Progesterone Withdrawal Research Articles

Nuclear Progesterone Receptors in the Human Pregnancy Myometrium: Evidence that Parturition Involves Functional Progesterone Withdrawal Mediated by Increased Expression of Progesterone Receptor-A

We examined whether human parturition involves functional progesterone withdrawal mediated by changes in myometrial expression of progesterone receptors (PRs)-A and -B. Our objectives were to: 1) measure PR-A and PR-B protein levels in human pregnancy myometrium and determine whether the PR-A to PR-B ratio changes with advancing gestation and labor onset; and 2) determine how changes in the PR-A to PR-B ratio affect myometrial cell progesterone responsiveness. PR protein levels and cellular localization were measured by Western blotting and immunohistochemistry, respectively, in lower uterine segment uterine wall tissue from preterm (<37 wk; not laboring; n = 5) and term (37-40 wk; not in labor: n = 6; in labor: n = 5) cesarean delivery. The capacity for PR-A and PR-B, alone and in combination, to mediate genomic progesterone responsiveness measured by the activity of a progesterone-responsive reporter plasmid was examined by artificially modulating their levels in the PHM1-31 myometrial cell line. PR-A and PR-B immunostaining was detected only in the nucleus of myometrial cells. The PR-A to PR-B protein ratio was 0.49 +/- 0.082 (mean +/- sem) in preterm tissue; increased to 1.03 +/- 0.071 (P < 0.001) in nonlaboring term tissue; and increased further to 2.65 +/- 0.344 (P < 0.001) in laboring term tissue. Only PR-B mediated progesterone-induced transcriptional activity. PR-A had no effect alone but markedly decreased PR-B-mediated progesterone responsiveness. Functional progesterone withdrawal in human parturition may be mediated by an increase in the myometrial PR-A to PR-B ratio due to increased PR-A expression.

Quantitative Cellular and Molecular Analysis of the Effect of Progesterone Withdrawal in a Murine Model of Decidualization1

The endometrium is a dynamic tissue that undergoes periodic growth, remodeling and breakdown under the influence of ovarian steroid hormones. To investigate the molecular mechanisms underlying these processes, we used a murine model to mimic the decidualization and regression observed in humans. Ovariectomized mice were treated sequentially with steroid hormones, and subsequently, to induce decidualization, oil was injected into the uterine lumen. The animals were then divided into progesterone-maintained and progesterone-withdrawal groups. In the latter group, a process similar to menstruation was induced. The uterine tissues were collected at several time-points after the induction of decidualization. Histological analysis demonstrated that decidualization and tissue degeneration were successfully induced with similar features to those observed during the human menstrual cycle. Immunohistochemical, morphometric, and microarray-based techniques were used to study the cellular and molecular changes. The volume fractions of leukocytes, macrophages, and neutrophils, but not endothelial cells, increased in decidualized uteri and decreased after major tissue degradation was completed. The microarray data show that the levels of many transcripts that encode immune-related factors changed during the time-course used for this model, and the transcript levels of many of these factors paralleled the changes observed in the volume fractions of the immune cells. The results of the present study suggest that this model is a useful alternative to the use of non-human primates. Our findings also show that immune cells are recruited into the menstruating endometrium, and that immune-related genes are regulated in the uterus throughout menstruation.

Progesterone receptor profile in the decidua and fetal membrane

Whereas in most mammals the onset of labor is preceded by a rapid fall in the maternal progesterone levels, in humans and in higher primates, maternal, fetal and amniotic fluid concentrations of progesterone are sustained before the onset of labor. Therefore, the mechanism for parturition, which has been proposed for humans, is 'functional' progesterone withdrawal. This review is focused on the expression profile, activity and interaction of the progesterone receptor (PR) isoforms in the decidua and the fetal membrane during the initiation of labor. Binding of progesterone to PR induces a significant conformational change on the receptor proteins. These changes result in dimerization, increased receptor phosphorylation and binding of receptor dimers to specific hormone responsive DNA elements in the promoter of target genes. Interaction with specific co-activator proteins and general transcription factors are responsible for the formation of a productive transcription initiation complex. The PR also mediates the activation of cytoplasmic signaling pathways, participating in the induction of signal transduction pathway in the cytoplasm. Balanced expression of the two major progesterone receptors isoforms is crucial for progesterone function as uterine muscle inhibitor. Change in PR isoforms profile seems to be responsible for decidual activation. Decidua without contractions shows consistent profile with PR-B being the dominant isoform. PR-A, PR-C and two additional truncated isoforms are also detected but in significantly smaller concentration. After initiation of contractions, a sharp decline in PR-B shifts the PR-A/PR-B ratio toward PR-A dominance. This shift in the decidua towards increase expression of progesterone receptor isoform A and decrease in PR isoform B is having a pivotal role in decidual activation and initiation of labor.

