ETA and ETB endothelin receptors in human myometrium characterized by the subtype selective ligands BQ123, BQ3020, FR139317 and PD151242

Control of endothelin-a receptor expression by progesterone is enhanced by synergy with Gata2

The endothelin-A receptor (Ednra) is involved in several physiological, pathological, and developmental pathways. Known for its function in vasoconstriction after being activated by endothelin-1, Ednra also controls cephalic neural crest cell development and appears to play a role in several pathologies, including cancer and periodontitis. However, the mechanisms regulating Ednra expression have not been identified despite its important functions. In this study, we investigated the role progesterone plays in Ednra gene expression in vivo and in vitro. In mice, pregnancy promotes Ednra expression in the heart, kidney, lung, uterus, and placenta, and the up-regulation is mediated by progesterone. We determined that the conserved region between -5.7 and -4.2 kb upstream of the mouse Ednra gene is necessary for the progesterone response. We also found that progesterone mediates Ednra activation through progesterone receptor B activation by its recruitment to PRE6, one of the 6 progesterone response elements found in that locus. However, gene activation by means of a GATA2 site was also necessary for the progesterone response. The Gata2 transcription factor enhances the progesterone response mediated by the progesterone receptor B. Together these results indicate that progesterone regulates Ednra expression by synergizing with Gata2 activity, a previously unknown mechanism. This mechanism may have an impact on pathologies involving the endothelin signaling.

Possible roles of oxytocin receptor and vasopressin-1α receptor in the pathomechanism of dysperistalsis and dysmenorrhea in patients with adenomyosis uteri

OBJECTIVE

To investigate the expression of oxytocin (OTR) and/or vasopressin (VP1αR) receptor in patients with and without adenomyosis uteri.

DESIGN

Retrospective nonrandomized study.

SETTING

University hospital endometriosis research center.

PATIENT(S)

Forty patients with histologically proven adenomyosis and 40 patients without adenomyosis who had undergone hysterectomy for dysmenorrhea, bleeding disorders, and fibroids.

INTERVENTION(S)

Immunohistochemical examination of both OTR and VP1αR expression in endometrium, myometrium, and adenomyotic lesions, and identification of smooth muscle cells using antibodies against OTR, VP1αR, and smooth muscle actin (sm-actin).

MAIN OUTCOME MEASURE(S)

The immunoreactive score (IRS) was used for expression of OTR, VP1αR, and sm-actin.

RESULT(S)

Expression of OTR in epithelial cells of adenomyotic lesions and surrounding myometrial cells was detectable. VP1αR was expressed only in myometrial cells and blood vessels. Using a specific anti-sm-actin antibody, another spindle cell population was characterized to represent smooth muscle cells which are in direct contact with the adenomyotic stroma. Compared with the unaffected myometrium, the surrounding adenomyosis-associated myometrium overexpressed OTR and showed changes in morphology. In the uteri of patients with adenomyosis, the junctional zone was often seen to be quite fissured.

CONCLUSION(S)

In addition to the specific expression of VP1αR, OTR expression and morphologic changes in the myometrial architecture of uteri having adenomyosis support the hypothesis that dysperistalsis plays an essential role in the development of endometriosis and dysmenorrhea. In the near future, specific inhibition of this receptor might yield a promising treatment for therapy.

Differential endothelin receptor expression and function in rat myometrial cells and leiomyoma ELT3 cells

Uterine leiomyoma are the most common benign tumors of the myometrium. We previously identified endothelin (ET)-1 as a proliferative and antiapoptotic factor in Eker rat-derived leiomyoma (ELT3) cells. A major role of ETB receptor in the prosurvival effect was revealed. Here we investigated, in ELT3 and myometrial cells, the respective contribution of ETA and ETB in the proliferative effect of ET-1. In myometrial cells, binding experiments show that ETA is almost exclusively expressed and stimulates phospholipase C (PLC) activity and ERK1/2 phosphorylation and proliferation. In ELT3 cells, ETB is expressed at about the same level as ETA, and the two receptors are differently coupled to Gi protein. The ETB agonist, sarafotoxin S6c, stimulates PLC activity 60% less than ET-1 but is as potent as ET-1 to increase ERK1/2 phosphorylation and induce proliferation. However, the ability of ETA to activate ERK1/2 is observed after ETB desensitization. Although ETA and ETB antagonists partially reduce ET-1 stimulated PLC activity, they are without effect on ET-1-induced ERK1/2 phosphorylation and proliferation. Only the simultaneous use of ETA and ETB antagonists reduces ET-1-triggered ERK1/2 activation. These unconventional properties of ETRs may reveal the existence of functional ETA-ETB heterodimers. Finally, treatment of ELT3 cells with ETB but not ETA-directed small interfering RNA reduces the proliferative effect of ET-1. All the data obtained in ELT3 cells strengthen the relation between ETB overexpression, which decreases the ETA to ETB ratio, and the ability of leiomyoma cells to highly proliferate and resist apoptosis.

