Oxytocin and vasopressin 1a receptor gene expression in the cycling or pregnant human uterus

Critical role of V1a vasopressin receptor in murine parturition†

The precise mechanisms of the reproductive physiological processes, such as labor initiation, are poorly understood. Oxytocin (OT) is one of the well-known uterotonics and is clinically adopted as a medication to facilitate childbirth. Vasopressin (VP), a posterior pituitary hormone similar to OT, has also been proposed to be involved in the reproductive physiology. In this study, we found that a total deficiency of V1a receptor subtype (V1aR) in mice resulted in a reduced number of pups, delayed labor initiation, and increased post-delivery hemorrhage compared with those in wild-type mice. Among the VP receptor subtypes, only V1aR was found to be expressed in the murine uterus, and its distribution pattern was different from that of the oxytocin receptor (OTR); V1aR expression was mainly distributed in the circular myometrium, whereas OTR was strongly expressed in both the circular and longitudinal myometrium. The maximum contractile force of the circular myometrium, induced by VP or OT, was attenuated in the pregnant uterus of Avpr1a-deficient mice. Contrarily, while OT expression was decreased in the Avpr1a-deficient uterus, OTR expression was significantly increased. These results suggest that V1aR deficiency not only reduces the uterine contractile force but also perturbs the expression of genes responsible for the reproductive physiology. Therefore, V1aR is necessary to exert the maximum contraction of the circular myometrium to deliver pups. This study revealed an important role of V1aR in physiological contraction and term parturition in mice.

OXTR overexpression leads to abnormal mammary gland development in mice

Oxytocin receptor (OXTR) is a G-protein-coupled receptor and known for regulation of maternal and social behaviors. Null mutation (Oxtr-/-) leads to defects in lactation due to impaired milk ejection and maternal nurturing. Overexpression of OXTR has never been studied. To define the functions of OXTR overexpression, a transgenic mouse model that overexpresses mouse Oxtr under β-actin promoter was developed ( ++ Oxtr). ++ Oxtr mice displayed advanced development and maturation of mammary gland, including ductal distention, enhanced secretory differentiation and early milk production at non-pregnancy and early pregnancy. However, ++ Oxtr dams failed to produce adequate amount of milk and led to lethality of newborns due to early involution of mammary gland in lactation. Mammary gland transplantation results indicated the abnormal mammary gland development was mainly from hormonal changes in ++Oxtr mice but not from OXTR overexpression in mammary gland. Elevated OXTR expression increased prolactin-induced phosphorylation and nuclear localization of STAT5 (p-STAT5), and decreased progesterone level, leading to early milk production in non-pregnant and early pregnant females, whereas low prolactin and STAT5 activation in lactation led to insufficient milk production. Progesterone treatment reversed the OXTR-induced accelerated mammary gland development by inhibition of prolactin/p-STAT5 pathway. Prolactin administration rescued lactation deficiency through STAT5 activation. Progesterone plays a negative role in OXTR-regulated prolactin/p-STAT5 pathways. The study provides evidence that OXTR overexpression induces abnormal mammary gland development through progesterone and prolactin-regulated p-STAT5 pathway.

Elevated utero/placental GR/NR3C1 is not required for the induction of parturition in the dog

The endocrine mechanisms that lead to initiation of parturition in dogs are still not fully understood. The prepartum luteolysis is associated with increased prostaglandin (PG) F2α secretion; however, there is no pregnancy- or parturition-related increase in estrogens. Moreover, unlike in other mammalian species, in the dog, increased peripartum levels of cortisol measured sporadically in maternal peripheral blood are not mandatory for normal parturition. Nevertheless, auto/paracrine effects of cortisol at the placental feto-maternal level cannot be excluded. Therefore, the aim of this study was to investigate the expression and localization of glucocorticoid receptor (GR/NR3C1) in canine utero/placental (Ut/Pl) units and uterine interplacental sites at selected time points during pregnancy (pre-implantation, post-implantation and mid-gestation), and at normal and antigestagen-induced parturition. The Ut/Pl expression of GR/NR3C1 did not change significantly from pre-implantation until mid-gestation; however, it was strongly induced during the prepartum luteolysis. Within the interplacental samples, expression of GR/NR3C1-mRNA was greater post-implantation than pre-implantation and did not change afterward, i.e. toward mid-gestation. Compartmentalization studies within the Ut/Pl units, involving placenta, endometrium and myometrium separately, performed at the prepartum luteolysis revealed the highest GR/NR3C1-mRNA levels in placenta compared with endometrium and myometrium. Interestingly, in antigestagen-treated mid-pregnancy dogs, Ut/Pl and interplacental GR/NR3C1-mRNA expression remained unaffected. At the cellular level, placental GR/NR3C1 was clearly detectable in placenta fetalis, i.e. in trophoblast cells. In conclusion, increased expression of GR/NR3C1 during normal parturition, but not following antigestagen-treatment, suggest that it is not required for initiating the signaling cascade of PG synthesis leading to the induction of parturition in the dog.

