Myometrial steroid concentration and oxytocin receptor density in parturient women at term

Neurosteroid involvement in threatened preterm labour

Introduction

The neurosteroid allopregnanolone modulates oxytocin expression in the brain, and its effects arise from its action on the GABAA receptor. Whether neurosteroid levels and the function of the GABAA receptor are involved in the risk of preterm labour in pregnant women is unknown.

Methods

Pregnant women with (n = 16) or without (n = 20) threatened preterm labour (TPL) in gestational week 33 + 6 days to 37 + 0 days were studied prospectively with procedures including foetal heart rate monitoring, vaginal examination, ultrasound examination and blood tests to determine allopregnanolone, progesterone and oxytocin levels. The GABAA receptor function in both groups was measured with a saccadic eye velocity test (SEVT).

Results

Plasma oxytocin levels were higher in the TPL group than in the control group (41.5 vs. 37.0 pmol/L, respectively, p = .021). Although the allopregnanolone and progesterone levels in both groups did not differ, there was a negative association between blood oxytocin and allopregnanolone (as predictor) levels in the TPL group (B: -3.2, 95% confidence interval (CI): -5.5 to -0.9, p = .012). As a predictor of TPL, progesterone was associated with cervix maturity (odds ratio: 1.02, 95% CI: 1.00-1.04, p = .038). SEVT showed that the women in both groups had similar GABAA receptor functions. In both groups, body mass index correlated with peak saccadic eye velocity (r = .34, p = .044) and negatively with allopregnanolone (r = -.41, p = .013).

Conclusions

Neurosteroid levels were unchanged in the peripheral blood of women with TPL, despite the increase in available oxytocin. Although the function of the GABAA receptor was unchanged in women with TPL, to ensure reliable results, saccadic eye velocity should be investigated during a challenge test with a GABAA receptor agonist.

The impact of progesterone and RU-486 on classic pro-labour proteins & contractility in human myometrial tissues during 24-hour exposure to tension & interleukin-1β

Increased expression of pro-labour genes that encode cyclooxygenase-2 (COX-2), oxytocin receptor (OTR) and connexin-43 (Cx43) at parturition is often attributed to P4 functional withdrawal, based on findings from animal models and human primary myometrial cells. However, the cause of reduced myometrial P4 responsiveness that promotes contractions at labour is not fully determined. Uterine stretch occurs with advancing gestation but most in vitro experimental models do not take this into consideration. We aimed to examine whether tissue-level myometrial stretch influences the ability of P4 to regulate pro-labour protein abundance by using myometrial biopsies from term gestation pregnant women to assess the impact of 24 h exposure to combinations of (i) stretch-mediated tension, (ii) P4 (100 nM) and (iii) an anti-progestin, RU-486 (1 μM). Firstly, we observed baseline COX-2 and Cx43 protein levels increased, whereas P4 content along with calponin-1 and progesterone receptor (PR) protein abundance decreased, in vehicle-treated tissues. P4 supplementation subtly reduced COX-2 levels in un-stretched tissues. Spontaneous and oxytocin-augmented contractility were unchanged by tissue culture exposure to P4 and/or RU-486. Interleukin-1β (IL-1β; 1 ng/ml) enhanced COX-2 protein and PGE₂ content in un-stretched tissues. Overall, tissue stretch may, in part, regulate P4-sensitive pro-labour protein levels, but this is likely to be reliant on interaction with other in utero factors that were absent in our tissue cultures. More complex culture conditions should be evaluated in future to aid further development of a physiologically relevant model to improve our understanding of in utero myometrial P4 responsiveness.

