Differential localization of endothelin ETA and ETB binding sites in human placenta

Human Placental Vascular Reactivity in Health and Disease: Implications for the Treatment of Pre-eclampsia

Adequate development of the placenta is essential for optimal pregnancy outcome. Pre-eclampsia (PE) is increasingly recognized to be a consequence of placental dysfunction and can cause serious maternal and fetal complications during pregnancy. Furthermore, PE increases the risk of neonatal problems and has been shown to be a risk factor for cardiovascular disease of the mother later in life. Currently, there is no adequate treatment for PE, mainly because its multifactorial pathophysiology remains incompletely understood. It originates in early pregnancy with abnormal placentation and involves a cascade of dysregulated systems in the placental vasculature. To investigate therapeutic strategies it is essential to understand the regulation of vascular reactivity and remodeling of blood vessels in the placenta. Techniques using human tissue such as the ex vivo placental perfusion model provide insight in the vasoactive profile of the placenta, and are essential to study the effects of drugs on the fetal vasculature. This approach highlights the different pathways that are involved in the vascular regulation of the human placenta, changes that occur during PE and the importance of focusing on restoring these dysfunctional systems when studying treatment strategies for PE.

Effects of Oxygen Tension and Normalization Pressure on Endothelin-Induced Constriction of Human Placental Chorionic Plate Arteries

OBJECTIVES

Fetoplacental blood vessels constrict in response to endothelin (ET-1) or reduced oxygen tension in the placental cotyledon perfused in vitro. In nonplacental resistance arteries, hypoxia and ET-1 induce constriction by promoting Ca2+ influx into smooth muscle through membrane ion channels, which include voltage-gated Ca2+ channels (VGCCs). We hypothesized that VGCCs are involved in ET-1-induced constriction of fetoplacental resistance vessels and that their contribution to constriction is enhanced at low oxygen tension.

METHODS

Chorionic plate small arteries from term placentas were studied using parallel wire myography. Arteries were normalized at 0.9 of L(5.1 kPa) ("low stretch" approximately 25 mm Hg; approximating physiologic vascular pressure) or 0.9 of L(13.3 kPa) ("high stretch" approximately 42 mm Hg) and experiments performed at oxygen tensions of 156, 38, and 15 mm Hg.

RESULTS

When chorionic plate arteries were normalized at low stretch, oxygen tension did not affect constriction to ET-1. Nifedipine (10(-4) M), a blocker of L-type VGCCs, inhibited ET-1 (EC80)-induced constriction to a similar extent at each oxygen tension (52% to 64% inhibition). In contrast, when arteries were normalized at high stretch, constriction to ET-1 was greater at 38 than at 156 or 15 mm Hg oxygen and nifedipine inhibition of ET-1-induced constriction was greater at 38 and 15 mm Hg than at 156 mm Hg oxygen.

CONCLUSIONS

VGCCs and nifedipine-insensitive processes underlie the contractile response of chorionic plate arteries to ET-1 and their relative contribution to vasoconstriction is modulated by oxygen tension when vessels are normalized at high stretch. However, contrary to our hypothesis, the response of chorionic plate arteries to ET-1 is not modulated by oxygen when vessels are normalized at physiologic pressure.

Acute effect of a dual ETA-ETB receptor antagonist on pulmonary arterial vasculature in preterm lamb fetuses with surgically induced diaphragmatic hernia

PURPOSE

To study the effects of tezosentan, a dual ETA and ETB receptor antagonist on the cardiopulmonary profile in a fetal lamb model of CDH in utero.

METHODS

A diaphragmatic hernia was surgically created at day 75 of gestation. During 45 min of tezosentan perfusion (1 mg/kg), hemodynamic parameters (pulmonary and aortic pressures, left pulmonary and aortic flows, left auricle pressure, heart rate) were measured at day 135 of gestation. Age-matched fetal lambs served as control animals. Secondarily, parietal tension of vessels rings of pulmonary arteries was assessed in organ baths under increasing concentration of tezosentan.

