The role of prostaglandins in human parturition

Identification of a feed-forward loop between 15(S)-HETE and PGE2 in human amnion at parturition

Human parturition is associated with massive arachidonic acid (AA) mobilization in the amnion, indicating that large amounts of AA-derived eicosanoids are required for parturition. Prostaglandin E2 (PGE2) synthesized from the cyclooxygenase (COX) pathway is the best characterized AA-derived eicosanoid in the amnion which plays a pivotal role in parturition. The existence of any other pivotal AA-derived eicosanoids involved in parturition remains elusive. Here, we screened such eicosanoids in human amnion tissue with AA-targeted metabolomics and studied their role and synthesis in parturition by using human amnion fibroblasts and a mouse model. We found that lipoxygenase (ALOX) pathway-derived 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE) and its synthetic enzymes ALOX15 and ALOX15B were significantly increased in human amnion at parturition. Although 15(S)-HETE is ineffective on its own, it potently potentiated the activation of NF-κB by inflammatory mediators including lipopolysaccharide, interleukin-1β, and serum amyloid A1, resulting in the amplification of COX-2 expression and PGE2 production in amnion fibroblasts. In turn, we determined that PGE2 induced ALOX15/15B expression and 15(S)-HETE production through its EP2 receptor-coupled PKA pathway, thereby forming a feed-forward loop between 15(S)-HETE and PGE2 production in the amnion at parturition. Our studies in pregnant mice showed that 15(S)-HETE injection induced preterm birth with increased COX-2 and PGE2 abundance in the fetal membranes and placenta. Conclusively, 15(S)-HETE is identified as another crucial parturition-pertinent AA-derived eicosanoid in the amnion, which may form a feed-forward loop with PGE2 in parturition. Interruption of this feed-forward loop may be of therapeutic value for the treatment of preterm birth.

miR-132-3p Modulates DUSP9-Dependent p38/JNK Signaling Pathways to Enhance Inflammation in the Amnion Leading to Labor

Labor is a process of inflammation and hormonal changes involving both fetal and maternal compartments. MicroRNA-132-3p (miR-132-3p) has been reported to be involved in the development of inflammation-related diseases. However, little is known about its potential role in labor onset. This study aimed to explore the mechanism of miR-132-3p in amnion for labor initiation. In the mouse amnion membranes, the expression of miR-132-3p was found to increase gradually during late gestation. In human amniotic epithelial cell line (WISH), upregulation of miR-132-3p was found to increase proinflammatory cytokines and cyclooxygenase 2 (COX2) as well as prostaglandin E2 (PGE2), which was suppressed by miR-132-3p inhibitor. Dual-specificity phosphatase 9 (DUSP9) was identified as a novel target gene of miR-132-3p, which could be negatively regulated by miR-132-3p. DUSP9 was present in the mouse amnion epithelial cells, with a decrease in its abundance at 18.5 days post coitum (dpc) relative to 15.5 dpc. Silencing DUSP9 was found to facilitate the expression of proinflammatory cytokines and COX2 as well as PGE2 secretion in WISH cells, which could be attenuated by p38 inhibitor SB203580 or JNK inhibitor SP600125. Additionally, intraperitoneal injection of pregnant mice with miR-132-3p agomir not only caused preterm birth, but also promoted the abundance of COX2 as well as phosphorylated JNK and p38 levels, and decreased DUSP9 level in mouse amnion membranes. Collectively, miR-132-3p might participate in inflammation and PGE2 release via targeting DUSP9-dependent p38 and JNK signaling pathways to cause preterm birth.

C/EBPδ drives key endocrine signals in the human amnion at parturition

Amnion-derived prostaglandin E2 (PGE2) and cortisol are key to labor onset. Identification of a common transcription factor driving the expression of both cyclooxygenase-2 (COX-2) and 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1), the key enzymes in their production, may hold the key to the treatment of pre-term labor. Here, we have found that the CCAAT enhancer binding protein δ (C/EBPδ) is such a transcription factor which underlies the feed-forward induction of COX-2 and 11β-HSD1 expression by their own products PGE2 and cortisol in human amnion fibroblasts so that their production would be ensured in the amnion for the onset of labor. Moreover, the abundance of C/EBPδ in the amnion increases along with COX-2 and 11β-HSD1 at term and further increases at parturition. Knockout of C/EBPδ in mice delays the onset of labor further supporting the concept. In conclusion, C/EBPδ pathway may be speculated to serve as a potential pharmaceutical target in the amnion for treatment of pre-term labor.

Altered productions of prostaglandins and prostamides by human amnion in response to infectious and inflammatory stimuli identified by mutliplex mass spectrometry

INTRODUCTION

Prostaglandins are critical for the onset and progression of labor in mammals, and are formed by the metabolism of arachidonic acid. The products of arachidonic acid, 2-arachidonoylglycerol (2-AG), and anandamide (AEA) have a similar lipid back bone but differing polar head groups, meaning that identification of these products by immunoassay can be difficult.

MATERIALS AND METHODS

In the current study, we present the use of mass spectrometry as multiplex method of identifying the specific end products of arachidonic and anandamide metabolism by human derived amnion explants treated with either an infectious agent (LPS) or inflammatory mediator (IL-1β or TNF-α).

RESULTS

Human amnion tissue explants treated with LPS, IL-1β, or TNF-α increased production of prostaglandin E₂ (PGE₂; p < 0.05) but decreased PGFM. Overall, PGE₂ production was greater compared to the other prostaglandins and prostamides irrespective of treatment.