Prostaglandin-Endoperoxide Synthase 1 Mediates the Timing of Parturition in Mice Despite Unhindered Uterine Contractility

Cyclooxygenase (COX)-derived prostaglandins stimulate uterine contractions and prepare the cervix for parturition. Prior reports suggest Cox-1 knockout (KO) mice exhibit delayed parturition due to impaired luteolysis, yet the mechanism for late-onset delivery remains unclear. Here, we examined key factors for normal onset of parturition to determine whether any could account for the delayed parturition phenotype. Pregnant Cox-1KO mice did not display altered timing of embryo implantation or postimplantation growth. Although messenger RNAs of contraction-associated proteins (CAPs) were differentially expressed between Cox-1KO and wild-type (WT) myometrium, there were no differences in CAP agonist-induced intracellular calcium release, spontaneous or oxytocin (OT)-induced ex vivo uterine contractility, or in vivo uterine contractile pressure. Delayed parturition in Cox-1KO mice persisted despite exogenous OT treatment. Progesterone (P4) withdrawal, by ovariectomy or administration of the P4-antagonist RU486, diminished the delayed parturition phenotype of Cox-1KO mice. Because antepartum P4 levels do not decline in Cox-1KO females, P4-treated WT mice were examined for the effect of this hormone on in vivo uterine contractility and ex vivo cervical dilation. P4-treated WT mice had delayed parturition but normal uterine contractility. Cervical distensibility was decreased in Cox-1KO mice on the day of expected delivery and reduced in WT mice with long-term P4 treatment. Collectively, these findings show that delayed parturition in Cox-1KO mice is the result of impaired luteolysis and cervical dilation, despite the presence of strong uterine contractions.

Stopping Oxytocin in Active Labor Rather Than Continuing it until Delivery: A Viable Option for the Induction of Labor

OBJECTIVE

Induction of labor (IOL), using intravenous oxytocin, is the artificial initiation of labor before its spontaneous onset for the purpose of delivery of the fetoplacental unit. Although there are various studies looking at dosages of oxytocin, only a few have addressed the issue of discontinuation of oxytocin in the active stage of labor. Thus, our study was conducted to evaluate the need for continuation versus discontinuation of oxytocin during active labor.

METHODS

This prospective, randomized controlled trial included 106 women who needed IOL. Oxytocin infusion was initiated at a rate of 3mIU/min and was incremental until 4-6cm cervical dilation. At this point the patients were randomly assigned into one of two groups. In group one, oxytocin was discontinued, and infusion was continued with 0.9% sodium chloride solution. In group two, oxytocin was continued at the same dose until delivery.

RESULTS

The duration of oxytocin infusion was 5.5 hours in the oxytocin discontinuation group and 11.0 hours in oxytocin continuation group (p<0.001). The total dose of oxytocin was significantly higher in group two (6.1 units vs. 16.5 units; p=<0.001). The induction-delivery interval was significantly less in group one (9.1 and 11.2 hours in group one and group two, respectively; p=0.023).

CONCLUSION

Oxytocin discontinuation in the active stage of labor did not prolong the active stage. The total duration of labor and total oxytocin dose were significantly less in the oxytocin discontinuation group. Our results suggest that oxytocin discontinuation is an alternative and viable option particularly in resource poor and economically challenged settings. It not only reduces the need for intense monitoring and prolonged oxytocin use-associated dangers but reduces the total cost of labor management.

Functional interactions between the oxytocin receptor and the β2-adrenergic receptor: implications for ERK1/2 activation in human myometrial cells

The Gq-coupled oxytocin receptor (OTR) and the Gs-coupled β(2)-adrenergic receptor (β(2)AR) are both expressed in myometrial cells and mediate uterine contraction and relaxation, respectively. The two receptors represent important pharmacological targets as OTR antagonists and β(2)AR agonists are used to control pre-term uterine contractions. Despite their physiologically antagonistic effects, both receptors activate the MAP kinases ERK1/2, which has been implicated in uterine contraction and the onset of labor. To determine the signalling pathways involved in mediating the ERK1/2 response, we assessed the effect of blockers of specific G protein-associated pathways. In human myometrial hTERT-C3 cells, inhibition of Gαi as well as inhibition of the Gαq/PKC pathway led to a reduction of both OTR- and β(2)AR-mediated ERK1/2 activation. The involvement of Gαq/PKC in β(2)AR-mediated ERK1/2 induction was unexpected. To test whether the emergence of this novel signalling mechanism was dependent on OTR expression in the same cell, we conducted experiments in HEK 293 cells that were transfected with the β(2)AR alone or co-transfected with the OTR. Using this approach, we found that β(2)AR-mediated ERK1/2 responses became sensitive to PKC inhibition only in cells co-transfected with the OTR. Inhibitor studies indicated the involvement of an atypical PKC isoform in this process. We confirmed the specific involvement of PKCζ in this pathway by assessing PKCζ translocation to the cell membrane. Consistent with our inhibitor studies, we found that β(2)AR-mediated PKCζ translocation was dependent on co-expression of OTR. The present demonstration of a novel β(2)AR-coupled signalling pathway that is dependent on OTR co-expression is suggestive of a molecular interaction between the two receptors.

