Evaluation of Proteasome and Immunoproteasome Levels in Plasma and Peritoneal Fluid in Patients with Endometriosis.

Endometriosis is a chronic disease in which the endometrium cells are located outside the uterine cavity. The aim of this study was to evaluate circulating 20S proteasome and 20S immunoproteasome levels in plasma and peritoneal fluid in women with and without endometriosis in order to assess their usefulness as biomarkers of disease. Concentrations were measured using surface plasmon resonance imaging biosensors. Patients with suspected endometriosis were included in the study-plasma was collected in 112 cases and peritoneal fluid in 75. Based on the presence of endometriosis lesions detected during laparoscopy, patients were divided into a study group (confirmed endometriosis) and a control group (patients without endometriosis). Proteasome and immunoproteasome levels in both the plasma (p = 0.174; p = 0.696, respectively) and the peritoneal fluid (p = 0.909; p = 0.284, respectively) did not differ between those groups. There was a statistically significant difference in the plasma proteasome levels between patients in the control group and those with mild (Stage I and II) endometriosis (p = 0.047) and in the plasma immunoproteasome levels in patients with ovarian cysts compared to those without (p = 0.017). The results of our study do not support the relevance of proteasome and immunoproteasome determination as biomarkers of the disease but suggest a potentially active role in the pathogenesis of endometriosis.

The mechanism of action of oxytocin antagonist nolasiban in ART in healthy female volunteers.

RESEARCH QUESTION: What are the effects of the oxytocin receptor (OTR) antagonist nolasiban on uterine contractions, endometrial perfusion and endometrial mRNA expression? DESIGN: Randomized, double-blind, parallel-group, mechanism-of-action study with nolasiban. Forty-five healthy, pre-menopausal women were treated with placebo, 900 mg or 1800 mg nolasiban on the day corresponding to blastocyst transfer. Ultrasonographic uterine contraction frequency and endometrial perfusion were assessed, and endometrial biopsies analysed by next-generation sequencing. RESULTS: Both doses of nolasiban showed decreased contraction frequency and increased endometrial perfusion depending on the time point assessed. At 1800 mg, 10 endometrial genes (DPP4, CNTNAP3, CNTN4, CXCL12, TNXB, CTSE, OLFM4, KRT5, KRT6A, IDO2) were significantly differentially expressed (adjusted P < 0.05). Of these, OLFM4, DPP4 and CXCL12 were regulated in the same direction as genes involved in implantation during the window of implantation. In addition, three genes (DPP4, CXCL12 and IDO2) were associated with decidualization and endometrial receptivity. CONCLUSIONS: These data expand our knowledge of the mechanism of action of nolasiban in increasing pregnancy rates after embryo transfer. The results suggest more marked effects of nolasiban 1800 mg compared with the 900 mg dose, supporting testing at higher doses in IVF patients.

Role of sphingolipids in the pathogenesis of intrahepatic cholestasis.

BACKGROUND & AIMS: Intrahepatic cholestasis of pregnancy (ICP) is the most common pregnancy-related liver disorder that affects from 0.2% to 15.6% pregnant women. The disease is connected with increased risk of fetal morbidity and mortality, but is unfortunately detected quite late. The diagnosis of ICP is based on only one manifestation: pruritus which mainly affects soles and palms. METHODS: Twenty intrahepatic cholestasis of pregnancy (ICP) women and twenty healthy pregnant women (control group) took part in the study. In the study group, blood sampling for baseline measurements was performed on the first day of hospital stay - before the commencement of treatment with ursodeoxycholic acid (UDCA) - and repeated after 7 days of 900 mg UDCA per day. An additional blood sample was collected on the second day after childbirth. In the control group, blood samples were collected directly after hospital admission. We compared plasma sphingolipids in samples of the subjects from ICP and ICP + UDCA-treated groups as well as the ICP group after delivery with the healthy controls. RESULTS: Of all sphingolipids, the median values of C16-Cer and C18-Cer were significantly higher in the plasma of cholestasis patients not treated with UDCA as compared to the control. Following 7 days of UDCA treatment, a considerable decrease in C16-Cer, C18-Cer and the total concentration of bile acids was noted as compared to the baseline. CONCLUSION: It is known that sphingolipids serve as modulators of liver regeneration. We assume these substances could be potential markers for detecting early onsets of intrahepatic cholestasis of pregnancy.

Oxytocin antagonism reverses the effects of high oestrogen levels and oxytocin on decidualization and cyclooxygenase activity in endometrial tissues.