CONCLUSIONS

The findings of the current study are in keeping with the literature which describes amnion tissues as predominantly producing PGE₂. The use of mass spectrometry for the differential identification of prostaglandins, prostamides, and other eicosanoids may help better elucidate mechanisms of preterm labor, and lead to new targets for the prediction of risk for preterm labor and/or birth.

Reduced Expression of Hydrogen Sulfide-Generating Enzymes Down-Regulates 15-Hydroxyprostaglandin Dehydrogenase in Chorion during Term and Preterm Labor

Chorionic NAD-dependent 15-hydroxyprostaglandin dehydrogenase (PGDH) plays a pivotal role in controlling the amount of prostaglandins in the uterus and has been implicated in the process of labor. Prior studies identified hydrogen sulfide-generating enzymes cystathionine-β-synthetase (CBS) and cystathionine-γ-lyase (CSE) in fetal membranes. We investigated whether hydrogen sulfide is involved in the regulation of PGDH expression in the chorion during labor. The chorionic tissues were obtained from pregnant women at preterm in labor and at term in labor or not in labor at term. Levels of CSE and CBS and hydrogen sulfide production rate were down-regulated in term in labor and preterm in labor groups compared with not in labor at term group. The CBS level correlated to PGDH expression in the chorion. Hydrogen sulfide donor NaHS and precursor l-cysteine dose-dependently stimulated PGDH expression and activity in cultured chorionic trophoblasts. The effect of l-cysteine was blocked by CBS inhibitor and CBS siRNA but not by CSE inhibitor and CSE siRNA. Hydrogen sulfide treatment suppressed miR-26b and miR-199a expression in chorionic trophoblasts. miR-26b and miR-199a mimics blocked hydrogen sulfide upregulation of PGDH expression. Our results indicate that hydrogen sulfide plays pivotal roles in maintenance of PGDH expression in the chorion during human pregnancy. Reduced expression of hydrogen sulfide-generating enzymes contributes to an increased amount of prostaglandins in the uterus during labor.

Expression of 15-Hydroxyprostaglandin Dehydrogenase in Human Chorion Is Associated with Peroxisome Proliferator-Activated Receptor Isoform Expression in Term Labor

Chorionic NAD-dependent 15-hydroxy prostaglandin dehydrogenase (PGDH) plays a pivotal role in controlling the amount of prostaglandins in the uterus. Peroxisome proliferator-activated receptors (PPARs) are implicated to be involved in parturition. In this study, we investigated whether PPARs are involved in control of PGDH expression in chorion. The chorionic tissues were collected from the following groups of the women with singleton pregnancy: term no labor (TNL), term labor (TL) and preterm labor (PTL). Chorionic trophoblasts were isolated and cultured in vitro. Immunocytochemistry analysis showed that PPARα, PPARβ, and PPARγ were localized to trophoblasts in chorion. The protein levels of PGDH, PPARβ, and PPARγ were localized to trophoblasts in chorion. The protein levels of PPARα, PPARβ, and PPARγ were reduced in TL tissues compared to that of TNL group. PPARα, PPARβ, and PPARγ expression correlated to PGDH in TNL tissues, whereas only PPARγ expression correlated to PGDH in TL chorion tissues. PGDH expression was decreased in PTL tissues compared with TL group, whereas the expression of PPARs was not significantly different between TL and PTL groups. The agonists of three PPARs dose-dependently stimulated PGDH activity, mRNA, and protein expression in cultured chorionic cells. PPARs did not affect the stability of PGDH mRNA but stimulated the transcriptional activity of HPGD gene. Our results suggest that PPARs play pivotal roles in maintenance of PGDH expression in chorion during human pregnancy.

PGF2α modulates the output of chemokines and pro-inflammatory cytokines in myometrial cells from term pregnant women through divergent signaling pathways

Prostaglandin F2α (PGF2α) plays a critical role in the initiation and process of parturition. Since human labor has been described as an inflammatory event, we investigated the role of PGF2α in the inflammatory process using cultured human uterine smooth muscle cells (HUSMCs) isolated from term pregnant women as a model. Using a multiplex assay, HUSMCs treated with PGF2α changed their output of a number of cytokines and chemokines, with a distinct response pattern that differed between HUSMCs isolated from the upper and lower segment region of the uterus. Confirmatory enzyme-linked immunosorbent assays (ELISAs) showed that PGF2α stimulated increased output of interleukin (IL) 1β, IL6, IL8 (CXCL8) and monocyte chemotactic protein-1 (MCP1, also known as chemokine (c-c motif) ligand 2, CCL2) by HUSMCs isolated from both upper and lower uterine segments. In contrast, PGF2α inhibited tumor necrosis factor α (TNFα) release by HUMSCs from the lower uterine segment while the output of TNFα was undetectable in the upper segment. Small interfering (si) RNA mediated knockdown of the PGF2α receptor prevented the changes in cytokine and chemokine output by the HUSMCs. Since the PGF2α receptor (PTGFR) couples via the Gq protein and subsequently activates the phospholipase C (PLC) and protein kinase C (PKC) signaling pathways, we examined the role of these pathways in PGF2α modulation of the cytokines. Inhibition of PLC and PKC reversed the effects of PGF2α. PGF2α activated multiple signaling pathways including extracellular signal-regulated kinases (ERK) 1/2, phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K), P38, calcineurin/nuclear factor of activated T-cells (NFAT) and NF-κB signaling. Inhibition of ERK reversed PGF2α-induced IL1β, IL6 and CCL2 output, while inhibition of PI3K blocked the effect of PGF2α on IL6, CXCL8 and CCL2 output and inhibition of NF-κB reversed PGF2α-induced IL1β and CCL2 output. NFAT was involved in PGF2α modulation of CCL2 and TNFα output. In conclusion, our results support a role of PGF2α in creating an inflammatory environment during the late stage of human pregnancy.

