Progesterone enhances the tocolytic effect of ritodrine in isolated pregnant human myometrium

The use of vaginal progesterone as a maintenance therapy in women with arrested preterm labor: a double-blind placebo-randomized controlled trial

Background: The efficacy of maintenance tocolytic therapy after successful arrest of preterm labor remains controversial. The purpose of this study was to evaluate the efficacy of 400 mg of daily vaginal progesterone (cyclogest) after successful parenteral tocolysis to increase latency period and improvement of neonatal outcomes in women with threatened preterm labor.Materials and methods: In this randomized, double-blind, placebo-controlled trial, 85 participants were randomly allocated to either 400 mg daily of vaginal progesterone (n = 45) or placebo (n = 40) until 34 weeks of gestation. The primary outcomes were the time until delivery (latency period) and cervical length after 1 week of treatment. Secondary outcome were GA on delivery, type of delivery, incidence of low birth weight, perinatal morbidity and mortality.Results: Longer mean latency until delivery (53.6 ± 16.8 versus 34.5 ± 12.9) days p = .0001; longer mean of gestational age on delivery (37.5 ± 2.2 versus 34.2 ± 2.1) weeks p = .0001; cervical length after 1 week of treatment (27.5 ± 5.5 versus 20.7 ± 3.1) mm p = .0001; low birth weight 12 (29.3%) versus 19 (57.6%) p = .01; and NICU admission 9 (22%) versus 15 (45.5%), were significantly different between the two groups. No significant differences were found between neonatal death 1 (2.4%) versus 2 (6.1%), p = .43; RDS 5 (12.2%) versus 8 (24.2%), p = .17; and need to mechanical ventilator 2 (5.4%) versus 6 (18.2%) p = .136, for the progesterone and placebo groups, respectively.Conclusion: Daily administration of 400 mg vaginal progesterone after successful parenteral tocolysis may increase latency preceding delivery and improves cervical shortening and neonatal outcome in women with preterm labor. Further confirmatory studies are warranted.

Sharpey-Schafer Lecture 2019: From retroviruses to human birth

NEW FINDINGS

What is the topic of this review? The timing of birth is an important determinant of future health and well-being. This review examines the role of endogenous retroviruses as upstream regulators of key biological functions of the placenta, including cell-cell fusion, modulation of the maternal immune system, and the production of key pregnancy hormones. What advances does it highlight? Endogenous retroviruses are an obligate requirement for successful human reproduction. The products of retroviral elements, incorporated into the germline millions of years ago, have been co-opted to serve vital biological roles within the placenta that ultimately dictate the length of human pregnancy and therefore well-being trajectories.

ABSTRACT

Gestational length at the time of birth is an important determinant of future health and well-being, yet the physiological regulation of the onset of labour in humans remains obscure. The evolution of egg formation and internal fertilisation in amniotes required a mechanism to suppress the contractile activity of the oviduct that is provided by progesterone. Delivery of the egg is then associated with the withdrawal of progesterone and a return of contractile activity to the reproductive tract. In mammals, the process of pregnancy is complicated further by the need to protect the fetus from potential attack by the maternal immune system. There is increasing evidence that retroviruses incorporated into the mammalian germline in the evolutionary past play a key role in suppressing the maternal immune reaction to the developing conceptus, organising the development of the placenta and perhaps, in humans, modulating the action of progesterone, determining gestational length and the onset of labour. It seems that the presence of an endogenous retrovirus is an obligate requirement for human reproduction.

Prenatal resident-intruder stress decreases levels of allopregnanolone in the cortex, hypothalamus, and midbrain of males, and increases levels in the hippocampus and cerebellum of female, juvenile rat offspring

Prenatal stress (PNS) can influence behaviors associated with cognition, reward and emotional regulation, which are controlled by brain areas such as the cortex, hippocampus, hypothalamus, midbrain and cerebellum. Allopregnanolone in these regions modulates behavioral and parasympathetic effects. The current study tested whether exposing pregnant dams to 5 days of resident-intruder stress on prenatal days 15-20 for 10 min altered the levels of allopregnanolone in cortex, hypothalamus, hippocampus, midbrain, and cerebellum of male and female juvenile offspring. In cortex, hypothalamus, and midbrain of male rats exposed to prenatal stress, levels of allopregnanolone were significantly lower compared to all other groups. In the hippocampus and cerebellum, among females exposed to prenatal stress levels were significantly higher compared to all other groups. These differences in allopregnanolone levels varying by prenatal stress, sex and brain regions provide insight in potential mechanism of stress regulation and etiopathophysiology of stress-related disorders.