Effect of Neurosteroid Withdrawal on Spontaneous Recurrent Seizures in a Rat Model of Catamenial Epilepsy

Women with epilepsy often report an increase in seizures at the time of menstruation, a condition referred to as catamenial epilepsy. Perimenstrual seizure exacerbation has long been known to be associated with an abrupt withdrawal of progesterone. The progesterone’s antiseizure effect is due in part to its conversion to the “neurosteroid” allopregnanolone. However, there is no specific animal model of catamenial epilepsy. In this study, we sought to develop a rat model of catamenial seizure exacerbation based on the premise that allopregnanolone withdrawal leads to the exacerbation of spontaneous seizures in epileptic state. Chronic epilepsy was induced in rats by treatment with pilocarpine. Rats were monitored for spontaneous seizures during 2–6 months post pilocarpine. EEG was recorded from hippocampus and cortex. Pilocarpine treatment was associated spontaneous seizures after latency of 60 days post pilocarpine. The average seizure frequency was 15 seizures per week. At 5 months post pilocarpine, majority of rats exhibited bilateral neurodegeneration and a robust aberrant mossy fiber sprouting. To model catamenial seizure exacerbation, epileptic rats were subjected to repeated neurosteroid withdrawal by a pseudopregnancy-finasteride paradigm. Neurosteroid withdrawal showed a tendency of increased seizure frequency, including exacerbation of EEG discharges. Thus, this neurosteroid withdrawal paradigm in epileptic rats may provide a suitable animal model of catamenial seizure exacerbation for use in testing novel agents. ∗∗ Supported by NIH/NINDS grant NS052158 ∗∗

Myometrial Progesterone Responsiveness

Progesterone actions in human pregnancy are controlled by the extent of myometrial progesterone responsiveness. Current progress in unraveling the biochemistry for myometrial progesterone responsiveness at the genomic and nongenomic levels have lead to novel hypotheses regarding the role of these pathways in the hormonal control of human pregnancy and parturition. For the genomic pathway, progesterone interacts with the type-B nuclear progesterone receptor (nPR-B), which decreases expression of contraction-associated genes. For the nongenomic pathway, progesterone interacts with membrane-associated PRs (mPRs) to modulate directly intracellular Ca2+ and cyclic adenosine monophosphate (cAMP) levels. During most of human pregnancy the genomic and nongenomic pathway cooperate to maintain myometrial relaxation. However, at parturition the relaxing actions of progesterone are nullified by changes in myometrial progesterone responsiveness. This occurs by (1) increased expression of the nPR variants (e.g., PR-A and/or PR-C) and changes in nPR coregulator levels that together repress the transcriptional activity of PR-B; and (2) increased expression of specific mPRs, especially mPRss, which augments contractility by decreasing intracellular cAMP. Functional progesterone withdrawal may be induced by locally produced prostaglandins that alter myometrial nPR expression. This may be an important physiological link between the control of parturition and the immune/inflammatory process.

Progesterone increases metabolic rate and progesterone withdrawal enhances epithelial integrity of mammary epithelium

