Serotonin metabolism in the fetus in preeclampsia

Vascular contraction of umbilical arteries of pregnant women with preeclampsia

Objective

Potassium channels have an important role in the vascular adaptation during pregnancy and a reduction in the expression of adenosine triphosphate-sensitive potassium channels (Katp) has been linked to preeclampsia. Activation of Katp induces vasodilation; however, no previous study has been conducted to evaluate the effects of the inhibition of these channels in the contractility of preeclamptic arteries. Glibenclamide is an oral antihyperglycemic agent that inhibits Katp and has been widely used in vascular studies.

Methods

To investigate the effects of the inhibition of Katp, umbilical arteries of preeclamptic women and women with healthy pregnancies were assessed by vascular contractility experiments, in the presence or absence of glibenclamide. The umbilical arteries were challenged with cumulative concentrations of potassium chloride (KCl) and serotonin.

Results

There were no differences between the groups concerning the maternal age and gestational age of the patients. The percentage of smokers, caucasians and primiparae per group was also similar. On the other hand, blood pressure parameters were elevated in the preeclamptic group. In addition, the preeclamptic group presented a significantly higher body mass index. The newborns of both groups presented similar APGAR scores and weights.

Conclusion

In the presence of glibenclamide, there was an increase in the KCl-induced contractions only in vessels from the PE group, showing a possible involvement of these channels in the disorder.

An Endogenous Aryl Hydrocarbon Receptor Ligand Induces Preeclampsia-like Phenotypes: Transcriptome, Phosphoproteome, and Cell Functions

Background

Preeclampsia (PE) is one hypertensive disorder and a leading cause of maternal and fetal mortality and morbidity during human pregnancy. Aryl hydrocarbon receptor (AhR) is a transcription factor, which regulates vascular functions. Exogenous and endogenous AhR ligands can induce hypertension in animals. However, if dysregulation of endogenous AhR ligands contributes to the pathophysiology of PE remains elusive.

Methods

We measured AhR activities in human maternal and umbilical vein sera. We also applied physiological, cellular, and molecular approaches to dissect the role of endogenous AhR ligands in vascular functions during pregnancy using pregnant rats and primary human umbilical vein endothelial cells (HUVECs) as models.

Results

PE elevated AhR activities in human umbilical vein sera. Exposure of pregnant rats to an endogenous AhR ligand, 2-(1'H-indole-3'-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE) increased blood pressure and proteinuria, while decreased uteroplacental blood flow and reduced fetal and placental weights, all of which are hallmarks of PE. ITE dampened vascular growth and fetal sex-specifically altered immune cell infiltration in rat placentas. ITE also decreased cell proliferation and cell monolayer integrity in HUVECs in vitro . RNA sequencing analysis revealed that ITE dysregulated transcriptome in rat placentas and HUVECs in a fetal sex-specific manner. Bottom-up phosphoproteomics showed that ITE disrupted phosphoproteome in HUVECs. These ITE-dysregulated genes and phosphoproteins were enriched in biological functions and pathways which are highly relevant to diseases of heart, liver, and kidney, vascular functions, inflammation responses, cell death, and kinase inhibition.

Conclusions

Dysregulation of endogenous AhR ligands during pregnancy may lead to the development of PE with underlying impaired vascular functions, fetal sex-specific immune cell infiltration and transcriptome, and phosphoproteome. Thus, this study has provided a novel mechanism for the development of PE and potentially other forms of hypertensive pregnancies. These AhR ligand-activated genes and phosphoproteins might represent promising therapeutic and fetal sex-specific targets for PE-impaired vascular functions.

The Function of the Kynurenine Pathway in the Placenta: A Novel Pharmacotherapeutic Target?

