Myometrial Progesterone responsiveness and the Control of Human Parturition

Obesity in pregnancy: altered onset and progression of labour

BACKGROUND

the incidence of obesity increases in all developed countries to frightful percentages, also in women of reproductive age. Maternal obesity is associated with important obstetrical complications; and this group also exhibits a higher incidence of prolonged pregnancies and labours.

OBJECTIVE

to review the literature on the pathophysiology of onset and progression of labour in obese woman and translate this knowledge into practical recommendations for clinical management.

METHODS

a literature review, in particular a critical summary of research, in order to determine associations, gaps or inconsistencies in this specific but limited body of research.

FINDINGS

the combination of a higher incidence of post-term childbirths and increased inadequate contraction pattern during the first stage of labour suggests an influence of obesity on myometrial activity. A pathophysiologic pathway for altered onset and progression of labour in obese pregnant women is proposed.

CONCLUSIONS

analysis of the literature shows that obesity is associated with an increased duration of pregnancy and prolonged duration of first stage of labour.

IMPLICATIONS FOR PRACTICE

an adapted clinical approach is suggested in these patients.

Outcome of vaginal progesterone as a tocolytic agent: randomized clinical trial

Vaginal progesterone has a potential beneficial effect in postponing of preterm labor by suppression of prostaglandins cascades. Although different studies evaluated the use of progesterone for preterm birth, the exact effect of which on prolongation of pregnancy remains unclear. Seventy two women who underwent preterm labor were managed by magnesium sulfate. Then they were randomly assigned to continue pregnancy either by applying vaginal progesterone (400 mg) until delivery or without using any drug. Gestational age mean at the time of delivery (P = 0.039) and postponing delivery mean time (P = 0.048) were significantly higher in progesterone group. Comparison of neonatal outcomes between two groups of patients showed meaningful benefits of progesterone in increasing of neonatal weight, reduction of low birth weight babies, and lowing neonate admitted in NICU.

An evolutionary test of the isoform switching hypothesis of functional progesterone withdrawal for parturition: humans have a weaker repressive effect of PR-A than mice

BACKGROUND

A decrease in maternal serum progesterone (P4) concentrations precedes the onset of labor in most placental mammals. Humans differ by maintaining high levels of P4 throughout birth. Parturition in humans probably includes mechanisms that undercut the pregnancy sustaining function of P4. One attractive hypothesis is the isoform switching hypothesis (ISH). ISH is supported by in vitro evidence that progesterone receptor isoform A (PR-A) inhibits PR-B and that the PR-A/PR-B ratio increases towards term.

MATERIALS AND METHODS

Here, we test the hypothesis that isoform switching is an adaptation to high levels of P4 at term, predicting that, in humans, PR-A mediated repression of PR-B is stronger than in mouse. We use reporter assays with human and mouse PRs to detect species differences in the repressive effects of PR-A.

RESULTS

We found that human PR-B is less sensitive to repression by human PR-A than mouse PR-B, contrary to our prediction. The difference between human and mouse PR-B sensitivity is most pronounced at PR-A/PR-B ratios typical for the preterm myometrium.

CONCLUSIONS

Our results are inconsistent with the ISH. We speculate that, instead, the lower sensitivity of human PR-B to PR-A may be relevant for the maintenance of pregnancy at high progesterone levels and increasing PR-A concentrations towards term.

Acculturation, depressive symptoms, estriol, progesterone, and preterm birth in Hispanic women

We examined the effects of acculturation, depressive symptoms, progesterone, and estriol (E3) as predictors of preterm birth (PTB) in pregnant Hispanic women. This cross-sectional study recruited a sample of 470 Hispanic women between 22- and 24-week gestation from physician practices and community clinics. We used the CES-D to measure maternal depressive symptoms. We measured acculturation by English proficiency on the Bidimensional Acculturation Scale, residence index by years in the USA minus age, nativity, and generational status. Serum progesterone and E3 were analyzed by EIA. Ultrasound and medical records determined gestational age after delivery. In χ (2) analysis, there were a significantly greater percentage of women with higher depressive scores if they were born in the USA. In a structural equation model (SEM), acculturation (English proficiency, residence index, and generational status) predicted the estriol/progesterone ratio (E/P), and the interaction of depressive symptoms with the E/P ratio predicted PTB. Undiagnosed depressive symptoms during pregnancy may have biological consequences increasing the risk for PTB.

Treatment of abnormal vaginal flora in early pregnancy with clindamycin for the prevention of spontaneous preterm birth: a systematic review and metaanalysis

The purpose of this study was to determine whether the administration of clindamycin to women with abnormal vaginal flora at <22 weeks of gestation reduces the risk of preterm birth and late miscarriage. We conducted a systematic review and metaanalysis of randomized controlled trials of the early administration of clindamycin to women with abnormal vaginal flora at <22 weeks of gestation. Five trials that comprised 2346 women were included. Clindamycin that was administered at <22 weeks of gestation was associated with a significantly reduced risk of preterm birth at <37 weeks of gestation and late miscarriage. There were no overall differences in the risk of preterm birth at <33 weeks of gestation, low birthweight, very low birthweight, admission to neonatal intensive care unit, stillbirth, peripartum infection, and adverse effects. Clindamycin in early pregnancy in women with abnormal vaginal flora reduces the risk of spontaneous preterm birth at <37 weeks of gestation and late miscarriage. There is evidence to justify further randomized controlled trials of clindamycin for the prevention of preterm birth. However, a deeper understanding of the vaginal microbiome, mucosal immunity, and the biology of BV will be needed to inform the design of such trials.

Progestin treatment for the prevention of preterm birth

Progestin supplementation appears to be a promising approach to both preventing initiation of preterm labor and treating it once it is already established, given the role of progesterone in maintaining pregnancy, as well as support from basic and clinical research. Progesterone and 17α-hydroxyprogesterone acetate slow the process of cervical ripening, and this is the rationale for prophylactic long-term progestin supplementation mostly studied so far. However, progesterone (but not 17α-hydroxyprogesterone acetate) also inhibits myometrial activity even after the cervix has already ripened. Moreover, these effects depend greatly on the vehicle used and the route of administration. Understanding different mechanisms of action, as well as the importance of progestin formulation, vehicle and route of administration, is the key to finding the optimal progestin treatment for prevention of preterm birth.

Development and function of the human fetal adrenal cortex: a key component in the feto-placental unit

Continuous efforts have been devoted to unraveling the biophysiology and development of the human fetal adrenal cortex, which is structurally and functionally unique from other species. It plays a pivotal role, mainly through steroidogenesis, in the regulation of intrauterine homeostasis and in fetal development and maturation. The steroidogenic activity is characterized by early transient cortisol biosynthesis, followed by its suppressed synthesis until late gestation, and extensive production of dehydroepiandrosterone and its sulfate, precursors of placental estrogen, during most of gestation. The gland rapidly grows through processes including cell proliferation and angiogenesis at the gland periphery, cellular migration, hypertrophy, and apoptosis. Recent studies employing modern technologies such as gene expression profiling and laser capture microdissection have revealed that development and/or function of the fetal adrenal cortex may be regulated by a panoply of molecules, including transcription factors, extracellular matrix components, locally produced growth factors, and placenta-derived CRH, in addition to the primary regulator, fetal pituitary ACTH. The role of the fetal adrenal cortex in human pregnancy and parturition appears highly complex, probably due to redundant and compensatory mechanisms regulating these events. Mounting evidence indicates that actions of hormones operating in the human feto-placental unit are likely mediated by mechanisms including target tissue responsiveness, local metabolism, and bioavailability, rather than changes only in circulating levels. Comprehensive study of such molecular mechanisms and the newly identified factors implicated in adrenal development should help crystallize our understanding of the development and physiology of the human fetal adrenal cortex.

