Autacoids and the control of vascular tone in the human umbilical-placental circulation

The implications of the purinergic signaling throughout pregnancy

Purinergic signaling is a necessary mechanism to trigger or even amplify cell communication. Its ligands, notably adenosine triphosphate (ATP) and adenosine, modulate specific membrane-bound receptors in virtually all human cells. Regardless of the stage of the pregnancy, cellular communication between maternal, placental, and fetal cells is the paramount mechanism to sustain its optimal status. In this review, we describe the crucial role of purinergic signaling on the regulation of the maternal-fetal trophic exchanges, immune control, and endocrine exchanges throughout pregnancy. The nature of the modulation of both ATP and adenosine on the embryo-maternal interface, going through placental invasion until birth delivery depends on the general maternal-fetal health state and consequently on the selective activation of their specific receptors. In addition, an increasing number of studies have been demonstrating the pivotal role of ATP and adenosine in modulating deleterious effects of suboptimal conditions of pregnancy. Here, we discuss the role of purinergic signaling on the balance that coordinates the embryo-maternal exchanges and a promising therapeutic venue in the context of pregnancy disorders.

Fetal High-Density Lipoproteins: Current Knowledge on Particle Metabolism, Composition and Function in Health and Disease

Cholesterol and other lipids carried by lipoproteins play an indispensable role in fetal development. Recent evidence suggests that maternally derived high-density lipoprotein (HDL) differs from fetal HDL with respect to its proteome, size, and function. Compared to the HDL of adults, fetal HDL is the major carrier of cholesterol and has a unique composition that implies other physiological functions. Fetal HDL is enriched in apolipoprotein E, which binds with high affinity to the low-density lipoprotein receptor. Thus, it appears that a primary function of fetal HDL is the transport of cholesterol to tissues as is accomplished by low-density lipoproteins in adults. The fetal HDL-associated bioactive sphingolipid sphingosine-1-phosphate shows strong vasoprotective effects at the fetoplacental vasculature. Moreover, lipoprotein-associated phospholipase A2 carried by fetal-HDL exerts anti-oxidative and athero-protective functions on the fetoplacental endothelium. Notably, the mass and activity of HDL-associated paraoxonase 1 are about 5-fold lower in the fetus, accompanied by an attenuation of anti-oxidative activity of fetal HDL. Cholesteryl ester transfer protein activity is reduced in fetal circulation despite similar amounts of the enzyme in maternal and fetal serum. This review summarizes the current knowledge on fetal HDL as a potential vasoprotective lipoprotein during fetal development. We also provide an overview of whether and how the protective functionalities of HDL are impaired in pregnancy-related syndromes such as pre-eclampsia or gestational diabetes mellitus.

Impaired vasocontractile responses to adenosine in chorionic vessels of human term placenta from pregnant women with pre-existing and gestational diabetes

BACKGROUND

There is clinical and experimental evidence for altered adenosine signalling in the fetoplacental circulation in pregnancies complicated by diabetes, leading to adenosine accumulation in the placenta. However, the consequence for fetoplacental vasocontractility is unclear. This study examined contractility to adenosine of chorionic vessels from type 1 diabetes mellitus, gestational diabetes mellitus and normal pregnancies.

METHODS

Chorionic arteries and veins were isolated from human placenta from normal, gestational diabetes mellitus and type 1 diabetes mellitus pregnancies. Isometric tension recording measured responses to adenosine and the thromboxane A₂ analogue U46619 (thromboxane A₂ mediates fetoplacental vasoconstriction to adenosine). Adenosine and thromboxane prostanoid receptor protein expression was determined by immunoblotting.

RESULTS

Adenosine elicited contractions in chorionic arteries and veins which were impaired in both gestational diabetes mellitus and type 1 diabetes mellitus. Contractions to potassium chloride were unchanged. Adenosine A_2A and A_2B receptor protein levels were not different in gestational diabetes mellitus and normal pregnancies. Contractions to U46619 were unaltered in gestational diabetes mellitus arteries and increased in type 1 diabetes mellitus arteries. Overnight storage of vessels restored contractility to adenosine in gestational diabetes mellitus arteries and normalized contraction to U46619 in type 1 diabetes mellitus arteries.

CONCLUSION

These data are consistent with the concept of aberrant adenosine signalling in diabetes; they show for the first time that this involves impaired adenosine contractility of the fetoplacental vasculature.

Molecular and cellular underpinnings of normal and abnormal human placental blood flows

Abnormal placental function is well-established as a major cause for poor pregnancy outcome. Placental blood flow within the maternal uteroplacental compartment, the fetoplacental circulation or both is a vital factor in mediating placental function. Impairment in flow in either or both vasculatures is a significant risk factor for adverse pregnancy outcome, potentially impacting maternal well-being, affecting immediate neonatal health and even influencing the long-term health of the infant. Much remains unknown regarding the mechanistic underpinnings of proper placental blood flow. This review highlights the currently recognized molecular and cellular mechanisms in the development of normal uteroplacental and fetoplacental blood flows. Utilizing the entities of preeclampsia and fetal growth restriction as clinical phenotypes that are often evident downstream of abnormal placental blood flow, mechanisms underlying impaired uteroplacental and fetoplacental blood flows are also discussed. Deficiencies in knowledge, which limit the efficacy of clinical care, are also highlighted, underscoring the need for continued research on normal and abnormal placental blood flows.

