Pharmacologic characterization of the oxytocin receptor in human uterine smooth muscle cells

Effectiveness of atosiban in women with previous single implantation failure undergoing frozen-thawed blastocyst transfer: study protocol for a randomised controlled trial

BACKGROUND

Uterine contractions may interfere with embryo implantation in assisted reproductive technology. To reduce these contractions and improve success rates, the oxytocin antagonist atosiban has been suggested for administration during embryo transfer. The aim of this study is to evaluate the effectiveness of atosiban in increasing live birth rates among women who have previously experienced a single implantation failure and are scheduled for single blastocyst transfer.

METHODS AND ANALYSIS

We conduct a single-centre randomised controlled study comparing atosiban and placebo in women undergoing a single blastocyst transfer with a previous failed blastocyst transfer. Women with endocrine or systemic illnesses, recurrent miscarriages, uterine malformations or fibroids, untreated hydrosalpinx, endometriosis (stage III or IV) or uterine fibroids, as well as women undergoing preimplantation genetic testing, are ineligible. The primary outcome is live birth resulting from the frozen-thawed embryo transfer. Secondary outcomes include biochemical/clinical pregnancy, miscarriage, ectopic pregnancy, multiple pregnancies as well as maternal and perinatal outcomes. We plan to recruit 1100 women (550 women per group). This will allow us to demonstrate or refute an increase in live birth rate from 40% to 50%. Data analysis will follow the intention-to-treat principle. We will measure patterns of uterine peristalsis which will allow subgroup analysis for women with or without uterine peristalsis.

ETHICS AND DISSEMINATION

This study has been approved by the Institutional Review Board of Northwest Women's and Children's Hospital (No. SZ2019001). Written informed consent will be obtained from each participant before randomisation. The results of the trial will be presented at scientific meetings and reported in publications.

TRIAL REGISTRATION NUMBER

ChiCTR1900022333.

An Octopus-Derived Peptide with Antidiuretic Activity in Rats

Discovering new drug candidates with high efficacy and few side effects is a major challenge in new drug development. The two evolutionarily related peptides oxytocin (OXT) and arginine vasopressin (AVP) are known to be associated with a variety of physiological and psychological processes via the association of OXT with three types of AVP receptors. Over decades, many synthetic analogs of these peptides have been designed and tested for therapeutic applications; however, only a few studies of their natural analogs have been performed. In this study, we investigated the bioactivity and usefulness of two natural OXT/AVP analogs that originate from the marine invertebrate Octopus vulgaris, named octopressin (OTP) and cephalotocin (CPT). By measuring the intracellular Ca2+ or cyclic AMP increase in each OXT/AVP receptor subtype-overexpressing cell, we found that CPT, but not OTP, acts as a selective agonist of human AVP type 1b and 2 receptors. This behavior is reminiscent of desmopressin, the most widely prescribed antidiuretic drug in the world. Similar to the case for desmopressin, a single intravenous tail injection of CPT into Sprague-Dawley rats reduced urine output and increased urinary osmolality. In conclusion, we suggest that CPT has a significant antidiuretic effect and that CPT might be beneficial for treating urological conditions such as nocturia, enuresis, and diabetes insipidus.

Pharmacological chaperones for the oxytocin receptor increase oxytocin responsiveness in myometrial cells

Oxytocin is a potent uterotonic agent administered to nearly all patients during childbirth in the United States. Inadequate oxytocin response can necessitate Cesarean delivery or lead to uterine atony and postpartum hemorrhage. Thus, it may be clinically useful to identify patients at risk for poor oxytocin response and develop strategies to sensitize the uterus to oxytocin. Previously, we showed that the V281M variant in the oxytocin receptor (OXTR) gene impairs OXTR trafficking to the cell surface, leading to a decreased oxytocin response in cells. Here, we sought to identify pharmacological chaperones that increased oxytocin response in cells expressing WT or V281M OXTR. We screened nine small-molecule agonists and antagonists of the oxytocin/vasopressin receptor family and identified two, SR49059 and L371,257, that restored both OXTR trafficking and oxytocin response in HEK293T cells transfected with V281M OXTR. In hTERT-immortalized human myometrial cells, which endogenously express WT OXTR, treatment with SR49059 and L371,257 increased the amount of OXTR on the cell surface by two- to fourfold. Furthermore, SR49059 and L371,257 increased the endogenous oxytocin response in hTERT-immortalized human myometrial cells by 35% and induced robust oxytocin responses in primary myometrial cells obtained from patients at the time of Cesarean section. If future studies demonstrate that these pharmacological chaperones or related compounds function similarly in vivo, we propose that they could potentially be used to enhance clinical response to oxytocin.

Analysis of decay kinetics of the cytosolic calcium transient induced by oxytocin in rat myometrium smooth muscle cells

The method of kinetic analysis of the relaxation phase of the mechanical response of the smooth muscle previously proposed by Burdyga and Kosterin was applied to study the dynamics of the decay of oxytocin-induced calcium transients in cytosol of the rat myometrium smooth muscle cell detected by a fluorescence signal generated by a calcium-sensitive probe fluo-4 using a laser scanning confocal microscope. The experimental data were well linearized in the coordinates ln [(F_m - F)/F] vs lnt (F and F_m are the current fluorescence intensity of the calcium probe and the fluorescence intensity at the maximum of the calcium transient, respectively, while t is the time). The empirical parameters n and τ were determined by which the maximal normalized relaxation rate V_n was calculated for five different ROIs (regions of interest) in the myocyte cytosol. It proved to be almost the same for all ROIs. The maximal normalized relaxation rate calculated from the fluorescence intensity was always lower than that calculated from the corresponding calcium concentration, i.e. the cytosolic Ca²⁺ concentration in the relaxation phase decreases faster than the corresponding fluorescence intensity. The value of the maximal normalized relaxation rate calculated both from the fluorescence intensity and from the force of oxytocin-induced contractions of isolated rat uterus longitudinal smooth muscles (according to Tsymbalyuk and Kosterin) was exactly the same. This indicates that in the relaxation phase, the decreasing curves of both the fluorescence intensity and the contraction forces coincide.

The cannabinoid receptor CB1 affects the proliferation and apoptosis of adenomyotic human uterine smooth muscle cells of the junctional zone: a mechanism study

BACKGROUND

The denomyotic junctional zone (JZ) plays an important role in the pathogenesis of adenomyosis. Proliferating cell nuclear antigen (PCNA) is an important nuclear marker of cell proliferation. This study aimed to evaluate the effects of the cannabinoid receptor CB1 on proliferation and apoptosis in the JZ in women with and without adenomyosis.

METHODS

JZ smooth muscle cells (JZSMCs) of the adenomyosis and control groups were collected and cultivated. Immunohistochemistry and immunoblotting were used for protein localization and expression detection of CB1 and PCNA. Additionally, qRT-PCR was used to quantitatively analyse the mRNA expression of the two. AM251 and ACEA were used to regulate the function of CB1 receptors, and CCK-8 assay and flow cytometry assay were used to verify the proliferation and apoptosis of JZSMCs after regulation.