Preterm and term labour in multiple pregnancies

The association between multiple pregnancy and preterm labour is well-established, with >50% of multiple births delivering before 37 weeks. However, there remains limited understanding of the factors predisposing to early delivery of twins. Physiological stimuli to the onset of parturition, including stretch, placental corticotrophin-releasing hormone and lung maturity factors, may be stronger in multiple pregnancies due to the increased fetal and placental mass. Pathological processes including infection and cervical insufficiency also have a role. Treatments that prevent preterm birth in singleton pregnancies, such as progesterone and cervical cerclage appear to be ineffective in multiple pregnancies. This article reviews aspects of preterm birth in twins and higher order multiples including epidemiology, prediction and prevention of preterm labour and potential mechanisms controlling onset of parturition. Evidence relating to the management of labour in preterm and term multiples is also discussed.

Characterization of the myometrial transcriptome and biological pathways of spontaneous human labor at term

AIMS

to characterize the transcriptome of human myometrium during spontaneous labor at term.

METHODS

myometrium was obtained from women with (n=19) and without labor (n=20). Illumina HumanHT-12 microarrays were utilized. Moderated t-tests and false discovery rate adjustment of P-values were applied. Real-time quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) was performed for a select set of differentially expressed genes in a separate set of samples. Enzyme-linked immunosorbent assay and Western blot were utilized to confirm differential protein production in a third sample set.

RESULTS

1) Four hundred and seventy-one genes were differentially expressed; 2) gene ontology analysis indicated enrichment of 103 biological processes and 18 molecular functions including: a) inflammatory response; b) cytokine activity; and c) chemokine activity; 3) systems biology pathway analysis using signaling pathway impact analysis indicated six significant pathways: a) cytokine-cytokine receptor interaction; b) Jak-STAT signaling; and c) complement and coagulation cascades; d) NOD-like receptor signaling pathway; e) systemic lupus erythematosus; and f) chemokine signaling pathway; 4) qRT-PCR confirmed over-expression of prostaglandin-endoperoxide synthase-2, heparin binding epidermal growth factor (EGF)-like growth factor, chemokine C-C motif ligand 2 (CCL2/MCP1), leukocyte immunoglobulin-like receptor, subfamily A member 5, interleukin (IL)-8, IL-6, chemokine C-X-C motif ligand 6 (CXCL6/GCP2), nuclear factor of kappa light chain gene enhancer in B-cells inhibitor zeta, suppressor of cytokine signaling 3 (SOCS3) and decreased expression of FK506 binding-protein 5 and aldehyde dehydrogenase in labor; 5) IL-6, CXCL6, CCL2 and SOCS3 protein expression was significantly higher in the term labor group compared to the term not in labor group.

CONCLUSIONS

myometrium of women in spontaneous labor at term is characterized by a stereotypic gene expression pattern consistent with over-expression of the inflammatory response and leukocyte chemotaxis. Differential gene expression identified with microarray was confirmed with qRT-PCR using an independent set of samples. This study represents an unbiased description of the biological processes involved in spontaneous labor at term based on transcriptomics.

Steroid metabolome in fetal and maternal body fluids in human late pregnancy

Despite the extensive research during the last six decades the fundamental questions concerning the role of steroids in the initiation of human parturition and origin and function of some steroids in pregnancy were not definitely answered. Based on steroid metabolomic data found in the literature and our so far unpublished results, we attempted to bring new insights concerning the role of steroids in the sustaining and termination of human pregnancy, and predictive value of these substances for estimation of term. We also aimed to explain enigmas concerning the biosynthesis of progesterone and its bioactive catabolites considering the conjunctions between placental production of CRH, synthesis of bioactive steroids produced by fetal adrenal, localization of placental oxidoreductases and sustaining of human pregnancy. Evaluation of data available in the literature, including our recent findings as well as our new unpublished data indicates increasing progesterone synthesis and its concurrently increasing catabolism with approaching parturition, confirms declining production of pregnancy sustaining 5β-pregnane steroids providing uterine quiescence in late pregnancy, increased sulfation of further neuroinhibiting and pregnancy sustaining steroids. In contrast to the established concept considering LDL cholesterol as the primary substrate for progesterone synthesis in pregnancy, our data demonstrates the functioning of alternative mechanism for progesterone synthesis, which is based on the utilization of fetal pregnenolone sulfate for progesterone production in placenta. Close relationships were found between localization of placental oxidoreductases and consistently higher levels of sex hormones, neuroactive steroids and their metabolites in the oxidized form in the fetus and in the reduced form in the maternal compartment.

The role of progesterone in prevention of preterm birth

Preterm birth continues to provide an enormous challenge in the delivery of perinatal health care, and is associated with considerable short and long-term health consequences for surviving infants. Progesterone has a role in maintaining pregnancy, by suppression of the calcium-calmodulin-myosin light chain kinase system. Additionally, progesterone has recognized anti-inflammatory properties, raising a possible link between inflammatory processes, alterations in progesterone receptor expression and the onset of preterm labor. Systematic reviews of randomized controlled trials evaluating the use of intramuscular and vaginal progesterone in women considered to be at increased risk of preterm birth have been published, with primary outcomes of perinatal death, preterm birth <34 weeks, and neurodevelopmental handicap in childhood. Eleven randomized controlled trials were included in the systematic review, involving 2714 women and 3452 infants, with results presented according to the reason women were considered to be at increased risk of preterm birth. While there is a potential beneficial effect in the use of progesterone for some women considered to be at increased risk of preterm birth, primarily in the reduction in the risk of preterm birth before 34 weeks gestation, it remains unclear if the observed prolongation of pregnancy translates into improved health outcomes for the infant.

Pharmacologic actions of progestins to inhibit cervical ripening and prevent delivery depend on their properties, the route of administration, and the vehicle

OBJECTIVE

The purpose of this study was to evaluate cervical changes and delivery at term during pregnancy in rats after various progestin treatments.

STUDY DESIGN

Pregnant rats were treated by various routes and vehicles with progesterone, 17-alpha-hydroxyprogesterone caproate (17P), R5020, and RU-486. Delivery time was determined and cervical ripening was assessed in vivo by collagen light-induced fluorescence.

RESULTS

The cervix is rigid in the progesterone injection, 17P, and vaginal R5020 groups vs controls. Vaginal progesterone had no effect. RU-486 treatment softened the cervix during preterm delivery. Only subcutaneous injected progesterone, R5020 (subcutaneous and vaginal), and topical progesterone in sesame and fish oil inhibits delivery. Delivery is not changed by subcutaneous injection of 17P, vaginal progesterone, oral progesterone, and topical progesterone in Replens (Crinone; Columbia Labs, Livingston, NJ).

