Expression of the three endothelin genes and plasma levels of endothelin in pre-eclamptic and normal gestations

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.

Endothelin type B (ETB) receptors: friend or foe in the pathogenesis of pre-eclampsia and future cardiovascular disease (CVD) risk?

In a recent issue of Clinical Science, Stanhewicz et al. investigated persistent microvascular dysfunction in women up to 16 months postpartum. The authors found sensitivity to the pressor effects of endothelin-1 (ET-1) was enhanced when compared with women who had a normotensive pregnancy. Importantly, the authors demonstrated that this effect was mediated via the endothelin type B (ET_B) receptors. Therefore, the present study highlights the possibility that alterations in the localization of the ET_B receptor contributes to the pathogenesis of pre-eclampsia and future cardiovascular disease (CVD) risk. Currently, there is great interest in the role of the endothelin system in pre-eclampsia. Targetting the endothelin system, potentially by modulating upstream pathways to prevent ET_B receptor dysfunction, may improve health outcomes for women and their offspring during pre-eclampsia and later life.

Physiopathology of human embryonic implantation: clinical incidences

Embryo implantation consists of a series of events promoting the invasion of the endometrium and then the uterine arterial system by the extra-embryonic trophoblast. In order for this semi-heterologous implantation to succeed, the endometrium has to first undergo a number of structural and biochemical changes (decidualization). The decidua's various constituents subsequently play a role in the embryonic implantation. The third step is the transformation of the uterine vascular system and the growth of the placenta, which will provide the foetoplacental unit with nutrients. Several physiopathological aspects will be discussed: 1) the implantation window, regulated by maternal and embryonic hormonal secretions and thus influenced by any defects in the latter: dysharmonic luteal phase, 21-hydroxylase block, abnormal integrin expression, 2) the successive trophoblast invasions of uterine vessels which, when defective, lead to early embryo loss or late-onset vascular pathologies, as preeclampsia, 3) the pregnancy's immunological equilibrium, with a spontaneously tolerated semi-allogeneic implant, 4) the impact of pro-coagulant factors (thrombophilia) on the pregnancy's progression, 5) the environment of the uterus, ranging from hydrosalpinx to uterine contractions. In summary, the least anatomical or physiological perturbation can interfere with human embryonic implantation - a very particular phenomenon and a true biological paradox.

The emerging role of endothelin-1 in the pathogenesis of pre-eclampsia

Pre-eclampsia (PE) is the most frequently encountered medical complication during pregnancy. It is characterized by a rise in systemic vascular resistance with a relatively low cardiac output and hypovolemia, combined with severe proteinuria. Despite the hypovolemia, renin-angiotensin system (RAS) activity is suppressed and aldosterone levels are decreased to the same degree as renin. This suggests that the RAS is not the cause of the hypertension in PE, but rather that its suppression is the consequence of the rise in blood pressure. Abnormal placentation early in pregnancy is widely assumed to be an important initial event in the onset of PE. Eventually, this results in the release of anti-angiogenic factors [in particular, soluble Fms-like tyrosine kinase-1 (sFlt-1)] and cytokines, leading to generalized vascular dysfunction. Elevated sFlt-1 levels bind and inactivate vascular endothelial growth factor (VEGF). Of interest, VEGF inhibition with drugs like sunitinib, applied in cancer patients, results in a PE-like syndrome, characterized by hypertension, proteinuria and renal toxicity. Both in cancer patients treated with sunitinib and in pregnant women with PE, significant rises in endothelin-1 occur. Multiple regression analysis revealed that endothelin-1 is an independent determinant of the hypertension and proteinuria in PE, and additionally a renin suppressor. Moreover, studies in animal models representative of PE, have shown that endothelin receptor blockers prevent the development of this disease. Similarly, endothelin receptor blockers are protective during sunitinib treatment. Taken together, activation of the endothelin system emerges as an important pathway causing the clinical manifestations of PE. This paper critically addresses this concept, taking into consideration both clinical and preclinical data, and simultaneously discusses the therapeutic consequences of this observation.

Endothelin-dependent vasoconstriction in human uterine artery: application to preeclampsia

BACKGROUND

Reduced uteroplacental perfusion, the initiating event in preeclampsia, is associated with enhanced endothelin-1 (ET-1) production which feeds the vasoconstriction of uterine artery. Whether the treatments of preeclampsia were effective on ET-1 induced contraction and could reverse placental ischemia is the question addressed in this study. We investigated the effect of antihypertensive drugs used in preeclampsia and of ET receptor antagonists on the contractile response to ET-1 on human uterine arteries.

