Effect of oxytocin receptor blockade on rat myometrial responsiveness to prostaglandin f(2)(alpha)

PGF2α induces a pro-labour phenotypical switch in human myometrial cells that can be inhibited with PGF2α receptor antagonists

Preterm birth is the leading cause of infant morbidity and mortality. There has been an interest in developing prostaglandin F2α (PGF2α) antagonists as a new treatment for preterm birth, although much of the rationale for their use is based on studies in rodents where PGF2α initiates labour by regressing the corpus luteum and reducing systemic progesterone concentrations. How PGF2α antagonism would act in humans who do not have a fall in systemic progesterone remains unclear. One possibility, in addition to an acute stimulation of contractions, is a direct alteration of the myometrial smooth muscle cell state towards a pro-labour phenotype. In this study, we developed an immortalised myometrial cell line, MYLA, derived from myometrial tissue obtained from a pregnant, non-labouring patient, as well as a novel class of PGF2α receptor (FP) antagonist. We verified the functionality of the cell line by stimulation with PGF2α, resulting in Gαq-specific coupling and Ca2+ release, which were inhibited by FP antagonism. Compared to four published FP receptor antagonists, the novel FP antagonist N582707 was the most potent compound [Fmax 7.67 ± 0.63 (IC50 21.26 nM), AUC 7.30 ± 0.32 (IC50 50.43 nM), and frequency of Ca2+ oscillations 7.66 ± 0.41 (IC50 22.15 nM)]. RNA-sequencing of the MYLA cell line at 1, 3, 6, 12, 24, and 48 h post PGF2α treatment revealed a transforming phenotype from a fibroblastic to smooth muscle mRNA profile. PGF2α treatment increased the expression of MYLK, CALD1, and CNN1 as well as the pro-labour genes OXTR, IL6, and IL11, which were inhibited by FP antagonism. Concomitant with the inhibition of a smooth muscle, pro-labour transition, FP antagonism increased the expression of the fibroblast marker genes DCN, FBLN1, and PDGFRA. Our findings suggest that in addition to the well-described acute contractile effect, PGF2α transforms myometrial smooth muscle cells from a myofibroblast to a smooth muscle, pro-labour-like state and that the novel compound N582707 has the potential for prophylactic use in preterm labour management beyond its use as an acute tocolytic drug.

Oxytocin Receptor Antagonists, Atosiban and Nolasiban, Inhibit Prostaglandin F2α-induced Contractions and Inflammatory Responses in Human Myometrium

Oxytocin receptor antagonists (OTR-A) have been developed as tocolytics for the management of preterm labour due to the significant role of oxytocin (OT) in the onset of both term and preterm labour. Similar to OT, prostaglandins (PGs) play key roles in myometrial contractility and cervical ripening. Inhibition of PG synthesis/activity is used to delay preterm birth. Thus, targeting the PG pathway in combination with an OTR-A may be an effective strategy for delaying preterm delivery. In this study, we examined the effects of atosiban and nolasiban on PGF_2α-induced contractions and pro-inflammatory responses in human pregnant myometrium. Both OTR-As, atosiban and nolasiban, inhibited PGF_2α-induced contractions in a dose-dependent manner (p < 0.001 and p < 0.01, respectively). These inhibitory effects involved the suppression of PGF_2α-mediated increase in intracellular calcium levels. In addition, the OTR-As significantly suppressed PGF_2α-induced activation of pro-inflammatory pathways such as NF-κB and mitogen activated protein kinases (MAPKs), and the subsequent expression of contraction-associated-protein, COX-2. We have demonstrated that atosiban and nolasiban not only inhibit contractions elicited by OT, but also inhibit contractions and inflammation induced by PGF_2α. This suggests a possible crosstalk between OTR and PG receptor signalling and highlights the importance of understanding G protein-coupled receptor interactions/crosstalk in the development of future tocolytics.

Prostaglandin D2 evokes potent uterine contraction via the F prostanoid receptor in postpartum rats

Prostaglandin (PG) D₂, a prostanoid known to have hypotensive effect, can evoke increased in vitro prepartum myometrial contraction resulting from up-regulation of the F prostanoid (FP) receptor. The present study further determined postpartum rat uterine responses to PGD₂ to evaluate the possibility of the prostanoid becoming a therapeutic for postpartum uterine atony, a major cause of postpartum hemorrhage that can lead to maternal morbidity. In vitro and in vivo postpartum uterine responses to PGD₂ were determined and compared to those of prepartum rats. Here we show that in postpartum myometrial strips PGD₂ did evoke a contraction sensitive to FP receptor antagonism. Interestingly, this response was not only to a greater extent than that of prepartum rats, but also comparable with the contraction obtained with PGF_2α, a therapeutic for postpartum uterine atony but contradicted in conditions including hypertension. Indeed, PGD₂ was also found to cause increases of basal uterine contraction under in vivo conditions. Western blots revealed that the expression of FP receptors in postpartum myometrium was higher than that of prepartum rats. Moreover, we noted that the amount of PGD₂ produced in postpartum uteri, although lower than that of prepartum rats, was increased compared to non-pregnant conditions. These results thus demonstrate that due to a further up-regulation or high expression of myometrial FP receptors, PGD₂ can evoke potent uterine contraction postpartum, and hence the prostanoid, which is naturally synthesized in uterine tissues, could be a potential therapeutic for postpartum uterine atony, especially in settings, such as hypertension.

