Human Uterine Contractility Research Articles

Progesterone, but not 17-alpha-hydroxyprogesterone caproate, inhibits human myometrial contractions

The aim was to determine whether progesterone (P4) or 17-alpha-hydroxyprogesterone caproate (17P) directly inhibit human uterine contractility in vitro and thereby clarify their mechanisms of action. Myometrial tissues were suspended in organ chambers and exposed for 2 to 20 hours to varying concentrations of P4 or 17P or solvent. Contractile activity was registered, stored, and analyzed. Dose response curves were then generated for P4 or 17P at various times. P4 significantly inhibited spontaneous contractility dose dependently. The inhibition was not blocked by RU486 but was reversible after washing. Surprisingly, 17P dose dependently stimulated contractility. HPLC and GC-MS methods were used to determine the detectable concentrations of progestins in the baths. P4, at concentrations equivalent to those present in the placenta and uterus, inhibit spontaneous myometrial contractility in vitro by nongenomic mechanisms.

Histone deacetylase inhibitors and a functional potent inhibitory effect on human uterine contractility

This study was undertaken to investigate the effects of 3 histone deacetylase inhibitors on human uterine contractility. Biopsy specimens of human myometrium were obtained at elective cesarean section (n = 18). Dissected myometrial strips suspended under isometric conditions, undergoing spontaneous, and oxytocin-induced contractions, were subjected to cumulative additions of 3 histone deacetylase inhibitors: trichostatin A, suberic bishydroxamate (1 nmol/L-10 micromol/L) and valproic acid (100 nmol/L--1 mmol/L). Control experiments were run simultaneously. Integrals of contractile activity were measured by using the PowerLab hardware unit and Chart v3.6 software. Data were analyzed by using 1-way analysis of variance, followed by post hoc analysis. All 3 histone deacetylase inhibitor compounds exerted a potent and cumulative inhibitory effect on spontaneous (n = 18) and oxytocin-induced (n =18) contractility. The mean maximal inhibition values for the 3 compounds were as follows: trichostatin A, 46-54% (P < .05); valproic acid, 35-36% (P < .05); and suberic bishydroxamate, 53-65% (P < .05). The histone deacetylase inhibitors trichostatin A, valproic acid, and suberic bishydroxamate exerted a potent inhibitory effect on human uterine contractions. This raises the possibility that this new class of compounds may have tocolytic potential, in addition to their current clinical indications. We speculate that this inhibitory effect may be linked, at least in part, to the ability of histone deacetylase inhibitors to induce the expression of genes involved in maintaining myometrial quiescence via epigenetic mechanisms but may also potentially involve nonepigenetic pathways.

The role of THOA in calcium sensitization in human myometrial smooth muscles

Improved understanding of the regulation of contractions of uterine smooth muscle (myometrium) is essential to develop more successful strategies for prevention of premature birth, which remains the most common cause of infant death and disability. Oxytocin (OT) and prostaglandin (PG) F2a are potent myometrial stimulants which induce an increase in intracellular Ca++. This activates myosin light chain kinase (MLCK) and subsequently the cell’s contractile machinery. However, there is poor correlation between the rise in Ca++ and the strength of the myometrial contraction. Contractile strength greatly increases at the time of parturition partly due to Ca++-independent factors that sensitize the muscle to the rise in intracellular Ca++. In vascular smooth muscle, one key regulator in this process of Ca++ sensitization is the monomeric G-protein, RhoA which in turn activates Rho-associated kinase (ROK). Studies in the rat myometrium have shown that RhoA and ROK are involved in enhancing OT-induced contractions. The potential role of the RhoA/ROK system in uterine contractility at the time of parturition has not been investigated in the human myometrium or in human cell lines. &#x0D; We propose to investigate the role of RhoA/ROK in the human myometrium using molecular cloning techniques. We have constructed expression plasmids for wild type, dominant positive (constitutively active), and dominant negative (constitutively inactive) isoforms of RhoA and synthesized purified proteins using a bacterial (BL21) translation system. These constructs will be introduced into primary and immortalized human myocytes using the protein transduction domain (TAT) derived from the HIV virus, which is capable of introducing whole proteins into mammalian cells. RhoA activation/translocation to the plasma membrane will be visualized using real time confocal microscopy in experiments where the RhoA proteins have been tagged with green fluorescent protein (GFP). Following introduction of the normal and mutant G-proteins, the downstream targets of activated ROK will be assayed for phosphorylation status using near infrared (NIR) fluorescence imaging of western blots or in-cell westerns. These targets include the myosin binding subunit (MBS) of myosin light chain phosphatase (MLCP), and two peptide phosphatase inhibitors of MLCP, CPI-17 and PHI-1. In addition, we propose to measure ROK activity directly using a direct enzyme assay. We will monitor calcium transients using fluorescence microscopy to verify the calcium independence of our measurements. These experiments will determine the role of the RhoA/ROK system in the mechanisms that may determine human uterine contractility. This information may direct new strategies to prevent or treat preterm labour.