Deleterious genetic variants in ciliopathy genes increase risk of ritodrine-induced cardiac and pulmonary side effects

Background

Ritodrine is a commonly used tocolytic to prevent preterm labour. However, it can cause unexpected serious adverse reactions, such as pulmonary oedema, pulmonary congestion, and tachycardia. It is unknown whether such adverse reactions are associated with pharmacogenomic variants in patients.

Methods

Whole-exome sequencing of 13 subjects with serious ritodrine-induced cardiac and pulmonary side-effects was performed to identify causal genes and variants. The deleterious impact of nonsynonymous substitutions for all genes was computed and compared between cases (n = 13) and controls (n = 30). The significant genes were annotated with Gene Ontology (GO), and the associated disease terms were categorised into four functional classes for functional enrichment tests. To assess the impact of distributed rare variants in cases with side effects, we carried out rare variant association tests with a minor allele frequency ≤ 1% using the burden test, the sequence Kernel association test (SKAT), and optimised SKAT.

Results

We identified 28 genes that showed significantly lower gene-wise deleteriousness scores in cases than in controls. Three of the identified genes—CYP1A1, CYP8B1, and SERPINA7—are pharmacokinetic genes. The significantly identified genes were categorized into four functional classes: ion binding, ATP binding, Ca²⁺-related, and ciliopathies-related. These four classes were significantly enriched with ciliary genes according to SYSCILIA Gold Standard genes (P < 0.01), thus representing ciliary genes. Furthermore, SKAT showed a marginal trend toward significance after Bonferroni correction with Joubert Syndrome ciliopathy genes (P = 0.05). With respect to the pharmacokinetic genes, rs1048943 (CYP1A1) and rs1804495 (SERPINA7) showed a significantly higher frequency in cases than controls, as determined by Fisher’s exact test (P < 0.05 and P < 0.01, respectively).

Conclusions

Ritodrine-induced cardiac and pulmonary side effects may be associated with deleterious genetic variants in ciliary and pharmacokinetic genes.

Progesterone in normal and pathological pregnancy

Progesterone is an essential hormone in the process of reproduction. It is involved in the menstrual cycle, implantation and is essential for pregnancy maintenance. It has been proposed and extensively used in the treatment of different gynecological pathologies as well as in assisted reproductive technologies and in the maintenance of pregnancy. Called "the pregnancy hormone", natural progesterone is essential before pregnancy and has a crucial role in its maintenance based on different mechanisms such as: modulation of maternal immune response and suppression of inflammatory response (the presence of progesterone and its interaction with progesterone receptors at the decidua level appears to play a major role in the maternal defense strategy), reduction of uterine contractility (adequate progesterone concentrations in myometrium are able to counteract prostaglandin stimulatory activity as well as oxytocin), improvement of utero-placental circulation and luteal phase support (it has been demonstrated that progesterone may promote the invasion of extravillous trophoblasts to the decidua by inhibiting apoptosis of extravillous trophoblasts). Once the therapeutic need of progesterone is established, the key factor is the decision of the best route to administer the hormone and the optimal dosage determination. Progesterone can be administered by many different routes, but the most utilized are oral, the vaginal and intramuscular administration. The main uses of progesterone are represented by: threatened miscarriage, recurrent miscarriage and preterm birth (in the prevention strategy, as a tocolytic agent and also in the maintenance of uterine quiescence).

Preterm labor: current pharmacotherapy options for tocolysis

INTRODUCTION

In the developed world, preterm birth is in quantity and in severity the most important issue in obstetric care. Adverse neonatal outcome is strongly related to gestational age at delivery. Since the pathophysiological mechanism of preterm birth is not yet completely unraveled, the development of successful preventive strategies is hampered. When preterm labor is actually threatening, current pharmacological therapies focus on inhibition of preterm contractions. This allows for transportation of the mother to a center with a neonatal intensive care unit and administration of corticosteroids to enhance fetal lung maturation. Globally, however, large practice variation exists.

