Differential regulation of nitric oxide in the rat uterus and cervix during pregnancy and labour

In vitro study of carbetocin, an oxytocin receptor agonist, and 4-phenylfuroxan-3-carbonitrile, a NO-releasing agent, as cervical dilatators in sheep

The aim was to study the effect of 4-phenylfuroxan-3-carbonitrile (Fx), a NO-releasing agent, and carbetocin, an oxytocin receptor agonist, on matrix metalloproteinases-2 (MMP-2) activity and PGE2 production in cervix from cycling sheep. Cervical explants were incubated during 12 h with MEM supplemented with increasing concentrations of Fx in DMSO (2 %) (0 to 300 μg/mL) with Cb (100 ng/mL) (Experiment 1, n = 15) and DMSO (2 %), DMSO + Cb (100 ng/mL) or DMSO + Fx (30 μg/mL) (Experiment 2, n = 10), and their respective controls. In the supernatants, activated (A) and latent (L) MMP-2 activities were determined by a SDS-PAGE zymography, PGE2 concentration by immunoassay and NO production indirectly as nitrites by spectrophotometry. Data were analyzed by ANOVA. The Cb treatment increase the A MMP-2 activity in DMSO (Experiment 1 at follicular phase and Experiment 2) or alone (Experiment 2) and increase the L MMP-2 activity (Experiments 1 and 2) (P < 0.02). The DMSO treatment also increase the L MMP2 activity (Experiment 2) (P < 0.0001). Treatment with Fx + DMSO increased the concentration of accumulated nitrites in the supernatant (P < 0.0001) (Experiment 1), but did not affect or decrease the activity of A and L MMP-2 (P < 0.04) (Experiments 1 and 2). The PGE2 concentration trend to increase with Cb treatment (P = 0.0614) and decrease with Fx+DMSO treatment (P < 0.0001) (Experiment 2). In conclusion, Cb and/or DMSO treatment of cervical explants increase the MMP-2 activity through PGE2-independent mechanisms, but Fx in DMSO fail in this, suggesting that the pre-treatment with Cb and/or DMSO could be used to increase cervical dilation in ewes.

Isosorbide Mononitrate Versus Dinoprostone for Cervical Ripening During Labor Induction: a Systematic Review and Meta-analysis of Randomized Controlled Trials

The objective of this study was to conduct a systematic review and meta-analysis of all randomized controlled trials (RCTs) that evaluated isosorbide mononitrate (ISMN) versus dinoprostone, a prostaglandin E2 (PGE2) analogue, in promoting cervical ripening during labor induction. We searched five major databases from inception till 02 May 2021. We assessed the risk of bias of included studies. We meta-analyzed various endpoints (n=12) and pooled the endpoints as mean difference (MD) or risk ratio (RR) with 95% confidence interval (CI). Overall, 4 RCTs met the inclusion criteria, comprising 818 patients; equally 409 patients were allocated to ISMN and PGE2 groups. Overall, the RCTs had a low risk of bias. The mean change in Bishop score at 24 h was significantly lower in disfavor of the ISMN group. The mean time from drug administration to delivery was significantly longer in disfavor of the ISMN group. The rate of oxytocin need was significantly higher in disfavor of the ISMN group. The rate of vaginal delivery at 24 h was significantly lower in disfavor of the ISMN group. The rates of headache and palpitations were significantly higher in disfavor of the ISMN group. The rate of abnormal fetal heart rate was significantly lower in favor of the ISMN group. There was no significant difference between both groups with regard to rates of cesarean delivery, postpartum hemorrhage, uterine hyperstimulation, and NICU admission. Compared with PGE2, ISMN appeared less effective for cervical ripening prior to labor induction and correlated with higher drug-related maternal toxicities.

Signaling Pathways Regulating Human Cervical Ripening in Preterm and Term Delivery

At the end of gestation, the cervical tissue changes profoundly. As a result of these changes, the uterine cervix becomes soft and vulnerable to dilation. The process occurring in the cervical tissue can be described as cervical ripening. The ripening is a process derivative of enzymatic breakdown and inflammatory response. Therefore, it is apparent that cervical remodeling is a derivative of the reactions mediated by multiple factors such as hormones, prostaglandins, nitric oxide, and inflammatory cytokines. However, despite the research carried out over the years, the cellular pathways responsible for regulating this process are still poorly understood. A comprehensive understanding of the entire process of cervical ripening seems crucial in the context of labor induction. Greater knowledge could provide us with the means to help women who suffer from dysfunctional labor. The overall objective of this review is to present the current understanding of cervical ripening in terms of molecular regulation and cell signaling.

Roles of Nitric Oxide in the Regulation of Reproduction: A Review

Nitric oxide (NO) has attracted significant attention as a stellar molecule. Presently, the study of NO has penetrated every field of life science, and NO is widely distributed in various tissues and organs. This review demonstrates the importance of NO in both male and female reproductive processes in numerous ways, such as in neuromodulation, follicular and oocyte maturation, ovulation, corpus luteum degeneration, fertilization, implantation, pregnancy maintenance, labor and menstrual cycle regulation, spermatogenesis, sperm maturation, and reproduction. However, the mechanism of action of some NO is still unknown, and understanding its mechanism may contribute to the clinical treatment of some reproductive diseases.

Addition of vaginal isosorbide mononitrate for labor induction in pregnancies complicated by hypertensive diseases of pregnancy: a randomized controlled trial

BACKGROUND

Pregnancies complicated by hypertensive disease of pregnancy often require labor induction. Rates of cesarean delivery range from 15% to 60% in this population. Nitric oxide deficiency has been shown to underlay the pathophysiology of preeclampsia, and nitric oxide promotes cervical ripening.

OBJECTIVE

We hypothesized that addition of vaginal isosorbide mononitrate for labor induction could decrease the rate of cesarean delivery in pregnancies with hypertensive disease of pregnancy.

STUDY DESIGN

This study was a double-blind, placebo-controlled, randomized trial of patients with singleton pregnancy at ≥24 weeks' gestation undergoing labor induction for hypertensive diseases of pregnancy between November 2017 and February 2020. Participants were eligible if their Bishop score was <6 and if their cervical dilation was ≤2 cm. In addition, participants received up to 3 doses of 40 mg isosorbide mononitrate in addition to misoprostol for labor induction. Labor management was per healthcare provider preference. The primary outcome was rate of cesarean delivery. Secondary outcomes included the length of labor and frequency of intrapartum adverse events, including the use of intrapartum antihypertensive agents.

