alone increased TPH protein expression and the addition of P had no further effect, whereas E+P increased hypothalamic serotonin and E alone had no effect. The localization of ERbeta, but not ERalpha or PR, in the dorsal raphe nucleus suggests that E acting via ERbeta within serotonin neurons increases expression of TPH, but that P acting via other neurons and transsynaptic stimulation may effect changes in TPH enzymatic activity, which in turn, would lead to an increase in serotonin synthesis.

Endocrine defects in mice carrying a null mutation for the progesterone receptor gene.

Mice carrying a null mutation of the progesterone receptor gene exhibit several reproductive abnormalities, including anovulation, attenuated lordotic behavior, uterine hyperplasia, and lack of mammary gland development. The hormonal correlates of these abnormalities are unknown, however, and were the focus of these studies. Serum samples from female wild-type (WT) and progesterone receptor knockout (PRKO) mice were obtained and analyzed by RIA for LH, FSH, PRL, estrogen (E2), and progesterone. Hypothalamic tissues were also processed for measurement of LHRH by RIA. Serum LH levels in PRKO mice were found to be elevated by approximately 2-fold over basal (metestrus) values in WT mice. By contrast, basal FSH levels were not different in PRKO and WT mice. Basal levels of E2 and progesterone in serum were likewise similar in the two groups, as were hypothalamic LHRH concentrations. Basal PRL levels were slightly higher in PRKO vs. WT mice. Ovariectomy of both groups of mice was accompanied by significant increases in both LH and FSH. At 5 days following ovariectomy, LH levels were elevated in both groups by 2-fold over PRKO basal and 4-fold over WT basal levels; however, by 10 days postovariectomy LH levels had continued to rise to a greater extent in PRKO mice than in WT animals. The FSH response to ovariectomy was greater for the PRKO mice at 5 days, but was no different from WT at 10 days. Of seven PRKO mice that were exposed to male odor, none exhibited preovulatory surges 3 days later, on the day of presumptive proestrus; this was in marked contrast with WT females, in which 100% exhibited robust LH surges. These results confirm the essential role of progesterone receptors in the regulation of hypothalamic and/or pituitary processes that govern gonadotropin secretion. The finding that basal LH levels are elevated in PRKO mice confirms that circulating progesterone normally conveys a significant portion of the total ovarian negative feedback control of the gonadotropin. That gonadotropin responses to ovariectomy are slightly enhanced in PRKO mice suggests that adrenal progesterone may contribute to the imposition of negative feedback control. The apparent inability of PRKO mice to respond to male odor suggests that anovulation in these mice may not be solely due to reproductive abnormalities within the ovary itself; rather, PRKO mice additionally harbor neuroendocrine defects that render them incapable of mounting normal preovulatory gonadotropin surges. It remains to be determined how the absence of PR in brain and pituitary of PRKO mice may produce this hormonal acyclicity and, conversely, how the presence of PR in brain and pituitary of WT mice may be obligatory in the generation of gonadotropin surges.

Asymmetry in progestin receptor levels and sexual behavior in female rats.

There are reports of hemispheric asymmetry in the control of sexual receptivity by the hypothalamus in the female rat. In the present study, we investigated whether there is an asymmetry in the distribution of progestin receptors in the hypothalamus, and whether the asymmetry in distribution is associated with receptivity as indicated by lordosis quotients. Degree of hemispheric asymmetry in hypothalamic progestin receptor (PR) levels was associated with higher lordosis quotients regardless of the direction of asymmetry. In a second study, as in the first study, degree (and not direction) of asymmetry of PR levels in the hypothalamus was associated with receptive behavior. In addition, the results suggest a possible link between left-biased asymmetry in frontal cortical PR levels and proceptive behavior. These studies are the first evidence of relationships between hemispheric asymmetry in progestin receptor levels and behavior.