Contractility and Calcium Signaling of Human Myometrium Are Profoundly Affected by Cholesterol Manipulation: Implications for Labor?

The authors elucidate cholesterol's effect on human uterine contractility and calcium signaling to test the hypotheses that elevation of cholesterol decreases uterine activity and that oxytocin cannot augment contraction when cholesterol is elevated. The effects of cholesterol extraction with methyl beta-cyclodextrin and enrichment with low-density lipoproteins and cholesterol on contractile activity and intracellular calcium signaling in spontaneous or oxytocin-stimulated myometrium are determined. Force occurring spontaneously and with oxytocin is significantly increased by cholesterol extraction. Cholesterol enrichment profoundly inhibits force production in a dose-dependent manner and could reverse the effects of cholesterol extraction. Qualitatively similar results are found for nonpregnant and pregnant laboring and non-laboring myometrium. These contractile changes are related to changes in intracellular Ca2+ . Thus, elevated cholesterol is deleterious to contractility and Ca2+ signaling in human myometrium. Cholesterol may contribute to uterine quiescence but could cause difficulties in labor in obese/dyslipidemic women, consistent with their increased cesarean delivery rates.

Protein kinase C and human uterine contractility

Abnormalities in uterine contractility are thought to contribute to several clinical problems, including preterm labor. A better understanding of the mechanisms controlling uterine activity would make it possible to propose more appropriate and effective management practices than those currently in use. Recent advances point to a role of the protein kinase C (PRKC) family in the regulation of uterine smooth muscle contraction at the end of pregnancy. In this review, we highlight recent work that explores the involvement of individual PRKC isoforms in cellular process, with an emphasis on the properties of PRKCZ isoform.

HDA inhibition and human uterine contractility

HDA inhibition and human uterine contractility

The adipose tissue secretory product ghrelin and human uterine contractility

The adipose tissue secretory product ghrelin and human uterine contractility

Inhibitory effect of leptin on human uterine contractility in vitro

The purpose of this study was to investigate the effects of leptin on human uterine contractility in vitro. Biopsies of human myometrium were obtained at elective cesarean section (n = 18). Dissected myometrial strips suspended under isometric conditions, undergoing spontaneous and oxytocin-induced contractions, were exposed to cumulative additions of leptin in the concentration range of 1 nmol/L to 1 micromol/L. Control strips were run simultaneously. Integrals of contractile activity were measured using the PowerLab hardware unit and Chart v3.6 software. Leptin exerted a potent and cumulative inhibitory effect on spontaneous and oxytocin-induced contractions compared to control strips. The mean maximal inhibition values were as follows: 46.794 +/- 5.133% (n = 6; P < .001) for spontaneous contractions and 42.323 +/- 3.692% (n = 6; P < .001) for oxytocin-induced contractions. There was an apparent reduction in both frequency and amplitude of contractions. This physiologic inhibitory effect of leptin on uterine contractility may play a role in the dysfunctional labor process associated with maternal obesity, and the resultant high cesarean section rates.