Advances in the role of oxytocin receptors in human parturition

Oxytocin (OT) is a neurohypophysial hormone which has been found to play a central role in the regulation of human parturition. The most established role of oxytocin/oxytocin receptor (OT/OTR) system in human parturition is the initiation of uterine contractions, however, recent evidence have demonstrated that it may have a more complex role including initiation of inflammation, regulation of miRNA expression, as well as mediation of other non-classical oxytocin actions via receptor crosstalk with other G protein-coupled receptors (GPCRs). In this review we highlight both established and newly emerging roles of OT/OTR system in human parturition and discuss the expanding potential for OTRs as pharmacological targets in the management of preterm labour.

Application of atosiban in frozen-thawed cycle patients with different times of embryo transfers

This prospective cohort study aimed to examine the effects of atosiban, given before transfer of frozen-thawed embryo to women with different number of embryo transfer (ET) cycles. Atosiban treatment significantly increased implantation rate and clinical pregnancy rate in the third and more than three ET groups. However, there were no significant increases in the above parameters in the first and second ET groups. Our study showed that patients those who underwent the third or more than three ET cycles were inclined to higher uterine contractions and serum oxytocin level, thus atosiban treatment starting from the third ET cycle may be effective in improving embryo implantation. This is the first study to evaluate the optimal atosiban treatment window corresponding to the number of ET cycles of the patients.

Molecular changes induced by repeated restraint stress in the heart: the effect of oxytocin receptor antagonist atosiban

Even though stress belongs to the most common lifestyle risk factors of cardiovascular diseases, there are only limited data on direct influence of stressors on the heart. The aim of the present study was to explore selected protein signaling pathways in response to repeated immobilization stress in the heart tissue. Effects of simultaneous treatment with atosiban, an oxytocin receptor antagonist, on stress-induced changes in the heart were also investigated. Male Wistar rats were exposed to repeated immobilization (2 h daily, lasting 2 weeks). The results showed increased phosphorylation of Akt kinase, enhanced levels of Bcl-2, and decreased levels of cleaved caspase-3 in the left ventricle in response to chronic stress independently of the treatment. Exposure to restraint led to the rise of HSP-90 and p53 in vehicle-treated rats only. Stress failed to modify MMP-2 activity and ultrastructure of the heart tissue. Treatment with the oxytocin/vasopressin receptor antagonist atosiban reversed stress-induced rise in HSP-90 and p53 proteins. In conclusion, our data demonstrate that repeated restraint stress induces Akt kinase activation and this is associated with elevation of anti-apoptotic proteins (Bcl-2) and down-regulation of pro-apoptotic proteins (cleaved caspase-3). These findings suggest that activation of pro-survival anti-apoptotic Akt kinase pathway plays an important role in molecular mechanisms underlying responses and adaptation of the rat heart to repeated stress exposure. The results further indicate a regulatory role of oxytocin/vasopressin in the control of stress-induced activation in HSP-90 and related proteins.

Effects of atosiban on stress-related neuroendocrine factors

Atosiban, an oxytocin/vasopressin receptor antagonist, is used to decrease preterm uterine activity. The risk of preterm delivery is undoubtedly associated with stress, but potential side effects of atosiban on neuroendocrine functions and stress-related pathways are mostly unknown. These studies were designed to test the hypothesis that the chronic treatment of rats with atosiban modulates neuroendocrine functions under stress conditions. Male rats were treated (osmotic minipumps) with atosiban (600 μg/kg per day) or vehicle and were restrained for 120 min/day for 14 days. All animals were treated with a marker of cell proliferation 5-bromo-2-deoxyuridine. Anxiety-like behavior was measured using an elevated plus-maze. Treatment with atosiban failed to modify plasma concentrations of the stress hormones ACTH and corticosterone, but led to a rise in circulating copeptin. Atosiban increased prolactin levels in the non-stressed group. Oxytocin receptor mRNA levels were increased in rats exposed to stress. Treatment with atosiban, in both control and stressed animals, resulted in a decrease in oxytocin receptor gene expression in the hypothalamus. No changes were observed in vasopressin receptor 1A and 1B gene expression. The decrease in hippocampal cell proliferation induced by stress exposure was not modified by atosiban treatment. This study provides the first data, to our knowledge, revealing the effect of atosiban on gene expression of oxytocin receptors in the brain. Atosiban-induced enhancement of plasma copeptin indicates an elevation in vasopressinergic tone with potential influence on water-electrolyte balance.