Prostaglandin F2α regulates the expression of uterine activation proteins via multiple signalling pathways

Prostaglandin F2α (PGF2A) has multiple roles in the birth process in addition to its vital contractile role. Our previous study has demonstrated that PGF2A can modulate uterine activation proteins (UAPs) in cultured pregnant human myometrial smooth muscle cells (HMSMCs). The objective of this study was to define the signalling pathways responsible for PGF2A modulation of UAPs in myometrium. It was found that PGF2A stimulated the expression of (GJA1) connexin 43 (CX43), prostaglandin endoperoxide synthase 2 (PTGS2) and oxytocin receptor (OTR) in cultured HMSMCs. The inhibitors of phospholipase C (PLC) and protein kinase C (PKC) blocked PGF2A-stimulated expression of CX43. The inhibitors of ERK, P38 and NFκB also blocked the effect of PGF2A on CX43 expression, whereas PI3K and calcineurin/nuclear factor of activated T-cells (NFAT) pathway inhibitors did not reverse the effect of PGF2A on CX43. For PTGS2 and OTR, PLC, PI3K, P38 and calcineurin/NFAT signalling pathways were involved in PGF2A action, whereas PKC and NFκB signalling were not involved. In addition, PGF2A activated NFAT, PI3K, NFκB, ERK and P38 signalling pathways. Our data suggest that PGF2A stimulates CX43, PTGS2 and OTR through divergent signalling pathways.

Secreted phospholipase A2 is increased in meconium-stained amniotic fluid of term gestations: potential implications for the genesis of meconium aspiration syndrome

BACKGROUND

Meconium-stained amniotic fluid (MSAF) represents the passage of fetal colonic content into the amniotic cavity. Meconium aspiration syndrome (MAS) is a complication that occurs in a subset of infants with MSAF. Secreted phospholipase A2 (sPLA2) is detected in meconium and is implicated in the development of MAS. The purpose of this study was to determine if sPLA2 concentrations are increased in the amniotic fluid of women in spontaneous labor at term with MSAF.

MATERIALS AND METHODS

This was a cross-sectional study of patients in spontaneous term labor who underwent amniocentesis (n = 101). The patients were divided into two study groups: (1) MSAF (n = 61) and (2) clear fluid (n = 40). The presence of bacteria and endotoxin as well as interleukin-6 (IL-6) and sPLA2 concentrations in the amniotic fluid were determined. Statistical analyses were performed to test for normality and bivariate analysis. The Spearman correlation coefficient was used to study the relationship between sPLA2 and IL-6 concentrations in the amniotic fluid.

RESULTS

Patients with MSAF have a higher median sPLA2 concentration (ng/mL) in amniotic fluid than those with clear fluid [1.7 (0.98-2.89) versus 0.3 (0-0.6), p < 0.001]. Among patients with MSAF, those with either microbial invasion of the amniotic cavity (MIAC, defined as presence of bacteria in the amniotic cavity), or bacterial endotoxin had a significantly higher median sPLA2 concentration (ng/mL) in amniotic fluid than those without MIAC or endotoxin [2.4 (1.7-6.0) versus 1.7 (1.3-2.5), p < 0.05]. There was a positive correlation between sPLA2 and IL-6 concentrations in the amniotic fluid (Spearman Rho = 0.3, p < 0.05).

CONCLUSION

MSAF that contains bacteria or endotoxin has a higher concentration of sPLA2, and this may contribute to induce lung inflammation when meconium is aspirated before birth.

Prostaglandins and cervical dilatation

The efficacy of labour is determined by uterine, fetopelvic and cervical factors. Whereas the first two of these are well recognized, acknowledgement of the modulating function of the cervix during labour is relatively new. In particular, clarification of the synthesis and metabolism of prostaglandins has contributed considerably to our understanding of the biological control of the cervix.

Endocrinology of labour

Preterm labour, defined as delivery before 37 weeks of completed pregnancy, continues to present a major problem in clinical obstetrics and remains the major contributory factor to the perinatal mortality and morbidity statistics. While it is now possible, with recent advances in neonatal care, to take infants delivered very prematurely and provide them with the lifelines that will ensure their ultimate discharge from the neonatal intensive care nursery, the cost of this form of management – in terms both of health care funds and of emotion – is extraordinarily high. Hence there remains a strong rationale for attempting to understand the underlying biochemistry and physiology of labour in order to develop methods of recognizing the patient in true preterm labour, and of developing better strategies to prevent or to manage this condition. In the best of our neonatal intensive care settings, survival of the infant born at 28–30 weeks’ gestation, or greater than 1500 grams, may be greater than 90%. Thus, the clinical management strategy may be directed more towards sustaining intrauterine life for 4–6 weeks in those patients presenting in preterm labour before this time in order to gain time for intrauterine maturation of these fetuses before they are delivered to the tertiary care NICU setting.