RESULTS

We demonstrated that in normal JZSMCs CB1 and PCNA messenger RNA (mRNA) and protein expression was significantly higher in the proliferative phase of the menstrual cycle than in the secretory phase. CB1 and PCNA expression in JZSMCs from women with ADS was significantly higher than that in control women and did not significantly differ across the menstrual cycle. CB1 receptor antagonist AM251 inhibited the proliferation of adenomyotic JZSMCs in a dose-dependent manner. The CB1 receptor agonist ACEA significantly promoted the proliferation of adenomyotic JZSMCs. The apoptosis rate of adenomyotic JZSMCs treated with AM251 was significantly higher than that of JZSMCs from the untreated control group. The apoptosis rate was significantly decreased in the ACEA group compared with that in the untreated control group. Furthermore, AM251 suppressed the phosphorylation of AKT and Erk1/2 in adenomyotic JZSMCs. The CB1 agonist ACEA significantly promoted the phosphorylation of AKT and Erk1/2.

CONCLUSIONS

Our results indicated that the levels of CB1 and PCNA were increased in patients with adenomyosis and that cyclic changes were lost. CB1 may affect uterine JZ proliferation and apoptosis in adenomyosis by enhancing AKT and MAPK/Erk signalling.

Skeletal Muscle-Specific Activation of Gq Signaling Maintains Glucose Homeostasis

Skeletal muscle (SKM) insulin resistance plays a central role in the pathogenesis of type 2 diabetes. Because G-protein-coupled receptors (GPCRs) represent excellent drug targets, we hypothesized that activation of specific functional classes of SKM GPCRs might lead to improved glucose homeostasis in type 2 diabetes. At present, little is known about the in vivo metabolic roles of the various distinct GPCR signaling pathways operative in SKM. In this study, we tested the hypothesis that selective activation of SKM G_q signaling can improve SKM glucose uptake and whole-body glucose homeostasis under physiological and pathophysiological conditions. Studies with transgenic mice expressing a G_q-linked designer GPCR selectively in SKM cells demonstrated that receptor-mediated activation of SKM G_q signaling greatly promoted glucose uptake into SKM and significantly improved glucose homeostasis in obese, glucose-intolerant mice. These beneficial metabolic effects required the activity of SKM AMPK. In contrast, obese mutant mice that lacked both Gα_q and Gα₁₁ selectively in SKM showed severe deficits in glucose homeostasis. Moreover, GPCR-mediated activation of G_q signaling also stimulated glucose uptake in primary human SKM cells. Taken together, these findings strongly suggest that agents capable of enhancing SKM G_q signaling may prove useful as novel antidiabetic drugs.

In vitro comparison of liposomal drug delivery systems targeting the oxytocin receptor: a potential novel treatment for obstetric complications

Introduction

Targeted intervention to the uterus has great potential for the treatment of obstetric complications (eg, preterm birth, dysfunctional labor, and postpartum hemorrhage) by improving the effectiveness and safety of therapeutic compounds. In particular, targeting the oxytocin receptor (OTR) is a novel approach for drug delivery to the uterus. The aim of this study was to report the complete data set for the pharmaceutical synthesis and in vitro characterization of PEGylated liposomes conjugated with anti-OTR monoclonal antibodies (OTR-Lipo) or atosiban (ATO-Lipo, OTR antagonist).

Methods

OTR-targeted liposomal platforms composed of 1,2-distearoyl-sn-glycero-2-phosphocholine and cholesterol were prepared according to the method of dried lipid film hydration. Ligands were conjugated with the surface of liposomes using optimized methods to maximize conjugation efficiency. The liposomes were characterized for particle size, ligand conjugation, drug encapsulation, liposome stability, specificity of binding, cellular internalization, mechanistic pathway of cellular uptake, and cellular toxicity.

Results

Both OTR-Lipo and ATO-Lipo showed significant and specific binding to OTRs in a concentration-dependent manner compared to all control groups. There was no significant difference in binding values between OTR-Lipo and ATO-Lipo across all concentrations evaluated. In addition, OTR-Lipo (81.61%±7.84%) and ATO-Lipo (85.59%±8.28%) demonstrated significantly increased cellular internalization in comparison with rabbit IgG immunoliposomes (9.14%±1.71%) and conventional liposomes (4.09%±0.78%) at 2.02 mM phospholipid concentration. Cellular association following liposome incubation at 4.05 mM resulted in similar findings. Evaluation of the mechanistic pathway of cellular uptake indicated that they undergo internalization through both clathrin- and caveolin-mediated mechanisms. Furthermore, cellular toxicity studies have shown no significant effect of both liposomal platforms on cell viability.

Conclusion

This study further supports OTRs as a novel pharmaceutical target for drug delivery. OTR-targeted liposomal platforms may provide an effective way to deliver existing therapies directly to myometrial tissue and avoid adverse effects by circumventing non-target tissues.

Synthesis and in vitro characterization of oxytocin receptor targeted PEGylated immunoliposomes for drug delivery to the uterus

Targeted delivery of therapeutics to the uterus is an important goal in the treatment of obstetric complications, such as preterm labour, postpartum hemorrhage, and dysfunctional labour. Current treatment for these obstetric complications is challenging, as there are limited effective and safe therapeutic options available. We have developed a targeted drug delivery system for the uterus by conjugating anti-oxytocin receptor (OTR) antibodies to the surface of PEGylated liposomes (OTR-PEG-ILs). The functionality of the OTR-PEG-ILs has previously been evaluated on human and murine myometrial tissues as well as in vivo in a murine model of preterm labour. The aim of this study was to report the pharmaceutical synthesis and characterization of the OTR-PEG-ILs and investigate their specific cellular interaction with OTR-expressing myometrial cells in vitro. Immunoliposomes composed of 1,2-distearoyl-sn-glycero-2-phosphocholine (DSPC) and cholesterol were prepared using an optimized method for the coupling of low concentrations of antibody to liposomes. The liposomes were characterized for particle size, antibody conjugation, drug encapsulation, liposome stability, specificity of binding, cellular internalization, mechanistic pathway of cellular uptake, and cellular toxicity. Cellular association studies demonstrated specific binding of OTR-PEG-ILs to OTRs and significant cellular uptake following binding. Evaluation of the mechanistic pathway of cellular uptake indicated that they undergo internalization through both clathrin- and caveolin-mediated mechanisms. Furthermore, cellular toxicity studies have shown no significant effect of OTR-PEG-ILs or the endocytotic inhibitors on cell viability. This study further supports oxytocin receptors as a novel pharmaceutical target for drug delivery to the uterus.

