Effects of cGMP and the nitric oxide donors glyceryl trinitrate and sodium nitroprusside on contractions in vitro of isolated myometrial tissue from pregnant women

Arrest of mouse preterm labor until term delivery by combination therapy with atosiban and mundulone, a natural product with tocolytic efficacy

There is a lack of FDA-approved tocolytics for the management of preterm labor (PL). In prior drug discovery efforts, we identified mundulone and mundulone acetate (MA) as inhibitors of in vitro intracellular Ca2+-regulated myometrial contractility. In this study, we probed the tocolytic potential of these compounds using human myometrial samples and a mouse model of preterm birth. In a phenotypic assay, mundulone displayed greater efficacy, while MA showed greater potency and uterine-selectivity in the inhibition of intracellular-Ca2+ mobilization. Cell viability assays revealed that MA was significantly less cytotoxic. Organ bath and vessel myography studies showed that only mundulone exerted inhibition of myometrial contractions and that neither compounds affected vasoreactivity of ductus arteriosus. A high-throughput combination screen identified that mundulone exhibits synergism with two clinical-tocolytics (atosiban and nifedipine), and MA displayed synergistic efficacy with nifedipine. Of these combinations, mundulone+atosiban demonstrated a significant improvement in the in vitro therapeutic index compared to mundulone alone. The ex vivo and in vivo synergism of mundulone+atosiban was substantiated, yielding greater tocolytic efficacy and potency on myometrial tissue and reduced preterm birth rates in a mouse model of PL compared to each single agent. Treatment with mundulone after mifepristone administration dose-dependently delayed the timing of delivery. Importantly, mundulone+atosiban permitted long-term management of PL, allowing 71% dams to deliver viable pups at term (>day 19, 4-5 days post-mifepristone exposure) without visible maternal and fetal consequences. Collectively, these studies provide a strong foundation for the development of mundulone as a single or combination tocolytic for management of PL.

Arrest of mouse preterm labor until term delivery by combination therapy with atosiban and mundulone, a natural product with tocolytic efficacy

Currently, there is a lack of FDA-approved tocolytics for the management of preterm labor (PL). In prior drug discovery efforts, we identified mundulone and its analog mundulone acetate (MA) as inhibitors of in vitro intracellular Ca 2+ -regulated myometrial contractility. In this study, we probed the tocolytic and therapeutic potential of these small molecules using myometrial cells and tissues obtained from patients receiving cesarean deliveries, as well as a mouse model of PL resulting in preterm birth. In a phenotypic assay, mundulone displayed greater efficacy in the inhibition of intracellular-Ca 2+ from myometrial cells; however, MA showed greater potency and uterine-selectivity, based IC 50 and E max values between myometrial cells compared to aorta vascular smooth muscle cells, a major maternal off-target site of current tocolytics. Cell viability assays revealed that MA was significantly less cytotoxic. Organ bath and vessel myography studies showed that only mundulone exerted concentration-dependent inhibition of ex vivo myometrial contractions and that neither mundulone or MA affected vasoreactivity of ductus arteriosus, a major fetal off-target of current tocolytics. A high-throughput combination screen of in vitro intracellular Ca 2+ -mobilization identified that mundulone exhibits synergism with two clinical-tocolytics (atosiban and nifedipine), and MA displayed synergistic efficacy with nifedipine. Of these synergistic combinations, mundulone + atosiban demonstrated a favorable in vitro therapeutic index (TI)=10, a substantial improvement compared to TI=0.8 for mundulone alone. The ex vivo and in vivo synergism of mundulone and atosiban was substantiated, yielding greater tocolytic efficacy and potency on isolated mouse and human myometrial tissue and reduced preterm birth rates in a mouse model of PL compared to each single agent. Treatment with mundulone 5hrs after mifepristone administration (and PL induction) dose-dependently delayed the timing of delivery. Importantly, mundulone in combination with atosiban (FR 3.7:1, 6.5mg/kg + 1.75mg/kg) permitted long-term management of PL after induction with 30 μg mifepristone, allowing 71% dams to deliver viable pups at term (> day 19, 4-5 days post-mifepristone exposure) without any visible maternal and fetal consequences. Collectively, these studies provide a strong foundation for the future development of mundulone as a stand-alone single- and/or combination-tocolytic therapy for management of PL.

The Effects of Nitroglycerin on the Oxytocin Dose-Response Profile in Oxytocin-Desensitized and Naïve Human Myometrium: An In Vitro Study

BACKGROUND

Nitroglycerin is used for acute reduction in uterine tone. Prolonged oxytocin exposure causes desensitization of oxytocin receptors. It is unknown if nitroglycerin exposure impacts the subsequent action of oxytocin in the setting of oxytocin receptor desensitization. This study investigated the effects of nitroglycerin on oxytocin-desensitized and oxytocin-naïve human myometrium and the subsequent response to oxytocin dose-response testing in vitro.

METHODS

Myometrial samples from 17 elective cesarean deliveries were divided into strips and allocated to 1 of 4 groups: (1) oxytocin desensitized and no nitroglycerin; (2) oxytocin desensitized and nitroglycerin; (3) oxytocin naïve and nitroglycerin; and (4) oxytocin naïve and no nitroglycerin. Final analysis included 28 strips per group. Nitroglycerin groups were exposed to incremental concentrations of nitroglycerin, while no nitroglycerin groups were kept in control (physiological salt) solution. All groups then underwent oxytocin dose-response testing. Primary outcome was motility index (amplitude × frequency; grams × contractions per 10 minutes [g·c/10 min]). Secondary outcomes were amplitude (g), frequency (contractions/10 minutes), and area under the curve (g·s). All outcomes (nitroglycerin and oxytocin dose-response periods) were expressed as a percentage change from baseline. Values were log transformed, compared using regression modeling and reported as the ratio of 2 geometric means (relative difference).