Placental Stem Villus Arterial Remodeling Associated with Reduced Hydrogen Sulfide Synthesis Contributes to Human Fetal Growth Restriction

Intrauterine fetal growth restriction (IUGR) is often associated with compromised umbilical arterial flow, indicating increased placental vascular resistance. Oxidative stress is causatively implicated. Hydrogen sulfide maintains differentiated smooth muscle in vascular beds, and its synthetic enzyme cystathionine-γ-lyase (CSE) is down-regulated in growth-restricted placentas. We hypothesized that remodeling of resistance arteries in stem villi contributes to IUGR by compromising umbilical blood flow via oxidative stress, reducing hydrogen sulfide signaling. Stem villus arteries in human IUGR placentas displaying absent or reversed end-diastolic flow contained reduced myosin heavy chain, smooth muscle actin, and desmin, and increased markers of dedifferentiation, cellular retinol-binding protein 1, and matrix metalloproteinase 2, compared to term and preterm controls. Wall thickness/lumen ratio was increased, lumen diameter decreased, but wall thickness remained unchanged in IUGR placentas. CSE correlated positively with myosin heavy chain, smooth muscle actin, and desmin. Birth weight correlated positively with CSE, myosin heavy chain, smooth muscle actin, and desmin, and negatively with cellular retinol-binding protein 1 and matrix metalloproteinase 2. These findings could be recapitulated in vitro by subjecting stem villus artery explants to hypoxia-reoxygenation, or inhibiting CSE. Treatment with a hydrogen sulfide donor, diallyl trisulfide, prevented these changes. IUGR is associated with vascular remodeling of the stem villus arteries. Oxidative stress results in reduction of placental CSE activity, decreased hydrogen sulfide production, and smooth muscle cell dedifferentiation in vitro. This vascular remodeling is reversible, and hydrogen sulfide donors are likely to improve pregnancy outcomes.

Role of the fetoplacental endothelium in fetal growth restriction with abnormal umbilical artery Doppler velocimetry

Growth-restricted fetuses with absent or reversed end-diastolic velocities in the umbilical artery are at substantially increased risk for adverse perinatal and long-term outcome, even in comparison to growth-restricted fetuses with preserved end-diastolic velocities. Translational studies show that this Doppler velocimetry correlates with fetoplacental blood flow, with absent or reversed end-diastolic velocities signifying abnormally elevated resistance within the placental vasculature. The fetoplacental vasculature is unique in that it is not subject to autonomic regulation, unlike other vascular beds. Instead, humoral mediators, many of which are synthesized by local endothelial cells, regulate placental vascular resistance. Existing data demonstrate that in growth-restricted pregnancies complicated by absent or reversed umbilical artery end-diastolic velocities, an imbalance in production of these vasoactive substances occurs, favoring vasoconstriction. Morphologically, placentas from these pregnancies also demonstrate impaired angiogenesis, whereby vessels within the terminal villi are sparsely branched, abnormally thin, and elongated. This structural deviation from normal placental angiogenesis restricts blood flow and further contributes to elevated fetoplacental vascular resistance. Although considerable work has been done in the field of fetoplacental vascular development and function, much remains unknown about the mechanisms underlying impaired development and function of the human fetoplacental vasculature, especially in the context of severe fetal growth restriction with absent or reversed umbilical artery end-diastolic velocities. Fetoplacental endothelial cells are key regulators of angiogenesis and vasomotor tone. A thorough understanding of their role in placental vascular biology carries the significant potential of discovering clinically relevant and innovative approaches to prevention and treatment of fetal growth restriction with compromised umbilical artery end-diastolic velocities.

Control of the fetoplacental circulation

This year marks the 250th anniversary of the discovery by William Hunter of the existence of two distinct circulations within the human placenta. Until relatively recently the placenta has been viewed with “respect” – a passive structure which occasionally elicited fear and anxiety if implanted either too low or too deep. More recently our understanding of perinatal physiology, blood flow regulation and epidemiological data linking prenatal events with adult disease has created renewed interest in the placenta. This review will focus on the regulation of fetal blood flow in the placenta, the possible mechanisms whereby it may be deranged and why this might be relevant to adult disease.

Intérêt du sulfate de magnésium dans la prise en charge de la prééclampsie

In case of eclampsia, and especially in case of preeclampsia, no consensus exist in order to treat or to prevent convulsions by routine use of magnesium sulphate, at least in France. However, a large, multicentre, randomised trial compared the efficacy of magnesium sulphate with diazepam or phenytoin in eclamptic women. In this trial, magnesium sulphate was associated with a significantly lower rate of recurrent seizures and lower rate of maternal death than that observed with other anticonvulsants. The primary objective of magnesium sulphate prophylaxis in women with preeclampsia is to prevent or reduce the rate of eclampsia and complications associated with eclampsia. There are 3 large randomised controlled trials comparing the use of magnesium sulphate to prevent convulsions in patients with severe preeclampsia: the first one was vs phenytoin, the second vs placebo, and the third vs nimodipine. Patients receiving magnesium sulphate presented a significant lower risk of eclampsia than that observed with other comparison groups, probably by decreasing the cerebral perfusion pressure, thus avoiding a cerebral barotrauma. However, several arguments balance a wide use of magnesium sulphate: the prevalence of eclampsia in the Western world is very low, the use of magnesium sulphate does not affect the neonatal morbidity and mortality, and it is associated with a high rate of side effects, sometimes severe, such as respiratory depression. Thus, the benefit to risk ratio has to guide the use of magnesium sulphate and is directly correlated to the prevalence of eclampsia according to the risk of considered group. 1) The rate of seizures in women with mild preeclampsia not receiving magnesium sulphate is very low. Magnesium sulphate may potentially be associated with a higher number of adverse maternal effects. Therefore, the benefit to risk ratio does not support routine use of magnesium sulphate prophylaxis in this group. 2) On the other hand, the higher rate of seizures in women with severe preeclampsia (2.0%), especially in those who have imminent eclampsia, justifies prophylaxis with magnesium sulphate.