Phasic contractions of the mouse vagina and cervix at different phases of the estrus cycle and during late pregnancy

BACKGROUND/AIMS

The pacemaker mechanisms activating phasic contractions of vaginal and cervical smooth muscle remain poorly understood. Here, we investigate properties of pacemaking in vaginal and cervical tissues by determining whether: 1) functional pacemaking is dependent on the phase of the estrus cycle or pregnancy; 2) pacemaking involves Ca2+ release from sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA) -dependent intracellular Ca2+ stores; and 3) c-Kit and/or vimentin immunoreactive ICs have a role in pacemaking.

METHODOLOGY/PRINCIPAL FINDINGS

Vaginal and cervical contractions were measured in vitro, as was the distribution of c-Kit and vimentin positive interstitial cells (ICs). Cervical smooth muscle was spontaneously active in estrus and metestrus but quiescent during proestrus and diestrus. Vaginal smooth muscle was normally quiescent but exhibited phasic contractions in the presence of oxytocin or the K+ channel blocker tetraethylammonium (TEA) chloride. Spontaneous contractions in the cervix and TEA-induced phasic contractions in the vagina persisted in the presence of cyclopiazonic acid (CPA), a blocker of the SERCA that refills intracellular SR Ca2+ stores, but were inhibited in low Ca2+ solution or in the presence of nifedipine, an inhibitor of L-type Ca2+channels. ICs were found in small numbers in the mouse cervix but not in the vagina.

CONCLUSIONS/SIGNIFICANCE

Cervical smooth muscle strips taken from mice in estrus, metestrus or late pregnancy were generally spontaneously active. Vaginal smooth muscle strips were normally quiescent but could be induced to exhibit phasic contractions independent on phase of the estrus cycle or late pregnancy. Spontaneous cervical or TEA-induced vaginal phasic contractions were not mediated by ICs or intracellular Ca2+ stores. Given that vaginal smooth muscle is normally quiescent then it is likely that increases in hormones such as oxytocin, as might occur through sexual stimulation, enhance the effectiveness of such pacemaking until phasic contractile activity emerges.

Oxytocin: its mechanism of action and receptor signalling in the myometrium

Oxytocin is a nonapeptide hormone that has a central role in the regulation of parturition and lactation. In this review, we address oxytocin receptor (OTR) signalling and its role in the myometrium during pregnancy and in labour. The OTR belongs to the rhodopsin-type (Class 1) of the G-protein coupled receptor superfamily and is regulated by changes in receptor expression, receptor desensitisation and local changes in oxytocin concentration. Receptor activation triggers a number of signalling events to stimulate contraction, primarily by elevating intracellular calcium (Ca(2+) ). This includes inositol-tris-phosphate-mediated store calcium release, store-operated Ca(2+) entry and voltage-operated Ca(2+) entry. We discuss each mechanism in turn and also discuss Ca(2+) -independent mechanisms such as Ca(2+) sensitisation. Because oxytocin induces contraction in the myometrium, both the activation and the inhibition of its receptor have long been targets in the management of dysfunctional and preterm labours, respectively. We discuss current and novel OTR agonists and antagonists and their use and potential benefit in obstetric practice. In this regard, we highlight three clinical scenarios: dysfunctional labour, postpartum haemorrhage and preterm birth.

Exposure to chronic isolation modulates receptors mRNAs for oxytocin and vasopressin in the hypothalamus and heart

The goal of our study was to explore the effect of social isolation stress of varying durations on the plasma oxytocin (OT), messenger ribonucleic acid (mRNA) for oxytocin receptor (OTR), plasma arginine vasopressin (AVP) and mRNA for V1a receptor of AVP (V1aR) expression in the hypothalamus and heart of socially monogamous female and male prairie voles (Microtus ochrogaster). Continuous isolation for 4 weeks (chronic isolation) increased plasma OT level in females, but not in males. One hour of isolation every day for 4 weeks (repeated isolation) was followed by a significant increase in plasma AVP level. Chronic isolation, but not repeated isolation, significantly decreased OTR mRNA in the hypothalamus and heart in both sexes. Chronic isolation significantly decreased cardiac V1aR mRNA, but no effect on hypothalamic V1aR mRNA expression. We did not find a gender difference within repeated social isolation groups. The results of the present study reveal that although chronic social isolation can down-regulate gene expression for the OTR in both sexes, the release of the OT peptide was increased after chronic isolation only in females, possibly somewhat protecting females from the negative consequences of isolation. In both sexes repeated, but not chronic, isolation increased plasma AVP, which could be permissive for mobilization and thus adaptive in response to a repeated stressor. The differential effects of isolation on OT and AVP systems may help in understanding mechanisms through social interactions can be protective against emotional and cardiovascular disorders.