METHODOLOGY/PRINCIPAL FINDINGS

Experiments were performed, ex vivo, on human uterine artery samples obtained after hysterectomy. We studied variations in isometric tension of arterial rings in response to the vasoconstrictor ET-1 and evaluated the effects of various vasodilators and ET-receptor antagonists on this response. Among antihypertensive drugs, only dihydropyridines were effective in blocking and reversing the ET-1 contractile response. Their efficiency, independent of the concentration of ET-1, was only partial. Hydralazine, alpha-methyldopa and labetalol had no effect on ET-1 induced contraction which is mediated by both ET(A) and ET(B) receptors in uterine artery. ET receptors antagonists, BQ-123 and BQ-788, slightly reduced the amplitude of the response to ET-1. Combination of both antagonists was more efficient, but it was not possible to reverse the maximal ET-1-induced contraction with antagonists used alone or in combination.

CONCLUSION

Pharmacological drugs currently used in the context of preeclampsia, do not reverse ET-1 induced contraction. Only dihydropyridines, which partially relax uterine artery previously contracted with ET-1, might offer interesting perspectives to improve placental perfusion.

Pathophysiology of hypertension in response to placental ischemia during pregnancy: a central role for endothelin?

BACKGROUND

Preeclampsia is new-onset hypertension with proteinuria during pregnancy. The initiating event in preeclampsia has been postulated to involve reduced placental perfusion, which leads to widespread dysfunction of the maternal vascular endothelium.

OBJECTIVE

The main objective of this brief review was to highlight some of the recent advances in our understanding of the mechanisms whereby the endothelin (ET) system, via ET type A (ETA) receptor activation, modulates blood pressure in preeclamptic women and in animal models of pregnancy-related hypertension.

METHODS

This review focused on the role of ET and tumor necrosis factor-alpha (TNF-alpha) in preeclampsia, with emphasis on the pathophysiology of hypertension in response to placental ischemia in animal models of pregnancy. Relevant published data were identified by searching PubMed and supplemented with contributions from our laboratory.

RESULTS

Studies in preeclamptic women indicate that their hypertension is associated with increases in ET synthesis. Recent studies in pregnant rats indicate that the ET system is activated in response to reductions in uterine perfusion pressure and to chronic elevations in serum TNF-alpha concentrations. In these 2 animal models, the findings also suggest that ET A receptor activation may play a role in mediating hypertension.

CONCLUSIONS

Although recent studies in animal models implicate an important role for the ET system in preeclampsia, the usefulness of selective ET A receptor antagonists for the treatment of hypertension in women with preeclampsia remains unclear. This important question will not be answered until well-controlled clinical studies using specific ET A receptor antagonists are conducted for women with preeclampsia.

Pathophysiology of hypertension during preeclampsia: linking placental ischemia with endothelial dysfunction

Studies over the last decade have provided exciting new insights into potential mechanisms underlying the pathogenesis of preeclampsia. The initiating event in preeclampsia is generally regarded to be placental ischemia/hypoxia, which in turn results in the elaboration of a variety of factors from the placenta that generates profound effects on the cardiovascular system. This host of molecules includes factors such as soluble fms-like tyrosine kinase-1, the angiotensin II type 1 receptor autoantibody, and cytokines such as tumor necrosis factor-alpha, which generate widespread dysfunction of the maternal vascular endothelium. This dysfunction manifests as enhanced formation of factors such as endothelin, reactive oxygen species, and augmented vascular sensitivity to angiotensin II. Alternatively, the preeclampsia syndrome may also be evidenced as decreased formation of vasodilators such as nitric oxide and prostacyclin. Taken together, these alterations cause hypertension by impairing renal pressure natriuresis and increasing total peripheral resistance. Moreover, the quantitative importance of the various endothelial and humoral factors that mediate vasoconstriction and elevation of arterial pressure during preeclampsia remains to be elucidated. Thus identifying the connection between placental ischemia/hypoxia and maternal cardiovascular abnormalities in hopes of revealing potential therapeutic regimens remains an important area of investigation and will be the focus of this review.