HO in pregnancy

The enzyme heme oxygenase (HO) has been implicated in several physiological functions throughout the body including control of vascular tone and regulation of the inflammatory and apoptotic cascades as well as contributing to the antioxidant capabilities in several organ systems. These various properties attributed to HO are carried out through the catalytic products of heme degradation, namely carbon monoxide (CO), biliverdin, and free iron (Fe2+). As the newly emerging roles of HO in normal organ function have come to light, researchers in several disciplines have assessed the role of this enzyme in various physiological and pathological changes taking place in the human body over a lifetime. Included in this new wave of interest is the involvement of HO, and its by-products, in the normal function of the vital organ of pregnancy, the placenta. In this review the role of HO, and its catalytic products, will be examined in the context of pregnancy. The different isoforms of the HO enzyme (HO-1, HO-2, HO-3) have been localized throughout placental tissue, and have been shown to be physiologically active. The HO protein and more specifically its catalytic by-products (CO, biliverdin, and Fe2+) have been postulated to be involved in the maintenance of uterine quiescence throughout gestation, regulation of hemodynamic control within the uterus and placenta, regulation of the apoptotic and inflammatory cascades in trophoblast cells, and the maintenance of a balance of the oxidant-antioxidant status within the placental tissues. The association between this enzyme system, and its above-noted roles throughout pregnancy, with the hypertensive disorder of pregnancy preeclampsia (PET), will also be examined. It is hypothesized that a decrease in HO expression and/or activity throughout gestation would be capable of initiating several pathological processes involved in the etiology of PET. This hypothesis has led to further discussion emphasizing the possibility of novel therapeutic designs targeting this enzyme system for the treatment of PET.

A comparison of magnesium sulfate and nimodipine for the prevention of eclampsia

OBJECTIVE

Magnesium sulfate may prevent eclampsia by reducing cerebral vasoconstriction and ischemia. Nimodipine is a calcium-channel blocker with specific cerebral vasodilator activity. Our objective was to determine whether nimodipine is more effective than magnesium sulfate for seizure prophylaxis in women with severe preeclampsia.

METHODS

We conducted an unblinded, multicenter trial in which 1650 women with severe preeclampsia were randomly assigned to receive either nimodipine (60 mg orally every 4 hours) or intravenous magnesium sulfate (given according to the institutional protocol) from enrollment until 24 hours post partum. High blood pressure was controlled with intravenous hydralazine as needed. The primary outcome measure was the development of eclampsia, as defined by a witnessed tonic-clonic seizure.

RESULTS

Demographic and clinical characteristics were similar in the two groups. The women who received nimodipine were more likely to have a seizure than those who received magnesium sulfate (21 of 819 [2.6 percent] vs. 7 of 831 [0.8 percent], P=0.01). The adjusted risk ratio for eclampsia associated with nimodipine, as compared with magnesium sulfate, was 3.2 (95 percent confidence interval, 1.1 to 9.1). The antepartum seizure rates did not differ significantly between groups, but the nimodipine group had a higher rate of postpartum seizures (9 of 819 [1.1 percent] vs. 0 of 831, P=0.01). There were no significant differences in neonatal outcome between the two groups. More women in the magnesium sulfate group than in the nimodipine group needed hydralazine to control blood pressure (54.3 percent vs. 45.7 percent, P<0.001).

CONCLUSIONS

Magnesium sulfate is more effective than nimodipine for prophylaxis against seizures in women with severe preeclampsia.

Thromboxane A(2) limits differentiation and enhances apoptosis of cultured human trophoblasts

Prostanoids influence differentiation in diverse cell types. Altered expression of cyclooxygenase and prostaglandins has been implicated in the pathophysiology of placental dysfunction, which results in preeclampsia and fetal growth restriction. We hypothesized that prostanoids modulate differentiation and apoptosis in cultured human trophoblasts. Villous cytotrophoblasts were isolated from term human placentas and cultured in serum-free medium. The level of human chorionic gonadotropin was used as a marker of biochemical differentiation of primary trophoblasts, and syncytia formation was used as a marker of morphologic differentiation. Of the prostanoids tested, we found exposure to thromboxane A(2) hindered both biochemical and morphologic differentiation of cultured trophoblasts. As expected, human chorionic gonadotropin levels in the media were elevated in a concentration-dependent manner in the presence of the thromboxane synthase inhibitor, sodium furegrelate, or the thromboxane A(2) receptor blocker SQ 29,548. Furthermore, thromboxane A(2) enhanced trophoblast apoptosis, determined using terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining, cell morphology, and a concentration-dependent increase in p53 expression. We conclude that thromboxane A(2) hinders differentiation and enhances apoptosis in cultured trophoblasts from term human placenta. We speculate that thromboxane may contribute to placental dysfunction by restricting differentiation and enhancing apoptosis in human trophoblasts.

Autacoid interactions in the regulation of blood flow in the human placenta

1. Interactions between autacoids may play important roles in the regulation of blood flow in the foetal placenta. In order to investigate this aspect of placental haemodynamics, human normal-term placentae were perfused in vitro and the responses of the foetal vessels to various combinations of vasoactive agents were determined. 2. Vasoconstriction responses to 5-hydroxytryptamine (5-HT) were potentiated in the presence of endothelin-1 (ET-1), the thromboxane A2-mimetic U46619 and a nitric oxide synthase inhibitor, N-nitro-L-arginine (NOLA), but not in the presence of angiotensin II. 3. N-Nitro-L-arginine caused vasoconstriction of the perfused placenta and indomethacin attenuated this effect and blocked the potentiation of the 5-HT response by NOLA. 4. Indomethacin did not affect ET-1-induced pressure increases and infusion of U46619 had no effect on release of ET-like immunoreactivity into the foetal placental circulation. 5. The present study provides evidence of interactions between several autacoids in human perfused placentae in vitro. These interactions may play important roles in foetal placental haemodynamics in normal or pathological situations.