Arrestins differentially regulate histamine- and oxytocin-evoked phospholipase C and mitogen-activated protein kinase signalling in myometrial cells

BACKGROUND AND PURPOSE

The uterotonins oxytocin and histamine, mediate contractile signals through specific G protein-coupled receptors, a process which is tightly controlled during gestation to prevent preterm labour. We previously identified G protein-coupled receptor kinase (GRK)2 and GRK6 as respective cardinal negative regulators of histamine H(1) and oxytocin receptor signalling. GRK-mediated phosphorylation promotes arrestin recruitment, not only desensitizing receptors but activating an increasing number of diverse signalling pathways. Here we investigate potential roles that arrestins play in the regulation of myometrial oxytocin/histamine H(1) receptor signalling.

EXPERIMENTAL APPROACH

Endogenous arrestins2 and 3 were specifically depleted using RNA-interference in a human myometrial cell line and the consequences of this for G protein-coupled receptor-mediated signalling were assessed using Ca(2+) /inositol 1,4,5-trisphophate imaging and standard mitogen-activated protein kinase (MAPK) assays.

KEY RESULTS

Depletion of arrestin3, but not arrestin2 enhanced and prolonged H(1) receptor-stimulated Ca(2+) responses, whilst depletion of either arrestin increased oxytocin receptor responses. Arrestin3 depletion decreased H(1) receptor desensitization, whilst removal of either arrestin isoform was equally effective in preventing oxytocin receptor desensitization. Following arrestin3 depletion oxytocin-induced phospho-extracellular signal-regulated kinase1/2 signals were diminished and histamine-stimulated signals virtually absent, whereas depletion of arrestin2 augmented extracellular signal-regulated kinase1/2 responses to each agonist. Conversely, depletion of arrestin3 enhanced p38 signals to each agonist, whilst arrestin2 suppression increased oxytocin-, but not histamine-induced p38 MAPK responses.

CONCLUSIONS AND IMPLICATIONS

Arrestin proteins are key regulators of H(1) and oxytocin receptor desensitization, and play integral roles mediating uterotonin-stimulated MAPK-signalling. These data provide insights into the in situ regulation of these receptor subtypes and may inform pathophysiological functioning in preterm labour.

Regulation of oxytocin receptor responsiveness by G protein-coupled receptor kinase 6 in human myometrial smooth muscle

Oxytocin plays an important role in the progression, timing, and modulation of uterine contraction during labor and is widely used as an uterotonic agent. We investigated the mechanisms regulating oxytocin receptor (OTR) signaling in human primary myometrial smooth muscle cells and the ULTR cell-line. Oxytocin produced concentration-dependent increases in both total [(3)H]inositol phosphate accumulation and intracellular Ca(2+) concentration ([Ca(2+)](i)); however, responses were greater and more reproducible in the ULTR cell line. Assessment of phospholipase C activity in single cells revealed that the OTR desensitizes rapidly (within 5 min) in the presence of oxytocin (100 nm). To characterize OTR desensitization further, cells were stimulated with a maximally effective concentration of oxytocin (100 nm, 30 sec) followed by a variable washout period and a second identical application of oxytocin. This brief exposure to oxytocin caused a marked decrease (>70%) in OTR responsiveness to rechallenge and was fully reversed by increasing the time period between agonist challenges. To assess involvement of G protein-coupled receptor kinases (GRKs) in OTR desensitization, cells were transfected with small interfering RNAs to cause specific > or =75% knockdown of GRKs 2, 3, 5, or 6. In both primary myometrial and ULTR cells, knockdown of GRK6 largely prevented oxytocin-induced OTR desensitization; in contrast, selective depletion of GRKs 2, 3, or 5 was without effect. These data indicate that GRK6 recruitment is a cardinal effector of OTR responsiveness and provide mechanistic insight into the likely in vivo regulation of OTR signaling in uterine smooth muscle.

