Topographical distribution of prostaglandin E receptors in human myometrium

Arachidonic acid induces production of 17,20β-dihydroxy-4-pregnen-3-one (DHP) via a putative PGE2 receptor in fish follicles from the Eurasian perch

The effects of docosahexaenoic, eicosaenoic and arachidonic acids (DHA, EPA and ARA, respectively) on sex-steroid and prostaglandin (PG) production were investigated in Eurasian perch (Perca fluviatilis) follicles using an in- vitro incubation technique. Only ARA was able to induce the production of 17,20β-dihydroxy-4-pregnen-3-one (DHP), the hormone produced by vitellogenic follicles undergoing final meiotic maturation, as well as the production of PGE2 and PGF2α by the follicles. This work also investigated, using a preliminary pharmacological approach, the presence of a functional PGE2-like receptor in fish follicles. Exogenous PGE2 and butaprost (specific agonist of the EP2 receptor) stimulated DHP production. A second experiment assayed the cyclic adenosine monophosphate (cAMP) production by the follicles after 24 h of incubation with the agonist and antagonist of the EP2 receptor. As observed in mammals, we concluded that the cAMP produced in response to PGE2 was probably mediated by an intracellular mechanism via a PGE2-like receptor. This is the first pharmacological indication of this type of receptors in fish follicles. This study also indicates that ARA, and its derivatives, PGE2 and PGF2α, may act on final follicle maturation in Eurasian perch.

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.

Endocrine regulation of menstruation

In women, endometrial morphology and function undergo characteristic changes every menstrual cycle. These changes are crucial for perpetuation of the species and are orchestrated to prepare the endometrium for implantation of a conceptus. In the absence of pregnancy, the human endometrium is sloughed off at menstruation over a period of a few days. Tissue repair, growth, angiogenesis, differentiation, and receptivity ensue to prepare the endometrium for implantation in the next cycle. Ovarian sex steroids through interaction with different cognate nuclear receptors regulate the expression of a cascade of local factors within the endometrium that act in an autocrine/paracrine and even intracrine manner. Such interactions initiate complex events within the endometrium that are crucial for implantation and, in the absence thereof, normal menstruation. A clearer understanding of regulation of normal endometrial function will provide an insight into causes of menstrual dysfunction such as menorrhagia (heavy menstrual bleeding) and dysmenorrhea (painful periods). The molecular pathways that precipitate these pathologies remain largely undefined. Future research efforts to provide greater insight into these pathways will lead to the development of novel drugs that would target identified aberrations in expression and/or of local uterine factors that are crucial for normal endometrial function.

Cyclooxygenase enzymes and prostaglandins in reproductive tract physiology and pathology

Prostaglandins, thromboxanes (TX) and leukotrienes, collectively referred to as eicosanoids, are cyclooxygenase (COX) metabolites of arachidonic acid (AA). Prostaglandins, have been recognised for many years as key molecules in regulating reproductive tract physiology and pathology. Numerous recent studies in in vitro model systems and knockout mouse models have demonstrated specific functional roles for the respective cyclooxygenase enzymes, prostaglandins and prostanoid receptors. Here we review the findings obtained in several of these studies with emphasis on the roles played by cyclooxygenase enzymes and prostaglandins, specifically prostaglandin E2 (PGE2) and F2alpha in reproductive tract physiology and pathology.

Cyclooxygenase-2 overexpression inhibits cathepsin D-mediated cleavage of plasminogen to the potent antiangiogenic factor angiostatin

Overexpression of cyclooxygenase (COX)-2 and enhanced synthesis of prostaglandin E2 (PGE2) have been implicated in human endometrial pathologies. To investigate the molecular role of COX-2, the Ishikawa human endometrial epithelial cell line was stably transfected with the pIRES2 vector containing COX-2 cDNA in either the sense or antisense directions. PGE2 concentrations were significantly elevated in the cells transfected with the COX-2 sense compared with wild-type cells or cells transfected with the antisense cDNA (P < 0.01). Elevated PGE2 synthesis was associated with enhanced expression and signaling of PGE2 receptors (EP). cDNA array analysis revealed differential expression of cathepsin D between the COX-2 sense and antisense cells. Cathepsin D RNA and protein expression was 6.7- and 2.1-fold lower in the COX-2 sense compared with COX-2 antisense cells respectively. Cathepsin D is known to cleave plasminogen to the potent antiangiogenic factor angiostatin. To investigate differential angiostatin generation, conditioned media from COX-2 sense, COX-2 antisense and wild-type cells were incubated with plasminogen and subsequently subjected to Western blot analysis. In comparison to wild-type cells, the cleavage of plasminogen to angiostatin was abolished when incubated in COX-2 sense cells conditioned media and elevated when incubated in COX-2 antisense cells conditioned media. Coincubation of plasminogen with the cathepsin D inhibitor pepstatin A inhibited the cleavage of plasminogen to angiostatin in the COX-2 antisense conditioned media. These data demonstrate that COX-2 exerts a negative feedback on the expression of cathepsin D. This in turn reduces the generation of the antiangiogenic factor angiostatin, hence promoting a proangiogenic environment.