Functional in vitro tension measurements of fascial tissue - a novel modified superfusion approach

INTRODUCTION

While two laboratory techniques are commonly used to assess the tensile properties of muscle tissue, emerging evidence suggests that the fascial components of these tissues also serve an active role in force generation. Hence, we investigated whether these techniques are sensitive for assessment of fascial micromechanics.

METHODS

Force measurements on dissected fascial tissue were performed either using the classical immersion organ bath or using an improved superfusion approach simulating pulsed pharmacological triggers. Rat deep dorsal fascial strips as well as rat testicular capsule were pharmacologically challenged either with mepyramine or oxytocin.

RESULTS

The classical immersion technique yielded a lower force response to mepyramine than the superfusion method (median: 367.4 vs. 555.4µN/mm(2)). Pause in irrigation before application reduced irregularities during bolus application. The superfusion approach was improved further by the following points: The high sensitivity of the superfusion method to bolus addition was voided by deviation of fluid supply during bolus addition.

CONCLUSION

Although both methods demonstrated pharmacologically induced contractile responses in lumbar fascia samples, the modified superfusion method may improve force registrations of slow contracting fascial tissue and minimize artefacts of fluid application.

Effects of combined progesterone and 17β-estradiol treatment on the transcriptome of cultured human myometrial smooth muscle cells

A transcriptomic analysis of cultured human uterine smooth muscle cells (hUtSMCs) was performed to examine gene expression profiles in smooth muscle in an environment containing the two major steroid hormones that regulate the human myometrium in physiological states associated with estrous, pregnancy, labor, and pathophysiological states such as leiomyoma and endometrial cancer. hUtSMCs were treated with progesterone (P4) and 17β-estradiol (E2) individually and in combination, in the presence and absence of RU486 (mifepristone). Transcription of many genes was modulated in the presence of P4 or E2 alone, but almost six times more genes were transcriptionally modulated in the presence of the P4/E2 hormone combination. In total 796 annotated genes were significantly differentially expressed in the presence of both P4 and E2 relative to their expression in untreated cells. Functional withdrawal of P4 by addition of RU486 effectively reversed almost all transcriptional changes caused by P4/E2 treatment. Gene ontology analysis of differentially expressed genes revealed a strong association between P4/E2 treatment and downregulated expression of genes involved in cell communication, signal transduction, channel activity, inflammatory response, and differentiation. Upregulated processes included cell survival, gene transcription, steroid hormone biosynthesis, muscle development, insulin receptor signaling, and cell growth.

Transcriptomic effects of estradiol treatment on cultured human uterine smooth muscle cells

Contractility of the myometrial smooth muscle cells during the estrous cycle and pregnancy is modulated by estrogen but the temporal expression of estrogen (relative to progesterone) and the type of contraction involved are distinctly different in pregnancy and estrous. This in vitro cell culture study investigated the global gene expression profile of human uterine smooth muscle cells (hUtSMCs) following 17β-estradiol (E2) treatment. In response to E2 treatment 540 genes, many of which have not been previously described as estrogen responsive, were identified as significantly differentially expressed. These genes are involved in biological processes that include muscle contraction, cell migration and adhesion, apoptosis and phosphorylation. Evidence from this study suggests that 17β-estradiol may have effects that are contrary to an overall contraction phenotype. The hUtSMC in vitro culture system is a useful model to investigate steroid effects on smooth muscle cells and may provide additional clues as to how smooth muscle cells behave in vivo.

Sequence variants in oxytocin pathway genes and preterm birth: a candidate gene association study

Background

Preterm birth (PTB) is a complex disorder associated with significant neonatal mortality and morbidity and long-term adverse health consequences. Multiple lines of evidence suggest that genetic factors play an important role in its etiology. This study was designed to identify genetic variation associated with PTB in oxytocin pathway genes whose role in parturition is well known.

Methods

To identify common genetic variants predisposing to PTB, we genotyped 16 single nucleotide polymorphisms (SNPs) in the oxytocin (OXT), oxytocin receptor (OXTR), and leucyl/cystinyl aminopeptidase (LNPEP) genes in 651 case infants from the U.S. and one or both of their parents. In addition, we examined the role of rare genetic variation in susceptibility to PTB by conducting direct sequence analysis of OXTR in 1394 cases and 1112 controls from the U.S., Argentina, Denmark, and Finland. This study was further extended to maternal triads (maternal grandparents-mother of a case infant, N=309). We also performed in vitro analysis of selected rare OXTR missense variants to evaluate their functional importance.

Results

Maternal genetic effect analysis of the SNP genotype data revealed four SNPs in LNPEP that show significant association with prematurity. In our case–control sequence analysis, we detected fourteen coding variants in exon 3 of OXTR, all but four of which were found in cases only. Of the fourteen variants, three were previously unreported novel rare variants. When the sequence data from the maternal triads were analyzed using the transmission disequilibrium test, two common missense SNPs (rs4686302 and rs237902) in OXTR showed suggestive association for three gestational age subgroups. In vitro functional assays showed a significant difference in ligand binding between wild-type and two mutant receptors.

Conclusions

Our study suggests an association between maternal common polymorphisms in LNPEP and susceptibility to PTB. Maternal OXTR missense SNPs rs4686302 and rs237902 may have gestational age-dependent effects on prematurity. Most of the OXTR rare variants identified do not appear to significantly contribute to the risk of PTB, but those shown to affect receptor function in our in vitro study warrant further investigation. Future studies with larger sample sizes are needed to confirm the findings of this study.

β-Arrestin mediates oxytocin receptor signaling, which regulates uterine contractility and cellular migration

Desensitization of the oxytocin receptor (OXTR) in the setting of prolonged oxytocin exposure may lead to dysfunctional labor, which increases the risk for cesarean delivery, and uterine atony, which may result in postpartum hemorrhage. The molecular mechanism for OXTR desensitization is through the agonist-mediated recruitment of the multifunctional protein β-arrestin. In addition to its desensitizing function, β-arrestins have recently been shown to simultaneously activate downstream signaling. We tested whether oxytocin stimulation promotes β-arrestin-mediated OXTR desensitization in vivo and activates β-arrestin-mediated mitogen-activated protein kinase (MAPK) growth signaling. Uterine muscle strips isolated from wild-type mice exhibited diminished uterine contractility following repeated exposure to oxytocin, whereas uterine muscle strips from β-arrestin-1 and β-arrestin-2 knockout mice showed no desensitization. Utilizing siRNA knockdown of β-arrestin-1 and β-arrestin-2 in HEK-293 cells expressing the OXTR, we demonstrated oxytocin-mediated MAPK signaling that was dependent on β-arrestin-1 and β-arrestin-2. Wild-type and β-arrestin-1 and β-arrestin-2 knockout mice receiving intravenous oxytocin also demonstrated oxytocin-mediated MAPK signaling that was dependent on β-arrestin-1 and β-arrestin-2. Finally, to test the significance of β-arrestin-mediated signaling from the OXTR, HEK-293 cells expressing the OXTR showed β-arrestin-dependent proliferation in a cell migration assay following oxytocin treatment. In conclusion, β-arrestin is a multifunctional scaffold protein that mediates both desensitization of the OXTR, leading to decreases in uterine contractility, and MAPK growth signaling following stimulation by oxytocin. The development of unique OXTR ligands that prevent receptor desensitization may be a novel approach in the treatment of adverse clinical events secondary to prolonged oxytocin therapy.