Regulation of oxytocin receptor responsiveness by G protein-coupled receptor kinase 6 in human myometrial smooth muscle

Oxytocin plays an important role in the progression, timing, and modulation of uterine contraction during labor and is widely used as an uterotonic agent. We investigated the mechanisms regulating oxytocin receptor (OTR) signaling in human primary myometrial smooth muscle cells and the ULTR cell-line. Oxytocin produced concentration-dependent increases in both total [(3)H]inositol phosphate accumulation and intracellular Ca(2+) concentration ([Ca(2+)](i)); however, responses were greater and more reproducible in the ULTR cell line. Assessment of phospholipase C activity in single cells revealed that the OTR desensitizes rapidly (within 5 min) in the presence of oxytocin (100 nm). To characterize OTR desensitization further, cells were stimulated with a maximally effective concentration of oxytocin (100 nm, 30 sec) followed by a variable washout period and a second identical application of oxytocin. This brief exposure to oxytocin caused a marked decrease (>70%) in OTR responsiveness to rechallenge and was fully reversed by increasing the time period between agonist challenges. To assess involvement of G protein-coupled receptor kinases (GRKs) in OTR desensitization, cells were transfected with small interfering RNAs to cause specific > or =75% knockdown of GRKs 2, 3, 5, or 6. In both primary myometrial and ULTR cells, knockdown of GRK6 largely prevented oxytocin-induced OTR desensitization; in contrast, selective depletion of GRKs 2, 3, or 5 was without effect. These data indicate that GRK6 recruitment is a cardinal effector of OTR responsiveness and provide mechanistic insight into the likely in vivo regulation of OTR signaling in uterine smooth muscle.

[Spontaneous uterine rupture of an unscarred uterus during labor: case report and review of the literature]

Uterine rupture during labor is a serious and uncommon obstetrical complication that can lead to severe prognosis for the mother and her child if not immediately diagnosed and treated. Most spontaneous uterine ruptures occur during labor in parturients with a scarred uterus and are much rarer on an unscarred uterus. We report the case of a uterine rupture on unscarred uterus to a 32 year-old woman after a labor induced by intravaginal prostaglandin and intravenous ocytocine injection. Our management is compared with the data from literature.

Use of a novel and highly selective oxytocin receptor antagonist to characterize uterine contractions in the rat

Spontaneous and induced uterine contractions in the rat were found to be inhibited by a novel and selective oxytocin receptor antagonist GSK221149A (3R,6R)-3-Indan-2-yl-1-[(1R)-1-(2-methyl-1,3-oxazol-4-yl)-2-morpholin-4-yl-2-oxoethyl]-6-[(1S)-1-methylpropyl]-2,5-piperazinedione. GSK221149A displayed nanomolar affinity (K(i) = 0.65 nM) for human recombinant oxytocin receptors with >1,400-fold selectivity over human V1a, V1b, and V2 receptors. GSK221149A had similar affinity (K(i) = 4.1 nM) and selectivity for native oxytocin receptors from rat and produced a functional, competitive block of oxytocin-induced contractions in isolated rat myometrial strips with a pA(2) value of 8.18. Intravenous administration of GSK221149A produced a dose-dependent decrease in oxytocin-induced uterine contractions in anesthetized rats with an ID(50) = 0.27 +/- 0.60 mg/kg (corresponding plasma concentrations were 88 ng/ml). Oral administration of GSK221149A (5 mg/kg) was effective in inhibiting oxytocin-induced uterine contractions after single and multiple (4-day) dosing. Spontaneous uterine contractions in late-term pregnant rats (19-21 days gestation) were significantly reduced by intravenous administration of 0.3 mg/kg of GSK221149A. These results provide further evidence that selective oxytocin receptor antagonism may offer an effective treatment for preterm labor.