CONCLUSION

Inhibition of cervical ripening and delivery by progestins depends on many factors that include their properties, the route of administration, and the vehicle. This study suggests reasons that the present treatments for preterm labor are not efficacious.

Human effector/initiator gene sets that regulate myometrial contractility during term and preterm labor

OBJECTIVE

Distinct processes govern transition from quiescence to activation during term (TL) and preterm labor (PTL). We sought gene sets that are responsible for TL and PTL, along with the effector genes that are necessary for labor independent of gestation and underlying trigger.

STUDY DESIGN

Expression was analyzed in term and preterm with or without labor (n=6 subjects/group). Gene sets were generated with logic operations.

RESULTS

Thirty-four genes were expressed similarly in PTL/TL but were absent from nonlabor samples (effector set); 49 genes were specific to PTL (preterm initiator set), and 174 genes were specific to TL (term initiator set). The gene ontogeny processes that comprise term initiator and effector sets were diverse, although inflammation was represented in 4 of the top 10; inflammation dominated the preterm initiator set.

CONCLUSION

TL and PTL differ dramatically in initiator profiles. Although inflammation is part of the term initiator and the effector sets, it is an overwhelming part of PTL that is associated with intraamniotic inflammation.

The distribution of placental oxidoreductase isoforms provides different milieus of steroids influencing pregnancy in the maternal and fetal compartment

Using information based on the steroid metabolome in maternal and fetal body fluids, we attempted to ascertain whether there is a common mechanism, which is based on the placental distribution of various isoforms of 17β-hydroxysteroid dehydrogenases and aldo-keto reductases. This system simultaneously provides a higher proportion of active progestogens in fetal circulation and a higher proportion of active estrogens and GABAergic steroids in the maternal compartment. The data obtained using gas chromatography-mass spectrometry completely support the aforementioned hypothesis. We confirmed a common trend to higher ratios of steroids with hydroxy-groups in the 3α-, 17β-, and 20α-positions to the corresponding 3-oxo-, 17-oxo-, and 20-oxo-metabolites, respectively, in the maternal blood when compared with the fetal circulation, and the same tendency was obvious in the 3α-hydroxy/3β-hydroxy steroid ratios. A decreasing trend was observed in the ratios of active estrogens and neuro-inhibitory steroids to their inactive counterparts in fetal and maternal body fluids. This was probably associated with a limited capacity of placental oxidoreductases in the converting of estrone to estradiol during the transplacental passage. Although we observed a decreasing trend in pregnancy-sustaining steroids with increasing gestational age, we recorded rising levels of estradiol and particularly of estriol, regardless of the limited capacity of placental oxidoreductases. Besides the estradiol, which is generally known as an active estrogen, estriol may be of importance for the termination of pregnancy with respect to its excessive concentrations near term which allows its binding to estrogen receptors.

Abnormal Progesterone and Corticotropin Releasing Hormone Levels are Associated with Preterm Labour

Introduction: This study examined whether maternal plasma progesterone and corticotropin releasing hormone (CRH) concentrations can predict the likelihood of preterm labour. Materials and Methods: Maternal plasma progesterone and CRH concentrations were examined in a total of 51 women. The subject cohort included 20 women who were followed from the beginning of the third trimester (28 to 34 weeks gestation), half of whom delivered early preterm and half of whom were not in labour and subsequently delivered at full term (n = 10 per group). In a follow-up experiment, 31 women who were admitted during labour for delivery were examined, 15 of whom delivered preterm and 16 of whom delivered at full term. Comparisons between women who delivered preterm and those who delivered at full term were made by t-tests. Results: Mean progesterone concentration was approximately 30% lower at 28 to 34 weeks gestation in women who delivered prematurely than in women who delivered at term (P <0.001). Meanwhile, mean CRH concentration was 6-fold higher at 28 to 34 weeks gestation in women who experienced spontaneous preterm labour than in those who went into labour at term (P <0.001). Preterm mothers had lower progesterone (P <0.05) and CRH (P <0.01) levels during active labour than full-term mothers. Progesterone levels normalised within 24 hours of delivery in preterm mothers, while CRH levels remained slightly elevated (P <0.01). Conclusions: Maternal progesterone and CRH measurements taken early in the third trimester may be of use as biochemical markers of pregnancies at high risk of premature labour. Introduction: This study examined whether maternal plasma progesterone and corticotropin releasing hormone (CRH) concentrations can predict the likelihood of preterm labour. Materials and Methods: Maternal plasma progesterone and CRH concentrations were examined in a total of 51 women. The subject cohort included 20 women who were followed from the beginning of the third trimester (28 to 34 weeks gestation), half of whom delivered early preterm and half of whom were not in labour and subsequently delivered at full term (n = 10 per group). In a follow-up experiment, 31 women who were admitted during labour for delivery were examined, 15 of whom delivered preterm and 16 of whom delivered at full term. Comparisons between women who delivered preterm and those who delivered at full term were made by t-tests. Results: Mean progesterone concentration was approximately 30% lower at 28 to 34 weeks gestation in women who delivered prematurely than in women who delivered at term (P <0.001). Meanwhile, mean CRH concentration was 6-fold higher at 28 to 34 weeks gestation in women who experienced spontaneous preterm labour than in those who went into labour at term (P <0.001). Preterm mothers had lower progesterone (P <0.05) and CRH (P <0.01) levels during active labour than full-term mothers. Progesterone levels normalised within 24 hours of delivery in preterm mothers, while CRH levels remained slightly elevated (P <0.01). Conclusions: Maternal progesterone and CRH measurements taken early in the third trimester may be of use as biochemical markers of pregnancies at high risk of premature labour.

Prevention of preterm birth based on short cervix: progesterone

Preterm delivery, which occurs in about 5%-13% of pregnancies in most countries, is the main cause of neonatal morbidity and mortality. Symptomatic treatment of pregnancies presenting in preterm labor with corticosteroids has improved perinatal outcome but has not reduced the incidence of preterm delivery. Recent evidence suggests that the rate of preterm delivery may be reduced by the prophylactic use of progesterone in women with a history of preterm delivery and in those with a short cervical length identified by routine transvaginal sonography. This review summarizes the evidence (level A evidence) of the effectiveness of progesterone on the rate of preterm birth.

Progesterone levels in cesarean and normal delivered term placentas

BACKGROUND

One of the most important hormones synthesized by the placenta during pregnancy is progesterone. The regulating mechanisms of progesterone synthesis and the mechanism responsible for the spontaneous onset of labor in women are still not fully understood. Progesterone is thought to have been involved in human parturition. The objective of this study was to compare the levels of progesterone in the human placentas, at the end of the gestation (37-41 weeks) in vaginal versus cesarean deliveries, and to evaluate the pattern of progesterone accumulation, instantly following its synthesis by the human placenta at the end of the pregnancy.