RESULTS

No significant difference was observed in motility index following nitroglycerin administration in oxytocin-desensitized versus oxytocin-naïve groups (relative difference = 19.0%; 95% confidence interval [CI], -32.6 to 109.9; P = .55). On oxytocin dose-response testing, motility index was highest in oxytocin-naïve and no nitroglycerin samples (group 4) (1.356 g·c/10 minutes) followed by oxytocin-naïve and nitroglycerin (group 3) (0.882 g·c/10 minutes), oxytocin-desensitized and no nitroglycerin (group 1) (0.769 g·c/10 minutes), and oxytocin-desensitized and nitroglycerin (group 2) (0.651 g·c/10 minutes) samples. Motility index was significantly reduced in group 1 vs 4 (relative difference = -43.3%; 95% CI, -66.5 to -4.1; P = .034) and group 2 vs 4 (relative difference = -52.0%; 95% CI, -70.9 to -20.8; P = .004). While in groups 3 vs 4, both amplitude (relative difference = -17.8%; 95% CI, -30.9 to -2.2; P = .27) and area under the curve (AUC; relative difference = -17.5%; 95% CI, -30.7 to -1.8; P = .030) were reduced.

CONCLUSIONS

Nitroglycerin-induced relaxation was not different between oxytocin-desensitized and oxytocin-naïve human myometrial strips in vitro. However, oxytocin-induced contractility was attenuated after nitroglycerin exposure in both oxytocin-desensitized and oxytocin-naïve samples, with maximum attenuation observed in desensitized tissues. This finding warrants further clinical studies to explore uterine responsiveness to oxytocin in women with oxytocin-augmented labors after nitroglycerin administration.

Monitoring uterine contractility in mice using a transcervical intrauterine pressure catheter

In mouse models used to study parturition or pre-clinical therapeutic testing, measurement of uterine contractions is limited to either ex vivo isometric tension or operative intrauterine pressure (IUP). The goal of this study was to: (1) develop a method for transcervical insertion of a pressure catheter to measure in vivo intrauterine contractile pressure during mouse pregnancy, (2) determine whether this method can be utilized numerous times in a single mouse pregnancy without affecting the timing of delivery or fetal outcome and (3) compare the in vivo contractile activity between mouse models of term and preterm labor (PTL). Visualization of the cervix allowed intrauterine pressure catheter (IUPC) placement into anesthetized pregnant mice (plug = day 1, delivery = day 19.5). The amplitude, frequency, duration and area under the curve (AUC) of IUP was lowest on days 16-18, increased significantly (P < 0.05) on the morning of day 19 and reached maximal levels during by the afternoon of day 19 and into the intrapartum period. An AUC threshold of 2.77 mmHg discriminated between inactive labor (day 19 am) and active labor (day 19 pm and intrapartum period). Mice examined on a single vs every experimental timepoint did not have significantly different IUP, timing of delivery, offspring number or fetal/neonatal weight. The IUP was significantly greater in LPS-treated and RU486-treated mouse models of PTL compared to time-matched vehicle control mice. Intrapartum IUP was not significantly different between term and preterm mice. We conclude that utilization of a transcervical IUPC allows sensitive assessment of in vivo uterine contractile activity and labor progression in mouse models without the need for operative approaches.

Nitric oxide donors for cervical ripening and induction of labour

BACKGROUND

Sometimes it is necessary to bring on labour artificially because of safety concerns for the mother or baby. This review is one of a series of reviews of methods of labour induction using a standardised protocol.

OBJECTIVES

To determine the effects of NO donors (isosorbide mononitrate (ISMN), isosorbide dinitrate (ISDN), nitroglycerin and sodium nitroprusside) for third trimester cervical ripening or induction of labour, in comparison with placebo or no treatment or other treatments from a predefined hierarchy.

SEARCH METHODS

We searched Cochrane Pregnancy and Childbirth's Trials Register (15 August 2016) and the reference lists of trial reports.

SELECTION CRITERIA

Clinical trials comparing NO donors for cervical ripening or labour induction with other methods listed above it on a predefined list of methods of labour induction. Interventions include NO donors (isosorbide mononitrate, isosorbide dinitrate, nitroglycerin and sodium nitroprusside) compared with other methods listed above it on a predefined list of methods of labour induction.

DATA COLLECTION AND ANALYSIS

This review is part of a series of reviews focusing on methods of induction of labour, based on a generic protocol. Three review authors independently assessed trials for inclusion, assessed risk of bias and extracted data. In this update, the quality of the evidence for the main comparison was assessed using the GRADE approach.