Oxytocin for induction of labor

Oxytocin is the most common pharmacologic agent used for the induction and augmentation of labor. Oxytocin protocols can be divided into high-dose and low-dose protocols depending on the initial dose and the amount and rate of sequential increase in dose. Despite the frequency with which oxytocin in used in clinical practice, there is little consensus regarding which protocol is most appropriate. The purpose of this chapter is to review the most current data concerning recommendations for the use of oxytocin in the induction of labor, including cases of intrauterine fetal demise and vaginal birth after cesarean.

Targeting the oxytocin receptor to relax the myometrium

Oxytocin acting via its receptor is involved in the myometrial hyperactivity of preterm labour and possibly also in that of primary dysmenorrhoea. The closely related hormone vasopressin acting on its uterine receptor of type V1a may also contribute to the myometrial hyperactivity of these conditions. Several pharmaceutical compounds inhibiting these receptors are, therefore, under development and one substance, atosiban, has now been registered in many countries for the treatment of preterm labour. This compound blocks both the oxytocin and the vasopressin V1a receptor. The efficacy is at least as pronounced as that of other types of drugs and side effects are much reduced. In this overview, present knowledge about receptor-mediated effects of oxytocin and vasopressin on myometrial activity is summarised. Furthermore, the therapeutic use of oxytocin and vasopressin V1a receptor antagonists in preterm labour and primary dysmenorrhoea is discussed.

Comparative routes of oxytocin administration in crated farrowing sows and its effects on fetal and postnatal asphyxia

Oxytocin is used to induce and control parturition; nevertheless, an increase in uterine contractions decreases blood flow and gaseous exchange through the uterus predisposing to intra-partum mortality in pigs. The objective of the present study was to evaluate the effect of different oxytocin administration routes on myometrial activity, fetal intrauterine hypoxia and postnatal asphyxia in crated farrowing sows. Yorkshire x Landrace hybrid sows (n = 300), that were approaching the time of parturition, were randomly assigned into six groups. Each group included 50 sows, 10 for each of the parities from one to five. A 40-IU oxytocin dosage was administered by intramuscular (IM), or intravulvar (IVU) routes, or 20 IU was administered via intravenous (IV) route. Groups 1 (G1), 3 (G3) and 5 (G5) were administered 0.9% saline solution (NaCl) IM, IVU and IV, respectively, whereas groups 2 (G2), 4 (G4) and 6 (G6) were treated with oxytocin IM, IVU and IV, respectively. There was a significantly (P < 0.05) greater number of intra-partum stillbirths (IPS) for the oxytocin treatments, as compared with the control groups, especially with the IVU and IV routes; a lesser number of IPS and lesser IPS with broken umbilical cords was observed with the IM administration route. Oxytocin and control IV administration resulted in longer farrowing durations. Administration of IV-oxytocin resulted in a greater number (P < 0.05) of intrauterine distressed neonates compared with its corresponding control and interpreted through dips II, a fetal cardiac frequency deceleration which determines acute fetal suffering. Independent of the route of oxytocin administration, the treatments resulted in twice as many dips II compared with the respective control groups. The use of the cardiotocograph proved to be an excellent tool for establishing the oxytocin response dose in farrowing sows. A greater number of piglets born alive, which had undergone bradycardia, also showed severe acidosis and greater meconium staining in oxytocin-treated sows, indicating that the administration time (at birth of the first piglet) as well as the dosage used were not adequate treatment regimens in the present study. Further studies will be conducted to evaluate different dosages and oxytocin administration timing to determine the most desirable treatment regimen to increase myometrial contractibility without compromising fetal welfare and neonatal survival.