Progesterone receptors (PR) were documented in a bovine mammary epithelial cell line (BME-UV), which allowed us to test the hypothesis that progesterone (PRG) has direct effects on mammary epithelial function. PR were identified in BME-UV cells at the mRNA and protein (Western blot) levels. Thus, BME-UV cells were grown as confluent monolayers in either no added hormones, PRG, prolactin (PRL), and PRG + PRL over a 14 day culture period. Parturition was simulated in vitro by using PRG-free medium for the final day in culture. PRG exposure caused an immediate and substantial increase in glucose utilization that was maintained for at least 10 days of continued PRG exposure. Small effects on transepithelial electrical resistance (Rte) were identified in the presence of these hormones. However, treatment including PRG and PRL for the first 13 days of culture, but lacking PRG for the final 24 hours prior to assay substantially increased Rte. The results demonstrate that PRG exposure is directly associated with an increase in mammary cell metabolism. PRG also ‘primed’ the epithelial cells for a rapid transition to greater Rte when PRG was withdrawn. This suggests that PRG increases metabolic activity of mammary epithelial cells during pregnancy and that the sudden reduction in circulating PRG levels at parturition signals the rapid closure of mammary epithelial tight junctions. [USDA NRI, RRO17686 NCRR NIH Support]

Neutrophil depletion retards endometrial repair in a mouse model

The contribution of the high abundance of inflammatory cells present in the human endometrium prior to and during menstruation is unknown with respect to endometrial repair and/or menstruation. In this study, the presence and localisation of markers for key inflammatory cells have been examined in a mouse model of endometrial breakdown and repair and the functional contribution of neutrophils has been determined. In the model, decidualisation is artificially induced and progesterone support withdrawn; the endometrial tissue progressively breaks down by 24 h after progesterone withdrawal and, by 48 h, has usually undergone complete repair. Neutrophils have been identified in low abundance in decidual tissue, rise in number during breakdown and are most abundant during early repair. Macrophages are barely detectable during breakdown or repair in this model, whereas uterine natural killer cells are found only in intact decidua. The functional contribution of neutrophils to endometrial breakdown and repair has been assessed via neutrophil depletion by using the antibody RB6-8C5. This antibody significantly depletes neutrophils from the circulation and tissue, affects endometrial breakdown and markedly delays endometrial repair. This study has therefore demonstrated that neutrophils are the most abundant leucocyte in this model and that they play an important functional role in the processes of endometrial breakdown and repair.

Membrane progesterone receptor expression in the myometrium at term before and after the onset of labor

Progesterone maintains pregnancy by promoting myometrial quiescence through genomic and non-genomic pathways and labor is initiated by progesterone withdrawal. The role of non-genomic progesterone actions in human pregnancy and parturition are not clearly understood. Non-genomic progesterone actions are mediated by membrane-bound PRs (mPRs): mPRα, mPRβ, mPRγ, and progesterone receptor membrane components -1 and -2 (PGRMC-1 and PGRMC-2). The goal of this study was to measure the extent of mPR expression in the term human myometrium and determine whether levels change in association with the onset of labor.

A critical period of progesterone withdrawal precedes menstruation in macaques.

Macaques are menstruating nonhuman primates that provide important animal models for studies of hormonal regulation in the uterus. In women and macaques the decline of progesterone (P) at the end of the cycle triggers endometrial expression of a variety of matrix metalloproteinase (MMP) enzymes that participate in tissue breakdown and menstrual sloughing. To determine the minimal duration of P withdrawal required to induce menses, we assessed the effects of adding P back at various time points after P withdrawal on both frank bleeding patterns and endometrial MMP expression. Artificial menstrual cycles were induced by treating the animals sequentially with implants releasing estradiol (E2) and progesterone (P). To assess bleeding patterns, P implants were removed at the end of a cycle and then added back at 12, 24, 30, 36, 40, 48, 60, or 72 hours (h) after the initial P withdrawal. Observational analysis of frank bleeding patterns showed that P replacement at 12 and 24 h blocked menses, replacement at 36 h reduced menses but replacement after 36 h failed to block menses. These data indicate that in macaques, a critical period of P withdrawal exists and lasts approximately 36 h. In other similarly cycled animals, we withdrew P and then added P back either during (12–24 h) or after (48 h) the critical period, removed the uterus 24 h after P add back and evaluated endometrial MMP expression. Immunocytochemistry showed that replacement of P during the critical period suppressed MMP-1, -2 and -3 expression along with menses, but replacement of P at 48 h, which failed to suppress mense, suppressed MMP-1 and MMP-3 but did not block MMP-2. We concluded that upregulation of MMPs is essential to menses induction, but that after the critical period, menses will occur even if some MMPs are experimentally blocked.

