The comparative effects of big endothelin-1, endothelin-1, and endothelin-3 in the human fetal-placental circulation

Investigation of endothelin-1 type A receptor gene polymorphism (-231 G > A) in preeclampsia susceptibility

OBJECTIVE

Preeclampsia is considered as a multifactorial disorder with a genetic predisposition. Alterations in the endothelin-1 (ET-1) system are considered to take part in triggering the vasoconstriction seen in preeclampsia.

METHODS

In order to investigate the possible association of the -231 G > A polymorphism in the endothelin-1 type A receptor gene (EDNRA), previously shown to be associated with other conditions characterized by vasospasm, we examined 77 Caucasian preeclamptic women and 67 matched controls including normotensive subjects without history of thromboembolic event, abnormalities in blood pressure, proteinuria, edema and preeclampsia. The genotype was assessed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) on genomic DNA extracted from blood samples. Case vs. control allele frequencies and genotype distributions were compared.

RESULTS

No significant differences were found when considering both genotype (chi(2) = 0.58, p = 0.75) and allelic frequencies (chi(2) = 0.08, p = 0.77). Furthermore, no significant genotype-related difference was found in relation to clinical features, such as gestational age at onset, systolic and diastolic blood pressure, proteinuria on admission and delivery week.

CONCLUSIONS

No association between the -231 G > A polymorphism in the EDNRA gene and preeclampsia as well as any correlation with the main clinical features of the disorder were found, thus excluding a role for this polymorphism in susceptibility to preeclampsia.

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.

Vasoactive responses of veins isolated from the human placental chorionic plate

The control of the blood flow within the fetoplacental circulation is poorly understood despite the essential role of the placenta in pregnancy. Our aim was to assess the vasoactive responses of veins from the placental chorionic plate. Biopsies were obtained from term placentae from uncomplicated pregnancies. Small veins from the chorionic plate were dissected free from surrounding tissue and studied using parallel wire myography. Human placental chorionic plate veins developed maintained constrictions to the thromboxane-mimetic U46619. Endothelium-dependent agonists did not promote venous relaxation. However, NO donation with the endothelial-independent agent, sodium nitroprusside, elicited significant relaxation. Venous constriction to U46619 and relaxation to sodium nitroprusside were modified by adjustment of media oxygen tension and normalization parameters. Human placental chorionic plate veins respond to vasoactive agents and may play a role in the control of the blood flow in the fetoplacental circulation.

Role of placenta in preeclampsia

Preeclampsia, which manifests itself as hypertension, proteinuria, and edema in pregnancy, requires the presence of trophoblast tissue but not a fetus. It is characterized by abnormal trophoblast invasion of the spiral arteries of the decidua and myometrium leading to a failure to establish an adequate uteroplacental blood flow and, therefore, is thought to give rise to relatively hypoxic trophoblast tissue. This, in turn, may promote an exaggerated state of oxidative stress in the placenta. This hypoxia/oxidative stress may then further attenuate trophoblast invasion but also alters placental villous angiogenesis leading to a poorly developed fetoplacental vasculature with abnormal reactivity. Oxidative stress per se may also affect vascular reactivity, blood flow, and oxygen and nutrient delivery to the fetus, which ultimately may be compromised. The synthetic and transport functions of the syncytiotrophoblast may also be altered, and there is an increased rate of trophoblast apoptosis. The linkage among abnormal trophoblast invasion, trophoblast dysfunction, and the maternal disease remains unidentified. The presumptive humoral factor that is released by the preeclamptic placenta to cause maternal disease remains elusive. Current therapies to prevent preeclampsia aim toward preventing the maternal syndrome, not preventing the primary pathophysiology.

Characterization of small arteries isolated from the human placental chorionic plate

Despite the essential role of the placenta in pregnancy, the control of the blood flow within the fetoplacental circulation is poorly understood. A handful of myography studies have directly assessed the role of vasoactive agonists in fetoplacental vasculature contractility but have used a range of steady-state conditions. Our aim, therefore, was to determine the optimal vessel diameter and oxygen tension to assess vascular function in small arteries isolated from the chorionic plate of normal term placentae. Biopsies were obtained from term placentae from uncomplicated pregnancies. Small arteries were dissected from the chorionic plate, mounted onto a wire myograph in HCO3(-) -buffered physiological salt solution at 37 degrees C and equilibrated for 20 min. Two methods for normalization of the optimal length/diameter for contractility of chorionic plate small arteries were assessed. Both classical normalization (CN) and length-tension curve (LTC) methods produced similar data. These data were agonist-independent. Data for CN and LTC were unaffected but maximal force generation (for U46619) was decreased in reduced oxygen tensions. Using conditions for optimal tension production in chorionic plate small arteries the thromboxane-mimetic U46619 produced the greatest and most reproducible constrictive effect. Relaxations were only achieved with endothelial-independent agonists (sodium nitroprusside and papaverine).