MAIN RESULTS

We included 23 trials (including a total of 4777 women). Included studies compared NO donors with placebo, vaginal prostaglandin E2 (PGE2), intracervical PGE2, vaginal misoprostol and intracervical Foley catheter. The majority of the included studies were assessed as being at low risk of bias. Nitric oxide versus placebo There was no evidence of a difference for any of the primary outcomes analysed: vaginal delivery not achieved in 24 hours (risk ratio (RR) 0.97, 95% confidence interval (CI) 0.83 to 1.15; one trial, 238 women; low-quality evidence), uterine hyperstimulation with fetal heart rate (FHR) changes (RR 0.09, 95% CI 0.01 to 1.62; two trials, 300 women; low-quality evidence), caesarean section (RR 0.99, 95% CI 0.88 to 1.11; nine trials, 2624 women; moderate-quality evidence) or serious neonatal morbidity/perinatal death (average RR 1.61, 95% CI 0.08 to 33.26; two trials, 1712 women; low-quality evidence). There were no instances of serious maternal morbidity or death (one study reported this outcome).There was a reduction in an unfavourable cervix at 12 to 24 hours in women treated with NO donors (average RR 0.78, 95% CI 0.67 to 0.90; four trials, 762 women), and this difference was observed in both subgroups of standard release and slow release formulation. Women who received NO donors were less likely to experience uterine hyperstimulation without FHR rate changes (RR 0.05, 95% CI 0.00 to 0.80; one trial, 200 women), and more likely to experience side effects, including nausea, headache and vomiting. Nitric oxide donors versus vaginal prostaglandins There was no evidence of any difference between groups for uterine hyperstimulation with FHR changes or caesarean section (RR 0.97, 95% CI 0.78 to 1.21; three trials, 571 women). Serious neonatal morbidity and serious maternal morbidity were not reported. There were fewer women in the NO donor group who did not achieve a vaginal delivery within 24 hours (RR 0.63, 95% CI 0.47 to 0.86; one trial, 400 primiparae women). Nitric oxide donors versus intracervical prostaglandins One study reported a reduction in the number of women who had not achieved a vaginal delivery within 24 hours with NO donors (RR 0.63, 95% CI 0.47 to 0.86; one trial, 400 women). This result should be interpreted with caution as the information was extracted from an abstract only and a full report of the study is awaited. No differences were observed between groups for uterine hyperstimulation with FHR changes (RR 0.33, 95% CI 0.01 to 7.74; one trial, 42 women) or serious neonatal morbidity/perinatal death (RR 0.33, 95% CI 0.01 to 7.74; one trial, 42 women). Fewer women in the NO donor group underwent a caesarean section in comparison to women who received intracervical prostaglandins (RR 0.63, 95% CI 0.44 to 0.90; two trials, 442 women). No study reported on the outcome serious maternal morbidity or death. Nitric oxide donors versus vaginal misoprostol There was a reduction in the rate of uterine hyperstimulation with FHR changes with NO donors (RR 0.07, 95% CI 0.01 to 0.37; three trials, 281 women). There were no differences in caesarean section rates (RR 1.00, 95% CI 0.82 to 1.21; 761 women; six trials) and no cases of serious neonatal morbidity/perinatal death were reported. One study found that women in the NO donor group were more likely to not deliver within 24 hours (RR 5.33, 95% CI 1.62 to 17.55; one trial, 150 women). Serious maternal morbidity or death was not reported.In terms of secondary outcomes, there was an increase in cervix unchanged/unfavourable with NO (RR 3.43, 95% CI 2.07 to 5.66; two trials, 151 women) and an increase in the need for oxytocin augmentation with NO induction (RR 2.67, 95% CI 1.31 to 5.45; 7 trials; 767 women), although there was evidence of significant heterogeneity which could not be fully explained. Uterine hyperstimulation without FHR was lower in the NO group, as was meconium-stained liquor, Apgar score less than seven at five minutes and analgesia requirements. Nitric oxide donors versus intracervical catheter There was no evidence on any difference between the effects of NO and the use of a Foley catheter for induction of labour for caesarean section (RR 1.00, 95% CI 0.39 to 2.59; one trial, 80 women). No other primary outcomes were reported. One study of 75 participants did not contribute any data to the review.For all comparisons, women who received NO donors were more likely to experience side effects such as headache, nausea or vomiting.

AUTHORS' CONCLUSIONS

Available data suggests that NO donors can be a useful tool in the process of induction of labour causing the cervix to be more favourable in comparison to placebo. However, additional data are needed to assess the true impact of NO donors on all important labour process and delivery outcomes.

High-Throughput Screening of Myometrial Calcium-Mobilization to Identify Modulators of Uterine Contractility

The uterine myometrium (UT-myo) is a therapeutic target for preterm labor, labor induction, and postpartum hemorrhage. Stimulation of intracellular Ca²⁺-release in UT-myo cells by oxytocin is a final pathway controlling myometrial contractions. The goal of this study was to develop a dual-addition assay for high-throughput screening of small molecular compounds, which could regulate Ca²⁺-mobilization in UT-myo cells, and hence, myometrial contractions. Primary murine UT-myo cells in 384-well plates were loaded with a Ca²⁺-sensitive fluorescent probe, and then screened for inducers of Ca²⁺-mobilization and inhibitors of oxytocin-induced Ca²⁺-mobilization. The assay exhibited robust screening statistics (Z´ = 0.73), DMSO-tolerance, and was validated for high-throughput screening against 2,727 small molecules from the Spectrum, NIH Clinical I and II collections of well-annotated compounds. The screen revealed a hit-rate of 1.80% for agonist and 1.39% for antagonist compounds. Concentration-dependent responses of hit-compounds demonstrated an EC₅₀ less than 10μM for 21 hit-antagonist compounds, compared to only 7 hit-agonist compounds. Subsequent studies focused on hit-antagonist compounds. Based on the percent inhibition and functional annotation analyses, we selected 4 confirmed hit-antagonist compounds (benzbromarone, dipyridamole, fenoterol hydrobromide and nisoldipine) for further analysis. Using an ex vivo isometric contractility assay, each compound significantly inhibited uterine contractility, at different potencies (IC₅₀). Overall, these results demonstrate for the first time that high-throughput small-molecules screening of myometrial Ca²⁺-mobilization is an ideal primary approach for discovering modulators of uterine contractility.

Transdermal nitroglycerin for the treatment of preterm labor: a systematic review and metaanalysis

OBJECTIVE

The purpose of this study was to evaluate the efficacy and safety of transdermal nitroglycerin as a tocolytic agent in women with preterm labor.

STUDY DESIGN

We conducted a systematic review and metaanalysis of randomized controlled trials.

