Human Myometrial Contractility Research Articles

PKA and AKIP1 interact to mediate cAMP-driven COX-2 expression: A potentially pivotal interaction in preterm and term labour.

Previously, we showed that cAMP increased COX-2 expression in myometrial cells via MAPK. Here, we have extended these observations, using primary myometrial cell cultures to show that the cAMP agonist, forskolin, enhances IL-1β-driven COX-2 expression. We then explored the role of A-kinase interacting protein (AKIP1), which modulates the effect of PKA on p65 activation. AKIP1 knockdown reversed the effect of forskolin, such that its addition inhibited IL-1β-induced COX-2 mRNA expression and reduced the IL-1β-induced increase in nuclear levels of p65 and c-jun. Forskolin alone and with IL-1β increased IκBα mRNA expression suggesting that in the context of inflammation and in the presence of AKIP1, cAMP enhances p65 activation. AKIP1 knockdown reversed these changes. Interestingly, AKIP1 knockdown had minimal effect on the ability of forskolin to repress either basal OTR expression or IL-1β-stimulated OTR mRNA expression. AKIP1 was up-regulated by IL-1β, but not stretch and was repressed by cAMP. The mRNA expression of AKIP1 increased in early labour in tandem with an increase in COX-2 mRNA and protein. AKIP1 protein levels were also increased with inflammation and stretch-induced preterm labour. Our results identify a second important cAMP effector-switch occurring at term in human myometrium and suggest that a hitherto unrecognized interaction may exist between AKIP1, NFκB and AP-1. These data add to the proposition that cAMP acts as a key regulator of human myometrial contractility.

668 Uterorelxant effect of adiponectin and omentin on In Vitro human myometrial contractility

The onset of parturition in pregnant women with obesity is frequently delayed. Without induction, these women are nearly twice as likely as normal-weight women to have prolonged pregnancies even after control for birth weight. Adipokines are cell signaling mediators secreted by the adipose tissue, many of which are now known to be closely linked to metabolic regulation including smooth muscle function. In this study, we aimed to investigate the role of adiponectin, and omentin on the in vitro functional contractility of isolated myometrial samples. Myometrial strips alongside the upper part of the low transverse uterine incisions were obtained at the time of the cesarean birth from 22 healthy, non-laboring, pregnant women, scheduled for elective cesarean birth at term. In isolated muscle tissue baths, myometrial strips were prepared under isometric conditions, undergoing spontaneous and oxytocin-induced contractions, were exposed to cumulative doses of adiponectin and omentin in the concentration range of 1 nmol/L to 10 umol/L. Control experiments were performed simultaneously. Both adiponectin and omentin exerted significant uterorelaxant effect ( reduction in amplitude and frequency of contractions) on the myometrial samples, in both spontaneous and oxytocin-induced contractions, in vitro. The inhibitory effect was in the region of 36 % for adiponectin, and 33 % for omentin in tissue baths with spontaneous contractions and in the region of 31% for adiponectin and 30% for omentin in tissue baths with oxytocin-induced contractions. In this study, we show the inhibitory role of adiponectin and omentin on human myometrial contractility, in vitro. These findings reiterate the physiological role of metabolic changes associated with maternal weight on myometrial contractility. The cellular mechanisms, and the potential clinical implications are not fully understood which could be addressed in future studies.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

515 Repurposing of FDA-approved lead drugs as potentiators of uterine contractility in postpartum hemorrhage

Current medical options for management of postpartum hemorrhage preclude universal application due to their potential for adverse side effects. The objective of this study was to test the ex vivo efficacy of uterine-selective, FDA-approved drugs with no known cardiopulmonary toxicities repurposed for use at the human myometrial level. Lead drugs that selectively regulate human myometrial contractility were identified in prior studies using in vitro high throughput drug screening for calcium mobilization in myometrial cells. In this study, functional ex vivo isometric contractility was assessed via organ bath assays to determine uterotonic activity of mefloquine and pimavanserin on the human myometrial tissue. Human myometrial tissue was obtained at the time of cesarean delivery from non-laboring women meeting inclusion and exclusion criteria. Myometrial tissue strips (∼6-8 per biopsy) were submerged in organ baths (37°C, 95%O2, 5%CO2) containing Kreb’s Bicarbonate Solution and suspended under 3-gram isometric conditions. Tissues that displayed rhythmic spontaneous contractions were treated with cumulative concentrations (10pM – 0.1mM) of either mefloquine, pimavanserin or vehicle control (DMSO) at 20min intervals. Contractile activity was recorded and analyzed for frequency, amplitude, and area under the curve. Drug response relative to spontaneous contractile activity was analyzed, and non-linear regression models were used to generate concentration-response curves. Comparisons of fit were performed to determine if the non-linear curves of mefloquine and pimavanserin were significantly different (p<0.05) from DMSO. We performed 57 experiments in myometrial samples obtained from 12 women. There was no significant difference in the amplitude, frequency, or area under the curve between the vehicle control, mefloquine, and pimavanserin. Neither mefloquine nor pimavanserin induces ex vivo uterotonic activity in human myometrial tissue.