Differential regulation of prostaglandin production mediated by corticotropin-releasing hormone receptor type 1 and type 2 in cultured human placental trophoblasts

Prostaglandin (PG) production by intrauterine tissues plays a key part in the control of pregnancy and parturition. The present study was to investigate the role of placenta-derived CRH and CRH-related peptides in the regulation of PG synthesis and metabolism. We found that placental trophoblasts expressed both CRH-R1 and CRH-R2. Treatment of cultured placental cells with either a CRH or urocortin I (UCNI) antibody resulted in a significant decrease in PGE2 release. Both CRH and UCNI antibodies significantly decreased mRNA and protein expression of synthetic enzymes cytosolic phospholipase A2 (cPLA2) and cyclooxygenase (COX)-2 and increased mRNA and protein expression of 15-hydroxyprostaglandin dehydrogenase (PGDH), the key enzyme of PG metabolism. CRH-R1/-R2 antagonist astressin and CRH-R1 antagonist antalarmin significantly inhibited PGE2 release, whereas CRH-R2 antagonist astressin-2b had no effect on PGE(2) release. Administration of astressin decreased expression of cPLA2 but had no effect on COX-2 expression. Antalarmin reduced cPLA2 and COX-2 expression, whereas astressin-2b did not alter cPLA2 expression but increased COX-2 expression. PGDH expression was enhanced by these three antagonists. Cells treated with exogenous CRH and UCNI showed an increase in PGE(2) release and expression of cPLA2 and COX-2 but a decrease in PGDH expression. UCNII and UCNIII had no effect on PGE2 release but decreased COX-2 and PGDH expression. Our results suggested CRH and CRH-related peptides act on CRH-R1 and CRH-R2 to exert different effects on PG biosynthetic enzymes cPLA2 and COX-2 and thereby modulate output of PGs from placenta, which would be important for controlling pregnancy and parturition.

Changes of nuclear factor kappa B (NF-κB), cyclooxygenase-2 (COX-2) and matrix metalloproteinase-9 (MMP-9) in human myometrium before and during term labor

OBJECTIVE

To investigate the changes of nuclear factor kappa B (NF-kappaB), cyclooxygenase-2 (COX-2) and matrix metalloproteinase-9 (MMP-9) in human term myometrium before and during term labor.

STUDY DESIGN

Myometrium was obtained from women undergoing cesarean delivery at term before (n=16) and after labor (n=12). Immunostaining of NF-kappaB subunits (p65/p50) and Western blot analysis of NF-kappaB subunits, MMP-9 and COX-2 proteins were compared. Human term myocyte cultures were stimulated with IL-1beta. Activation of NF-kappaB was assessed by evaluating changes in the inhibitory protein IkappaB; regulation of COX-2 and MMP-9 levels was studied using Western blot analysis and gelatin zymography.

RESULTS

In contrast to a significant increase in the level of COX-2 and MMP-9 proteins, p65 and p50 decreased significantly in the after-labor group compared to the before-labor group. After treatment with IL-1beta, IkappaB was degraded by almost 90% within 5 min and became undetectable by 15 min. IL-1beta stimulation increased the levels of COX-2 protein and the gelatinolytic activities of MMP-9, both of which were inhibited by NF-kappaB inhibitors.

CONCLUSIONS

Human term labor is associated with changes in NF-kappaB and increased expression of COX-2 and MMP-9 in the myometrium. NF-kappaB pathway activation and subsequent increments of COX-2 and MMP-9 were observed in human term myocyte cultures.

Nuclear prostaglandin receptors: role in pregnancy and parturition?

The key regulatory role of prostanoids [prostaglandins (PGs) and thromboxanes (TXs)] in the maintenance of pregnancy and initiation of parturition has been established. However, our understanding of how these events are fine-tuned by the recruitment of specific signaling pathways remains unclear. Whereas, initial thoughts were that PGs were lipophilic and would easily cross cell membranes without specific receptors or transport processes, it has since been realized that PG signaling occurs via specific cell surface G-protein coupled receptors (GPCRs) coupled to classical adenylate cyclase or inositol phosphate signaling pathways. Furthermore, specific PG transporters have been identified and cloned adding a further level of complexity to the regulation of paracrine action of these potent bioactive molecules. It is now apparent that PGs also activate nuclear receptors, opening the possibility of novel intracrine signaling mechanisms. The existence of intracrine signaling pathways is further supported by accumulating evidence linking the perinuclear localization of PG synthesizing enzymes with intracellular PG synthesis. This review will focus on the evidence for a role of nuclear actions of PGs in the regulation of pregnancy and parturition.

Epidermal growth factor modulation of prostaglandins and nitrite biosynthesis in rat fetal membranes

The production of prostaglandins (PGs) and nitric oxide (NO) by amnion tissue may play a significant role in parturition. It is thought that epidermal growth factor (EGF) may be one of the fetal signals that governs the initiation of labor. The aim of the present study was to investigate the effect of EGF in vivo on the PGs and nitrite production of rat fetal membranes. We have evaluated the regulation of PGs and nitrite production in rat fetal membranes ex vivo. The intra-uterine administration of EGF 500 ng in day 21 of pregnancy induced increases in PGE(2) (P<0.001) and PGF(2alpha) (P<0.01) compared to the control fetal membranes from pregnant rats on day 22. Also, this dose of EGF diminished nitrate production significantly (P<0.01). We found that fetal membranes at term (days 18-22 of gestation) expressed EGF-R. The NO donor, nitroprussiate 300 and 600 microM, elicited an inhibitory effect on the PGE(2) and PGF(2alpha) stimulated synthesis. On the other hand, indomethacin 10(-6) and 10(-7)M, a non-selective cyclooxygenase inhibitor, reverted the inhibitory effect exerted by EGF. Hence, rat fetal membranes were found to express epidermal growth factor receptors and, under the effect of EGF, PGs and nitrites production pathways interact probably to prevent a toxic effect caused by an exacerbated synthesis of these mediators.