RESEARCH QUESTION: What is the in-vitro effect of oxytocin receptor (OTR) antagonism on parameters of receptivity in human endometrial explants and endometrial stromal cell lines cultured in oestradiol-rich conditions mimicking ovarian stimulation? DESIGN: Experimental in-vitro study on endometrial tissue explants collected by aspiration biopsy from 30 women undergoing fertility treatment and cultured endometrial tHESC cell line. The study examined the effects of high oestradiol, oxytocin and OTR antagonist on parameters of decidualization (cell viability and prolactin secretion) as well as cyclooxygenase-1/2 (COX-1/2) activity and prostaglandin F2α (PGF2α) secretion. Changes in expression of OXTR and COX-2 genes were examined using quantitative polymerase chain reaction (qPCR). RESULTS: In experiments on cultured endometrial cell line, high oestradiol and oxytocin similarly limited the viability of cells. In cultured endometrial explants both also decreased the secretion of prolactin (a marker of decidualization) and augmented endometrial COX-2 activity and formation of PGF2α. Oxytocin antagonist atosiban was confirmed to reverse the above effects, both in the endometrial line and endometrial explants. Addition of atosiban to cultures acted analogously in experiments employing both oxytocin and high oestradiol. CONCLUSIONS: Oxytocin antagonist reversed the effects of high oestradiol and oxytocin on parameters related to endometrial receptivity in conditions mimicking ovarian stimulation. This might point to a novel, endometrium-related mechanism to support embryo implantation achieved by the application of oxytocin antagonist prior to embryo transfer.

Simultaneous analysis of bisphenol A fractions in maternal and fetal compartments in early second trimester of pregnancy.

Background Bisphenol A (BPA) is an estrogenic, endocrine-disrupting compound widely used in the industry. It is also a ubiquitous environmental pollutant. Its presence was confirmed in human fetuses, which results from maternal exposure during pregnancy. The mechanisms behind maternal-fetal transfer, and relationships between pregnant women and fetal exposures remain unclear. The aim of this study was to assess the impact of maternal exposure to BPA on the exposure of the fetus. Methods Maternal plasma and amniotic fluid samples were collected from 52 pregnant women undergoing amniocentesis for prenatal diagnosis of chromosomal abnormalities. BPA was measured by gas chromatography-mass spectrometry (GC-MS). The permeability factor - a ratio of fetal-to-maternal BPA concentration - was used as a measure delineating the transplacental transfer of BPA. Results The median concentration of maternal plasma BPA was 8 times higher than the total BPA concentration in the amniotic fluid (8.69 ng/mL, range: 4.3 ng/mL-55.3 ng/mL vs. median 1.03 ng/mL, range: 0.3 ng/mL-10.1 ng/mL). There was no direct relationship between the levels of BPA in maternal plasma and amniotic fluid levels. The permeability factor, in turn, negatively correlated with fetal development (birth weight) (R = -0.54, P < 0.001). Conclusion Our results suggest that the risk of fetal BPA exposure depends on placental BPA permeability rather than the levels of maternal BPA plasma concentration and support general recommendations to become aware and avoid BPA-containing products.

Potential first trimester metabolomic biomarkers of abnormal birth weight in healthy pregnancies.

OBJECTIVE: Macrosomia and low birth weight (LBW) can be associated with pregnancy complications and may affect the long-term health of the child. The aim of this study was to evaluate the metabolomic serum profiles of healthy pregnant women to identify early biomarkers of macrosomia and LBW and to understand mechanisms leading to abnormal fetal growth not related to mother's body mass index or presence of gestational diabetes. METHOD: Serum samples from 770 women were collected between the 12th and 14th gestational week. Delivery samples were divided into three groups according to the infant birth weight as follows: low, <2500 g; normal, 2500-4000 g; and high >4000 g. Samples from women with any complications of pregnancy were excluded. Serum fingerprinting was performed by LC-QTOF-MS. RESULTS: Lower levels of phospholipids, lysophospholipids, and monoacylglycerols; low vitamin D3 metabolites; and increased bilirubin level were associated with macrosomia. Because most changes involved lipids, as a concept of validation, adipocyte fatty acid-binding protein (A-FABP) levels were measured and found correlated with the studied lipids and birth weight. CONCLUSION: Serum fingerprinting in early pregnancy can predict the risk of macrosomia. Serum levels of A-FABP and several lipids are promising prognostic markers for macrosomia in healthy pregnancies.