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.

Cyclooxygenase enzymes and prostaglandins in pathology of the endometrium

Prostaglandins are bioactive lipids produced from arachidonic acid by cyclooxygenase (COX) enzymes and specific terminal prostanoid synthase enzymes. After biosynthesis, prostaglandins exert an autocrine-paracrine function by coupling to specific prostanoid G protein-coupled receptors to activate intracellular signalling and gene transcription. For many years, prostaglandins have been recognized as key molecules in reproductive biology by regulating ovulation, endometrial physiology and proliferation of endometrial glands and menstruation. More recently, a role for COX enzymes and prostaglandins has been ascertained in reproductive tract pathology, including carcinomas, menorrhagia, dysmenorrhoea and endometriosis. Although the mechanism by which prostaglandins modulate these pathologies is still unclear, a large body of evidence supports a role for COX enzymes, prostaglandins and prostaglandin receptor signalling pathways in angiogenesis, apoptosis and proliferation, tissue invasion and metastases and immunosuppression. Here, an overview is provided of some of the findings from these studies with specific emphasis on the role of COX enzymes, prostaglandin E(2) and F(2alpha) in disorders of endometrial proliferation and menstruation in non-pregnant women.

Tumor necrosis factor alpha stimulates adenylyl cyclase activity in human myometrial cells

Cytokines such as tumor necrosis factor alpha (TNFalpha) have been implicated in amniotic fluid infections and preterm and term labor. The underlying mechanisms are incompletely understood. In some smooth muscle cells, TNFalpha affects function of the beta-adrenergic/adenylyl cyclase pathway. The present study was performed to examine the effects of chronic TNFalpha exposure on adenylyl cyclase activity in cell cultures of human myometrium. Chronic TNFalpha exposure led to a dose- and time-dependent increase in basal-, GTP-, NaF-, and forskolin-stimulated adenylyl cyclase (AC) activity. The increase in AC activity was not mediated by changes in the expression of the heterotrimeric G proteins G(s)alpha or G(i)alpha as determined by immunoblotting. In addition, increases in AC activity occurred in the presence of indomethacin, indicating that these changes were not provoked by TNFalpha-induced changes in prostaglandin production. The present results suggest that TNFalpha-induced increases in AC activity in human myometrial cells obtained from the lower uterine segment occur at the level of G-protein/AC interaction or at the level of the AC enzyme itself.

Interleukin-1beta induces glycosaminoglycan synthesis via the prostaglandin E2 pathway in cultured human cervical fibroblasts

The aim of this study was to identify, in cultured human cervical fibroblasts, the mechanisms by which interleukin (IL)-1beta induces the synthesis of glycosaminoglycans (GAG) and to explore the putative role of prostaglandin E(2) (PGE(2)) in this process. Exposure of the cells for 24 h to IL-1beta induced a significant (P < 0.05) dose-dependent increase in GAG synthesis. IL-1beta (1 ng/ml) induced the expression of cyclooxygenase-2 (COX-2) protein 6 h after treatment, accompanied by a 7.5-fold increase in PGE(2) production. We confirmed that NS398, a selective COX-2 inhibitor, dose-dependently blocked PGE(2) augmentation following IL-1beta treatment. AH23848, the selective EP(4) receptor antagonist, completely abolished IL-1beta-induced GAG synthesis, whereas AH6809, an EP(2) receptor antagonist, had no effect on the stimulatory effects of IL-1beta. Furthermore, we demonstrated that 6 h exposure to IL-1beta induced a notable increase in EP(4) receptor mRNA expression and a decrease in EP(1) receptor mRNA but had no effect on the expression of EP(2) and EP(3) receptor transcripts. In conclusion, these findings indicate that IL-1beta not only induced GAG synthesis by increasing COX-2 protein expression and the subsequent PGE(2) production but also enhanced the responsiveness of cervical fibroblasts to PGE(2) by selectively up-regulating EP(4) receptor mRNA expression. These results suggest that PGE(2) may regulate human cervical ripening in an autocrine/paracrine manner via EP(4) receptors.