Plasma and platelet concentration and platelet uptake of serotonin in normal and pre-eclamptic pregnancies

Pharmacologic and methodologic advances over the last decade have resulted in a body of information implicating serotonin as a mediator in the genesis of pre-eclamptic hypertension. Platelets contain the largest storage of serotonin in peripheral blood and have the ability to take up this amine from surroundings, store and release it by several mechanisms. Plasma and platelet serotonin concentrations and platelet serotonin uptake have been measured in 8 non-pregnant women, 12 normal pregnant women and 8 women with severe pre-eclampsia. Plasma serotonin concentration was significantly higher in severely preeclamptic women, compared with age and gestation matched normal pregnant women. In addition, plasma serotonin concentration was directly related to systolic and diastolic blood pressure with severity of the syndrome. Furthermore, platelet serotonin concentration in women with pre-eclampsia was significantly higher than in non-pregnant controls, but it was not significantly different from the normal pregnant women. Moreover, serotonin is effectively taken up by platelets through a saturable transport process. The calculated apparent Km for serotonin uptake process did not differ significantly among non-pregnant women, normal pregnant women and women with pre-eclampsia. However, Vmax values were significantly higher in women with pre-eclampsia than in the normotensive pregnant women. As the actions of serotonin in the periphery could be terminated primarily by active uptake system by platelets and placenta, significant alterations in the rate of transport could result in physiologically significant changes in serotonin levels. These data raise the possibility that abnormal regulation of transporter function is involved in the etiology of pre-eclampsia.

Mediation by 5-HT2 receptors of 5-hydroxytryptamine-induced contractions of human placental vein

1. In isolated human placental chorionic vein segments, 5-hydroxytryptamine (5-HT; 10(-8) to 5 x 10(-5) M) elicited concentration-dependent contractions with EC50 = 5.5 (5.2-5.7) x 10(-8) M) and Emax = 93.1 +/- 7.3% of 75 mM KCl-induced contraction. 2. The agonist of 5-HT2 receptors, alpha-methyl-5-hydroxytryptamine, and the selective agonist of 5-HT1 receptors, N,N-dipropyl-5-carboxamidotryptamine and 5-carboxamidotryptamine, induced pronounced concentration-related contractions, which reached 71.1 +/- 6.0%, 53.0 +/- 5.0% and 75.0 +/- 7.8% at the highest dose tested, respectively. The agonist of 5-HT3 receptor, 2-methyl-5-hydroxytryptamine, reached a maximum averaging 36.7 +/- 5.1% of the maximal response to KCl. 3. The 5-HT1 and 5-HT3 receptor antagonists, methiothepin and metoclopramide (10(-7) to 10(-6) M) did not alter the response to 5-HT. However, ketanserin (10(-7) to 10(-6) M), a 5-HT2 receptor antagonist, induced significant inhibition of the concentration-response curve to 5-HT. 4. Contractile responses to 5-carboxamidotryptamine and 2-methyl-5-hydroxytryptamine were not affected by methiothepin and metoclopramide, respectively, whereas ketanserin significantly attenuated the contractile response to these agonists. 5. In conclusions, our study shows that 5-HT2 receptors mediate contraction of the human placental vein with no obvious role for 5-HT1-like, or 5-HT3 receptors.

Ethanol and parturition: a role for prostaglandins

A common pattern of birth defects was reported in children born to alcoholic women over 20 years ago. Shortly thereafter the constellation of defects became known as the Fetal Alcohol Syndrome, and reports from around the world served to acknowledge the pervasiveness of the disorder. Simultaneously with the clinical reports, animal models were developed to characterize the full spectrum of the teratogenic effects of ethanol. Not only did these animal models serve to define the actions of ethanol on fetal growth and development at the molecular pharmacological, neuroanatomical, and behavioral level, but unintentionally, they have resulted in renewed scientific interest in the effects of ethanol on pregnancy and parturition itself. The purpose of this review is twofold. First we will consolidate and summarize data from both clinical and basic research that pertains to ethanol and parturition. These data will demonstrate that ethanol consumption during pregnancy results in both delayed as well as premature delivery depending upon the pattern of consumption and timing of exposure. With these data as a background, the second objective will be to present a theoretical case for prostaglandins as possible mediators of ethanol-induced effects on the onset of parturition.

The release of 15-hydroxyeicosatetraenoic acid by human placental trophoblast is increased in preeclampsia

OBJECTIVE

We tested the hypothesis that trophoblast produces 15-hydroxyeicosatetraenoic acid, and its level is elevated in trophoblast from preeclamptic women compared with normal. We also used selective enzymatic inhibitors to determine the relative contributions of 15-lipoxygenase and the two isozymes of prostaglandin H synthase to 15-hydroxyeicosatetraenoic acid levels.

STUDY DESIGN

Cytotrophoblasts isolated from placentas of normal or preeclamptic women were cultured in the presence or absence of enzyme inhibitors. Media levels of 15-hydroxyeicosatetraenoic acid were measured by radioimmunoassay.

RESULTS

When compared with normal pregnancies, cytotrophoblasts from preeclamptic pregnancies released up to fivefold higher levels of 15-hydroxyeicosatetraenoic acid. Aspirin, an inhibitor of both the prostaglandin H synthase-1 and prostaglandin H synthase-2 isozymes, and nordihydroguaiaretic acid, a selective inhibitor of lipoxygenases, both significantly inhibited 15-hydroxyeicosatetraenoic acid production. In contrast, the selective prostaglandin H synthase-2 inhibitor NS-398 had no effect on 15-hydroxyeicosatetraenoic acid release in the absence of aspirin, but NS-398 reduced 15-hydroxyeicosatetraenoic acid levels in normal trophoblast pretreated with aspirin.

