Differential regulation of prostaglandin EP and FP receptors in pregnant sheep myometrium and endometrium during spontaneous term labor

Labor-Associated Regulation of Prostaglandin E and F Synthesis and Action in the Ovine Amnion and Cervix

OBJECTIVE

Prostaglandins (PGs) are key regulators of cervical dilatation and membrane breakdown at the onset of labor. PG synthase and receptor expression has been previously documented in uterine tissues; however, mechanisms governing the changes occurring in the cervix and amnion are less well established. The aim of the current study was to determine the level of expression of PG synthetic enzymes and receptors in these tissues in association with induced labor in sheep.

METHODS

Labor was induced in sheep at 135 days of gestation by continuous fetal dexamethasone infusion. Amnion and cervical tissue was obtained before and after labor for measurement of mRNA encoding enzymes (cytosolic phospholipase A2 [cPLA2], PGH synthase-2 [PGHS-2], PGF synthase [PGFS], and PGE synthase [PGES]) and receptors (FP and EP1-4) by real-time polymerase chain reaction (PCR).

RESULTS

cPLA2 expression increased significantly in cervical tissue at labor onset, whereas expression of the other enzymes measured did not change. There was a marked rise in EP3 expression in the cervix, but abundance of this receptor was lower than EP2 and FP expression, which did not change. The amnion exhibited a labor-associated decrease in PGHS-2, PGFS, and FP mRNA expression.

CONCLUSION

The regulation of PG synthesis and action occurring in the amnion and cervix in association with labor appear to differ markedly between the two tissues, indicating tissue-specific roles for PGs. The data support a role for increased PG synthesis and action in the cervix and suggest a decrease in PG production and action in the amnion, in sharp contrast to the pattern reported in human amnion.

Does aberrant expression of cyclooxygenase-2 and prostaglandin-E2 receptor genes lead to abortion in Chlamydia trachomatis-infected women

OBJECTIVE

The aim of the study was to characterize the expression of cyclooxygenase-2 (COX-2) and prostaglandin-E2 (PGE2) genes in spontaneously aborted tissues from women infected with Chlamydia trachomatis.

METHODS

A total of 135 spontaneous aborters (Group I) and 45 induced aborters (controls; Group II) attending Obstetrics and Gynaecology Department at Safdarjung hospital (New Delhi, India), were enrolled. Polymerase chain reaction (PCR) assay was performed to detect C. trachomatis DNA in endometrial curettage tissue (ECT). Differential expression of COX-2 and PGE2 receptors at mRNA level was analysed in ECT using reverse transcription PCR and real-time PCR.

RESULTS

In total, 14.8% patients were diagnosed as C. trachomatis-positive in Group I whereas all control patients were C. trachomatis-negative. Qualitative expression of COX-2 (p < 0.05) and PGE2 (p < 0.0001) receptors was found increased in C. trachomatis-positive patients (Group I) in comparison to controls. Quantitative real-time PCR analysis also showed upregulation in transcript levels of both COX-2 (p < 0.002) and PGE2 (p < 0.0001) receptors in infected patients (Group I) versus Group II. COX-2 and PGE2 expression was higher (p < 0.002) in recurrent spontaneous aborters in comparison to sporadic spontaneous aborters.

CONCLUSIONS

Results suggest that chlamydial infection leads to upregulation of COX-2 in C. trachomatis-positive recurrent spontaneous aborters, which probably mediates increased prostaglandin synthesis.

Temporal analysis of prostaglandin F2α receptor, caspase 3, and cyclooxygenase 2 messenger RNA expression and prostaglandin F2α receptor and cyclooxygenase 2 protein expression in endometrial tissue from multiparous Nelore (Bos taurus indicus) cows treated with cloprostenol sodium during puerperium

The use of cloprostenol sodium in puerperium is questionable, as both favorable and unfavorable responses during the uterine involution process have been reported in the literature. This study is based on the hypothesis that cloprostenol sodium promotes modifications in the prostaglandin F2α receptor (FP), caspase 3 (CASP-3), and cyclooxygenase 2 (COX-2) mRNA expression that may favor the process of postpartum uterine involution in multiparous Nelore (Bos taurus indicus) females. Additionally, we aimed to describe the presence and immunolocalization of the FP and COX-2 protein in endometrial tissue at different postpartum time points in these females. Multiparous Nelore cows (n = 24) were treated with cloprostenol sodium (n = 12) or saline solution (n = 12) on postpartum Days 1 and 4 (Day 0 = birth), and endometrial biopsies were performed with a Yomann biopsy instrument and collected on Days 1, 7, 14, 28, and 42 postpartum. The mRNA expression from samples on the Days 1, 7, 14, 28, and 42 and the protein expression from samples on the Days 1, 14, 28, and 42 were then analyzed. The treated cows had altered FP and CASP-3 mRNA expression, and FP and COX-2 protein were observed in the endometrial surface epithelium, the stroma, and the glandular epithelium, with cytoplasmic immunolocalization. Although we attribute the change in CASP-3 mRNA expression to physiological phenomena, the results obtained for FP mRNA expression opens new doors for the study of hormonal protocols associated with cloprostenol sodium in the puerperium of Zebu females.