Formation of proinflammatory cytokines in human term myometrium is stimulated by lipopolysaccharide but not by corticotropin-releasing hormone

Human term myometrium is poorly characterized as a source of proinflammatory mediators involved in parturition. We have investigated the basal expression of cytokines in myometrium, as well as the effects of CRH and lipopolysaccharide (LPS) on cytokine release. Explants from term myometrium were challenged with CRH or LPS (1 microg/mL each) in short-term tissue culture. Interleukin (IL)-1beta++, IL-6, IL-8, and tumor necrosis factor (TNF)alpha concentrations in the medium were quantified by enzyme immunoassay. The major cytokines released after 24 h were IL-6 and IL-8. All cytokines investigated were stimulated significantly by LPS (P: < 0. 05) but not by CRH. Messenger RNA levels of these cytokines were investigated by RT-PCR. IL-1beta+ and IL-6 messenger RNA were present in preterm and term myometrium before and during labor, whereas IL-8 and TNFalpha were expressed only by myometrium in active labor. Furthermore, myometrial CRH receptors and macrophages were characterized immunohistochemically. We conclude that human term myometrium is a site of production of proinflammatory cytokines and is involved in the inflammation-like reactions mediating the birth process. Cytokine release in term myometrium seems not to be under control of CRH.

The ovarian and cervical regions of the rat uterus display a different contractile response to serotonin and prostaglandin F2alpha. I. The estrous cycle

In pharmacological studies using isolated tissues, the sensitivity to different agonists may vary depending on the anatomical region. The aim of the present study was to evaluate the in vitro contractile response to serotonin, prostaglandin F2alpha, and oxytocin of the ovarian and the cervical uterine segments isolated from rats in the four different stages of the rat estrous cycle. Non-cumulative curves were recorded for both, the ovarian and the cervical uterine segments. The cervical portion displayed a higher contractile response to serotonin and a lower response to PGF2alpha than the ovarian portion. Oxytocin induced similar responses in both uterine segments. The uterine ovarian segment displayed a similar sensitivity to serotonin in all the estrous cycle stages, whereas in the cervical segment, influenced by estrogens in diestrus and proestrus, an increase in contractility was observed. According to these findings, serotonin might participate in the spermatozoa transport toward the oviduct. The higher response of the ovarian portion to prostaglandin F2alpha is in line with its role during labor and delivery.

Preterm labour

Spontaneous preterm labour remains a major obstetric problem because of the high incidence of neonatal mortality or long-term handicap associated with it. The drugs available for the management of preterm labour are poorly effective and have potentially serious side-effects for the mother or fetus. In recent years, there has been a remarkable increase in the knowledge of the biochemical mechanism underlying uterine quiescence and contractility. Many of the G protein-coupled receptors that participate in the regulation of myometrial activity have been cloned and characterized, and their intracellular signalling pathways have been elucidated. The role of G protein receptor kinases in uterine tachyphylaxis is better understood. New developments in our understanding of the cellular mechanisms involved in uterine contractions in idiopathic and infection-associated preterm labour are expected, which will lead to better, more selective therapy for this problem. However, much research remains to be done before the mechanism of human parturition is fully understood.