AREAS COVERED

The aim of this review is to provide an overview of current pharmacological therapies for preterm labor.

EXPERT OPINION

For the initial tocolysis, the use of atosiban or nifedipine for 48 h is recommended based on the largest effectiveness and most favorable side effect profile. However, since data that convincingly indicate the beneficial effect of tocolytics on neonatal outcome are lacking, it might well be that tocolytics are ineffective. The role of progesterone in treatment of acute tocolysis is limited, but it might play a role in the prevention of preterm labor or as sensitizer for other tocolytic agents.

Progesterone inhibition of oxytocin signaling in endometrium

Expression of the oxytocin receptor (OXTR) in the endometrium of ruminant species is regulated by the ovarian steroids progesterone (P) and estradiol (E). Near the end of the estrous cycle, long-term exposure of endometrial epithelial cells to P results in loss of genomic P receptors (PGRs), leading to an increase in E receptors (ERs). Genomic regulation of the OXTR is mediated via suppression of ER signaling by P. Upon OT binding at the plasma membrane of endometrial cells, a signaling cascade is generated stimulating release of prostaglandin F2α (PGF2α). Transport of PGF2α to the ovary results in release of OT by luteal cells in a positive feedback loop leading to luteal regression. This signaling cascade can be rapidly blocked by exposing endometrial cells to physiologic levels of P. This mini review will focus on the mechanisms by which P may act to block OXTR signaling and the luteolytic cascade in the ruminant endometrium, with special focus on both non-genomic signaling pathways and non-receptor actions of P at the level of the plasma membrane. While this review focuses on ruminant species, non-classical blockage of OXTR signaling may be important for fertility in women.

Effects of progesterone treatment on expression of genes involved in uterine quiescence

An important action of progesterone during pregnancy is to maintain the uterus in a quiescent state and thereby prevent preterm labor. The causes of preterm labor are not well understood, so progesterone action on the myometrium can provide clues about the processes that keep the uterus from contracting prematurely. Accordingly, we have carried out Affymetrix GeneChip analysis of progesterone effects on gene expression in immortalized human myometrial cells cultured from a patient near the end of pregnancy. Progesterone appears to inhibit uterine excitability by a number of mechanisms, including increased expression of calcium and voltage-operated K(+) channels, which dampens the electrical activity of the myometrial cell, downregulation of agents, and receptors involved in myometrial contraction, reduction in cell signal components that lead to increased intracellular Ca(2+) concentrations in response to contractile stimuli, and downregulation of proteins involved in the cross-linking of actin and myosin filaments to produce uterine contractions.

Prenatal Stress Alters Progestogens to Mediate Susceptibility to Sex-Typical, Stress-Sensitive Disorders, such as Drug Abuse: A Review

Maternal-offspring interactions begin prior to birth. Experiences of the mother during gestation play a powerful role in determining the developmental programming of the central nervous system. In particular, stress during gestation alters developmental programming of the offspring resulting in susceptibility to sex-typical and stress-sensitive neurodevelopmental, neuropsychiatric, and neurodegenerative disorders. However, neither these effects, nor the underlying mechanisms, are well understood. Our hypothesis is that allopregnanolone, during gestation, plays a particularly vital role in mitigating effects of stress on the developing fetus and may mediate, in part, alterations apparent throughout the lifespan. Specifically, altered balance between glucocorticoids and progestogens during critical periods of development (stemming from psychological, immunological, and/or endocrinological stressors during gestation) may permanently influence behavior, brain morphology, and/or neuroendocrine-sensitive processes. 5α-reduced progestogens are integral in the developmental programming of sex-typical, stress-sensitive, and/or disorder-relevant phenotypes. Prenatal stress (PNS) may alter these responses and dysregulate allopregnanolone and its normative effects on stress axis function. As an example of a neurodevelopmental, neuropsychiatric, and/or neurodegenerative process, this review focuses on responsiveness to drugs of abuse, which is sensitive to PNS and progestogen milieu. This review explores the notion that allopregnanolone may effect, or be influenced by, PNS, with consequences for neurodevelopmental-, neuropsychiatric-, and/or neurodegenerative- relevant processes, such as addiction.