Differential COX localization and PG release in Thy-1(+) and Thy-1(-) human female reproductive tract fibroblasts

A key role exists for prostaglandins (PGs) in reproductive health, including fertility and parturition. However, the cellular sources and regulation of PG production by cyclooxygenase (COX) in the human female reproductive tract remain poorly understood. We recently reported that human female reproductive tract fibroblasts are divisible into distinct subsets based on their Thy-1 surface expression. Herein, we demonstrate that the expression, induction, and subcellular localization of COX-1 and COX-2 and the downstream PG biosynthesis are markedly different between these subsets. Specifically, Thy-1(+) fibroblasts highly express COX-1, which is responsible for high-level PGE(2) production, a feature usually attributed to the COX-2 isoenzyme. In contrast, COX-2, generally considered an inducible isoform, is constitutively expressed in the Thy-1(-) subset, which only minimally produces PGE(2). The intracellular signaling pathways for COX regulation also differ between the subsets. Determination of differences in signal transduction, COX expression and localization, and PG production by human reproductive fibroblast subtypes supports the concept of fibroblast heterogeneity and the possibility that these subsets may play unique roles in tissue homeostasis and in inflammation.

Expression of cyclooxygenase-2 and prostanoid receptors by human myometrium

Prostanoids play an important role in the regulation of parturition. All reproductive tissues, including fetal membranes, decidua, and myometrium, have the capacity to synthesize prostanoids, and fetal membranes have been shown to express elevated levels of cyclooxygenase-2 (Cox-2) at the onset of labor. We have now investigated the expression of Cox-2 in human myometrium. Myometrial samples collected from women in labor during lower segment cesarean section expressed 15-fold higher levels of Cox-2 messenger ribonucleic acid (mRNA) compared to myometrial specimens collected from women not in labor, as detected by Northern blot analysis. Immunohistochemical detection of Cox-2 protein showed cytoplasmic staining in the smooth muscle cells of the myometrium. Cultured myometrial cells expressed low levels of Cox-2 mRNA under baseline conditions, but interleukin-1beta (IL-1beta) caused a 17-fold induction of expression of the Cox-2 transcript after incubation for 6 h. IL-1beta also induced expression of biologically active Cox-2 protein, as detected by immunofluorescence, Western blot analysis, and measuring the conversion of arachidonic acid to prostanoids in the presence and absence of a Cox-2-selective inhibitor, NS-398. PGE2 receptor subtype EP2 mRNA was expressed in cultured myometrial smooth muscle cells, whereas transcripts for EP1, EP3, EP4, FP, and IP were low or below the detection limit as measured by Northern blot analysis. However, IL-1beta stimulated expression of EP4 receptor mRNA. Our data suggest that expression of Cox-2 transcript is elevated at the onset of labor in myometrial smooth muscle cells, which may depend on induction by cytokines. As, in addition to Cox-2, the expression of prostanoid receptors is regulated, not only the production of prostanoids, but also responsiveness to them, may be modulated.

Transfer and metabolism of prostaglandin E(2)in the dual perfused human placenta

Prostaglandins (PGs) are potent paracrine hormones that are important for the control of several functions in the uterus and fetus during pregnancy and parturition. PGs are rapidly metabolized to inactive metabolites by prostaglandin dehydrogenase (PGDH). However, the regulation of transfer and metabolism of PGs across the placenta is not well understood. This study used an in vitro dual perfused human placental cotyledon preparation to examine the production of the potent vasoactive and myometrial stimulants PGE(2)and PGF(2alpha), transfer of PGs from the maternal to the fetal circulation and the metabolism of PGs by PGDH. Secretion of PGE(2)was greater into the fetal compared to the maternal circulation. PGE(2)output was higher than PGF(2alpha)and concentrations of PGE(2)and PGF(2alpha)metabolites (PGEM and PGFM) were greater in both fetal and maternal outputs when compared to the primary prostaglandins. Infusion of PGE(2)into the maternal circulation did not result in increased PGE(2)efflux but PGEM was output was increased, demonstrating a rapid and efficient metabolism by the placenta. There was no significant transfer of PGE(2)across to the fetal circulation, although there was some transfer but in the form of inactivated PGEM. There was no significant interconversion of PGE(2)to PGF(2alpha)by the 9-keto-reductase pathway. Expression of PGDH as detected by immunoblot was high in placenta. This PGDH was localized throughout the syncytiotrophoblast at the fetal-maternal interface and also in extravillous trophoblast cells. The presence of PGDH at this site acts to stabilize output of primary PG from the placenta and also as a barrier preventing transfer to the fetal circulation, resulting in the separation of PG homeostasis in the fetus and mother.

Expression of prostaglandin H synthase isoforms in human myometrium at parturition

OBJECTIVE

The purpose of this study was to identify the isoforms and splicing patterns of prostaglandin H synthase present in pregnant human lower-segment myometrium and determine whether there is differential expression of the isoforms or splice variants with respect to gestational age or parturition.

STUDY DESIGN

Lower-segment myometrium was collected at cesarean section at term (>37 weeks) or preterm (<37 weeks) from patients who were or were not in labor. Total messenger ribonucleic acid was isolated and reverse transcribed. Polymerase chain reaction for prostaglandin H synthase isoforms 1 and 2 and calponin were performed. Primers designed to characterize the splicing patterns of exon 9 of prostaglandin H synthase-1 were used.