Thrombin and PAR1-activating peptide: effects on human uterine contractility in vitro

ObjectiveThrombin enhances uterine contractions in animal models, which is an effect that is mediated through protease-activated receptors. The aims of this study were to investigate the effects of thrombin on spontaneous human uterine contractility in vitro, in tissue obtained in the presence and absence of pregnancy, and to investigate the effects of a specific protease-activated receptor 1–activating peptide on human pregnant myometrial contractility. Study designIsometric recordings were performed under physiologic conditions on myometrial strips that were obtained from elective cesarean delivery and premenopausal hysterectomy specimens. The effects of thrombin (0.5 to 5.0 U/mL) and a specific protease-activated receptor 1–activating peptide (1 nmol/L to 10 μmol/L) on integrals of contractile activity were measured and compared with control values. ResultsThrombin exerted a potent stimulatory effect on human myometrial contractility. For pregnant and nonpregnant myometrium, this effect was significant at concentrations of ≥3.0 U/mL and 1.0 U/mL, respectively, with net maximal stimulatory effects of 44.5% (5.0 U/mL, P<.001) and 40.42% (3.0 U/mL, P<.001), respectively. The protease-activated receptor 1–activating peptide also mediated a significant uterotonic effect (55.1% increase) on human pregnant myometrial contractility at 10 μmol/L concentration (P<.001). ConclusionThis uterotonic effect of thrombin suggests that it may play a role in the pathophysiologic condition of human uterine contractions in association with intrauterine bleeding. The similar uterotonic effect that is elicited by protease-activated receptor 1–activating peptide suggests a major role for protease-activated receptor-1 in the thrombin-mediated contractile effect.

Effects of L-type Ca(2+)-channel blockade, K(+)(ATP)-channel opening and nitric oxide on human uterine contractility in relation to gestational age and labour.

Relative uterine inactivity during pregnancy changes to vigorous rhythmic contractility during labour. We hypothesized that mechanisms involved in the regulation of uterine quiescence and contractility differ between term and preterm myometrium and in labour and non-labour states. Myometrial strips, prepared from biopsies taken at Caesarean section from labouring and non-labouring women preterm and at term, were mounted in organ chambers for isometric tension recording. Oxytocin (10(-9) mol/l) was added to maintain stable contractions, and effects of various inhibitors of uterine contractility were studied. The inhibitory effects of L-type Ca(2+)-channel blocker nifedipine and ATP-sensitive K(+)-channel opener pinacidil were greater in myometrium from the non-labour versus the labour group, both preterm and at term. In addition, pinacidil's effect was greater at term compared with preterm in the non-labour group. Mg(2+) and the nitric oxide donor sodium nitroprusside significantly inhibited contractility in all groups without significant differences with regard to labour or gestational age. Decreased inhibition of human uterine contractility by L-type Ca(2+)-channel blockers and K(+)(ATP)-channel openers in preterm and term labour may reflect changes in expression and activity of these channels. Effects of nitric oxide and Mg(2+) are not affected by gestational age or labour.

Effects of sublingual nitroglycerin on human uterine contractility during the active phase of labor

Nitroglycerin is administered intravenously in acute obstetric emergencies to relax the uterus. However, complications (eg, hypotension, acute uterine bleeding) are frequent, which prompted a search for alternative routes of administration. We hypothesized that the sublingual administration of nitroglycerin would reduce uterine tone and contractility with few complications. Intrauterine pressure was measured in 12 women who were actively laboring (>4 cm dilatation, regular contractions) with epidural analgesia and who were alert and responsive throughout the study. In a double-blind fashion, subjects were randomized to receive either placebo or sublingual nitroglycerin (3 doses, 800 μg each) 10 minutes apart. The obstetric anesthesiologist continuously monitored maternal blood pressure and fetal heart rate. Cervical dilatation was assessed at the beginning and the end of the protocol. The area under the intrauterine pressure curve (integral) was used to estimate uterine contractility. Intrauterine pressure was analyzed before the randomization code was broken. Nitroglycerin did not alter the intrauterine pressure integral after the first dose (placebo, 3147 mm Hg · s [95% CI, 2206-4088] vs nitroglycerin, 4146 mm Hg · s [95% CI, 2451-5841]; P =.22), second dose (placebo, 3123 mm Hg · s [95% CI, 2447-3799] vs nitroglycerin, 3611 mm Hg · s [95% CI, 2723-4499]; P =.28), or third dose (placebo, 3303 mm Hg · s [95% CI, 2616-3990] vs nitroglycerin, 3810 mm Hg · s [95% CI, 2306-5314]; P =.45). Cervical dilation, basal uterine tone, duration and frequency of uterine contractions, or fetal heart rhythm remained unaffected. Maternal mean arterial pressure decreased significantly after nitroglycerin was administered. All women were delivered vaginally without intervention. Three doses of sublingual nitroglycerin (800 μg per dose) reduce neither uterine activity nor tone, despite lowering maternal blood pressure. If a clinical option, sublingual nitroglycerin will require a higher dose, which would place mother and fetus at risk for complication. (Am J Obstet Gynecol 2002;187:235-8.)