Pathophysiology of preeclampsia: links with implantation disorders

The phenomenon of implantation anchors the embryo into the uterine wall and produces a hemochorial placenta that maintains the pregnancy and fetal growth. Implantation and placentation are intimately linked and cannot be dissociated either in time or in space. Preeclampsia is characterized by hypertension and proteinuria. It is secondary to an anomaly of the invasion of the uterine spiral arteries by extra-villous cytotrophoblast cells, associated with local disruptions of vascular tone, of immunological balance and inflammatory status, and sometimes with genetic predispositions. Preeclampsia is a disease of early pregnancy, a form of incomplete spontaneous abortion, but is expressed late in pregnancy. Aspirin may play a favorable role in implantation which is related to the genesis of preeclampsia and some cases of intra-uterine growth restriction. The most important points in obtaining a preventive effect from low-dose aspirin during the pregnancy are early treatment (before 13 weeks of gestation) and the prescription of a sufficient dose (more than 100 mg per day).

Searching for preeclampsia genes: the current position

Although there is substantial evidence that preeclampsia has a genetic background, the complexity of the processes involved and the fact that preeclampsia is a maternal-fetal phenomenon does not make the search for the molecular basis of preeclampsia genes easy. It is possible that the single phenotype 'preeclampsia' in fact should be divided into different sub-groups on genetic or biochemical level. In the present review, the preeclampsia phenotype and its pathophysiologic features are discussed. Family studies and postulated inheritance models are summarized. A systematic overview is given on the numerous candidate gene studies and gene-expression studies performed so far and on the currently available genome-wide scan data. Despite extensive research the molecular genetic basis of preeclampsia remains unclear. Future studies will hopefully enhance our insights in the molecular pathogenesis of preeclampsia.

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.

Endothelin type a receptor blockade attenuates the hypertension in response to chronic reductions in uterine perfusion pressure

A chronic reduction in uterine perfusion pressure in pregnant rats is associated with a significant elevation in mean arterial pressure (MAP) and reduction in kidney function. The purpose of this study was to examine the role of endothelin in mediating the hypertension in response to chronic reductions in uterine perfusion pressure in conscious, chronically instrumented, pregnant rats. MAP in pregnant rats with chronic reductions in uterine perfusion pressure (123.0+/-1.8 mm Hg) was significantly higher than that in control pregnant rats (101.3+/-4.0 mm Hg). Renal expression of preproendothelin mRNA as determined by ribonuclease protection assay was also significantly elevated in the medulla (>45%, P<0.05) and in the cortex (>22%, P:<0.05) of the pregnant rats with chronic reductions in uterine perfusion pressure compared with control pregnant rats. Chronic administration of the selective endothelin type A receptor antagonist (ABT-627, 5 mg/kg per day for 10 days) markedly attenuated the increase in MAP observed in the pregnant rats with chronic reductions in uterine perfusion pressure (103.3+/-5.6 mm Hg, plus endothelin antagonist; P<0.05). However, endothelin type A receptor blockade had no significant effect on blood pressure in the normal pregnant animals (96.0+/-2.7 mm Hg, plus endothelin antagonist). These findings suggest that endothelin plays a major role in mediating the hypertension produced by chronic reductions in uterine perfusion pressure in pregnant rats.

Long terminal repeats are used as alternative promoters for the endothelin B receptor and apolipoprotein C-I genes in humans

To examine the potential regulatory involvement of retroelements in the human genome, we screened the transcribed sequences of GenBank and expressed sequence tag data bases with long terminal repeat (LTR) elements derived from different human endogenous retroviruses. These screenings detected human transcripts containing LTRs belonging to the human endogenous retrovirus-E family fused to the apolipoprotein CI (apoC-I) and the endothelin B receptor (EBR) genes. However, both genes are known to have non-LTR (native) promoters. Initial reverse transcription-polymerase chain reaction experiments confirmed and authenticated the presence of transcripts from both the native and LTR promoters. Using a 5'-rapid amplification of cDNA ends protocol, we showed that the alternative transcripts of apoC-I and EBR are initiated and promoted by the LTRs. The LTR-apoC-I fusion and native apoC-I transcripts are present in many of the tissues tested. As expected, we found apoC-I preferentially expressed in liver, where about 15% of the transcripts are derived from the LTR promoter. Transient transfections suggest that the expression is not dependent on the LTR itself, but the presence of the LTR increases activity of the apoC-I promoter from both humans and baboons. The native EBR-driven transcripts were also detected in many tissues, whereas the LTR-driven transcripts appear limited to placenta. In contrast to the LTR of apoC-I, the EBR LTR promotes a significant proportion of the total EBR transcripts, and transient transfection results indicate that the LTR acts as a strong promoter and enhancer in a placental cell line. This investigation reports two examples where LTR sequences contribute to increased transcription of human genes and illustrates the impact of mobile elements on gene and genome evolution.