The differential expression of myometrial connexin-43, cyclooxygenase-1 and -2, and Gs alpha proteins in the upper and lower segments of the human uterus during pregnancy and labor

There is evidence from many studies indicating that a number of specific quiescent and contractile associated proteins are temporally regulated in the myometrium during pregnancy. In this present investigation we provide data that strongly suggest that myometrial connexin-43, cyclooxygenase-1 and -2 (COX-1 and -2), and Gs alpha proteins are also spatially expressed within the human uterus during pregnancy and labor. Using paired lower and upper segment myometrial samples taken from individual women at term and during spontaneous labor, we have measured the expression of these proteins by immunoblotting with specific antibodies. We report that the myometrial gap junction connexin-43 protein is expressed at much greater levels in the upper uterine compared to the lower uterine segment and that this difference is even more pronounced during the course of labor. Conversely, myometrial COX-1 and -2 proteins appear to be expressed at much greater levels in the lower compared to the upper uterine segment. Moreover, the level of expression of both proteins is unaffected by the onset of parturition. In contrast, myometrial Gs alpha protein appears to be uniformly expressed in both lower and upper segments and is similarly down-regulated during parturition, as previously reported. The differential expression of COX-1 and -2 and connexin-43 in the uterus may allow cervical ripening before and dilatation during labor and facilitate effective propagation of contractions from fundus to cervix, which may be further facilitated by the down-regulation of Gs alpha at the onset of parturition.

Prostaglandin-induced changes and the influence of cyclo-and lipoxygenase inhibitors on the uterine collagen concentration in late pregnancy in rats

During late pregnancy, the influence of PGF2 alpha and PGE2 on the collagen concentration in a rat's uterus was analysed. In order to evaluate the influence of endogenous prostaglandins and leukotrienes on connective tissue metabolism, a cyclooxygenase inhibitor (Diclofenac) and a dual cyclo-and 5-lipoxygenase inhibitor (BW755C) were administered prior to the collection of samples. Total collagen and its soluble fraction as well as water content were determined in the uteri in a population of 58 pregnant rats treated with PGF2 alpha (n = 16), PGE2 (n = 11), Diclofenac (n = 11), BW755C (n = 7) and controls (n = 13). The most evident changes in tissue hydration and collagen concentration were observed in the PGF2 alpha and Diclofenac treated groups. The results clearly show the affinity of PGF2 alpha to the uterus and the role of endogenous PGs in the maintenance of pregnancy by influencing connective tissue metabolism.

Preterm labour: a pharmacological challenge

Preterm labour is a major cause of perinatal mortality and morbidity, but its prevention is difficult because most of the available drugs lack uterine selectivity and have potentially serious side-effects for the mother or the foetus. In this article, Andrés López Bernal and colleagues discuss new evidence that shows pregnancy is associated with changes in G protein signalling and second messenger formation in human myometrium. During gestation uterine relaxation is favoured by a pronounced increase in G alpha s levels, thereby facilitating the effect of agonists that increase cAMP formation. The change in G alpha s is reversed in spontaneous labour enabling the uterus to become responsive to contractile agents. Although it is not established that these changes in G protein function are causally related to the spontaneous onset of labour, nevertheless they provide a novel viewpoint towards increased understanding of the cellular mechanisms of uterine contractility, which may result in better drugs for the management of preterm labour.

Modulation of human myometrial PGE2 receptor by GTP characterization of receptor subtype

We studied PGE2 specific binding sites in human myometrial microsomes prepared from uterine specimens obtained by hysterectomy (women between 38 and 55 years of age). Competition experiments showed that the potency order for various prostaglandins (PGs) was: PGE2 > or = PGE1 >> PGF2 alpha > Iloprost > or = Carbacyclin >> ZK 110841 (PDG2 analogue). These relative affinities indicated that the receptor was of the EP type. In kinetic experiments GTP, GppNHp and GTP gamma S increased the rate of PGE2 binding (steady state was reached more rapidly in the presence of nucleotides) but maximal specific binding was not significantly different. Complete dissociation could not be obtained, even in the presence of GTP. Only 50% of maximal binding was readily dissociable. The dissociation rate was 4.56.10(-4) sec-1 (half time of about 660 sec) and in the presence of GTP analogues it was slightly increased (k-1 = 7.16 10(-4) sec-1, half time 420 sec.). Scatchard analysis of saturation curves showed an increase in ligand receptor affinity in the presence of GTP or nucleotide analogues: the Kd shifted from 9.66 +/- 2.8.10(-9) M to 4.96 +/- 1.25.10(-9) M, but the number of binding sites did not change significantly (310 +/- 37 to 350 +/- 17 fmol/mgP). The effect of GTP was observed at a concentration of 5.10(-4)M. GppNHp and GTP gamma S were effective at 1.10(-5) M. Pretreatment of myometrial membranes with pertussis or cholera toxins had no effect on PGE2 binding to membrane sites. Our conclusion is that GTP induced conversion of a population of low affinity sites into a population of higher affinity sites. This effect of guanine nucleotides was described in adipocytes and kidney medulla. Competition studies with PGE2 analogues (sulprostone, 17-phenyl-omega-trinor PGE2, M&B 28,767, misoprostol, butaprost) showed that this receptor mediates a contractile response and is probably an EP3 subtype.