Identification of prostaglandin E2 receptors mediating perinatal masculinization of adult sex behavior and neuroanatomical correlates

Prostaglandin E2 (PGE2) mediates the organization of male rat sexual behavior and medial preoptic area (MPOA) neuroanatomy during a sensitive perinatal window. PGE2 is up-regulated in response to estradiol, and initiates a two-fold increase in dendritic spines densities on neurons. All the four receptors for PGE2 and EP1-4 are present in developing POA, a critical region controlling male sexual behavior. Previous studies explored that EP receptors are involved in PGE2-induction of neonatal levels of spinophilin protein, a surrogate marker for dendritic spine formation, but did not assess behavioral masculinization. Here, we used two approaches, suppression of EP receptor expression with antisense oligonucleotides and activation of EP receptors with selective agonists, to test which receptors are necessary and sufficient, respectively, for the effects of PGE2 on behavior and neuronal morphology. In female rats, neonatal treatment with antisense oligonucleotides against EP2 or EP4 but not EP1 or EP3 completely prevented the expression of adult behavior organized by PGE2 exposure. The effects of ONO-DI-004, ONO-AE-259-01, ONO-AE-248, and ONO-AE1-329 (EP1-4 agonists respectively) were equivalent to PGE2 treatment, which suggests activating any EP receptor neonatally suffices in masculinizing sex behavior. When given alone, not all EP agonists increased neonatal POA spinophilin levels; yet giving each agonist neonatally increased adult levels. Moreover, adult spinophilin levels significantly correlated with two measures of male sexual behavior. The body of evidence suggests that EP2 and EP4 are both necessary and sufficient for PGE2-induced masculinization of sex behavior, whereas EP1 and EP3 provide redundant roles.

Immunohistochemical demonstration of cyclooxygenase-2 (COX-2) and prostaglandin receptors EP2 and FP expression in the bovine intercaruncular uterine wall around term

During parturition, uterine-derived prostaglandins (PG) play an outstanding role regarding the functional elimination of the corpus luteum and the promotion of uterine contraction. The rate-limiting enzyme cyclooxygenase-2 (COX-2), highly regulated in a cell-type and localization specific manner throughout pregnancy, is involved in uterine prostanoid production. Prostaglandins exert their effects via G-protein-coupled receptors. Distribution and cellular localization of these receptors are decisive factors for prostaglandin-mediated actions. Since both COX-2 and PG receptors have only been assessed during pregnancy in the cow, these parameters were localized immunohistochemically near term to evaluate their specific role at parturition. Thus, during two periods, segments of the intercaruncular uterine wall were collected from cows at slaughter being eight and nine months pregnant, from cattle during caesarean section, and after spontaneous calving. Results reveal that COX-2 was mainly localized in the cytoplasm of surface epithelial cells with a high expression in animals with induced parturition. The enzyme could also be found in lower concentrations within the glandular epithelium without any effect of gestational time or labour. In contrast to relaxant prostaglandin E receptor type 2 (EP2), not showing any change in all tissue layers observed, contractile prostaglandin F(2alpha) receptor (FP) was modulated during the peripartal period revealing a peak expression in animals with induced parturition. FP was localized in surface and glandular epithelial cells as well as in endometrial stroma and myometrial smooth muscle cells. Our study indicates that labour and induction of parturition may have an effect on amounts of immunohistochemically detectable COX-2 and FP. EP2 remains rather unchanged during the peripartal period. COX-2 and FP thus contribute via changes in amount and distribution to mechanisms associated with parturition.

Localization and steroid regulation of prostaglandin E2 receptor protein expression in ovine cervix

Although prostaglandin E2 (PGE2) has been identified as a central mediator of the cervical ripening process, the mechanisms responsible for PGE2 ripening are still poorly understood, partly because of the lack of information concerning the precise cellular localization and regulation of PGE2 (EP) receptors in the cervix. To provide new insights into the mechanisms of cervical ripening, we used indirect immunofluorescence to localize cervical EP receptor protein expression in ovariectomized ewes and examined the effect of administration of progesterone or estradiol. EP receptors were widely distributed in cervical blood vessels, epithelium of the cervical canal, circular and longitudinal muscles, and stroma. Estradiol replacement decreased EP1 and EP3 receptor protein in blood vessel media (by 23 and 31% respectively, P < 0.05) and decreased EP1 receptor protein expression in the longitudinal muscle layer (by 27%, P < 0.05). Stromal EP1 and EP3 receptor protein expression was also reduced by estradiol (by 29 and 20% respectively, P < 0.05). Progesterone replacement had no significant effect on EP receptor protein expression. The arterial changes would favor PGE2-induced vasodilatation, subsequent edema and leukocyte infiltration during the cervical ripening process whereas the muscular alterations would facilitate smooth muscle relaxation and cervical dilatation. Furthermore, estradiol provoked perinuclear localization of EP3 receptor protein in the longitudinal muscle layer. This latter result suggests that cellular EP receptor localization is regulated by estradiol and that PGE2 may also control smooth muscle contraction and regulate ovine cervical dilatation in an intracrine manner via EP3 receptors.