RESULTS

89 women were randomized to the isosorbide mononitrate group, and 87 women were randomized to the placebo group. Cesarean delivery rates were similar in both groups (32.6% vs 25.3%; relative risk, 1.29; 95% confidence interval, 0.81-2.06; P=.39). Maternal headache was increased in patients exposed to isosorbide mononitrate (42.7% vs 31%; relative risk, 1.52; 95% confidence interval, 1.04-2.23; P=.04). Clinical chorioamnionitis was increased in the placebo group (0% vs 8%; P=.02). Secondary outcomes were similar between groups.

CONCLUSION

The addition of vaginal isosorbide mononitrate for labor induction in pregnancies complicated by hypertensive disease of pregnancy did not result in fewer cesarean deliveries.

Exosomal delivery of NF-κB inhibitor delays LPS-induced preterm birth and modulates fetal immune cell profile in mouse models

Accumulation of immune cells and activation of the pro-inflammatory transcription factor NF-κB in feto-maternal uterine tissues is a key feature of preterm birth (PTB) pathophysiology. Reduction of the fetal inflammatory response and NF-κB activation are key strategies to minimize infection-associated PTB. Therefore, we engineered extracellular vesicles (exosomes) to contain an NF-κB inhibitor, termed super-repressor (SR) IκBα. Treatment with SR exosomes (1 × 1010 per intraperitoneal injection) after lipopolysaccharide (LPS) challenge on gestation day 15 (E15) prolonged gestation by over 24 hours (PTB ≤ E18.5) and reduced maternal inflammation (n ≥ 4). Furthermore, using a transgenic model in which fetal tissues express the red fluorescent protein tdTomato while maternal tissues do not, we report that LPS-induced PTB in mice is associated with influx of fetal innate immune cells, not maternal, into feto-maternal uterine tissues. SR packaged in exosomes provides a stable and specific intervention for reducing the inflammatory response associated with PTB.

Immunology and the immunological response to pregnancy

The immune system in humans is a complex system capable of discriminating self from non-self, and mounting appropriate allogenic immune responses to protect themselves from foreign organisms. This system is made up of two arms of defense: the first one is a non-specific arm (innate), in which humans are born with and do not require antigenic recognition. The second one is specific arm (humoral) involving B and T cells that are capable of mounting responses to particular antigen with immense specificity. Both of these systems importantly interact with each other to protect humans in the most effective and efficient manner. Defects or malfunctions in these systems can result in a variety of illnesses and conditions. The immunology of pregnancy is a very unique, highly controlled system, which allows for survival of a fetus (semi-allograft), whilst simultaneously protecting a pregnant woman. There are immune shifts in pregnancy, which are well established to facilitate maternal-fetal tolerance. This promotes the concept that the immune system is not suppressed, but instead modulated to facilitate a pregnancy and explain the differential response to various pathogens in pregnancy. During pregnancy, the development of a fetal immunological system also occurs with intricate interaction between the maternal and fetal interface. The mechanism is preterm and term birth is poorly understood, but the immunological response has been well documented for both the pathological and physiological scenarios.

Gasotransmitters in pregnancy: from conception to uterine involution

Gasotransmitters are endogenous small gaseous messengers exemplified by nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S or sulfide). Gasotransmitters are implicated in myriad physiologic functions including many aspects of reproduction. Our objective was to comprehensively review basic mechanisms and functions of gasotransmitters during pregnancy from conception to uterine involution and highlight future research opportunities. We searched PubMed and Web of Science databases using combinations of keywords nitric oxide, carbon monoxide, sulfide, placenta, uterus, labor, and pregnancy. We included English language publications on human and animal studies from any date through August 2018 and retained basic and translational articles with relevant original findings. All gasotransmitters activate cGMP signaling. NO and sulfide also covalently modify target protein cysteines. Protein kinases and ion channels transduce gasotransmitter signals, and co-expressed gasotransmitters can be synergistic or antagonistic depending on cell type. Gasotransmitters influence tubal transit, placentation, cervical remodeling, and myometrial contractility. NO, CO, and sulfide dilate resistance vessels, suppress inflammation, and relax myometrium to promote uterine quiescence and normal placentation. Cervical remodeling and rupture of fetal membranes coincide with enhanced oxidation and altered gasotransmitter metabolism. Mechanisms mediating cellular and organismal changes in pregnancy due to gasotransmitters are largely unknown. Altered gasotransmitter signaling has been reported for preeclampsia, intrauterine growth restriction, premature rupture of membranes, and preterm labor. However, in most cases specific molecular changes are not yet characterized. Nonclassical signaling pathways and the crosstalk among gasotransmitters are emerging investigation topics.

Dynamic Function and Composition Changes of Immune Cells During Normal and Pathological Pregnancy at the Maternal-Fetal Interface

A successful pregnancy requires a fine-tuned and highly regulated balance between immune activation and embryonic antigen tolerance. Since the fetus is semi-allogeneic, the maternal immune system should exert tolerant to the fetus while maintaining the defense against infection. The maternal-fetal interface consists of different immune cells, such as decidual natural killer (dNK) cells, macrophages, T cells, dendritic cells, B cells, and NKT cells. The interaction between immune cells, decidual stromal cells, and trophoblasts constitute a vast network of cellular connections. A cellular immunological imbalance may lead to adverse pregnancy outcomes, such as recurrent spontaneous abortion, pre-eclampsia, pre-term birth, intrauterine growth restriction, and infection. Dynamic changes in immune cells at the maternal-fetal interface have not been clearly stated. While many studies have described changes in the proportions of immune cells in the normal maternal-fetus interface during early pregnancy, few studies have assessed the immune cell changes in mid and late pregnancy. Research on pathological pregnancy has provided clues about these dynamic changes, but a deeper understanding of these changes is necessary. This review summarizes information from previous studies, which may lay the foundation for the diagnosis of pathological pregnancy and put forward new ideas for future studies.