RESULTS

The predominant polymerase chain reaction product in all samples corresponds to prostaglandin H synthase-1 messenger ribonucleic acid spliced to include exon 9, but a less-abundant polymerase chain reaction product corresponding to prostaglandin H synthase-1 messenger ribonucleic acid spliced at the internal donor site of exon 9 was also detected. Prostaglandin H synthase-2 messenger ribonucleic acid was detected in human myometrium at a lower abundance than prostaglandin H synthase-1, and neither prostaglandin H synthase-1 or prostaglandin H synthase-2 messenger ribonucleic acid expression changed significantly with gestational age or labor.

CONCLUSION

Both prostaglandin H synthase-1 and prostaglandin H synthase-2 isoforms are present in human myometrium. The prostaglandin H synthase-1 messenger ribonucleic acid that includes all of exon 9 encodes the predominant prostaglandin H synthase-1 isoform present in human myometrium. No significant alterations in the expression or splicing patterns for prostaglandin H synthase-1 were detected with respect to gestational age or the onset of labor; but prostaglandin H synthase-1 expression appeared higher at term in anticipation of labor. Although prostaglandin H synthase-2 is present in human myometrium, induction of prostaglandin H synthase-2 does not occur in lower-segment myometrium at parturition.

Reduced production of PGE2 and PGF2 alpha from decidual cell cultures supplemented with N-3 polyunsaturated fatty acids

A diet rich in n-3 polyunsaturated fatty acid (PUFA) may reduce the intrauterine production of prostaglandins and prolong pregnancy. We tested this hypothesis by assessing the influence of various PUFAs on the spontaneous production of PGE2 and PGF2 alpha from decidual cell cultures. In addition, we assessed prostaglandin and cytokine production stimulated by lipopolysaccharides (LPS) in order to mimic parturition where infection is involved. In both settings, we found that after supplementing with n-3 PUFA, PGE2 and PGF2 alpha were significantly reduced. After supplementing with n-6 PUFA, there was a significant increase in both prostaglandins. Both n-3 and n-6 PUFAs reduced the production of interleukin 1 (IL-1), while n-6 PUFAs reduced TNF production. PUFAs did not influence IL-6 production. Our findings support the hypothesis that dietary n-3 PUFA may prolong pregnancy by reducing intrauterine production of prostaglandins.

Detection of acyl-CoA synthetase, acyl-CoA:lysophospholipid acyltransferase and phospholipase A2 activities in non-pregnant and pregnant guinea-pig uterine tissues

Acyl-CoA synthetase (ACS), acyl-CoA:lysophospholipid acyltransferase (ACLAT) and phospholipase (PL) A2 activities were detected in guinea-pig endometrium on days 7 and 15 of the cycle, and on days 15, 29 and 36 of pregnancy. Ovariectomy of non-pregnant animals resulted in an increase in the apparent activities of these three enzymes which was reversed by treatment with oestradiol and/or progesterone. ACS, ACLAT and PLA2 activities were detected in day 15 conceptuses, and in the placenta, sub-placenta, chorion and amnion on days 29 and 36 of pregnancy. Apparent activities of the enzymes were generally higher in the fetal membranes than in the placental tissue. This study has established that the enzymes involved in turnover of arachidonic acid in phospholipids are present in tissues in the non-pregnant and pregnant guinea-pig uterus. The higher apparent activities of enzymes (ACS and ACLAT) involved in arachidonic acid uptake compared to the enzyme (PLA2) involved in arachidonic acid release is in agreement with there being very low concentrations of free arachidonic acid in tissues.

Cytokine and prostaglandin production by amnion cells in response to the addition of different bacteria

OBJECTIVE

Our goal was to evaluate the effect of Escherichia coli, Bacteroides fragilis, Mycoplasma hominis, and Staphylococcus aureus on cytokine and prostaglandin production by amnion cells in vitro.

STUDY DESIGN

Amnion cells were obtained from women undergoing elective cesarean section before the onset of labor and cultured in a primary cell culture. Confluent amnion cells were incubated with heat-inactivated bacteria in different concentrations (10(1) to 10(6) colony-forming units/ml) for 48 hours. Samples for quantification of interleukin-1 beta, interleukin-6, interleukin-8, tumor necrosis factor-alpha, and prostaglandin E2 were collected at 6, 12, 24, and 48 hours.

RESULTS

Under basal conditions, minor amounts of interleukin-6 and interleukin-8 were detectable. Incubation of amnion cells with E. coli enhanced the secretion of interleukin-8 and also induced an transient increase of prostaglandin E2 in a dose-dependent manner. B. fragilis produced an increase in the secretion of interleukin-6 and interleukin-8. M. hominis and S. aureus did not cause an increase in either interleukin-6, interleukin-8, or prostaglandin E2.

CONCLUSION

The gram-negative bacteria E. coli and B. fragilis stimulated interleukin-6 and interleukin-8 to a greater degree than the other bacteria investigated in this study. This finding may be of clinical interest in the onset of preterm birth.