Oxytocin induces the migration of prostate cancer cells: involvement of the Gi-coupled signaling pathway

Expression of genes that encode oxytocin (OXT) and vasopressin (AVP) and their cognate receptors in normal and diseased prostates are only partially characterized. Reverse transcription and PCR were used to examine the expression of these genes in normal prostate epithelial and stromal cell lines, k-ras-transformed prostate epithelial cell lines, and in four prostate cancer cell lines. Secreted and cell-associated OXT peptide was measured by an enzyme immunoassay. OXT and its receptor (OXTR) were expressed in all eight prostate cell lines. Cell-associated OXT peptide was also found in all prostate epithelial cell lines except in DU145 cells. Neither AVP nor its cognate receptors (V1a receptor and V2 receptor) were expressed in any prostate cell line examined. These data point to the OXTR as the primary target of OXT and AVP, and suggest that OXT might be an autocrine/paracrine regulator in human prostate. We found that OXT induces the migration of PC3 and PC3M, but not DU145 prostate cancer cells. The effect of OXT is distinct from the epidermal growth factor (EGF)-induced migration of prostate cancer cells, in which ERK1/2 and EGF receptor kinase activities were required. When cells were pretreated with pertussis toxin, the effect of OXT, but not EGF, on cell migration was abolished. Pretreatment with the cyclic AMP analogue, 8-Br-cAMP, did not affect OXT-induced cell migration, which eliminated the nonspecific effect of pertussis toxin. We conclude that a Gi-dependent mechanism is involved in OXTR-mediated migration of prostate cancer cells, and indicates a role for OXTR in prostate cancer metastasis.

Treatment with oxytocin antagonists before embryo transfer may increase implantation rates after IVF

This report aimed to examine the effects of atosiban on pregnancy outcome after IVF-embryo transfer. A prospective, randomized, placebo-controlled clinical study was performed. A total of 180 women undergoing intracytoplasmic sperm injection who had top-quality embryos were randomly allocated into treatment and control groups. All the patients had infertility due to tubal factor, hormonal-anovulatory disorders, male factor or unexplained reasons. The treatment group received intravenous administration of atosiban before embryo transfer with a total administered dose of 37.5 mg. In the control group, the same number of cycles was performed with placebo medication. The clinical pregnancy rate (PR) per cycle and implantation rate (IR) per transfer were 46.7% and 20.4% in the atosiban-treated group, which were significantly higher than in the control group (28.9% and 12.6%, respectively, P=0.01). The miscarriage rates of groups 1 and 2 were 16.7% and 24.4%, respectively (P=0.01). These results have indicated that atosiban increases the IR and PR after IVF-embryo transfer. These results suggest that atosiban treatment before embryo transfer is effective in priming of the uterus for implantation. This is the first study to investigate the possible contributions of atosiban for improving the PR after IVF-embryo transfer.

Oxytocin-induced cell growth proliferation in human myometrial cells and leiomyomas

OBJECTIVE

To assess the expression of the oxytocin receptor (OTR) and the role of oxytocin (OT) in the proliferation of myometrial and leiomyoma cells.

DESIGN

Prospective laboratory study.

SETTING

Research laboratory at the Italian National Research Council.

PATIENT(S)

Twenty-two women who underwent therapeutic myomectomy for fibroids.

INTERVENTION(S)

Primary cultures of leiomyoma and myometrium cells were established from eutopic and ectopic myometrial tissues. An immortalized myometrial cell line (h-TERTmyo) and a leiomyosarcoma cell line (SK-UT-1) were also characterized.

MAIN OUTCOME MEASURE(S)

Expression of OTR and desmin mRNA was determined by quantitative real-time polymerase chain reaction. Cell growth was determined by 3-[4,5-dimethylthiazol-2-yl]5-(3-carboxymethoxyphenyl)2-(4-sulfophenyl)-2H tetrazolium assay. Apoptosis was determined by annexin V cell staining and flow cytometry analysis.

RESULT(S)

Oxytocin stimulated proliferation of primary myometrial and leiomyoma cells but inhibited the proliferation of h-TERTmyo and SK-UT-1, indicating a change in phenotype during immortalization. A progressive and rapid decrease in desmin and OTR mRNA was observed in primary cultures, indicating that myometrial cells dedifferentiate very rapidly in culture. The relative expression of OTR mRNA varied widely in both myometrial and leiomyoma smooth muscle cells, but there was no significant difference.

CONCLUSION(S)

These results indicate that OT stimulates the proliferation of both myometrial and leiomyoma cells, demonstrating that the OT/OTR system plays an important role in regulating uterine cell growth and providing a rationale for evaluating the use of OTR antagonists in managing uterine myomas.

Central endogenous vasopressin induced by central salt-loading participates in body fluid homeostasis through modulatory effects on neurones of the paraventricular nucleus in conscious rats

Peripherally secreted arginine vasopressin (AVP) plays a role in controlling body fluid homeostasis, and central endogenous AVP acts as a neurotransmitter or neuromodulator. The limbic system, which appears to exert an inhibitory effect on the endocrine hypothalamus, is also innervated by fibres that contain AVP. We examined whether central endogenous AVP is also involved in the control of body fluid homeostasis. To explore this possibility, we examined neuronal activity in the paraventricular nucleus of the hypothalamus (PVN), periventricular parts of the PVN and limbic brain areas, as well as AVP mRNA expression in the PVN and the peripheral secretion of AVP after central salt-loading in rats that had been pretreated i.c.v. with the AVP V(1) receptor antagonist OPC-21268. Neuronal activity in the PVN evaluated in terms of Fos-like immunoreactivity (FLI), especially in the parvocellular subdivisions, was suppressed. On the other hand, FLI was enhanced in the lateral septum, the bed nucleus of the stria terminalis and the anterior hypothalamic area. Similarly, AVP mRNA expression was enhanced in the magnocellular subnucleus of the PVN, despite the lack of a significant difference in the peripheral AVP level between OPC-21268- and vehicle-pretreated groups. We recorded renal sympathetic nerve activity (RSNA) as sympathetic nerve outflow during central salt-loading. The suppression of RSNA was significantly attenuated by i.c.v. pretreatment with OPC-21268. These results suggest that the suppression of RSNA during central salt-loading might be the result of a decrease in neuronal activity in the parvocellular subdivisions of the PVN via the inhibitory action of central endogenous AVP. The parvocellular and magnocellular neurones in the PVN might show different responses to central salt-loading to maintain body fluid homeostasis as a result of the modulatory role of central endogenous AVP.