RESULTS

Thirteen studies were included (1302 women) comparing transdermal nitroglycerin vs placebo (2 studies; n = 186); β2-adrenergic receptor agonists (9 studies; n = 1024); nifedipine (1 study; n = 50); and magnesium sulfate (1 study; n = 42). There were no significant differences between transdermal nitroglycerin and placebo for delivery within 48 hours of the initiation of treatment or at <28, <34, or <37 weeks of gestation, adverse neonatal outcomes, and neurodevelopmental status at 24 months of life. Nevertheless, 1 study found a marginally significant reduction in the risk of a composite outcome of major neonatal morbidity and perinatal death (3/74 [4.1%] vs 11/79 [13.9%]; relative risk, 0.29; 95% confidence interval, 0.08-1.00). When compared with β2-adrenergic receptor agonists, transdermal nitroglycerin was associated with a significant reduction in the risk of preterm birth at <34 and <37 weeks of gestation, admission to the neonatal intensive care unit, use of mechanical ventilation, and maternal side effects. There were no significant differences between transdermal nitroglycerin and nifedipine and magnesium sulfate in delivery within 48 hours of treatment and pregnancy prolongation, respectively. Overall, women who received transdermal nitroglycerin had a higher risk of headache.

CONCLUSION

Although transdermal nitroglycerin appears to be more effective than β2-adrenergic receptor agonists, the current evidence does not support its routine use as a tocolytic agent for the treatment of preterm labor. Further double-blind placebo-controlled trials are needed.

Role of serine-threonine phosphoprotein phosphatases in smooth muscle contractility

The degree of phosphorylation of myosin light chain 20 (MLC20) is a major determinant of force generation in smooth muscle. Myosin phosphatases (MPs) contain protein phosphatase (PP) 1 as catalytic subunits and are the major enzymes that dephosphorylate MLC20. MP regulatory targeting subunit 1 (MYPT1), the main regulatory subunit of MP in all smooth muscles, is a key convergence point of contractile and relaxatory pathways. Combinations of regulatory mechanisms, including isoform splicing, multiple phosphorylation sites, and scaffolding proteins, modulate MYPT1 activity with tissue and agonist specificities to affect contraction and relaxation. Other members of the PP1 family that do not target myosin, as well as PP2A and PP2B, dephosphorylate a range of proteins that affect smooth muscle contraction. This review discusses the role of phosphatases in smooth muscle contractility with a focus on MYPT1 in uterine smooth muscle. Myometrium shares characteristics of vascular and other visceral smooth muscles yet, during healthy pregnancy, undergoes hypertrophy, hyperplasia, quiescence, and labor as physiological processes. Myometrium presents an accessible model for the study of normal and pathological smooth muscle function, and a better understanding of myometrial physiology may allow the development of novel therapeutics for the many disorders of myometrial physiology from preterm labor to dysmenorrhea.

Altered endometrial expression of endothelial nitric oxide synthase in women with unexplained recurrent miscarriage and infertility

Endothelial nitric oxide synthase (eNOS) has diverse roles in the female reproductive system including a role in blastocyst implantation. Aberrant expression of eNOS could therefore be significant in the pathogenesis of disorders of implantation. In this study, eNOS protein and mRNA levels in the endometrium of women with recurrent miscarriages, unexplained infertility and a control group were determined by compartmental quantitative immunohistochemistry and real-time reverse-transcription PCR. eNOS was found to be immunolocalized to all layers of the endometrium and vascular endothelium. eNOS protein was higher in glandular epithelium (P = 0.004) and luminal epithelium (P = 0.002), but not vascular endothelium and stroma, in women with recurrent miscarriage. Similarly, in women with unexplained infertility, eNOS was significantly higher (P < 0.03) in luminal epithelium but not in any other compartments compared with the control group. The levels of mRNA confirmed the protein data, demonstrating higher eNOS mRNA in the endometrium of women with recurrent miscarriage and unexplained infertility compared with controls. In conclusion, increased expression of eNOS in glandular and luminal epithelium of the endometrium in women with recurrent miscarriages and unexplained infertility suggests a detrimental effect of excess nitric oxide in endometrial receptivity and implantation.

Nitric oxide donors for cervical ripening and induction of labour

BACKGROUND

Sometimes it is necessary to bring on labour artificially because of safety concerns for the mother or baby. This review is one of a series of reviews of methods of labour induction using a standardised protocol.Induction of labour occurs in approximately 20% of pregnancies in the UK. The ideal agent for induction of labour would induce cervical ripening without causing uterine contractions. Currently most commonly used cervical ripening or induction agents result in uterine activity or contractions, or both. Cervical ripening without uterine contractility could occur safely in an outpatient setting and it may be expected that this would result in greater maternal satisfaction and lower costs.

OBJECTIVES

To determine the effects of nitric oxide (NO) donors for third trimester cervical ripening or induction of labour, in comparison with placebo or no treatment or other treatments from a predefined hierarchy.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 December 2010) and the reference lists of trial reports and reviews.

SELECTION CRITERIA

Clinical trials comparing NO donors for cervical ripening or labour induction to other methods listed above it on a predefined list of methods of labour induction. The trials include some form of random allocation to either group; and report one or more of the prestated outcomes. NO donors (isosorbide mononitrate, nitroglycerin and sodium nitroprusside) are compared to other methods listed above it on a predefined list of methods of labour induction.

DATA COLLECTION AND ANALYSIS

This review is part of a series of reviews focusing on methods of induction of labour. Three review authors independently assessed trials for inclusion, assessed risk of bias and extracted data.

MAIN RESULTS

We considered 19 trials; we included 10 (including a total of 1889 women) trials, excluded eight trials and one trial report is awaiting classification. Included studies compared NO donors to placebo, vaginal prostaglandin E2, intracervical PGE2 and vaginal misoprostol. All included studies were of a generally high standard with a low risk of bias.There are very limited data available to compare nitric oxide donors to any other induction agent. There is no evidence of any difference between any of the prespecified outcomes when comparing NO donors to other induction agents, with the exception of an increase in maternal side effects.