Endothelin-l in feto-placental tissues from normotensive pregnant women and women with pre-eclampsia

AIMS

The pathogenesis of pre-eclampsia is still unclear. Placental hypoperfusion, which precedes the maternal manifestations of pre-eclampsia, could be due to some vasoconstrictor factor/s like endothelin-1. The aim of the study therefore was to estimate the levels of endothelin-1 in feto-placental tissue homogenates from normotensive pregnant women and women with pre-eclampsia.

METHOD AND MATERIAL

Fresh, vaginally delivered placentae from ten normotensive pregnant women and nine women with pre-eclampsia were carefully dissected and 4 gm each of amnion, chorion laeve, placental plate chorion, fetal placenta (fetal surface of the placenta) and maternal placenta (surface of the placenta attached to the uterine wall) were obtained. These tissues were then thoroughly washed in a 0.5 M phosphate buffer, pH 7.5, at room temperature and then individually homogenized for one minute in 4 ml of the same buffer. After centrifugation the supernatant was removed. The pellet was re-suspended in buffer, re-homogenized and then centrifuged. The supernatant was removed and the procedure was repeated once again and the three supernatants of each tissue were pooled. Endothelin-1 was estimated by RIA. All results are presented as mean+/-SEM. Statistical analysis was performed using students 't' test for unpaired samples and a 'p' value of <0.05 was considered significant.

RESULTS

In tissues from normotensive pregnant women, no significant differences were evident in endothelin-1 concentrations in the chorion laeve, fetal placenta and maternal placenta but were significantly higher than those in the amnion and placental plate chorion (p<0.01). In tissues from pre-eclamptic women, no significant differences were evident between endothelin-1 concentrations in the chorion laeve, placental plate chorion and fetal placenta. Mean endothelin-1 concentration in the amnion and maternal placenta were significantly lower than those in chorion laeve, placental plate chorion and fetal placenta (p<0.01). Endothelin-1 concentrations were significantly higher in the amnion, chorion laeve, placental plate chorion and fetal placenta from women with pre-eclampsia when compared to tissues from normotensive pregnant women (p<0.01).

CONCLUSIONS

Endothelin-1 levels were significantly higher in the placental tissues from women with pre-eclampsia. Endothelin-1, being a powerful vasoconstrictor, could cause significant vasoconstriction in the placental vasculature, and alterations in endothelin-1 levels in placental vasculature may therefore have a role in the pathogenesis of pre-eclampsia.

The expression and localization of neutral endopeptidase 24.11/CD10 in human gestational trophoblastic diseases

Neutral endopeptidase 24.11 (NEP)/CD10 is a cell-surface peptidase that hydrolyzes various bioactive peptides. NEP is distributed in both normal and neoplastic cells and plays a functional role by modulating cellular responses to peptide substrates. Recently, NEP has been shown to be expressed in normal placental trophoblasts, suggesting its physiological role during pregnancy. In the present study, we investigated the expression of NEP in hyperplastic and anaplastic trophoblasts in gestational trophoblastic diseases (GTDs). Flow cytometric analysis demonstrated that NEP was expressed in all choriocarcinoma cell lines examined. The NEP enzyme activity in these cell lines correlated with cell-surface protein levels and was abolished by the NEP inhibitor phosphoramidon. On immunoblot analysis, NEP protein was detected in both hydatidiform mole and choriocarcinoma tissues as a double band of 95 and 100 kDa similar to that of the normal placental tissues. Immunohistochemical analysis revealed that NEP was present on syncytiotrophoblasts, while no or very faint NEP immunoreactivity was observed on cytotrophoblasts in the normal placenta. Similarly, NEP in hydatidiform mole and invasive mole was localized on the membrane of syncytiotrophoblasts, but not on hyperplastic cytotrophoblasts. In contrast, in choriocarcinoma, NEP was highly expressed not only on syncytiotrophoblastic cells but also on invading anaplastic cytotrophoblasts. In addition, NEP was also expressed on intermediate trophoblasts in placental site trophoblastic tumors. In summary, this is the first study demonstrating the expression of NEP/CD10 in GTDs. The differential localization of NEP among various trophoblastic tumors suggests that NEP may play a functional role in the regulation of trophoblast transformation and human chorionic gonadotropin secretion.