Reproductive hormones in plasma over the menstrual cycle in primary dysmenorrhea compared with healthy subjects

The pathogenesis of primary dysmenorrhea is still poorly understood. The objective of the present investigation was to study differences in plasma concentrations of reproductive hormones in women with primary dysmenorrhea vs. healthy controls. In a prospective, parallel-group study we determined the plasma concentrations of oxytocin, vasopressin, follicle-stimulating hormone (FSH), luteinizing hormone (LH), 17beta-estradiol (17beta-E2), progesterone and prostaglandin F 2alpha metabolite (15-keto-13,14-dihydro-PGF 2alpha) over one menstrual cycle in eight women with primary dysmenorrhea and eight healthy volunteers. In dysmenorrheic women the plasma concentration of oxytocin was significantly higher at menstruation (p = 0.0084) and that of vasopressin significantly lower at ovulation (p = 0.0281) compared with healthy women. They had also higher FSH levels in the early follicular phase (p = 0.0087) and at menstruation (p = 0.0066) and the 17beta-E2 concentration was higher in the late follicular phase (p = 0.0449). No differences were seen for LH, progesterone and PGF 2alpha metabolite. The differences of oxytocin, vasopressin, FSH and 17beta-E2 concentrations found in plasma suggest an involvement of these hormones in mechanisms of primary dysmenorrhea. These mechanisms seem to be mainly regulated through the hypothalamus and pituitary. The influence of oxytocin on the non-pregnant uterus seems to be more important than earlier believed.

Oxytocin Receptor Is Differentially Expressed in Mouse Endometrium and Embryo during Blastocyst Implantation

The oxytocin (OT)-oxytocin receptor (OTR) system of the mammalian uterus has mainly been studied in relation to its involvement in the onset of labor. The aim of this study was to elucidate the in vivo expression and localization pattern of OTR in the mouse endometrium and embryo during implantation, as well as OTR mRNA expression in the in vitro developing mouse embryo. The expression of OTR or OT was detected immunohistochemically in uterine tissue sections of 5- to 8-week-old female mice between days 4 and 10 of an established pregnancy. In addition, the expression of OTR mRNA was detected by means of reverse transcription polymerase chain reaction (RT-PCR) in mouse oocytes and embryos up to the blastocyst stage. The mean ratios of normalized expression levels of OTR gene in all samples were also calculated. The recorded increase in OTR mRNA immediately after fertilization could mean a possible role of OT in this process, as OTR mRNA gradually decreased after the four-cell stage of pre-embryonic development. The differential expression of OTR during embryonic apposition and embryonic invasion/placentation in the mouse uterus suggests a potential role of OT in the implantation process of the mouse. It is possible that the interaction of OTR with the hormones included in the ovulation induction regiments utilized today in in vitro fertilization (IVF) could be affecting the receptivity/quality of the implanting endometrium.

Targeting the oxytocin receptor to relax the myometrium

Oxytocin acting via its receptor is involved in the myometrial hyperactivity of preterm labour and possibly also in that of primary dysmenorrhoea. The closely related hormone vasopressin acting on its uterine receptor of type V1a may also contribute to the myometrial hyperactivity of these conditions. Several pharmaceutical compounds inhibiting these receptors are, therefore, under development and one substance, atosiban, has now been registered in many countries for the treatment of preterm labour. This compound blocks both the oxytocin and the vasopressin V1a receptor. The efficacy is at least as pronounced as that of other types of drugs and side effects are much reduced. In this overview, present knowledge about receptor-mediated effects of oxytocin and vasopressin on myometrial activity is summarised. Furthermore, the therapeutic use of oxytocin and vasopressin V1a receptor antagonists in preterm labour and primary dysmenorrhoea is discussed.

Expression of the oxytocin and V1a vasopressin receptors in human myometrium in differing physiologic states and following misoprostol administration

OBJECTIVE

To assess relative expression levels of mRNA for the oxytocin receptor (OTR) and the V1a vasopressin receptor (V1aR) in human myometrium in various physiologic states and to determine if misoprostol exposure affects the expression of mRNA for these receptors.

STUDY DESIGN

Using semiquantitative reverse transcription-polymerase chain reaction, we analyzed myometrial samples from 37 women (10 menopausal, 10 nongravid premenopausal, 10 gravidae, 7 premenopausal misoprostol-treated nongravid women) for the specific expression of mRNA messages for OTR and V1aR. The presence of the OTR and V1aR protein was confirmed by immunohistochemistry.

RESULTS

We found that the expression of OTR was significantly higher in gravid compared to premenopausal nongravid (p < 0.0001), misoprostol-treated (p < 0.001) and menopausal myometrium (p < 0.0001). Differences in V1aR expression were not statistically significant among the four study groups.