[Uterine contractile activity at embryo transfer--as a new pharmacotherapeutic target in assisted reproduction]. / Czynnosc skurczowa macicy przed transferem zarodków jako nowy punkt docelowy farmakoterapii w leczeniu nieplodnosci.

Uterine contractile activity plays an important role in the reproduction of mammals, influencing sperm transport in the genital tract and positioning of the implanting embryo within the uterine cavity In humans, apart from the time of menses, the activity of a non-pregnant uterus is usually not perceived, and it is also not a subject of any routine clinical testing. Major contractile factors in non-gravid uteri are oxytocin and prostaglandins, locally produced within the endometrium. Oxytocin synthesis and expression of its receptors is gradually increasing in the follicular phase, following an increase in estrogen levels, and reaches its peak in the periovulatory period. In stimulated cycles, where supraphysiological estradiol concentrations are present, uterine contractile activity can be elevated. Exaggerated uterine contractions before embryo transfer are observed in one third of women undergoing controlled ovarian stimulation. Detection of such patients could enable their qualification for pharmacologic treatment. Evaluation of uterine contractions in such cases should be done non-invasively in order to avoid any endometrial trauma. Ultrasound evaluation of the movements of endometrial interface can be applied. Pharmacologic treatment of elevated uterine contractility before embryo transfer could improve the success rates of fertility treatments. So far application of beta mimetics or non-steroid anti-inflammatory drugs has not been associated with any progress. Oxytocin receptor system in the myometrium and the endometrium is a potential target for new class of medications aiming to improve implantation rates. This review summarizes up-to-date knowledge on the significance of uterine contractile activity in embryo implantation and describes the emerging new treatment targets in assisted reproduction.

The SPRi determination of cathepsin L and S in plasma and peritoneal fluid of women with endometriosis.

PURPOSE: Endometriosis is a common disease with a complex pathomechanism and atypical symptoms, often leading to delayed diagnosis. Currently, the sole method for confirming the presence of the disease is through laparoscopy and histopathological examination of collected tissue. However, this invasive procedure carries potential risk and complications, necessitating the exploration of non-surgical diagnostic methods for endometriosis. This study aims to analyze peritoneal fluid and plasma samples for the expression of cathepsin L and cathepsin S to identify potential biomarkers for non-invasive diagnostic approaches to endometriosis. MATERIAL AND METHODS: In this cross-sectional study, plasma and peritoneal fluid samples were obtained during laparoscopy from 63 patients diagnosed with chronic pelvic pain or infertility. The study group consisted of women with confirmed endometriosis. The concentrations of cathepsins L and S were determined using an SPRi biosensor. RESULTS: The study did not reveal significant differences in the concentrations of cathepsin L and cathepsin S between the control group and the study group, both in peritoneal fluid and plasma. CONCLUSIONS: Based on the results of this study, it appears that cathepsins L and S are not suitable candidates as biomarkers for endometriosis.

Is the leptin/BMI ratio a reliable biomarker for endometriosis?

Background: The aim of this study was to analyze the concentration of leptin in peritoneal fluid and plasma and to assess their role as potential biomarkers in the diagnosis of endometriosis. Materials & methods: Leptin adjusted for BMI (leptin/BMI ratio) was measured using surface plasmon resonance imaging (SPRI) biosensors. Patients with suspected endometriosis were included in the study. Plasma was collected from 70 cases, and peritoneal fluid from 67 cases. Based on the presence of endometriosis lesions detected during laparoscopy, patients were divided into a study group and a control group (patients without endometriosis). Results: Leptin/BMI ratio in plasma did not differ between women with endometriosis and the control group (0.7159 ± 0.259 vs 0.6992 ± 0.273, p= 0,7988). No significant differences were observed in peritoneal leptin/BMI ratio levels in patients with and without endometriosis (0.6206 ± 0.258 vs 0.6215 ± 0.264, p= 0,9896). Plasma and peritoneal leptin/BMI ratios were significantly lower in women with endometriosis - related primary infertility compared to women with endometriosis without primary infertility (0.640 ± 0.502 vs 0.878 ± 0.623, p < 0.05). The difference was observed in case of primary infertility, but not in terms of the secondary one. No significant differences were noted between leptin/BMI ratio in the proliferative phase and the secretory phase (0.716 ± 0.252 vs 0.697 ± 0.288, p= 0,7785). Conclusion: The results of present study do not support the relevance of leptin concentration determination as a biomarker of the endometriosis. Due to the limited number of samples in the tested group, further studies are needed to confirm its role.