Progesterone Receptor Repression of Prolactin/Signal Transducer and Activator of Transcription 5-Mediated Transcription of the β-Casein Gene in Mammary Epithelial Cells

Prolactin (PRL) and glucocorticoids act synergistically to stimulate transcription of the beta-casein milk protein gene. Signal transducer and activator of transcription 5 (Stat5) mediates PRL-dependent trans-activation, and glucocorticoid potentiation occurs through cross talk between glucocorticoid receptor (GR) and Stat5 at the beta-casein promoter. In the mouse, progesterone withdrawal leads to terminal differentiation and secretory activation of the mammary gland at parturition, indicating progesterone's role in repressing milk protein gene expression during pregnancy. To investigate the mechanism of the inhibitory action of progesterone, experiments were performed with cell culture systems reconstituted to express progesterone receptor (PR), the PRL receptor/Stat5 signaling pathway, and GR, enabling evaluation of PR, GR, and Stat5 interactions at the beta-casein promoter. With COS-1, normal murine mammary gland, HC-11, and primary mammary epithelial cells, progestin-PR directly repressed the PRL receptor/Stat5a signaling pathway's mediation of PRL-induced beta-casein transcription. Progestin-PR also inhibited glucocorticoid-GR enhancement of PRL induced trans-activation of beta-casein. Inhibition depended on a functional PR DNA binding domain and specific PR-DNA interactions at the beta-casein promoter. Chromatin immunoprecipitation assays in HC-11 cells revealed recruitment of PR and Stat5a to the beta-casein promoter by progestin or PRL, respectively. Recruitment was disrupted by cotreatment with progestin and PRL, suggesting a mutual interference between activated PR and Stat5a. Without PRL, progestin-PR also recruited Stat5a to the beta-casein promoter, suggesting that recruitment of an unactivated form of Stat5a may contribute to inhibition of beta-casein by progesterone. These results define a negative cross talk between PR and Stat5a/GR that may contribute to the physiological role of progesterone to repress lactogenic hormone induction of the beta-casein gene in the mammary gland during pregnancy.

Changes in expression of the δ subunit of the GABAA receptor and in receptor function induced by progesterone exposure and withdrawal

Type A receptors for GABA (GABA(A) receptors) that contain the delta subunit are located predominantly at extrasynaptic sites and are implicated in modulation of neuronal excitability through tonic inhibition. We have examined the effects of chronic exposure to and subsequent withdrawal of progesterone or the progesterone metabolite 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THPROG) on expression of the delta subunit of GABA(A) receptors and on receptor function in cultured rat hippocampal neurons. Progesterone treatment for 1 day increased the amounts of both delta subunit mRNA and protein, whereas such treatment for 6 days induced marked decreases in the abundance of both the mRNA and protein. Subsequent progesterone withdrawal up-regulated expression of the delta subunit, which was significantly increased at 9-12 h after withdrawal. These effects of progesterone were mimicked by 3alpha,5alpha-THPROG and blocked by the 5alpha-reductase inhibitor finasteride. They were also accompanied by parallel changes in the function of GABA(A) receptors in hippocampal neurons. These results show that chronic exposure to and withdrawal of progesterone induce differential effects on both expression of the delta subunit of GABA(A) receptors and receptor function that are mediated by 3alpha,5alpha-THPROG. They are consistent with the notion that this progesterone metabolite plays a key physiological role in modulation of GABAergic synapses.

Tapered progesterone withdrawal promotes long-term recovery following brain trauma

We previously demonstrated that after traumatic brain injury (TBI), acute progesterone withdrawal (AW) causes an increase in anxiety behaviors and cerebro-cellular inflammation compared to tapered progesterone withdrawal (TW). Our current study investigates the behavioral and cellular effects of AW two weeks after termination of treatments to determine the longer-term influence of withdrawal after injury. Adult, male Sprague-Dawley rats received either bilateral frontal cortex contusion (L) or sham (S) surgery. Rats were injected at 1 and 6 h post-injury, then every 24 h for six days. Vehicle (V)-treated rats were given 9 injections of 22.5% cyclodextrin, whereas AW rats received 9 injections of 16 mg/kg progesterone and TW rats received 7 injections of P at 16 mg/kg, followed by one at 8 mg/kg and one at 4 mg/kg. On day 8, sensory neglect and locomotor activity tests were initiated. Animals were killed 22 days post-TBI and the brains prepared for either molecular or histological analysis. Western blotting revealed increased brain-derived neurotrophic factor (BDNF) and heat shock protein 70 (HSP70) in TW vs. AW animals. P53 was increased in VL animals, whereas all progesterone-treated groups were equivalent to shams. TW animals had markedly decreased sensory neglect compared to AW animals and increased center time in locomotor activity assays. In addition, lesion reconstruction revealed a decreased lesion size for TWL over AWL over VL animals. Glial fibrillary acidic protein (GFAP) immunofluorescent staining followed this pattern as well. In conclusion, after TBI, AW affects select behaviors and molecular markers in the chronic recovery period.