Effects of the renal medullary pH and ionic environment on vasopressin binding and signaling

The kidney has a cortico-medullary interstitial gradient of decreasing pH and increasing concentrations of sodium chloride and urea, but the influence of these gradients on receptor signaling is largely unknown. Here, we measured G-protein coupled receptor function in LLC-PK1 cells acutely exposed to conditions mimicking different kidney regions. Signaling through the parathyroid hormone receptor, normally expressed in the cortex, was greatly reduced at an acidic pH similar to that of the inner medulla. Parathyroid hormone receptor, tagged with green fluorescent protein, showed no ligand-induced internalization. In contrast, under both acidic and hyperosmotic conditions, vasopressin increased intracellular cAMP, and upon binding to its type 2 receptor (V2R) was internalized and degraded. Dose-displacement binding assays with selective vasopressin/oxytocin receptor ligands under inner medullary conditions indicated a shift in the V2R pharmacological profile. Oxytocin did not bind to the V2R, as it does under normal conditions and the vasopressin type 1 receptor (V1R) had reduced affinity for vasopressin compared to the V2R in low pH and high osmolality. We suggest that the cortico-medullary gradient causes a receptor-specific selectivity in ligand binding that is of functional significance to the kidney. While the gradient is important for urinary concentration, it may also play a substantial role in fine-tuning of the vasopressin response through the V2R.

Oxytocin-induced activation of eukaryotic elongation factor 2 in myometrial cells is mediated by protein kinase C

The nonapeptide oxytocin (OT) mediates a wide spectrum of biological action, many of them related to reproduction. Recently, we have shown that OT exerts a trophic effect on uterine smooth muscle cells and induces dephosphorylation, and thus activation, of the translation elongation factor eukaryotic elongation factor 2 (eEF2). The present study was designed to elucidate the mechanisms underlying this novel action of OT in the well-characterized human myometrial cell line hTERT-C3. Pathways known to induce eEF2 dephosphorylation are mammalian target of rapamycin (mTOR), and the MAPKs ERK1/2 and p38. Using a panel of chemical inhibitors of specific signaling pathways, we determined that none of these pathways played a role in OT-mediated eEF2 dephosphorylation. Because the OT receptor is a G protein-coupled receptor linked to Galphaq, we tested the possibility that this OT action was mediated via protein kinase C (PKC). PKC activity was blocked by application of the general PKC chemical inhibitor Go6983 or by incubation with the cell-permeable PKC inhibitor peptide myr-psi PKC. With either approach, the effect of OT on eEF2 dephosphorylation was suppressed, indicating that the PKC pathway is essential for this OT action. Consistent with this idea, we also found that direct stimulation of PKC with the phorbol ester phorbol 12-myristate 13-acetate induced eEF2 dephosphorylation. Moreover, we observed that the stimulatory effect of OT on [(35)S]methionine incorporation into nascent proteins was blocked by PKC inhibition. Overall, these results define a novel hormonal signaling pathway that leads to eEF2 dephosphorylation and activation of protein synthesis.

Contractile reactivity of human myometrium in isolated non-pregnant uteri

BACKGROUND

Perfusion of the isolated uterus has been shown to be a feasible experimental system for studies of the human endometrium and myometrium. Utilizing our established experimental perfusion model we perfused 20 uteri for 27 h and investigated the contractile reactivity of the myometrium in response to 17beta-estradiol (E2) and oxytocin (OT).

METHODS

Uteri of group A (n = 4) were stimulated with OT; group B (n = 4) was treated continuously with E2; group C (n = 4) received both E2 and OT for 27 h; group D (n = 4) was perfused for 27 h with E2 with the addition of OT for the last 3 h of the experiment; group E (n = 4) as control group remained without any treatment. The pressure and duration of uterine contractions were recorded during the entire perfusion period using intramural and endoluminal pressure catheters.

RESULTS

Compared to the other treatment groups and controls, the most effective myometrial activity was achieved in group D during the OT stimulation period. No relevant myometrial activity was detected in the control group.

CONCLUSIONS

Continuous E2 treatment, with the addition of OT for the last 3 h of the 27 h perfusion period, led to the most pronounced uterotonic effects in the presented experimental condition.

Oxytocin receptor signaling in myoepithelial and cancer cells

Oxytocin (OT) plays a crucial role as a mediator of breast myoepithelial cell contraction, the process responsible for the ejection of milk during lactation, and is also involved in myoepithelial cell proliferation and postpartum mammary gland proliferation. Furthermore, although a number of breast cancer cells have oxytocin receptors (OTRs), it has been reported that OT stimulates, inhibits, or has no effect on cell proliferation. As these different effects seem to be mediated by different signaling pathways elicited by OTR stimulation, we here review the regulation of OTR signaling in different cell systems and discuss how understanding the molecular basis of receptor coupling specificity has become extremely important for understanding the role played by OTRs in regulating cell growth.

Effects of YM218, a nonpeptide vasopressin V1A receptor-selective antagonist, on human vasopressin and oxytocin receptors

The binding and signal transduction characteristics of YM218 ((Z)-4'-{4,4-difluoro-5-[2-oxo-2-(4-piperidinopiperidino)ethylidene]-2,3,4,5-tetrahydro-1H-1-benzoazepine-1-carbonyl}-2-methyl-3-furanilide hemifumarate), a newly synthesized, potent arginine vasopressin (AVP) V(1A) receptor-selective antagonist, were examined using cloned human AVP receptors (V(1A), V(1B) and V(2)) stably expressed in Chinese hamster ovary (CHO) cells and human uterine smooth muscle cells (USMCs) expressing oxytocin receptors. YM218 potently inhibited specific binding of [(3)H] AVP to V(1A) receptors, exhibiting a K(i) value of 0.30 nM. In contrast, YM218 exhibited much lower affinity for V(1B), V(2) and oxytocin receptors, exhibiting K(i) values of 25,500 nM, 381 nM and 71.0 nM, respectively. In CHO cells expressing V(1A) receptors, YM218 potently inhibited the AVP-induced increase in intracellular Ca(2+) concentration ([Ca(2+)](i)), exhibiting an IC(50) value of 0.25 nM. However, in human USMCs expressing oxytocin receptors, YM218 exhibited a much lower potency in inhibiting the oxytocin-induced [Ca(2+)](i) increase, showing an IC(50) value of 607 nM, and had no effect on the AVP-induced [Ca(2+)](i) increase in CHO cells expressing V(1B) receptors. Furthermore, in CHO cells expressing V(2) receptors, YM218 did not potently inhibit the production of cAMP stimulated by AVP, showing an IC(50) value of 62.2 nM. In all assays used, YM218 did not exhibit any agonistic activity. These results demonstrate that YM218 is a potent, nonpeptide human V(1A) receptor-selective antagonist, and that YM218 will be a valuable new tool to gain further insight into the physiologic and pharmacologic actions of AVP.