Use of oxytocin in penned sows and its effect on fetal intra-partum asphyxia

The objective of the present study was to evaluate in penned sows the effect of two commercial oxytocin products on umbilical cord pathology, degree of asphyxia and intra-partum mortality. This study included 120 sows divided in three groups of 40 animals with eight animals for parities one to five per subgroup, respectively. Group 1 (G(1)) or control received saline solution while oxytocin groups (G(2)) and (G(3)) were injected at the onset of fetal expulsion with two oxytocin products. The doses of oxytocin were as follow: Primiparous sows weighing less than 130 kg received 20 IU; multiparous sows weighing 130-180 g received 30 IU, and those above 250 kg, 40 IU. Piglets born alive and/or dead were classified at birth using a subjective scale based on the degree of meconium staining on skin. Umbilical cords of intra-partum stillbirths (IPS) were classified as adhered or ruptured and subdivided into four categories: without pathological changes, edematous, congested and hemorrhagic. Result analyses revealed significant differences (P < 0.01) between groups 1 and 2, and 1 and 3 regarding the following traits: expulsion interval (min) (X: G(1) 27.7; G(2) 22.6; G(3) 22.2), IPS with a severe stain degree (X: G(1) 0.10; G(2) 0.45; G(3) 0.50), IPS with ruptured umbilical cords (X: G(1) 0.07; G(2) 0.42; G(3) 0.47), and detectable heartbeats in IPS (X: G(1) 0.27; G(2) 0.25; G(3) 0.22). Treatment with oxytocin reduced the duration of the expulsion of the fetus, increased the number of IPS with ruptured umbilical cords and with severe meconium-stain degree and reduced the number of fetuses with inspiration attempts. Furthermore, the use of this hormone increased the need for obstetric assistance due to increased frequency of dystocia.

Tocolysis with atosiban: experience in the management of premature labor before 24 weeks of pregnancy

OBJECTIVE

Atosiban has been shown to be an effective tocolytic agent with a low rate of side effects during 24 to 33 weeks of gestation. Atosiban acts through selective, competitive inhibition of both oxytocin and vasopressin, so that there are reasons to assume that a tocolytic effect can also be achieved earlier in the pregnancy.

STUDY DESIGN

In this prospective, randomized pilot study, 20 women in the 18th through 24th week of gestation who presented at our hospital with preterm labor were treated with atosiban. In the control group 20 women received saline infusions. All patients received antibiotic therapy. A cervical cerclage was performed when indicated as was correction of the vaginal pH.

RESULTS

The tocolytic effect began after 3-10 min (median: 6.5 min). Treatment time until the complete absence of contractions was 3-12 h (median: 7.5 h). Pregnancies were prolonged between 11.1 and 21.7 weeks (median: 15.6 weeks) in the atosiban group vs. 10.5-19.1 weeks in the control group. If well tolerated, atosiban was continued. There were no significant alterations in the routine laboratory parameters, circulation parameters, and fluid balance.

CONCLUSION

In summary, atosiban showed itself to be effective for tocolytic treatment for premature labor, even during 18 and 24 weeks of pregnancy, while exhibiting its known, favorable profile of side effects.

Spontaneous contractions of myometrium from humans, non-human primate and rodents are sensitive to selective oxytocin receptor antagonism in vitro

OBJECTIVES

To determine whether: 1. oxytocin receptor antagonists influence spontaneous contractions of myometrium from humans, non-human primates and rodents (in vitro), and 2. vasopressin V1a receptor antagonism is important for inhibition of spontaneous contractions in human myometrium.

DESIGN

In vitro pharmacology of spontaneous contractions of myometrium from humans and animals.

SETTING

The research laboratories of a university department of obstetrics and gynaecology and a pharmaceutical industry research centre.