Polyamine effects on human myometrial contractility

Objective: This study was undertaken to investigate the effects of the polyamine spermine on human uterine contractility. Study design: Under physiologic conditions, an isometric tension recording was performed in isolated myometrial strips from biopsy specimens obtained at elective cesarean delivery (n = 24 specimens) and from premenopausal hysterectomy specimens (n = 6 specimens). The effects of spermine (1 μmol/L-10 mmol/L in cumulative doses) on spontaneous, agonist-induced myometrial contractions were measured, and dose response curves were constructed. The pD2 (−log EC50) values and the maximal inhibition values achieved were compared for spontaneous and agonist-induced contractions. Results: Spermine exerted a potent relaxant effect on all spontaneous and agonist-induced myometrial contractions, with mean maximal inhibition values between 62.8% ± 4.3% and 91.4% ± 1.8% and pD2 values between 2.66 ± 0.23 and 4.01 ± 0.20. Its inhibitory effect varied significantly with different contraction types (pD2, P < .05; mean maximal inhibition, P < .001), and it was least potent on BAY K 8644-elicited contractions (pD2, P < .05; mean maximal inhibition, P < .01). Conclusion: The polyamine spermine exerts a potent relaxant effect on human uterine tissue. This effect appears to be mediated, at least partially, by calcium antagonism. Polyamines may play a role in the maintenance of uterine quiescence during pregnancy. (Am J Obstet Gynecol 2002;186:778-83.)

Expression and modulation of Rho kinase in human pregnant myometrium.

There is little information outlining the role of Rho kinase, RhoA, and calcium sensitization in regulation of human uterine contractility during pregnancy. The aims of this study were to investigate the expression of RhoA, and the Rho kinases ROCK I and ROCK II in human pregnant myometrium, to evaluate the effects of Rho kinase inhibition on pregnant human myometrial contractility in vitro, and to compare these effects with those of the calcium channel blocker nifedipine. RT-PCR using primers for RhoA, ROCK I and ROCK II was performed on mRNA isolated from human pregnant myometrium. Isometric recording was performed in isolated myometrial strips obtained at Caesarean section. The effects of the Rho kinase inhibitor Y-27632 (1 nmol/l to 10 mmol/l), and nifedipine (1 nmol/l to 10 mmol/l), on oxytocin (0.5 nmol/l) induced contractions were measured and compared. Expression of RhoA, ROCK I and ROCK II mRNA was identified in human pregnant myometrium (n = 3). Y-27632 exerted a potent relaxant effect on myometrial contractility with a pD(2) value (+/- SEM) of 7.63 +/- 0.38 (n = 6). The maximum net relaxant effect (+/- SEM) was 72.3 +/- 6.1% (n = 6). Corresponding values for nifedipine were 7.24 +/- 0.48 (n = 6; P = 0.469) and 93.40 +/- 3.1% (n = 6; P = 0.028). Rho A/Rho kinase-mediated calcium sensitization may play role in the physiology of human parturition, and pharmacological inhibition of this pathway may therefore provide a novel approach to tocolysis for pre-term labour.