Upregulation of PSCDBP, TLR2, TWIST1, FLJ35382, EDNRB, and RGS12 gene expression in human myometrium at labor

The regulatory mechanisms underlying myometrial smooth muscle contractility during labor are poorly understood. The authors therefore investigated the transcriptional profile of the changes that occur in the human myometrium at term pregnancy when compared with that at labor. Microarray technology was used to identify differentially expressed genes in human myometrium at labor. Real-time fluorescence reversetranscriptase polymerase chain reaction (RT-PCR) was subsequently performed to verify the microarray data. Semiquantitative RT-PCR, Western blotting, and microscopy methodologies were also used. Certain novel genes were found to be upregulated in human myometrium at labor. Of these, PSCDBP, TLR2, TWIST1 , FLJ35382, andRGS12 have not been previously characterized or identified in human myometrium. EDNRB is the other novel labor-associated gene whose reported expression is also upregulated at labor. All 6 genes were expressed on human myometrial smooth muscle cells. These novel upregulated genes are involved in multiple pathways that may be associated with a variety of cellular processes including inflammation, transcriptional regulation, and intracellular signaling.

Cloprostenol, a prostaglandin F(2alpha) analog, induces hypoxia in rat placenta: BOLD contrast MRI

Blood oxygen level dependent (BOLD) contrast was used to monitor hypoxia induced by cloprostenol, a prostaglandin F(2alpha) (PGF(2alpha)) analog, in the rat embryo-placental unit (EPU). It is shown that administration of cloprostenol (0.025 mg/rat) at mid-gestation (day 16) reduced EPU oxygenation, as detected by BOLD contrast MRI, in correlation with induction of vascular endothelial growth factor (VEGF) gene (Vegfa) expression in the corresponding placenta (r = 0.56, p = 0.03). Elevated VEGF mRNA expression in response to cloprostenol treatment was also observed at early gestation (day 9) in the forming placenta (p = 0.04) and uterus (p = 0.03). Cloprostenol increased the expression levels of endothelin-1 (ET-1) gene (Edn1) (p = 0.03) and its corresponding peptide (p = 0.02) in the forming placenta, as well as the expression of the endothelin receptor type A (ETA) gene (Ednra) in both the forming placenta (p = 0.009) and the uterus (p = 0.01). The levels of the endothelin receptor type B (ETB) gene (Ednrb) were not affected in response to cloprostenol, but a significant elevation in the expression level of this receptor was observed in the uterus at mid- and late gestation (day 22) (p = 0.04 and 0.01 respectively), suggesting a role for ETB in the vasodilatory status of the pregnant uterus. It is suggested that PGF(2alpha) induces uteroplacental vasoconstriction in the rat, and that ET-1 may take part in mediating this effect, probably via activation of ETA receptor. The uteroplacental vasoconstriction induces hypoxia, as manifested by significant changes in BOLD MRI and by upregulation of VEGF.

Identification of interactive gene networks: a novel approach in gene array profiling of myometrial events during guinea pig pregnancy

OBJECTIVE

The transition from myometrial quiescence to activation is poorly understood, and the analysis of array data is limited by the available data mining tools. We applied functional analysis and logical operations along regulatory gene networks to identify molecular processes and pathways underlying quiescence and activation.

STUDY DESIGN

We analyzed some 18,400 transcripts and variants in guinea pig myometrium at stages corresponding to quiescence and activation, and compared them to the nonpregnant (control) counterpart using a functional mapping tool, MetaCore (GeneGo, St Joseph, MI) to identify novel gene networks composed of biological pathways during mid (MP) and late (LP) pregnancy.

RESULTS

Genes altered during quiescence and or activation were identified following gene specific comparisons with myometrium from nonpregnant animals, and then linked to curated pathways and formulated networks. The MP and LP networks were subtracted from each other to identify unique genomic events during those periods. For example, changes 2-fold or greater in genes mediating protein biosynthesis, programmed cell death, microtubule polymerization, and microtubule based movement were noted during the transition to LP.

CONCLUSION

We describe a novel approach combining microarrays and genetic data to identify networks associated with normal myometrial events. The resulting insights help identify potential biomarkers and permit future targeted investigations of these pathways or networks to confirm or refute their importance.