A gentle introduction to gasotransmitters with special reference to nitric oxide: biological and chemical implications

Nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S) are gaseous molecules of major impact in biology. Despite their toxicity, these molecules have profound effects on mammalian physiology and major implications in therapeutics. At tiny concentrations in human biology, they play key signaling and regulatory functions and hence are now labeled as “gasotransmitters.” In this literature survey, an introduction to gasotransmitters in relevance with NO, CO and H2S has been primarily focused. A special attention has been given to the conjoint physiological, pathophysiological and therapeutic aspects of NO in this work. In addition to the aforementioned elements of the investigation being reported, this report gives a detailed account of some of the recent advancements covering the NO release from both the nitro as well as nitroso compounds. The importance of the metallic center on the eve of producing the reduction center on NO and to develop photolabile properties have been elaborated within the effect of a few examples of metallic centers. Also, theoretical investigations that have been reported in the recent past and some other current theories pertaining to NO chemistry have been enlightened in this review. From the overall study, it is eminent that a number of facts are yet to be explored in context with NO for deeper mechanistic insights, model design for these molecules, other key roles and the search to find the best fit formalism in theoretical chemistry.

Influence of MBL2 and NOS3 polymorphisms on spontaneous preterm birth in North East Brazil: genetics and preterm birth

Background: The mannose-binding lectin (MBL2) and nitric oxide synthase 3 (NOS3) genes are associated with the immune response against inflammatory processes, have been reported as possibly related with premature birth. Until now, most of the researches regarding the genetic influence of prematurity have revealed limited results because only investigating the child or the mothers' genotypes, thus not exploring the possible effects of interactions between these genotypes or the interactions with environmental factors related to the duration of pregnancy.Objective: We performed a replica study investigating the influence of single nucleotide polymorphisms (SNPs) in MBL2 and NOS3 genes on premature birth, also considering socioeconomic, demographic, and gestational factors.Materials and methods: We conducted a case-control study with 189 mother-infant dyads, with 104 spontaneous preterm births and 85 term births from Recife, Brazil. We used peripheral blood samples and umbilical cord samples to extract DNA. Functional SNPs at exon 1 and promoter region of MBL2 and NOS3 RS1799983 SNP were genotyped using direct sequencing and fluorescent allelic specific TaqMan^® assays respectively. Data were analyzed using the Statistical Package for the Social Sciences (SPSS^®) program with bivariate association and logistic multivariate regression tests.Results: We observed a prevalence of MBL2 wild-type genotype in the mother-infant dyad of the preterm group and polymorphic genotype in the mother-infant dyad of term birth. The haplotype LYA predominated in our sample, being more frequent in the preterm group, while the haplotype LYB, correlated with lower levels of MBL protein, was more frequent in the term birth group. About NOS3 RS1799983 SNP, the G/G genotype was more frequent throughout the sample. The heterozygous genotype predominated among women from the preterm group, showed a borderline difference between the groups. When MBL2 genotypes of the mother and son were analyzed together, codon 54 of MBL2 remained associated with prematurity. When the variables with p value lower than .20 in the bivariate analysis were analyzed by logistic regression, the low weight of the pregnant woman in relation to the gestational age, the occurrence of preterm premature rupture of membranes, urinary tract infection during birth and maternal history of other premature births were risk factors to prematurity. On the other hand, the presence of B allele at codon 54 of maternal MBL2 was a protective factor for the occurrence of spontaneous premature birth. In contrast, a borderline association was established between the maternal genetic variation within NOS3 gene and the outcome studied.Conclusions: Our study, limited by the small number of patients enrolled, indicates that MBL2 and NOS3 functional SNPs are associated with the occurrence of spontaneous prematurity and the regulation of the maternal inflammatory response. Despite these results are in agreement with previously reports, our findings do not replicate the ones reported in a large genome-wide association study performed on quite high number of subjects. Thus, we can conclude that MBL2 and NOS3 functional SNPs are plausible candidate risk factors just in few preterm birth cases, and consequently they cannot be included in the general diagnostic practice.

Nicotine alters progesterone and estradiol levels during the first trimester of pregnancy in Wistar rats

OBJECTIVE

This study was designed to investigate the effect of nicotine on serum progesterone and estradiol levels as possible cause of abortion during first trimester of gestation in female Wistar rats.

METHODS

Fourteen female rats with regular estrous cycles in the same phase of cycle were divided into two groups (Control and Nicotine-treated) with each group receiving 1ml of distilled water and 1mg/kg of nicotine respectively for the first seven days of pregnancy (GD1-7). The animals were sacrificed on the 8th day and blood samples were collected for hormonal analyses. Ovaries and uteruses were excised, weighed, and prepared for histological study.

RESULTS

This study revealed a significant decrease in serum progesterone and estradiol levels in the nicotine-treated group when compared to controls. The histological findings equally showed degeneration in the cytoarchitecture of the ovary of the nicotine-treated group.

CONCLUSION

The observed hormonal imbalances and alteration in the cytoarchitecture of the ovary caused by nicotine in the first trimester of pregnancy may result in abortion during this period.

Is nitric oxide an essential mediator in cervical inflammation and preterm birth?

OBJECTIVE

Cervical ripening is an obligatory step in the process of preterm birth. We hypothesize an inflammatory challenge to the cervix, which leads to an increase in nitric oxide production, disrupting the cervical epithelial barrier leading to preterm birth.

STUDY DESIGN

For this study, three experiments were performed: (i) Using a mouse model, pregnant mice were treated with an intrauterine injection of saline or lipopolysaccharide (LPS). Mice were sacrificed and cervices were collected for molecular analysis. (ii) Immortalized ectocervical and endocervical cells were treated with either LPS or the nitric oxide donor sodium nitroprusside (SNP). Media and RNA was collected for analysis. (iii) The integrity of the epithelial cell barrier was evaluated using an in vitro permeability assay.

RESULTS

The expression of inducible nitric oxide synthase (iNOS) was increased in our mouse model with LPS (p < .005). In vitro, LPS did not increase nitrate or nitrite concentrations or mRNA expression of iNOS. Permeability increased in the presence of LPS (p < .01), but was unchanged after treatment with SNP.

CONCLUSIONS

These studies show that LPS increases the expression of the iNOS in an animal model of preterm birth, but the nitric oxide metabolites nitrate and nitrite do not initiate the pro-inflammatory LPS-induced breakdown of the cervical epithelial barrier.