(L-)tryptophan is metabolized via the kynurenine pathway into several kynurenine metabolites with distinct functions. Dysfunction of the kynurenine pathway can lead to impairments in vascular regulation, immune regulation, and tolerance. The first and rate limiting enzyme of this pathway, indoleamine 2,3-dioxygenase (IDO), is highly expressed in the placenta and reduced in placentas from complicated pregnancies. IDO is essential during pregnancy, as IDO inhibition in pregnant mice resulted in fetal loss. However, the exact function of placental IDO, as well as its exact placental localization, remain controversial. This review identified that two isoforms of IDO; IDO1 and IDO2, are differently expressed between placental cells, suggesting spatial segregation. Furthermore, this review summarizes how the placental kynurenine pathway is altered in pregnancy complications, including recurrent miscarriage, preterm birth, preeclampsia, and fetal growth restriction. Importantly, we describe that these alterations do not affect maternally circulating metabolite concentrations, suggesting that the kynurenine pathway functions as a local signaling pathway. In the placenta, it is an important source of de novo placental NAD⁺ synthesis and regulates fetal tryptophan and kynurenine metabolite supply. Therefore, kynurenine pathway interventions might provide opportunities to treat pregnancy complications, and this review discusses how such treatment could affect placental function and pregnancy development.

Differential Distribution of Tryptophan-Metabolites in Fetal and Maternal Circulations During Normotensive and Preeclamptic Pregnancies

Preeclampsia (PE) is a hypertensive pregnancy, which is a leading cause of maternal and fetal morbidity and mortality during pregnancy. L-Tryptophan (Trp) is an essential amino acid, which can be metabolized into various biologically active metabolites. However, the levels of many circulating Trp-metabolites in human normotensive pregnancies (NT) and PE are undetermined. This study quantified the levels of Trp-metabolites in maternal and umbilical vein sera from women with NT and PE. Paired maternal and umbilical blood samples were collected from singleton pregnant patients. Twenty-five Trp-metabolites were measured in serum samples using liquid chromatography with tandem mass spectrometry. The effects of L-kynurenine (Kyn) and indole-3-lactic acid (ILA), on function of human umbilical vein endothelial cells (HUVECs), were also determined. Twenty Trp-metabolites were detected. The levels of 9 Trp-metabolites including Kyn and ILA were higher (P < 0.05) in umbilical vein than maternal serum, whereas 2 (5-hydroxy-L-tryptophan and serotonin) were lower (P < 0.05) in umbilical vein compared to maternal serum. PE significantly (P < 0.05) elevated ILA levels in maternal and umbilical vein sera. Kyn dose-dependently decreased (P < 0.05) cell viability. Kyn and ILA dose- and time-dependently (P < 0.05) increased monolayer integrity in HUVECs. These data suggest that these Trp-metabolites are important in regulating endothelial function during pregnancy, and the elevated ILA in PE may antagonize increased endothelial permeability occurring in PE.

The Serotonin-Immune Axis in Preeclampsia

PURPOSE OF REVIEW

To review the literature and detail the potential immune mechanisms by which hyperserotonemia may drive pro-inflammation in preeclampsia and to provide insights into potential avenues for therapeutic discovery.

RECENT FINDINGS

Preeclampsia is a severe hypertensive complication of pregnancy associated with significant maternal and fetal risk. Though it lacks any effective treatment aside from delivery of the fetus and placenta, recent work suggests that targeting serotonin systems may be one effective therapeutic avenue. Serotonin dysregulation underlies multiple domains of physiologic dysfunction in preeclampsia, including vascular hyporeactivity and excess platelet aggregation. Broadly, serotonin is increased across maternal and placental domains, driven by decreased catabolism and increased availability of tryptophan precursor. Pro-inflammation, another hallmark of the disease, may drive hyperserotonemia in preeclampsia. Interactions between immunologic dysfunction and hyperserotonemia in preeclampsia depend on multiple mechanisms, which we discuss in the present review. These include altered immune cell, kynurenine pathway metabolism, and aberrant cytokine production mechanisms, which we detail. Future work may leverage animal and in vitro models to reveal serotonin targets in the context of preeclampsia's immune biology, and ultimately to mitigate vascular and platelet dysfunction in the disease. Hyperserotonemia in preeclampsia drives pro-inflammation via metabolic, immune cell, and cytokine-based mechanisms. These immune mechanisms may be targeted to treat vascular and platelet endophenotypes in preeclampsia.