Regional Expression of Prostaglandin E2 and F2alpha Receptors in Human Myometrium, Amnion, and Choriodecidua with Advancing Gestation and Labor1

The change from uterine quiescence to enhanced contractile activity may be due to the differential expression of prostaglandin receptors within the myometrium and fetal membranes, in a temporal and topographically distinct manner. To address this question, we determined the localization and expression of the PGE2 receptor subtypes (PTGER1-4) and the PGF2alpha receptor (PTGFR) in paired upper and lower segment myometrium, amnion, and choriodecidual samples throughout human pregnancy, with and without labor. All receptor subtypes were found throughout the muscle layers in both the upper and lower uterine segments, colocalizing with alpha smooth muscle actin. A change in intracellular localization was observed at term labor, where PTGER1 and PTGER4 were predominately associated with the nucleus. Minimal changes in the expression of the PGE2 and PGF2alpha receptor subtypes were observed with gestational age, labor, or between the upper and lower myometrial segments. Receptor expression in maternal and fetal tissues differed between the receptor subtypes; PTGER1 and PTGER4 were predominately expressed in the fetal membranes, PTGER2 was greatest in the myometrium, whereas PTGER3 and PTGFR were similarly expressed in the myometrium and fetal membranes. Myometrial activation through the prostaglandin receptors is perhaps more subtle and may be mediated by a balance between one or several of the prostaglandin receptor subtypes together with other known contraction associated proteins. Lack of coordination in receptor expression between the myometrium and fetal membranes may indicate different regulatory mechanisms between these tissues, or it may suggest a function for these receptors in the amnion and choriodecidua that is independent of that seen in the myometrium.

Thrombin and interleukin-1beta regulate HOXA10 expression in human term decidual cells: implications for preterm labor

CONTEXT

Preterm delivery is commonly caused by intraamniotic infection with expression of proinflammatory cytokines (IL-1beta) or by abruption resulting in generation of decidual thrombin. Although human parturition is not preceded by overt progesterone withdrawal, progesterone resistance likely leads to labor. The uteri of Hoxa10(-/-) mice demonstrate progesterone resistance; several genes, including prostaglandin receptors, are inappropriately regulated in response to progesterone.

OBJECTIVE

We hypothesized that IL-1beta or thrombin would decrease HOXA10 expression, contributing to the progestin-resistant environment. We analyzed expression of HOX genes and their regulation by IL-1beta or thrombin in decidual cells.

DESIGN AND SETTING

We conducted an in vitro experiment at an academic medical center.

INTERVENTION

Term decidual cells were treated with estradiol (E(2)) or E(2) plus medroxyprogesterone acetate followed by addition of thrombin or IL-1beta.

MAIN OUTCOME MEASURE

HOX mRNA was evaluated by microarray and confirmed by quantitative RT-PCR. Protein expression was detected using immunohistochemistry and Western analysis.

RESULTS

HOXA9, HOXA10, and HOXA11 were expressed in decidual cells and regulated by IL-1beta and thrombin. HOXA10 was further analyzed because of its association with progesterone responsiveness. After E(2) treatment, IL-1beta and thrombin decreased HOXA10 mRNA by 94 and 81%, respectively. After E(2) plus medroxyprogesterone acetate treatment, IL-1beta and thrombin resulted in an 86 and 72% decrease in HOXA10 mRNA, respectively. A similar decrease was noted in HOXA10 protein expression.

CONCLUSION

The expression of HOXA10 protein at term indicates that it may have a role in maintaining decidual cell phenotype and pregnancy. The dramatic decrease of HOXA10 in response to IL-1beta or thrombin may contribute to progestin resistance in preterm labor, mimicking progesterone resistance seen in Hoxa10(-/-) mice.

Anti-inflammatory and relaxatory effects of prostaglandin E2 in myometrial smooth muscle

The onset of human labour is complex and involves multiple mediators, prostaglandins, cytokines and chemokines. However, whilst prostaglandins are routinely used for labour induction and inhibitors of prostaglandin synthesis are used to prevent pre-term labour, these practices are not invariably successful, and the rationale for their use is equivocal. As COX-2 and prostaglandin E(2) (PGE(2)) production is increased towards term, we have investigated the effect of PGE(2) and other cAMP-elevating agents on events associated with labour induction. Time-dependent increases in granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-8 (IL-8) release were observed following treatment of primary human myometrial smooth muscle (HMSM) cells with IL-1beta, via mechanisms that required de novo transcription and translation. Prior treatment with PGE(2) (1 microM) produced 86 and 80% decreases in GM-CSF and IL-8 release, respectively. Similarly, the cAMP analogue, 8-bromo-cAMP (8Br-cAMP) and the phosphodiesterase-4 (PDE(4)) inhibitor, rolipram, also repressed GM-CSF and IL-8 release. In addition, PGE(2), 8Br-cAMP, rolipram and salbutamol all had a dose-dependent inhibitory effect on spontaneous myometrial contractions in vitro. In this study, PGE(2) reduced the release of factors associated with cervical ripening and attenuated force development in myometrial smooth muscle, raising the possibility that in myometrium, PGE(2) may act to down-regulate some of the processes that contribute to the onset of human labour and may be beneficial in helping to maintain pregnancy towards term.