Adriana and Luisa Castellucci award lecture 1999: role of oxygen in the regulation of trophoblast gene expression and invasion

Changes in oxygen levels characterize normal and pathological human placentation. For example, relatively low Po(2)values are present around the blastocyst during implantation and in the placenta of the first trimester of pregnancy, a time of maximal trophoblast invasion. Our studies have revealed that low oxygen levels stimulate the in vitro invasiveness of cultured first trimester trophoblasts. This increased invasive ability is linked to elevated expression of some components of the plasminogen activator system and requires the participation of a putative haem protein. As gestation proceeds beyond the first trimester, and the extent of trophoblast invasion decreases, placental oxygen levels rise with a corresponding increase in blood flow. However, during certain pathological conditions, such as pre-eclampsia/intrauterine growth restriction, impaired remodelling of the uterine spiral arterioles leads to vessels with reduced diameters and localized regions of placental ischaemia/hypoxia. Placental hypoxia in the second half of gestation, as a consequence of reduced uteroplacental blood flow, may result in aberrant expression of genes that contribute to the pathophysiology of pre-eclampsia. Some of these genes encode certain cytokines and vasoactive molecules. We have also identified other genes whose expression is regulated by oxygen. Expression of one of them is induced in trophoblast and other cell types cultured under low oxygen levels and the product of the gene is a 43-kDa protein which we have termed PROXY-1. Compared to placental tissues and membranes isolated from uncomplicated pregnancies, PROXY-1 expression is elevated in tissues from pre-eclamptic pregnancies such as chorionic villi of peri-infarct regions, basal plate and membrane decidua, as well as chorion. Overall, these observations suggest that oxygen levels play an important role in placentation and in the pathophysiology of certain complications of pregnancy.

High-performance liquid chromatographic assay of the diadenosine polyphosphates in human platelets

Diadenosine pentaphosphate (Ap5A) and diadenosine hexaphosphate (Ap6A) were recently identified in human platelets and were shown to be important modulators of cardiovascular function. Here we describe an HPLC assay for quantitating Ap3A, Ap4A, Ap5A, and Ap6A contents in human platelets simultaneously. Di(1,N6-ethenoadenosine) hexaphosphate was used as internal standard. The extraction procedure consists of (a) deproteinization, (b) selective concentration of the diadenosine polyphosphates with a boronate affinity chromatography, and (c) desalting prior to the HPLC analysis. The assay was validated by PSD-MALDI-mass spectrometry and by addition of authentic diadenosine polyphosphate to platelet samples. The assay was carried out by an ion-pair reversed-phase perfusion chromatography. In platelets from human blood the following amounts of diadenosine polyphosphates were determined: Ap3A, 192.5 +/- 151.0 nM; Ap4A, 223.8 +/- 172.3 nM; Ap5A, 100.2 +/- 81.1 nM; Ap6A, 32.0 +/- 19.6 nM (mean +/- SD, n = 105). The described assay can be used with less than 20 ml blood and allows quantitation of the diadenosine polyphosphates in the picomole range.

Vasoactive mediators in pregnancy-induced hypertensive disorders: a longitudinal study

OBJECTIVE

The objective of this study was to evaluate the extent to which endothelin and the eicosanoids prostacyclin and thromboxane A2 are involved in the pathophysiology of gestational hypertension and preeclampsia.

STUDY DESIGN

In a longitudinal design, venous blood samples and 24-hour urine specimens were collected from 396 women in each trimester of pregnancy. After delivery of all patients, venous plasma endothelin was assessed in 20 subjects with identified preeclampsia, 48 subjects with gestational hypertension, and 59 normotensive subjects. Urinary excretions of the thromboxane A2 and of the prostacyclin metabolites thromboxane B2 and 6-keto-prostaglandin F1 alpha were assessed in 16 subjects with preeclampsia, 35 subjects with gestational hypertension, and 31 normotensive subjects.