41In vitro human myometrial contractility in pregnancies complicated with obesity

The onset of parturition in pregnant women with obesity is frequently delayed. Without induction, these women are nearly twice as likely as normal-weight women to have prolonged pregnancies. Obesity has been shown to be an independent risk factor for cesarean birth, even after controlling for birth weight. It has been suggested that myometrial contractility is impaired in women with obesity. In this study we aimed to investigate whether contractility is truly reduced in women with obesity compared to their normal-weight counterparts utilizing an in vitro experiment model. Myometrial strips alongside the upper part of the low transverse uterine incisions were obtained at the time of the cesarean birth from 22 healthy, non-laboring, pregnant women, scheduled for elective cesarean birth at term. Strips were transferred to the laboratory and underwent dissection into tissue samples, each approximately 5 mm long, 2 mm wide, and 1 mm thick. In isolated muscle tissue baths, each tissue was attached to a stationary hook and the other end was attached to a force transducer and mounted for isometric recording under 2 gm of tension. Tissues were prepared under isometric conditions and underwent both spontaneous and oxytocin-induced contractions. Control experiments were performed simultaneously. Total of 11 participants with obesity and 11 normal-weight participants were enrolled. In both spontaneous and oxytocin-induced contractions, there was a significant reduction in amplitude of contractions between normal-weight and participants with obesity (P= 0.04, and P=0.049 in spontaneous and oxytocin-induced contractions respectively) and a significant reduction in frequency of contractions between groups (P= 0.01, and P=0.02 in spontaneous and oxytocin-induced contractions respectively). Obesity may impair the ability of the uterus to contract in labor which might contribute to the increased cesarean birth rate in women with obesity. This study reiterates the importance of preconception counseling on optimizing weight prior to pregnancy.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Justicia flava leaf extract potently relaxes pregnant human myometrial contractility: a lead plant for drug discovery of new tocolytic drugs.

What is the central question of this study? Can Justicia flava leaf extract (JF) inhibit human myometrial contractility as was previously shown in mouse myometrium? What is the main finding and its importance? JF abolished human myometrial contractions and therefore presents as a lead plant in drug discovery studies involving drugs for preterm birth. In the search for new potent therapies for preterm labour, Justicia flava leaf extract (JF) was previously shown to potently inhibit uterine contractility in both pregnant and non-pregnant mouse uterus. This study took the investigation a step further and investigated the activity of JF on pregnant human myometrial contractility. JF potently inhibited human myometrial contractility in a concentration-dependent manner. This pilot study provides evidence that JF should be further investigated as a lead plant in the drug discovery of new uterine relaxants.

Hyponatraemia reversibly affects human myometrial contractility. An in vitro pilot study.