Biochemistry and physiology of preterm labour and delivery

Human parturition is associated with profound changes in uterine connective tissue affecting mainly the cervix, but the endocrine control of cervical ripening remains obscure. Connective tissue changes are also implicated in premature rupture of the membranes, a problem often associated with preterm delivery, and it is believed that local inflammatory infiltration may play a role in both this condition and cervical ripening, but it is difficult to define which changes precede parturition and which are a consequence of the trauma of labour. Chorioamnionitis can cause preterm labour by provoking the release of inflammatory mediators in the decidua/fetal membranes area and it is likely that activation of prostaglandin release by decidual macrophages is involved in triggering labour. However, the role of macrophages and other bone marrow derived cells in normal labour and in labour associated with chorioamnionitis needs to be defined. It is likely that treatment with a combination of antibiotics and prostaglandin synthase inhibitors and/or other anti-inflammatory drugs is the most appropriate therapeutic approach. Idiopathic preterm labour and spontaneous labour at term are probably due to changes in the sensitivity of the myometrium to endogenous agonists. Recent progress in cell signalling pathways, such as the characterization of regulatory G proteins and the cloning of hormone receptors, should clarify the mechanism of action of relaxing and contracting agents on myometrial cells and should provide the means for the development of new therapeutic agents of high effectiveness and selectivity. This approach should result in better management of both term and preterm labour.

In vitro characterization of prostanoid receptors on human myometrium at term pregnancy

1. Prostanoid receptors present on the pregnant human myometrium in vitro have been characterized according to the receptor classification proposed by Coleman et al. (1984) using natural prostanoids and synthetic, selective analogues and antagonists where available. 2. Prostaglandin E2 (PGE2) produced a biphasic effect consisting of an initial excitation followed by a dose-related inhibition. The EP2/EP3-receptor agonists, rioprostil and misoprostol, produced similar effects to PGE2, however, the excitatory event of the misoprostol response was related to dose. The EP1/EP3-receptor agonist, sulprostone, evoked a purely excitatory response which was unaffected by AH6809. The selective EP2-receptor agonist butaprost produced a long-lasting dose-dependent inhibition of activity. The results from these prostanoids indicated that inhibitory EP2- and excitatory EP3-receptors are present on myometrium from pregnant donors at term. 3. PGF2 alpha and the synthetic FP-receptor agonist, fluprostenol, caused equipotent excitatory effects, indicating the presence of contractile FP-receptors. 4. PGD2 produced a biphasic effect of which the inhibition appeared dose-related and was antagonized by the selective DP-receptor antagonist BW A868C. The selective DP-receptor agonist, BW245C, produced a potent inhibitory effect that was competitively antagonized by BW A868C (pA2 = 8.6). 5. PGI2 produced a biphasic response qualitatively similar to PGE2. The EP1/IP-receptor agonist, iloprost, produced an occasional unquantifiable excitation and dose-related inhibition. The selective IP-receptor prostanoid, cicaprost, evoked only an inhibitory response. 6. The stable thromboxane A2 (TXA2)-mimetic, U46619, produced potent excitation which was competitively antagonized by the TP-receptor antagonist, GR32191 (pA2 = 7.2). 7. The prostanoids tested indicate that a heterogeneous population of prostanoid receptors are presen ton human myometrium from pregnant donors. It may be concluded that excitation is EP3-, FP- and TP-receptor-mediated and inhibition is EP2-, DP- and IP-receptor-mediated. Comparison of data obtained from non-pregnant specimens indicates that the lower segment tissue from pregnant donors demonstrated more pronounced responses to EP2 and IP-receptor activation.