Better preservation of endothelial function and decreased activation of the fetal renin-angiotensin pathway with the use of pulsatile flow during experimental fetal bypass

OBJECTIVE

Pulsatile flow was shown to overcome the progressive rise in peripheral and placental vascular resistances observed during steady-flow bypass, this rise being counteracted by inhibition of nitric oxide synthase. This study quantifies the release of endothelial vasoactive substances during a 60-minute in utero model of fetal bypass.

METHODS

Fetuses were randomly allocated into 1 of 2 groups (steady flow, n = 8, or pulsatile flow, n = 13) and subjected to bypass through central cannulation and perfusion with either a centrifugal or pulsatile (125 beats x min(-1)) blood pump.

RESULTS

Lactate concentration was high, starting at fetal exteriorization and increasing during fetal preparation in the 2 groups. Once bypass was established, the rise was significant only in the steady-flow group. Plasma nitric oxide metabolites, similar before bypass, reached higher levels during pulsatile flow at the end of bypass (99+/-9 vs. 82+/-23 micromol x L(-1); P =.037). Levels of urinary nitric oxide metabolites were significantly higher in the pulsatile-flow than in the steady-flow group (764+/-143 vs. 508+/-240 micromol x L(-1); P =.005). Plasma cyclic guanosine monophosphate levels increased after 30 minutes of bypass in the pulsatile-flow group (25+/-18 vs. 12+/-8 pmol x mL(-1); P =.004), and urinary cyclic guanosine monophosphate excretion was higher in the pulsatile-flow group (517+/-450 vs. 118+/-78 pmol x mL(-1); P =.024). Plasma endothelin-1 levels increased in the 2 groups and were higher in the steady-flow group at 30 minutes (27+/-5 vs. 23+/-2 pg x mL(-1); P =.04) and 60 minutes of bypass (39+/-7 vs 32 +/- 6 pg x mL(-1); P =.04). Plasma renin concentration increased significantly during bypass only in the steady-flow group (26+/-10 vs. 57+/-42 in ng A1 x mL(-1) x h(-1); P =.04).

CONCLUSIONS

Improved placental and peripheral perfusion during fetal pulsatile-flow bypass may be mediated by preservation of fetal/maternal endothelial nitric oxide biosynthetic mechanisms and/or decreased activation of the fetal renin-angiotensin pathway.

Mechanisms of endothelin-1-induced contraction in isolated placental veins from normal full-term and preterm pregnancies

This study characterizes the reactivity of human chorionic plate vein in full-term (39.4+/-0.3 weeks of gestation) and preterm (34.4+/-0.6 weeks of gestation) pregnancy to endothelin-1 (ET-1) and attempts to characterize ET-1 receptor subtype, and the contribution of nitric oxide and cyclooxygenase products in these responses. In placental veins from full-term and preterm pregnant women, cumulative addition of ET-1 (10(-10)-10(-6) M) caused marked and long-lasting concentration-dependent contractile responses. The mean EC(50) and E(max) values for ET-1-induced venoconstriction did not differ between the full-term and preterm pregnancy groups. In the veins from preterm placental preparations, the ET(A) receptor-selective antagonist cyclo(D-alpha-aspartyl-L-propyl-D-valyl-L-leucyl-D-tryptophyl (BQ123) reduced the ET-1-induced contraction by 28.6+/-2.4%, compared to a decline in tension of 51.2+/-4.2% in the full-term placental vessels. The ET(B) receptor-selective antagonist, N-[N-[N-[2,6-dimethyl-1piperidinyl)carbonyl]-4-methyl-L-leucyl]-1-(methoxycarbonyl)-D-tryptophyl]-D-norleucinemonosodium (BQ788), did not influence ET-1-induced contraction in placental vein from both pregnancy groups in terms of maximal contraction and sensitivity. Pretreatment with the cyclooxygenase inhibitor, indomethacin (1 microM) and the nitric oxide synthase inhibitor N(w)-nitro-L-arginine (NOLA, 100 microM) did not significantly affect either the EC(50) or the maximum contraction to ET-1 in veins from normal full-term and preterm preparations. The results of this study suggest that there is no correlation between ET-1-induced vasoconstriction and gestational age and that this vasoconstriction is mediated predominantly via ET(A) receptor subtype in both groups of pregnant women, independent of NO and eicosanoids.

