Contractility Of Human Myometrium Research Articles

Dual effect of nifedipine on pregnant human myometrium contractility: Implication of TRPC1.

Nifedipine, an L‐type voltage‐gated Ca2+ channel (L‐VGCC) blocker, is one of the most used tocolytics to treat preterm labor. In clinical practice, nifedipine efficiently decreases uterine contractions, but its efficacy is limited over time, and repeated or maintained nifedipine‐based tocolysis appears to be ineffective in preventing preterm birth. We aimed to understand why nifedipine has short‐lasting efficiency for the inhibition of uterine contractions. We used ex vivo term pregnant human myometrial strips treated with cumulative doses of nifedipine. We observed that nifedipine inhibited spontaneous myometrial contractions in tissues with high and regular spontaneous contractions. By contrast, nifedipine appeared to increase contractions in tissues with low and/or irregular spontaneous contractions. To investigate the molecular mechanisms activated by nifedipine in myometrial cells, we used the pregnant human myometrial cell line PHM1‐41 that does not express L‐VGCC. The in vitro measurement of intracellular Ca2+ showed that high doses of nifedipine induced an important intracellular Ca2+ entry in myometrial cells. The inhibition or downregulation of the genes encoding for store‐operated Ca2+ entry channels from the Orai and transient receptor potential‐canonical (TRPC) families in PHM1‐41 cells highlighted the implication of TRPC1 in nifedipine‐induced Ca2+ entry. In addition, the use of 2‐APB in combination with nifedipine on human myometrial strips tends to confirm that the pro‐contractile effect induced by nifedipine on myometrial tissues may involve the activation of TRPC channels.

395 Dual effect of nifedipine on term pregnant human myometrium contractility

Nifedipine, L-type voltage-gated Ca2+ channels (L-VGCC) blocker, is one of the most used tocolytics to treat preterm labor. In clinical practice, nifedipine efficiently decreases uterine contractions but its efficacy is limited overtime (48h). The aim of this study was to understand why nifedipine has short-lasting efficiency for inhibition of uterine contractions. Term pregnant human myometrial strips with different ex vivo contractile capacities [either regular (n=6) or irregular (n=5) spontaneous contractions] were mounted in an organ bath, and treated with cumulative doses of nifedipine. Tissue contractility in response to nifedipine was analyzed. Then, to investigate the molecular mechanisms activated by nifedipine in myometrial cells with irregular contractile capacity, we used the pregnant human myometrial cell line PHM1-41 that does express L-VGCC. Cells were transfected with siRNA for ORAI1, a non-voltage gated Ca2+ channel, and STIM1, the ORAI1 regulator. Both transfected and non-transfected cells were treated with different doses of nifedipine. Evolution of intracellular Ca2+ level was monitored with a Ca2+ indicator dye. Treatment of myometrial strips with cumulative doses of nifedipine inhibited spontaneous myometrial contraction in tissues with high contractility, even at low doses. On the contrary, nifedipine treatment appeared to increase contractions in tissues with low contractility (Fig1). In vitro, high doses of nifedipine (>10-6M) induced an important intracellular Ca2+ entry in myometrial cells (Fig2). Nifedipine-induced Ca2+ influx was not affected by knock-down of ORAI1 and STIM1 neither individually, nor together This study highlighted existence of a dual action of nifedipine. In addition to inhibit contraction in contracting myometrial tissue, we showed that nifedipine had an opposite pro-contractile effect in weak-contracting muscle. This effect could involve an activation of Ca2+ entry into myometrial cells, but this process does not seem to involve neither STIM1 nor ORAI1 Ca2+ channel.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Influence of oxytocin receptor single nucleotide sequence variants on contractility of human myometrium: an in vitro functional study