Identification, characterization and biological activity of oxytocin receptor in the developing human penis

Although abnormalities of the male external genitalia (MEG) are a relatively common problem, little is known concerning the molecular mechanisms that finely regulate penile development. We report here the expression of the oxytocin receptor (OTR) gene by real-time RT-PCR in human fetal tissues (11th-12th week of gestation), including the MEG. The developing penis expressed a very high level of OTR mRNA, only a half log(10) unit lower than fetal central nervous system, used as a positive control. The OTR protein is also highly expressed (western, immunohistochemistry and binding studies) and immunolocalized both in the mesenchymal body and in the surrounding blood capillaries, which will later constitute penile trabeculae and sinusoids. Binding studies using [125I]oxytocin antagonist ([125I]OTA) in cultured human fetal penile smooth muscle cells (hfPSMC) revealed the presence of specific OTR with a high capacity and affinity for oxytocin (OT) and for OTA. Increasing concentrations of OT dose-dependently induced intracellular Ca2+ mobilization. Furthermore, OTR mediated an increase in the proliferation and the migration of hfPSMC. In conclusion, we demonstrate that in the developing human MEG, OTR is highly expressed and might be involved in coordinating timely and appropriate proliferation and migration of the penile cells. Thus, OTR might represent an additional target for investigating human fetal MEG organogenesis.

Design of peptide oxytocin antagonists with strikingly higher affinities and selectivities for the human oxytocin receptor than atosiban

The peptide oxytocin (OT) antagonist atosiban, approved for tocolytic use in Europe (under the tradename Tractocile), represents an important new therapeutic advance for the treatment of premature labor. This paper presents some new peptide OT antagonists which offer promise as superior tocolytics. The solid phase synthesis is reported of four pairs of L and D-2-naphthylalanine (L/D-2Nal) position-2 modified analogs of the following four oxytocin (OT) antagonists: des-9-glycinamide [1-(beta-mercapto-beta,beta-pentamethylene propionic acid), 2-O-methyltyrosine, 4-threonine]ornithine-vasotocin (desGly-NH(2),d(CH(2))(5)[Tyr(Me)(2),Thr(4)]OVT) (A); the Tyr-NH(2) (9) analog of (A), d(CH(2))(5)[Tyr(Me)(2),Thr(4),Tyr-NH(2) (9)]OVT (B); the Eda(9) analog of (A), d(CH(2))(5)[Tyr(Me)(2),Thr(4),Eda(9)]OVT (C); and the retro COCH(2)Ph(4-0H)(10) modified analog of (C), d(CH(2))(5)[Tyr(Me)(2),Thr(4),Eda(9)<-- COCH(2)Ph(4-0H)(10)]OVT (D). The eight new analogs of A-D are (1) desGly-NH(2),d(CH(2))(5)[D-2Nal(2),Thr(4)]OVT, (2) desGly-NH(2),d(CH(2))(5)[2-Nal(2),Thr(4)]OVT, (3) d(CH(2))(5)[D-2Nal(2),Thr(4),Tyr-NH(2) (9)]OVT, (4) d(CH(2))(5)[2Nal(2),Thr(4),Tyr-NH(2) (9)]OVT, (5) d(CH(2))(5)[D-2Nal(2),Thr(4),Eda(9)]OVT, (6) d(CH(2))(5)[2Nal(2),Thr(4),Eda(9)]OVT, (7) d(CH(2))(5)[D-2Nal(2),Thr(4),Eda(9)<-- COCH(2)Ph(4-0H)(10)]OVT, (8) d(CH(2))(5)[2Nal(2),Thr(4),Eda(9)<-- COCH(2)Ph(4-OH)(10)]OVT. Peptides 1-8 were evaluated for agonistic and antagonistic activities in in vitro and in vivo rat bioassays, in rat OT receptor (rOTR) binding assays and in human OT receptor (hOTR) and human vasopressin (VP) vasopressor (V(1a)) receptor (hV(1a)R) binding assays. Also reported are the hOTR and hV(1a)R affinity data for atosiban and for B. None of the eight peptides exhibit oxytocic or vasopressor agonism. Peptides 1-8 exhibit weak antidiuretic agonism (activities in the range 0.014-0.21 U/mg). Peptides 1-6 exhibit potent in vitro (no Mg(2+)) OT antagonism (anti-OT pA(2) values range from 7.63 to 8.08). Peptides 7 and 8 are weaker OT antagonists. Peptides 1-6 are all OT antagonists in vivo (estimated in vivo anti-OT pA(2) values in the range 6.94-7.23). Peptides 1-8 exhibit vasopressor antagonism, anti-V(1a) pA(2) values in the range 5.1-7.65. Peptides 1-8 exhibit high affinities for the rOTR (K(i) values = 0.3-7.8 nM). Peptides 1-4 and B exhibit surprisingly very high affinities for the hOTR; their K(i) values are 0.17, 0.29, 0.07, 0.14 and 0.59 nM, respectively. Peptides 1-4 and B exhibit respectively 449, 263, 1091, 546 and 129 times greater affinity for the hOTR than atosiban (K(i) = 76.4 nM). Peptides 1-4 exhibit high affinities for the hV(1a)R (K(i)s = 1.1 nM, 1.3 nM, 0.19 nM and 0.54 nM, all higher than the hV1(a)R affinities exhibited by atosiban (K(i) = 5.1 nM) and by B (K(i) = 5.26 nM). Because of their strikingly higher affinities for the hOTR than atosiban, peptides 1-4 and B exhibit gains in anti hOT/anti hV(1a) receptor selectivity compared with atosiban of 93, 64, 39, 56 and 127, respectively. These OT antagonists are thus promising candidates for development as potential new tocolytic agents.

Effect of an oxytocin receptor antagonist and rho kinase inhibitor on the [Ca++]i sensitivity of human myometrium

OBJECTIVE

The purpose of this study was to assess the possible mechanism and effect of oxytocin receptor on the sensitization of the contractile proteins to [Ca(++)](i).

STUDY DESIGN

Myometrial strips were prepared from biopsy specimens that had been taken at term (37-40 weeks of gestation) cesarean delivery from 22 women, before the onset of labor. Simultaneous measurements of [Ca(++)](i) and tension were performed on spontaneously contracting strips. The effects of a specific oxytocin receptor antagonist, L371,257, and a rho kinase inhibitor, Y-27632, on the [Ca(++)](i) and tension transients were determined.