The uterine junctional zone

Magnetic resonance imaging has revealed that the endometrio-myometrial interface constitutes a distinct, hormone-dependent uterine compartment termed the junctional zone. In the non-pregnant uterus, highly specialized contraction waves originate exclusively from the junctional zone and participate in the regulation of diverse reproductive events, such as sperm transport, embryo implantation, and menstrual shedding. Conversely, growing evidence suggests that disruption of the normal endometrio-myometrial interface plays an integral role in diverse reproductive disorders. This chapter reviews our current understanding of the mechanisms that govern the cyclic changes in the uterine junctional zone and summarizes the evidence implicating the endometrio-myometrial interface in normal uterine physiology and pathological processes.

History of adenomyosis

Although the claim has been made that there are early descriptions of what today we call endometriosis and adenomyosis in theses presented in Europe in the late 17(th) and during the 18(th) centuries, the first description of the condition initially named 'adenomyoma' is that provided in 1860 by the German pathologist Carl von Rokitansky, who found endometrial glands in the myometrium and designated this finding as 'cystosarcoma adenoids uterinum'. Over the following 50 years 'adenomyoma' (and endometriosis) were considered pathologies separate from the so-called 'haemorrhagic ovarian cysts', and it was not until 1921 that this condition was recognized to be of endometriotic origin. The first systematic description of what is today known as adenomyosis was the work of Thomas Stephen Cullen who, at the turn of the 19(th) century, fully researched the 'mucosal invasion' already observed by a number of investigators in several parts of the lower abdominal cavity. Cullen clearly identified the epithelial tissue invasion as being made of 'uterine mucosa' and defined the mechanism through which the mucosa invades the underlying tissue. In 1925, 2 years before Sampson created the term 'endometriosis', Frankl created a name for the mucosal invasion of the myometrium and clearly described its anatomical picture; he called it 'adenomyosis uteri' and explained that 'I have chosen the name of adenomyosis, which does not suggest any inflammatory genesis as do terms like adenometritis, adenomyositis, adenomyometritis, still employed'. The current definition of adenomyosis was finally provided in 1972 by Bird who stated: 'Adenomyosis may be defined as the benign invasion of endometrium into the myometrium, producing a diffusely enlarged uterus which microscopically exhibits ectopic non-neoplastic, endometrial glands and stroma surrounded by the hypertrophic and hyperplastic myometrium'.

Regulation of the endothelin/endothelin receptor system by interleukin-1{beta} in human myometrial cells

Proinflammatory cytokines produced at the fetomaternal interface, such as IL-1beta, have been implicated in preterm and term labor. The present study was performed to evaluate the influence of IL-1beta on the endothelin (ET)/ET receptor system in human myometrial cells. We report that myometrial cells under basal conditions not only respond to but also secrete ET-1, one of the main regulators of uterine contractions. Prolonged exposure of the cells to IL-1beta led to a decrease in prepro-ET-1 and ET-3 mRNA correlated with a decrease in immunoreactive ET-1 and ET-3 levels in the culture medium. Whereas ETA receptor expression at both protein and mRNA levels was not affected by IL-1beta treatment, we demonstrated an unexpected predominance of the ETB receptor subtype under this inflammatory condition. Whereas the physiological function of ETB remains unclear, we confirmed that only ETA receptors mediate ET-1-induced myometrial cell contractions under basal conditions. By contrast, prolonged exposure of the cells to IL-1beta abolished the contractile effect induced by ET-1. Such a regulation of IL-1beta on the ET release and the balance of ETA to ETB receptors leading to a loss of ET-1-induced myometrial cell contractions suggest that complex regulatory mechanisms take place to constraint the onset of infection-induced premature contractions.

In vitro responsiveness of human post-menopausal myometrium to endothelin-1 and ovarian steroids