Immunohistochemical localization of ECE-1 in the human placenta

Over the last several years, endothelin (ET-1) has emerged as an important mediator in the pathogenesis of pre-eclampsia and preterm labour, as well as in the normal function of gestational tissues. While the distribution of ET and its binding sites in the human placenta have been well studied, much less has so far been reported about the distribution of placental ET-1 processing enzymes. By immunohistochemical analysis and immunofluorescence, endothelin-converting enzyme-1 (ECE-1), the enzyme that synthesizes ET-1, is localized to five distinct cell populations in the human placenta: (1) the endothelial cells lining the maternal basal plate blood vessels, (2) the intermediate trophoblasts, (3) the endothelial cells lining the chorionic villous blood vessels, (4) the chorionic villous stromal cells and (5) the chorionic villous trophoblasts. The localization of ECE-1 corresponds with the previously reported distribution of ET-1 in the human placenta and is in accordance with the function of this enzyme in regulating vascular tone through synthesis of ET-1. The abundance of ECE-1 in the basal plate is consistent with a second possible function of this enzyme in affecting uterine contractions. ECE-1 may serve as a target for prognosis and therapy in states of pathologically altered vascular tone and/or altered myometrial smooth muscle tone in gestation.

Endothelin concentrations in monochorionic twins with severe twin-twin transfusion syndrome

The objective of this study was to determine endothelin (ET-1) concentrations in monochorionic twin fetuses with and without twin-twin transfusion syndrome (TTTS). Fourteen monochorionic twin pregnancies complicated by TTTS and six without TTTS were studied. Matched maternal and fetal blood samples were obtained both in utero and at birth. Amniotic fluid samples were also collected from twin pairs. ET-1 concentrations were measured by radio-immunoassay. ET-1 concentrations in recipient fetuses were higher than in the donors both in utero(P < 0.001) and at birth (P < 0.01). Fetal concentrations of ET-1 in donors were similar to non-TTTS twins. Plasma ET-1 concentrations were significantly higher (P < 0.01) in recipient fetuses with severe hydrops than those with mild/no hydrops. Maternal concentrations of ET-1 were comparable in the two groups. Endothelin concentrations in recipient twins were 2(1/2) times higher than in their co-twins and this was related to the severity of hydrops.

Role of the endothelium in placental dysfunction after fetal cardiac bypass

BACKGROUND

Fetal cardiac bypass causes placental dysfunction, characterized by increased placental vascular resistance, decreased placental blood flow, hypoxia, and acidosis. Vasoactive factors produced by the vascular endothelium, such as nitric oxide and endothelin 1, are important regulators of placental vascular tone and may contribute to this placental dysfunction.

METHODS

To investigate the role of the vascular endothelium in placental dysfunction related to fetal cardiac bypass, we studied 3 groups of fetal sheep. In the first group (n = 7) we determined placental hemodynamic responses before and after bypass to an endothelium-dependent vasodilator (acetylcholine), an endothelium-independent vasodilator (nitroprusside), and endothelin 1. In the second group (n = 8) a nonspecific endothelin receptor blocker (PD 145065) was administered and placental hemodynamic values were measured before and after bypass. In the third group (n = 5) endothelin 1 levels were measured before and after bypass.

RESULTS

Before fetal cardiac bypass exogenous endothelin 1 decreased placental blood flow by 9% and increased placental resistance by 9%. After bypass endothelin 1 decreased placental flow by 47% and increased resistance by 106%. There was also a significant attenuation of the placental vascular relaxation response to acetylcholine after bypass, whereas the response to nitroprusside was not significantly altered. In fetuses that received the PD 145065, placental vascular resistance increased significantly less than in control fetuses (28% versus 62%). Similarly, placental blood flow decreased significantly more (from 6. 3 +/- 3.1 to 28.3 +/- 10.4 pg/mL; P =.01) in control fetuses than in fetuses receiving PD 145065 (33% versus 20%). Umbilical venous endothelin 1 levels increased significantly in fetuses exposed to fetal bypass but did not change in control fetuses.