CONCLUSION

The expression of OTR mRNA in myometrium is markedly increased during late gestation. V1aR expression is present in all physiologic states, and does not appear to be altered by the presence or absence of labor. Misoprostol administration does not appear to have an effect on OTR and V1aR mRNA receptor expression.

Mechanical stretch up-regulates the human oxytocin receptor in primary human uterine myocytes

Oxytocin receptor (OTR) expression is increased before the onset of labor in all models of parturition. However, the mechanisms responsible for the increase in OTR expression are uncertain. Animal data suggest that uterine stretch increases OTR mRNA expression. In primary cultures of human uterine smooth muscle cells obtained from nonpregnant (NP) women and pregnant women before (NL) and after (L) the onset of labor, we investigated the effect of stretch on the expression of OTR mRNA and DNA binding of activator protein-1 (AP-1), CCAAT/enhancer binding protein (C/EBP)beta, and nuclear factor-kappaB transcription factors. OTR expression was least in NL, intermediate in NP, and greatest in L cells. Stretch of NL cells resulted in up-regulation of OTR mRNA expression associated with increased OTR gene promoter activity. Stretch of NP and L cells did not affect OTR mRNA expression. The increased promoter activity was associated with increased DNA binding of C/EBP and AP-1 but not nuclear factor-kappaB transcription factors. Overexpression of C/EBP, but not AP-1, increased OTR promoter activity. We conclude that stretch of NL cells results in increased OTR mRNA expression probably through increased C/EBPbeta DNA binding. These data suggest that stretch contributes to the massive increase in OTR expression before the onset of human labor.

Oxytocin mRNA content in the endometrium of non-pregnant women

OBJECTIVE

To study oxytocin mRNA in the human endometrium at different phases of the menstrual cycle.

DESIGN

An exploratory study in non-pregnant women.

SETTING

The Department of Obstetrics and Gynecology, Lund University Hospital, Sweden.

PARTICIPANTS

Thirty-three women of fertile age undergoing hysterectomy or endometrial curettage on routine benign gynaecologic indications.

METHODS

Endometrial tissue was obtained throughout the menstrual cycle. The presence of oxytocin mRNA was investigated by in situ hybridisation and by real time PCR.

MAIN OUTCOME MEASURES

Oxytocin mRNA signalling intensity found by in situ hybridisation of tissue obtained at different times of the menstrual cycle. Relative amounts of oxytocin mRNA measured by real time PCR.

RESULTS

The signal for oxytocin mRNA obtained by in situ hybridisation was more pronounced in glandular epithelial cells than in stromal cells. Furthermore, it was most marked around mid-cycle. The expression of oxytocin mRNA was confirmed by real time PCR.

CONCLUSIONS

The results indicate that oxytocin may be synthesised in the endometrium of non-pregnant women, particularly in the glandular epithelial cells. Hormone released from these sources may have a paracrine action on the uterus. Oxytocin mRNA expression seems to be ovarian hormone dependent with the highest concentration around mid-cycle.

Detection of corticotropin-releasing hormone receptors R1 and R2 (CRH-R1, CRH-R2) using fluorescence immunohistochemistry in the myometrium of women delivering preterm or at term

OBJECTIVE

To determine differences in expression of corticotropin-releasing hormone receptors R1 and R2 in the myometrium of women delivering preterm or at term, with or without labor.

MATERIAL AND METHODS

Small pieces of myometrial smooth muscle were taken from forty patients undergoing caesarian section. One sample each was taken from all preterm and term patients, with and without labor. Antibodies against CRH-R1/2 and CRH-R2 were used for localization by conventional fluorescence immunohistochemistry. The evaluation of staining was based on examination of the entire histologic section by three independent observers.

RESULTS

In women at term, CRH-R2 levels were elevated before labor and decreased with the onset of labor. In eight of 10 term samples from women in labor, no staining was detected. In preterm patients we found no difference in CRH-R2 staining between women with and without labor. The intensity of staining for CRH-R1/2 was generally uniform in all four groups.

CONCLUSION

The high level of CRH-R2 expression in term patients without labor, together with the subsequent decrease of CRH-R2 in the myometrium during progression of labor, is consistent with the possibility that CRH may have autocrine/paracrine effects on myometrial contractility in the lower segment of the uterus.

Increased plasma concentrations of vasopressin, oxytocin, cortisol and the prostaglandin F2alpha metabolite during labour in the dog

AIM

This study investigated if the plasma vasopressin concentration increases during labour in the dog and whether the change in vasopressin correlates with that of oxytocin, 15-ketodihydro-PGF2alpha and cortisol.