It has been shown in vitro that endothelin 1 (ET1) differentially affects the human myometrial contractility according to the hormonal profile of women. Our purpose was to test the hypothesis that ovarian steroids influence the ET1 induced myometrial contractility. We performed three types of experiments. Myometrial tissues were exposed to 17beta-oestradiol (E), progesterone (P), E plus P (E+P) in concentrations 10(-10)M, 10(-8)M, 10(-7)M, 10(-6)M and 10(-4)M (Type I), ET1 in concentrations 10(-10)M, 10(-9)M, 10(-8)M, 10(-7)M and 10(-6)M (Type II) and E+ET1, P+ET1 and E+P+ET1 in concentrations ranging from 10(-10)M to 10(-6)M (Type III). Tissue exposure to E, P and E+P did not significantly alter the pattern of spontaneous myometrial motility. ET1 (10(-6)M) induced a sustained long-lasting contraction, the initial part of which lasted 34 +/- 4 min, elevating the initial baseline by 190 +/- 20%. This was followed by ripples of gradually increasing amplitude with no regular contractions up to the end of the period of observation (120 min). Addition of P or E+P to ET1 markedly restricted (p<0.05) the elevation of initial baseline (P+ET1: 68 +/- 8%, P+E+ET1: 67 +/- 8%), and significantly shortened (p<0.01) the duration of the alterations (P+ET1: 21 +/- 3 min, P+E+ET1: 26 +/- 3 min). These results demonstrate the lack of any significant effect of E and P or their combinations on the pattern of spontaneous myometrial motility in post-menopausal women. However, P alone or in combination with E exerted an inhibitory action on ET1 -induced contractility on human post-menopausal myometrium. The physiological significance of these findings remains to be clarified.

Oxytocin receptor expression in smooth muscle cells of peritoneal endometriotic lesions and ovarian endometriotic cysts

OBJECTIVE

To investigate the expression of oxytocin receptor (OTR) in peritoneal and ovarian endometriotic lesions.

DESIGN

Retrospective nonrandomized study.

SETTING

University hospital endometriosis research center.

PATIENT(S)

Premenopausal women with histologically confirmed endometriosis were selected. Peritoneal endometriotic lesions (n = 120); ovarian endometriotic cysts (n = 40); peritoneal biopsies, distant from the endometriotic lesion (n = 55); and unaffected peritoneal biopsies from patients without endometriosis (n = 11) were obtained. Hysterectomy specimens from patients without endometriosis and/or adenomyosis were used for controls (n = 10).

INTERVENTION(S)

Histopathological examination of peritoneal and ovarian specimens for OTR expression and identification of smooth muscle cells by immunohistochemistry staining with antibodies against OTR and smooth muscle actin. In addition, Western blot analysis, double-immunofluorescence, and in vitro studies with primary cell cultures have been performed.

MAIN OUTCOME MEASURE(S)

Comparison of the immunoreactive score of the OTR and smooth muscle actin expression with the smooth muscle content in peritoneum with and without endometriosis.

RESULT(S)

In the epithelial cells of endometriotic lesions, we could demonstrate a high OTR expression. The stromal cells were OTR negative with the exception of some single cells. By using a monoclonal anti-smooth muscle actin antibody, these cells could be identified as intrastromal OTR-positive smooth muscle cells. The peritoneum of women with endometriosis shows a significantly higher smooth muscle content than the peritoneum of women without endometriosis. There were no significant differences between the smooth muscle content of active or inactive lesions and the stage of disease.

CONCLUSION(S)

Oxytocin receptor is expressed in smooth muscle cells and epithelial cells of peritoneal endometriotic lesions and ovarian endometriotic cysts. The inhibition of OTR by specific inhibitors might be a useful approach for the treatment of endometriosis-associated pain.

Endometrial-myometrial interface: relationship to adenomyosis and changes in pregnancy

The endometrial-myometrial interface (EMI) is an important region of the human uterus, which has attracted little research attention. This mucosal-muscular interface has characteristic features when compared with other similar interfaces in the human body. It lacks an intervening tissue layer and as a result, the endometrium sits directly on the myometrium rendering it vulnerable to invasion by the endometrium. Both endometrium and myometrium are sensitive to sex steroids, and their structure and function depend to a large extent on the sex hormonal milieu. Endometrium, which forms one border of the EMI, is a complex tissue consisting of several polarized microenvironments. At a cellular level, sex steroids interact with local mediators secreted by a variety of cell types and are important in maintaining the complex structure and function of the endometrium. Basal endometrium contains prominent aggregates of leukocytes that may be important in controlling local cell growth and function. Myometrium also has a distinct zonal anatomy. The recently described junctional zone differs structurally and functionally from the outer myometrium, although these functions are not yet clearly understood. Embryologically, it originates from müllerian ducts together with endometrium, whereas the outer myometrium has a non-müllerian origin. During early pregnancy, the EMI is disturbed by invading trophoblast. Alterations of myometrial intercellular matrix proteins together with expression of appropriate receptors by the trophoblast seem to regulate this unique interaction. The EMI also is disrupted in adenomyosis. The sequence of events taking place at the EMI during development of this pathology is still debated.