RESULTS

Application of L371,257 (90 nmol/L) to spontaneously contracting muscle strips reduced peak tension to 43%+/-12% of its original value without affecting peak [Ca(++)](i) (105%+/-15%). More tension is developed at each [Ca(++)](i) during the falling phase, relative to the rising phase of each spontaneous contraction; this asymmetric [Ca(++)](i)-tension relationship was abolished by L371,257. The subsequent application of oxytocin (3 micromol/L) reversed the effects of the antagonist on tension. An inhibitor of rho kinase (Y-27632) caused a concentration-dependent inhibition of spontaneous contractions without affecting the underlying Ca(++) signals. The addition of oxytocin (1 nmol/L) to spontaneously active myometrium increased both the duration of the Ca(++) signal and the sensitivity of the contractile machinery to [Ca(++)](i); only the latter effect was prevented by Y-27632.

CONCLUSION

Oxytocin independently regulates the duration of the periodic Ca(++) signals and the sensitivity of the contractile machinery to Ca(++). The latter is likely to be mediated by rho kinase, which is essential for the effective coupling of increases in [Ca(++)](i) to tension.

Adult cardiac Sca-1-positive cells differentiate into beating cardiomyocytes

Although somatic stem cells have been reported to exist in various adult organs, there have been few reports concerning stem cells in the heart. We here demonstrate that Sca-1-positive (Sca-1+) cells in adult hearts have some of the features of stem cells. Sca-1+ cells were isolated from adult murine hearts by a magnetic cell sorting system and cultured on gelatin-coated dishes. A fraction of Sca-1+ cells stuck to the culture dish and proliferated slowly. When treated with oxytocin, Sca-1+ cells expressed genes of cardiac transcription factors and contractile proteins and showed sarcomeric structure and spontaneous beating. Isoproterenol treatment increased the beating rate, which was accompanied by the intracellular Ca(2+) transients. The cardiac Sca-1+ cells expressed oxytocin receptor mRNA, and the expression was up-regulated after oxytocin treatment. Some of the Sca-1+ cells expressed alkaline phosphatase after osteogenic induction and were stained with Oil-Red O after adipogenic induction. These results suggest that Sca-1+ cells in the adult murine heart have potential as stem cells and may contribute to the regeneration of injured hearts.

Regulation of oxytocin receptor expression in cultured human myometrial cells by fetal bovine serum and lysophospholipids

Oxytocin receptor (OTR) expression in human myometrium increases over 150-fold from the beginning of pregnancy to the end. In the present studies, we examined potential mechanisms of OTR up-regulation, using myometrial cells in primary culture from women in late gestation. OTR ligand-binding sites and steady-state mRNA levels were down regulated by serum starvation, and up-regulated by restoration of fetal bovine serum (FBS). Transcriptional activity of the OTR gene was the same with or without FBS treatment, but FBS increased OTR mRNA half-life about 5-fold. Lysophospholipids (lysophosphatidic acid and sphingosine 1-phosphate), which are present in serum, had similar effects as FBS. Lysophospholipid receptor mRNAs of the endothelial differentiation gene (Edg) family (Edgs 1, 3, 4, and 5) were demonstrated in myometrial cells by RT-PCR. These G protein-coupled receptors have been shown to be coupled to G(i/o) and to mediate activation of phosphoinositol 3-phosphate kinase. Indeed, the effects of the lysophospholipids and FBS were completely blocked by pertussis toxin, a G(i/o) inhibitor. Likewise, inhibition of G(i/o) signaling by elevation of intracellular cAMP or inhibition of phosphoinositol 3-phosphate kinase blocked FBS effects on OTR mRNA stability. We do not presently understand the mechanisms of OTR up-regulation in human myometrium in vivo, but the present studies might lead to the description of mRNA-stabilizing factors whose activity can be quantified in tissue samples during pregnancy to elucidate the process of OTR up-regulation.

Design of oxytocin antagonists, which are more selective than atosiban

We report the solid phase synthesis of four pairs of L- and D-thienylalanine (Thi/D-Thi) position two modified analogues of the following four oxytocin (OT) antagonists: des-9-glycinamide [1-(beta-mercapto-beta,beta-pentamethylene propionic acid), 2-O-methyltyrosine, 4-threonine]ornithine-vasotocin (desGly(NH2)9,d (CH2)5[Tyr(Me)2,Thr4]OVT) (A); the Tyr-(NH2)9 analogue of (A), d(CH2)5[Tyr(Me)2,Thr4,Tyr-(NH2)9]OVT (B); the Eda9 analogue (where Eda = ethylenediamine) of (A), d(CH2)5[Tyr(Me)2, Thr4, Eda9]OVT (C); and the retro Tyr10 modified analogue of (C), d(CH2)5[Tyr(Me)2, Thr4, Eda9<--Tyr10]OVT (D). The eight new analogues of A-D are (1) desGly(NH2),d(CH2)5[Thi2,Thr4]OVT, (2) desGly(NH2),d(CH2)5[D-Thi2,Thr4]OVT, (3) d(CH2)5[Thi2, Thr4,Tyr-(NH2)9]OVT, (4) d(CH2)5[D-Thi2,Thr4,Tyr-(NH2)9]OVT (5) d(CH2)5[Thi2,Thr4Eda9]OVT, (6) d(CH2)5[D-Thi2,Thr4,Eda9]OVT, (7) d(CH2) [Thi2,Thr4,Eda9<--Tyr10]OVT, (8) d(CH2),[D-Thi2,Thr4,Eda9<--Tyr10]OVT. We also report the synthesis of (C). Peptides 1-8 and C were evaluated for agonistic and antagonistic activities in in vitro and in vivo OT assays, in in vivo vasopressor (V1a receptor) assays and in in vivo antidiuretic (V2 receptor) assays. None of the eight peptides nor C exhibit oxytocic or vasopressor agonism. Peptides 1-8 are extremely weak V2 agonists (antidiuretic activities range from < 0.0005 to 0.20 U/mg). Peptide C is a weak mixed V2 agonist/antagonist. Peptides 1-8 and C exhibit potent in intro (no Mg2+) OT antagonism (anti-OT pA2 values range from 7.76 to 8.05). Peptides 1-8 are all OT antagonists in vivo (estimated in vivo anti-OT pA2 values range from 6.54-7.19). With anti-V1a pA2 values of approximately 5-5.80, peptides 1-8 exhibit marked reductions in anti-V1a potencies relative to those of the parent peptides A-D (anti-V1a pA2 range from 6.48 to 7.10) and to l-deamino[D-Tyr(Et)2, Thr4]OVT (Atosiban, trade name Tractocile) (anti-V1a pA2-6.14). Atosiban has recently been approved in Europe for clinical use for the prevention of premature labour (Pharm. J. 264(7-100): 871). Peptides 1-8 exhibit striking gains in in vitro anti-OT/anti-V1a selectivities with respect to the parent peptides A, B, C and D and to Atosiban. Peptides 1-8 exhibit anti-OT (in vitro)/anti-V1a selectivities of 450, 525, 550, 450, approximately 1080, 116, 355, 227 respectively. The corresponding values for A-D and Atosiban are 30, 4.2, 4.3, 2.6 and 37. With the exception of peptide 6, the remaining seven peptides exhibit 3-18-fold gains in anti-OT (in vivo)/anti-V1a selectivity with respect to Atosiban, peptides 1-8 exhibit anti-OT (in vivo)/anti-V1a selectivities of 22, approximately 82, approximately 82, 147, approximately 83, 11, 31 and 42. By comparison, Atosiban exhibits an anti-OT (in vivo)/anti-V1a selectivity = 8. With an estimated in vivo anti-OT pA2 value = 7.19+/-0.06, peptide 4 is equipotent with Atosiban (pA2 = 7.05+/-0.05). However, with its significantly reduced anti-vasopressor potency, pA2 = approximately 5, it is approximately 18 times more selective for OT receptors with respect to VP V1a receptors than Atosiban. Since we have shown that V1a antagonism could be an unwanted side-effect in tocolytics, peptide 4 and some of the OT antagonists reported here have advantages over Atosiban and thus may be suitable candidates for evaluation as potential tocolytic agents for the treatment of preterm labour.