l-Tryptophan-Induced Vasodilation Is Enhanced in Preeclampsia: Studies on Its Uptake and Metabolism in the Human Placenta

l-tryptophan induces IDO (indoleamine 2,3-dioxygenase) 1-dependent vasodilation. IDO1 is expressed in placental endothelial cells and downregulated in preeclampsia. Hypothesizing that this may contribute to diminished placental perfusion, we studied l-tryptophan-induced vasodilation in healthy and early-onset preeclampsia placental arteries, focusing on placental kynurenine pathway alterations. Despite IDO1 downregulation, kynurenine pathway metabolite concentrations (measured with ultra-performance liquid chromatography-tandem mass spectrometry) were unaltered in preeclamptic versus healthy placentas. Most likely, this is due to enhanced l-tryptophan uptake, evidenced by increased l-tryptophan levels in preeclamptic placentas. Ex vivo perfused cotyledons from healthy and preeclamptic placentas released similar amounts of l-tryptophan and kynurenine pathway metabolites into the circulations. This release was not altered by adding l-tryptophan in the maternal circulation, suggesting that l-tryptophan metabolites act intracellularly. Maternally applied l-tryptophan did appear in the fetal circulation, confirming placental passage of this essential amino acid. After in vitro incubation of placental arteries with IDO1-upregulating cytokines interferon-γ and tumor necrosis factor-α, l-tryptophan induced vasodilation. This vasodilation was attenuated by both IDO1 and nitric oxide (NO) synthase inhibitors. Despite IDO1 downregulation, l-tryptophan-induced relaxation was enhanced in preeclamptic versus healthy placental arteries. However, cytokine stimulation additionally upregulated the LAT (l-type amino acid transporter) 1 in preeclamptic placental arteries only. Vasodilation to the lipophilic, transporter independent ethyl ester of l-tryptophan was reduced in preeclamptic versus healthy placental arteries, in agreement with reduced IDO1 expression. In conclusion, l-tryptophan induces IDO1- and NO-dependent relaxation in placental arteries, which is determined by l-tryptophan uptake rather than IDO1 expression. Increased l-tryptophan uptake might compensate for reduced IDO1 expression in preeclamptic placentas.

Association of urinary concentrations of phthalate metabolites with quinolinic acid among women: A potential link to neurological disorders

BACKGROUND

Quinolinic acid (QA), a neuroactive metabolite produced during tryptophan degradation, is implicated in the pathogenesis of several neurological disorders. Phthalates are structurally similar to QA, and exposure to phthalates has demonstrated increased QA production and excretion in rodent studies. We recently showed that very high exposure to dibutyl phthalate was associated with higher concentrations of urinary QA in men. However, no human studies examined the associations between background (low) phthalate exposures and QA.

OBJECTIVES

To examine the associations of urinary concentrations of phthalate metabolites with QA.

METHODS

Female participants (N = 126) who participated in a prospective cohort study at the Massachusetts General Hospital Fertility Center provided 758 urine samples (273 during pregnancy and 485 during non-pregnancy). Concentrations of 11 phthalate metabolites and QA in urine were measured. We used multivariable linear mixed effect models to estimate the percent change in urinary QA concentrations associated with a doubling (100%) of urinary phthalate metabolite concentration, and evaluated whether there was effect modification by pregnancy status.

RESULTS

Women's mean (standard deviation) age was 34.2 (4.0) years with a body mass index of 23.5 (3.7) kg/m2. The women were primarily Caucasian (92%), had at least a college degree (98%), and none were current smokers. Pairwise Spearman correlations between concentrations for phthalate metabolites and QA measured in the same urine samples ranged from 0.36 for MEHP to 0.68 for dibutyl phthalate (DBP) metabolites. In multivariable-adjusted models, the percent change in urinary QA concentrations was significantly higher for each doubling of several urinary phthalate metabolite concentrations. For example, each doubling of DBP metabolites was associated with a 13.7% (95%CI: 10.6, 16.9)% higher QA. Associations between the low molecular weight phthalate metabolites and QA were stronger among samples collected during pregnancy as compared to non-pregnancy samples from the same women.

CONCLUSIONS

Urinary concentrations of several phthalate metabolites were positively associated with QA among women. These findings, along with the known neurotoxicity of QA, warrant the need to examine whether QA concentrations may serve as a pathway for the adverse neurodevelopment outcomes found in children's health studies.

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.