Contributions to the dynamics of cervix remodeling prior to term and preterm birth

Major clinical challenges for obstetricians and neonatologists result from early cervix remodeling and preterm birth. Complications related to cervix remodeling or delivery account for significant morbidity in newborns and peripartum mothers. Understanding morphology and structure of the cervix in pregnant women is limited mostly to the period soon before and after birth. However, evidence in rodent models supports a working hypothesis that a convergence of factors promotes a physiological inflammatory process that degrades the extracellular collagen matrix and enhances biomechanical distensibility of the cervix well before the uterus develops the contractile capabilities for labor. Contributing factors to this remodeling process include innervation, mechanical stretch, hypoxia, and proinflammatory mediators. Importantly, the softening and shift to ripening occurs while progesterone is near peak concentrations in circulation across species. Since progesterone is required to maintain pregnancy, the premise of this review is that loss of responsiveness to progesterone constitutes a common final mechanism for remodeling the mammalian cervix in preparation for birth at term. Various inputs are suggested to promote signaling between stromal cells and resident macrophages to drive proinflammatory processes that advance the soft cervix into ripening. With infection, pathophysiological processes may prematurely drive components of this remodeling mechanism and lead to preterm birth. Identification of critical molecules and pathways from studies in various rodent models hold promise for novel endpoints to assess risk and provide innovative approaches to treat preterm birth or promote the progress of ripening at term.

Changes in Cervical Nitric Oxide Concentration Correlate With Bishop Score and Cervical Length Modifications in Prostaglandin E2-Mediated Induction of Labor

OBJECTIVE

Nitric oxide (NO) plays a fundamental role in cervical ripening and it is synthesized in the human cervix. We studied the effect of the dinoprostone on cervical NO release in pregnant women, and we investigated the relationship between cervical NO metabolites, cervical length, and Bishop score.

METHODS

Seventy-seven women underwent induction of labor at > or = 37 weeks of gestation, due to post-term pregnancy (23.8%), oligohydramnios (36.3) or preeclampsia (29.9%). Cervical fluid samples for NO metabolites (NOx), Bishop score, and cervical length were assessed immediately before (time 0 [T0]) and 6 hours after (T6) the local application of dinoprostone, a commercially available prostaglandin E2 (PGE2) analog.

RESULTS

The mean patients' age was 34 +/- 3.2 years, mean gestational age at enrollment was 284 +/- 9.2 days, and nulliparous represented 31.2% of the study population. At time 0, Bishop score was less than 4 in 74% (57/77) of the subjects, mean cervical length was 28.6 +/- 5.8 mm, mean NOx concentration was 208.6 +/- 103.8 microM/mL; 6 hours later, at T6, the mean cervical length decreased to 19.5 +/- 8.8 mm, and the mean NOx concentration increased up to 316.7 +/- 240.9 microM/mL. Data were unaffected by parity or by regular uterine contraction patterns. A statistically significant positive correlation was found between changes in cervical NOx levels and Bishop score modification (P < .01; r = .494), as well as between the modification of NO metabolites concentration and cervical shortening (P < .01; r = .307).

CONCLUSIONS

Prostaglandin (PG)-induced cervical ripening is associated with local NO release. NO plays an active role in cervical remodeling since it positively correlates with both cervical shortening and Bishop score increase. NO oxide and PG are the two pathways that, cross activating each other, trigger the cascade of events responsible of cervical ripening.

Role of NO-cGMP pathway in ovine cervical relaxation induced by Erythroxylum caatingae Plowman

Erythroxylum caatingae Plowman has a myorelaxing effect on smooth muscle tissue. We investigated the effect of the crude ethanolic extract of E. caatingae Plowman (Ec-EtOH) on the contractility of the ovine cervix. In an isometric system, circular strips were subjected to 90mM potassium (K(+)) or 30μM carbamylcholine (CCh)-induced contraction. We then exposed the tissue to cumulative concentrations of Ec-EtOH (1-729 μg/ml). In other bath solutions, the tissues were exposed to l-NG-nitroarginine methyl ester (l-NAME; 100μM), l-NAME (100μM)+l-arginine (300μM), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, ODQ; 5μM), 4-aminopyridine (4-AP; 3mM), tetraethylammonium (TEA; 0.3mM), glybenclamide (1μM), atosiban (10μM) or verapamil (3μM), followed by the addition of Ec-EtOH (1-729 μg/ml). We also evaluated the effect of cervical Ec-EtOH infusion (2mg) on cervical contractility in vivo. Ec-EtOH decreased cervical contractility induced by K(+) or CCh, and 729 μg/ml Ec-EtOH decreased 85.4±5.1% the amplitude of basal contractility in vitro, with an EC50 of 17.9±3.7 μg/ml. This effect of Ec-EtOH was prevented by l-NAME or ODQ. l-arginine impaired the blunting effect of l-NAME on cervical relaxation caused by Ec-EtOH. However, the potassium channel blockers 4-AP, TEA, and glybenclamide did not modify this myorelaxation triggered by Ec-EtOH. Ec-EtOH also decreased acetylcholine-induced contractions in tissue preincubated with verapamil. In addition, Ec-EtOH decreased ovine cervical contractions in vivo. Thus, Ec-EtOH had a relaxant effect on ovine cervical contractions. This may involve the nitric oxide signal, mediated by cGMP cellular transduction, and be related to intracellular calcium sequestration.

Comparing the effect of oral and vaginal isosorbide dinitrate in pre-induction cervical ripening in term pregnancy: A controlled clinical trial

Background:

Cervical ripening for labor induction is one of the most important issues in midwifery. Isosorbide dinitrate (ISDN) is one of the most important choices that have been proposed for cervical ripening, but still there are controversies regarding its prescription. The present study aimed to evaluate the effects of vaginal and oral ISDN compared to the control group for pre-induction cervical ripening.

Materials and Methods:

In this non-blinded clinical trial, 149 nulliparous women with term or prolonged pregnancy were randomly selected and divided into three groups by block randomization. The intervention group included vaginal (50 subjects, 40 mg) and oral (49 subjects, 20 mg) ISDN groups. The third group was the control group (50 subjects) which did not receive any medication. The amount of ripening was given by Bishop score evaluated before taking medication and 24 h after taking it.

Results:

After 24 h, Bishop score in vaginal ISDN group significantly increased compared to the oral ISDN and control groups (P < 0.001 for both). Although the increase in Bishop score was lower in the oral ISDN group than in the vaginal group, it had a statistically significant increase in comparison to the control group (P = 0.001). All the three groups were matched regarding pregnancy termination and cesarean causes, and there was no statistically significant difference among the three groups (P > 0.05).