CONCLUSIONS

The basal endothelial regulatory mechanisms of placental vascular tone were deranged after fetal cardiac bypass. Endothelin receptor blockade, which substantially reduced postbypass placental dysfunction, and other interventions aimed at preserving endothelial function may be effective means of optimizing fetal outcome after cardiac bypass.

Endothelin-induced contractions in placental arteries is mediated by both ETA- and ETB-receptors

We have examined the contractile response to the vasoconstrictor endothelin-1 (ET-1) in uteroplacental arteries from normal pregnant women in the presence and absence of specific ET-receptor antagonists and agonists, and the vasodilator nitric oxide. Segments of placental arteries (n = 97) obtained from 37 placentas immediately after delivery were mounted in organ baths superfused with Krebs-Ringer solution at 37 degrees C. The tension was recorded isometrically and registered on a polygraph. We found that the placental artery segments responded to ET with a dose-dependent vasoconstriction. Half-maximal response was obtained at 2.6 x 10(-8) M. At 10(-7) M, the contractile response was 52% of the maximum KCl-response. The ET-1 induced contraction at 10(-7) M was inhibited by 74% after addition of the ETA-antagonist BQ-123 (10(-6) M), and by 58% by the ETB-antagonist BQ-788 (10(-6) M). Both BQ-123 and BQ-788 almost completely abolished the response to ET (10(-7) M). The selective ETB-agonist IRL-1620 also elicited vasoconstriction in the placental artery with a half maximal response at 8 x 10(-7) M. On a molar basis at 10(-7) M, the contraction by IRL-1620 as compared to ET was 30-fold lower. The contractile response of IRL-1620 (10(-6) M) was inhibited by 99% by BQ-788 (10(-6) M). After pre-contraction of the placental arteries with ET-1 (10(-7) M), the vessels relaxed in response to the nitric oxide donor, nitroglycerin (10(-6) M). The present results show that ET-1 contracts placental arteries through both ETA- and ETB-receptor activation. Nitric oxide (10(-6) M) was able to relax more than half of the initial ET-1 contraction, indicating that nitric oxide may be an important vasodilator in the placenta.

Cardiopulmonary bypass in a gravid patient: perioperative changes in endothelin levels

Transient elevations of the potent vasoconstrictive peptide endothelin have been reported to occur with the institution of cardiopulmonary bypass. We measured plasma endothelin levels in a 24-year-old gravid patient undergoing a mitral valve replacement operation. Plasma endothelin levels increased by more than 250% in the first 24 hours postoperatively and remained elevated above baseline values at 36 hours postoperatively.

Differential distribution of endothelin receptor subtypes in placentae from normal and growth-restricted pregnancies

The endothelins (ETs) are potent vasoconstrictor peptides that bind to two distinct receptors, ETA and ETB. This study compares the localization of ETA and ETB receptors in placentae complicated by intrauterine growth retardation (IUGR) and abnormal umbilical Doppler waveform, gestationally matched controls, fetuses that were small for gestational age (SGA), and normal term placentae. Quantitative autoradiography was performed using ETA and ETB subtype-selective ligands. Both ETA and ETB receptors were expressed in the human placenta. Gestational and fetal size effects on the receptor density within stem villi were found, but no effect of abnormal placental blood flow could be demonstrated. A distinct spatial distribution of receptor subtypes within the placenta was observed. Smooth muscle cells expressed both receptors with ETA expression predominant in the proximal regions of the villous tree and ETB abundant in the periphery and decidua. Both receptors were also expressed at lower density on paravascular stromal cells in stem villi. Although these data do not demonstrate aberrant localization of ET receptors in IUGR and SGA placentae, the spatially distinct distribution of ET receptors in the human placenta suggests that ETs play a role in modulation of placental blood flow.