Subjecting Dams to Early Life Stress and Perinatal Fluoxetine Treatment Differentially Alters Social Behavior in Young and Adult Rat Offspring

Recently, the putative association between selective serotonin reuptake inhibitor (SSRI) exposure during pregnancy and the development of social disorders in children has gained increased attention. However, clinical studies struggle with the confounding effects of maternal depression typically co-occurring with antidepressant treatment. Furthermore, preclinical studies using an animal model of maternal depression to study effects of perinatal SSRI exposure on offspring social behavior are limited. Therefore, the aim of this study was to investigate effects of perinatal fluoxetine exposure on juvenile and adult social behavior in male and female rat offspring, using an animal model of maternal vulnerability. We exposed heterozygous serotonin transporter (SERT) deficient female rats to early life maternal separation stress, and used this as a model for maternal vulnerability. Control and early life stressed heterozygous serotonin transporter knockout (SERT) dams were treated with the SSRI fluoxetine or vehicle throughout gestation and lactation. Subsequently, both male and female wildtype (SERT+/+) and heterozygous (SERT+/-) rat offspring were tested for pup ultrasonic vocalizations (USVs), juvenile social play behavior and adult social interaction. Fluoxetine treatment of the dams resulted in a reduced total USV duration in pups at postnatal day 6, especially in SERT+/+ males. Perinatal fluoxetine exposure lowered social play behavior in male offspring from both control and early life stressed dams. However, in females a fluoxetine-induced reduction in juvenile play behavior was only present in offspring from control dams. Offspring genotype did not affect juvenile play behavior. Despite fluoxetine-induced behavioral effects at juvenile age, fluoxetine reduced male adult social behavior in offspring from control dams only. Effects of fluoxetine on female adult social behavior were virtually absent. Interestingly, early life stress in dams increased adult social exploration in vehicle exposed SERT+/+ female offspring and total social behavior in fluoxetine exposed adult SERT+/- male offspring. Furthermore, SERT+/- males appeared less social during adulthood compared to SERT+/+ males. Overall, the present study shows that chronic blockade of the serotonin transporter by fluoxetine during early development has a considerable impact on pup USVs, juvenile social play behavior in both male and female offspring, and to a lesser extent on male social interaction in adulthood.

The Effects of Bumetanide on Human Umbilical Artery Contractions

The authors investigate the effect of bumetan ide, an inhibitor of NKCC1 and a loop diuretic, on the tone of human umbilical artery (HUA). Rings of HUA (n = 35) from vaginal deliveries were suspended for isometric tension recordings in organ baths. Cumulative concentration-response curves to serotonin, histamine, and KCl were performed in the absence (control) or in the presence of bumetanide. The relaxant effect of bumetanide was also evaluated in serotonin- and histamine-induced contractions. Bumetanide inhibited HUA tone in serotonin- and histamine-induced contractions with significant changes in the potency (pD(2)) and maximum contractile response (E(max)) values. However, only pD( 2) values for KCl-induced contraction significantly changed in the presence of bumetanide. Bumetanide caused concentration-dependent and sustained relaxations in serotonin-induced contraction; however, there was refractoriness in histamine-induced contraction. These findings raise the possibility that NKCC1 may play a role in the regulation of the umbilical artery tone.

Tryptophan metabolism, disposition and utilization in pregnancy

Tryptophan (Trp) requirements in pregnancy are several-fold: (1) the need for increased protein synthesis by mother and for fetal growth and development; (2) serotonin (5-HT) for signalling pathways; (3) kynurenic acid (KA) for neuronal protection; (4) quinolinic acid (QA) for NAD(+) synthesis (5) other kynurenines (Ks) for suppressing fetal rejection. These goals could not be achieved if maternal plasma [Trp] is depleted. Although plasma total (free + albumin-bound) Trp is decreased in pregnancy, free Trp is elevated. The above requirements are best expressed in terms of a Trp utilization concept. Briefly, Trp is utilized as follows: (1) In early and mid-pregnancy, emphasis is on increased maternal Trp availability to meet the demand for protein synthesis and fetal development, most probably mediated by maternal liver Trp 2,3-dioxygenase (TDO) inhibition by progesterone and oestrogens. (2) In mid- and late pregnancy, Trp availability is maintained and enhanced by the release of albumin-bound Trp by albumin depletion and non-esterified fatty acid (NEFA) elevation, leading to increased flux of Trp down the K pathway to elevate immunosuppressive Ks. An excessive release of free Trp could undermine pregnancy by abolishing T-cell suppression by Ks. Detailed assessment of parameters of Trp metabolism and disposition and related measures (free and total Trp, albumin, NEFA, K and its metabolites and pro- and anti-inflammatory cytokines in maternal blood and, where appropriate, placental and fetal material) in normal and abnormal pregnancies may establish missing gaps in our knowledge of the Trp status in pregnancy and help identify appropriate intervention strategies.