METHODS

Progesterone levels in human placental tissue were determined by immunochemiluminescent analysis, following tissue homogenization. Progesterone secretion and accumulation pattern in the placental tissue was demonstrated using the ex vivo, closed, dual perfusion system of isolated human placental cotyledon.

RESULTS

Immunochemiluminescent analysis of progesterone levels in human normal and cesarean-delivered placentas showed that placentas following normal vaginal delivery store higher concentrations of progesterone, and produce progesterone more intensively. Results obtained from 120-min perfusions (of vaginal and cesarean-delivered placentas) showed that progesterone tended to accumulate in the maternal rather than the fetal compartment.

CONCLUSIONS

These data indicate that progesterone levels continuously rise till the end of pregnancy, with no apparent drop in progesterone levels during the labor process. In addition, progesterone is released from the syncytiotrophoblast preferably into the maternal component of the placental tissue.

The cytoplasmic 60 kDa progesterone receptor isoform predominates in the human amniochorion and placenta at term

BACKGROUND

The mechanism that initiates human parturition has been proposed to be 'functional progesterone withdrawal' whereby the 116 kDa B-isoform of the progesterone receptor (PR-B) switches in favour of the 94 kDa A-isoform (PR-A) in reproductive tissues. Recently, other PR isoforms, PR-S, PR-C and PR-M generated from the same gene have been identified and partially characterised.

METHODS AND RESULTS

Using immunohistochemical, western blotting and RT-PCR techniques, evidence is provided that indicates the major PR isoform present in human term fetal membranes (amnion and chorion) and syncytiotrophoblast of the placenta is neither of the classical nuclear PR-B or PR-A isoforms but is the N-terminally truncated 60 kDa PR-C isoform. Evidence is also provided that this 60 kDa isoform resides in the cytoplasm of the expressing cell types. Data are also presented to show that PR-B, PR-A and PR-S isoforms are essentially absent from the amnion and chorion, whereas PR isoforms A, B, C and S are all present in the decidua, with PR-A being the major isoform. The syncytiotrophoblast of the placenta contains the cytoplasmic 60 kDa isoform, but not isoforms PR-A, PR-B or PR-S.

CONCLUSION

The major PR isoform in the amnion, chorion and placenta is a 60 kDa protein that could be PR-C, suggesting that the cytoplasmic isoform has a specific role in extra-embryonic tissues and may be involved in the regulation of human parturition.

In vitro study of the tocolytic effect of oroxylin A from Scutellaria baicalensis root

Scutellariae Radix is one of the well-known tocolytic Chinese herbs. Oroxylin A is isolated from the root of Scutellaria baicalensis. The main syndrome of preterm birth is caused by uterus contractions from excitatory factors. Administration of tocolytic agents is a strategy to prevent the occurrence of preterm births. The aim of this study was to investigate the effects of oroxylin A on contractions of uterine strips isolated from non-pregnant female Wistar rats (250~350 g). Contractions of the uterus were induced with acetylcholine (Ach) (1 μM), PGF_2α (0.1 μM), oxytocin (10^-3 U/ml), KCl (56.3 mM), tetraethylammonium (TEA; 1 and 10 mM), 4-aminopyridine (4-AP; 5 mM), glipizide (30 μM), a nitric oxide synthase (NOS) inhibitor (LNNA; 10^-3M), a β-receptor blocker (propranolol; 10 μM), and a cyclooxygenase inhibitor (indomethacin; 60 μM). The inhibitory effects of the amplitude and frequency of spontaneous contractions by oroxylin A were antagonized with Ach (IC₅₀ 22.85 μM), PGF_2α (IC₅₀27.28 μM), oxytocin (IC₅₀ 12.34 μM), TEA; 1 and 10 mM (IC₅₀ 52.73 and 76.43 μM), 4-AP (IC₅₀ 67.16 μM), and glipizide (IC₅₀27.53 μM), but oroxylin A was not influenced by Ca²⁺-free medium, LNNA, propranolol, or indomethacin. Otherwise, oroxylin A-mediated relaxation of the rat uterus might occur through opening of uterine calcium-dependent potassium channels or adenosine triphosphate potassium channel activation. This suggests that oroxylin A is the tocolytic principle constituent of Scutellariae Radix, and oroxylin A may provide a lead compound for new tocolytic drug development in the future.

Progesterone after previous preterm birth for prevention of neonatal respiratory distress syndrome (PROGRESS): a randomised controlled trial

BACKGROUND

Neonatal respiratory distress syndrome, as a consequence of preterm birth, is a major cause of early mortality and morbidity during infancy and childhood. Survivors of preterm birth continue to remain at considerable risk of both chronic lung disease and long-term neurological handicap. Progesterone is involved in the maintenance of uterine quiescence through modulation of the calcium-calmodulin-myosin-light-chain-kinase system in smooth muscle cells. The withdrawal of progesterone, either actual or functional is thought to be an antecedent to the onset of labour. While there have been recent reports of progesterone supplementation for women at risk of preterm birth which show promise in this intervention, there is currently insufficient data on clinically important outcomes for both women and infants to enable informed clinical decision-making. The aims of this randomised, double blind, placebo controlled trial are to assess whether the use of vaginal progesterone pessaries in women with a history of previous spontaneous preterm birth will reduce the risk and severity of respiratory distress syndrome, so improving their infant's health, without increasing maternal risks.

METHODS

DESIGN

Multicentered randomised, double blind, placebo-controlled trial.

INCLUSION CRITERIA

pregnant women with a live fetus, and a history of prior preterm birth at less than 37 weeks gestation and greater than 20 weeks gestation in the immediately preceding pregnancy, where onset of labour occurred spontaneously, or in association with cervical incompetence, or following preterm prelabour ruptured membranes. Trial Entry & Randomisation: After obtaining written informed consent, eligible women will be randomised between 18 and 23+6 weeks gestation using a central telephone randomisation service. The randomisation schedule prepared by non clinical research staff will use balanced variable blocks, with stratification according to plurality of the pregnancy and centre where planned to give birth. Eligible women will be randomised to either vaginal progesterone or vaginal placebo. Study Medication & Treatment Schedules: Treatment packs will appear identical. Woman, caregivers and research staff will be blinded to treatment allocation. Primary Study Outcome: Neonatal Respiratory Distress Syndrome (defined by incidence and severity).

SAMPLE SIZE

of 984 women to show a 40% reduction in respiratory distress syndrome from 15% to 9% (p = 0.05, 80% power).

DISCUSSION

This is a protocol for a randomised trial.

Regional changes in the spatio-temporal pattern of progesterone receptor (PR) expression in the guinea-pig genital tract as parturition approaches

Normal parturition in guinea-pig involves changes in responsiveness of the genital tract to estrogen and progesterone. To better characterize endocrine control of guinea-pig parturition, protein and mRNA expression of estrogen receptor-alpha (ERalpha) and progesterone receptor (PR) were quantitatively evaluated in lower (LUS) and upper (UUS) uterine segments, cervix (C) and pubic symphyseal ligament (PSL) at three stages of pregnancy (established based on interpubic distance, 0mm: non-relaxed group, 4-6mm: 5 days before parturition, 11-14 mm: 1-2 days prepartum) and immediately after parturition. Towards parturition, no changes in PR mRNA levels were recorded in the UUS, whereas the LUS displayed a gradual increase. PR transcripts exhibited decreased levels during parturition in C and PSL. Levels of PR mRNA were increased in the LUS compared with that of the UUS only at parturition. Regarding protein expression during parturition, PR levels decreased in the UUS whereas in the LUS increased. In C and PSL, PR protein expression decreased 1-2 days prepartum and remained low during parturition. None of the regions studied showed changes in mRNA or protein expression of ERalpha. Therefore, functional regionalization of the guinea-pig genital tract is associated with changes in the spatio-temporal pattern of PR expression as parturition approaches.