Progesterone withdrawal effects in the open field test can be predicted by elevated plus maze performance

Allopregnanolone (3alpha-hydroxy-5alpha-pregnane-20-one) is a ring-A-reduced metabolite of progesterone, which is naturally produced during the luteal phase of the menstrual cycle, during pregnancy and by stressful events. The steroid hormone inhibits neural functions through increased chloride ion flux through the GABAA receptor. The effects and subsequent withdrawal symptoms are similar to those caused by alcohol, benzodiazepines and barbiturates. This study examined the withdrawal effects of progesterone with regards to the influence of individual baseline exploration and risk taking. Rats were tested on the elevated plus maze (EPM) before hormonal treatment, in order to evaluate differences in risk taking and exploration of open and elevated areas. Treatment consisted of ten consecutive once a day progesterone or vehicle s.c. injections. On the last day of treatment, estradiol was injected in addition to progesterone, followed by a 24-h withdrawal before testing in the open field test (OF). Progesterone-treated rats showed a withdrawal effect of open area avoidance in the OF. The vehicle-treated control rats showed strong correlations between the EPM and OF parameters. This relationship was not found for the progesterone group at withdrawal. Rats with greater numbers of open arm entrance in the EPM pretest showed an increased sensitivity to progesterone withdrawal (PWD) compared to rats with low exploration and risk taking. The results indicate that the effects of PWD relate to individual exploration and risk taking. Furthermore, the possible analogy of PWD and PMS/PMDD in relation to individual traits is discussed.

Mifepristone-induced cervical ripening: Structural, biomechanical, and molecular events

The purpose of this study was to assess the structural, biomechanical, and biochemical effects of mifepristone-induced progesterone withdrawal on the rat cervix to identify possible mechanisms by which mifepristone incites cervical ripening. After the administration of mifepristone, cervical tensile strength was determined by the cervical creep method. With polarized light microscopy and transmission electron microscopy, collagen organization and microstructure were quantified. Matrix metalloproteinase expression was assessed by Western Blot and Real-time reverse transcriptase-polymerase chain reaction. Mifepristone induced a decrease in cervical tensile strength at mid gestation that was associated with a decrease in collagen organization. Additionally, mifepristone led to collagen fragmentation with a significant decrease in fibril length and diameter, although fibril bundling remained unaffected. Matrix metalloproteinase-2 expression increased after the administration of mifepristone. Mifepristone-induced cervical ripening is associated with collagen degradation, and the collagenase activity of matrix metalloproteinase-2 may play a role in this process.

Thrombin and Interleukin-1β Regulate HOXA10 Expression in Human Term Decidual Cells: Implications for Preterm Labor