CONCLUSIONS

The data indicate that 15-hydroxyeicosatetraenoic acid is produced in trophoblasts and its release by cytotrophoblasts is higher in preeclamptic pregnancies compared with normal controls. Both lipoxygenase and prostaglandin H synthase contribute to 15-hydroxyeicosatetraenoic acid production, and aspirin reduces 15-hydroxyeicosatetraenoic acid secretion. We suggest 15-hydroxyeicosatetraenoic acid plays a role in the oxidation of lipoproteins and the endothelial damage characteristic of preeclampsia.

Vascular effects of PTHrP (1-34) and PTH (1-34) in the human fetal-placental circulation

The aim of this study was to examine the vasodilatory effects of parathyroid hormone-related protein (PTHrP) (1-34) and parathyroid hormone (PTH) (1-34) on the human fetal-placental circulation utilising an in vitro placental perfusion model. In all experiments, the vasculature of an isolated human placental cotyledon was pre-constricted with the thromboxane A2 mimetic U46619. A simple dose of PTHrP (1-34) or PTH (1-34) (1.7-300 nM) was then infused into the fetal-placental circulation of the cotyledon. In other experiments, cotyledons were repeatedly infused with PTHrP (1-34) or PTH (1-34) (51.3 nM). Vasodilatory responses were significantly reduced in response to repeated exposure to PTHrP (1-34) (P < 0.001), indicating that this peptide desensitizes the fetal-placental vasculature. PTHrP (1-34) and PTH (1-34) equipotently stimulated a significant vasodilation of the fetal-placental circulation (P < 0.0001). The PTHrP receptor antagonist [Asn10, Leu 11]PTHrP (7-34) (102 nM) was infused in U46619-constricted placentae in the presence and absence of PTHrP (1-34) (10.2 nM). The PTHrP antagonist alone had no significant effect in the fetal-placental circulation. The antagonist significantly attenuated the response to PTHrP (1-34) (P < 0.015). Based on the data obtained in this study it is suggested that locally produced PTHrP (1-34) may be involved in the regulation of normal human fetal-placental vascular tone in autocrine and/or paracrine fashion.

Serotonin-induced vasoconstriction is mediated by thromboxane release and action in the human fetal-placental circulation

The possibility that prostanoids mediate the contractile response of serotonin on placental vessels was investigated. Rings of chorionic plate arteries and veins with and without endothelium were suspended in an organ bath for recording isometric mechanically activity. Serotonin caused dose-dependent contractions that were significantly attenuated by indomethacin (cyclo-oxygenase inhibitor, 10 microM) and SQ29,548 (thromboxane receptor antagonist, 1 microM). Pretreatment of placental venous and arterial rings with indomethacin decreased sensitivity (EC50) to serotonin of 2.3- and 1.9-fold, respectively. Pretreatment with SQ29,548 decreased sensitivity to serotonin of twofold in veins and 2.1-fold in arteries. In the endothelium-denuded placental arteries and veins, pretreatment with indomethacin and SQ29,548 reduced the serotonin-induced contraction in a similar way to that obtained in the endothelium-intact vessels. In isolated perfused cotyledon through the fetal circulation, serotonin caused a significant increase in perfusion pressure and stimulated thromboxane release 1.9-fold compared with basal values. Therefore, serotonin-induced vasoconstriction in the human fetoplacental circulation appears to be mediated in part by thromboxane release or action. This effect is not dependent on mediators released from the endothelium. The present study provides evidence for the participation of thromboxane A2 in the contractile response to serotonin in the human placental circulation. The ability of serotonin to release thromboxane A2 which is also a potent vasoconstrictor agent, may be important in increase fetoplacental resistance, one of the features of pre-eclampsia.

Effects of variation in oxygen tension on responses of the human fetoplacental vasculature to vasoactive agents in vitro

The human placenta perfused in vitro with Krebs' solution has been used to examine the effects of low oxygen tension on the vasoreactivity of the fetal placental vessels to several vasodilator and vasocontrictor autacoids. Increases in fetal arterial perfusion pressure (FAP) produced by endothelin-1 (ET-1, human), the thromboxane A2-mimetic U46619, 5-hydroxytryptamine (5-HT), angiotensin II (A II) and bradykinin (BK) were examined under conditions of high ( >or= 450 mmHg) and low <or= 50 mmHg) O2 tension. Similarly, decreases in pressure produced by adenosine triphosphate (ATP) and arachidonic acid (AA) were examined. The effects of these autacoids on the fetoplacental vasculature during low oxygen perfusion was compared to that obtained following nitric oxide synthase inhibition with N omega-nitro-L-arginine, (L-NOARG, 100 microns). Increases in FAP caused by ET-1, U46619, and 5-HT on fetoplacental blood vessels were not altered significantly at low oxygen tension, although that in response to BK was enhanced. Increases in FAP caused by A II were unchanged at low oxygen tension. ATP-induced decreases in FAP were reduced whereas AA-mediated changes were unchanged. Both low oxygen tension and L-NOARG produced an elevation in basal perfusion pressure. Perfusion of the human placenta with Krebs' solution of low oxygen tension may compromise placental vascular function. Impaired placental oxygenation may contribute to the development and severity of vasoconstriction in the placenta associated with pre-eclampsia/pregnancy induced hypertension.