Angiogenesis gene expression in mouse uterus during the common pathway of parturition

OBJECTIVE

The objective of the study was to investigate changes in the expression of angiogenesis-related genes during the common terminal pathway of parturition including spontaneous labor at term, as well as preterm labor (PTL), induced by either bacteria or ovariectomy.

STUDY DESIGN

Preterm pregnant mice (14.5 days of gestation) were treated with the following: (1) intrauterine injection of media; (2) intrauterine injection of heat-inactivated Escherichia coli; (3) ovariectomy; and (4) sham operation. Tissues from mice at term (19.5 days of gestation) were collected at term not in labor, term in labor, and 12 hours postpartum. Angiogenesis-related gene expression levels were quantitated by the measurement of specific mRNAs in uterine tissue by RT-qPCR and analyzed by repeated-measures analysis of variance.

RESULTS

The following results were found: (1) microarray analysis of the uterine transcriptome indicated an enrichment for the gene ontology category of angiogenesis in bacteria-induced PTL samples (P < or = .093); (2) several genes related to angiogenesis demonstrated significantly increased expression in samples in either term spontaneous labor or preterm labor; and (3) qRT-PCR measurements demonstrated that spontaneous term labor and preterm labor induced by either bacteria or ovariectomy all substantially increased the expression of multiple angiogenesis-related genes (P < or = .0003; Angpt2, Ctgf, Cyr61, Dscr1, Pgf, Serpine1, Thbs1, and Wisp 1).

CONCLUSION

Spontaneous labor at term, as well as pathologically induced preterm labor, all result in greatly increased expression of angiogenesis-related genes in the uterus.

Delayed parturition and altered myometrial progesterone receptor isoform A expression in mice null for Krüppel-like factor 9

Preterm and delayed labor conditions are devastating health problems with currently unknown etiologies. We previously showed that the transcription factor Krüppel-like factor 9 (KLF9) influences the expression and/or transcriptional activity of receptors for estrogen and progesterone in endometrial cells in vivo and in vitro. Given that estrogen and progesterone differentially regulate uterine myometrial contractility during gestation, we hypothesized that lack of KLF9 could compromise myometrial function, leading to defects in parturition. To test this, we used mice null for Klf9 to evaluate gestation length, response to the progesterone receptor (PGR) antagonist RU486, expression levels of steroid receptor proteins, nuclear receptor coactivator and contractility-associated genes, and nuclear factor-kappaB (NF-kappaB) DNA binding activity in myometrium near term. Klf9 knockout (KO) mice exhibited delayed parturition by 1-2 days relative to wild-type (WT) counterparts, in the absence of fetal genotype contribution and differences in serum estrogen and progesterone levels. Knockout mice near term were refractory to the abortive action of RU486, and they displayed aberrant myometrial expression patterns of nuclear PGR-A and NF-kappaB p65/RELA relative to WT mice. Myometrial expression levels of nuclear estrogen receptor-alpha did not differ, whereas those for Oxtr and Crebbp mRNAs were lower, in KO versus WT mice. Results indicate that KLF9 contributes to the regulation of PGR-associated components in the myometrium necessary for timely onset of parturition in mice. The present study highlights the potential utility of Klf9 null mice to investigate the pathophysiology of parturition defects involving PGR signaling.

The human progesterone receptor shows evidence of adaptive evolution associated with its ability to act as a transcription factor

The gene encoding the progesterone receptor (PGR) acts as a transcription factor, and participates in the regulation of reproductive processes including menstruation, implantation, pregnancy maintenance, parturition, mammary development, and lactation. Unlike other mammals, primates do not exhibit progesterone withdrawal at the time of parturition. Because progesterone-mediated reproductive features vary among mammals, PGR is an attractive candidate gene for studies of adaptive evolution. Thus, we sequenced the progesterone receptor coding regions in a diverse range of species including apes, Old World monkeys, New World monkeys, prosimian primates, and other mammals. Adaptive evolution occurred on the human and chimpanzee lineages as evidenced by statistically significant increases in nonsynonymous substitution rates compared to synonymous substitution rates. Positive selection was rarely observed in other lineages. In humans, amino acid replacements occurred mostly in a region of the gene that has been shown to have an inhibitory function (IF) on the ability of the progesterone receptor to act as a transcription factor. Moreover, many of the nonsynonymous substitutions in primates occurred in the N-terminus. This suggests that cofactor interaction surfaces might have been altered, resulting in altered progesterone-regulated gene transcriptional effects. Further evidence that the changes conferred an adaptive advantage comes from SNP analysis indicating only one of the IF changes is polymorphic in humans. In chimpanzees, amino acid changes occurred in both the inhibitory and transactivation domains. Positive selection provides the basis for the hypothesis that changes in structure and function of the progesterone receptor during evolution contribute to the diversity of primate reproductive biology, especially in parturition.

Overview. Preterm labour: mechanisms and management

Preterm birth remains a major cause of perinatal mortality and long term handicap in surviving infants. This is one of the most important clinical problems in Europe and across the world. While some preterm births are iatrogenic, associated with severe complications of pregnancy (e.g. hypertensive disorders, antepartum haemorrhage, infection), or the result of multiple pregnancies following assisted reproduction, a high proportion of preterm births occur following spontaneous preterm labour of unknown cause. Early intervention in this group of women would have a significant impact on neonatal mortality and morbidity figures. However, the endocrine changes preceding parturition in women remain elusive and this makes it difficult to predict spontaneous labour at term, let alone preterm labour. Moreover our understanding of myometrial physiology remains rudimentary, limiting our options to devise improved pharmacological strategies to control uterine contractility when this is indicated. There is a need for concerted European and international research efforts to improve our knowledge of the mechanism of labour in women, to identify diagnostic markers to predict preterm labour and to develop uterine selective drugs to inhibit uterine contractions in a safe and efficient manner. This aim will be achieved by multidisciplinary research efforts from academics and industry, using traditional laboratory and clinical research methods, as well as novel technologies.

Functional genomics of the pregnant uterus: from expectations to reality, a compilation of studies in the myometrium

Background

Studies on the human myometrium have reported on different microarrays containing different sets of genes or ESTs. However each study profiled only a small number of patients due to various constraints. More profiling information would be an addition to our knowledge base of parturition.

Methods

We compiled from five human studies, transcriptional differences between the non pregnant myometrium (NP), preterm myometrium (PTNIL), term myometrium not in labor (TNIL) and term myometrium in labor (TIL). Software modules developed by the Draghici's group at Wayne State University (Detroit, MI, USA) were used to propose a hierarchical list of several KEGG pathways most likely adjusted to changes observed in microarray experiments.