467 Effects of sublingual nitroglycerin (NTG) on human uterine contractility during active phase of labor

467 Effects of sublingual nitroglycerin (NTG) on human uterine contractility during active phase of labor

Influence of 5α- and 5β-reduced progestins on the contractility of isolated human myometrium at term

It is very well known that progesterone induces uterine relaxation on myometrium contractile activity. However, little attention has been paid to the effect induced by its metabolites on human uterine contractility. Therefore, we set out to analyze the potential relaxing effect of some 5α- and 5β-reduced progesterone derivatives on the spontaneous contractility of myometrium from pregnant women. Samples were obtained by caesarian section at 38–40 weeks of pregnancy. Spontaneous uterine contractions were recorded in vitro in the presence of progesterone, or progestins independently, at different non-cumulative μM concentrations. The progestins elicited an immediate relaxing effect that was concentration-dependent. With the exception of two 5α-reduced progestins (5α and 3β,5α), the remaining progestins used in the present study were more potent than progesterone. The potency order with respect to their IC 50 values was: 3α,5α (35 μM) > 5β (81 μM) > 3β,5β (156 μM) > 3α,5β (205 μM) > P 4 (225 μM) > 5α (19 mM) > 3β,5α (28 mM). When tissues were washed, the contractile activity was recovered. This rapid and reversible relaxing effect was not blocking by antiprogestin RU 486, suggesting that is not through receptor-mediated genomic action. The metabolites from progesterone may also determine the pattern of motility, ensuring the necessary quiescent environment to prevent abortion during gestation.

Fetal heart rate and uterine contractility during maternal exercise at term

OBJECTIVE: Our aim was to assess the physiologic response of human fetal heart rate and uterine contractility to moderately strenuous maternal exercise. STUDY DESIGN: We measured fetal heart rate and intrauterine pressure with the use of internal monitoring before, during, and after maternal exercise at a heart rate of 140 beats/min on a cycle ergometer in 30 term women admitted for elective induction of labor. The fetal heart rate tracings were assessed by three observers and were classified according to Fischer et al. and Nijhuis et al., and the frequency and intensity of uterine contractions were determined. RESULTS: Fetal outcome was good in all cases. There were no significant differences in Fischer scores between rest, exercise, and recovery periods. The fetuses displayed a heart rate pattern A and B, indicative of behavioral states 1F or 2F, 85% of the time, with state changes apparently independent of exercise. Uterine activity increased significantly during the exercise period, with a 5.5-fold increase in contraction frequency and a fourfold increase in time-pressure integral compared with rest, with rapid recovery after the exercise. CONCLUSION: Exercise in healthy pregnant women at term does not cause a change in fetal heart rate pattern suggestive of fetal distress or a change in fetal behavioral pattern, but it does significantly increase uterine activity. (A M J O BSTET G YNECOL 1996;174:43-8.)

Involvement of a nitric oxide-cyclic guanosine monophosphate pathway in control of human uterine contractility during pregnancy

OBJECTIVES: The aims of the study were to investigate whether a nitric oxide-cyclic guanosine monophosphate relaxation pathway is present in the human uterus and whether it differentially inhibits contractility during pregnancy and labor. STUDY DESIGN: Myometrial strips were obtained from pregnant women who were either in labor or not in labor and from nonpregnant women. Nitrites and cyclic guanosine monophosphate production by the tissues and contractile responses to nitric oxide modifiers were measured. RESULTS: Biochemical assays revealed that nitric oxide (nitrites) and cyclic guanosine monophosphate are generated by the human uterus. Cyclic guanosine monophosphate production by the uterus was increased by l-arginine (the substrate for nitric oxide) and diethylamine/nitric oxide (a nitric oxide donor) and decreased by nitro- l-arginine methyl ester (an inhibitor of nitric oxide synthase). Spontaneous contractility in vitro was increased by nitro- l-arginine methyl ester and decreased by diethylamine/nitric oxide, which furthermore produced a dose-dependent inhibition of contractility, and the median effective dose of inhibition in tissues from nonlaboring pregnant patients (1.5 ± 0.4 μmol/L) is substantially lower than in tissues from laboring pregnant (21.7 ± 7.4 μmol/L or nonpregnant (20.8 ± 4.4 μmol/L) women. These studies show that the nitric oxide-cyclic quanosine monophosphate system exists in the human uterus and that it inhibits contractility. Furthermore, the relaxation responsiveness to nitric oxide is elevated during pregnancy and decreased during labor. CONCLUSION: A nitric oxide-cyclic guanosine monophosphate relaxation pathway is present in the human uterus and may be responsible for maintaining uterine quiescence during pregnancy. A decrease in uterine relaxation responsiveness to nitric oxide at term may play a role in the initiation of labor.