METHODS

Five beagle dogs each delivered three to seven puppies. Blood samples were taken from a catheter inserted into the cephalic vein during labour and by venepuncture during the other periods.

RESULTS

Vasopressin concentration increased from 2 +/- 0 pmol L-1 (anoestrus) to 26 +/- 11 pmol L-1 at the birth of the first puppy, remained high at the birth of the second puppy and then decreased. Oxytocin increased from 63 +/- 5 pmol L-1 (anoestrus) to 166 +/- 19 pmol L-1 at the birth of the first puppy and remained elevated throughout labour. The PGF2alpha metabolite concentration increased from 0.2 +/- 0.0 nmol L-1 (anoestrus) to 66 +/- 17 nmol L-1 at the birth of the first puppy and remained elevated 1 h after the completion of parturition. The cortisol concentration increased from 49 +/- 9 nmol L-1 (anoestrus) to 242 +/- 35 nmol L-1 at the birth of the first puppy, remained high during the birth of the second puppy and then declined.

CONCLUSIONS

The plasma level of vasopressin was strongly correlated with that of cortisol but less with that of the PGF2alpha metabolite, and not significantly with the concentration of oxytocin. This indicates that the four hormones play different roles during labour in the dog.

Inhibitory effects of SR 49059 on oxytocin-and vasopressin-induced uterine contractions in non-pregnant women

BACKGROUND

Compounds that block uterine oxytocin and vasopressin V1a receptors have a therapeutic potential in preterm labor and primary dysmenorrhoea. The orally active vasopressin V1a receptor antagonist, SR49059, inhibits the effect of vasopressin on human uterine activity in vivo, but the influence on the response to oxytocin is unknown.

METHODS

In a placebo-controlled, double-blind, parallel-group, four-dose comparison, the inhibitory effect of SR 49059 on oxytocin- and vasopressin-induced uterine contractions in humans was investigated. Sixteen healthy female subjects, who had previously undergone sterilization with tubal ligation, participated in intrauterine pressure recordings at one of the first 3 days of bleeding of two menstrual cycles. Intravenous bolus injections of 10 pmol/kg body weight of vasopressin (Period 1) and of 50 pmol/kg body weight of oxytocin (Period 2) were given 1 h before and 1, 2 and 4 h after oral administration of 0 (placebo), 25, 75 or 200 mg of SR 49059. The area between the recording curve and zero level of intrauterine pressure (AUC) was calculated. Vital signs as well as urine and plasma safety parameters were measured. The plasma concentrations of oxytocin, vasopressin and the study drug were also estimated.

RESULTS

The plasma concentrations of SR 49059 appeared to be dose related, with mean maximal values of 62.0, 163.7 and 468.0 ng/ml in the 25, 75 and 200 mg dose groups, respectively, in Period 1 with vasopressin and 34.4, 116.7 and 418.0 ng/mL, respectively, in Period 2 with oxytocin. Tmax was observed at about 1 h. The cumulative AUC over 50 min after vasopressin injection per se was significantly higher than that after oxytocin in spite of a five times lower dose and lower plasma concentrations. Pretreatment by SR 49059 caused a dose-related reduction in AUCs for vasopressin, whereas no such effect was seen for oxytocin. With vasopressin as an agonist, a lower diastolic blood pressure was observed in all SR 49059 treatment groups, but not with oxytocin.

CONCLUSIONS

The much higher potency of vasopressin compared with oxytocin on uterine activity in non-pregnant women at menstruation was confirmed. SR 49059 dose-dependently inhibits vasopressin-induced contractions, whereas such an effect was not seen with the present doses of SR 49059 and oxytocin. A marked reduction by SR 49059 of diastolic blood pressure after vasopressin injection was observed, indicating an inhibition by this compound of vascular vasopressin receptors.