Amniotic fluid endothelin-1 levels are increased in pregnancy-induced hypertension and intrauterine growth retardation

Endothelin-1 (ET-1) is a potent vasoconstrictor released by vascular endothelium. Because endothelial cell damage is considered determinant in the pathophysiology of pregnancy-induced hypertension (PIH), this study was conducted to evaluate the role of ET-1 produced by feto-placental tissues in PIH. Amniotic fluid samples obtained by amniocentesis from patients with PIH (N = 33), intrauterine growth retardation (IUGR) (N = 16), and PIH associated with IUGR (N = 12) were evaluated for ET-1 and compared to 42 normotensive pregnancies using a specific radioimmunoassay. ET-1 levels were significantly increased in PIH (35.6 +/- 1.9 pg/ml) and IUGR groups (33.8 +/- 4.6 pg/ml) compared to controls (20.8 +/- 1.4 pg/ml) (P < 0.01). In patients with PIH associated with IUGR, ET-1 concentrations were higher (P < 0.05) with no correlation with the severity of IUGR. Our data indicate that in PIH and IUGR ET-1 production and/or secretion is enhanced in the amniotic compartment, suggesting that the peptide may contribute to the pathophysiologic modification observed in these conditions.

Endothelial modulation of vasoconstrictor responses to endothelin-1 in human placental stem villi small arteries

1. The aim of this study was to assess the role of endothelial cells in the modulation of vasocontractile responses to endothelin-1 (ET-1) of human placental vasculature. 2. Isolated stem villi small arteries (diameter = 170-250 microns) were obtained from healthy parturients who underwent caesarean surgery during the 39th week of pregnancy for cephalo-pelvic disproportion. Isometric tension was measured in vascular rings mounted in a myograph system and challenged with ET-1 (10(-12) to 10(-6) M). 3. The vasocontractile response to ET-1 was significantly (P < 0.001) increased in endothelial-denuded (active tension = 1156 +/- 214 mN mm-1) as compared with endothelial-preserved vascular rings (active tension = 458 +/- 48 mN mm-1). This difference was significantly (P < 0.05) but only partly abolished by the NO synthase inhibitor N omega-nitro-L-arginine (L-NOARG, 10(-4) M). 4. In endothelial-preserved rings submaximally precontracted with 5-hydroxytryptamine (10(-6) M), ET-1 (10(-12) to 10(-9) M) induced dose-dependent relaxation (maximum relaxation = 70 +/- 7%) at 10(-9) M, which was followed, at higher doses (10(-8) to 10(-6) M), by a contraction. In contrast, no relaxation was seen in endothelial-denuded rings. The relaxation in rings with endothelium was significantly (P < 0.001) reduced by L-NOARG (10(-4) M. Moreover, it was totally abolished by combined pretreatment with L-NOARG (10(-4) M) and the sulphonylurea glibenclamide (10(-5) M). 5. In conclusion, endothelial cells modulate the vascular responses to ET-1 through the release of NO and a substance acting on the ATP-sensitive K+ channel of smooth muscle of stem villi small arteries from healthy parturients.

Increased immunohistochemical expression of neutral metalloendopeptidase (enkephalinase; EC 3.4.24.11) in villi of the human placenta with pre-eclampsia

The purpose of this study was to identify the presence of placental neutral metalloendopeptidase (NEP; enkephalinase; EC 3.4.24.11) in human normotensive and pre-eclamptic pregnancy. The localization of NEP in placentae from normotensive, chronic hypertensive and pre-eclamptic pregnancies was carried out on fresh frozen tissues by using a monoclonal primary antibody developed against human common acute lymphoblastic leukaemia antigen (CD10) together with the avidin-biotin-peroxidase method. In placentae from normotensive, chronic hypertensive and superimposed pre-eclamptic pregnancies, intense staining was found in the extravillous trophoblast, and also in fibroblasts of the chorionic plate and stem villi. Light to moderate staining was noted in the villous-associated trophoblast and in some cells from the villous core. In cases of pre-eclampsia, very intense staining was detected not only on the surface, but also in the cytoplasm of the villous-associated trophoblast. The increased expression of placental NEP in pre-eclampsia suggests that this enzyme may be involved in the regulation of the local concentration of circulating biologically active peptides at the fetomaternal interface, and thus could be implicated in the pathophysiological changes of this syndrome.