AUTHORS' CONCLUSIONS

NO donors do not appear currently to be a useful tool in the process of induction of labour. More studies are required to examine how NO donors may work alongside established induction of labour protocols, especially those based in outpatient settings.

Oral misoprostol and vaginal isosorbide mononitrate for labor induction: a randomized controlled trial

OBJECTIVE

To estimate whether vaginal isosorbide mononitrate, added to oral misoprostol for cervical ripening and labor induction, shortens time to vaginal delivery.

METHODS

A prospective, randomized trial was conducted. Women scheduled for labor induction between 32 and 42 weeks and with unfavorable cervices (modified Bishop score 6 or lower) were randomized to receive oral misoprostol every 4 hours, up to four doses, with or without isosorbide mononitrate every 6 hours, up to two doses. A strict protocol was used, including timing of oxytocin use and amniotomy. Side effects were assessed 6 hours after study initiation. One hundred forty-two patients were required to detect a change in time to vaginal delivery of 4 hours (alpha=.05 and beta=.20). Data were analyzed by intent to treat. Student's t, chi square, Fisher's exact, and Mann-Whitney tests were used where appropriate with P< or =.05 deemed significant.

RESULTS

One hundred fifty-six women were randomized; three were excluded after randomization. Seventy-eight women received misoprostol, and 78 received misoprostol with isosorbide mononitrate. Demographic characteristics were similar between groups. The time to vaginal delivery was not reduced when isosorbide mononitrate was added to misoprostol. Cesarean delivery rates and contraction and fetal heart rate abnormalities were similar between groups. Side effects were also similar between groups, except that women given isosorbide mononitrate experienced headaches more often. Neonatal outcomes were similar between groups.

CONCLUSION

The addition of vaginal isosorbide mononitrate to oral misoprostol for cervical ripening and labor induction did not reduce time to vaginal delivery and was associated with a greater incidence of headache.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, www.clinicaltrials.gov, NCT00374621.

LEVEL OF EVIDENCE

I.

The extracorporeal perfusion of the swine uterus as an experimental model: The effect of tocolytic drugs

OBJECTIVE

Comparison of the effect of tocolytic drugs on isolated swine uterus preparations.

STUDY DESIGN

Forty swine uteri were perfused with the aim to preserve a viable organ, which should be responsive to oxytocic hormones and tocolytic pharmaca. An intrauterine catheter recorded the pressure changes. After initiation of rhythmical uterine contractions we administered known tocolytic drugs (fenoterol, ritodrine, terbutaline, propofol, acetylsalicylic acid, alcohol, atosiban, verapamil, and glyceryl trinitrate) in various concentrations.

RESULTS

Perfusate pH and lactate, partial oxygen and carbon dioxide tensions, and oxygen saturation in the perfusate showed good preservation of the organ for up to 8h. All substances showed a tocolytic effect on the swine uterus. The effect varied substantially with regard to the length of the contraction free intervals, which was our main effect parameter. Fenoterol, acetylsalicylic acid, and alcohol showed the most and glyceryl trinitrate the least powerful effect.

CONCLUSIONS

A direct comparison of various tocolytic substances in the same experimental model showed the best effect for fenoterol. Furthermore, we could demonstrate that the swine uterus perfusion system is a suitable model to study the influence of various conditions like the administration of drugs or the induction of oxidative stress on the uterus function.

Nitric oxide donor-induced inhibition of pregnant rat uterine spontaneous contractile activity and release of nitric oxide from uterus measured by microdialysis

Our aim was to study whether nitric oxide (NO) donor-induced inhibition of pregnant rat myometrium contractility correlates with the release of NO. Uterine rings from mid-pregnant and late pregnant Sprague-Dawley rats were used for isometric tension recording. Concentration-response relationships to sodium nitroprusside (SNP), nitroglycerine (NTG) and diethylamine (DEA)/NO were assessed. The time course of NO release after addition to the organ chambers of the 3 NO-donors was assessed by the detection of NO products NOx (NO3+NO2) using the microdialysis probe by a HPLC-NO detector system. DEA/ NO induced greater inhibition of the spontaneous contractile activity of uterine rings from mid-pregnant rats than SNP or NTG. In uterine rings from late pregnant rats, however, the maximal inhibition of the contractility by all 3 NO-donors were significantly less. The NOx levels measured in the uterine ring walls from either mid-pregnant or late pregnant rats significantly increased after DEA/ NO as compared to the basal levels or the levels after NTG or SNP. The decrease of NO-donor-induced inhibition of rat myometrium contractility, with unchanged formation of NOx, at term, suggests that the changes in NO signaling are responsible for gestational age-dependent attenuation of the inhibitory effect.

Intracervical application of the nitric oxide donor isosorbide dinitrate for induction of cervical ripening: a randomised controlled trial to determine clinical efficacy and safety prior to first trimester surgical evacuation of retained products of conception

OBJECTIVE

To determine the therapeutic efficacy and safety of a nitric oxide (NO) isosorbide dinitrate donor to induce cervical ripening of women with missed abortions before surgical evacuation of the uterus.

DESIGN

A prospective, randomised, double-blind controlled trial.

SETTING

Tertiary referral maternity teaching hospital. Population Sixty women with missed abortions and no cervical dilation.

METHODS

Women requesting surgical evacuation of the uterus were randomly selected to receive endocervical 80 mg/1.5 mL isosorbide dinitrate gel solution (n= 30) or 400 mug/1.5 mL misoprostol gel solution (n= 30) every 3 hours to a maximum of four doses or until reaching cervical ripening. Vital signs and symptoms were recorded at baseline and then every 3 hours until finishing therapy. Adverse events, such as headache, abdominal pain, pelvic pain, backache, nausea and vomiting, were evaluated.

MAIN OUTCOME MEASURES

Probability of reaching cervical ripening >8 mm Hegar dilator; evaluated at 3, 6, 9 and 12 hours after application of isosorbide dinitrate or misoprostol.