Fluctuating gene expression and localized cellular distribution of vasoactive intestinal contractor (VIC) in mouse uterus

To understand the physiological roles of vasoactive intestinal contractor (VIC) and endothelin-2 (ET-2) in the uterus, we examined the expression levels of VIC mRNA by real-time quantitative reverse transcription-linked polymerase chain reaction (RT-PCR) and characterized the cellular distribution of VIC peptide and mRNA by immunostaining and in situ hybridization in mouse uterus. In pregnant mouse uterus, VIC mRNA expression changed considerably between Days 10.5 and 12.5 of pregnancy. The expression levels were significantly (p<0.05) higher (approximately fivefold) in the later stage of pregnancy (Days 12.5-17.5) than in the earlier stage (Days 7.5-10.5). In nonpregnant uterus, VIC mRNA expression was significantly (p <0.05) higher (approximately threefold) in proestrus and estrus than in diestrus. Immunohistochemical studies demonstrated the presence of VIC peptide in endometrial epithelial cells, myometrial cells, and vascular smooth muscle cells during the estrous cycle and pregnancy and after parturition. Notably, myometrial cells showed dominant immunostaining in proestrus and estrus, in the later pregnancy stage, and in the early postpartum period, analogous to the expression pattern of VIC mRNA. In situ hybridization confirmed localization of VIC mRNA in myometrial cells. These findings suggest that VIC may play an important role in the function of myometrial cells.

Characterization of functional endothelin receptors in the porcine myometrium

To characterize the endothelin (ET) receptor that mediates the contraction induced by ET-1 in the porcine myometrium, we carried out a contraction study, radioligand binding study and molecular study (reverse transcription polymerase chain reaction) for detection of ET receptor-coding genes (mRNA). ET-1 (1 nM-1 microM) caused a tetrodotoxin-insensitive contraction in both longitudinal and circular muscles, but the longitudinal muscle was more sensitive to ET-1 than was the circular muscle. On the other hand, ET-3 and sarafotoxin S6c were less effective to cause a contractile response. The contraction induced by ET-1 was markedly inhibited by BQ123 and FR139317, but BQ788 only slightly inhibited the response induced by ET-1. The radioligand binding study indicated the presence of a single class of 125I-ET-1 binding sites with the same Kd value in both muscle layers. However, Bmax in the longitudinal muscle (3252 fmol/mg protein) was significantly higher than that in the circular muscle (1883 fmol/mg protein). ET-1 and FR139317 inhibited the specific 125I-ET-1 binding completely, but ET-3, sarafotoxin S6c and BQ3020 only slightly inhibited the specific binding (inhibition, 10-20%), suggesting that ET(A) is the dominant ET receptor subtype in the porcine myometrium. The results of the molecular study indicated the expression of both ET(A) and ET(B) receptor-coding genes in the porcine myometrium. In conclusion, ET-1 causes contraction of the porcine myometrium through activation of the ET(A) receptor present on smooth muscle cells. There is a marked muscle layer-related difference (longitudinal muscle > circular muscle) in the ET-1-induced contraction and the ET(A) receptor concentration.

Contribution of protein kinase C to ET-1-induced proliferation in human myometrial cells

The role of protein kinase C (PKC) in endothelin-1 (ET-1)-induced proliferation of human myometrial cells was investigated. ET-1 dose dependently stimulated DNA synthesis and the number of cultured myometrial cells. Inhibition of PKC by calphostin C or Ro-31-8220 or downregulation of PKC eliminated the proliferative effects of ET-1. The failure of two protein tyrosine kinase (PTK) inhibitors (tyrphostin 51 and tyrphostin 23) to affect ET-1-induced proliferation supports the hypothesis of noninvolvement of the tyrosine kinase signaling pathway in this process. The expression and distribution of PKC isoforms were examined by Western blot analysis. The five PKC isoforms (PKC-alpha, -beta1, -beta2, -zeta, -epsilon) evidenced in human myometrial tissue were found to be differentially expressed in myometrial cells, with a predominant expression of PKC-alpha and PKC-zeta. Treatment with phorbol 12, 13-dibutyrate (PDBu) resulted in the translocation of all five isoforms to the particulate fraction, whereas ET-1 induced a selective increase in particulate PKC-beta1, PKC-beta2, and PKC-epsilon. Our findings that multiple PKC isoforms are differentially responsive to ET-1 or PDBu suggest that they play distinct roles in the myometrial growth process.