BackgroundOxytocin receptor (OXTR) gene variants have been shown to affect the prevalence of preterm birth, mode of delivery and oxytocin (OXT) requirements for labor induction and augmentation. We hypothesized that this might be associated with different myometrium responses to oxytocin. Our aim was to investigate the influence of a selection of eight OXTR gene single nucleotide variants on oxytocin-induced stimulation of human myometrium contractility in vitro.MethodsHuman myometrium biopsies were collected during elective cesarean sections at term, if patients had given informed consent. Myometrial strips were submerged under tension in an organ bath and allowed to contract; the remaining material was stored at − 80 °C for further determination of relevant genetics and mRNA level. The area under the curve (AUC) of all contractions taking place in the absence of OXT and of those occurring upon OXT addition (for 30 min each) was measured. OXT stimulation, defined as the ratio between AUC measurements after OXT addition and those in the absence of OXT was calculated for each strip. TaqMan™ Assays were used to detect the allele distribution of the eight OXTR variants and to determine the relative amounts of OXTR-mRNA in the samples. For each variant, oxytocin stimulation of contractility was compared between samples homozygous for the reference allele (reference group) and samples with at least one variant allele (variant group) by linear regression.ResultsSixty samples were included in the present study. For rs1042778, rs11706648, rs4686301, rs53576, rs237895, and rs237902, OXT stimulation was similar in the reference and in the variant groups. However, the values of OXT stimulation differed significantly between the reference and the variant groups for rs4686302 (3.1 vs. 4.1 times; p = 0.022) and rs237888 (3.2 vs. 5.5 times; p = 0.001). No significant differences between the levels of OXTR-mRNA in the various reference and corresponding variant groups were detected.ConclusionsPatients with variant alleles of rs237888 and/or rs4686302 may be more sensitive to oxytocin stimulation, explaining why these sequence variants have been associated with lower cesarean section prevalence and premature birth, respectively.

The Effect of Intermittent Oxytocin Pretreatment on Oxytocin-induced Contractility of Human Myometrium In Vitro

(Anesth Analg. 2019;128(4):671–678. Doi:10.1213/ANE.0000000000002834) Uterine atony is the leading cause of postpartum hemorrhage, which is responsible for nearly a quarter of maternal deaths worldwide. One risk factor for uterine atony is exposure to large quantities of oxytocin during labor induction and augmentation. Compared with nonlaboring women delivering via cesarean, laboring women who receive oxytocin augmentation require 9 times more oxytocin in order to achieve adequate uterine tone during cesarean delivery (CD). Previous studies have compared a pulsatile oxytocin administration technique with continuous infusion in terms of time from initiation of infusion to delivery, but none have compared these techniques in terms of postpartum hemorrhage rate. This study aimed to compare intermittent oxytocin pretreatment with continuous oxytocin for effect on subsequent oxytocin-induced myometrial contractility.

Title: Effects of Ephedrine, Phenylephrine and Norepinephrine on Contractility of Human Myometrium and Umbilical Arteries: An In-vitro Study

Title: Effects of Ephedrine, Phenylephrine and Norepinephrine on Contractility of Human Myometrium and Umbilical Arteries: An In-vitro Study

The Effect of Intermittent Oxytocin Pretreatment on Oxytocin-Induced Contractility of Human Myometrium In Vitro.

Prolonged continuous oxytocin administration during labor may induce oxytocin receptor desensitization, which attenuates the response of the myometrium to further oxytocin, increasing the risk of postpartum hemorrhage. The literature comparing pulsatile (intermittent) versus continuous oxytocin administration for induction and augmentation of labor is inconsistent with regard to maternal outcomes. We aimed to determine the effect of intermittent versus continuous oxytocin preexposure on myometrial responsiveness to subsequent oxytocin. We hypothesized that intermittent oxytocin pretreatment would result in superior subsequent oxytocin-induced contractility than continuous oxytocin pretreatment. This in vitro study was undertaken using myometrium obtained from women undergoing elective cesarean deliveries. Each myometrial strip was mounted in an individual organ bath with physiological salt solution under homeostatic conditions and allocated to one of 3 groups: (1) control (no pretreatment); (2) continuous (pretreatment with oxytocin 10(-5) M for 2 hours); or (3) intermittent (pretreatment with alternating oxytocin 10 M and physiological salt solution every 15 minutes, for 2 hours). After pretreatment, dose-response testing to oxytocin 10(-5) to 10(-5) M was performed and contractile parameters were measured. The primary outcome was motility index (MI, amplitude × frequency) of contractions. Eighteen women were recruited, and 86 successful experiments were performed (control n = 29, continuous n = 28, intermittent n = 29). The means (standard errors) of MI (√g·contractions/10 min) in the control, continuous, and intermittent groups were 2.34 (0.09), 1.78 (0.09), and 2.13 (0.11), respectively. The MI was significantly reduced in the continuous group when compared to the control (estimated difference [95% confidence interval {CI}], -0.56 [-0.81 to -0.31]; P < .01) and intermittent group (estimated difference [95% CI], -0.35 [-0.62 to -0.08]; P = .01). There was no significant difference in MI between the intermittent and control group (estimated difference [95% CI], -0.21 [-0.51 to 0.09]; P = .17). Human myometrium remains more responsive to subsequent oxytocin after intermittent compared to continuous exposure to oxytocin, most likely due to reduction in oxytocin receptor desensitization, or facilitation of receptor resensitization in the intermittent group. Hence, intermittent oxytocin administration during labor warrants further investigation as a technique to preserve uterine oxytocin responsiveness.