Vasopressin-induced contraction of uterus is mediated solely by the oxytocin receptor in mice, but not in humans

In the non-pregnant mouse myometrium, both arginine vasopressin and oxytocin induced contractions (pD(2)=8.55+/-0.13 and 9.23+/-0.09, respectively). The effect of oxytocin was the most potent, while the maximum contractions induced by these two peptides were almost of the same magnitude. Both vasopressin- and oxytocin-induced contractions were strongly inhibited by an oxytocin receptor antagonist, CL-12-42 (d(CH(2))(5)[Tyr(Me)(2),Thr(4),Tyr-NH(2)(9)]OVT), and weakly inhibited by a vasopressin V(1a) receptor antagonist, SR49059 ((2S)1-[(2R,3S)-5-chloro-3-(2-chlorophenyl)-1-(3,4-dimethoxybenzene-sulfonyl)-3-hydroxy-2,3-dihydro-1H-indole-2-carbonyl]-pyrrolidine-2-carboxamide). Similar results were obtained in the pregnant mouse myometrium. These results suggest that not only oxytocin- but also vasopressin-induced contraction is mediated by the activation of oxytocin receptors in the mouse myometrium. A reverse transcription polymerase chain reaction study failed to reveal mRNA of the vasopressin V(1a) receptor in the mouse myometrium. In contrast, in the non-pregnant human myometrium, vasopressin-induced contraction was inhibited by SR49059. Oxytocin showed no effect on the myometrium. These results suggest that there are significant differences in the functional receptors and contractile responses to vasopressin and oxytocin in the human and mouse uteri.

The involvement of progesterone in the onset of human labour

Progesterone is essential for the maintenance of pregnancy, and acts to promote uterine quiescence. In many species progesterone levels fall prior to the onset of labour but no fall has been observed in humans. The concept of 'functional' progesterone withdrawal in association with labour has been proposed and a number of mechanisms have been suggested. Recent potential mechanisms of functional withdrawal include changes in progesterone receptor (PR) isoforms, regulation of PR responsive genes through nuclear factor kappaB (NF-kappaB) promoter sites and the non-genomic effects of progesterone or its metabolites.

Intraoperative injection of prostaglandin F2alpha in a patient undergoing hysteroscopic myomectomy

OBJECTIVE

To present a case of one-step total hysteroscopic myomectomy using prostaglandin F(2alpha).

DESIGN

Case report.

SETTING

University hospital.

PATIENT(S)

A 38-year-old woman with a sessile submucous leiomyoma.

INTERVENTION(S)

Hysteroresectoscopy using an intraoperative injection of prostaglandin F(2alpha) under laparoscopic monitoring.

MAIN OUTCOME MEASURES

Endoscopic appearance, clinical symptoms, and imaging diagnosis.

RESULT(S)

After resection of the protruding portion of the myoma, injection of prostaglandin F(2alpha) was used to cause the remnant to project into the uterine cavity, allowing complete removal.

CONCLUSION(S)

Intraoperative use of prostaglandin F(2alpha) may allow one-step hysteroresectoscopy of a sessile submucous leiomyoma.

Involvement of oxytocin and vasopressin in the pathophysiology of preterm labor and primary dysmenorrhea

Important sources of oxytocin and vasopressin in the human, apart from the supraoptic and paraventricular nuclei of the brain, may be the fetus during labor as well as the endometrium and decidua of the uterus itself. The release of oxytocin and vasopressin to plasma is under influence of ovarian steroids. The two hormones stimulate uterine contractions in pregnant and non-pregnant women via myometrial oxytocin and vasopressin V1a receptors. At the onset of human labor preterm or at term no clear rise in the maternal plasma concentration of oxytocin and/or vasopressin has been demonstrated, but there may be an increased pulse frequency of the release of oxytocin to plasma with the advance of labor. Vasopressin is more potent than oxytocin on isolated myometrium from women undergoing Cesarean section at term. The myometrial concentration of the two receptors is about equal. At the onset of labor preterm and at term there is a tendency to an increase in the density of oxytocin and vasopressin V1a receptors, but there may be a heterogeneous expression of at least the former receptor between different myometrial cells. In advanced labor or after oxytocin treatment the receptors are markedly downregulated. The importance of oxytocin and vasopressin in mechanisms of preterm labor is confirmed by the therapeutic effect in the condition of the oxytocin and vasopressin V1a receptor blocking oxytocin analogue, atosiban. In women with primary dysmenorrhea the plasma concentration of vasopressin is elevated. The in vivo effect of vasopressin on uterine activity in non-pregnant women is about five times more pronounced than that of oxytocin, and it increases premenstrually. Correspondingly, the density of vasopressin V1a and oxytocin receptors vary to the same degree, and a premenstrual rise in the former receptor is seen. Atosiban and the non-peptide compound, SR 49059, which binds to the two receptors in a similar way as atosiban, are therapeutically effective in dysmenorrhea.

The role of arginine vasopressin in human labour: functional studies, fetal production and localisation of V1a receptor mRNA

OBJECTIVE

To investigate labour-associated changes in: 1. the myometrial contractile response to arginine vasopressin compared with oxytocin in vitro 2. fetal production of arginine vasopressin and 3. myometrial vasopressin V1a receptor mRNA.