Plasma and Peritoneal Fluid Annexin A2 Levels in Patients with Endometriosis.

Introduction: Endometriosis is an inflammatory-related reproductive age disease characterized by the presence of endometrial cells outside the uterine cavity. Current laboratory practice does not provide specific markers for detecting and assessing the advancement of endometriosis in either plasma or peritoneal fluid. The severity of disease is assessed in stages from I to IV based on the results of laparoscopic inspection. The protein annexin A2 (ANXA2) has been reported to be associated with inflammatory processes. Aim of the Study: The study aimed to investigate and compare ANXA2 protein concentration using the ELISA method in plasma and peritoneal fluid in a group of women with endometriosis compared to controls. Materials and Methods: Biological material was collected during a multicenter, cross-sectional study, which was conducted at eight departments during elective laparoscopy from 53 women with and 40 women without endometriosis. Patients were divided by endometriosis stage and infertility status, and then compared with subgroups. Analysis included the Chi-square test for categorical variables, Mann-Whitney U-test and two-sided Wilcoxon rank-sum test for continuous variables. Results: Women with endometriosis had significantly elevated plasma ANXA2 levels compared to women without endometriosis (mean concentrations 28.69 vs 19.61 ng/L, p=0.01). Differences in peritoneal fluid ANXA2 levels were statistically insignificant (mean concentrations of 23.7 vs 22.97 ng/L, p=0.06). Plasma concentrations in patients with stage III and IV endometriosis were significantly higher compared to controls (mean concentrations of 24.19 vs 19.71 ng/L, p=0.03). No such differences were observed in plasma when comparing stages I-II vs III-IV, and stages I-II vs controls (mean concentrations of 33.82 vs 24.19 ng/L, p=0.72 and 33.82 vs 19.71 ng/L, p=0.12, respectively). Comparison of samples from patients with or without infertility, primary or secondary infertility, endometriosis with or without infertility, and non-endometriosis with or without infertility showed no significant differences in the plasma nor in the peritoneal fluid concentrations. Conclusion: ANXA2 is possibly involved in the pathogenesis of endometriosis, especially in advanced stages. Due to the limited group of tested samples, further studies are needed to confirm its role.

Spontaneous rupture of unscarred uterus in the early second trimester: a case report of placenta percreta.

BACKGROUND: Prevalence of uterine rupture at delivery has been recently estimated at less than 1 in 2500 deliveries. Spontaneous uterine rupture in the early mid-trimester (16 weeks gestation or less), is far less frequent. We report a case of uterine rupture due to placenta percreta in otherwise uncomplicated pregnancy CASE: A 35-year-old, gravida 5, para 5, at 15wk 2d gestation (menstrual age) with negative history of uterine scarring suddenly developed symptoms of incipient hypovolemic shock while being hospitalized for imminent miscarriage. On exploratory laparotomy we found a midline uterine rupture infiltrated by the placenta. Supracervical hysterectomy was performed. Postoperative lab analysis confirmed the elevated serum AFP levels. CONCLUSION: Abnormal placentation and subsequent uterine rupture should be taken into consideration also in women in the second trimester who have no history of uterine instrumentation.

Oxytocin and vasopressin V(1A) receptors as new therapeutic targets in assisted reproduction.

Embryo transfer, the final stage of IVF/embryo transfer (IVF/ET) treatment, independently influences treatment outcome.Successful embryo implantation following embryo transfer, among other factors, is also dependant on uterine receptivity.Uterine contractile activity may adversely affect the implantation. Although increased contractions have been found in approximately 30% of patients undergoing embryo transfer, to date it has not been a subject to any diagnosis or therapy. Pharmacological tocolytics may be expected to improve pregnancy rates; however, targeting uterine adrenergic receptors, calcium channels or prostaglandin synthesis has since proven ineffective. The novel class of drugs which could be the most useful in this indication is oxytocin antagonists. In animal models, oxytocin significantly reduced embryo implantation rates, and this was reversed by an oxytocin antagonist. In humans, peptidyl oxytocin and mixed vasopressin V1A/oxytocin antagonists have been found to significantly reduce uterine contractions in egg donors undergoing mock embryo transfer. It has further been demonstrated that the vasopressin V1A/oxytocin receptor antagonist atosiban can improve pregnancy success in patients with recurrent IVF failures. This article reviews the uterine oxytocin/vasopressin V1A receptor systems and their potential influence on embryo implantation. It is suggested that the clinical application of oxytocin antagonists might improve results of IVF/ET treatment.