The tryptophan utilization concept in pregnancy

The decrease in maternal plasma total (free + albumin-bound) tryptophan (Trp) during the third pregnancy trimester is attributed to induction of indoleamine 2,3-dioxygenase (IDO). When measured, free [Trp] is increased because of albumin depletion and non-esterified fatty acid elevation. The Trp depletion concept in pregnancy is therefore not supported because of incorrect interpretation of changes in Trp disposition and also for not addressing mouse strain differences in Trp-related responses and potential inhibition of Trp transport by the IDO inhibitor 1-methyl tryptophan. Application of the Trp utilization concept in pregnancy offers several physiological advantages favoring fetal development and successful outcome, namely provision of Trp for fetal protein synthesis and growth, serotonin for signaling pathways, kynurenic acid for neuroprotection, quinolinic acid for NAD⁺ synthesis, and other kynurenines for suppression of T cell responses. An excessive increase in Trp availability could compromise pregnancy by undermining T cell suppression, e.g., in pre-eclampsia.

Contractile responses of the human umbilical artery to KCl and serotonin in Ca-free medium and the effects of levcromakalim

It is known that K(ATP) channel openers inhibit the release and refilling of Ca(2+) from intracellular stores. The present study was designed to test the effects of levcromakalim in human umbilical artery (HUA) rings stimulated by serotonin (5-HT) and KCl in Ca-free medium. Umbilical cords were obtained at vaginal or cesarean deliveries from healthy, term pregnancies. After the isolation, HUA rings were placed in organ baths in solution with indomethacin (10(-5) M) and N(G)-nitro-L-arginine methyl ester (L-NAME) (10(-3) M) at 37 degrees C and aerated with 95% O(2) and 5% CO(2) for the measurement of isometric force. In Ca-free solution with Ethylene glycol-bis (ss-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) (2 mM) the contractions produced by 5-HT (10(-6) M) and KCl (40 mM) decreased significantly. Afterwards, HUA rings were treated with 5-HT and KCl in repeated manner in Ca-free medium. In contrast to KCl, 5-HT induced contractions reduced in each application, progressively. Levcromakalim (10(-4) M) abolished the contractions elicited by 5-HT. On the other hand, levcromakalim had a little but significant inhibitory effect on KCl induced contraction in Ca-free medium. These results suggest that Ca(2+) is not the only transduction pathway in KCl produced contractions of HUA smooth muscle cells.

U46619-mediated vasoconstriction of the fetal placental vasculature in vitro in normal and hypertensive pregnancies

OBJECTIVES

To measure in-vitro responses to the thromboxane A2 (TxA2) mimetic U46619 in the fetal placental vasculature of human placentae from normotensive women and those with pre-eclampsia. Furthermore, to compare fetal vascular responses to endothelin-1,5-hydroxytryptamine, potassium chloride (KCl) and prostacyclin (PGI2) in placentae from normal or pre-eclamptic pregnancies.

METHODS

Single placental lobules of intact placentae were bilaterally perfused in situ (fetal and maternal) with constant flows of Krebs' solution. Changes in fetal arterial perfusion pressure during intra-arterial infusion of vasoactive agents were recorded. Fetal placental vasoconstrictor concentration response curves were obtained to U46619 (0.01-300 nmol/l), endothelin-1 (0.4-160 nmol/l), KCl (3-300 mmol/l) and 5-hydroxytryptamine (0.03-30 mumol/l). In addition, vasodilator concentration response curves were obtained for PGI2 (1.2-350 nmol/l) in the fetal placental circulation during submaximal increases in perfusion pressure with prostaglandin F2 alpha (PGF2 alpha; 0.7-2.0 mumol/l).

RESULTS

The maximum increase in perfusion pressure caused by U46619 in placentae from normotensive women was 194 +/- 25 mmHg. The maximum response to U46619 was significantly reduced in the placentae from women with pre-eclampsia (104 +/- 21 mmHg). In contrast, there were no differences in constrictor responses to endothelin-1,5-hydroxytryptamine and KCl, or in dilator responses to PGI2 in placentae obtained from either normotensive women or those with pre-eclampsia.