Maternal parity and functional contractility of human myometrium in vitro in the third trimester of pregnancy.

It is well established that the duration of the first and second stages of labor are shorter in parous women than in their nulliparous counterparts, a phenomenon not well understood. The aim was to examine the effect of maternal parity on contractile parameters of human myometrium. Myometrial strips were excised from n = 74 women at cesarean delivery and recordings of contractile activity analyzed and compared across three clinical groups: 1. No previous delivery (P0); 2. One previous delivery (P1); 3. Greater than one previous delivery (P>1). There was a trend towards greater mean contractile force in the P>1 group than the P1 and P0 groups (P = 0.412). Frequency of contractions was less in the P1 group than in the P0 and P>1 groups(P = 0.027). No differences were observed in relation to all other parameters. Excluding frequency, no intrinsic differences were observed in thefunctional parameters of humanuterine contractions in relation to parity.

Effect of dual tocolysis with fenoterol and atosiban in human myometrium.

Objectives To measure the tocolytic effect of the combination of the oxytocin receptor antagonist atosiban with the β-mimetic agent fenoterol on human myometrium of pregnant women. Methods An in vitro study of contractility in human myometrium at the Laboratory of the Department of Obstetrics, University Hospital of Zürich, Switzerland, was performed. Thirty-six human myometrial biopsies were obtained during elective caesarean sections of singleton pregnancies at term. Tissue samples were exposed to atosiban, fenoterol and the combination of atosiban with fenoterol. Contractility was measured as area under the curve during 30 min of spontaneous contractions. The effect of treatment was expressed as the percentage of change from basal activity during 30 min of exposure. Differences were calculated using a paired Wilcoxon signed-rank test. An additive effect of dual tocolysis was assumed when no significant difference was detected between the observed and expected inhibition of dual tocolysis. When inhibition was greater or lower than expected, the dual combination was characterised as "synergistic" or "antagonistic", respectively. Results Atosiban and fenoterol alone suppressed contractions by a median of 43.2% and 29.8%, respectively. The combination of atosiban plus fenoterol was measured at a level of 67.3% inhibition. There was no significant difference in the expected (63.2%) and observed inhibition effect of dual tocolysis (P=0.945). Conclusion This study demonstrated an additive effect of dual tocolysis of atosiban and fenoterol on human myometrium in vitro, but no synergistic or antagonistic effect.

25: Insulin exerts an inhibitory effect on the contractility of human pregnant myometrium in vitro

It has been demonstrated that human pregnant myometrium from women with Diabetes Mellitus (DM) displays poorer contractility than myometrium from non-diabetics. Since insulin has been shown to reduce the contractility of airway smooth muscle, we tested the hypothesis that the contractility of human myometrium from term pregnancy is reduced by insulin, and this may contribute to the debate on elevated cesarean delivery rates for dysfunctional labor in women with DM. Myometrial biopsies were obtained from women (n = 21) undergoing planned caesarean delivery at term, with informed consent and institutional approval. Myometrial strips were mounted for isometric recording in physiological salt solution (PSS) and stimulated by the addition of oxytocin (1 nM). Matched strips (2 or 3 per biopsy) were challenged with cumulative addition of vehicle or insulin, and the effects on contractility were measured and compared to controls. In the second series of experiments paired strips were treated with insulin (0.2 μM), or vehicle, for 15 min before oxytocin was added in cumulative increasing concentrations. Finally, the effect of a single concentration of insulin (0.2 μM) on spontaneous contractile activity was assessed. Insulin inhibited oxytocin induced contractions by 20 ± 8 % of those in vehicle-treated and time-matched controls with an IC50 of 0.13 μM (pIC50 = 6.8 ± 0.7, n = 5). Pre-treatment with insulin shifted the concentration-effect curve to oxytocin when compared to vehicle-treated controls, but the differences in curve parameters were not significant (paired t-test, P>0.05, n = 10). Insulin inhibited spontaneous contractions by 21 ± 7% (n = 6), in comparison to vehicle time-matched controls. Insulin exerts an inhibitory effect on human myometrial contractility in vitro. This effect of insulin may contribute to the poorer uterine contractility, and increased cesarean delivery rates, observed in pregnant women with Diabetes Mellitus.

