M. Cervar

Altered release of endothelin‐1,2 and thromboxane B2 from trophoblastic cells in pre‐eclampsia

The aim of the study was to investigate whether pre‐eclampsia is associated with an altered release of vasoactive substances from trophoblastic cells in vitro. Trophoblastic cells from 15 uncomplicated control pregnancies and 18 pre‐eclamptic pregnancies at preterm (weeks 31–36; n = 12) and term (weeks 37–40; n = 21) were cultured for 5 days. The concentrations of angiotensin II (AII), endothelin‐1,2 (ET‐1,2), thromboxane B2 (TXB2), 6‐keto‐prostaglandin F1α (6‐keto‐PGF1α) and leukotriene B4 (LTB4) were measured daily in culture media for 5 days by radioimmunoassay. In pre‐eclampsia, concentrations of ET‐1,2 were decreased (P < 0.01) at both preterm and term, TXB2 concentrations were increased P < 0.05) only at preterm and the TXB2–6‐keto‐PGF1α ratio was increased at both preterm and term (P < 0.01) as compared with the controls. Concentrations of AII, 6‐keto‐PGF1α and LTB4 were similar to the controls. The data suggest that pre‐eclampsia is associated with a decreased release of ET‐1 and an increased release of TXB2 from trophoblastic cells in vitro

PRE-ECLAMPSIA AND GESTATIONAL AGE DIFFERENTLY ALTER BINDING OF ENDOTHELIN-1 TO PLACENTAL AND TROPHOBLAST MEMBRANE PREPARATIONS

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

Self-regulation of the endothelin receptor system in choriocarcinoma cells.

The human trophoblast secretes endothelin-1 (ET-1) and expresses ET receptors. The present study tested whether the transformed BeWo, JAR and JEG-3 choriocarcinoma cells: (1) secrete endothelin-1 (ET-1); (2) express both ET-A and ET-B receptor subtypes; and (3) have the potential to allow for autologous regulation of ET-receptor proteins. The cells were cultured for 24/48 h with or without 10% FCS and, in experiments on receptor regulation, with ET-1 (5-20 nM and 10 microM). ET-1 secretion was measured by RIA and receptor levels by immunoblotting. All cell types secreted ET-1 albeit at different levels and sensitivity to FCS. All cell lines expressed both ET-A (JEG-3>BeWo=JAR) and ET-B (JEG-3=JAR>BeWo) receptor subtypes, which could be up- and downregulated depending on ET-1 concentration, culture time and FCS presence. It is concluded that BeWo, JAR and JEG-3 choriocarcinoma cells secrete ET-1 and express both ET-A and ET-B receptor subtypes. The receptor levels can be regulated by ET-1. This provides the molecular basis for an autocrine system with the potential of autologous regulation of yet unidentified ET-1-induced functions.

The endothelin/endothelin receptor system of human trophoblast in normal and pre-eclamptic pregnancies

Summary Endothelins and their receptors are the most potent vasoconstricting system which has been identified in vascular tissues including human placenta. Over the past years the expression of this system in a variety of non-vascular tissues has suggested the existence of functions not related to the regulation of vascular tone. In the human trophoblast endothelin biosynthesis and secretion along with endothelin-binding sites were identified indicating autocrine or paracrine regulation of yet unidentified ET-effects. Changes in the ET-system of term trophoblast in preeclampsia suggest its implication in this disease, which originates from inadequate trophoblast invasion in the first trimester. Recent results with first trimester trophoblast showing a mitogenic activity, and the discovery of the novel invasion-promoting effect have opened new avenues of research in the field of trophoblast-derived endothelin-1 and its receptors.

Drug actions in preeclampsia: Aspirin, but not magnesium chloride or dihydralazine, differentially inhibits cultured human trophoblast release of thromboxane and prostacyclin without affecting angiotensin II, endothelin-1, or leukotriene B4 secretion

OBJECTIVE We hypothesized that aspirin Mg++, and dihydralazine affect the release of vasoactive agents from cultured human placental trophoblast. STUDY DESIGN Cytotrophoblasts isolated from placentas of preterm or term deliveries of 14 healthy control women and 15 preeclamptic women were cultured in Dulbeccos modified Eagles medium for 5 days in the presence or absence of either 0.1 mmol/L aspirin, 3 mmol/L magnesium chloride, or 136 ng/ ml dihydralazine. Vasoactive substances were quantitated by radioimmunoassay with mean +/- SEM percentage of untreated cells (= 100%) compared by the Mann-Whitney U test and analysis of variance. RESULTS Aspirin inhibited (p < 0.01) both thromboxane and prostacyclin on days 1 and 2 in culture but not on days 3 to 5 unless the Dulbeccos modified Eagles medium was supplemented with arachidonic acid. Aspirin inhibition was greater (p < 0.01) for thromboxane in cells cultured 24 hours after preeclamptic pregnancy (preterm 29.9% +/- 6.8%, term 20.1% +/- 5.9%) compared with normal controls (preterm 66.3% +/- 10.6%, term 68.9% +/- 11.6%). Aspirin reduced (p < 0.01) the ratio of thromboxane to prostacyclin in media of cells from preeclampsia (untreated 27.8 +/- 7.2, aspirin 13.3 +/- 4.4), but aspirin had no effect on this ratio in cultures from control normal pregnancies (untreated 6.8 +/- 2.9, aspirin 4.8 +/- 1.1). Neither magnesium chloride nor dihydralazine affected trophoblast prostanoid production, and no drug altered the media levels of angiotensin II, endothelin-1, or leukotriene B4. CONCLUSION Aspirin selectively inhibits trophoblast prostanoid production. This inhibition depends on the availability of arachidonic acid and the presence or absence of preeclampsia. Magnesium and dihydralazine effects in pregnancy are not related to altered release of trophoblast vasoactive compounds.