RESULTS

Endothelin levels showed a second-trimester drop in all groups. In all 3 gestational trimesters a high correlation was found between the excretion of thromboxane B2 and that of 6-keto-prostaglandin F1 alpha (P <.001). The overall thromboxane B2 and 6-keto-prostaglandin F1 alpha urinary excretions increased throughout pregnancy and the overall thromboxane B2 /6-keto-prostaglandin F1 alpha ratio decreased. No significant differences in endothelin, thromboxane B2, and 6-keto-prostaglandin F1 alpha excretion levels or in thromboxane B2 /6-keto-prostaglandin F1 alpha ratios were found between women with preeclampsia, gestational hypertension, and normotension. Only in a small group of patients with severe preeclampsia (n = 2) and severe gestational hypertension (n = 2) were increased second-trimester endothelin values and increased thromboxane B2 /6-keto-prostaglandin F1 alpha ratios found.

CONCLUSION

In this longitudinal study we found no evidence for prostacyclin deficiency or increased endothelin levels in preeclampsia. Only women with severe preeclampsia and severe gestational hypertension expressed increased endothelin levels and thromboxane dominance over prostacyclin.

Differential display analysis of oxygen-mediated changes in gene expression in first trimester human trophoblast cells

Physiologic or pathologically induced periods of exposure to relatively low levels of oxygen during pregnancy affect the expression and function of certain genes in the placenta. In this study, the differential display technique was utilized to identify genes that are regulated in cultured cytotrophoblast cells by exposure to low levels of oxygen. Using this approach, four genes, which have been designated HRF-1, HRF-2, HRF-6, and HRF-8, were cloned and partially characterized. Northern blot analysis showed that clones HRF-1 and HRF-2 were downregulated in response to exposure to low levels of oxygen, whereas expression of HRF-6 and HRF-8 was increased. DNA sequencing and sequence analysis revealed that HRF-1 may represent an alternatively spliced or tissue-specific form of the Kruppel family zinc finger protein znfp104 gene. Clone HRF-2 showed a high degree of identity with exons 9, 10 and 11 of N33, a gene that is located within a homozygously deleted region of metastatic prostate cancer. Clones HRF-6 and HRF-8 did not exhibit significant sequence identity with known sequences in GenBank and may represent novel genes. None of these genes have previously been shown to be present in trophoblast cells, nor have their expressions been shown to be regulated by oxygen. This study demonstrates that the differential display technique is a novel and effective method to analyse oxygen-mediated changes in gene expression in trophoblast cells.

Review: immunobiology of preeclampsia

Preeclampsia has been recognized clinically since the time of Hippocrates: however its etiology and pathophysiology remain enigmatic. This pregnancy-specific syndrome typically presents in late pregnancy as hypertension, edema, and proteinuria. Investigations over the past 15 years have revealed that preeclampsia is associated with abnormal placentation, reduced placental perfusion, endothelial cell dysfunction, and systemic vasospasm. Since it occurs more commonly in primigravidae and in women with underlying collagen-vascular diseases, an immunological component has long been suspected. Increased prevalence in high-order and molar pregnancies and those associated with increased placental mass suggests that trophoblastic volume and fetal antigen load are correlated with the syndrome. Epidemiological reports indicate that the prevalence of preeclampsia is decreased in women who received heterologous blood transfusions, practiced oral sex, or when a long period of cohabitation preceded an established pregnancy. Conversely, the use of condoms as a primary mode of contraception is associated with a higher risk of preeclampsia. These studies suggest that prior exposure to foreign or paternal antigens imparts a protection against the likelihood of developing preeclampsia. Clinical evidence of cellular and humoral immune dysfunction is associated with the syndrome. Fibrin and complement deposition and "foam" cells in atherosis lesions resemble the histopathology of renal allograft rejection. Relative T-cell, natural killer cell, and neutrophil activation have been reported in preeclampsia and circulating cytokines and antiphospholipid antibodies are more prevalent in preeclampsia than in normal pregnant women. These abnormalities are consistent with the systemic endothelial cell dysfunction that has been postulated as a pathophysiological feature of preeclampsia. While such associations do not prove causality, they suggest testable hypotheses for continued basic and clinical investigation of this major complication of human pregnancy.