RESULTS

The probabilities of induction of cervical ripening by isosorbide dinitrate and misoprostol after four repeated doses at 3-hour intervals were significantly different (P<0.001). Efficacy of therapy after 12 hours was 97% for the isosorbide dinitrate group and 70% for the misoprostol group. Systolic and diastolic blood pressures were lower after administration of isosorbide dinitrate than prostaglandin analogues. The difference in the mean systolic and diastolic blood pressure between treatment groups was greatest at 3 hours, with a difference of 7.7 mmHg (P<0.001) and 5.9 mmHg (P<0.003), respectively. The most frequent side effect associated with isosorbide dinitrate administration was headache, which occurred in 18 out of 30 patients, compared with only 5 out of 30 women in the misoprostol group [relative risk (RR) 2.41, 95% confidence interval (CI) 1.45-4.03, P<0.001). Women treated with misoprostol reported mainly pelvic pain (RR 3.24, 95% CI 1.99-5.27, P<0.001).

CONCLUSIONS

Intracervical administration of 80 mg isosorbide dinitrate in women with missed abortions appears to be effective for cervical ripening prior to surgical evacuation of the uterus. Differences in the incidence of non-serious adverse events are not likely to be clinically significant.

Sublingual nitroglycerin for management of retained placenta

OBJECTIVE

The aim of the study was to investigate the effect of sublingual nitroglycerin for management of retained placenta and to assess possible adverse effects of the treatment.

METHOD

Twenty-four women were randomly selected to receive either 1 mg nitroglycerin or placebo tablets sublingually if intravenous oxytocin and controlled umbilical cord traction had failed to expel the placenta. Success rate for delivery of placenta, blood pressure, pulse rate, blood loss, and various side effects were examined.

RESULT

All 12 women in the nitroglycerin group had successful delivery of placenta, while removal of placenta was successful in only one of the 12 women in the placebo group. No adverse effects of clinical importance were registered.

CONCLUSION

Sublingual nitroglycerin for treatment of retained placenta seems to be effective without causing serious adverse effects. However, the definite clinical value needs to be evaluated in larger series of patients.

Involvement of a nitric oxide-cyclic guanosine monophosphate pathway in control of fallopian tube contractility

Fallopian tube smooth muscle contractions are physiologically related to transport of the ovum within the oviduct. Nitric oxide (NO) has proved to be a mediator of tubal contractility. The main pathway by which NO exerts its relaxing effect on tubal contractions has not been fully elucidated. NO-mediated effects may be cyclic guanosine monophosphate (cGMP)-dependent or cGMP-independent. The objective of the present study was to investigate whether a NO-cGMP pathway is present in the Fallopian tube and, if present, to examine whether this pathway is involved in tubal contractility. Tubal smooth muscle strips were mounted in organ baths for measurement of tissue cGMP and for isometric recording of contractile activity. Following administration of the NO donor spermine NONOate a more than three-fold increase in tissue levels of cGMP was measured. Pretreatment with inhibitors of cGMP production prior to administration of spermine NONOate resulted in similar levels of cGMP as found in strips exposed to only plain buffer solution. Administration of spermine NONOate to muscle baths resulted in a significant inhibition of contractile activity, while pretreatment with inhibitors of cGMP production almost eliminated the relaxing effect of the NO donor. This study showed that a NO-cGMP pathway is present in the Fallopian tube and that the pathway is involved in Fallopian tube contractility.

Oxytocin Modulates Nitric Oxide Generation by Human Fetal Membranes at Term Pregnancy

PROBLEM

Nitric oxide (NO), an important mediator of the inflammatory response, is involved in several reproductive processes including pregnancy and labor. Uterus, placenta and fetal membranes are significant sources of NO. Presently, there is no information on factors regulating NO production by fetal membranes.

METHOD OF STUDY

Human fetal membranes at term gestation were cultured for 24 hr in the presence of oxytocin. The concentrations of NO metabolites nitrites in culture medium were determined by the Griess reaction. The presence of inducible nitric oxide synthase (iNOS) was determined by reverse transcriptase-polymerase chain reaction and Western blot.

RESULTS

Oxytocin increased nitrite release by fetal membranes. Messenger ribonucleic acid iNOS expression was also enhanced by oxytocin. These effects were more marked in tissues obtained after labor than before labor.

CONCLUSIONS

Oxytocin exerts an overall stimulatory effect on NO release by fetal membranes. This action might be of relevance in the biomolecular processes leading to parturition.

Vaginal administration of the nitric oxide donor isosorbide mononitrate for cervical ripening at term: a randomized controlled study

OBJECTIVE

Our aim was to examine the effect of the nitric oxide donor isosorbide mononitrate on the uterine cervix at term and to evaluate possible adverse effects of this treatment.

STUDY DESIGN

Term pregnant women were randomly selected to receive either 40 mg vaginally administered isosorbide mononitrate or placebo 4 hours before elective cesarean section. Cervical status, maternal blood pressure, maternal pulse rate, fetal heart rate, umbilical arterial Doppler indices, and various side effects were examined.

RESULTS

Isosorbide mononitrate induced a significant increase in cervical distensibility. It also caused a significant change in maternal blood pressure and maternal pulse rate. In addition, the frequency of maternal headache and palpitations was significantly higher in the isosorbide mononitrate group versus the placebo group. However, the intensity of these symptoms was moderate.

CONCLUSION

Vaginal administration of 40 mg of isosorbide mononitrate induces cervical ripening at term. Although the majority of women experienced side effects, no serious clinical maternal or fetal adverse effects, resulting in specific medication or emergency cesarean section, were diagnosed.