Results

The differential expression of 118 genes could be dispatched in 14 main KEGG pathways that were the most representative of the changes seen in NP and PTNIL, versus TNIL or TIL. Despite the potential of multiple pitfalls inherent to the use of the microarray technology, gene module analysis of the myometrial transcriptome reveals the activation of precise signaling pathways, some of which may have been under evaluated.

Conclusion

The remodelling and maturation processes that the uterus undergoes in pregnancy appear clearly as phenomena which last during the full course of gestation. It is attested by the nature of the main signaling pathways represented, in the comparison of the PTNIL versus TNIL uterus. Comparatively, the onset of labor is a phenomenon which remains less well characterized by these methods of analysis, possibly because it is a phenomenon occurring in too short a window to have been grasped by the studies carried out up to now.

Circulating levels of pregnanolone isomers during the third trimester of human pregnancy

This study addresses the question of whether changes in the biosynthesis and metabolism of neuroactive pregnanolone isomers (PIs) might participate in the timing of parturition in humans. The time profiles of unconjugated allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one, P3alpha5alpha), pregnanolone (3alpha-hydroxy-5beta-pregnan-20-one, P3alpha5beta), isopregnanolone (3beta-hydroxy-5alpha-pregnan-20-one, P3beta5alpha) and epipregnanolone (3beta-hydroxy-5beta-pregnan-20-one, P3beta5beta), pregnenolone, their polar conjugates, progesterone, 5alpha-dihydroprogesterone (P5alpha), and 5beta-dihydroprogesterone (P5beta) were monitored in the plasma of 30 healthy women during the third trimester of pregnancy, at 1-week intervals from the 30th week of gestation using GC-MS. Changes in the steroid levels were evaluated by two-way ANOVA with gestational age and subject as independent factors. The mean concentrations of free PIs ranged from 2 to 50 nmol/L, while the mean levels of their polar conjugates were 40-100 x higher. The ratio of 5alpha-PIs to progesterone significantly but inconspicuously culminated in the 35th week. The decelerating biosynthesis of free 5beta-PIs from the 31st week and their escalating sulfation was found from the 30th week. The changes were particularly evident in the second most abundant PI pregnanolone that may, like the allopregnanolone, sustain the pregnancy via attenuation of hypothalamic GABA(A)-receptors and prevent uterine contractility via binding to nuclear pregnane X receptor.

Steroid hormone control of myometrial contractility and parturition

The precise temporal control of uterine contractility is essential for the success of pregnancy. For most of pregnancy, progesterone acting through genomic and non-genomic mechanisms promotes myometrial relaxation. At parturition the relaxatory actions of progesterone are nullified and the combined stimulatory actions of estrogens and other factors such as myometrial distention and immune/inflammatory cytokines, transform the myometrium to a highly contractile and excitable state leading to labor and delivery. This review addresses current understanding of how progesterone and estrogens affect the contractility of the pregnancy myometrium and how their actions are coordinated and controlled as part of the parturition cascade.

Cervical length changes during preterm cervical ripening: effects of 17-alpha-hydroxyprogesterone caproate

OBJECTIVE

The purpose of this study was to evaluate whether 17-alpha-hydroxyprogesterone caproate (17P) treatment affect changes in cervical length.

STUDY DESIGN

Women with singleton pregnancy, between 25 and 33 + 6 weeks of gestation, who were hospitalized for preterm labor were included. Patients with rupture of membranes and/or signs of chorioamnionitis were excluded. Sixty undelivered patients were allocated randomly to either observation or to receive 341 mg of 17P intramuscularly, twice each week until gestational week 36. Cervical length was measured by transvaginal ultrasound scanning at discharge and at day 7 and 21 after discharge. Statistical comparisons were done with analysis of variance and chi-square test.

RESULTS

Shortening of the cervix in the observation group (30 cases) was higher than in the 17P group (30 cases) both at day 7 (2.37 +/- 2.0 mm vs 0.83 +/- 1.74 mm; P = .002) and day 21 (4.60 +/- 2.73 mm vs 2.40 +/- 2.46 mm; P = .002). Treatment with 17P was associated with both a reduction in the risk of cervical shortening of > or = 4 mm (odds ratio, 0.18; 95% CI, 0.04-0.66) and in the risk of preterm delivery (odds ratio, 0.15; 95% CI, 0.04-0.58).

CONCLUSION

Undelivered patients after preterm labor undergo progressive shortening of the cervix, which is attenuated by 17P treatment.

Progestin inhibits and thrombin stimulates the plasminogen activator/inhibitor system in term decidual stromal cells: implications for parturition

OBJECTIVE

Labor is associated with 'decidual activation' with increased proteolysis and extracellular matrix degradation. The balance between plasminogen activator inhibitor-1 (PAI-1) and urokinase (uPA) and tissue-type plasminogen activator (tPA) is an important determinant of proteolytic activity at the maternal-fetal interface. Thrombin released at the time of placental abruption (decidual hemorrhage) is known to promote decidual proteolysis and uterine contractions. This study investigates the separate and interactive effects of steroid hormones and thrombin on PAI-1, uPA, and tPA expression by term decidual cells (DCs).

STUDY DESIGN

Term DCs were isolated by enzymatic digestion, purified, and depleted of leukocytes. Cells were treated with estradiol (10(-8) mol [E2]), medroxyprogesterone acetate (10(-7) mol [MPA]), both, or vehicle for 7 days. After 24-hour incubation with or without thrombin (0.1-2.5 U/mL), levels of PAI-1, uPA, and tPA in conditioned supernatant were measured by specific ELISA and Western blotting. Levels of PAI-1 and uPA mRNA were measured by quantitative RT-PCR.

RESULTS

In the cultured term DCs, ELISA measurements indicated that basal output of PAI-1 was about 2 logs higher than that of either uPA or tPA (2.5 +/- 0.7 ng/mL per microg protein, 13.4 +/- 6.3 pg/mL per microg protein, and 25.4 +/- 10.8 pg/mL per microg protein, respectively). Although E2 alone did not affect PAI-1 output, MPA and E2+MPA significantly enhanced PAI-1 production (2.5 +/- 0.7 vs 8.2 +/- 2.0 ng/mL per microg protein for E2+MPA [3.3-fold]; P < .01). By contrast, uPA output was inhibited by exposure to MPA (13.4 +/- 6.3 vs 2.6 +/- 1.1 pg/mL per microg protein [0.2-fold]; P < .05), whereas tPA production was not affected by MPA. Thrombin did not significantly affect uPA and tPA production by term DCs. In contrast, in E2+MPA-treated term DCs, thrombin, a hemostatic proinflammatory cytokine, selectively increased PAI-1 output in a dose-dependent fashion, which could be blocked by the selective thrombin inhibitor, hirudin. Western blotting confirmed the effects of MPA and thrombin in elevating secreted levels of PAI-1. Unlike the increase in PAI-1 output elicited by thrombin, term DCs were unresponsive to either of the classic proinflammatory cytokines, TNFalpha or IL-1beta. Corresponding effects on PAI-1 mRNA levels were elicited by MPA and thrombin as seen for PAI-1 protein expression, suggesting that these up-regulatory effects are transcriptionally mediated.