Effect of magnesium sulfate on oxytocin-induced contractility in human myometrium: an in vitro study.

The purpose of this study was to determine the contractile patterns induced by oxytocin in myometrium exposed to magnesium sulfate (MgSO4). We hypothesized that MgSO4 pretreatment would reduce oxytocin-induced myometrial contractions in both oxytocin-naïve and oxytocin-desensitized myometrium. In this prospective in vitro study, myometrial samples were obtained from 26 women undergoing elective Cesarean deliveries. Samples were divided into six groups. Four groups were apportioned to no pretreatment (control group), oxytocin 10-5 M pretreatment (desensitization group), MgSO4 3.5 mM pretreatment, and MgSO4 3.5 mM + oxytocin 10-5M pretreatment. This was followed by dose-response testing to oxytocin 10-10 to 10-5M in all four groups. Two additional groups included MgSO4 3.5 mM pretreatment and MgSO4 3.5 mM + oxytocin 10-5 M pretreatment, followed by dose-response testing to oxytocin along with MgSO4 3.5 mM. The outcomes were motility index (MI), as defined by the amplitude (g) × frequency of myometrial contractions (c) over ten minutes, and area under the curve (AUC). In oxytocin-naïve myometrium, the mean (standard error [SE]) MI was not affected by MgSO4 pretreatment [3.31 (0.20) √g⋅c/10 min] as compared with control (P = 0.88), even when MgSO4 was continued during dose-response testing [2.50 (0.19) √g⋅c/10 min; P = 0.41]. In the oxytocin-desensitized model, mean (SE) MI was not affected by MgSO4 pretreatment [2.60 (0.21) √g⋅c/10 min; P = 0.68], but when MgSO4 was continued during the dose-response period, the MI was significantly reduced compared with control [1.89 (0.13) √g⋅c/10 min; P < 0.001]. The results for AUC were similar to MI, except for a significant reduction in oxytocin-naïve myometrium when MgSO4 was continued during dose-response testing (P = 0.02). Magnesium sulfate pretreatment does not impair oxytocin-induced myometrial contractility in oxytocin-naïve or desensitized myometrium unless it is continued during oxytocin dose-response testing. These results suggest that its tocolytic effect is likely dependent on an extracellular mechanism. The study was registered with ClinicalTrials.gov, number NCT02647268.

Magnetically Bioprinted Human Myometrial 3D Cell Rings as A Model for Uterine Contractility.

Deregulation in uterine contractility can cause common pathological disorders of the female reproductive system, including preterm labor, infertility, inappropriate implantation, and irregular menstrual cycle. A better understanding of human myometrium contractility is essential to designing and testing interventions for these important clinical problems. Robust studies on the physiology of human uterine contractions require in vitro models, utilizing a human source. Importantly, uterine contractility is a three-dimensionally (3D)-coordinated phenomenon and should be studied in a 3D environment. Here, we propose and assess for the first time a 3D in vitro model for the evaluation of human uterine contractility. Magnetic 3D bioprinting is applied to pattern human myometrium cells into rings, which are then monitored for contractility over time and as a function of various clinically relevant agents. Commercially available and patient-derived myometrium cells were magnetically bioprinted into rings in 384-well formats for throughput uterine contractility analysis. The bioprinted uterine rings from various cell origins and patients show different patterns of contractility and respond differently to clinically relevant uterine contractility inhibitors, indomethacin and nifedipine. We believe that the novel system will serve as a useful tool to evaluate the physiology of human parturition while enabling high-throughput testing of multiple agents and conditions.

Maternal body mass index and spontaneous contractility of human myometrium in pregnancy.