Conclusion:

Prescribing vaginal ISDN for cervical ripening was effective, and it can be used with confidence.

Functional and morphological development of the womb throughout life

The uterus undergoes changes throughout a woman's life, beginning with her own embryonic development when she is still in the womb, commencing a monthly cycle at the onset of adulthood, and undergoing dramatic changes during pregnancy and parturition. The impact of preterm labour and other perinatal health problems is significant, both in human and financial terms; therefore the study of the physiological and regulatory changes which the uterus undergoes can be of enormous potential benefit. Here we briefly review the current state of knowledge, with an emphasis on the importance of changes in connectivity in the uterine smooth muscle cell network and on recent mathematical modelling work aimed at elucidating the role of spatial heterogeneity in this connected network.

Immune cells in term and preterm labor

Labor resembles an inflammatory response that includes secretion of cytokines/chemokines by resident and infiltrating immune cells into reproductive tissues and the maternal/fetal interface. Untimely activation of these inflammatory pathways leads to preterm labor, which can result in preterm birth. Preterm birth is a major determinant of neonatal mortality and morbidity; therefore, the elucidation of the process of labor at a cellular and molecular level is essential for understanding the pathophysiology of preterm labor. Here, we summarize the role of innate and adaptive immune cells in the physiological or pathological activation of labor. We review published literature regarding the role of innate and adaptive immune cells in the cervix, myometrium, fetal membranes, decidua and the fetus in late pregnancy and labor at term and preterm. Accumulating evidence suggests that innate immune cells (neutrophils, macrophages and mast cells) mediate the process of labor by releasing pro-inflammatory factors such as cytokines, chemokines and matrix metalloproteinases. Adaptive immune cells (T-cell subsets and B cells) participate in the maintenance of fetomaternal tolerance during pregnancy, and an alteration in their function or abundance may lead to labor at term or preterm. Also, immune cells that bridge the innate and adaptive immune systems (natural killer T (NKT) cells and dendritic cells (DCs)) seem to participate in the pathophysiology of preterm labor. In conclusion, a balance between innate and adaptive immune cells is required in order to sustain pregnancy; an alteration of this balance will lead to labor at term or preterm.

The association between maternal biomarkers and pathways to preterm birth in twin pregnancies

OBJECTIVE

We sought to estimate the association between cervical length (CL) and fetal fibronectin (fFN) and each pathway leading to preterm birth in twin pregnancies.

METHODS

Cohort study of 560 patients with twin pregnancies who underwent routine serial CL and fFN screening from 22 to 32 weeks in one maternal fetal medicine practice during 2005-2013. We calculated the association between a short CL (≤20 mm) or positive fFN with overall preterm birth <32 weeks, and then subdivided the analysis into preterm birth <32 weeks from preterm labor, preterm premature rupture of membranes (PPROM) and indicated causes. We excluded cases of monochorionic-monoamniotic placentation, vasa previa, twin-twin transfusion and patients with cerclage.

RESULTS

The overall rate of preterm birth <32 weeks was 6.9% (3.9% from preterm labor, 1.6% from PPROM and 1.4% indicated). A short cervix was associated with preterm birth <32 weeks arising from preterm labor (12.4% versus 2.0%, p < 0.001), but not PPROM (1.9% versus 1.3%, p = 0.651). Positive fFN was associated with preterm birth <32 weeks both from preterm labor (17.0% versus 2.4%, p < 0.001) as well as from PPROM (5.7% versus 1.0%, p = 0.034). Neither was significantly associated with preterm birth <32 weeks from indicated causes.

CONCLUSIONS

The mechanism leading toward preterm influences the accuracy of screening tests chosen to assess risk in twin pregnancies. A shortened cervical length and positive fFN is associated with spontaneous preterm labor and birth <32 weeks. However, PPROM does not appear to be preceded by a short cervix, but is preceded by a positive fFN. Neither test is associated with an indicated preterm birth.

Intravaginal isosorbide dinitrate or misoprostol for cervical ripening prior to induction of labour: a randomised controlled trial

In this randomised double-blind controlled trial, 130 healthy pregnant women with term pregnancy who scheduled for labour induction with Bishop's score < 5, were recruited. They were assigned randomly to vaginal administration of isosorbide dinitrate (ISDN) (40 mg) or misoprostol (25 μg), which were repeated after 4 h as needed. The efficacies of medications were evaluated by predetermined primary and secondary outcome variables for cervical ripening and induction of labour and delivery. There was no significant difference in Bishop's score 8 h after drug administration between the ISDN and misoprostol groups. However, in the ISDN group, labour induction was needed more frequently and the time from start of medication to the beginning of active phase of labour was significantly longer.

System-level biomechanical approach for the evaluation of term and preterm pregnancy maintenance

Preterm birth is the primary contributor to perinatal morbidity and mortality, with those born prior to 32 weeks disproportionately contributing compared to those born at 32-37 weeks. Outcomes for babies born prematurely can be devastating. Parturition is recognized as a mechanical process that involves the two processes that are required to initiate labor: rhythmic myometrial contractions and cervical remodeling with subsequent dilation. Studies of parturition tend to separate these two processes rather than evaluate them as a unified system. The mechanical property characterization of the cervix has been primarily performed on isolated cervical tissue, with an implied understanding of the contribution from the uterine corpus. Few studies have evaluated the function of the uterine corpus in the absence of myometrial contractions or in relationship to retaining the fetus. Therefore, the cervical-uterine interaction has largely been neglected in the literature. We suggest that a system-level biomechanical approach is needed to understand pregnancy maintenance. To that end, this paper has two main goals. One goal is to highlight the gaps in current knowledge that need to be addressed in order to develop any comprehensive and clinically relevant models of the system. The second goal is to illustrate the utility of finite element models in understanding pregnancy maintenance of the cervical-uterine system. The paper targets an audience that includes the reproductive biologist/clinician and the engineer/physical scientist interested in biomechanics and the system level behavior of tissues.

Effect of lipopolysaccharide on the production of prostaglandin E2 and inhibition of uterine contractions by nitric oxide in pregnant inducible nitric oxide synthase knockout mice

AIM

The aim of the present study was to evaluate the effect of lipopolysaccharide (LPS) on the production of prostaglandin E2 (PGE2) and inhibition by nitric oxide (NO) of spontaneous contractions of uterine rings from pregnant inducible isoform of nitric oxide synthase knockout (iNOS KO) mice.