Mitogen-activated protein kinase cascade is involved in endothelin-1-induced rat puerperal uterine contraction

The regulation of mitogen-activated protein (MAP) kinase by endothelin-1 (ET-1) in cultured rat puerperal uterine myometrial cells was investigated. ET-1 caused the rapid stimulation of MAP kinase activity. ET-1-induced MAP kinase activation is neither extracellular Ca2+- nor intracellular Ca2+-dependent. ET-1 stimulation also led to an increase in phosphorylation of son-of-sevenless (SOS), and transfection of dominant negative SOS attenuated the ET-1-induced MAP kinase activity. Phorbol-12-myristate 13-acetate (PMA) also induced the MAP kinase activity, but pretreatment of the cultured cells with PMA, to down-regulate protein kinase C (PKC), did not abolish the activation of MAP kinase by ET-1. In addition, down-regulation of PKC had no effect on ET-1-induced SOS phosphorylation. Pertussis toxin, which inactivates Gi/Go proteins, blocked the ET-1-induced MAP kinase activation but not the PMA-induced MAP kinase activation. The results suggested that MAP kinase is acutely activated by ET-1 through a pertussis toxin-sensitive G protein and SOS, not through the PMA-sensitive PKC. In addition, although reverse-transcriptase PCR assays detected messenger RNA for both ET- 1 receptor subtypes in cultured rat puerperal uterine myometrial cells, ET-1-induced MAP kinase activity and uterine contraction were blocked by treatment with BQ485, an antagonist selective for an ET type A receptor (but not by BQ788, an ET type B receptor antagonist). Ritodrine, which is known to relax uterine muscle contraction, attenuated ET-1-induced MAP kinase activity. We further examined the role of MAP kinase pathway in uterine contraction using an inhibitor of MEK activity, PD098059. This inhibitor completely inhibited the ET-1-induced MAP kinase activation and partially, but significantly, inhibited the ET-1-induced uterine contraction. These results indicate that ET-1-induced MAP kinase signaling cascade may play an important role in the ET-1-induced uterine contraction.

Endothelin receptor type A and B gene expression in human nonpregnant, term pregnant, and preeclamptic uterus

OBJECTIVE

The aim of this study was to quantify the gene expression of ETA and ETB receptors within the different uterine segments of nonpregnant, normal pregnant, and preeclamptic women.

STUDY DESIGN

Biopsy samples from the cervix, isthmus, and corpus uteri were obtained from eight nonpregnant, nine term pregnant, and seven preeclamptic women. The concentration of ETA and ETB receptor messenger ribonucleic acid were determined by a solution hybridization technique with complementary ribonucleic acid probes. Results are presented in counts per minute per microgram of total nucleic acid as mean +/- SEM.

RESULTS

The expression of messenger ribonucleic acid encoding the ETA receptor was generally higher in the upper than in the lower uterine segment in nonpregnant, normal pregnant, and preeclamptic myometrium, whereas the opposite pattern was seen with regard to ETB. During normal pregnancy the concentrations of ETA receptor messenger ribonucleic acid in the corpus and ETB receptor messenger ribonucleic acid in the isthmus were significantly elevated compared with those in nonpregnant women. This enhanced gene expression was, however, not observed in the preeclamptic group.

CONCLUSION

Our finding of segmentally differentiated endothelin receptor gene expression is compatible with a role for endothelin-1 in stimulating uterine contractions through ETA receptors during spontaneous labor and suggests a relaxing effect of the ETB receptor on the myometrium.

Differential distribution of endothelin peptides and receptors in human adrenal gland

Sub-type selective ligands revealed a differential distribution of endothelin (ET) receptors within human adrenal glands. High densities of ETA receptors were localized, using [125I]-PD151242, to the smooth muscle layer of the arteries, smaller vessels within the capsular plexus and to the secretory cells of zona glomerulosa (KD = 139.8 +/- 39.7, Bmax = 69.7 +/- 9.1 fmol mg-1 protein, mean of 3 individuals+/-sem). ETB receptors were present in the medulla (KD = 145.2 +/- 16.4, Bmax = 75.5 +/- 12.3), zona glomerulosa (KD = 100.6 +/- 35.1, Bmax = 63.1 +/- 10.0), fasiculata (KD 145.1 +/- 16.2, Bmax = 67.9 +/- 6.9) and reticularis (KD = 118.2 +/- 18.6, Bmax = 71.9 +/- 6.5). ETB receptors were not detected within the smooth muscle of the vasculature. Messenger RNA encoding both sub-types was present in adrenals. ET-like immunoreactivity was localized to the cytoplasm of the endothelial cells from arteries supplying the gland and resistance vessels within the capsular plexus. Staining was also detected in these cells using anti-big ET-1 and less intensely with anti-big ET-2 antisera but not within cells within the cortex or medulla. Big ET-3-like immunoreactivity was localized to secretory cells of the medulla. Staining was not found using antiserum that could detect ET-3, suggesting further processing of big ET-3 may occur within the plasma, and that the adrenals could be a source of ET-3. The presence of ET-1 was confirmed by high performance liquid chromatography and radioimmunoassay although ET-3 was not detected. The results suggest that ET-1 is the predominant mature isoform, which is localized mainly to adrenal vasculature, particularly the capsular plexus, and may contribute to blood flow regulation in the gland.