There is controversy as to whether maternal body mass index (BMI) influences the contractility of human myometrium in pregnancy. The aim of this study was to examine spontaneous contractile activity of human pregnant myometrium in vitro, with respect to maternal BMI. Myometrial tissue specimens were obtained at cesarean delivery from 74 women with BMI values ranging from 19 to 50.1 kg m-2. By recording in vitro from eight strips per donor (590 strips in total), several parameters of spontaneous contractile activity were monitored. The relationship between BMI and contractility was evaluated using linear regression analysis. There was a significant correlation between maximum amplitude (P=0.007) and mean contractile force (P=0.001) with increasing BMI. However, the time to onset of contractions (P=0.009), and time taken to reach maximal amplitude (P=0.020) also increased with increasing BMI. No significant correlation was observed with BMI for other parameters studied. The mean maximum amplitude value for spontaneous contractions was 37±1 mN, the mean contractile force for spontaneous contractions was 4.1±0.1 mN, the average time to the first spontaneous contraction was 11.3±0.6 min and the average frequency of contractions was 6.5±0.2 per hour. These results suggest that the time to onset of contractions is increased with increasing maternal BMI, but that the force developed is greater. In all other respects, human uterine contractility is unaffected by increasing BMI. These findings underline the complexity of regulation of uterine contractility in labor with elevated maternal BMI.

The Recovery Time of Myometrial Responsiveness After Oxytocin-Induced Desensitization in Human Myometrium In Vitro.

Postpartum hemorrhage secondary to uterine atony is a leading cause of maternal morbidity. Prolonged exposure to oxytocin for labor augmentation can result in the desensitization phenomenon, a decrease in the responsiveness of myometrium to further oxytocin. It is currently not known whether waiting for a specific time interval after the cessation of oxytocin allows the oxytocin receptors to resensitize and recover, thereby improving subsequent oxytocin-induced myometrial contractility. We aimed to investigate the effect of a rest period of 30, 60, and 90 minutes after oxytocin administration on the recovery of oxytocin-desensitized human myometrium in vitro. We hypothesized that the longer the rest period, the better the responsiveness and subsequent oxytocin-induced contractility of the myometrium. Myometrial tissue was obtained from women undergoing elective cesarean deliveries. The myometrial sample was dissected into 4 strips, and each strip was mounted in a single organ bath with physiological salt solution (PSS) under homeostatic conditions and then pretreated for 2 hours with oxytocin 10 M. After pretreatment, each strip was washed with PSS and allowed to rest in PSS solution for 30, 60, or 90 minutes. At the end of the rest period, dose-response testing to oxytocin 10 to 10 M was performed. A control group consisted of oxytocin dose-response testing without any oxytocin pretreatment. Contractile parameters were measured and compared among the groups after square root transformation. The primary outcome was motility index (frequency × amplitude), and secondary outcomes included frequency, amplitude, and area under the curve. Fifty-five experiments were conducted from samples obtained from 16 women. The mean motility index (√g·contractions/10 min) during the dose-response curve (oxytocin 10 to 10 M) in the control group was significantly greater than all the experimental groups; the mean estimated differences (95% confidence intervals) were -1.33 (-2.50 to -0.15, P = 0.02), -1.59 (-2.68 to -0.50, P = 0.004), and -1.88 (-2.97 to -0.80, P = 0.001) for the 30-, 60-, and 90-minute groups, respectively. When the experimental groups were compared, there were no significant differences in any of the contractility parameters; however, confidence intervals were wide. Our study shows that oxytocin pretreatment attenuates oxytocin-induced contractility in human myometrium despite a rest period of up to 90 minutes after oxytocin administration. However, we were unable to determine whether increasing the rest period from 30 to 90 minutes results in improvement in myometrial contractility because of our small sample size relative to the variability in the contractile parameters. Further laboratory and clinical in vivo studies are necessary to determine whether a rest period up to 90 minutes results in improvement in myometrial contractility. In addition, further experimental studies are necessary to determine the key mechanisms of oxytocin receptor resensitization.

Maternal Age and Contractility of Human Myometrium in Pregnancy.