Regulation of non-pregnant human uterine contractility: Effect of antihor mones

Uterine contractility was recorded on cycle day LH+6 to LH+8 in a control and treatment cycle in 14 healthy non-pregnant volunteers. In the treatment cycle the subjects received either 50 mg of the antiprogestin RU 486 daily for three days or 40 mg of the anti-estrogen tamoxifen daily for two days. The treatment started on day LH+2. During the recording, 2 to 5 μg PGF 2α was administered into the uterine cavity. The plasma levels of progesterone and estrogen were the same in both the control and treatment cycles. RU 486 caused a significant increase in uterine contractility expressed in Montevideo Units (MU) and a decrease in uterine tonus in comparison with corresponding data obtained in the control cycle. Following treatment with tamoxifen, uterine contractility was lower but the difference was not significant. PGF 2α invariably caused a stimulation of uterine contractility. However, treatment with the antihormones did not influence the response. The result of the present study indicates that the change in uterine contractility occurring in the latter part of the menstrual cycle and during menstruation is due to progesterone withdrawal.

Are leukotrienes involved in human uterine contractility?

The effects of leukotrienes (LT) on the contractility of human and rat myometrial strips in vitro were compared with the effects of prostaglandins (PGs) and oxytocin. Preparations of human myometrial membranes were investigated for the presence and characteristics of LTC4 receptors. Neither the peptido-leukotrienes (LTC4, LTD4, LTE4) nor LTB4 had any consistent effect, stimulatory or inhibitory, on human pregnant or non-pregnant myometrium, at doses up to 1.25 microM; nor did they have any effect in rat non-pregnant myometrium. As expected, PGE2, PGF2 alpha (0.3 microM) and oxytocin (5 nM) stimulated human pregnant myometrium. PGF2 alpha stimulated and PGE2 inhibited human non-pregnant myometrium but oxytocin had no effect; all three compounds stimulated rat non-pregnant myometrium. The binding of 3H-LTC4 to human myometrium was specific (LTC4 greater than LTD4 much greater than LTE4, LTB4, PGE2, PGF2 alpha, arachidonic acid) but of low affinity compared with the binding of 3H-PGE2 to the same membrane preparations. These data support the view that leukotrienes have little direct influence on myometrial contractility.

Amniotic fluid 5-hydroxyeicosatetraenoic acid in preterm labor

5-Hydroxyeicosatetraenoic acid (5-HETE) is an arachidonate lipoxygenase product capable of stimulating human uterine contractility in a dose-dependent manner in vitro. The purpose of this study was to determine if preterm labor is associated with changes in the concentration of this metabolite in amniotic acid. Amniotic fluid was obtained by transabdominal amniocentesis from three groups of women with preterm labor: group 1 — women without intraamniotic infection who responded to tocolysis (n = 32); group 2 — women without intraamniotic infection who failed to respond to tocolysis (n = 22); and group 3 — women with intraamniotic infection (n = 14). 5-HETE was determined by radioimmunoassay. The median amniotic fluid concentration of 5-HETE in women who responded to tocolysis (median = 1412 pg/ml; range: 111–3547) was significantly lower than in women who delivered despite tocolysis (median = 2052 pg/ml; range 136–7774) and women with intraamniotic infection (median = 1876 pg/ml; range: 543–7033) [p < 0.05]). No difference in amniotic fluid concentrations' of 5-HETE were found between women in groups 2 and 3 (p > 0.05).