Evidence that corticotropin-releasing hormone modulates myometrial contractility during human pregnancy

As human pregnancy advances, CRH increases exponentially and is hypothesized to trigger the transition from myometrial quiescence to active contractions at labor. Paradoxically, CRH stimulates cAMP production, suggesting it should cause relaxation. To evaluate CRH as a mediator of quiescence, the effect of CRH on contractions in preterm and term myometria with concurrent progesterone (P4) was determined. In late gestation, we hypothesized that high concentrations of CRH down-regulate agonist-activated-cAMP relaxatory pathways and that increased phosphodiesterase (PDE) activity induces heterologous down-regulation of agonist-activated-cAMP pathways. CRH caused dose-dependent relaxation of spontaneously contracting myometrial strips of 31 +/- 8% (mean +/- sem; n = 12) and 35 +/- 20% (n = 3) in term and preterm samples, respectively. CRH with P4 pretreatment caused a 40 +/- 13% (n = 4) reduction in contractility, whereas in matched samples, CRH alone exerted a 26 +/- 6% (n = 4) reduction, with a shift of CRH dose-response curves (P < 0.01, ANOVA). Pretreatment of strips with 10(-7) m CRH did not attenuate relaxation induced by subsequent CRH (n = 3) or salbutamol (beta(2)-agonist) treatment (n = 9). PDE inhibition by rolipram showed a 2.2- and 1.5-fold increase in maximal relaxation induced by CRH and salbutamol, respectively, with a shift of both dose-response curves (P < 0.05 and P < 0.01, ANOVA). In conclusion, CRH at physiological concentrations acts synergistically with P4 contributing to myometrial quiescence. P4 withdrawal may reduce CRH-mediated relaxation. Our functional model does not support homologous or heterologous down-regulation of agonist-stimulated-cAMP pathways by high CRH concentrations. PDE inhibition potentiates CRH and salbutamol-induced relaxation. Up-regulation of PDEs, through chronic cAMP elevation by CRH, could provide a mechanism for down-regulation of agonist-stimulated-cAMP pathways at term.

Progesterone decreases the relaxing effect of the beta3-adrenergic receptor agonist BRL 37344 in the pregnant rat myometrium

Although the published results regarding the function of the beta(3)-adrenergic receptors (beta(3)-ARs) in the regulation of smooth muscle activity are very promising, the question of the mechanism of beta(3)-ARs' action in the pregnant myometrium cannot be fully answered by human investigations. To assess whether it possesses an essential role in the regulation of uterine contractility in pregnant rats, as in humans, we performed functional, western blotting and molecular biology experiments on the late-pregnant rat myometrium. The influence of progesterone on the function of the beta(3)-ARs was also investigated. We demonstrated the presence and the functional activity of the beta(3)-ARs in the late-pregnant rat myometrium. The maximum dose-dependent uterus-relaxing effect of the selective beta(3)-agonist BRL 37344 was recorded at the end of pregnancy in rats, similarly as in humans. The extent of its relaxing action was regarded as moderate. The expression of beta(3)-AR protein and mRNA remained unchanged during the investigated period. The administration of progesterone had no effect on the beta(3)-AR mRNA and protein expression or the maximum relaxation effect of BRL 37344, but shifted the dose-response curve to the right and decreased the synthesis of the second messenger, cAMP. It can be concluded that the beta(3)-ARs play an additional role in the regulation of the contractile activity of the pregnant rat uterus. The inhibitory effect of progesterone on the functional activity of the beta(3)-ARs may have important consequences in the case of human application if this effect is also demonstrated in pregnant human myometrial tissue.