Prostanoid receptors in human uterine myocytes: the effect of reproductive state and stretch

In the human, prostanoids are known to be important mediators of uterine relaxation and contraction during pregnancy and parturition. We have previously shown that stretch of uterine smooth muscle cells increased prostaglandin H synthase 2 (PGHS-2) mRNA expression, PGHS-2 peptide synthesis and activity, however, the net effect on uterine contractility of this increase in prostaglandin synthesis would be determined by the expression of the different prostanoid receptors. Therefore, the aims of this study were to establish the expression of prostanoid receptor mRNA in uterine myocytes obtained from women in different reproductive states and to test the hypothesis that stretch of uterine myocytes alters prostanoid receptor mRNA expression to promote uterine contractility. Myocytes were isolated from women undergoing hysterectomy (NP) and pregnant women undergoing LSCS either before (NL) or after the onset of labour (L) and were subjected to 11% stretch for 1 h (n = 6 in all cases). Copy numbers of the individual receptors varied widely with reproductive state but followed the pattern: FP > IP = DP = EP-4 > TP = EP-3 = EP-2 > EP-1. FP mRNA expression was significantly lower in the NL group compared to the NP group and EP-3, EP-4 and TP mRNA expression was significantly lower in both NL and L groups compared to NP group levels. The level of mRNA expression of EP-1, EP-2, DP and IP did not differ between NP, NL and L groups. Stretch of cells derived from the NP group resulted in a significant decrease in EP-4 mRNA expression alone and of the NL group a significant decrease in EP-2 mRNA expression alone. Stretch had no effect on cells derived from the L group. These data show that pregnancy is associated with a significant reduction in 3 of 4 pro-contraction associated prostanoid receptor mRNA expression and 1 of 4 pro-relaxant. Stretch elicited no consistent change in prostanoid receptor mRNA expression.

Specific PGF(2alpha) receptor (FP) antagonism and human uterine contractility in vitro

OBJECTIVE

PGF(2alpha) acts through its receptor, FP, as an important smooth muscle contractile agent. The aim of this study was to investigate the effects of specific FP antagonism, using the novel-specific FP non-competitive antagonist THG113.31, on spontaneous and agonist-elicited contractions in pregnant and non-pregnant human myometrium in vitro.

DESIGN

Scientific study.

SETTING

University hospital and laboratories. Population Women undergoing caesarean section or hysterectomy.

METHODS

Biopsies of human myometrium were obtained at elective caesarean section (n= 22) and from hysterectomy specimens from premenopausal women (n= 8). Dissected strips were mounted in tissue baths under physiological conditions. The effects of THG113.31 on spontaneous and oxytocin-induced contractions, in pregnant myometrium, and on phenylephrine-induced contractions, in non-pregnant myometrium, were measured. The effects of PGF(2alpha) on spontaneous contractions, in pregnant tissue, in the presence and absence of THG113.31, were investigated. The integrals of contractile activity measured were compared with those from simultaneously run control experiments. The pD(2) and mean maximal effect observed for THG113.31, and for PGF(2alpha) in the presence and absence of THG113.31, were calculated.

MAIN OUTCOME MEASURES

Changes in contractility.

RESULTS

THG113.31 exerted a potent relaxant effect in both spontaneous and oxytocin-induced contractility in pregnant tissue (P < 0.001), and phenylephrine-induced contractility in non-pregnant tissue (P < 0.001), compared with control experiments. PGF(2alpha) exerted a significant contractile effect on spontaneous contractions in pregnant tissue and this effect was not significantly attenuated by THG113.31 (P > 0.05).

CONCLUSION

THG113.31 exerted a significant relaxant effect on human spontaneous and oxytocin-induced contractility but did not alter PGF(2alpha)-elicited contractility. These data raise questions about the exact mechanism of effect of THG113.31 and its interaction with FP. The uterorelaxant potency of THG113.31 in human myometrium in vitro indicates that it may be of limited use as a tocolytic compound.

Sufficient Progesterone-Priming Prior to Estradiol Stimulation Is Required for Optimal Induction of the Cervical Prostaglandin System in Pregnant Sheep at 0.7 Gestations1

The purposes of this study were to determine the separate and interactive functions of progesterone and estradiol in regulating the cervical prostaglandin (PG) system in pregnant sheep at 0.7 gestations. At 106-108 days of gestational age (dGA), ewes were treated with vehicle for 14 days (n = 5) or vehicle for 12 days followed by estradiol 5 mg twice a day, intramuscularly for 2 days (n = 5) or progesterone 100 mg, twice a day, intramuscularly for 14 days (n = 5) or progesterone 100 mg twice a day, intramuscularly for 10 days and then 2 days vehicle followed by estradiol 5 mg twice a day intramuscularly for 2 days (n = 5). At 121-123 dGA, cervical tissues were obtained under halothane anesthesia. Cervical RNA and protein were extracted and analyzed for prostaglandin-endoperoxide synthase 2 (COX2), two PGE(2) receptors, PTGER2 and PTGER4, and estrogen receptor alpha (ESR1) by Northern and Western blot analysis. Immunocytochemistry and in situ hybridization were applied to localize cellular distribution of COX2, PTGER2, and PTGER4 in the cervix. Data were analyzed by ANOVA. COX2 and PTGER4 mRNAs and proteins were increased (P < 0.05) in ewes treated with combined estradiol and progesterone but not in ewes treated with estradiol or progesterone alone compared with controls. ESR1 mRNA was increased in ewes treated with progesterone and estradiol plus progesterone. In contrast, PTGER2 mRNA and protein remained the same after all treatments. COX2 mRNA and protein were localized only in cervical glandular epithelial cells, whereas PTGER2 and PTGER4 were localized in both cervical glandular epithelial and smooth muscle cells. In conclusion, these data suggest that additional progesterone priming at 0.7 gestations synergizes with estradiol to induce cervical COX2, PTGER4, and ESR1 and support our hypothesis that stimulation of the cervical PG system by estradiol is optimized by sufficient progesterone priming in the pregnant sheep cervix.