Endothelial modulation of vascular tone and 5-hydroxytryptamine-induced responses in human chorionic arteries and veins

1. In vitro studies were undertaken to evaluate the potential role of endothelium through release of vasodilators compounds on basal tension and on vasoconstrictor response induced by 5-hydroxytryptamine (5-HT) in chorionic arteries and veins rings from normotensive gestants. 2. N omega-nitro-L-arginine (100 microM) and methylene blue (10 microM) increased significantly the basal tension in chorionic arteries but not in veins. However, indomethacin (10 microM) inhibited the basal tension in both kinds of vessels. 3. The sensitivity to 5-HT was significantly lower in placental arteries than in veins. Removal of endothelium increased the sensitivity of placental arteries to 5-HT in 2.2-fold; however, in veins denudation had no significant effect. 4. N omega-nitro-L-arginine potentiated the 5-HT-induced tone in both types of vessels, but the increase of contraction was greater in chorionic arteries than in veins. However, indomethacin decreased the 5-HT-induced contractions in arteries and veins. 5. These results indicate that NO is more important than vasodilators prostanoids in the control of vascular tone and in 5-HT-induced placental contractile response.

The interaction of nitric oxide and superoxide in the human fetal-placental vasculature

OBJECTIVE

Our purpose was to study the interaction of nitric oxide and superoxide anion on the vasculature of the isolated perfused human placental cotyledon.

STUDY DESIGN

Isolated placental cotyledons were preconstricted with the thromboxane mimetic U46619, and fetal perfusion pressure was used as an index of response. The interaction of nitric oxide and O2- was studied by three protocols: (1) with endogenous nitric oxide, (2) with addition of exogenous nitric oxide, and (3) with inhibition of nitric oxide synthesis by the nitric oxide synthase inhibitor N-nitro-L-arginine. O2- was generated by infusion of purine-xanthine oxidase. Statistical significance of response to treatment was determined by paired t test.

RESULTS

Infusion of xanthine oxidase with purine in the presence of endogenous nitric oxide resulted in vasodilation (p < 0.05). Vasodilation was more pronounced in the presence of exogenous nitric oxide (p < 0.008). Coinfusion of xanthine oxidase with purine in the presence of N-nitro-L-arginine to inhibit nitric oxide synthesis resulted in vasoconstriction.

CONCLUSION

We conclude that, rather than superoxide inactivating nitric oxide, interaction of the two radicals generates in the placental vasculature a vasodilator, which may be peroxynitrite.

Effect of ethanol on prostacyclin, thromboxane, and prostaglandin E production in human umbilical veins

The purpose of this study was to determine the effects of ethanol on prostacyclin (PGI2), prostaglandin E (PGE), and thromboxane (TXA2) production in perfused human umbilical veins. PGI2, PGE, and TXA2 levels were measured from human umbilical veins perfused with either 25, 50, or 100 mM ethanol by radioimmunoassay of their stable metabolites. Alcohol content was measured by an enzymatic spectrophotometric assay. Data were analyzed by ANOVA and Fisher's Protected Least Significant Difference Test. Ethanol decreased PGI2 production in a concentration-dependent manner (p < 0.05). In a concentration of 25 mM, ethanol did not affect PGI2 production, whereas 50 mM decreased levels after 60 min of perfusion (p < 0.01). With 100 mM ethanol, PGI2 production was decreased after 15, 30, and 60 min of perfusion (ps < 0.05), and the TXA2/PGI2 ratio was significantly elevated at all time points (p < 0.01). Ethanol (100 mM) did not affect TXA2 or PGE production. Reduction of PGI2 levels and the increase in the TXA2/PGI2 ratio seen after ethanol perfusion in umbilical veins may cause vascular disruption in the umbilical-placental circulation. This may, in part, be a contributing mechanism to the teratogenic effects of ethanol.

Human umbilical vessels: responses to agents frequently used in obstetric patients

OBJECTIVE

Our purpose was to study the effects of some drugs frequently used in pregnant women on isolated human umbilical artery and vein segments.

STUDY DESIGN

Umbilical artery and vein rings from normal term pregnancies were mounted in Krebs-bicarbonate solution in organ baths for isometric tension recording. Rings were contracted with potassium chloride (60 mmol/L) or U46619 (10(-8) mol/L) and then exposed to cumulative concentrations of nimodipine, nifedipine, nicardipine, phenytoin, magnesium sulfate, and hydralazine. Concentration-response curves were constructed by means of the difference in the percent relaxation between test and control vessels. Data analysis was by repeated measures analysis of variance, Newman-Keuls test, and the unpaired Student t test as appropriate. A value of p < 0.05 was considered statistically significant.

RESULTS

All the agents studied were effective umbilical vasodilators, except for hydralazine, which had minimal effect. The dihydropyridine calcium antagonists were more potent vasodilators than were the other agents studied. Nifedipine was the most potent calcium blocker and was the only dihydropyridine that relaxed the umbilical vein to a greater extent than the umbilical artery.

CONCLUSION

The most commonly used drugs in preeclampsia have variable effects on the umbilical vessels.

Placental insights into neurodevelopmental and other childhood diseases

Deficient information regarding placental pathology has compromised epidemiological investigations of cerebral palsy, mental retardation, and other diseases. This article reviews light microscopic signs of low placental blood flow, fetal nucleated red blood cells, villitis (villous inflammatory lesions), chorangiosis (placental villous capillary hypervascularity), meconium staining, and chorioamnionitis. These findings can be used with data of birth weight, head circumference, and length to document the duration of fetal disease. The article includes pathophysiological considerations; for example, chorioamnionitis and fetal meconium discharge may cause autacoids to produce fetal hypoperfusion of the fetal brain and other vital organs.

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.