In a previous study we found a significant correlation between dystocia and hyponatraemia that developed during labour. The present study examined a possible causal relationship. In vitro studies often use area under the curve (AUC) determined by frequency and force of contractions as a measure of myometrial contractility. However, a phase portrait plot of isometric contraction, obtained by plotting the first derivate of contraction against force of contraction, could indicate that bi-or multiphasic contractions might be less effective compared to the smooth contractions. Myometrial biopsies were obtained from 17 women undergoing elective caesarean section at term. Each biopsy was divided into 8 strips and mounted isometrically in a force transducer. Seven biopsies were used in the first part of the study when half of the strips were immersed in the hyponatraemic study solution S containing Na+ 120 mmol/L and observed for 1 hour, followed by 1 hour in normonatraemic control solution C containing Na+ 136 mmol/L, then again in S for 1 hour, and finally 1 hour in C. The other half of the strips were studied in reverse order, C-S-C-S. The remaining ten biopsies were included in the second part of the study. Response to increasing doses of oxytocin (OT) in solutions S and C was studied. In the first part of the study we calculated AUC, and created phase portrait plots of two different contractions from the same strip, one smooth and one biphasic. In both parts of the study we registered frequency and force of contractions, and described appearance of the contractions. First part of the study: Mean (median) contractions per hour in C: 8.7 (7.6), in S 14,3 (13). Mean (SD) difference between groups 5.6 (4.2), p = 0.018. Force of contractions in C: 11.8 (10.2) mN, in S: 10.8 (9.2) mN, p = 0.09, AUC increased in S; p = 0.018. Bi-/multiphasic contractions increased from 8% in C to 18% in S, p = 0.001. All changes were reversible in C. Second part of the study: Frequency after OT 1.65 x 10-9 M in C:3.4 (2.9), in S: 3.8 (3.2), difference between groups: p = 0.48. After OT 1.65 x 10-7 M in C: 7.8 (8.9), increase from previous OT administration: p = 0.09, in S: 8.7 (9.0), p = 0.04, difference between groups, p = 0.32. Only at the highest dose of OT dose was there an increase in force of contraction in S, p = 0.05, difference between groups, p = 0.33. Initial response to OT was more frequently bi/multiphasic in S, reaching significance at the highest dose of OT(1.65 x 10-7 M), p = 0.015. when almost all contractions were bi/multiphasic. Hyponatraemia reversibly increased frequency of contractions and appearance of bi-or multiphasic contractions, that could reduce myometrial contractility. This could explain the correlation of hyponatraemia and instrumental delivery previously observed. Contractions in the hyponatraemic solution more frequently showed initial multiphasic contractions when OT was added in increasing doses. Longer lasting labours carry the risk both of hyponatraemia and OT administration, and their negative interaction could be significant. Further studies should address this possibility.

Bryophyllum pinnatum enhances the inhibitory effect of atosiban and nifedipine on human myometrial contractility: an in vitro study

BackgroundThe herbal medicine Bryophyllum pinnatum has been used as a tocolytic agent in anthroposophic medicine and, recently, in conventional settings alone or as an add-on medication with tocolytic agents such as atosiban or nifedipine. We wanted to compare the inhibitory effect of atosiban and nifedipine on human myometrial contractility in vitro in the absence and in the presence of B. pinnatum press juice (BPJ).MethodsMyometrium biopsies were collected during elective Caesarean sections. Myometrial strips were placed under tension into an organ bath and allowed to contract spontaneously. Test substances alone and at concentrations known to moderately affect contractility in this setup, or in combination, were added to the organ bath, and contractility was recorded throughout the experiments. Changes in the strength (measured as area under the curve (AUC) and amplitude) and frequency of contractions after the addition of all test substances were determined. Cell viability assays were performed with the human myometrium hTERT-C3 and PHM1–41 cell lines.ResultsBPJ (2.5 μg/mL), atosiban (0.27 μg/mL), and nifedipine (3 ng/mL), moderately reduced the strength of spontaneous myometrium contractions. When BPJ was added together with atosiban or nifedipine, inhibition of contraction strength was significantly higher than with the tocolytics alone (p = 0.03 and p < 0.001, respectively). In the case of AUC, BPJ plus atosiban promoted a decrease to 48.8 ± 6.3% of initial, whereas BPJ and atosiban alone lowered it to 70.9 ± 4.7% and to 80.9 ± 4.1% of initial, respectively. Also in the case of AUC, BPJ plus nifedipine promoted a decrease to 39.9 ± 4.6% of initial, at the same time that BPJ and nifedipine alone lowered it to 78.9 ± 3.8% and 71.0 ± 3.4% of initial. Amplitude data supported those AUC data. The inhibitory effects of BPJ plus atosiban and of BPJ plus nifedipine on contractions strength were concentration-dependent. None of the test substances, alone or in combination, decreased myometrial cell viability.ConclusionsBPJ enhances the inhibitory effect of atosiban and nifedipine on the strength of myometrial contractions, without affecting myometrium tissue or cell viability. The combination treatment of BPJ with atosiban or nifedipine has therapeutic potential.

Spontaneous Human Myometrial Contractility in the Third Trimester of Pregnancy in Relation to Past Mode of Delivery.