There is controversy as to whether maternal age exerts an influence on the contractility of human myometrium in pregnancy. The aim of this study was to examine a series of functional contractile parameters of human myometrium in vitro, over a broad range of maternal ages. Myometrial tissue specimens were obtained at cesarean delivery from 32 women with maternal ages ranging from 28 to 52 years. Using in vitro recordings, a number of contractile parameters including maximal amplitude, mean contractile force, time to maximal amplitude, maximum rate of rise, and occurrence of simple and complex (biphasic and multiphasic) contractions were examined for spontaneous and induced contractile activity. The relationship between maternal age and individual parameters was evaluated using linear regression analysis. For all contractile parameters examined, for both spontaneous and induced contractions, no significant correlation was observed with maternal age between 28 and 52 years. The mean maximum amplitude values for spontaneous and oxytocin-induced contractions were 23 ± 3 and 43 ± 5 mN, respectively. The mean contractile forces for spontaneous and oxytocin-induced contractions were 1.5 ± 0.2 and 6.5 ± 0.9 mN, respectively. There was no variation in the proportion of biphasic or multiphasic contractions with maternal age. These results indicate there is no significant functional impairment of uterine contractility and no lack in responsiveness of myometrium in vitro, in the older mother. These findings do not support the concept that there may be a biological basis for dysfunctional labor or increased cesarean delivery rates in older parturients.

Effects of the polyphenol resveratrol on contractility of human term pregnant myometrium.

The ideal agent for prevention and treatment of uterine abnormal contractility has not been found. The polyphenol resveratrol possesses a wide spectrum of pharmacologic properties, but its influence on the contractility of human myometrium is not defined. The present study evaluated the effect of resveratrol on the oxytocin-induced contractions of human term pregnant myometrium in vitro and the contribution of different K(+) channels to resveratrol action. Resveratrol induced a concentration-dependent relaxation of myometrium contractions (pD2 value and maximal responses were 4.52 and 82.25%, respectively). Glibenclamide, a selective blocker of ATP-sensitive (KATP), iberiotoxin, a selective blockers of big-calcium sensitive (BK(Ca)) and 4-aminopiridine, a non-selective blocker of voltage-sensitive (Kv) channels induced a significant shift to the right of the concentration-response curves of resveratrol. Inhibition achieved by 0.1 mM resveratrol was insensitive to all K(+) channel blockers. A K(+) channel opener, pinacidil, inhibited oxytocin-induced contractions of pregnant myometrium with comparable potency and efficacy to resveratrol (pD2 values and maximal relaxation were 4.52 and 83.67%, respectively). Based on K(+) channel opener/blocker affinities, it appears that the inhibitory response of resveratrol involves different myometrial K(+) channels. When applied in high concentrations, resveratrol has an additional K(+)-channel-independent mechanism(s) of action. Furthermore, immunohistochemistry staining and western blot analyses detected the presence and distribution of KATP, BK(Ca) and Kv channel proteins in pregnant myometrium.

Immunolocalization and expression of small‐conductance calcium‐activated potassium channels in human myometrium

Small-conductance calcium-activated potassium (SK3) channels have been detected in human myometrium and we have previously shown a functional role of SK channels in human myometrium in vitro. The aims of this study were to identify the precise localization of SK3 channels and to quantify SK3 mRNA expression in myometrium from pregnant and non-pregnant women. Myometrial biopsies were obtained from pregnant (n = 11) and non-pregnant (n = 11) women. The expression of SK3 channels was assessed using immunohistochemistry and SK3 mRNA was determined by qRT-PCR. In non-pregnant myometrium SK3 immunoreactivity was observed in CD34 positive (CD34+) interstitial Cajal-like cells (ICLC), now called telocytes. Although CD34+ cells were also present in pregnant myometrium, they lacked SK3 immunoreactivity. Furthermore, the immunohistochemical results showed that SK3 expression in vascular endothelium was similar between the two groups. CD117 immunoreactivity was only detected in small round cells that resemble mast cells. Compared to non-pregnant myometrium we found significantly less SK3 mRNA in pregnant myometrium. We demonstrate that SK3 channels are localized solely in CD34+ cells and not in smooth muscle cells, and that the molecular expression of SK3 channels is higher in non-pregnant compared to pregnant myometrium. On the basis of our previous study and the present findings, we propose that SK3 activators reduce contractility in human myometrium by modulating telocyte function. This is the first report to provide evidence for a possible role of SK3 channels in human uterine telocytes.