Expression of prostaglandin transporter in the bovine uterus and fetal membranes during pregnancy

Uteroplacental prostaglandins (PGs) play pivotal roles in the maintenance and termination of pregnancy in mammals. In the present study, we have characterized the expression of prostaglandin transporter (PGT) in placentome caruncles, intercaruncular tissues, fetal membranes, and utero-ovarian plexus during pregnancy in cattle. Pregnant bovine uteri were collected and classified into six groups covering the entire gestational length. In caruncles and intercaruncular tissues, PGT mRNA (also known as SLC02A1) and PGT protein were highly expressed at the late stage of pregnancy compared to the early and mid stages, whereas the level of expression is constant and low in fetal membranes throughout pregnancy. PGT mRNA and PGT protein were expressed at a constant level in the utero-ovarian plexus both ipsilateral and contralateral to corpus luteum throughout the course of pregnancy. Overall, the relative expression of PGT mRNA and PGT protein were higher in caruncles than in intercaruncular tissue and fetal membranes, whereas no differences were detected between intercaruncular tissues and fetal membranes at any stage of gestation. Immunohistochemistry indicated that PGT was preferentially expressed in caruncular epithelial cells of placentomes and endometrial luminal epithelial and myometrial smooth muscle cells of the intercaruncular regions. The level of PGT expression was comparatively higher in maternal components than in fetal components. In conclusion, differential spatiotemporal tissue-specific expression of PGT in uterine and intrauterine tissues suggests a role for this transporter in the exchange of PGs between the maternal and the fetal compartments, as well as for intrauterine metabolism of PGs during pregnancy.

Prostaglandin E and F Receptor Expression and Myometrial Sensitivity at Labor Onset in the Sheep1

Prostaglandins (PGs) play a pivotal role in the initiation and progression of term and preterm labor. Uterine activity is stimulated primarily by PGE(2) and PGF(2alpha) acting on prostaglandin E (EP) and prostaglandin F (FP) receptors, respectively. Activation of FP receptors strongly stimulates the myometrium, whereas stimulation of EP receptors may lead to contraction or relaxation, depending on the EP subtype (EP1-4) expression. Thus, the relative expression of FP and EP1-4 may determine the responsiveness to PGE(2) and PGF(2alpha). The aims of this study were to characterize the expression of EP1-4 and FP in intrauterine tissues and placentome, together with myometrial responsiveness to PG, following the onset of dexamethasone-induced preterm and spontaneous term labor. Receptor mRNA expression was measured using quantitative real-time polymerase chain reaction using species-specific primers. There was no increase in myometrial contractile receptor expression at labor onset, nor was there a change in sensitivity to PGE(2) and PGF(2alpha). This suggests expression of these receptors reaches maximal levels by late gestation in sheep. Placental tissue showed a marked increase in EP2 and EP3 receptor expression, the functions of which are unknown at this time. Consistent with previous reports, these results suggest that PG synthesis is the main factor in the regulation of uterine contractility at labor. This is the first study to simultaneously report PG E and F receptor expression in the key gestational tissues of the sheep using species-specific primers at induced-preterm and spontaneous labor onset.

Identification and localization of prostaglandin E2 receptors in upper and lower segment human myometrium during pregnancy

Prostaglandin E2 (PGE2) plays a key role in the maintenance of human pregnancy and labour onset. PGE2 can elicit diverse actions within the uterus depending on the PGE2 receptors (EP1, EP2, EP3 and EP4) expressed. By signalling through different intracellular pathways the EP receptors may inhibit or promote smooth muscle contractility. Nine different EP3 receptor splice variants have been identified with divergent signalling pathways. RT-PCR and immunohistochemistry were utilized to identify and localize EP receptor isoforms within the upper segment (US) and lower segment (LS) myometrium. EP1 was significantly increased in the LS myometrium with term labour. EP3 (and EP3 splice variants EP3I(1b), EP3II, EP3III and EP3IV) was down-regulated in pregnancy (US and/or LS) with a further decrease at term labour in the LS. Overall, expression of EP2 was significantly higher in the LS while EP3 was significantly higher in the US. No significant EP4 changes were observed. Consistent with the RT-PCR results, immunohistochemistry confirmed the presence and, interestingly, showed nuclear localization of EP receptors in the myometrium with higher EP1 expression and lower expression of EP3. The differential regulation of EP receptors within the myometrium indicates that they may play a role in controlling the onset and maintenance of human labour.

Effect of interferon-tau on prostaglandin biosynthesis, transport, and signaling at the time of maternal recognition of pregnancy in cattle: evidence of polycrine actions of prostaglandin E2