La progesterona y sus metabolitos en el funcionamiento del sistema nervioso central / Progesterone and its metabolites the functions of the central nervous system

La progesterona (P4) y sus metabolitos participan en distintas funciones del sistema nervioso central (SNC) entre las que destacan la excitabilidad neuronal, la reproducción, y las conductas asociadas a ésta. P4 y sus metabolitos actúan en las neuronas y en las células gliales a través de su interacción con: 1) receptores intracelulares específicos; 2) sitio de regulación presentes en los receptores a neurotransmisores; y 3) canales iónicos. Por estos mecanismos se inducen cambios en la expresión de genes específicos, la formación de segundos mensajeros y la conductancia iónica. La mayoría de las acciones de los metabolitos de P4 en el SNC, ocurren a nivel membranal, mientras que las de P4 son principalmente a nivel nuclear y están mediadas por la activación de los receptores intracelulares. Así, P4 y sus metabolitos pueden modificar el funcionamiento de distintas regiones del SNC, a corto (milisegundos), mediano (minutos) y largo plazo (horas y días). El conocimiento de los mecanismos moleculares por los cuales P4 y sus metabolitos participaron en el funcionamiento del SNC, permitirá entender procesos biológicos fundamentales como la conducta sexual y la reproducción; además, contribuirá al diseño de terapias alternativas en el tratamiento de diferentes trastornos neurológicos y psiquiátricos como la epilepsia, la ansiedad, el síndrome premenstrual y algunos tumores cerebrales que tienen regulación hormonal

The central oxytocin pulse generator: a pacemaker for luteolysis.

Oxytocin (OT) is released from the neurohypophysis into the jugular vein of sheep in small 1-2 min pulses (ca. 10 pg/ml) in both cyclic and ovariectomized sheep. In intact cycling sheep, additional hour long bursts of OT (up to 200 pg/ml) occur in peripheral blood during luteolysis at intervals of 6 to 9 hrs which appear to regulate large luteolytic pulses of uterine prostaglandin F2a (PGF2a). Since the ovine corpus luteum (CL) also synthesizes OT, experiments were performed to distinguish between the relative contributions of the neurohypophysis and the CL to the large bursts of OT secreted during luteolysis. Two models were used. First, ovariectomized sheep were given exogenous E and/or P by constant infusion to simulate levels during the estrous cycle. Second, in tact cycling sheep, the CL was surgically excised during the luteal phase to exclude the CL as a source of OT and, at the same time, subject the animals to the withdrawal of P. Pulses of OT in jugular vein plasma were determined by RIA or biometry of the uterus. The findings are summarized as follows: In ovariectomized sheep, maintained on low E (0.05 g/hr) to preserve the OT pulse generator, infusion of E (1 microgram, 2 micrograms or 4 micrograms/hr) for 12 to 36 hr, caused a series (4 to 6) of rapid increases in OT pulse frequency each lasting 1 to 2 hrs at intervals of 3 hrs. The time of onset of high frequency pulses was dose-dependent. Withdrawal of 10 day infusions of P (500 micrograms/hr) superimposed on low E (0.05 microgram/hr) also evoked a series of high frequency episodes of OT pulses beginning 24 hrs after P withdrawal. In intact sheep, surgical removal of the CL resulted in a series of high frequency pulses similar in duration and frequency to those following the withdrawal of P in the ovariectomized animal. We conclude that: (1) an increase in E or returning E action causes the OT pulse generator to alter its frequency intermittently thus producing a series of 4 to 6 episodes of high frequency pulses of OT. (2) Similar changes can be evoked by withdrawal of P either by terminating an infusion of P in the presence of E in the ovariectomized sheep or by surgically removing the CL from the ovary in the intact sheep. (3) At the end of the reproductive cycle, the central OT pulse generator appears to act as a pacemaker which, acting on the endometrial OT receptors, triggers a series of pulses of PGF2a from the uterus and hence causes regression of the CL. In the sheep and other ruminants, an intermittent supplemental secretion of OT from the CL, triggered via the central OT pulse generator, may also be required to amplify the luteolytic pulses of PGF2a from the uterus. (4) In addition to the well established interaction of ovarian steroid hormones, and the hypothalamic pituitary system for the initiation of the reproductive cycle via the gonadotrophins, there is now good evidence for an interaction of ovarian steroids and the posterior pituitary for terminating the reproductive cycle.