The selective endothelin ETA receptor antagonist FR139317 inhibits neointimal thickening in the rat

Endothelin is known as a potent mitogenic mediator. We tested the in vivo ability of FR139,317((R)2-[(R)-2-[(S)-2-[[1-(hexahydro- 1H-azepinyl)]carbonyl]amino-4-methylpentanoyl] amino-3-[3-(1-methyl-1 H-indoyl)]propionyl]amino-3-(2-pyridyl)propionic acid), a selective antagonist of the endothelin ETA receptor subtype, to inhibit neointimal thickening following photochemically induced injury of the endothelium of rat femoral artery. FR139,317 (32 mg/kg s.c., twice a day) was administered for 3 weeks after the injury. FR139,317 significantly decreased the neointimal area (76.3%) without changing the medial area. Therefore, it is suggested that endothelin may play an important role, via mainly endothelin ETA receptors, in neointima formation in injured artery.

Endothelin receptors in human coronary artery and aorta

1. ETA and ETB-selective and non-selective ligands were used to define the endothelin receptors in the media (vascular smooth muscle layer) of human aorta and coronary artery. Saturation experiments with iodinated endothelin-1 (ET-1), endothelin-2 and sarafotoxin 6b (S6b) identified high affinity binding sites in aorta (KD [125I]-ET-1 0.33 +/- 0.02 nM (n = 9), KD [125I]-ET-2 1.04 +/- 0.23 nM (n = 5), KD [125I]-S6b 0.15 +/- 0.01 nM (n = 9 +/- s.e.mean)) and coronary artery (KD [125I]-ET-1 0.43 +/- 0.10 nM, KD [125I]-ET-2 0.71 +/- 0.17 nM, KD [125I]-S6b 0.27 +/- 0.03 nM (n = 3 +/- s.e.mean)). Hill coefficients (nH) approached unity in each case. 2. No specific binding was detectable with [125I]-ET-3 (4 pM-4 nM) in aorta. Unlabelled ET-3 competed monophasically with [125I]-ET-1 in aorta (KD, 8.21 +/- 1.62 nM, compared to unlabelled ET-1 KD, 0.60 +/- 0.20 nM) (n = 3 +/- s.e.mean). In coronary artery, the KD and Bmax values calculated from [125I]-ET-3 saturation experiments were 2.13 +/- 1.39 nM and 20.6 +/- 12.9 fmol mg-1 protein, respectively (n = 3 +/- s.e.mean). 3. ETA antagonists competed monophasically for [125I]-ET-1 (100 pM) binding sites with nanomolar or subnanomolar affinity in the aorta (KD BQ123, 0.47 +/- 0.13 nM; KD FR139317, 0.40 +/- 0.10 nM; KD PD151242, 2.09 +/- 0.48 nM) and coronary artery (KD FR139317, 0.41 +/- 0.13 nM; KD PD151242, 3.60 +/- 0.74 nM) (n = 3 +/- s.e.mean). However, two site fits were preferred on analysis of competition experiments with ETB-selective agonists versus [125I]-ET-1 in coronary artery (BQ3020: KDETA 0.96 +/- 0.14 microM, KD ETB 1.34 +/- 1.08 nM and sarafotoxin 6c: KD ETA 1.15 +/- 0.14 microM, KD ETB 1.77 +/- 0.72 nM) (n = 3 +/- s.e.mean). The selectivity of the agonists for ETB receptors (700 fold) was lower than reported in other species. 4. Sarafotoxin 6b (2 pM-2 microM) completely inhibited [125I]-ET-1 (100 pM) binding in aorta (KD 1.36 +/- 0.22 nM) (n = 3 +/- s.e.mean). The non-peptide compounds Ro462005 and bosentan, competed with [125I]-ET-1 binding in coronary artery with KD values of 0.19 +/- 0.04 microM and 2.94 +/- 0.95 nM, respectively (n = 3 +/- s.e.mean). 5. Inhibition of [125I]-ET-2 and [125I]-S6b binding by FR139317 was similar to the inhibition of [125I]-ET-1 binding in both arteries, being monophasic with KD values in the same range. 6. ETA receptors in coronary artery media were detected by [125I]-PD151242 (KD 0.23 +/- 0.04 nM, Bmax 10.1 +/- 1.2 fmol mg-1 protein) (n = 3 +/- s.e.mean). [125I]-BQ3020, an ETB-selective radioligand, indicated the presence of a smaller population of ETB receptors in this tissue (KD 0.60 +/- 0.31 nM, Bmax 4.5 +/- 2.1 fmol mg-1 protein) (n = 3 +/- s.e.mean). 7. Autoradiography with [125I]-PD151242 and [125I]-BQ3020 confirmed the predominance of ETA receptors in the media of both arteries. 8. The results of this study indicate that ETA receptors predominate in the vascular smooth muscle of human cardiac arteries, with a small and variable population of ETB receptors detectable in the coronary artery.