Vaginal application of the nitric oxide donor isosorbide mononitrate for preinduction cervical ripening: a randomized controlled trial to determine effects on maternal and fetal hemodynamics

OBJECTIVE

Our aim was to assess the effects of vaginally administered isosorbide mononitrate (a nitric oxide donor) on maternal and fetal hemodynamics in pregnant women at term.

STUDY DESIGN

We conducted a randomized controlled trial. Women were randomly selected to receive vaginally administered isosorbide mononitrate, 20 mg (n = 13) or 40 mg (n = 11), or to undergo a vaginal examination only (n = 12). Maternal pulse, blood pressure, and fetal heart rate were recorded at baseline and then every 30 minutes until 360 minutes. Umbilical artery resistance index and pulsatility index measurements were performed at 0, 180, and 330 minutes.

RESULTS

Maternal pulse rate was greater after the administration of isosorbide mononitrate, 20 or 40 mg, compared with the pulse rate in the vaginal examination-only group (greatest difference in means, 21 beats/min; P <.01). Maternal systolic and diastolic blood pressures were greater in the 20-mg and 40-mg isosorbide mononitrate groups than in the vaginal examination-only group (greatest difference in mean systolic and diastolic blood pressure, 15 and 16 mm Hg, respectively; P <.02 and P <.001, respectively). Fetal heart rate was greater in the 40-mg isosorbide mononitrate group than in either the 20-mg isosorbide mononitrate group or the vaginal examination-only group (difference in mean, 15 beats/min; P <.05). No woman required treatment for maternal or fetal tachycardia or maternal hypotension. Neither dose of isosorbide mononitrate had a significant effect on umbilical artery resistance or pulsatility index.

CONCLUSIONS

Vaginal administration of 20 or 40 mg isosorbide mononitrate to pregnant women at term has an effect on both maternal and fetal hemodynamics, but this effect is not clinically significant.

Regulation of cyclic guanosine monophosphate-dependent protein kinase in human uterine tissues during the menstrual cycle

Contractility of uterine smooth muscle is essential for the cyclic shedding of the endometrial lining and also for expulsion of the fetus during parturition. The nitric oxide (NO)-cGMP signaling pathway is involved in smooth muscle relaxation. The downstream target of this pathway essential for decreasing cytoplasmic calcium and muscle tone is the cGMP-dependent protein kinase (PKG). The present study was undertaken to localize expression of PKG in tissues of the female reproductive tract and to test the hypothesis that uterine smooth muscle PKG levels vary with the human menstrual cycle. Immunohistochemistry was used to localize PKG in myometrium, cervix, and endometrium obtained during proliferative and secretory phases. The PKG was localized to uterine and vascular smooth muscle cells in myometrium, stromal cells in endometrium, and a small percentage of cervical stromal cells. Using Western blot analysis and protein kinase activity assays, the expression of PKG was reduced significantly in progesterone-dominated uteri compared with myometrium from postmenopausal women or women in the proliferative phase. These findings support a role for PKG in the control of uterine and vascular smooth muscle contractility during the menstrual cycle.

Oxytocics reverse the tocolytic effect of glyceryl trinitrate on the human uterus

OBJECTIVES

To investigate the effect of glyceryl trinitrate on isolated human pregnant uterine strips and whether the uterine relaxation induced by glyceryl trinitrate could be reversed by oxytocics used in current clinical practice.

DESIGN

In vitro pharmacological study.

SETTING

Department of Obstetrics & Gynaecology, National University of Singapore, National University Hospital.

PARTICIPANTS

Eighteen women who delivered by caesarean section at term.

METHODS

Myometrial strips were preloaded with an initial tension of 1.5g in organ baths containing Krebs-Henseleit solution which was aerated with oxygen in 5% carbon dioxide and maintained at 37 degrees C, pH 7.4. The effect of glyceryl trinitrate was studied in strips displaying regular spontaneous contractions. The ability of oxytocin, ergometrine or prostaglandin F2alpha to stimulate uterine contractions was assessed in strips where uterine activity was significantly inhibited by glyceryl trinitrate.

RESULTS

Glyceryl trinitrate reduced the amplitude and frequency of spontaneous uterine contractions in a concentration-dependent manner, although the sensitivity of the myometrial strips varied considerably from one specimen to another. The concentration of glyceryl trinitrate producing complete inhibition of myometrial contractions ranged from 44-705 microM. In the presence of glyceryl trinitrate which markedly depressed spontaneous contractions, oxytocin (20 mU/mL), ergometrine (6.15 microM) and prostaglandin F2alpha (6.15 microM) were capable of reversing the uterine activity to either higher than or the untreated level of contractility.

CONCLUSIONS

This study demonstrates that glyceryl trinitrate is a potent uterine relaxant in vitro and that the tocolytic effect could be reversed with ease by oxytocics.

Molecular mechanism of cGMP-mediated smooth muscle relaxation

Contraction and relaxation of smooth muscle is a tightly regulated process involving numerous endogenous substances and their intracellular second messengers. We examine the key role of cyclic guanosine monophosphate (cGMP) in mediating smooth muscle relaxation. We briefly review the current art regarding cGMP generation and degradation, while focusing on the recent identification of the molecular mechanisms underlying cGMP-mediated smooth muscle relaxation. cGMP-induced SM relaxation is mediated mainly by cGMP-dependent protein kinase activation. It involves several molecular events culminating in a reduction in intracellular Ca(2+) concentration and a decrease in the sensitivity of the contractile system to Ca(2+). We propose that the cGMP-induced decrease in Ca(2+) sensitivity is a strategic way to achieve "active relaxation" of the smooth muscle. In summary, we present compelling evidence supporting a key role for cGMP as a mediator of smooth muscle relaxation in physiological and pharmacological settings.