RESULTS

In CDH group, under perfusion of tezosentan, pulmonary artery pressure decreased from 45.8 ± 4.1 to 37.6 ± 5.9 mmHg (P < 0.05). Pulmonary artery flow and pulmonary vascular resistance remained constant. In control group, pulmonary artery flow increased from 153.9 ± 15.8 to 233.4 ± 26 ml/min (P < 0.05). Pulmonary artery pressure did not vary. Subsequently calculated pulmonary vascular resistance decreased. In organ bath, no significant relaxation was observed.

CONCLUSION

In this fetal lamb model of CDH, tezosentan decreased pulmonary artery pressure but did not modify pulmonary blood flow. Endothelin may play a role in the regulation of pulmonary vascular tone in utero.

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.

The human placenta from heavy smokers: evaluation of vasoactive peptides by immunohistochemistry

The study aimed to demonstrate the expression of nitric oxide converting enzyme, nitric oxide synthase (e-NOS), and endothelin-1 (Et-1) in formalin-fixed paraffin-embedded placental tissue, and to demonstrate a difference in staining intensity between heavy smokers and non-smokers. Term placentas from pregnancies from otherwise healthy women smoking 15 or more cigarettes per day (heavy smokers) and term placentas from a matching group of non-smokers were included. The antibodies for Et-1 and e-NOS are recommended for cryostat sections. We evaluated the antibodies on paraffin-embedded tissue combined with the streptavidin-biotin-peroxidase technique. Et-1 and e-NOS were demonstrated in the placental vasculature, the trophoblast, and the amnion. A blinded comparative study showed no reproducible significant differences in the staining intensity of the antigen-antibody reaction to Et-1 and e-NOS between the two groups.

Nitric oxide donors mediate vasodilation in human placental arteries partly through a direct effect on potassium channels

We have investigated the involvement of potassium channels in the NO-induced relaxation of small ET-1 precontracted arteries from placentas of normal pregnancies in the presence of the potassium channel modulating agents charybdotoxin, 4-AP, glibenclamide, TEA and the blocker of soluble guanylyl cyclase, ODQ, respectively. We have studied the effect of the NO-donor S-nitroso-N-acetylpenicillamine (SNAP) in vessels precontracted by different concentrations of potassium and we have also investigated the presence of BK(Ca) channels in placental arteries by immunohistochemistry and immunoblotting. Our results show that charybdotoxin, an inhibitor of large- and intermediate-conductance Ca(2+)-activated potassium channels, inhibits relaxation in placental arteries. In presence of both charybdotoxin and ODQ, the inhibition of relaxation was significantly stronger, which indicates that NO-induced relaxation of human placental arteries is partly mediated through cGMP, and partly through a direct effect on potassium channels of the BK(Ca) type. The NO-donor SNAP preferentially relaxes contractions induced by 75 mM K(+) as compared to 100 mM K(+). This effect profile is a unique feature of drugs acting by K(+) channel opening. The immunohistochemistry shows that BK(Ca) channels are located both in smooth muscle and in endothelium in placental arteries.

Immunohistochemical localization of endothelin-1 in human placenta from normal and growth-restricted pregnancies

The purpose of this study was to investigate whether the localization of endothelin-1 (ET-1) immunoreactivity differs in human placental tissues from third-trimester normal and intrauterine growth restricted (IUGR) pregnancies. Immunohistochemistry for ET-1 was performed on human placentas from 30 IUGR and 30 uncomplicated pregnancies matched for gestational age. The distribution and intensity of ET-1 immunoreactivity was assessed by a semiquantitative scoring system. Doppler flow velocity waveform analysis of the umbilical artery was performed in each patient before delivery. ET-1 was localized diffusely in placental specimens from normal and IUGR pregnancies. The localization of ET-1 immunoreactivity was significantly higher in the capillary endothelial cells of villi as well as in the endothelial, decidual, and trophoblastic cells of the basal plate in placentas from normal pregnancies than from IUGR pregnancies. There was no significant difference in placental ET-1 immunoreactivity between IUGR pregnancies with normal and abnormal umbilical artery Doppler flow velocity waveforms. Placental ET-1 immunoreactivity was significantly higher in the decidual and trophoblastic cells of the basal plate and the capillary endothelial cells of villi in normal pregnancies than in IUGR pregnancies with normal umbilical artery Doppler flow velocity waveforms. However, only the decidual and trophoblastic cells of the basal plate demonstrated significantly higher abundant localization of ET-1 immunoreactivity in normal pregnancies than in IUGR pregnancies with abnormal umbilical artery Doppler flow velocity waveforms. In conclusion, our findings suggest that the lower expression of ET-1 in placental tissues from IUGR pregnancies might be secondary to an adaptive mechanism to reduce the vasoconstrictor effect of ET-1.