MATERIAL AND METHODS

iNOS KO and wild-type mice were sacrificed 6 h after intraperitoneal (i.p.) administration of LPS on day 14 of gestation. Uterine rings were equilibrated in Krebs-Henseleit solution for isometric tension recording. In part of the uterine rings, placental tissues were left attached. The bathing solution was analyzed for PGE2 by radioimmunoassay. Changes in spontaneous contractions in response to cumulative concentrations of L-arginine, diethylamine/nitric oxide (DEA/NO), and 8-bromo-cyclic guanosine monophosphate (8-br-cGMP) were determined.

RESULTS

Treatment with LPS increased PGE2 production by uterine rings from wild-type and iNOS-KO mice. DEA/NO and 8-br-cGMP inhibited spontaneous contractions in uterine rings in the absence or presence of placenta, in both LPS-treated and LPS-untreated animals. LPS treatment attenuated maximal inhibition induced by the agents, both in the absence and presence of placental tissues in iNOS KO and wild-type mice.

CONCLUSION

LPS induces PG production in mice myometrium that is not dependent on the integrity of iNOS, while LPS could induce pathophysiological iNOS obstruct uterine quiescence by physiological iNOS. Infection affects uterine contractile activity through PG production, as well as through placental and genetic factors. NO may be a double-edged sword in pregnant mice myometrium.

High iNOS mRNA and protein localization during late pregnancy suggest a role for nitric oxide in mouse pubic symphysis relaxation

Remodeling and relaxation of the mouse pubic symphysis (PS) are central events in parturition. The mouse PS remodels in a hormone-controlled process that involves the modification of the fibrocartilage into an interpubic ligament (IpL), followed by its relaxation prior to parturition. It is recognized that nitric oxide synthase (NOS) and consequently nitric oxide (NO) generation play important roles in extracellular matrix modification, and may promote cytoskeleton changes that contribute to the remodeling of connective tissue, which precedes the onset of labor. To our knowledge, no studies thus far have investigated inducible nitric oxide synthase (iNOS) expression, protein localization, and NO generation in the mouse PS during pregnancy. In this work, we used a combination of the immunolocalization of iNOS, its relative mRNA expression, and NO production to examine the possible involvement of iNOS in remodeling and relaxation of the mouse IpL during late pregnancy. The presence of iNOS was observed in chondrocytes and fibroblast-like cells in the interpubic tissues. In addition, iNOS mRNA and NO production were higher during preterm labor on Day 19 of pregnancy (D19) than NO production on D18 or in virgin groups. The significant increase in iNOS mRNA expression and NO generation from the partially relaxed IpL at D18 to the completely relaxed IpL at D19 may indicate that NO plays an important role in late pregnancy during relaxation of the mouse IpL.

Decreased type III collagen expression in human uterine cervix of prolapse uteri

The precise mechanism of prolapse uteri is not fully understood. There is evidence to suggest that abnormalities of collagen, the main component of extracellular matrix, or its repair mechanism, may predispose women to prolapse. To investigate the characteristic structure of human uterine cervix of patients with prolapse uteri, various types of collagen expression in the uterine cervix tissues of the prolapse uteri were compared to those of normal uterine cervix. After informed consent, 36 specimens of uterine cervical tissues were obtained at the time of surgery from 16 postmenopausal women with prolapse uteri (stage III-IV by the Pelvic Organ Prolapse Quantification examination) and 20 postmenopausal women without prolapse uteri (control group). Collagens were extracted from the uterine cervix tissues by salt precipitation methods. The relative levels of various collagens were evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The uterine cervix was longer in the patients with prolapse uteri than those of postmenopausal controls without prolapse uteri. The ratios of type III to type I collagen in the uterine cervical tissues were significantly decreased in the prolapse uteri, as compared to those of the postmenopausal uterine cervix without prolapse. These results suggest that decreased type III collagen expression may play an important role in determing the physiology and structure of the uterine cervix tissues of prolapse uteri.

Effect of isosorbide mononitrate for cervical ripening before surgical termination of pregnancy in the first trimester

OBJECTIVE

To evaluate the efficacy of isosorbide mononitrate (IMN) for cervical ripening prior to first trimester surgical termination of pregnancy.

METHODS

A prospective, double-blind, randomized, placebo-controlled trial. Women scheduled for surgical termination of a nonviable fetus before 12 weeks of gestation from October 2008 to June 2009 were enrolled and randomly assigned to receive either 20 mg vaginally of IMN (n=24) or a placebo (n=24) 4 hours before suction evacuation. Cervical dilation before evacuation was assessed with 10-mm Hegar dilators followed by smaller sizes that were measured until the instrument passed freely through the internal os. Cervical dilation, adverse effects, termination complications, and patient satisfaction were the main outcomes.

RESULTS

Mean cervical dilation was not significantly different between the IMN and placebo groups (6.29+/-0.99 mm vs 5.71+/-1.04 mm; P=0.05). Mean operative time did not differ between the groups (16+/-0.07 min vs 18+/-0.06 min; P=0.55), nor did patient satisfaction measured by visual analogue scale (7.04+/-1.68 vs 6.54+/-1.22; P=0.24).

CONCLUSION

IMN was comparable to placebo in terms of efficacy and patient satisfaction for cervical priming prior to first-trimester termination of pregnancy.

Tocolytic effect of delta9-tetrahydrocannabinol in mice model of lipopolysaccharide--induced preterm delivery: role of nitric oxide

INTRODUCTION

In this study, we explained that exogenous cannabinoid, Delta(9)-tetrahydrocannabinol (THC), has a preventive effect in a murine model of lipopolysaccharide (LPS)-induced preterm delivery and the contribution of nitric oxide (NO) pathway as a mechanism involved in this process.