Pre-eclampsia and gestational age differently alter binding of endothelin-1 to placental and trophoblast membrane preparations

The aim of the study was to compare the binding of endothelin-1 (ET-1) to membranes from placental tissue and trophoblast cells in normal and pre-eclamptic pregnancies. Plasma membranes from placental tissue and trophoblastic cells were prepared from 15 control and 18 pre-eclamptic pregnancies at either preterm (weeks 31-36) or term (weeks 37-40). ET-1 binding to tissue membranes was measured by a radioreceptor assay. In addition, binding of 56 nmol/l [125I]ET-1 to plasma membranes of trophoblastic cells was determined. In pre-eclampsia, placental membranes bound less (P < 0.01) ET-1 owing to fewer (P < 0.01) receptors at preterm than in the corresponding preterm controls. In contrast, binding of [125I]ET-1 to plasma membranes of trophoblast cells was higher (P < 0.01) in pre-eclampsia at both gestational stages than in the controls. Incubation of trophoblast cells with hydralazine reduced binding by 70%. We conclude that pre-eclampsia is associated with changes in the binding of ET-1 to its placental receptors. Moreover, the data suggest that pre-eclampsia affects non-trophoblast cells in the opposite manner to the trophoblast.

Endothelin-1 conversion and receptor characterization in human placental arteries

Endothelin-1-(1-21), a potent pressor peptide, is transcribed as big endothelin-(1-38) and converted to active peptide by endothelin-converting enzyme. The current investigation tested the hypothesis that human fetoplacental blood vessels convert big endothelin-1 to active peptide and that fetoplacental blood vessels respond to endothelin-1 by binding of the peptide to specific receptor sites. In the isolated perfused placental cotyledon the addition of big endothelin-1 to the perfusate caused a time-dependent increase in perfusion pressure that corresponded to the appearance of endothelin-1 in the perfusate. The properties of human placental endothelin-1 receptors were defined in binding studies performed on a plasma membrane fraction of small arteries (<1.0 mm) dissected from the placenta. Binding was saturable, reached steady state by 3 h at 25 degrees C, and was linear with protein concentration. Scatchard analysis of binding data indicated a single class of high-affinity binding sites with a dissociation constant of 27.6 +/- 2.3 pM and a density of 856 +/- 119 fmol/mg protein (n = 5). The potency order for competitive inhibition of the binding of 125I-labeled endothelin-1 [endothelin-1 = endothelin-2 > endothelin-3 = sarafotoxin S6b >> big endothelin-1 (human) = big endothelin-1 (porcine)] is most consistent with a type A endothelin receptor subtype. Phenylephrine, bradykinin, norepinephrine, atrial natriuretic factor, diltiazem, U-46619, and angiotensin II did not displace 125I-endothelin-1 binding. Endothelin receptors were shown to have an approximate molecular weight of 36,600 by polyacrylamide gel electrophoresis.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of endothelin, calcium channel blockade and EDRF inhibition on the contractility of human uteroplacental arteries

In order to examine the possibility that endothelin might be important in the regulation of placental blood flow, human uteroplacental vessels were superfused in vitro to study the contractile effect of endothelin as compared with a known strong contractor of placental blood vessels, serotonin (5-HT). The contractile responses were compared in the presence and absence of calcium channel blocking agents, as well as in the presence of L-NMA, an inhibitor of EDRF/nitric oxide. Endothelin (ET, 10(-10)-10(-6) M) and 5-HT (10(-8)-10(-4) M) induced contractions in the vessels. Maximal contractions in the presence of endothelin were elicited at 10(-7) M, whereas 5-HT elicited maximal contractions at 10(-5) M. At 10(-7) M, ET was more potent than 5-HT. The calcium-channel blocking agents nifedipine, diltiazem and NiCl2 relaxed the vessels by 5-15% from baseline. The contractile response to ET in the presence of nifedipine or diltiazem was reduced by 55 and 67%, respectively. The response of 5-HT in the presence of nifedipine was reduced by 58%. The contractile response to 5-HT as well as ET in the presence of both nifedipine and NiCl2 was not significantly lower than in the presence of nifedipine only. The EDRF-inhibiting agent L-NMA caused a small contractile response at concentrations of 10(-6)-10(-5) M. ET as well as 5-HT added after pretreatment with L-NMA produced a larger contractile response than ET or 5-HT alone. The results show that ET has a strong contractile effect on placental blood vessels at concentrations likely to occur during labor and delivery. The mechanism whereby ET as well as 5-HT contracts placental vessel smooth muscle appears to partly involve nifedipine- and diltiazem-sensitive calcium channels, but almost half of the response depends on mobilization of calcium through other means.