It is well established that women with a previous vaginal delivery have higher success rates in relation to vaginal birth after cesarean than those without. The aim of this study was to examine the effect of past mode of delivery on contractile parameters of human myometrium in vitro. Myometrial strips were excised from 64 women at cesarean delivery (CD) and recordings of spontaneous contractile activity analyzed and compared across three clinical groups: (1) women with no previous delivery (Group 1); (2) women with CD only (Group 2); and (3) women with a history of vaginal delivery and CD (Group 3). Myometrial samples from women in Group 3, women who had a previous vaginal delivery, had a significantly greater maximum amplitude of contractions (p < 0.05), a greater force (mean contractile force) of contractions (p < 0.01), and a faster rate of rise (p < 0.01) and relaxation of contractions (p < 0.05) than those in Groups 1 and 2. Many of the functional parameters of human uterine contractions are altered, or enhanced, in the women who have had a previous vaginal delivery, when compared with those without. This may partly explain the clinical differences observed in labor.

A Bufadienolide-Enriched Fraction of Bryophyllum pinnatum Inhibits Human Myometrial Contractility In Vitro.

Bryophyllum pinnatum has been used since the 1970s to prevent premature labour, first in anthroposophic hospitals and, more recently, also in the main Swiss perinatal centres. However, it is not known which compounds in B. pinnatum leaves contribute to the tocolytic effect. Here we studied the effects of a flavonoid-enriched fraction, the corresponding flavonoid aglycon mixture, a bufadienolide-enriched fraction, and B.pinnatum leaf press juice on human myometrial contractility in vitro. The strength (area under the curve and amplitude) and frequency of contractions were recorded using strips of human myometrium mounted in an organ bath system. Cell viability assays were performed with the human myometrium hTERT-C3 and PHM1 - 41 cell lines. Repeated addition of the flavonoid-enriched fraction, flavonoid aglycon mixture, bufadienolide-enriched fraction, or B. pinnatum leaf press juice led to a progressive decrease of contraction strength, without jeopardising the vitality of myometrium strips. The bufadienolide-enriched fraction was the most active, since 1 µg/mL of the bufadienolide-enriched fraction lowered the area under the curve to 40.1 ± 11.8% of the initial value, whereas 150 µg/mL of the flavonoid-enriched fraction, 6.2 µg/mL of the flavonoid aglycon mixture, and 10 µg/mL of the B. pinnatum leaf press juice were required to achieve comparable inhibition. Aprogressive increase of contraction frequency was observed, except in the case of the flavonoid aglycon mixture, which did not affect frequency. None of the test substances decreased myometrial cell viability, even at concentrations of 500 µg/mL of the flavonoid-enriched fraction, 40 µg/mL of the flavonoid aglycon mixture, 3.8 µg/mL of the bufadienolide-enriched fraction, and 75 µg/mL of the B. pinnatum leaf press juice, i.e., higher than those used in the myometrium experiments. Given the concentrations of flavonoids in the flavonoid-enriched fraction and B. pinnatum leaf press juice, and of bufadienolides in the bufadienolide-enriched fraction and B. pinnatum leaf press juice, it appears that bufadienolides may be mainly responsible for the relaxant effect.

395: Adiponectin and human myometrial contractility in vitro

Adiponectin, an adipokine, is present in lower concentrations in gestational diabetes (GDM) regardless of maternal BMI. Other adipokines have been suggested to have a role in myometrial contractility, and given the increased risk for cesarean delivery in pregnancies complicated by GDM, we sought to investigate the effect of adiponectin on myometrial contractility. Human myometrial tissue was obtained at scheduled cesarean delivery. Muscle bundles were dissected and suspended under isometric conditions, and muscle contraction was induced with electrical impulses. After a period of equilibration, human adiponectin was infused into the tissue baths. Peak contraction strength was recorded over the course of one hour. A total of 38 muscle bundles from 6 subjects were obtained. 19 bundles were exposed to 0.1 mcg of human adiponectin and 19 bundles were exposed to 1 mcg of human adiponectin. Those bundles exposed to 0.1 mcg had a mean increase in peak contractile force of 7.44%. Those bundles exposed to 1 mcg adiponectin had a mean increase in peak contractile force of 1.83%. Human adiponectin may increase human myometrial contractile force in vitro. No direct dose response was noted, and this needs more study. Further investigation of potential molecular mechanisms is needed, and may potentially provide a pharmacologic target to improve contractility in populations deficient in human adiponectin such as gestational diabetics.