Effects of YM471, a nonpeptide AVP V(1A) and V(2) receptor antagonist, on human AVP receptor subtypes expressed in CHO cells and oxytocin receptors in human uterine smooth muscle cells

YM471, (Z)-4'-[4,4-difluoro-5-[2-(4-dimethylaminopiperidino)-2-oxoethylidene]-2,3,4,5-tetrahydro-1H-1-benzoazepine-1-carbonyl]-2-phenylbenzanilide monohydrochloride, is a newly synthesized potent vasopressin (AVP) receptor antagonist. Its effects on binding to and signal transduction by cloned human AVP receptors (V(1A), V(1B) and V(2)) stably expressed in Chinese hamster ovary (CHO) cells, and oxytocin receptors in human uterine smooth muscle cells (USMC) were studied. YM471 potently inhibited specific [(3)H]-AVP binding to V(1A) and V(2) receptors with K(i) values of 0.62 nM and 1.19 nM, respectively. In contrast, YM471 exhibited much lower affinity for V(1B) and oxytocin receptors with K(i) values of 16.4 microM and 31.6 nM, respectively. In CHO cells expressing V(1A) receptors, YM471 potently inhibited AVP-induced intracellular Ca(2+) concentration ([Ca(2+)](i)) increase, exhibiting an IC(50) value of 0.56 nM. However, in human USMC expressing oxytocin receptors, YM471 exhibited much lower potency in inhibiting oxytocin-induced [Ca(2+)](i) increase (IC(50)=193 nM), and did not affect AVP-induced [Ca(2+)](i) increase in CHO cells expressing V(1B) receptors. Furthermore, in CHO cells expressing V(2) receptors, YM471 potently inhibited the production of cyclic AMP stimulated by AVP with an IC(50) value of 1.88 nM. In all assays, YM471 showed no agonistic activity. These results demonstrate that YM471 is a potent, nonpeptide human V(1A) and V(2) receptor antagonist which will be a valuable tool in defining the physiologic and pharmacologic actions of AVP.

Muscle layer- and region-dependent distributions of oxytocin receptors in the porcine myometrium

The aim of the present study was to clarify smooth muscle- and region-dependent distributions of the oxytocin receptor that mediates oxytocin-induced contraction in the nonpregnant porcine myometrium by means of mechanical and radioligand ([3H]-oxytocin) binding studies. In Krebs solution, oxytocin (0.1-300 nM) caused concentration-dependent contractions of the cornual myometrium, and the longitudinal muscle was more sensitive than the circular muscle. [Arg8]-vasopressin and [deamino-Cys1, D-Arg8]-vasopressin also contracted the myometrium, and the order of the potency was oxytocin > [Arg8]-vasopressin > [deamino-Cys(1), D-Arg(8)]-vasopressin. Treatment with a high concentration of oxytocin selectively inhibited the contraction of oxytocin and [Arg8]-vasopressin without affecting the responses of acetylcholine and high-K+. Selective cross inhibition was also observed in the presence of a high concentration of [Arg(8)]-vasopressin. The oxytocin-induced contraction was resistant to tetrodotoxin and atropine, but was reduced by verapamil or by the removal of external Ca2+, indicating that oxytocin has a direct action on smooth muscle cells and that extracellular Ca2+ plays an important role for the contraction. In Kumagai solution, oxytocin caused contraction of the cornual longitudinal muscle (-logEC50 = 8.5) but not the circular muscle. Longitudinal muscles of other regions (corpus and cervix) were also responsive to oxytocin, but the -logEC50 value differed from region to region (cornua > corpus = cervix). On the other hand, oxytocin failed to cause contraction of the corpus and cervical circular muscles. 3H-Oxytocin bound to crude membrane preparations of the myometrium in a concentration-dependent (0.084-2.7 nM) saturable manner. Scatchard analysis of equilibrium binding data revealed the presence of a single class of binding site with an apparent dissociation constant (Kd, 1.1-1.5 nM), but receptor density (Bmax) differed in the two muscle layer types (longitudinal muscle: circular muscle = 5:1) and tended to decrease from the cornua to the cervix. In conclusion, the receptor specific for oxytocin is present in the porcine myometrium and mediates the contractile responses of both oxytocin and [Arg8]-vasopressin. The distribution of the oxytocin receptors differs according to the type of muscle layer (longitudinal muscle > circular muscle) and the region of the uterus.

Activation of functional oxytocin receptors stimulates cell proliferation in human trophoblast and choriocarcinoma cell lines

Despite oxytocin receptors (OTR) being present in human chorio-decidual tissues, their expression and role in placental trophoblast cells in the context of tumor growth or physiological functions related to cell proliferation have never been examined. In the present study we demonstrate the presence and functionality of OTR in normal human trophoblast cell lines (ED77 and ED27) and a choriocarcinoma cell line (BeWo). RT-PCR and immunofluorescence analysis revealed the presence of OTR messenger RNA and protein in these cells. Binding studies using [(125)I]oxytocin ([(125)I]OT) antagonist confirmed the presence of specific binding sites in ED27, ED77, and BeWo cells. OTR functionality was demonstrated by measuring the OT-induced increase in the intracellular calcium concentrations. This effect was dose dependent and was blocked by the selective OT antagonist d(CH(2))(5)[Tyr(Me)(2),Thr(4), Tyr-NH(2)(9)]OVT (OT antagonist). Furthermore, two proteins with apparent molecular masses of 125 and 60 kDa became tyrosine phosphorylated in all of the cell lines after OT stimulation (and an additional protein of 45 kDa in BeWo choriocarcinoma cells), suggesting that this peptide can stimulate tyrosine kinase activity. Finally, we observed a dose-dependent OT stimulation of cell proliferation associated with OTR activation that was completely abolished by the selective OT antagonist. These findings provide the first evidence of the presence of functional OTR in normal trophoblast cell lines as well as in choriocarcinoma cells and show that a specific effect of OT on normal and neoplastic trophoblast is to promote cellular proliferation.