PROGESTERONE AND THE CONTROL OF HUMAN PREGNANCY AND PARTURITION

Almost 80 years ago George Corner and colleagues provided the first evidence that progesterone maintains pregnancy and that it does so, at least in part, by promoting myometrial relaxation. In the 1950s, Arpad Csapo proposed the “progesterone block hypothesis”, which posits that progesterone maintains pregnancy by promoting myometrial relaxation and that its withdrawal initiates a cascade of hormonal interactions that transforms the myometrium to a highly contractile state leading to the onset of labour. Csapo later proposed that contractility of the pregnant myometrium is determined by the balance between relaxation induced by progesterone and contraction induced by a cohort of signals including oestrogens, uterine distention and stimulatory uterotonins such as prostaglandins (PGs) and oxytocin (OT). According to this “seesaw” hypothesis, progesterone promotes myometrial relaxation by directly inducing relaxation and/or by inhibiting the production of, or myometrial responsiveness to, stimulatory uterotonins. These landmark concepts, though derived from studies of experimental animals, form the foundation for current understanding of progesterone's role in the physiology of human pregnancy. Remarkable progress has been made over the last 20–30 years in understanding the signal transduction pathways through which steroid hormones affect target cells. This knowledge has broadened the scope of Csapo's original paradigms and we are now beginning to unravel the specific signaling pathways and molecular interactions by which progesterone affects human myometrium and how its actions are controlled at the functional level. This is important for the development of progestin-based therapeutics for the prevention or suppression of preterm labour and preterm birth. Here we review recent progress in understanding the mechanisms by which progesterone sustains pregnancy and in particular how it promotes myometrial relaxation, how its relaxatory actions are nullified at parturition, and the hormonal interactions that induce progesterone withdrawal to determine the timing of human birth.

Progestational agents for the prevention of preterm birth

Abstract In a risk/benefit analysis, currently the use of PAs used in women with a previous history of PTB appears to be worthwhile though the impact on the PTB rate may be minor since 80-90% of women who deliver preterm have no past history. PTB is a heterogeneous condition. With the exception of extremes of gestational age, PTB is due in equal parts to SPTL, preterm prelabour rupture of the membranes (PPROM) and elective PTB for fetomaternal indications. The assessment of the use of PAs to prevent PTB should only relate to previous and subsequent SPTL and not to PTB due to fetomaternal indications.

Preventing cervical ripening: the primary mechanism by which progestational agents prevent preterm birth?

OBJECTIVE

Recent clinical trials suggest that progestational agents may prevent preterm birth, specifically in women with short cervices. These studies sought to assess novel pathways by which progestational agents (PAs) may modify signal transduction pathways that are involved in cervical ripening.

STUDY DESIGN

A microarray analysis was performed on pregnant mouse cervix that was exposed to a MPA. Appropriate microarray and cluster analyses were performed. Target genes of interest were investigated in both PA- and inflammation-exposed cervices by quantitative polymerase chain reaction and immunohistochemistry.

RESULTS

Microarray analysis identified both the previously recognized and novel pathways that are involved in cervical ripening. PAs differentially regulate expression of claudin-2, hyaluronan synthase 2, and lipocalin 2. Claudin expression is significantly decreased by inflammation, which is prevented by PAs.

CONCLUSION

PAs significantly modulate gene expression in the cervix in the presence and absence of inflammation. The regulation of these pathways, specifically claudin proteins, may be a critical mechanism by which PAs prevent preterm birth, especially in women with premature cervical shortening.

Gestagen treatment enhances the tocolytic effect of salmeterol in hormone-induced preterm labor in the rat in vivo

OBJECTIVE

The purpose of this study was to determine whether gestagen treatment enhances the effects of beta2-mimetics in hormone-induced preterm delivery in pregnant rats in vivo.

STUDY DESIGN

Preterm birth was induced with a combination of mifepristone and prostaglandin E2 on day 19 of pregnancy. The animals were treated with salmeterol or gestagens (progesterone or 17alpha-hydroxyprogesterone) or their combination. The treatments were launched on different days (15-18) of pregnancy. The efficacy of treatment was determined in terms of the delivery time counted from the mifepristone injection.

RESULTS

Salmeterol treatment delayed premature labor by 2.4 hours, whereas the delay because of the gestagen-salmeterol combinations was more than 5 hours. Progesterone had no effect on the delivery time.

CONCLUSION

Parallel treatment with salmeterol and gestagens can be more than twice as effective as salmeterol therapy alone. These results open up a possibility for human trials of combined beta2-agonist-gestagen therapy in threatening preterm delivery.