ET(A) and ET(B) receptors modulate the proliferation of human pulmonary artery smooth muscle cells

We determined the distribution of ET(A) and ET(B) receptors in pulmonary arteries from pulmonary hypertensive patients and control subjects, using in vitro autoradiography, and investigated their role in mediating the proliferative effects of endothelin-1 (ET-1) on distal human pulmonary artery smooth muscle cells (PASMCs). Distal arteries possessed more medial [(125)I]-ET-1 binding sites (105 +/- 10 versus 45 +/- 6 amol/mm(2); p < 0.001) and a greater proportion of ET(B) receptors than proximal arteries (36 +/- 3% versus 3 +/- 1%; p < 0.001). Receptor density in distal arteries and lung parenchyma was twofold greater (p < 0.05) in pulmonary hypertensive patients than in control subjects. ET-1 (10(-9)-10(-7) mol/L) stimulated DNA synthesis (147 +/- 10% of control subjects; p < 0.05) and attenuated the antiproliferative action of cicaprost and forskolin on PASMCs, these effects being mediated via ET(A) and ET(B) receptors. Serum-stimulated proliferation was attenuated by inhibiting either endogenous ET-1 release with phosphoramidon (10(-5) mol/L) or its action with PD145065 (10(-5) mol/L). Cicaprost (10(-10)-10(-7) mol/L) inhibited ET-1 release from PASMCs (49 +/- 16% of control after 24 h; p < 0.001) and increased intracellular cAMP levels, whereas ET(B) receptor stimulation selectively reduced cAMP levels. In conclusion, ET(A) and ET(B) receptors are differentially distributed in human pulmonary arteries. Both receptors promote the proliferation of PASMCs in vitro and may contribute to vascular remodeling in pulmonary hypertension.

[Regulation of fetal placental circulation]

The development and the reactivity of fetoplacental circulation appear to be extremely well coordinated phenomena which follow a precise chronology and are regulated by numerous angiogenic and vasoactive factors. The endothelium of the villous vessels, due to its capacity to release vasodilatating substances, would appear to play a crucial role in the gradual decrease in the vascular resistance of the placenta, thereby enabling it to meet the growing needs of the fetus right up until the end of pregnancy. In the endothelium, as in the smooth muscle of the placental vessels, control of production and mechanisms of action of the signal modulators of placental tone--endothelin 1, nitric oxide, prostanoids, etc.--as well as their dependence on oxygen, are far from being entirely elucidated. The study of their interactions could contribute to better evaluating the relative importance of each of them in the particular balances which are established at different stages of normal pregnancy, as well as during pathological situations (pre-eclampsia, intrauterine growth retardation, etc.) when placental blood flow and fetal development are at risk of being compromised.

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.

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.

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.

Uncoupling of calcium mobilization and entry pathways in endothelin-stimulated pituitary lactotrophs