The Association between Bisphenol A, Steroid Hormones, and Selected MicroRNAs Levels in Seminal Plasma of Men with Infertility.

Bisphenol A (BPA), the most common endocrine-disrupting chemical, has been associated with male reproductive dysfunctions. Recently, it has been shown that BPA may also affect miRNAs expression. Herein, we aimed to evaluate the association of BPA levels with steroid hormone concentration and circulating miRNAs levels to investigate the potential direct effect of BPA on homeostasis in the testis environment. The level of BPA in the seminal plasma of azoospermic men was significantly higher compared to the healthy control. The concentrations of estradiol (E2) and androstenedione (A) were significantly decreased in the seminal plasma of azoospermic men compared to the normospermic men. The levels of miR-let-7a, miR-let-7b, and miR-let-7c were significantly up-regulated, and the level of miR-518f was significantly down-regulated in the seminal plasma of the azoospermic men compared to the healthy control. The level of BPA correlated negatively with sperm concentration and normal semen morphology. A significant positive correlation was found between BPA levels and miR-let-7a and miR-let-7c levels, whereas BPA negatively correlated with miR-518f levels. Our results suggest that BPA may negatively affect sperm quality. Moreover, BPA correlated with the miR-let-7a, miR-let-7c, and miR-518f levels in seminal plasma, which suggests that BPA may act directly in seminal plasma, affecting the testicular environment.

Ectopic pregnancy confirming the transperitoneal transport of gametes/embryos--a case report.

UNLABELLED: To present a rare case of spontaneous ectopic pregnancy in a non-communicating heterotopic fallopian tube associated with unicornuate uterus without a rudimentary horn. Case report. SETTING: Tertiary referral obstetrics and gynecology center. PATIENT: A 36-year-old woman in her fourth pregnancy (para 1, abortus 2) presented at 5th gestational week with severe abdominal pain and circulatory instability. INTERVENTION: Heterotopic fallopian tube removal by laparotomy. Investigation of the origin of the spontaneous heterotopic fallopian tube pregnancy and exploration of the gross structural development of the urinary system. Spontaneous ectopic pregnancy in a non-communicating heterotopic fallopian tube coexisting with corpus luteum in the contralateral ovary supports the hypothesis of transperitoneal migration of gametes or embryos.

Reductionist and system approaches to study the role of infection in preterm labor and delivery.

A substantial number of patients with preterm labor and delivery do not show clinical signs of infection, however, it is the subclinical form which is the main causative factor and often results in premature delivery. The hitherto commonly applied methods of inflammation detection are based either on potentially hazardous amniocentesis or still insufficient inflammation-related protein measurement in the serum or other biological fluids. The advent of new "omics" technologies has led to a paradigm-shift in experimental approach which tends to primarily generate rather than form hypotheses. This has resulted in a surge of wealth of data composed of sets of individual or clusters of new genes and proteins that can be of potential importance as new markers of inflammation leading to preterm labor. It is hoped that as a result of those new methodologies the overall perception of medical research and practice would gradually change from reductionist to systems approach. Despite several successes of reductionism in the diagnosis and treatment of preterm labor it seems that system-based methodology would contribute to a more favorable personalized rather than one-for-all patient assistance. In this review we present the current knowledge on this new attractive field of medical studies with emphasis on early detection of infection related with preterm labor.

New research models and novel signal analysis in studies on preterm labor: a key to progress?

Preterm labor affects up to 20% of pregnancies, is considered a main cause of associated neonatal morbidity and mortality and is responsible for neonatal care costs of multimillion euros. In spite of that, the commercial market for this clinical indication is rather limited, which may be also related to high liability. Consequently, with only a few exceptions, preterm labor is not in the orbit of great interest of the pharmaceutical industry. Coordinated effort of research community may bring the change and help required to reduce the influence of this multifactorial syndrome on society. Between the novel techniques that are being explored in a SAFE (The Special Non-Invasive Advances in Fetal and Neonatal Evaluation Network) group, there are new research models of preterm labor as well as novel methodology of analysis of biological signals. In this article, we briefly describe new clinical and nonclinical human models of preterm labor as well as summarize some novel methods of data processing and analysis that may be used in the context of preterm labor.

Decreased serum level of macrophage inflammatory chemokine-3beta/CCL19 in preterm labor and delivery.