Recognition and establishment of pregnancy involve several molecular and cellular interactions among the conceptus, uterus, and corpus luteum (CL). In ruminants, interferon-tau (IFNtau) of embryonic origin is recognized as the pregnancy recognition signal. Endometrial prostaglandin F(2alpha) (PGF(2alpha)) is the luteolysin, whereas PGE(2) is considered a luteoprotective or luteotrophic mediator at the time of establishment of pregnancy. The interplay between IFNtau and endometrial PGs production, transport, and signaling at the time of maternal recognition of pregnancy (MRP) is not well understood. We have studied the expression of enzymes involved in metabolism of PGE(2) and PGF(2alpha), cyclooxygenase-1 (COX-1) and COX-2, PG synthases (PGES and PGFS), PG 15-dehydrogenase, and PG transporter as well as PGE(2) (EP2 and EP3) and PGF(2alpha) receptors. IFNtau influences cell-specific expression of COX-2, PGFS, EP2, and EP3 in endometrium, myometrium, and CL in a spatio-temporal and tissue-specific manner, whereas it does not alter COX-1, PGES, PG 15-dehydrogenase, PG transporter, or PGF(2alpha) receptor expression in any of these tissues. In endometrium, IFNtau decreases PGFS in epithelial cells and increases EP2 in stroma. In myometrium, IFNtau decreases PGFS and increases EP2 in smooth muscle cells. In CL, IFNtau increases PGES and decreases EP3. Together, our results show that IFNtau directly or indirectly increases PGE(2) biosynthesis and EP2-associated signaling in endometrium, myometrium, and CL during MRP. Thus, PGE(2) may play pivotal roles in endometrial receptivity, myometrial quiescence, and luteal maintenance, indicating polycrine (endocrine, exocrine, paracrine, and autocrine) actions of PGE(2) at the time of MRP. Therefore, the establishment of pregnancy may depend not only on inhibition of endometrial PGF(2alpha), but also on increased PGE(2) production in cattle.

Effects of gentamicin sulfate on the contractility of myometrium isolated from non-pregnant cows

Gentamicin sulfate, an aminoglycoside antibiotic known to cause depression of neuromuscular function, is a drug of choice in intrauterine antibiotic treatment of bovine chronical or subclinical uterine infections but its effects on the contractility of the cow uterus have not been studied. The aim of this study was to characterize, in vitro, the effect of gentamicin sulfate on spontaneous as well as prostaglandin F2alpha (PGF2alpha) and oxytocin-induced contractility of the non-pregnant cow uterus. Myometrial strips were isolated from non-pregnant cows in follicular phase and suspended in a jacketed organ bath filled with Krebs solution at 37 degrees C (pH 7.4) continuously bubbled with 95% oxygen and 5% carbon dioxide and isometric contractions were recorded using isometric force displacement transducer. After manifestation of the spontaneous contractions during equilibration period the test substances PGF2alpha (1 microM), oxytocin (2.5 mIU/ml bath fluid) and gentamicin sulfate (150-600 microm) were added to the bath. The effects of gentamicin sulfate on amplitude (g) and frequency of spontaneous and the agonist-induced contractions were evaluated by 20 min intervals. Data were statistically analyzed using the Student's t-test and Wilcoxon signed-rank test where appropriate. P <0.05 was considered to be significant. Gentamicin sulfate inhibited spontaneous, as well as oxytocin or PGF2alpha-induced contractions in a dose-dependent manner. Although both the frequency and amplitude of contractions were significantly inhibited by gentamicin sulfate, the effect on the frequency of the spontaneous and agonist-induced contractions were more prominent than on the amplitude. The result from this in vitro study indicated that gentamicin sulfate inhibits spontaneous as well as oxytocin and PGF2alpha-induced contractions of myometrium isolated from non-pregnant cows. This may be of importance considering the potentially negative effect of gentamicin sulfate on uterine involution in cows with puerperal endometritis, resulting in impairment of fertility performance.

A sheer pharmacologic approach to compare the contractile effects of PGF2α, dl-cloprostenol and d-cloprostenol on isolated uterine, tracheal, ileal and arterial smooth muscle preparations

The contractile effects of PGF2alpha and its cloprostenol analogs (D-enantiomer and racemate) were examined on isolated smooth muscle preparations (uterine, tracheal, ileal and arterial) from rat, guinea-pig and horse. DL- and D-cloprostenol were potent contractors of myometrium, but had negligible secondary effects on other types of smooth muscle, except artery whose response to the D-enantiomer may give rise to some concern.

Expression of prostanoid receptors in human lower segment pregnant myometrium

Prostanoids, especially prostaglandin (PG) E(2), are important mediators of uterine relaxation and contractions during gestation and parturition. Inhibitors of PG formation as well as PG analogues are used to modulate uterine tonus. So far, only limited data are available regarding the expression of prostanoid receptors in human pregnant myometrium. In the present study, the expression of the receptors for PGE(2) (EP1, EP2, EP3, EP4), PGF(2alpha) (FP), prostacyclin (IP), and thromboxane A(2) (TP) in human pregnant myometrium was studied by RT-PCR, in situ hybridization and immunohistochemistry. Myometrial tissue was obtained from five women at term and not in labour and from two women who delivered preterm. Tissue specimens were excised from the upper edge of the transverse lower uterine segment incision. In all tissues analysed, EP1, EP2, EP3, EP4, FP, TP and IP receptor mRNA and protein was detected. mRNA expression for PGD(2) (DP) receptor was not detected in the majority of tissue specimens. EP1, EP2, EP4, IP, TP and FP receptor protein was detected on myometrial smooth muscle cells, whereas EP3 receptor protein was only expressed by stromal and endothelial cells. In situ hybridization experiments yielded similar results. The expression of the EP2 receptor mRNA was inversely related to gestational age. We suggest that the contractile effect of PGE(2) at term is probably mediated directly by the EP1 receptor expressed in myometrial smooth muscle cells and indirectly by the EP3 receptor expressed in stromal cells and a decrease in EP2 receptor expression.