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.

Retosiban Prevents Stretch-Induced Human Myometrial Contractility and Delays Labor in Cynomolgus Monkeys.

ContextStretch of the myometrium promotes its contractility and is believed to contribute to the control of parturition at term and to the increased risk of preterm birth in multiple pregnancies.ObjectiveTo determine the effects of the putative oxytocin receptor (OTR) inverse agonist retosiban on (1) the contractility of human myometrial explants and (2) labor in nonhuman primates.DesignHuman myometrial biopsies were obtained at planned term cesarean, and explants were exposed to stretch in the presence and absence of a range of drugs, including retosiban. The in vivo effects of retosiban were determined in cynomolgus monkeys.ResultsProlonged mechanical stretch promoted myometrial extracellular signal-regulated kinase (ERK)1/2 phosphorylation. Moreover, stretch-induced stimulation of myometrial contractility was prevented by ERK1/2 inhibitors. Retosiban (10 nM) prevented stretch-induced stimulation of myometrial contractility and phosphorylation of ERK1/2. Moreover, the inhibitory effect of retosiban on stretch-induced ERK1/2 phosphorylation was prevented by coincubation with a 100-fold excess of a peptide OTR antagonist, atosiban. Compared with vehicle-treated cynomolgus monkeys, treatment with oral retosiban (100 to 150 days of gestational age) reduced the risk of spontaneous delivery (hazard ratio = 0.07, 95% confidence interval 0.01 to 0.60, P = 0.015).ConclusionsThe OTR acts as a uterine mechanosensor, whereby stretch increases myometrial contractility through agonist-free activation of the OTR. Retosiban prevents this through inverse agonism of the OTR and, in vivo, reduced the likelihood of spontaneous labor in nonhuman primates. We hypothesize that retosiban may be an effective preventative treatment of preterm birth in high-risk multiple pregnancies, an area of unmet clinical need.

The Synergic In Vitro Tocolytic Effect of Nifedipine Plus Ritodrine on Human Myometrial Contractility.

Many pharmacological agents have been investigated to manage preterm labor; we postulate that a combination of tocolytic drugs may achieve a better effect in the prevention of uterine contractions without dose-dependent adverse effects. The aim of this study was to evaluate the inhibitory effect of dual combinations of tocolytics in vitro. Human myometrium was obtained during elective cesarean sections (term without labor; n = 40). Myometrial strips were placed in organ baths for the measurement of isometric tension. Contractile activity was induced by oxytocin (10-8 mol/L), then a concentration-response curve to single or dual combinations of tocolytics was started. All studied tocolytics (nifedipine, ritodrine, nitroglycerin, atosiban, and NS-1619), when used alone, significantly inhibited myometrial contractions. When combined, nifedipine plus ritodrine produced a significantly greater inhibition of contractility than each drug alone in the midrange of concentrations. The combination of nifedipine plus nitroglycerin or nifedipine plus atosiban produced a significantly greater inhibition than nitroglycerin or atosiban alone but not greater than nifedipine. The combination of nifedipine plus NS-1619 (Ca+2-activated K+ [BKCa] channel opener) reduced the inhibitory effect of each drug. We concluded that a selected combination of tocolytics (nifedipine plus ritodrine) produced a significantly greater inhibitory effect on contractility than each drug alone at intermediate concentrations. Thus, specific combinations of tocolytics with different intracellular signaling pathways may have a synergic effect constituting a provocative new option for preterm labor treatment.

Inhibition by tadalafil of contractility of isolated nonpregnant human myometrium

Objective:To investigate the inhibitory effect of tadalafil on the contractility of isolated nonpregnant human myometrium.Materials and Methods:The ability of tadalafil (25, 40, and 63 μM) to inhibit 55 mM KCl-induced contractility of isolated nonpregnant human myometrium was studied. The ability of the ATP-sensitive potassium channel blocker glibenclamide (10 μM) and the calcium-sensitive potassium channel (BKCa) blocker iberiotoxin (100 nM) to reverse the inhibitory effect of 40 μM tadalafil on 55 mM KCl-induced myometrial contractility was also studied.Results:Tadalafil produced a concentration-dependent inhibition of myometrial contractility that was statistically significant at 40 and 63 μM concentrations of tadalafil. The inhibition by tadalafil of myometrial contractility was statistically significantly reversed by the concurrent administration of glibenclamide and iberiotoxin.Conclusions:These results suggest that tadalafil inhibits human myometrial contractility by opening ATP-sensitive potassium channels and BKCa channels. The opening of these channels could have been due to the action of raised intracellular levels of cGMP due to inhibition of PDE-5 by tadalafil. The results suggest that tadalafil could be investigated for use in clinical conditions requiring relaxation of the myometrium.