CONCLUSION

TxA2 receptor-mediated vasoconstriction is reduced in the fetal vasculature of placentae from women with pre-eclampsia, possibly to compensate for the increased levels of TxA2 seen in these conditions.

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.

Significant decrease of maternal serum serotonin levels in singleton pregnancies complicated by the HELLP syndrome

The purpose of this study was to compare peripartum maternal and umbilical cord serum serotonin levels in singleton pregnancies complicated by the HELLP syndrome (hemolysis, elevated liver enzymes, low platelets) or by severe preeclampsia with those of appropriate controls. The study population comprised 14 primigravidae women with class 1 or 2 HELLP syndrome (platelet count < 50,000 or < 100,000/mm3, elevated transaminase levels, evidence of hemolysis) and 17 women with severe preeclampsia (American College of Obstetricians and Gynecologists criteria). Serotonin was measured in maternal serum immediately before delivery and in umbilical cord serum by a highly sensitive 125I-radioimmunoassay. The control groups comprised 31 women who had uncomplicated deliveries at term (control group I) and another 31 at the gestational age matched to that of each patient (control group II). Maternal serum serotonin concentration was 59.5 +/- 36.1 ng/ml (mean +/- SD) in the HELLP group, versus 94.9 +/- 40.5 ng/ml in control group I (p = 0.043, U-test) and 88.7 +/- 29.4 ng/ml in control group II (p = 0.048). Levels in the preeclampsia group (51.6 +/- 32.2 ng/ml) were not different from those in the HELLP group but were equally decreased when compared to control groups I (p = 0.009) and II (p = 0.003). We have observed a similar depression of serum serotonin concentrations both in severe preeclampsia and in the HELLP syndrome, reflecting the decreased platelet content of serotonin. It is uncertain whether these changes may be causally involved in the pathogenesis of hypertensive disorders of pregnancy. Decreased serum serotonin concentration may serve as an additional marker for platelet activation in preeclampsia and in the HELLP syndrome.

Amplifying effect of endothelin-1 on serotonin-induced vasoconstriction of human umbilical artery

OBJECTIVE

The purpose of this study was to evaluate the role of endothelin-1 in serotonin-induced vasoconstriction in human umbilical artery.

STUDY DESIGN

Umbilical arteries collected from 41 normal subjects at term were cut helically and suspended in an organ bath for recording isometric mechanical activity. In study 1 we measured the concentration-contraction response to serotonin or endothelin-1 according to a cumulative concentration schedule. In study 2 vessels were preincubated with a subthreshold concentration of endothelin-1 (100, 250, or 500 pg/ml), and then serotonin was added cumulatively. In study 3 vessels were preincubated with H-7 (3 x 10(-6) mol/L), an inhibitor of protein kinase C, or with 12-tetradecanoylphorbol-13 acetate (10(-9) to 10(-7) mol/L), an activator of protein kinase C; then serotonin was added cumulatively. In study 4 vessels were suspended in a calcium-free solution containing 2 mmol/L ethylene glycol-bis(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid and 60 mmol/L potassium chloride, and then a cumulative concentration-response curve to calcium chloride (10(-7) to 10(-3) mol/L) was constructed for vessels pretreated with endothelin-1, 500 pg/ml or 5 ng/ml.

RESULTS

The threshold concentrations of serotonin and endothelin-1 were 5 and 1 ng/ml, respectively. A subthreshold concentration of endothelin-1 (250 or 500 pg/ml) potentiated significantly the concentration response to serotonin (p < 0.084, p < 0.009, by analysis of variance). Pretreatment with H-7 significantly suppressed the amplifying effect of endothelin-1 on serotonin-induced contraction. Treatment with 12-tetradecanoylphorbol-13 acetate (10(-7) or 10(-8) mol/L) significantly potentiated the contractile response to serotonin (p < 0.0003, p < 0.015). The sensitivity of the arterial segments to calcium chloride in the presence of a subthreshold concentration of endothelin-1 did not differ from that in the control group.

CONCLUSION

Endothelin-1 at a subthreshold concentration amplified the smooth muscle contraction induced by serotonin. The mechanism of action may be mediated by activation of intracellular protein kinase C.