Molecular cloning and characterization of bovine prostaglandin E2 receptors EP2 and EP4: expression and regulation in endometrium and myometrium during the estrous cycle and early pregnancy

Prostaglandins (PGs) play important functions in the reproductive system, and PGE(2) appears necessary for recognition of pregnancy. We have found that PGE(2) is able to increase cAMP generation in the bovine endometrium. There are two PGE(2) receptors (EP), EP2 and EP4, that are coupled to adenylate cyclase to generate cAMP, but these receptors have not been studied in the bovine. We have cloned and characterized bovine EP2 and EP4 receptors and studied their expression in the uterus. The amino acid sequences of bovine EP2 and EP4 possess a high degree (>80%) of identity with the other mammalian homologs. EP2 is expressed in most tissues, and EP4 is expressed only in intestine and testis. EP2 mRNA and protein are expressed in endometrium and myometrium during the estrous cycle, whereas EP4 is undetectable. The Western analysis indicates that EP2 is maximally expressed in both endometrium and myometrium between d 10 and 18 of the estrous cycle. Immunohistochemical localization reveals that EP2 protein is expressed in all cell types of endometrium and myometrium. On d 18, pregnancy up-regulates EP2 protein, primarily in endometrial stroma and myometrial smooth muscle cells. In conclusion, EP2 is the major cAMP-generating PGE(2) receptor expressed and regulated in the bovine uterus during the estrous cycle and early pregnancy.

In vitro response of prostaglandin E2 receptor (EP3) in the term pregnant rat uterus and cervix to misoprostol

We examined and compared the in vitro effects of misoprostol (synthetic prostaglandin E1 (PGE1) analogue) on prostaglandin E2 (PGE2) secretion and EP3 receptor mRNA expression in the pregnant rat myometrium and cervix at 19 days gestation. Myometrial and cervical tissue samples were exposed to media with or without misoprostol (50 or 100 pg/ml) and incubated for 15 and 30 min, and 1, 3, 6, 12, and 24 h. Media and tissue samples were collected for quantification of PGE2 and mRNA expression of rEP3alpha and rEP3beta receptor, respectively. PGE2 secretion increased (P < or = 0.05) in the myometrium exposed to 50 and 100 pg/ml misoprostol. Cervical PGE2 secretion increased following exposure to the 100 pg/ml dose only. In the myometrium, 50 and 100 pg/ml misoprostol induced elevations in rEP3alpha and rEP3beta receptor mRNA expression. rEP3alpha and rEP3beta receptor mRNA expression in the cervix was not different from controls. These data demonstrate that the EP3 receptor is differentially expressed in the myometrium and cervix in response to misoprostol. This may account for the ability of misoprostol to stimulate the myometrium when administered for cervical ripening.

THG113: a novel selective FP antagonist that delays preterm labor

PGF2alpha is an important smooth muscle contractile agent that exerts significant effects on myometrium and is implicated in labor. THG113 was recently identified as a PGF2alpha receptor (FP) antagonist. We characterized the specificity and selectivity of THG113, tested its effects on PGF2alpha-induced smooth muscle contraction, and assessed its efficacy in a model of endotoxin (LPS)-induced preterm labor. [125I]THG113 bound specifically to FP-expressing but not to native (not expressing FP) HEK293 cells. In FP-expressing HEK293 cells, THG113 markedly reduced PGF2alpha-elicited phosphoinositide hydrolysis (IC50 27 nM). Similarly, PGF2alpha-evoked microvascular (retinal) contraction was noncompetitively blocked (by > 90%) by THG113. In contrast, contraction to agonists of homologous prostanoid receptors EP1 and TP (17-phenyl-trinor PGE2 and U46619) was unaffected (< 1%) by high concentrations of THG113 (100 micromol/L); THG113 (100 micromol/L) also did not affect contraction to numerous other agents including platelet activating factor, endothelin, and angiotensin II. Force and duration of PGF2alpha-evoked contractions of myometrial strips of pig (non-pregnant, luteal phase) and mouse (immediately postpartum) were markedly reduced by THG113. In an endotoxin-induced preterm mouse model, lipopolysaccharide (50 microg intraperitioneal) injection at 16 days' gestation resulted in 100% delivery within 15 h; in contrast, 70% of those treated with THG113 (1 mg/day) delivered > 24 h later (at 18 days' gestation; term: 19 days). In addition, in mice injected with lipopolysaccharide and treated 6 h later with THG113 (0.1 mg bolus followed by 1 mg/day) 40% delivered > 48 h later. Fetuses of pregnant mice treated with THG113 were born alive, had higher birth weights (1.6 +/- 0.1 v 1.4 +/- 0.05 g), and appeared healthy. This study describes an effective and selective noncompetitive FP antagonist, THG113, which significantly delays preterm delivery; this provides the basis for future investigations for its use in tocolysis.

Prostanoid receptor subtypes

Prostanoids are a group of lipid mediators that include the prostaglandins (PG) and thromboxanes (TX). Upon cell stimulation, prostanoids are synthesized from arachidonic acid via the cyclooxygenase (COX) pathway and released outside the cells to exert various physiological and pathological actions in a variety of tissues and cells. The activities of prostanoids are mediated by specific G protein-coupled receptors, which have been classified on the basis of pharmacological experiments into eight types and subtypes according to their responsiveness to selective agonists and antagonists. These prostanoid receptors have been cloned from various species including human, and their distinct binding properties and signal transduction pathways have been characterized by analyses of cells expressing each receptor. Furthermore, the distribution patterns of prostanoid receptor mRNAs have been determined in tissues and cells for various species. This information is useful for understanding the molecular basis of the pathophysiological actions of prostanoids.