CONCLUSION

Progestin enhanced PAI-1 and inhibited uPA expression by term DCs, which may explain in part the pregnancy-prolonging properties of progesterone as a consequence of inhibited proteolytic activity at the maternal-fetal interface. Thrombin augmented PAI-1 expression in the absence of increased uPA or tPA expression by term DCs, suggesting that abruption-associated decidual proteolysis and preterm labor is mediated primarily by thrombin-enhanced matrix metalloproteinase expression rather than an indirect effect on the plasminogen activator/inhibitor system.

Mechanisms of progesterone action in inhibiting prematurity

Progesterone is a steroid hormone that plays an integral role in each step of human pregnancy. In early pregnancy, progesterone produced by the corpus luteum is critical to the maintenance of early pregnancy until the placenta takes over this function at 7 to 9 weeks of gestation, hence its name (pro-gestational steroid hormone). The role of progesterone in later pregnancy, however, is less clear. It has been proposed that progesterone may be important in maintaining uterine quiescence in the latter half of pregnancy by limiting the production of stimulatory prostaglandins and inhabiting the expression of contraction-associated protein genes within the myometrium. Although systemic progesterone withdrawl may not correlate directly with the onset of labour in humans, there is increasing evidence to suggest that progesterone exerts its influence indirectly via a 'functional' withdrawl at the level of the uterus. The molecular mechanisms by which progesterone is able to maintain uterine quiescence and prevent preterm birth in some high-risk women are not clear. Six putative mechanisms have been proposed in the literature by both US and other investigators and are explored in this review.

HCG--A new kid on the block in prematurity prevention

Human chorionic gonadotropin (HCG) is a molecule with multiple endocrine, paracrine, and immunoregulatory actions. Its importance for the enhancement of fertility, successful implantation, and survival of the conceptus in early gestation is recognized. However, studies conducted worldwide in recent years indicate that HCG may also play a significant role in maintaining pregnancy well after the first trimester. Emerging evidence suggests that different biomolecular and physiologic effects of HCG are concordantly directed toward inhibition of myometrial contractility to maintain pregnancy. These studies have prompted preliminary animal and human testing of HCG for the prevention of preterm birth. This article reviews the current knowledge as well as the future perspectives on HCG as a useful new tool in prematurity prevention.

Feto-placental communication system with the myometrium inpregnancy and parturition: the role of hormones, neurohormones, inflammatory mediators, and locally active factors

Pregnancy is a unique condition in which the conceptus is allowed to implant, survive, develop, and reach a considerable organ growth and maturation within the maternal body despite the fact that it is half genetically different from the mother. Moreover, it deeply influences the overall endocrine, metabolic, and immunological functions of the recipient mother. These objectives are accomplished through the establishment of several communication systems in which a large array of substances produced by the feto-placental unit reach specific maternal target organs and/or systems and modulate their function. The myometrium is a fundamental reproductive tissue involved in pregnancy maintenance as well as in labor onset and progression and is a potential target organ for such a communication system. An appropriate regulation of myometrial function is a key condition required for pregnancy to develop physiologically until full term is reached and for labor to start. Emerging experimental and clinical evidence suggests that a very complex feto-placental biomolecular communication system exists with the myometrium and is actively operative in the control of myometrial contractility in pregnancy and parturition through the production of a continuously increasing number of substances with endocrine, paracrine, and immunoregulatory actions.

Hormonal changes accompanying cigarette smoke-induced preterm births in a mouse model

Epidemiologic evidence indicates that maternal smoking increases the risk of preterm birth. While a number of plausible mechanisms for early delivery have been offered, the role of gestational hormones in this smoke-induced outcome is uncertain. Thus, a toxicologic study was performed to examine the effects and underlying hormonal mechanisms of mainstream cigarette smoke (MCS) exposure on gestational duration. Pregnant B6C3F1 mice were exposed by inhalation to MCS for 5 days/week (4 hrs/day) from Gestational Day (GD) 4 to parturition. Smoke-induced effects on gestational length, interpubic ligament length, maternal hormone secretion patterns (estradiol-17beta, progesterone, prolactin, and relaxin), body weight gain, postimplantation loss, litter size, and offspring sex ratio were examined. Dams exposed to MCS at a concentration equivalent to smoking less than one pack of cigarettes/day (carbon monoxide = 25 parts per million, total suspended particulates = 16 mg/m3) demonstrated a significant (P < 0.05) shortening of gestational duration (compared with pregnant, air-exposed mice). In addition, MCS-exposed mice sacrificed on GD 18 had significantly (P < 0.05) increased interpubic ligament length, elevated serum estrogen levels, and a reduced progesterone to estradiol-17beta ratio (compared with air-exposed controls); levels of progesterone and prolactin were only modestly decreased and increased, respectively, in the MCS-exposed mice. Smoke exposure had no significant effects on maternal relaxin levels, body weight gain, postimplantation loss, litter size, or sex ratio. Results of this study demonstrate that inhalation exposure of pregnant mice to a low dose of MCS shortens gestation and alters hormone secretory patterns, which are important for maintaining pregnancy and inducing parturition. These findings support the view that pregnant women who smoke (even modestly) may be at increased risk for preterm birth, and that early delivery may be related (at least partly) to MCS-induced.

Regulation of phosphodiesterase 5 expression and activity in human pregnant and non-pregnant myometrial cells by human chorionic gonadotropin

OBJECTIVES

This study has a twofold aim: 1) to investigate whether protein expression and enzyme activity of phosphodiesterase 5 (PDE5) can be detected in human myometrium and undergo changes in relation to the presence of pregnancy and/or labor; 2) to evaluate whether PDE5 expression and activity in myometrial cells can be influenced by human chorionic gonadotropin (HCG).

METHODS

Primary cultures of myometrial cells, obtained from non-pregnant women and from pregnant women at term, either before or during labor, were carried out in the presence of HCG or dibutyryl-cyclic AMP (db-cAMP), the non-hydrolizable analogue of cAMP. PDE5 expression in cultures of myometrial cells was detected by immunocytochemistry and western blot. PDE5 activity was detected in cell extracts by enzyme assay.

RESULTS

PDE5 is expressed and is functionally active in smooth muscle cells. Treatment of cell cultures with HCG and db-cAMP results in a reduction of PDE5 expression and activity. The effects of HCG and db-cAMP are exerted irrespective of the functional status of the myometrium (non-pregnant, pregnant not in labor, pregnant in labor).

CONCLUSIONS

PDE5 protein is expressed in human non-pregnant and pregnant myometrium. HCG reduces PDE5 expression and enzyme activity in smooth muscle cells, possibly through a pathway involving cAMP.