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.

Setting up a preterm prevention clinic: a practical guide

In gynaecology, specialist menopause, urogynae, colposcopy, infertility, pelvic pain and cancer, rapid access clinics exist at many teaching and busy district general hospitals in the UK. Similarly, in obstetrics many busy maternity units have fetal medicine clinics, dedicated twins clinics and maternal medicine clinics, incorporating various general medical conditions and conditions peculiarly appropriate to pregnancy such as haematological disorders, diabetes and epilepsy. In contrast, in very few hospitals is there a dedicated clinic for women at increased risk of preterm birth, yet this is the major cause of neonatal mortality and morbidity in the developed world. Such a situation may be due to the confusion created by the fact that preterm birth is a heterogeneous condition with multiple aetiologies and hence multiple therapeutic interventions. It is possible to identify a group of women at particularly high risk of preterm birth in whom screening and interventional techniques have the potential to reduce the mortality and morbidity associated with spontaneous preterm labour and preterm birth.

Emerging drug therapies for preventing spontaneous preterm labor and preterm birth

Preterm birth (PTB) is the main cause of neonatal mortality and morbidity in the developed world. Historically, the approach for the prevention of PTB has been reactive rather than proactive. With the introduction of new screening tests and a greater emphasis on prevention rather than treatment, a number of new approaches have been introduced that show promise. Progesterone, which is responsible for myometrial quiescence in pregnancy and is used in women with a previous history of PTB, is associated with a significant reduction in the incidence of PTB and low birth weight. Infection is an important cause of PTB in < or = 40% of women. The appropriate antibiotics administered early in pregnancy to women with abnormal genital tract flora have been associated with a 40-60% reduction in the incidence of PTB. Although there has been debate regarding the benefits of nutritional supplementation for the prevention of many complications of pregnancy, recent evidence suggests that fish oil supplementation can be shown to reduce the incidence of PTB in women at risk of PTB. Although these three proactive, preventative approaches show promise, further research is needed to establish the best agent, the optimum gestational age at commencement and cessation, the ideal candidate patient to achieve a response and the long-term feto-maternal benefits and/or side effects.

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.

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.

Examining the spatio-temporal expression of mRNA encoding the membrane-bound progesterone receptor-alpha isoform in human cervix and myometrium during pregnancy and labour

Human parturition is associated with a modification in the sensitivity of the myometrium to progesterone. The molecular basis for this change, however, remains unclear. It is well documented that progesterone can exert its effects through non-genomic mechanisms, including acting through membrane-bound progesterone receptors (mPRs). Recently, a novel membrane-bound PR, termed mPRalpha, was cloned. mPRalpha was unlike any other PR in the databases, but it was seen to have significant homology to G-protein-coupled receptors (GPCR). In this study, we examined the spatio-temporal expression of mPRalpha mRNA in human cervix and both lower and upper myometrial segments from non-pregnant (NP), pregnant (P) and spontaneously labouring (SL) women. We observed an incremental increase in mPRalpha mRNA expression in NP and P samples with the peak level being observed in SL tissues. No major differences were observed between upper or lower pregnant myometrial regions. Interestingly, levels of mPRalpha transcripts were substantially greater in labouring lower segment myometrium compared with labouring upper segment. Significantly, we failed to detect mPRalpha message in either unripe or ripe human cervices. These data suggest that mPRalpha protein function may play a role in regulating lower segment myometrial activity during labour. Whether it functions in the cervix, however, remains unclear.

Role of progestogens for the prevention of premature birth

Premature birth represents a major cause of perinatal morbidity and mortality. The short- and long-term sequelae of prematurity have serious consequences for newborn survival and health in later life. In addition, prematurity is a major problem with regard to health expenditure. Despite major progress in obstetrics, perinatology and neonatology, the percentage of premature birth persists and there is even a tendency towards a slight increase. Therefore, besides screening programmes for the detection of vaginal infections, additional therapeutic opportunities must be sought. According to previously published data, vaginal progesterone and intramuscular 17alpha-hydroxyprogesterone caproate should be considered possible treatment options for the prevention of preterm delivery.