Preterm delivery is commonly caused by intraamniotic infection with expression of proinflammatory cytokines (IL-1beta) or by abruption resulting in generation of decidual thrombin. Although human parturition is not preceded by overt progesterone withdrawal, progesterone resistance likely leads to labor. The uteri of Hoxa10(-/-) mice demonstrate progesterone resistance; several genes, including prostaglandin receptors, are inappropriately regulated in response to progesterone. We hypothesized that IL-1beta or thrombin would decrease HOXA10 expression, contributing to the progestin-resistant environment. We analyzed expression of HOX genes and their regulation by IL-1beta or thrombin in decidual cells. We conducted an in vitro experiment at an academic medical center. Term decidual cells were treated with estradiol (E(2)) or E(2) plus medroxyprogesterone acetate followed by addition of thrombin or IL-1beta. HOX mRNA was evaluated by microarray and confirmed by quantitative RT-PCR. Protein expression was detected using immunohistochemistry and Western analysis. HOXA9, HOXA10, and HOXA11 were expressed in decidual cells and regulated by IL-1beta and thrombin. HOXA10 was further analyzed because of its association with progesterone responsiveness. After E(2) treatment, IL-1beta and thrombin decreased HOXA10 mRNA by 94 and 81%, respectively. After E(2) plus medroxyprogesterone acetate treatment, IL-1beta and thrombin resulted in an 86 and 72% decrease in HOXA10 mRNA, respectively. A similar decrease was noted in HOXA10 protein expression. The expression of HOXA10 protein at term indicates that it may have a role in maintaining decidual cell phenotype and pregnancy. The dramatic decrease of HOXA10 in response to IL-1beta or thrombin may contribute to progestin resistance in preterm labor, mimicking progesterone resistance seen in Hoxa10(-/-) mice.

Progesterone Signaling in Human Myometrium through Two Novel Membrane G Protein-Coupled Receptors: Potential Role in Functional Progesterone Withdrawal at Term

Progestin withdrawal is a crucial event for the onset of labor in many mammalian species. However, in humans the mechanism of a functional progestin withdrawal is unclear, because progestin concentrations do not drop in maternal plasma preceding labor. We report the presence of two novel functional membrane progestin receptors (mPRs), mPRalpha and mPRbeta, in human myometrium that are differentially modulated during labor and by steroids in vitro. The mPRs are coupled to inhibitory G proteins, resulting in a decline in cAMP levels and increased phosphorylation of myosin light chain, both of which facilitate myometrial contraction. Activation of mPRs leads to transactivation of PR-B, the first evidence for cross-talk between membrane and nuclear PRs. Progesterone activation of the mPRs leads also to a decrease of the steroid receptor coactivator 2. Our data indicate the presence of a novel signaling pathway mediated by mPRs that may result in a functional progestin withdrawal, shifting the balance from a quiescent state to one of contraction.

Dickkopf-1, an Inhibitor of Wnt Signaling, Is Regulated by Progesterone in Human Endometrial Stromal Cells

Some members of the Wnt family, including ligands, receptors, inhibitors, and signaling components, are expressed in human endometrium. Dickkopf-1 (Dkk-1), a potent inhibitor of the Wnt signaling pathway, was recently found to be up-regulated in decidualizing endometrial stromal cells during the secretory phase of the menstrual cycle, suggesting regulation by progesterone. To test the hypothesis that progesterone regulates Dkk-1 expression in human endometrial stromal cells, we investigated the following effects on stromal cell expression of Dkk-1 mRNA and protein: decidualizing stimuli (progesterone or cAMP), RU486 (an inhibitor of progesterone action), and withdrawal of progesterone. Short-term treatment (up to 72 h, which corresponds to the full decidualized phenotype in response to cAMP and an early response to progesterone) did not reveal regulation of Dkk-1 mRNA or protein by cAMP but did show induction of Dkk-1 expression when the cells were treated with progesterone, an effect that was blocked by RU486. In long-term cultures (from 14 to 23 d, which corresponds to the full decidualized phenotype in response to progesterone), a significant increase in Dkk-1 mRNA and protein production was observed. Addition of RU486 or withdrawal of progesterone after long-term decidualization resulted in a decrease of Dkk-1 mRNA and protein to control levels. Estradiol alone had no effect on stromal Dkk-1 expression. These data strongly support regulation by progesterone of Dkk-1 mRNA synthesis and protein expression in human endometrial stromal cells and that the response is specific for progesterone and independent of cAMP and estradiol.