Poor Spontaneous and Oxytocin-Stimulated Contractility in Human Myometrium from Postdates Pregnancies

Prolongation of pregnancy i.e. going more than 10 days over the estimated due date, complicates up to 10% of all pregnancies and is associated with increased risk to both mother and fetus. Despite the obvious need for contractions of the uterus to end pregnancy, there have been no studies directly examining the role of uterine smooth muscle, myometrium, in the aetiology of prolonged pregnancy. This study tested the hypothesis that the intrinsic contractile characteristics of myometrium taken from women with prolonged pregnancy (>41 weeks and 3 days) was reduced compared to those delivering at term (39–41 weeks). We recruited women undergoing Caesarean Section (CS) delivery either pre-labour (n = 27) or in labour (n = 66) at term or postdates. The contractile ability of the postdates myometrium, whether spontaneous or elicited by oxytocin or high-K solution, was significantly reduced compared to term myometrium. These differences remained when adjusted for parity and other maternal characteristics. The findings remained significant when expressed per cross sectional area. Histological examination revealed no differences between the two groups. The contractile differences were however related to intracellular Ca transients suggesting an effect of [Ca] on reduced force production in the postdates group. In summary, myometrium from prolonged pregnancies contracts poorly in vitro even when stimulated with oxytocin and in active labour. Responses to high K+ and measurements of Ca suggest that alterations in excitation contraction coupling, rather than any histological changes of the myometrium, may underlie the differences between term and postdates myometrium. We show that postdates pregnancy is associated with poor myometrial activity and suggest that this may contribute to increased myometrial quiescence and hence, prolonged gestation.

Lipoxygenase and cyclooxygenase inhibitors reveal a complementary role of arachidonic acid derivatives in pregnant human myometrium

The aim of this study was to assess the involvement of lipoxygenase (LOX) metabolic pathways in uterine tissues from pregnant women as well as the combined inhibition of LOX and cyclooxygenase (COX) on contractile activity. Uterine biopsies were performed from consenting women undergoing elective caesarean sections at term (n = 24). Western blot analysis and isometric tension measurements were performed in vitro on fresh human myometrial strips. Concentration-response curves to arachidonic acid (AA) 861 and baicalein (5- and 12-LOX inhibitors, respectively) were performed. The combined effects of baicalein and indomethacin were also assessed. Contractile activities were quantified by calculating both amplitude and the area under the curve over 20 minute periods. 5- and 12-LOX were present in all tested tissues. Addition of AA861 or baicalein resulted in tocolytic effects (P < .05). Finally, the combined inhibition of both COX and 12-LOX pathways resulted in additive tocolytic effects. 5- and 12-LOX pathways modulate human myometrium contractility.

Maternal Obesity and its Relationship With Spontaneous and Oxytocin-Induced Contractility of Human Myometrium In Vitro

Maternal obesity is associated with increased rates of labor induction, dysfunctional labor requiring intrapartum cesarean delivery, and postpartum hemorrhage, implying that maternal obesity has an inhibitory effect on myometrial function and its ability to respond to oxytocin. This study aimed to use an in vitro model to investigate the relationship between maternal body mass index (BMI) and the ability of myometrium to contract spontaneously and in response to oxytocin. Linear mixed effects regression modeling was applied to contractile data from 609 strips from 85 women. No correlation was found between maternal BMI and any indices of spontaneous myometrial activity. A single addition of oxytocin increased contractility, however, this was not related to maternal BMI. Similarly, oxytocin concentration-response curves were unrelated to BMI. Overall, the results from this in vitro study suggest that the observed implications of obesity on parturition in vivo cannot be explained by a direct effect on myometrial contractile mechanisms per se.

Inhibition of isolated human myometrium contractility by minoxidil and reversal by glibenclamide

This study investigated the ability of the antihypertensive drug minoxidil to inhibit potassium chloride (KCl)-induced contractility of the isolated human myometrium. Twelve strips of myometrium obtained from 12 patients who underwent hysterectomy were triggered to contract with 55 mM KCl before and after incubation with 3 concentrations (1, 3 and 10 microM) of minoxidil. The percent inhibition by minoxidil on the extent of contraction, and the area under the contractile curve of KCl-induced contraction of the myometrial strips was determined. Furthermore, the effect of 10 microM glibenclamide on the inhibition generated by 3 microM minoxidil on KCl-induced contractility was studied. It was found that minoxidil produced a concentration-dependent inhibition of KCl-induced contractility of the myometrium and that glibenclamide reversed this inhibitory effect. These results suggest that the inhibitory effect of minoxidil on isolated human myometrium contractility may prove useful in clinical conditions requiring relaxation of the myometrium.