INTERVENTIONS

Samples of human myometrium were obtained at caesarean section. Tissue strips were suspended in organ baths for isometric force recording. Cumulative concentration effect curves to a selective oxytocin receptor antagonist (L-371,257) and a mixed oxytocin/vasopressin V1a receptor antagonist (atosiban) were obtained. The effect of L-371,257 was also determined in myometrium from non-pregnant rats and marmosets.

MAIN OUTCOME MEASURES

The inhibition of spontaneous myometrial contractions in vitro.

RESULTS

L-371,257 and atosiban significantly inhibited spontaneous activity of human myometrium in a concentration-related manner (P < 0.05), although the effect was more pronounced with L-371,257. Spontaneous contractions of myometrium from non-pregnant rats and marmosets were also inhibited by L-371,257 (atosiban was not tested).

CONCLUSIONS

Spontaneous contractions of myometrium from humans, marmosets and rats are, at least in part, dependent on oxytocin receptor activity, in vitro. L-371,257 and atosiban may be inverse agonists. Selective non-peptide oxytocin receptor antagonists may be effective tocolytics.

Non-genomic effects of progesterone on the signaling function of G protein-coupled receptors

Progesterone at concentrations between 10 microM and 200 microM affected the calcium signaling evoked by ligand stimulation of G protein-coupled receptors expressed in several cell lines. At 160 microM progesterone the signaling of all receptors was completely abolished. The effect of progesterone was fast, reversible and was not prevented by cycloheximide indicating its non-genomic nature. Overall, the action of progesterone was more cell type-specific than receptor-specific. Our results are in contrast to a recent report [Grazzini, E., Guillon, G., Mouillac, B. and Zingg, H.H. (1998) Nature 392, 509-512] in which a direct high-affinity interaction between the oxytocin receptor and progesterone was suggested.

Role of corticotropin-releasing hormone in onset of labour

Corticotropin-releasing hormone (CRH) derived from the placenta is secreted into the maternal circulation in large amounts during the third trimester of human pregnancy and may have an important role in the onset of labour. Although the biological role of CRH remains enigmatic, the presence of functional CRH receptors in the myometrium suggests that CRH may modulate myometrial contractility and hence parturition. CRH action is mediated via multiple receptor subtypes and pregnancy results in differential receptor expression. These receptors are primarily linked to the adenylate cyclase second messenger system, which would help the intracellular microenvironment to maintain the required myometrial quiescence. CRH can exert further actions such as inhibition of prostaglandin production to prevent contractions. At term under the influence of oxytocin there is a modification in the coupling mechanisms that leads to a decrease in the biological activity of the CRH receptor and in the generation of cyclic adenosine monophosphate which favours myometrial contractions. CRH, via distinct receptor subtypes, is then able to enhance the contractile response of the myometrium. This hypothesis places CRH in a central role in coordinating the smooth transition from a state of relaxation to one of contraction.

Intracellular calcium stores and agonist-induced contractions in isolated human myometrium

OBJECTIVE

We hypothesized that the release of calcium from intracellular stores contributes to the contractions produced by the agonists oxytocin, carbachol, and prostaglandin F(2 )(alpha ) in human myometrium.

STUDY DESIGN

Strips of myometrium were obtained at cesarean section and hysterectomy. The strips were loaded with the calcium-sensitive dye Indo-1 to enable simultaneous measurement of tension and intracellular calcium levels. Agonist-induced responses in the presence and absence of extracellular calcium were studied.

RESULTS

Strips of myometrium were obtained from 48 women not in labor undergoing cesarean section and 6 women not pregnant undergoing hysterectomy. An increase in intracellular calcium level after agonist stimulation invariably preceded an increase in tension. Intracellular calcium level returned to baseline before myometrial relaxation. Oxytocin, carbachol, and prostaglandin F(2)(alpha) all gave both force and intracellular calcium responses in the absence of extracellular calcium, although both these responses were only 26% to 40% of the maximal response when extracellular calcium was present.

CONCLUSIONS

Release of calcium from internal stores induced by oxytocin, carbachol, and prostaglandin F(2)(alpha) may contribute to agonist-induced myometrial force production.