The progesterone receptor in human term amniochorion and placenta is isoform C

The mechanism that initiates human parturition has been proposed to be functional progesterone withdrawal whereby the 116-kDa B isoform of the progesterone receptor (PR-B) switches in favor of the 94-kDa A isoform (PR-A) in reproductive tissues. Recently other PR isoforms, PR-S, PR-C, and PR-M generated from the same gene have been identified and partially characterized. Using immunohistochemical, Western blotting, and RT-PCR techniques, evidence is provided that the major PR isoform present in human term fetal membranes (amnion and chorion) and syncytiotrophoblast of the placenta is neither of the classical nuclear PR-B or PR-A isoforms but is the N terminally truncated 60-kDa PR-C isoform. Evidence is also provided that the PR-C isoform resides in the cytoplasm of the expressing cell types. Data are also presented to show that PR-B, PR-A, and PR-S isoforms are essentially absent from the amnion and chorion, whereas PR isoforms A, B, C, and S are all present in the decidua, with PR-A being the major isoform. The syncytiotrophoblast of the placenta contains the cytoplasmic PR-C isoform but not PR-A, PR-B, or PR-S. The major PR isoform in the amnion, chorion, and placenta is PR-C, suggesting that the cytoplasmic PR-C isoform has a specific role in extraembryonic tissues and may be involved in the regulation of human parturition.

Progesterone receptors in the human uterus and their possible role in parturition

An overview is given on the role of progesterone in parturition in the human. Progesterone withdrawal is considered to be a major event for the beginning of parturition. However, in the human, no evidence exists in favour of a decline in placental progesterone production prior to labour. Progesterone actions are mediated by two functionally different but structurally highly related intranuclear proteins, progesterone receptor (PR) A and PRB. In the human, functional progesterone withdrawal is thought to play a role. This may be mediated by a change in the expression of the two isoforms of the PR, with an increase in the PRA:PRB ratio, and this is accompanied by an increase in the expression of the estrogen receptor. These mechanisms are considered to be critical for the endocrine control of parturition.

Progesterone receptor isoform (A/B) ratio of human fetal membranes increases during term parturition

OBJECTIVE

The role of progesterone in the control of human parturition remains unsettled. Because there is no systemic progesterone withdrawal before the onset of labor, a 'functional progesterone withdrawal' has been proposed to be operative before human parturition. This may be accomplished by a change in the density of the progesterone receptor (PR) isoforms in myometrium and fetal membranes. The purpose of our study was to determine if spontaneous term labor is associated with changes of PR isoforms (PR-A and PR-B) in the fetal membranes.

STUDY DESIGN

Fetal membranes were obtained from women undergoing elective cesarean delivery at term (not in labor group), and from women with a vaginal delivery (labor group). The expression of PR isoforms was assessed by Western blot analysis of amnion and chorio-decidua. Densitometric analysis of PR-A/PR-B ratio was performed. Immunohistochemistry with specific antibodies to PR-A and PR-B was done. Nonparametric statistics were used for analysis.

RESULTS

1) The predominant isoform of PR in women not in labor was PR-B, and PR-A in patients in labor. The ratio of PR-A/PR-B in fetal membranes was significantly higher in women in labor than in those not in labor (for amnion, median 4.3, range [0.9-8.4] vs median 0.4, range [0.3-2.6], P < .001; for chorio-decidua, median 2.0, range [1.1-19.2] vs median 1.2, range [0.1-2.0], P < .05). 2) Fetal membranes expressed both types of PR. 3) Immunohistochemistry showed the presence of PR-A and PR-B in the cytoplasm of amnion epithelial cells, chorion trophoblast, and decidual cells.

CONCLUSION

Human parturition at term is associated with changes in PR isoforms in the fetal membranes and, thus, a local 'functional progesterone withdrawal' may operate in human parturition through this mechanism.

The molecular pathophysiology of bacterially induced preterm labor: insights from the murine model

Premature delivery, the most important problem in obstetrics in developed countries, continues to vex clinicians and researchers. Despite decades of investigation, the pathophysiology of premature labor is incompletely understood, and therapies or preventive strategies tailored to each of the many potential causes do not exist. The present review addresses one cause of prematurity, namely, intrauterine bacterial infection. Given the vastness of the literature for even this single etiology, we focus on the mouse as a model organism from which much can be learned about mammalian parturition. The underpinnings of bacterially induced labor are believed to involve a signaling cascade that begins with recognition of offending pathogens by cell-surface receptors (toll-like receptors). This cascade then operates through multiple branching and redundant pathways to bring about the changes within the gestational compartment that produce cervical ripening, labor, and ultimately delivery. The major challenge facing researchers is to understand the levels of complexity in the host response, so that prevention and treatment strategies may be sufficiently focused to minimize unwanted side effects, yet sufficiently broad to be effective. Given the complexity of the problem, this understanding can be aided by efficient model systems, of which one in vivo example is the mouse, an organism that shares with humans many similarities in the biochemical and molecular aspects of inflammation-induced preterm labor. We propose that tools with the power to assess simultaneously the myriad elements of the hypothesized signaling cascade (ie, genomic and proteomic technologies) are important components of the solution to the puzzle of parturition.

Different routes of progesterone administration and polycystic ovary syndrome: a review of the literature

Polycystic ovary syndrome (PCOS) is a common endocrine disorder in woman of reproductive age. Although extensive studies have been performed in past decades to investigate the pathobiological mechanisms underlying the unset of this disease, its etiology remains unknown. Progesterone is a hormone of paramount importance in ovulation, implantation and luteal phase support. Low levels of progesterone have been found in the early luteal phase in PCOS patients. Granulosa cells from polycystic ovaries show an altered progesterone production. Moreover, the lack of cyclical exposure to progesterone may have a role in the development of the gonadotropin and androgen abnormalities found in PCOS patients. Ovulation failure and progesterone deficiency may facilitate the hypothalamic-pituitary abnormalities causing the associated disordered luteinizing hormone secretion in PCOS. Progesterone may be administered to PCOS patients in the following cases: to induce withdrawal bleeding, to suppress secretion of luteinizing hormone, in ovulation induction in clomiphene citrate-resistant patients and in luteal phase support in assisted reproduction. We discuss the pharmacologic characteristics of the different routes of progesterone administration with reference to these diverse indications, the therapeutic objectives and patient compliance.

Mechanisms underlying "functional" progesterone withdrawal at parturition

Progesterone is a major factor maintaining uterine quiescence throughout pregnancy. In most species, peripheral progesterone levels decline before initiation of labor, and treatments that inhibit progesterone synthesis or action cause termination of pregnancy and/or premature deliveries. These findings suggest that progesterone withdrawal is required for activation of myometrial contractions. However, in humans, circulating progesterone levels remain elevated until birth, which leads to the notion that a "functional" progesterone withdrawal occurs before parturition. The apparent loss of progesterone sensitivity at term could be a consequence of several different mechanisms including: (1) the catabolism of progesterone in the uterus into inactive compounds; (2) alterations in progesterone receptor (PR) isoform ratios; (3) changes in cofactor protein levels affecting PR transactivation; and (4) inflammation-induced trans-repression of PR by nuclear factor kappaB. All of these mechanisms are potentially capable of decreasing uterine progesterone responsiveness at term, thus enabling the expression of pathways that originally were blocked by progesterone in early pregnancy. However, the specific uterine genes whose transcription is directly controlled by PR, and thus affected by "functional" progesterone withdrawal, remain to be identified.