The extravascular contractile system in the human placenta. Morphological and immunocytochemical investigations

In the human placenta, besides the fetal blood vessel system a second extravascular contractile system exists. It is localized in the chorionic plate and runs in a longitudinal direction and adjacent to fetal blood vessels into the stem villi, where it forms perivascular contractile sheaths. Characteristically, cells of the extravascular contractile system are extremely long and spindle-shaped and give rise to fine cell processes, by which they obviously contact each other or insert into the basement membrane of the trophoblast. They show immunoreactivity with desmin, vimentin, alpha-actin, myosin, nitric oxide synthase type I (brain form) and dipeptidyl peptidase IV. The ultrastructure suggests that cells of the extravascular contractile system are related to smooth muscle cells, including subpopulations with myofibroblastic features. In stem villi a few cells are nitric oxide synthase type I immunoreactive. These cells are thought to be specialized smooth-muscle-like cells of the extravascular contractile system or cells of the extravascular contractile system related to paraneurons that generate nitric oxide, which, in turn, may modulate the tone of perivascular contractile sheaths. The high dipeptidyl peptidase IV activity suggests that modulation of the extravascular contractile system may also occur by substance P.

Autacoids and control of human placental blood flow

1. Humans have a haemochorial, villous placenta. Uterine blood passes through maternal sinuses, bathing placental villi through which fetal blood circulates. Blood flow through each circulation is high and vascular resistance low. This haemodynamic situation is essential for efficient placental function. 2. The low placental vascular resistance is due to a lack of nervous influences together with pregnancy-induced changes promoting vasodilatation. Increases occur in output of the vasodilators prostacyclin and nitric oxide and also in membrane sodium pump activity. 3. Many autacoids are present in umbilical blood. Fetal vessels of the placenta develop intense vasoconstriction in the presence of some autacoids, such as thromboxane A2 and prostaglandins F2 alpha and E2, and respond weakly to others, such as angiotensin II and 5-hydroxytryptamine. Nevertheless, vasodilator influences predominate. 4. The diseases of pre-eclampsia and fetal growth retardation are associated with reduced output of nitric oxide and prostacyclin and with increased production of thromboxane A2 and endothelin-1. These changes promote vasoconstriction, increased vascular sensitivity to vasoconstrictor stimuli, platelet aggregation and intravascular coagulation, retarding blood flow and feto-placental growth. 5. Aspirin and glyceryl trinitrate have been investigated for possible therapeutic use in pre-eclampsia and fetal growth retardation. Improved drug therapy is likely as knowledge increases of the importance of autacoids in normal placental function and in the changes that occur during disease.

Effect of inhibition of nitric oxide synthase and guanylate cyclase on hydralazine-induced vasodilatation of the human fetal placental circulation

1. The vasodilator effects of hydralazine in vitro, using the Krebs' perfused human placental lobule was studied. Single placental lobules were bilaterally perfused (maternal and fetal sides 5 mL/min each, 95% O2, 5% CO2, 37 degrees C) and changes in fetal arterial pressure (FAP) and venous outflow (VO) were recorded. 2. Submaximal vasoconstriction was induced by KCl (20-50 mmol/L), which increased basal FAP from 22.8 +/- 1.7 to 91.3 +/- 3.9 mmHg (n = 9, P < 0.001), and decreased VO from 4.1 +/- 0.6 to 0.2 +/- 0.1 mL/min (n = 6, P < 0.01). 3. Hydralazine caused vasodilatation (IC50 1.9 mmol/L, n = 9) and increased VO in the presence of KCl-induced vasoconstriction. 4. Infusion of N omega-nitro-L-arginine (100 mumol/L) to block nitric oxide synthase caused the basal FAP to increase from 30.9 +/- 5.9 to 47.4 +/- 6.7 (n = 6, P < 0.05) and significantly potentiated hydralazine-induced vasodilatation (n = 7, P < 0.05). 5. The soluble guanylate cyclase inhibitor LY 83583 (6-anilino-5,8-quinolinedione) (1 mumol/L) significantly antagonized the vasodilatation produced by hydralazine (n = 5, P < 0.05). 6. Thus, Hydralazine appears to activate guanylate cyclase, leading to increased cyclic GMP in fetal arterial vascular smooth muscle to cause vasorelaxation. No evidence was obtained to suggest that hydralazine exerted its action by either releasing nitric oxide from endothelial cells in the placenta or acting as a nitric oxide donor.

Endothelium-derived relaxing factor and cyclic GMP-dependent vasorelaxation in human chorionic plate arteries

Endothelium derived relaxing factor (EDRF), now widely believed to be nitric oxide (NO), may play an important part in the control of fetoplacental vascular tone. To further explore this role we have determined the relaxation responses to exogenous NO and examined the temporal relationship between intracellular concentrations of cyclic GMP and vascular tone in isolated ring segments of human chorionic plate arteries. We have also determined the dose relations for the contractile agonists serotonin and the thromboxane analog U46619. Lastly, we have explored the relaxation responses to a wide range of agents known to elicit EDRF release in other vascular beds. Chorionic plate arteries relaxed significantly to exogenous NO with concomitant increases in cyclic guanosine monophosphate over basal values. ED50s for serotonin and U46619 were 1.48 x 10(-6) M and 3.39 x 10(-8) M respectively. The ED50 for NO derived from S-nitroso-N-acetyl-penicillamine was 1.28 x 10(-6) M. Endothelium-intact segments of chorionic plate arteries pre-contracted with either serotonin or U46619 failed to relax significantly to acetylcholine, adenosine diphosphate, A23187, bradykinin, and histamine and only minimally to substance P. We suggest that EDRF is likely to be important in the control of placental vascular tone, but that it is not possible to demonstrate its action in an unperfused experimental system.