Endothelin ETA receptors mediate human uterine smooth muscle contraction

Receptors mediating endothelin-induced contraction of myometrium were investigated in the human uterus. Endothelin-1 and endothelin-3 (10 pM to 0.3 microM) caused concentration-dependent contraction of myometrial strips. Endothelin-1 was approximately ten times more potent than endothelin-3, with pD2 values of 8.24 and 7.20, respectively. By contrast, two endothelin ETB receptor selective agonist, BQ 3020 (N-acetyl-[Ala11,15]endothelin-1-(6-21) and sarafotoxin 6c (up to 0.3 microM), did not induce contraction of human myometrium. The endothelin ETA receptor selective antagonist, FR139317 (1-hexahydroazepino-CO-Leu-D-Trp(CH3)-D-(2-pyridyl)alanine) (0.1, 0.3 and 1 microM), competitively antagonized the endothelin-1-elicited contraction, with a pA2 value of 7.10, whereas another endothelin ETA receptor-selective blocking drug, BQ 123 [cyclo(-D-Trp-D-Asp-Pro-D-Val-Leu)], behaved as a non-competitive antagonist. Pretreatment of myometrial strips with an endothelin ETB receptor selective antagonist, IRL 1038 ([Cys11-Cys15]endothelin-1-(11-21)), had no effect on contractions induced by endothelin-1. All these data indicate that only endothelin ETA receptors mediate endothelin-1-induced contractions of human myometrium.

Uterine junctional zone: function and disease

The myometrium is usually thought of as a homogeneous mass of smooth muscle fibres. However, magnetic resonance studies of the uterus have revealed two distinct zones--the subendometrial myometrium or junctional zone and the outer myometrium. The junctional zone is not only structurally but also functionally different from the outer myometrium. For instance, myometrial contractions in a non-pregnant woman originate exclusively from the junctional zone, and their amplitude, frequency, and direction depend on the phase of the cycle. Irregular thickening of the junctional zone has been proposed as the magnetic resonance criterion for the diagnosis of diffuse adenomyosis. However, this magnetic resonance appearance relies on the disruption of the inner myometrial architecture secondary to smooth muscle hyperplasia but does not provide proof of mucosal invasion of the myometrium. We postulate that adenomyosis is a dichotomous disease characterised primarily by disruption of the inner myometrial architecture and function, with secondary infiltration of endometrial elements into the myometrium under certain circumstances. This hypothesis focuses on the inner myometrium and may explain the high incidence of superficial adenomyosis in dysfunctional uterine bleeding.

Endothelin expression in the uterus

The endothelins (ETs) comprise a family of 21 amino acid peptides, ET-1, ET-2 and ET-3, first demonstrated as products of vascular endothelium. Subsequent work showed that they are also found in non-endothelial cells from a variety of tissues such as breast, parathyroid and adrenal gland. At first, the ETs were recognized for their pressor effects. However, ET administration in vivo initially caused hypotension at low concentrations by triggering the paracrine release of endothelial-derived vasodilators. The ETs exert powerful contractile actions on myometrium and other types of smooth muscle and are mitogenic, or co-mitogenic for fibroblasts, vascular smooth muscle and other cells. Demonstration of extravascular ET in endometrium has revealed a powerful vasoconstrictor which might act on the spiral arterioles to effect a powerful and sustained contraction of vascular smooth muscle. ETs might also contribute to the process of endometrial repair. In addition, the ETs appear to play a fundamental role in the control of uterine function in pregnancy. Effects on myometrial contractility have been implicated in the mechanisms governing the onset of normal and pre-term labour, and the peptides are likely to be key determinants of placental blood flow by binding to vascular smooth muscle receptors in the placenta.