STUDY DESIGN

Preterm delivery was induced by double dose of 35 microg/kg LPS with 3-hour interval on gestational day (gd) 15. Delta(9)-tetrahydrocannabinol was administered with (a) double dose (0.02, 0.05, 0.1, 0.5, 1, and 5 mg/kg) 1 hour before each LPS injection, on gd 15 and (b) single administration (0.05, 0.1, and 0.5 mg/kg,) on gds 13 and 14, and the double administration, 1 hour before each LPS injection. To assess the involved mechanism, either AM281 (CB1 receptor antagonist, 2 mg/kg) and AM630 (CB2 receptor antagonist, 5 mg/kg) or N(omega)-nitro-L-arginine methyl ester (L-NAME, 2 mg/kg) was administered 1 hour before each THC injection on gds 13, 14, and 15. The main outcome measurement was the incidence of preterm delivery after injection of last LPS dose. Any interaction in the incidence and time of preterm delivery was ruled out by administration of AM281, AM630, or L-NAME alone.

RESULTS

Chronic THC treatment (0.5 mg/kg) significantly decreased the incidence of LPS-induced premature labor and increased the delivery time. Both AM281 and L-NAME reversed THC-induced attenuation of preterm delivery rate and pregnancy duration. Unlike AM281, AM630 did not influence the rate of preterm delivery in THC-treated mice.

CONCLUSION

Delta(9)-Tetrahydrocannabinol contributes to the regulation of gestational duration in LPS-induced preterm delivery probably by NO coupling through the CB1 receptor.

Genetic background affects the biomechanical behavior of the postpartum mouse cervix

OBJECTIVE

We hypothesized that the genetic makeup has an impact on the functional behavior of the uterine cervix. Therefore, we compared the biomechanical properties of uterine cervix in postpartum in 2 strains of mice that differ in their underlying regenerative collagen remodeling characteristics: MRL/MpJ+/+ (MRL: high regenerative repair) and C57BL/6 (C57: low regenerative high fibrotic repair).

STUDY DESIGN

Cervical tensile proprieties were assessed on day 3, 15, and 60 postpartum in MRL (n = 14) and C57 (n = 13) mice (4-5 animals at each time point). Stress-strain curves were generated using Shimadzu EZ-test instrumentation. Cervical tissue was stretched by 0.42 mm/min until rupture. Parameters of viscoelasticity including slope (a measure of stiffness), yield point (YP; moment when tissue changes its proprieties from elastic to plastic), and break point (BP; measure of tissue strength) were recorded and analyzed blindly between strains. Data were normalized to the weight of the tissue and analyzed by 2-way analysis of variance. Histological and collagen birefringence evaluation of the uterine cervix (MRL: n = 4; C57: n = 4) was performed 5 days after delivery.

RESULTS

At 3 and 15 days postpartum, cervices of MRL mice were significantly more compliant than those of C57 (P < .001). MRL mice displayed a significant increase in stiffness from day 3 to day 60 (slope, median +/- SEM: day 3: 3.1 +/- 0.5 vs day 15: 20.3 +/- 4.9 vs day 60: 33.1 +/- 3.5 N/mm per gram; P < .001). In contrast, the stiffness of C57 cervices reached maximum on day 15 (slope day 3: 14.1 +/- 4.3 vs day 15: 40.0 +/- 6.5 N/mm per gram; P = .02) and rested at a similar level on day 60 (day 60: 26.1 +/- 7.0 N/mm per gram; day 60 vs day 15: P = .937). More force was required to reach YP in C57 on day 3 (C57: 72.5 +/- 14.7 vs MRL: 19.9 +/- 1.6 N/g; P < .001) but not on either day 15 (C57: 156.1 +/- 27.5 vs MRL: 109.2 +/- 26.0 N/g; P = .120) or on day 60 (C57: 143.4 +/- 26.5 vs MRL: 164.5 +/- 18.7 N/g; P = .412). There was a significant decrease in BP in both strains on both day 15 and day 60 compared with day 3 postpartum (P = .856 for strain, P = .008 for day). MRL mice displayed significantly less cervical collagen birefringence compared with C57 control (P < .001) but increased proteoglycan staining and increased water content.

CONCLUSION

We provide evidence that genetic makeup may have an impact on cervical tissue remodeling and function. There are significant differences in postpartum cervical stiffness and compliance that vary with the regenerative collagen remodeling phenotype.

Relationship between gene expression and function of uterotonic systems in the rat during gestation, uterine activation and both term and preterm labour

We have documented gestation- and labour- (preterm and term) dependent changes in expression of genes encoding contraction associated proteins in the rat uterus and correlated these changes with various parameters of uterine contractility. The data demonstrate increased expression of contractile agonist systems concurrent with decreased expression of relaxant systems after gestational day 20. Significant increases in expression of oxytocin (OT), its receptor (OTR), prostaglandin (PG) H synthase isoform 1 (PGHS-1) and PGF(2alpha) receptor (FP) occurred first, followed by increases in PGHS-2, connexin-43, endothelin-1 (ET-1) and the ET-1 receptor isoform ET(A). Expression of OTR and FP was significantly reduced during mid-gestation compared to non-pregnant animals. Expression of inducible nitric oxide synthase (iNOS) increased significantly during pregnancy then decreased concurrently with the increase in OTR and FP. Functional changes in uterine contractility accompany changes in gene expression. OT was the most potent contractile stimulant. Sensitivity of uterine strips to OT was reduced in early and mid-pregnancy then increased at uterine activation. Progesterone antagonist-induced preterm labour caused changes similar to those at normal term. Comparison of mRNA transcripts in separated endometrium and myometrium suggested that the endometrium is an important regulator of myometrial contractility, analogous to the relationship between endothelium and vascular smooth muscle. This novel combination of functional and genetic expression analyses provides new insight into the physiology of parturition.

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

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

Effects of oral l-arginine on the pulsatility indices of umbilical artery and middle cerebral artery in preterm labor

OBJECTIVE

The objective of the study was the estimation of the influence of oral supplementation with low-dose l-arginine on feto-placental circulation in women with threatened preterm labor.

STUDY DESIGN

Oral administration of 3g of L-arginine daily or placebo as a supplement to standard tocolytic therapy was tried in 70 women with threatened preterm delivery, randomly assigned to the L-arginine (n=37) or placebo (n=33) groups. Twenty-five and 20 completed the study, respectively. Doppler velocimetry of pulsatility indices (PI) of the umbilical (UA) and middle cerebral (MCA) arteries as well as pregnancy outcome and biochemical markers of nitric oxide synthesis (plasma amino acid and nitrite/nitrate levels, as well as 24 h nitrite/nitrate excretion with urine) were estimated.