In vitro characterization of prostanoid FP-, DP-, IP- and TP-receptors on the non-pregnant human myometrium

1. Prostaglandin F (PGF), PGD, PGI and thromboxane A2 (TXA2) receptors have been pharmacologically characterized on the non-pregnant human myometrium in vitro in accordance with the receptor classification proposed by Coleman et al. (1984). The tools for the classification include both natural prostanoids, synthetic, selective analogues and antagonists where available. 2. The potent excitatory actions of the natural FP-receptor prostanoid, PGF2 alpha, and the synthetic analogue, fluprostenol, indicate the presence of FP-receptors mediating contraction on the human myometrium. 3. PGD2 produced a biphasic response consisting of excitation followed by relaxation of spontaneous activity of the myometrium. The selective DP-receptor agonists, BW245C, produced purely inhibitory responses illustrating the presence of inhibitory DP-receptors in this tissue. The inhibitory responses of both PGD2 and BW245C were antagonized by the competitive DP-receptor antagonist, BWA 868C, providing conclusive evidence for the existence of DP-receptors. 4. PGI2 produced a biphasic response similar to PGD2. Iloprost, the EP1/IP-receptor agonist also produced a biphasic response, whilst the IP-receptor selective agonist, cicaprost, caused inhibition only, suggesting that inhibitory IP-receptors exist in the non-pregnant human myometrium. 5. The TXA2-mimetic, U46619, produced marked stimulation of the non-pregnant human myometrium and was approximately equipotent to PGF2 alpha and fluprostenol in this effect. The actions of U46619 were competitively antagonized by the TP-receptor antagonist GR32191 showing that excitatory TP-receptors exist in this tissue.6. All prostanoids tested, both natural and synthetic, had activity on the non-pregnant human myometrium in vitro, supporting the existence of a heterogeneous population of prostanoid receptors in this tissue. If the results from the present study are combined with those previously reported for EP-receptor agonists (Senior et al., 1991), it may be concluded that excitation may occur through FP-, TP-, EP3- and few EP,-receptors, whereas inhibition may occur through DP-, IP- and EP2-receptors.

Prostaglandin E production by the fetal membranes in unexplained preterm labour and preterm labour associated with chorioamnionitis

The production of prostaglandin E (PGE) by amnion, choriodecidua and placenta was measured in 45 women delivered after spontaneous preterm labour, in 10 women delivered electively preterm, in 30 women at elective caesarean section at term, and in 28 women after spontaneous labour at term. In the preterm labour group 24 women had normal placental histology, and gestational age was 34 (31-36) weeks (median and range); 18 women had evidence of chorioamnionitis and gestational age was significantly shorter, 30 (24-36) weeks; three other patients had placental abruption. In the absence of inflammatory infiltration of these tissues the highest PGE output (fmol/mg dry weight/2 h) was found after labour at term and the lowest after uncomplicated preterm labour: 2640 (360-15,580) (median and range) compared with 1414 (164-11,045) in amnion, 677 (100-3245) compared with 308 (39-1086) in choriodecidua, and 1200 (520-3022) compared with 578 (150-1859) in placenta, respectively. Tissues showing chorioamnionitis produced much higher outputs of PGE from amnion (12,278, 1799-82,617) and from choriodecidua (1018, 216-11,768), but not from placenta (616, 89-4131). Chorioamnionitis seems to cause very early preterm labour by increasing PG production in the amnion and choriodecidua.

Are leukotrienes involved in human uterine contractility?

The effects of leukotrienes (LT) on the contractility of human and rat myometrial strips in vitro were compared with the effects of prostaglandins (PGs) and oxytocin. Preparations of human myometrial membranes were investigated for the presence and characteristics of LTC4 receptors. Neither the peptido-leukotrienes (LTC4, LTD4, LTE4) nor LTB4 had any consistent effect, stimulatory or inhibitory, on human pregnant or non-pregnant myometrium, at doses up to 1.25 microM; nor did they have any effect in rat non-pregnant myometrium. As expected, PGE2, PGF2 alpha (0.3 microM) and oxytocin (5 nM) stimulated human pregnant myometrium. PGF2 alpha stimulated and PGE2 inhibited human non-pregnant myometrium but oxytocin had no effect; all three compounds stimulated rat non-pregnant myometrium. The binding of 3H-LTC4 to human myometrium was specific (LTC4 greater than LTD4 much greater than LTE4, LTB4, PGE2, PGF2 alpha, arachidonic acid) but of low affinity compared with the binding of 3H-PGE2 to the same membrane preparations. These data support the view that leukotrienes have little direct influence on myometrial contractility.