Paeoniflorin, a novel heat-shock protein inducing compound, and human myometrial contractility in vitro.

Heat shock proteins (HSPs) are synthesized in virtually all organisms in response to increases in temperature. They are associated with a relaxant effect on the human myometrium and are present in decreased concentration in the myometrium at the time of labor. Paeoniflorin is derived from Paeonia lactiflora and has been shown to induce the synthesis of HSPs in cultured mammalian cells. The purpose of the study was to evaluate the effect of paeoniflorin on human uterine contractility. Samples of human myometrium were taken at lower segment cesarean section. Dissected muscle strips were suspended under isometric conditions and exposed to cumulative additions of paeoniflorin in concentrations ranging from 1 nmol/L to 10 mol/L. Control experiments were simultaneously performed. Paeoniflorin was found to exert an inhibitory effect on spontaneous and agonist-induced contractions compared to control strips. The mean maximal inhibition values were: 42.21% ± 9.26 for spontaneous contractions (n = 6; P < 0.0001) and 47.84% ± 9.05 for oxytocin-induced contractions (n = 6; P < 0.0001). The HSP inducing compound, paeoniflorin, had a relaxant effect on human uterine contractility in vitro. These results reinforce the fact that HSPs may play a physiological role in the onset of labor and may also provide future targets for novel tocolytic treatments.

The Effect of an Oxytocin Receptor Antagonist (Retosiban, GSK221149A) on the Response of Human Myometrial Explants to Prolonged Mechanical Stretch.

Multiple pregnancy is a major cause of spontaneous preterm birth, which is related to uterine overdistention. The objective of this study was to determine whether an oxytocin receptor antagonist, retosiban (GSK221149A), inhibited the procontractile effect of stretch on human myometrium. Myometrial biopsies were obtained at term planned cesarean delivery (n = 12). Each biopsy specimen was dissected into 8 strips that were exposed in pairs to low or high stretch (0.6 or 2.4 g) in the presence of retosiban (1 μM) or vehicle (dimethylsulfoxide) for 24 hours. Subsequently, we analyzed the contractile responses to KCl and oxytocin in the absence of retosiban. We found that incubation under high stretch in vehicle alone increased the response of myometrial explants to both KCl (P = .007) and oxytocin (P = .01). However, there was no statistically significant effect of stretch when explants were incubated with retosiban (P = .3 and .2, respectively). Incubation with retosiban in low stretch had no statistically significant effect on the response to either KCl or oxytocin (P = .8 and >.9, respectively). Incubation with retosiban in high stretch resulted in a statistically significant reduction (median fold change, interquartile range, P) in the response to both KCl (0.74, 0.60-1.03, P = .046) and oxytocin (0.71, 0.53-0.91, P = .008). The greater the effect of stretch on explants from a given patient, the greater was the inhibitory effect of retosiban (r = -0.65, P = .02 for KCl and r= -0.73, P = .007 for oxytocin). These results suggest that retosiban prevented stretch-induced stimulation of human myometrial contractility. Retosiban treatment is a potential approach for preventing preterm birth in multiple pregnancy.

Inhibitory effect of visfatin and leptin on human and rat myometrial contractility.

The purpose of this study was to investigate the effect of visfatin on in vitro myometrial contractility in human and rat, and compare it to leptin. Myometrial strips from term pregnant women having a caesarean section or rats were dissected, superfused with physiological saline and the effects of visfatin (500pM-25nM) or leptin (1nM-1μM), on spontaneous and oxytocin-induced contractions were studied. After establishment of regular contractions, tissues were incubated for control and test response at 37°C for 20min, and then contractility was assayed. In human and rat myometrium, visfatin had similar dose dependent effects on contractility. In the human myometrium, compared with that of controls (100%), 10nM produced a significant (paired t-test) decrease in the 20min integral of spontaneous (64±8%, n=13) and oxytocin-induced contractions (55±9%, n=5), mean±SEM. In rat tissue the decrease was also significant (spontaneous, 76±7%, n=7; oxytocin-induced 68±6%, n=3). Leptin at this concentration (10nM) had no effect in rat or human, and even at a higher concentration (1μM) produced only a small inhibitory effect (~ 80%) on contractions. These data are the first to show that visfatin inhibits myometrial contractility and does so more potently than leptin. Our data suggest that increased output of visfatin and leptin in obese pregnant women may impair uterine contractility resulting in an unplanned Caesarean delivery.