In cells expressing Ca2+-mobilizing receptors, InsP3-induced Ca2+ release from intracellular stores is commonly associated with extracellular Ca2+ influx. Operation of these two Ca2+ signaling pathways mediates thyrotropin-releasing hormone (TRH) and angiotensin II (AII)-induced prolactin secretion from rat pituitary lactotrophs. After an initial hyperpolarization induced by Ca2+ mobilization from the endoplasmic reticulum (ER), these agonists generated an increase in the steady-state firing of action potentials, further facilitating extracellular Ca2+ influx and prolactin release. Like TRH and AII, endothelin-1 (ET-1) also induced a rapid release of Ca2+ from the ER and a concomitant spike prolactin secretion during the first 3-5 min of stimulation. However, unlike TRH and AII actions, Ca2+ mobilization was not coupled to Ca2+ influx during sustained ET-1 stimulation, as ET-1 induced a long-lasting abolition of action potential firing. This lead to a depletion of the ER Ca2+ pool, a prolonged decrease in [Ca2+]i, and sustained inhibition of prolactin release. ET-1-induced inhibition and TRH/AII-induced stimulation of Ca2+ influx and hormone secretion were reduced in the presence of the L-type Ca2+ channel blocker, nifedipine. Basal [Ca2+]i and prolactin release were also reduced in the presence of nifedipine. Furthermore, TRH-induced Ca2+ influx and secretion were abolished by ET-1, as TRH was unable to reactivate Ca2+ influx and prolactin release in ET-1-stimulated cells. Depolarization of the cells during sustained inhibitory action of ET-1, however, increased [Ca2+]i and prolactin release. These results indicate that L-type Ca2+ channel represents a common Ca2+ influx pathway that controls basal [Ca2+]i and secretion and is regulated by TRH/AII and ET-1 in an opposite manner. Thus, the receptor-mediated uncoupling of Ca2+ entry from Ca2+ mobilization provides an effective control mechanism in terminating the stimulatory action of ET-1. Moreover, it makes electrically active lactotrophs quiescent and unresponsive to other calcium-mobilizing agonists.

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.

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.

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.

Control of vascular resistance in the maternal and feto-placental arterial beds

This review aims to provide a comprehensive summary of the mechanisms involved in the physiological adaptation of the vasculature to pregnancy. Profound changes occur both systemically and in discrete circulations in the mother, but it is debatable which factors are responsible. Similarly, whilst the feto-placental circulation must be substantially controlled by humoral mechanisms, the exact role of each potential contributor is not known. In view of the hitherto unappreciated and very important role of the endothelium-derived vasodilator, nitric oxide, in the control of peripheral vascular resistance, considerable emphasis will be placed on the many recent investigations in this area.

Perichondrial localization of ETA receptor in rat tracheal and xiphoid cartilage and in fetal rat epiphysis

Autoradiographic studies using 125I-labeled endothelin-1 (ET-1) on sections of rat cartilage tissues, including the trachea, xiphisternum, and fetal rat epiphysis, revealed dense localization of endothelin receptors in the perichondrium. In contrast, the binding of ET-1 was not detected in the chondrocytes, cartilage matrix, and other connective tissues of the cartilage tissues tested. The perichondrial binding of 125I-ET-1 was completely abolished with BQ-123 [an endothelin receptor subtype A (ETA) antagonist] but not with BQ-3020 (an ETB agonist), and we demonstrated the perichondrial localization of ETA receptors. [3H]thymidine incorporation in vitro was significantly increased in rat xiphoid cartilage tissues exposed to ET-1. These findings suggest that the ET-1/ETA receptor system plays an important role in regulating cartilage metabolism and endochondral bone formation.

Endothelin-1 modulates renin and prolactin release from human decidua by different mechanisms

Endothelin (ET)-1 stimulates the synthesis and release of renin and inhibits the expression of prolactin (PRL) from term human decidual cells. To examine the mechanisms by which ET-1 exerts its differential effects on renin and PRL expression, we have studied total renin and PRL release from term human decidual cells in response to pharmacological agents that affect calcium- and protein kinase C-dependent mechanisms. Calcium ionophore A-23187 stimulated basal renin release and potentiated ET-1-stimulated renin release but had no effect on basal or ET-inhibited PRL release. The calcium channel blocker nifedipine inhibited ET-1-stimulated renin release but had no effect on PRL release. The protein kinase C agonist phorbol 12-myristate 13-acetate (PMA) stimulated basal renin release and potentiated the effect of ET-1 on renin release. However, PMA inhibited basal PRL release and also enhanced the inhibitory effect of ET-1. The PKC inhibitor staurosporine increased basal PRL release and completely reversed the inhibitory effect of ET on PRL release. These results indicate that the effects of ET-1 on both decidual renin and PRL release are dependent on the activation of protein kinase C. However, the effect of ET-1 on renin release appears to be dependent on extracellular calcium, whereas the effect on PRL is not influenced by extracellular calcium.

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)