Regulation of uterine contraction: mechanisms in preterm labor

Preterm labor (PTL) is defined as uterine irritability accompanied by cervical dilation and/or effecement that occurs before 37 weeks gestation. In most cases, PTL becomes preterm delivery (PTD), accounting for 8% to 10% of births in the United States. Fetuses born before 37 weeks' gestation are at risk for a multitude of health and developmental problems. Most perinatal morbidity and mortality in the United States are caused by PTL. It is a costly problem, in both monetary and human terms. Although some risk factors have been identified, they by no means identify, in advance, every case of PTL and PTD. Despite the understandable emphasis on attempts to find and test risk factors that predict PTL, the ultimate benefit--preventing PTD--will come only from an understanding of the physiologic mechanisms of parturition and how to halt those processes when they occur too early. This article reviews current approaches to preventing PTD, describes the biology of myometrial contraction, and discusses recent progress from several laboratories including the authors' that may shed light on approaches to inhibit uterine contractility in the setting of PTL.

Distinct regulation of nitric oxide and cyclic guanosine monophosphate production by steroid hormones in the rat uterus

It has previously been reported that uterine nitric oxide (NO) production is enhanced during rat pregnancy compared to non-pregnant, labouring or postpartum states. The present hypothesis is that these changes in uterine NO production during pregnancy are caused by the interplay of oestrogen and progesterone. It is further postulated that changes in cyclic guanosine monophosphate (cGMP) production closely follow the changes in uterine NO synthesis. To test these hypotheses a variety of hormonal regimens (17beta-oestradiol, progesterone and combinations) were applied to different rat models (prepubertal, non-pregnant intact and ovariectomized as well as pregnant rats). The production of nitric oxide (NO) as well as basal and in-vitro NO-stimulated cGMP tissue content were measured in parallel. NO production was measured by the accumulation of nitrites and nitrates in a 24 h incubation medium as analysed by Greiss reaction. cGMP content was measured by radioimmunoassay. Diethylenetriamine/NO (DETA/NO) was used as NO donor. NO production in the rat uterus was markedly increased by pregnancy compared to other physiological (prepubertal, or cycling dioestrus) and experimentally induced (OVX) states. In contrast, uterine cGMP was significantly decreased in pregnancy. Pregnancy also inhibited the elevation in uterine cGMP after in-vitro NO challenge. Chronic 17beta-oestradiol treatment in prepubertal and/or OVX models increased NO production and also mimicked the effect of pregnancy on cGMP. Administration of progesterone in prepubertal rats induced a parallel decrease in both uterine NO and cGMP. In conclusion, sex steroid hormones distinctly regulate uterine NO and cGMP production depending upon the dose and regimen used, as well as the animal's reproductive state.

Expression of nitric oxide synthase isoforms in pregnant human myometrium

1. Endogenous nitric oxide has been proposed to play a role in the control of myometrial contractility in pregnancy. In this study, the expression, localisation and regulation of nitric oxide synthase (NOS) isoforms have been examined in human pregnant myometrium and cultured human myometrial smooth muscle cells, by immunoblotting, immunohistochemistry and reverse transcription-polymerase chain reaction. 2. Immunoblotting of extracts from freshly isolated myometrial tissue, affinity-enriched for NOS proteins by precipitation with ADP-sepharose, revealed expression of endothelial NOS (eNOS or NOS3) in tissues from preterm, term non-labour and active labour at term. Inducible NOS (iNOS or NOS2) and neuronal NOS (nNOS or NOS1) proteins were not detected at any stage of pregnancy. 3. Immunohistochemical detection showed that expression of eNOS protein was restricted to the endothelium of the myometrial vasculature, with no staining detected in myometrial smooth muscle cells. 4. Messenger RNA for all three NOS isoforms was detected, although iNOS and nNOS mRNAs were detectable only with high cycle number, implying a low copy number. 5. NOS isoforms were not detectable in human myometrial smooth muscle cells cultured from term non-labour pregnancies. Cytokine stimulation of cultured myometrial cells did not induce iNOS expression or nitrite accumulation in the culture medium, although both iNOS protein and nitrite release were detected in the human pulmonary epithelial cell line A549. 6. Levels of eNOS protein and of NOS mRNA expression were not correlated with gestational stage, suggesting that endogenously produced NO is not likely to be a modulator of myometrial tone during human pregnancy.

Recent advances in the therapeutic management of preterm labour

Preterm labour and delivery pose an increasing problem to the obstetrician. Improvements in tocolysis with the recent introduction of new therapeutic targeting strategies, and a reappraisal of the safety and relative efficacy of some older compounds, have led to a tendency away from prescribing beta-sympathomimetic agents. Infection prophylaxis and promotion of fetal lung maturity are deemed advantageous, but treatment protocols have not been clarified. This review examines the important publications of the past year in these areas.

Use of nitroglycerin for uterine relaxation

Data from human and experimental animal research indicate that nitric oxide (NO), a novel messenger, formed during the nitric oxide synthase-catalyzed oxidation of L-arginine to L-citrulline, is involved in maintaining normal uterine tone during gestation. There are demonstrated and potential benefits of manipulating the L-arginine-NO system during pregnancy. Several recent case reports and case series have described the effective use of nitroglycerin (GTN), a NO donor compound, antenatally, intrapartum, and postpartum for acute uterine relaxation. Therapeutic indications for GTN range from facilitating external cephalic version, difficult vaginal or cesarean section delivery, and manual exploration of the uterus, to its use as a tocolytic. The intravenous regimen of GTN required to obtain the desired degree of uterine relaxation is extremely variable; intravenous bolus doses of 50 micrograms to 500 micrograms GTN with up to three repeated injections of 50 micrograms to 250 micrograms have been reported. Other methods of GTN administration include transdermal patches and sublingual spray. GTN, when used in low doses, may provide safe and effective uterine relaxation with no clinically apparent fetal or maternal adverse effects. However, clinical trials with use of objective methods of evaluating uterine tone and comparing GTN to other tocolytic agents are required before widespread use in advocated.