OBJECTIVE: Chemokines are small soluble molecules which mediate leukocyte migration and may be involved in the pathophysiology of preterm labor. We aimed to determine if serum concentrations of selected chemokines are changed in preterm labor and delivery. STUDY DESIGN: A novel array-based enzyme-linked immunosorbent assay was used to quantitate serum levels of nine chemokines from a single sample: MDC/CCL22, TARC/CCL17, ITAC/CXCL11, I-309/CCL1, IP-10/CXCL10, MIP-1alpha/CCL3, -1beta/CCL4, -3alpha/CCL20 and -3beta/CCL19. Women in preterm labor who delivered (n = 17), women at preterm pregnancy not in labor (n = 13) and women in labor at term (n = 8) participated. RESULTS: In the preterm delivery group of patients, the MIP-3beta/CCL19 concentration was in mean (+/-S.D.) 70.4+/-31.7 pg/mL, which was significantly lower than that in preterm gravidas not in labor of 123+/-34 pg/mL (p < 0.001) and those in labor at term of 118+/-25.6 pg/mL (p < 0.01). The other measured chemokines did not differ significantly. CONCLUSIONS: Of a small number of examined chemokines, we were able to show that one of them, MIP-3beta/CCL19 was significantly lower in women with preterm labor and delivery. Whether or not this chemokine has a potential as biochemical marker of preterm delivery remains to be determined.

Visualization of synchronization of the uterine contraction signals: running cross-correlation and wavelet running cross-correlation methods.

In physiological research, we often study multivariate data sets, containing two or more simultaneously recorded time series. The aim of this paper is to present the cross-correlation and the wavelet cross-correlation methods to assess synchronization between contractions in different topographic regions of the uterus. From a medical point of view, it is important to identify time delays between contractions, which may be of potential diagnostic significance in various pathologies. The cross-correlation was computed in a moving window with a width corresponding to approximately two or three contractions. As a result, the running cross-correlation function was obtained. The propagation% parameter assessed from this function allows quantitative description of synchronization in bivariate time series. In general, the uterine contraction signals are very complicated. Wavelet transforms provide insight into the structure of the time series at various frequencies (scales). To show the changes of the propagation% parameter along scales, a wavelet running cross-correlation was used. At first, the continuous wavelet transforms as the uterine contraction signals were received and afterwards, a running cross-correlation analysis was conducted for each pair of transformed time series. The findings show that running functions are very useful in the analysis of uterine contractions.

Differences in permeability of preterm and term fetal membranes to calcium ions - Preliminary report.

The metabolic activity of amniochorion contributes to the control of activation of labor-type uterine contractions. The study presents an experimental model of transport of calcium ions across the human amniochorion sampled directly after cesarean section in patients delivering both at term and prematurely. Transmembrane transport of calcium ions was lower in preterm vs. term tissue samples. The differences in permeability were most pronounced in the first 60 min of experiments. The results of the study provide evidence for the existence of an active mechanism of calcium transport which can contribute to regulating the contractility of the uterus.

Inhibitory effect of barusiban and atosiban on oxytocin-induced contractions of myometrium from preterm and term pregnant women.

BACKGROUND: A synthetic oxytocin analogue, barusiban, was shown to potently inhibit oxytocin-induced activity of myometrium from term pregnant women. The responsiveness to vasopressin was not influenced by the compound. OBJECTIVE: To test the effect of barusiban and a reference compound, atosiban, on oxytocin-induced activity of myometrium from women at preterm pregnancy in comparison to myometrium from women at term. METHODS: Fifteen preterm (30-36 gestational weeks) and 12 term pregnant women (38-41 weeks) who underwent cesarean delivery donated myometrial tissue for the study. Concentration-response curves following oxytocin administration to isolated myometrial strips were recorded in control experiments, in the presence of barusiban at concentrations of 2.5, 25, and 250 nM, and of atosiban at concentrations of 25, 250, and 750 nM. Effective concentration 50% (EC50) and pA2 values were calculated. RESULTS: Both antagonists in higher concentrations increased the EC50 values to oxytocin. The median pA2 value for preterm myometrium with barusiban was 9.76 and with atosiban 7.86. For term myometrium the corresponding pA2 results were 9.89 and 7.81, respectively. None of these pA2 values differed to any statistically significant degree. CONCLUSION: The selective oxytocin antagonist, barusiban, concentration-dependently inhibits oxytocin-induced myometrial contractions of both preterm and term myometrium at least as potently as atosiban. It remains to be determined if the selectivity of barusiban for the oxytocin receptor confers an advantage over atosiban as a tocolytic in preterm labor.