DESIGN

The contractile response to vasopressin (compared with oxytocin) was investigated in paired myometrial strips in vitro. Blood was taken from the umbilical artery and vein at delivery and arginine vasopressin measured by radio-immunoassay. V1a receptor mRNA was determined by in situ hybridisation.

RESULTS

Myometrium was more sensitive to arginine vasopressin than oxytocin (P<0.05 for frequency, amplitude and activity integral in paired strips) after, but not before labour. There was a marked umbilical arteriovenous difference in arginine vasopressin concentration at delivery suggesting fetal production which was not influenced by labour. Myometrial vasopressin V1a receptor mRNA was not increased after the onset of labour.

CONCLUSIONS

The human uterus is extremely sensitive to arginine vasopressin in vitro. Arginine vasopressin is produced by the fetus but fetal formation is not increased during labour.

DNA methylation of the human oxytocin receptor gene promoter regulates tissue-specific gene suppression

In the human oxytocin receptor (OTR) gene, there is a CpG island from 140 bp upstream to 2338 bp downstream of the transcription start site (TSS). We investigated whether the methylation state of this region affects the transcription of the OTR gene. HepG2 derived from human hepatoblastoma, in which OTR gene transcription was suppressed, was treated with a demethylating agent, 5-azacytidine (Aza-C) for 2 days. Semiquantitative RT-PCR indicated that OTR mRNA was significantly increased by Aza-C treatment in a dose-dependent manner. We estimated the level of methylation within the CpG islands of the OTR gene in peripheral blood leukocytes, nonpregnant uterine myometrium, term uterine myometrium and liver. A 1.5-kb region located 5' upstream of the translation start site was divided into four fragments. Each was amplified by PCR after complete digestion with methylation-sensitive restriction enzyme HpaII. The amount of PCR products was largest in the liver, suggesting that this CpG island in the OTR gene is most highly methylated in liver, where the gene is always inactivated. We compared the effect of in vivo methylation of the CpG island on transcriptional activity of an OTR-reporter plasmid. The reporter gene activity of expression plasmid -2860/+1342-GL3, containing the CpG island, in HepG2 cells was suppressed to 30.6% of the control level after methylation with SssI methylase, while that of -2840/+144-GL3, without the CpG island was suppressed only to 81.4%. The deletion of the segment (MT2) where the level of methylation was most different between liver and uterus (-2860/+1342(del)MT2-GL3) rescued the suppression rate to 68.0%. These results indicate that the methylation of the CpG island in the human OTR gene promoter suppressed its transcription at least in liver and may regulate tissue specific gene expression among organs.

Functional oxytocin receptors in a human endometrial cell line

OBJECTIVE

Our goal was to demonstrate expression and functionality of oxytocin receptors in a human endometrial cell line. This cell line could then be used for further investigation of the role of oxytocin in reproductive function at the cellular level.

STUDY DESIGN

Oxytocin receptor messenger ribonucleic acid expression was determined by reverse transcriptase-polymerase chain reaction deoxyribonucleic acid amplification with ribonucleic acid from confluent Ishikawa cells. Ligand binding to whole cells was evaluated by nonlinear regression analysis with an iodinated oxytocin antagonist. The coupling of the oxytocin receptor to signaling pathways was evaluated by measuring oxytocin-stimulated increases in intracellular calcium concentration, phosphorylation of ERK2 (extracellular-regulated protein kinase 2) mitogen-activated protein kinase, and prostaglandin E(2) release.

RESULTS

Polyacrylamide gel electrophoresis of the reverse transcriptase-polymerase chain reaction products demonstrated the presence of oxytocin receptor messenger ribonucleic acid in Ishikawa cells. Ligand-binding analysis of these cells demonstrated a single class of noninteracting sites, with a B(max) (maximal number of binding sites) of 77.7 fmol/mg deoxyribonucleic acid and an apparent dissociation constant of 8.3 x 10(-11) mol/L. Stimulation with 100-nmol/L oxytocin caused a rapid transient increase in intracellular free calcium concentration, which was blocked by 1-micromol/L oxytocin antagonist. Treatment of cells with oxytocin for 10 minutes resulted in a marked increase in the phosphorylation of ERK2, as determined by Western blot analysis, and a 5-fold increase in prostaglandin E(2) release.

CONCLUSION

This study is the first to demonstrate functional oxytocin receptors in an established human endometrial cell line. This cell line will be useful in elucidating the mechanisms of action of oxytocin in the reproductive tract at the molecular level.