Interleukin-1 beta induces the synthesis and activity of cytosolic phospholipase A2 and the release of prostaglandin E2 in human amnion-derived WISH cells

The objective of this study was to examine the expression and activity of cytosolic phospholipase A2 (cPLA2) in relation to prostaglandin E2 (PGE2) synthesis in human amnion-derived WISH cells in response to stimulation by interleukin-1 beta (IL-1 beta). cPLA2 activity was characterized by sensitivity to heat and acid treatment, stability to dithiothreitol, and inhibition by the specific inhibitor, arachidonyl trifluoromethyl ketone (AACOCF3). Treatment of WISH cells with IL-1 beta (0.01-1 ng/mL) for up to 24 h resulted in a significant increase in PGE2 release in a concentration- and time-dependent manner accompanied by increases both in total cellular cPLA2 activity and in cPLA2 protein levels detected by Western blot analysis. The parallel increase in total cellular cPLA2 activity and cPLA2 protein level indicates that IL-1 beta may induce the synthesis of cPLA2. Incubation of the cells with 10 microM AACOCF3 for 24 h significantly inhibited IL-1 beta-induced PGE2 production strongly suggesting that cPLA2 mediates IL-1 beta-induced PGE2 formation. In unstimulated cells, there is appreciable total cellular cPLA2 activity and protein, but these cells produce low amounts of PGE2 until stimulated by IL-1 beta, suggesting that cPLA2 translocation from cytosol to the membrane is necessary for its bioactivity. In contrast to IL-1 beta, treatment with phorbol ester (12-O-tetradecanoyl phorbol-13-acetate, TPA, 10(-10)-10(-6)M) for 24 h significantly inhibited total cellular cPLA2 activity in a concentration-dependent manner. The amount of total cellular cPLA2 protein seen on Western blot remained unchanged following TPA treatment. These data suggest that in WISH cells, IL-1 beta induces both translocation to the membrane and de novo synthesis of cPLA2 protein to sustain prostaglandin (PG) synthesis. In contrast, TPA may only cause cPLA2 translocation but no increase in cPLA2 protein synthesis, resulting in limited PG synthesis. Our results provide a mechanism for the effect of IL-1 beta on prostaglandin synthesis in human amnion cells and provide support for a role of cPLA2 in the mechanism initiating human parturition.

New biological and clinical roles for the n-6 and n-3 fatty acids

Four new findings of the biochemistry and biology of the essential n-6 and n-3 fatty acids have recently been demonstrated. These findings will augment current knowledge as to the role of the essential fatty acids in human health.

Uterine electromyography: a critical review

On the basis of a literature review, this work summarizes uterine animal and human electromyographic information obtained at cellular, myometrial, and abdominal levels during gestation and parturition. We show that both internal and external electromyograms occur in phase with intrauterine pressure increase and exhibit similar spectra, including a slow wave (0.01 < frequency < 0.03 Hz) probably because of mechanical artifacts and a fast wave whose frequency content can be subdivided into a low-frequency band always present in every contraction and a high-frequency band related to efficient parturition contractions. Application of classic spectral techniques to electromyogram envelopes has identified group propagation but not pacemaker areas. However, no time delay or classic propagation has been demonstrated by applying the same spectral techniques to the electromyogram itself, probably because of the nonlinearity and three-dimensional nature of the propagating process.

Mechanism of interleukin-1 beta stimulation of human amnion prostaglandin biosynthesis: mediation via a novel inducible cyclooxygenase

We have evaluated the mechanism by which interleukin-1 beta (IL-1 beta) increases amnion cell PGE2 production in a concentration-dependent manner. IL-1 beta-stimulated amnion cell PGE2 biosynthesis was time-dependent, and significant stimulation occurred within 2 h of incubation. IL-1 beta stimulation occurred in the presence of added arachidonic acid but was abrogated by treatment with cycloheximide and actinomycin D. Amnion cells treated with IL-1 beta recovered rapidly from aspirin pretreatment suggesting an action on fatty acid cyclooxygenase (COX). Increased amounts of COX protein were demonstrated by Western blot analysis within 2 h of IL-1 beta treatment of amnion cells. Northern blot analysis using a probe specific for a novel form of COX (COX-II) showed an increase in mRNA for this COX within 30 min. This finding using a homologous detection system and human cells of fetal origin in primary culture provides strong support for a physiological role for COX-II in man.

Eicosanoid production by intrauterine tissues before and after labor in short-term tissue culture

Prostanoid production by intrauterine tissues from pregnant and non-pregnant women has been studied intensively over the last decade. Little is known about the lipoxygenase metabolites of arachidonic acid (AA). The production of prostaglandins and HETEs by pregnancy specific human tissues was investigated in a short-term culture system. Tissue samples were obtained after uncomplicated pregnancies from placenta, fetal membranes and decidua of deliveries before (n = 6) and after the onset of labor (n = 8) and incubated for 1 hour in oxygenated HBSS. In the supernatant, PGE2, PGF2 alpha, 6-keto-PGF1 alpha and TXB2 were measured with RIA and 15-, 12- and 5-HETE with HPLC and UV-detection. The main AA-metabolite in all tissue incubations was 12-HETE. Decidua produced 12 to 28 times more prostaglandins than placenta and fetal membranes with 6-keto-PGF1 alpha as the main metabolite. The main cyclooxygenase derivative measured from placenta and fetal membrane incubations was TXB2. After labor, fetal membranes showed an increase in total prostaglandin (significant for PGE2) and a decrease in HETE synthesis. The physiologic significance of 12-HETE in reproduction is still poorly understood, but a shift in AA metabolism from HETEs to prostaglandins may be involved in the initiation of labor. Furthermore, these results point to different roles of the tissue compartments within the pregnant uterus for the parturition process.

Decrease in annexin I messenger ribonucleic acid expression in human amnion with labor

OBJECTIVE

Annexins are a superfamily of proteins that are thought to inhibit phospholipase A2 activity and hence inhibit prostaglandin production. The purpose of this study was to test the hypothesis that annexin I concentration in human amnion is reduced with labor and that this reduction is mediated by a decrease in annexin I messenger ribonucleic acid expression.