In vitro pharmacological characterization of the prostanoid receptor population in the non-pregnant porcine myometrium

In order to characterize prostanoid receptors present in the non-pregnant porcine uterus, the effects of naturally occurring prostaglandins (D2, E2, F2alpha, I2) and synthetic prostanoid receptor agonists on contractility of the longitudinal and circular muscles were examined in vitro. The potent contractile actions of prostaglandin F2alpha and cloprostenol indicate the presence of excitatory FP receptors in the porcine uterus. The longitudinal muscle was more sensitive to FP receptor agonists than was the circular muscle. Prostaglandin D2 produced an excitatory response in the longitudinal muscle but completely inhibited the spontaneous contraction of the circular muscle. BW-245C (5-(6-carboxyhexyl)-1-(3-cyclohexyl-3-hydroxypropyl)hydantoin, 1 nM-10 microM, a DP receptor agonist) inhibited the spontaneous contractions of both muscles, but the inhibition was conspicuously stronger in the circular muscle. Prostaglandin I2 caused excitatory and inhibitory responses in the longitudinal and circular muscles, respectively, at relatively high concentrations (10-100 microM). Cicaprost, an IP receptor agonist caused inhibition of the contraction in the circular muscle but contracted the longitudinal muscle. Iloprost, an EP(1)/IP receptor agonist, caused excitatory responses in both muscles at relative high concentrations. Prostaglandin E2 caused excitatory responses at 1-100 nM and inhibitory responses at 100 nM-10 microM in both muscle layers. ONO-DI-004 ((17S)-2,5-ethano-6-oxo-17,20-dimethyl prostaglandin E1, an EP1 receptor agonist) and ONO-AE-248 ((16S)-9-deoxy-9beta-chloro-15-deoxy-16-hyfroxy-17,17-trimethylene-19,20-didehydro prostaglandin F2, an EP3 receptor agonist) contracted the longitudinal muscle but had little effect on the circular muscle. ONO-AE1-259 (11,15-O-dimethyl prostaglandin E2, an EP2 receptor agonist) inhibited the spontaneous contractions of both muscle layers to almost the same degree, but ONO-AE1-329 (16-(3-methoxymethyl)phenyl-omega-tetranor-3,7-dithia prostaglandin E1, an EP4 receptor agonist) did not inhibit the myometrial contraction. The present results indicate that contractile (FP, EP1, EP3) and relaxatory (DP, IP, EP2) prostanoid receptors are present in the non-pregnant porcine uterus. There are marked muscle layer-related differences in the degree of responsiveness of prostanoid receptor agonists, and these differences suggest that there is a heterogeneous distribution of prostanoid receptors in the longitudinal and circular muscles (FP, EP1 and EP3, longitudinal muscle>circular muscle; DP, circular muscle>longitudinal muscle).

Effect of gestational age, corticosteroids, and birth on expression of prostanoid EP receptor genes in lamb and baboon ductus arteriosus

The aim of this study was to determine the effect of corticosteroids, gestational age, and birth on the expression of genes encoding prostanoid receptors in the lamb and baboon ductus arteriosus. The ductus arteriosus was obtained from 34 lambs and eight baboons, including chronically instrumented fetuses of both species exposed to either corticosteroid or vehicle. Expression of prostanoid receptor genes was quantified using Northern blot analysis relative to each of two housekeeping genes. Expression of both the EP3 and EP4 receptor genes was detected in lamb ductus and the level of expression of both genes was unaffected by corticosteroids. Expression of the EP4 receptor gene was lower in the ductus obtained from term lambs compared with preterm lambs and was lower still in neonatal animals, whereas no variation was observed in EP3 receptor gene expression. Expression of the EP4 receptor gene was also confirmed in fetal baboon ductus arteriosus, and maternal administration of corticosteroid did not reduce EP4 receptor gene expression in the baboon. We conclude that advancing gestational age and birth may inhibit prostaglandin E2-mediated relaxation of the ductus through a corticosteroid-independent reduction in EP4 receptor gene expression.

Effects of gestational age and labor on expression of prostanoid receptor genes in baboon uterus

We determined the effect of gestational age and labor on the regional expression of prostanoid receptor genes in baboon myometrium. Cesarean hysterectomy was performed on 15 pregnant baboons of known gestational age in the last third of pregnancy, five of them during spontaneous term labor. Expression of prostanoid receptor genes was studied using Northern blot analysis. Transcripts of similar size to the human were detected for prostanoid EP(1), EP(2), EP(3), EP(4), IP, FP, and TP receptor genes using Northern blot analysis. There were no gestational age-related changes in expression of these genes. Expression of EP(1), EP(3), and IP receptor RNA mRNA was significantly higher in myometrium from the fundus (compared with the lower segment), whereas EP(2) gene expression was significantly lower in the fundus. Labor was associated with a reduction in the regional variation of both EP(2) and IP receptor gene expression, but not EP(1) and EP(3) expression. Labor was also associated with an overall lower level of expression of EP(2) receptor mRNA. We conclude that regional and labor-related variation in myometrial expression of prostanoid receptor genes may have a key role in primate parturition.