RESULTS

Starting from the second week of therapy, the UA PI values were significantly lower in the L-arginine group than in the placebo group. Moreover, treatment with L-arginine caused a significant increase in MCA PI and cerebro-placental ratio (CPR) values. The changes in feto-placental circulation in the L-arginine group were not associated with any signs of increased nitric oxide synthesis.

CONCLUSION

Oral supplementation with low doses of L-arginine changed feto-placental blood flow distribution in patients with threatened preterm labor. The exact mechanism of L-arginine action on feto-placental circulation requires further investigation.

Regulation of the nitric oxide pathway genes by tetrahydrofurandiols: microarray analysis of MCF-7 human breast cancer cells

THF-diols (9,12-oxy-10,13-dihydroxyoctadecanoic and 10,13-oxy-9,12-dihydroxyoctadecanoic acids) are endocrine disrupters in rats and mitogens in breast cancer cells. Microarray analyses and real-time PCR analyses on RNA from THF-treated MCF-7 cells revealed a number of genes (caveolin 1, heat shock protein 90 alpha and 90 beta, vascular endothelial growth factor, ATPase, Ca++ transporting, ubiquitous) in the nitric oxide pathway (NOP) were targets for THF-diols. Chromatin immunoprecipitation studies suggest THF-diols modify of histone H4 acetylation at the caveolin 1 promoter via an epigenetic mechanism. These findings are consistent with the well-known involvement of NOP genes in cell proliferation and sexual behavior.

Racial differences in nitric oxide-dependent vasorelaxation

Along with the growing heterogeneity of the American population, ethnic/racial disparity is becoming a clear health issue in the United States. The awareness of ethnic/racial disparities has been growing because of considerable data gathered from recent clinical and epidemiological studies. These studies have highlighted the importance of addressing these differences in the diagnosis and treatment of various diseases potentially according to race. It is becoming particularly clear that there is a 2- to 3-fold racial difference in certain cardiovascular diseases (eg, preeclampsia) associated with dysfunctional nitric oxide-mediated vasodilation. In this review, the authors summarize the current literature on racial disparities in nitric oxide-mediated vasodilation in relation to cardiovascular health with an emphasis on vascular nitric oxide bioavailability as a balance between production via endothelial nitric oxide synthase and degradation through reactive oxygen species. The major hypotheses postulated on the biological basis of these differences are also highlighted.

Relationships of maternal serum levels of vascular endothelial growth factor and tensile strength properties of the cervix in a rat model of chronic hypoxia

OBJECTIVE

It has been shown that hypoxia leads to alterations in maternal serum levels of vascular endothelial growth factor (VEGF). In this study, we sought to test the hypothesis that chronic hypoxia increases maternal serum levels of VEGF, which in turn cause measurable changes in the viscoelastic properties of the rat uterine cervix.

STUDY DESIGN

Timed-pregnant adult Sprague-Dawley rats were exposed to hypoxia beginning on day 17 of gestation (term = day 22). The following groups of animals were studied: (1) nonpregnant controls (NP, n = 6); (2) normoxia 21% fraction of inspired oxygen (FiO2) (NMX, n = 6); and (3) severe hypoxia 10% FiO2 (HPX; n = 5). A hypoxic chamber was used to assure consistent hypoxic environment. Animals were killed on day 21 of gestation (before labor). Maternal blood was collected immediately following anesthesia and prior to euthanasia. Free serum levels of VEGF were measured by highly specific immunoassays. Tensile strength properties of the cervix were assessed using a stretching regimen designed to mimic labor. Physical parameters measured were: indicators of viscoelasticity (slope; measure of stiffness), plasticity (yield point [YP]; moment the tissue changes its properties from elastic to plastic), strength (break point [BP]; moment of tissue disruption), and displacement at YP (marks the duration of the viscoelastic phase of the stretching) and BP (a measure of the strength of the material). Data were normalized to the dry weight of the cervix.

RESULTS

Hypoxia is associated with increased serum levels of VEGF compared to NP or NMX groups (P = .001). Cervical stiffness was lower in NMX, compared with NP animals (P = .004), and was not significantly influenced by hypoxia (P > .05). Overall there was a significant inverse correlation between slope and maternal serum levels of VEGF (r = -0.85, P < .001). The force required to reach YP was significantly higher for the NP, compared with NMX and HPX groups (P = .004). Hypoxia did not alter the force required to reach the YP (NMX vs HPX, P > .05). Conversely, hypoxia significantly decreased the displacement at YP, indicating a shortening of the elastic phase (NMX vs HPX, P = .021). There was a significant inverse correlation between maternal serum levels of VEGF and the displacement at YP (r = -0.68, P = .002). In vivo, hypoxia decreased the force required to reached the BP (NMX vs HPX, P = .025), but there was no correlation between the levels of maternal serum VEGF and this indicator (r = -0.35, P = .170).

CONCLUSION

Chronic hypoxia induces measurable changes in maternal serum levels of VEGF and tensile properties of the rat cervix, specifically a shortening of the elastic phase. Hypoxia decreases the cervical strength to stretch and predisposes to rupture, but this effect seems to be unrelated to maternal serum levels of VEGF.

Nitric oxide in the human uterine cervix: endogenous ripening factor

The human uterine cervix can produce nitric oxide (NO), a free radical with an ultra-short half-life. The release of NO changes during pregnancy and is increased in early nonviable pregnancies compared to normal uncomplicated pregnancies. This review concentrates on the role of NO release in cervical ripening in pregnant women. Also some suggestions on future aspects are discussed.

Clinical use of nitric oxide donors and L-arginine in obstetrics

Nitric oxide (NO) is a free radical that plays a fundamental role in human physiology, being involved in the homeostasis of different functions. In obstetrics this molecule is determinant in the physiology of labor and cervical ripening; it possibly plays a fundamental role in the etiology of preeclampsia and intrauterine growth restriction, and it could also be utilized in view of its ability to induce smooth muscle relaxation. Several clinical trials have ascertained the ability of the topical application of NO donors to promote cervical ripening, and also labor induction. There is much less evidence on the use of NO donors in the vascular complications of pregnancy, either as prophylactics or therapeutic agents. Due to the capacity of NO to promote relaxation of smooth muscle, NO donors have been employed as tocolytics with performance similar to other agents. Moreover, although anecdotal, the experience of sudden uterine relaxation using NO donors in obstetric emergencies remains of great clinical value.