In vitro comparison of myometrial contractility induced by aglepristone-oxytocin and aglepristone-PGF2alpha combinations at different stages of the estrus cycle in the bitch

The aim of this in vitro study was to compare the uterokinetic activity of oxytocin and dinoprost, the natural PGF2α, with or without aglepristone, in canine myometrial fibers. Thirty-three bitches were allocated into one of four groups, depending on their estrous stage and whether or not they had received a treatment with aglepristone (metestrus aglepristone, n = 5; metestrus without treatment, n = 9; anestrus aglepristone, n = 9; anestrus without treatment, n = 10). After hysterectomy, longitudinal and circular uterine strips were mounted in organ baths. Oxytocin or PGF2α (10 nmol/l to 10 micromol/l) were applied non-cumulatively. A linear mixed effects models theory was used to compare the fiber effect, the aglepristone effect, and the treatment effect, from the area under the curves calculated from the contractile effect/concentration curves for each drug. Oxytocin and PGF2α induced concentration-dependent myometrial contractions in longitudinal (LF) and circular myometrial fibers (CF), indicating the presence of functional contractile oxytocin- and PGF2α-receptors in metestrus and anestrus. The contractile response to oxytocin was greater in LF than in CF in all of the groups; the response to PGF2α was greater in LF than in CF in non-treated bitches in anestrus and in treated bitches in metestrus. These results suggest that there is a difference in sensitivity or a heterogeneous distribution of oxytocin and PGF2α-receptors in the myometrial layers, which is independent of hormonal impregnation. The contractile response to oxytocin and PGF2α was significantly increased after aglepristone treatment in LF during metestrus, suggesting that the progesterone withdrawal induced by aglepristone has a role to play. The longitudinal myometrial layer also appeared to be the target for the two drugs at this stage. This study provides new information about canine uterine contractile activity, notably the differing behavior of myometrial CF and LF; in vivo studies are required to test the use of a combination of aglepristone and oxytocin in the treatment of canine pyometra.

Differences in muscarinic-receptor agonist-, oxytocin-, and prostaglandin-induced uterine contractions

OBJECTIVE

To investigate the contractile response of the perfused swine uterus to various receptor pathways (oxytocin, prostaglandins, and muscarine).

DESIGN

An extracorporeal perfusion model of the swine uterus was used that keeps the uterus in a functional condition and is appropriate for the study of physiologic questions.

INTERVENTION(S)

Oxytocin-, prostaglandin-, and carbachol-induced uterine contractility and peristalsis were assessed using an intrauterine double-chip microcatheter.

SETTING

University hospital.

MAIN OUTCOME MEASURE(S)

Intrauterine pressure profiles.

RESULT(S)

A dose-dependent increase in intrauterine pressure (IUP) in the isthmus uteri and corpus uteri was observed after the administration of prostaglandin F(2alpha) (PGF(2alpha)) and oxytocin, which reached a plateau after further stimulation. A dose-dependent increase in IUP in the isthmus uteri and corpus uteri was also observed after the administration of prostaglandin E(1) (PGE(1)) and prostaglandin E(2) (PGE(2)), with a plateau in IUP in the middle-concentration range and a decrease during the further course of stimulation. After administration of PGE(1), PGE(2), and PGF(2alpha), different directions of contraction waves were also observed. Carbachol also showed a unique contractility pattern, with isolated, very powerful, dose-dependent contractions with an IUP gradient, suggesting directed transport from the upper region to the lower region.

CONCLUSION(S)

This study demonstrated that oxytocin, the prostaglandins, and carbachol modulate contractility in nonpregnant swine uteri in a characteristic way, resulting in different contractility patterns.

Uterine contractility in response to different prostaglandins: results from extracorporeally perfused non-pregnant swine uteri

BACKGROUND

Prostaglandins (PGs) are important stimulators of uterine contractility. Limited data are available at present on the effects of different PGs on uterine contractility, measured using intraluminal pressure changes in the complete uterus. The goal of this study was to assess dynamic changes in uterine contractility and peristalsis in response to PGs in comparison with the effects of oxytocin administration.

METHODS

An extracorporeal perfusion model of swine uteri was used, which keeps the uterus in a functional condition, and is appropriate for the study of physiological questions. Oxytocin- and PG-induced uterine contractility and peristalsis were assessed using an intrauterine double-chip microcatheter.