STUDY DESIGN

Amnion and choriodecidua were collected from term singleton pregnancies, eight after spontaneous vaginal delivery and eight from elective cesarean section without labor. Annexin I protein was quantitated by Western blotting. Ribonucleic acid was isolated from amnion, and then annexin I messenger ribonucleic acid was identified by Northern hybridization and quantitated by slot blotting.

RESULTS

Annexin I (35 kd) was identified in amnion tissue. The concentration in the group undergoing labor (320 +/- 45 integrated optical density units, mean +/- SE) was significantly reduced (p < 0.05) compared with that in the group not undergoing labor (635 +/- 65 units). The size of the annexin I messenger ribonucleic acid was approximately 1.8 kb. The mean integrated optical density for the labor group (840 +/- 139 units, mean +/- SE) was significantly reduced (p < 0.05) compared with that of the nonlabor group (1912 +/- 464 units).

CONCLUSION

There is a significant decrease in annexin I messenger ribonucleic acid expression in human amnion with labor, corresponding to a significant decrease in annexin I protein concentration. This may contribute to the increased phospholipase A2 activity, arachidonic acid mobilization, and prostaglandin production at labor in humans.

Prostaglandins and teleost neurohypophyseal hormones induce premature parturition in the guppy, Poecilia reticulata

Administration of PGE2, PGF2 alpha, isotocin, and vasotocin to pregnant guppies during late gestation induced premature parturition. Indomethacin (10 micrograms/g body wt), the cyclooxygenase inhibitor, did not inhibit parturition at term, suggesting that some lipoxygenase metabolites may be involved in the induction of parturition. Pituitary extract, as well as LH-RH, did not induce premature parturition. It may be that in the guppy, in which ovulation occurs at the end of gestation just prior to parturition, gonadotropin is not involved in the induction of ovulation and parturition.

Pre-induction intracervical application of a highly viscous prostaglandin E2 gel in pregnant women with an unripe uterine cervix: a double-blind placebo-controlled trial

Intracervical application of prostaglandin E2 (PGE2) gel has shown to be an effective method for pre-induction cervical ripening in pregnant women with an unripe uterine cervix. Side effects are minimal, provided that the instillation is carefully restricted to the cervical canal. This requires--apart from a proper technique--an optimal gel formulation. For this reason a newly developed highly viscous PGE2 gel was evaluated in a randomized, double-blind, placebo-controlled multicentre trial. Within a 9-h study period, successful cervical ripening (increase in Bishop score to 6 or more) was achieved in 39 (56%) of the 70 patients in the PGE2 groups and in 23 (34%) of the 68% patients in the placebo group (P = 0.04). During the first 12 h after gel application, 25 (35%) of the women in the PGE2 group and 2 (3%) in the placebo group had a spontaneous delivery. No serious adverse reactions were observed. The data suggest that the use of this highly viscous PGE2 gel may be advantageous if strictly intracervical application is the primary objective.

Corticotrophin-releasing hormone production by the placenta and fetal membranes

Maturation of the fetal hypothalamic-pituitary-axis may be an important factor in the stimulation of the onset of parturition. Recent studies have found that corticotrophin-releasing hormone (CRH), the hypothalamic component of this axis is also present in the placenta and the fetal membranes. We review the evidence demonstrating that glucocorticoids stimulate the production of CRH by these tissues towards term, and this is manifest by increases in CRH concentrations in maternal and fetal plasma and in placental extracts, and by increased abundance of CRH mRNA in the placenta. We discuss how CRH secretion by the placenta and fetal membranes is controlled. We hypothesize that CRH may be an important signal in initiating of the onset and maintenance of term labour and may also be a factor in the etiology of premature labour, through stimulation of the fetal HPA axis, and through paracrine/autocrine interactions within the placenta, fetal membranes and decidua.

Prostaglandin production by amnion and decidual cells in response to bacterial products

Media from bacterial cultures have been tested for actions on prostaglandin biosynthesis by human amnion and decidual cells. The bacterial species, which are commonly associated with intrauterine infections, were Group B streptococcus, Escherichia coli, Fusobacterium nucleatum, Bacteroides fragilis, Gardnerella vaginalis, Neisseria gonorrhea, Mycoplasma hominis and Ureaplasma urealyticum. Overall, low doses of bacterial products were stimulatory of amnion prostaglandin production, whereas high doses were inhibitory. A similar pattern of results was obtained for effects on decidual prostaglandin production, although stimulatory actions at low doses were less pronounced. In all experiments interleukin 1 beta consistently induced a stimulation of prostaglandin production that greatly exceeded that caused by any bacterial product. It is possible that the inhibitory action of high doses of bacterial products on prostaglandin biosynthesis may contribute to the poor course of labor experienced by women with chorioamnionitis. Furthermore, these data lend credence to the view that the host response to infection (i.e. cytokine secretion) is the major mediator of subsequent preterm labor.

Dipalmitoylphosphatidylcholine (L-alpha-lecithin) stimulates phospholipase A2 activity in human amnion

In order to investigate the mechanism of dipalmitoylphosphatidylcholine (DPPC, L-alpha-lecithin) stimulation of the prostaglandin E (PGE) production of the amniotic membrane, effects of DPPC (50-800 micrograms/ml) on phospholipase A2 (PLA2), phospholipase C (PLC), PG endoperoxide synthase, and PGE synthase activities of human amniotic membrane were studied. Only PLA2 activity was increased by DPPC, suggesting that lecithin, the major surfactant component, increases the PGE production of the amniotic membrane by activating PLA2.