The effects of methyl palmitate, a putative regulator from perivascular fat, on the contractility of pregnant human myometrium

AimsMethyl palmitate is thought to cause relaxation in vascular smooth muscle by opening voltage-activated potassium channels. We have tested the hypothesis that methyl palmitate, a putative regulator from perivascular fat, is an inhibitor of the contractility of human pregnant myometrium and that its effects might partially explain the higher incidence of dysfunctional labor in obese women compared to those with normal body mass indices. Main methodsStrips of myometrium obtained with informed consent from women undergoing elective cesarean section at term were mounted in organ baths. Strips stimulated with oxytocin (1nM) or KCl (30mM) were exposed to cumulatively increasing concentrations of methyl palmitate up to 10μM. Similar strips were exposed to cumulative addition of the potassium channel blockers 4-aminopyridine and tetraethylammonium. The contractility of the strips was monitored and analyzed using conventional methods. Key findingsMethyl palmitate failed to inhibit oxytocin- or KCl-induced contractions over the concentration range tested. In fact, it exerted a slight excitatory effect in the presence of KCl, though not in the presence of oxytocin. The contractility of naïve strips was unaltered by exposure to 1μM methyl palmitate. Both 4-aminopyridine and tetraethylammonium produced concentration-dependent contractions of human pregnant myometrium providing pharmacological evidence for the presence of voltage-activated potassium channels in this preparation. SignificanceOur findings do not support the hypothesis that methyl palmitate is an inhibitor of human pregnant myometrial contractility. Alternate hypotheses must be pursued to explain the higher incidence of dysfunctional labor in obese women.

Oxytocin Pretreatment Attenuates Oxytocin-induced Contractions in Human Myometrium In Vitro

Background:Oxytocin receptor desensitization has been shown to occur in humans at biomolecular level and in isolated rat myometrium; however, its effect on human myometrial contractility has not been demonstrated. The objective of this in vitro study was to investigate the contractile response of hu

Oxytocin Pretreatment Attenuates Oxytocin-induced Contractions in Human Myometrium In Vitro

Oxytocin receptor desensitization has been shown to occur in humans at biomolecular level and in isolated rat myometrium; however, its effect on human myometrial contractility has not been demonstrated. The objective of this in vitro study was to investigate the contractile response of human pregnant myometrium to oxytocin after pretreatment with different concentrations of oxytocin for variable durations. Myometrial samples were obtained from 62 women undergoing elective cesarean deliveries under regional anesthesia. The strips were pretreated with oxytocin 10, 10, 10 M, or physiological salt solution (control) for 2, 4, 6, or 12 h, followed by a dose-response testing with oxytocin 10 to 10 M. Amplitude and frequency of contractions, motility index, and area under the curve during the dose-response period were recorded, analyzed with linear regression models, and compared among groups. Pretreatment with oxytocin 10 and 10 M significantly reduced motility index (estimate [standard error]: -0.771 [0.270] square root units, P = 0.005 and -0.697 [0.293], P = 0.02, respectively) and area under the curve (-3.947 [1.909], P = 0.04 and -4.241 [2.189], P = 0.05, respectively) compared with control group, whereas pretreatment with oxytocin 10 M did not significantly attenuate contractions. Increase in duration of oxytocin pretreatment from 2 to 12 h significantly decreased amplitude (type 3 generalized estimating equation analysis: chi-square = 14.0; df = 3; P = 0.003), motility index (chi-square = 9.3; df = 3; P = 0.03), and area under the curve (chi-square = 10.5; df = 3; P = 0.02), but not the frequency of oxytocin-induced contractions. Pretreatment with oxytocin decreases oxytocin-induced myometrial contractions in a concentration and time-dependent manner, likely as a function of the oxytocin receptor desensitization phenomenon.