Gonadal Steroid Modulation of Stress-Induced Hypothalamo-Pituitary-Adrenal Activity and Anxiety Behavior: Role of Central Oxytocin

Intracerebroventricular administration of oxytocin reduces anxiety behavior and hypothalamo-pituitary-adrenal (HPA) responses to stress in female rats. Similar changes are seen in late-pregnant rats, and oxytocin-sensitive pathways may mediate these effects. This study investigated anxiety behavior and stress responses using a gonadal steroid model of late pregnancy, which is known to increase endogenous oxytocin expression. Compared with continuous progesterone treatment, 3-d withdrawal of progesterone after 11-d treatment of ovariectomized rats with estradiol and progesterone resulted in increased binding of the oxytocin receptor ligand [(125)I]d(CH(2))(5)[Tyr(Me)(2),Thr(4),Tyr-NH(2)(9)]ornithine vasotocin in selective forebrain regions, including the ventrolateral septum and ventromedial hypothalamus. Behavior in the elevated plus-maze indicated that progesterone withdrawal had an anxiolytic effect, and this was associated with lower levels of c-fos mRNA expression in the ventral hippocampus, an area previously shown to be sensitive to oxytocin. In other groups of animals, the plasma corticosterone response to a psychological stress (10 min of 114 dB white noise) was significantly attenuated by this steroid manipulation. Furthermore, simultaneous infusion of the selective oxytocin receptor antagonist desGlyNH(2), d(CH(2))(5)[Tyr(Me)(2),Thr(4)]OVT during the period of progesterone withdrawal reversed this attenuation of noise-induced HPA activation, indicating a role for endogenous oxytocin in this effect. Thus, mimicking the steroid profile of late pregnancy leads to a reduction in anxiety behavior and attenuates HPA activity induced by mild stress. These effects appear to be mediated through the involvement of central oxytocin neurotransmission.

Hypoxia-Inducible Factor-1α Expression in Human Endometrium and Its Regulation by Prostaglandin E-Series Prostanoid Receptor 2 (EP2)

The menstrual cycle is a complex interaction of sex steroids, prostanoids, and cytokines that lead to coordinated tissue degradation, regeneration and repair. The transcription factor hypoxia-inducible factor (HIF-1) plays critical roles in cellular responses to hypoxia, the generation of an inflammatory response and vasculogenesis through transcriptional activation of angiogenic genes. We hypothesize that HIF-1 is expressed in human endometrium and that locally synthesized prostaglandins (PGE2 and PGF(2alpha)) regulate HIF-1 activity. Here we demonstrate that PGE2 up-regulates HIF-1alpha mRNA and protein via the E-series prostanoid receptor 2 (EP2), and this up-regulation is dependent on epidermal growth factor receptor kinase activity. We show the tight temporal-spatial confinement of HIF-1alpha protein expression in endometrium across the cycle. HIF-1alpha is expressed exclusively during the secretory and menstrual phases. Protein expression is maximal at progesterone withdrawal during the late secretory and menstrual phase. HIF-1alpha protein colocalizes with prostaglandin EP2 receptor in glandular cells. In contrast, HIF-1beta/aryl receptor nuclear translocator 1 expression occurs throughout the cycle but is maximal in glandular cells during the proliferative phase. This provides evidence for a role for HIF-1 in the menstrual cycle and demonstrates that HIF-1 activation in human endometrium may occur via a PGE2-regulated pathway and provides a coordinated pathway from progesterone withdrawal through to angiogenic gene expression via HIF-1.

Expression, localization and hormonal control of angiopoietin-1 in the rhesus macaque endometrium: potential role in spiral artery growth

Angiopoietin-1 (Ang-1) is an important angiogenic factor that has not been thoroughly studied in the primate endometrium. We evaluated the endometrial expression of Ang-1 and its receptor, Tie2, during induced menstrual cycles in rhesus macaques. Tie2 expression was confined to the vascular endothelium without marked change during the cycle. However, Ang-1 expression varied considerably during the cycle. In the proliferative phase, Ang-1 was only expressed in the basal zone glands, and this expression was estradiol (E2) dependent. In the early- to mid-secretory phase, Ang-1 expression spread to the upper glands, luminal epithelium and the vascular smooth muscle cells (VSMC) of spiral arteries. In the late secretory phase, the signal disappeared from the glands but remained elevated in the VSMC of spiral arteries. Notably, there was a significant correlation between VSMC proliferation and Ang-1 expression in the VSMC of the spiral arteries. Progesterone (P) withdrawal in the early secretory phase induced a decline in Ang-1 expression in the glands and VSMC of spiral arteries along with a complete suppression of VSMC proliferation. These data suggest, for the first time, that Ang-1 may play a key role in the P-dependent growth of the unique spiral arteries in the primate endometrium.