RESULTS

A dose-dependent increase in intrauterine pressure (IUP) in the isthmus uteri (P < 0.001) and the corpus uteri (P < 0.001) was observed after the administration of PGF(2alpha) and oxytocin, which reached a plateau after further stimulation. A dose-dependent increase in IUP in the isthmus uteri (P < 0.001) and the corpus uteri (P < 0.001) was also observed after the administration of PGE(1) and PGE(2), with a plateau in IUP in the middle-concentration range and a decrease in the course of further stimulation. PGE(2) caused significantly more contractions starting in the corpus uteri and moving to the isthmus uteri (P = 0.008). The direction of most contractions caused by PGE(1), PGE(2) and oxytocin differed from that of PGF(2alpha).

CONCLUSIONS

This study demonstrates that the PGs tested modulate contractility in non-pregnant swine uteri in a characteristic way, resulting in different contractility patterns.

Uterine motility in the reptileAnolis carolinensis: interactive effects of tension, prostaglandins, calcium, and vasotocin

Uteri of Anolis carolinensis exhibited spontaneous rhythmic contractions in vitro. Addition of arginine vasotocin (AVT) caused an immediate, strong, tonic contraction followed by rhythmic contractions with the same frequency as spontaneous contractions but of a greater amplitude. At low tension (1.5 g) the AVT-induced tonic contraction was blocked by low dose of indomethacin, suggesting that it is influenced by calcium rather than prostaglandins (PGs). An increase in tension (from 1.5 to 15 g) reduced the duration of the AVT-induced tonic contraction; this stretch-induced decrease was also blocked by indomethacin. Stretch also decreased the duration of the rhythmic contractions, but this stretch effect was not inhibited by indomethacin. The rest interval between rhythmic contractions was decreased by PGF2alpha and PGE2, and indomethacin or stretch blocked these PG effects. Indomethacin, AVT, or stretch alone did not affect PGF2alpha secretion from AVT-treated uteri. Stretch also reduced PGF2alpha secretion from AVT-treated uteri, an effect inhibited by indomethacin.

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.

Anatomical differences in uterine sensitivity to prostaglandin F(2alpha) and serotonin in non-pregnant rats

The ovarian steroids regulate the sensitivity of a population of uterine receptors to prostaglandin F(2alpha), serotonin and oxytocin. However, the uterine sensitivity to prostaglandin F(2alpha) and oxytocin does not coincide with the estrogen-induced increase in the number of receptors. Anatomical differences affect the uterine sensitivity to agonists. We investigated whether anatomical differences between ovarian and cervical uterine regions modulate the hormone-regulated sensitivity to prostaglandin F(2alpha), serotonin and oxytocin. Non-cumulative concentration-response curves for these agonists were recorded for ovarian and cervical uterine segments from adult ovariectomized rats treated with 17beta-estradiol, 17beta-estradiol+progesterone, or vehicle. The ovarian segments displayed a higher maximal response (E(max)) to prostaglandin F(2alpha) and a lower E(max) to serotonin than the cervical segments. Both uterine segments displayed a similar sensitivity to oxytocin. The ovariectomized controls displayed the highest E(max) and the lowest effective concentration 50 (EC(50)) for oxytocin and prostaglandin F(2alpha). Anatomical differences between ovarian and cervical uterine regions modulate the hormonal regulation of uterine sensitivity to serotonin and prostaglandin F(2alpha) in the non-pregnant rat uterus.

Effects of progesterone on gastric emptying and intestinal transit in male rats

AIM: To study the dose-dependent of progesterone (P) effect and the interaction between the oxytocin (OT) and P on gastrointestinal motility.

METHODS: In order to monitor the gastric emptying and intestinal transit, the SD male rats were intubated via a catheter with normal saline (3 mL/kg) containing Na₂⁵¹CrO₄ (0.5 μCi/mL) and 10% charcoal. OT was dissolved into normal saline and P was dissolved into 75% alcohol.

RESULTS: Low does of P (1 mg/kg, i.p.) enhanced the gastric emptying (75% ± 3%, P < 0.05) and high dose of P (5 mg/kg, i.p.) inhibit it (42% ± 11.2%, P < 0.01). P (1 mg/kg) increased the intestinal transit (4.2 ± 0.3, P < 0.05) while the higher dose (10-20 mg/kg) had no effect. OT (0.8 mg/kg, i.p.) inhibited the gastric emptying (23.5% ± 9.8%, P < 0.01). The inhibitory effects of P (20 mg/kg) (32% ± 9.7%, P < 0.05) and OT (0.8 mg/kg) on gastric emptying enhanced each other when the two chemicals were administrated simultaneously (17% ± 9.4%, P < 0.01).

CONCLUSION: Low dose of P increased GI motility while high dose of P decreased it. During the later period of pregnancy, elevated plasma level of OT may also participate in the gastrointestinal inhibition.