Endothelin-1 and big endothelin-1 levels in normal term pregnancy and in preeclampsia

To study the concentrations of endothelin-1 (ET-1) and its precursor, big ET-1, in samples of amniotic fluid, fetal urine, umbilical arterial and venous blood, retroplacental blood and maternal uterine and brachial venous blood obtained from normal and preeclamptic women. Samples were collected from 31 healthy pregnant women (16 in labor and 15 undergoing elective cesarean section) and 35 preeclamptic women (9 in labor and 26 undergoing cesarean section). Big ET-1 and ET-1 were measured by radioimmunoassay and the ET-1 to big ET-1 ratios were calculated. In preeclamptic women there was a significant elevation of ET-1 in the maternal brachial and uterine veins and of big-ET-1 in the brachial vein. The ET-1 concentrations and the ET-1/big ET ratios were significantly higher on the fetal side (i.e., in the umbilical vein and amniotic fluid) than in maternal blood, but in these sampling locations there was no difference between the normal pregnancy and preeclampsia group. A significant negative correlation (r = -0.67, P < 0.01) was found between plasma ET-1 in the umbilical vein and birth weight in the preeclamptic group. ET-1 was significantly higher in amniotic fluid than in the first neonatal urine of corresponding pregnancies (15.0 +/- 2.0 vs. 3.0 +/- 2.9 pmol/l, P < 0.05). The ET-1 and big ET-1 concentrations are significantly higher in fetal plasma and amniotic fluid than in maternal plasma, indicating increased endothelin converting enzyme activity and increased ET-1 production in utero. The elevated ET-1 concentration in maternal blood in preeclamptic compared with normal pregnant women and the negative correlation between ET-1 in the umbilical vein and birth weight suggest that ET-1 plays a pathophysiological role in preeclampsia and other conditions with intrauterine growth restriction.

Complexity and complicity in eclampsia: barriers or bridges?

The aetiology of pre-eclampsia-eclampsia remains largely unclarified, despite over 100 years of systematic study. The assumption that the triggering event is linear and amenable to reductionist techniques has characterized these efforts. The main purpose of this paper is to show that complexity and complicity characterize most pathophysiological processes in pre-eclampsia-eclampsia, a situation suggesting that similar mechanisms must exist at the origin of the disease. The unique configuration of the intervillous space and the intensity of energy transference through the fetomaternal interface offer many dysfunctional possibilities, even in clinically normal pregnancies. The most characteristic seem to be: the shedding and deportation of trophoblast, the fragmentation of villi, the escape of fetal blood, and events associated with trophoblast damage, degeneration and death. The pathogenic potential of these natural processes seems to depend on the association with amplifiers and permissive factors, which vary from person to person and from time to time. Thus, considering the convergence of multiple factors and the presence of nonlinearity in some of their interactions as a plausible working hypothesis, further exploration on this subject should adhere to the rules of this different reality. To find the best possible method of inquiry and to recognize its limitations will be the surest way to avoid failure.

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.

An endothelin-1 mediated autocrine growth loop involved in human renal tubular regeneration

Renal tubules have the capacity to regenerate following injury. We have investigated the possibility that tubular-derived endothelins, acting as autocrine growth factors, may be involved in this response in human kidney. ET-1 immunoreactivity was demonstrated by immunohistochemical staining in proximal tubules, distal cortical tubules and medullary collecting ducts of human kidney. In cultured human renal proximal tubular cells, RNAase protection assays demonstrated the expression of ET-1 and ET-2 mRNA's, and radioimmunoassay, following separation of conditioned medium by reverse phase HPLC, showed immunoreactive material which co-eluted with ET-1 and ET-2. Competition binding studies revealed the presence of at least two types of endothelin receptor: one with high and one with low affinity for ET-3 relative to ET-1. Analysis of cellular RNA by RT-PCR demonstrated expression of mRNA's for both ETA and ETB receptor subtypes. Combined blockade of ETA and ETB receptors (by PD-145065) but not that of ETA receptors alone (by BQ-123) blocked the mitogenic effect of exogenous or endogenous ET-1 and also profoundly suppressed endogenous ET-1 synthesis. By contrast, incubation with the ETB receptor agonist, BQ-3020, stimulated endogenous ET-1 synthesis. Exposure of the cells to hypoxia (1% O2 for 16 to 24 hr) resulted in specific up-regulation of ET-1 but not ET-2 gene expression. These findings reveal the existence of a hypoxia-inducible, autocrine growth system in human proximal tubular cells, which is mediated by ET-1 through the ETB receptor, and which could function in vivo as an autoregenerative system for restoring tubular integrity after injury. The widespread distribution of ET-1 peptide in different tubular segment suggests that ET-1 mediated tubular regeneration may also occur in other nephron segments.