Effects of the synthetic glucocorticoid triamcinolone acetonide on vasoactive hydrolases of the human placenta in vitro

Therapy with glucocorticoids during pregnancy is still debated. Previously reported effects of glucocorticoid application in rats resemble certain symptoms of preeclampsia. Therefore, we studied in vitro the effects of the synthetic glucocorticoid triamcinolone acetonide soluble (0.1-10 mM) on placental alpha-glutamyl amino-peptidase, microsomal alanyl aminopeptidase, dipeptidyl peptidase IV, acetylcholinesterase and butyrylcholinesterase in purified trophoblast monolayers and villous explants from first trimester (n = 5) and term placentae (n = 9) using bio- and histochemical methods. In term placentae quantitative histochemistry (microdensitometry) of trophoblast monolayers revealed an increase of alpha-glutamyl aminopeptidase and microsomal alanyl aminopeptidase activity up to 149% and 126% respectively, after treatment with supraphysiological doses. In trophoblast monolayers from first trimester alpha-glutamyl aminopeptidase activity was not affected, whereas microsomal alanyl aminopeptidase activity increased by 25%. Dipeptidyl peptidase IV staining was reduced to 26%. Biochemical measurements of alpha-glutamyl aminopeptidase and microsomal alanyl aminopeptidase activity in homogenates of cultured villi revealed effects similar to those found by microdensitometry in trophoblast monolayers. In contrast, dipeptidyl peptidase IV activity increased in explants of term placentae by 47%. Acetyl- and butyrylcholinesterase activities were reduced in term placental villi by 38% and 40%, respectively. The data indicate that glucocorticoids may affect the activity of hydrolases which are thought to be involved in local placental blood pressure modulation.

Cyclooxygenase gene expression in human endometrium and decidua

The objective of this study was to determine if genes for cyclooxygenase (COX) and 5-lipoxygenase, key enzymes in the synthesis of eicosanoids, are expressed in human endometrium and to determine if the level of expression is affected by decidualization or preeclampsia, a form of pregnancy-induced hypertension. RT-PCR was used to detect mRNA in tissues obtained from various patients. Results demonstrated that COX and 5-lipoxygenase genes are expressed in endometrium and decidua. COX gene expression in endometrium is 2-3-fold greater than in decidua while 5-lipoxygenase gene expression is similar. Neither COX nor 5-lipoxygenase gene expression in decidua is altered by changes resulting from preeclampsia. Thus, genes for key enzymes in the synthesis of eicosanoids are expressed in human endometrium and decidua. Selective down-regulation is evident as decidualization results in a significant reduction in the gene expression of COX, while 5-lipoxygenase gene expression remains unchanged.

Vascular actions of purines in the foetal circulation of the human placenta

1. The vasoactive effects of adenosine triphosphate (ATP), adenosine and other purines in the foetal circulation of the human placenta were examined. Single lobules of the placenta were bilaterally perfused in vitro with Krebs buffer (maternal and foetal sides 5 ml min-1 each, 95% O2:5% CO2, 37 degrees C). Changes in foetal vascular tone were assessed by recording perfusion pressure during constant infusion of each purine. To allow recording of the vasodilator effects, submaximal vasoconstriction was induced by concomitant infusion of prostaglandin F2 alpha (0.7-2.0 mumol l-1). 2. ATP (1.0-100 mumol l-1) usually caused concentration-dependent reductions in perfusion pressure. However, biphasic with initial transient increases, or only increases in pressure were sometimes observed. Falls in pressure caused by ATP were significantly reduced by addition to the perfusate of NG-nitro-L-arginine (L-NOARG) (100 mumol l-1) but not NG-nitro-D-arginine (D-NOARG) (100 mumol l-1). They were not influenced by addition of indomethacin (10 mumol l-1) or L-arginine (100 mumol l-1). 3. Adenosine (0.01-1.0 mmol l-1) consistently caused concentration-dependent reductions in perfusion pressure, this effect not being influenced by indomethacin. L-NOARG, but not D-NOARG, reduced the potency of adenosine approximately three fold. L-Arginine, but not D-arginine enhanced its potency by a similar amount. 4. 2-Methylthio-ATP, a selective P2 gamma agonist was approximately 50 times more potent than ATP as a vasodilator agent, always causing decreases in perfusion pressure. 5. Beta-gamma-Methylene ATP, a selective P20 agonist, was approximately 100 times more potent than ATP as a vasoconstrictor, but only caused transient increases in perfusion pressure.6. The rank order of vasodilator potencies of a selection of adenosine receptor agonists was, 2-chloroadenosine>>5-(N-cyclopropyl)-carboxamidoadenosine, >5-N-ethylcarboxamidoadenosine, >2-chloro-N6-cyclopentyladenosine, >CGS-21680 > N6-cyclohexyladenosine = adenosine. Vasodilatation due to adenosine was inhibited by the PI-A2 receptor antagonist 3,7-dimethyl-l-propargylxanthine(DMPX).7. These results suggest that ATP may cause an endothelium-dependent vasodilatation in the foetal vessels of the human placenta via activation of a P2y receptor linked to the formation of nitric oxide(NO). Vasodilatation caused by ATP may mask an accompanying vasoconstrictor effect mediated, via a P2X receptor, in the villous vascular smooth muscle. Adenosine acting on P1-A2 receptors, which are also present in the foetal vasculature, may require synergistic interaction with NO to achieve a maximal vasodilator response.

Release of a substance from the human placenta having digoxin-like immunoreactivity

1. The human placental lobule, perfused with a constant flow (5 mL/min) of Krebs' solution after delivery at term, released into the fetal perfusate a digoxin-like substance, as measured by a fluorescence polarization immunoassay. 2. Initially the venous concentration was 360 +/- 66.7 pmol/L digoxin equivalents. This level did not change significantly during fetal vasoconstriction induced by prostaglandin F2 alpha infusion and persisted for the duration of the experiment (1.5-2 h). 3. Infusion into the fetal circulation of Fab fragments of sheep antibodies to digoxin caused vasodilatation, indicated by a fall in perfusion pressure. 4. Thus a digoxin-like immunoreactive substance, previously reported to be present in the placenta, is released into the fetal circulation and may play a role in placental control of fetal vascular tone.