No change in calreticulin with fetal growth restriction in human and rat pregnancies

INTRODUCTION

Calreticulin is a ubiquitously expressed protein that was detected in the circulation and is significantly increased in maternal blood during human pregnancy compared to the non-pregnant state. Calreticulin is further increased in the plasma of women with the pregnancy-related disorder pre-eclampsia compared to normotensive pregnancy. The aims of this study were to compare calreticulin in human pregnancy with calreticulin in rat pregnancy, and to compare calreticulin during fetal growth restriction with normal control pregnancies.

METHODS

Women were recruited who either had normal pregnancies or had pregnancies complicated with fetal growth restriction; maternal blood samples and placentas were collected. Blood was also taken from women who were not-pregnant. Growth restriction was induced in pregnant rats by uterine vessel ligation; blood and placental samples were collected. Blood was also taken from non-pregnant rats. Western blot was used to quantify the placental expression of calreticulin and the concentrations of calreticulin in plasma.

RESULTS

Although calreticulin was significantly increased in maternal plasma during human pregnancy compared to the non-pregnant state; it did not increase in plasma during rat pregnancy. These results suggest that there may be differences in the role of extracellular calreticulin in human compared to rat pregnancy. Calreticulin was not significantly altered in either placental extracts or maternal plasma in both the human and rat pregnancies complicated by fetal growth restriction compared to gestational matched control pregnancies.

CONCLUSION

This study found that there was no change in calreticulin during human pregnancy complicated with fetal growth restriction or when growth restriction is induced in rats.

Decidua parietalis-derived mesenchymal stromal cells reside in a vascular niche within the choriodecidua

Mesenchymal stromal cells (MSCs) from gestational tissues represent promising cell populations with stem cell-like properties for use in regenerative medicine. Previously, we reported that MSCs in the chorionic villi of the human placenta reside in a vascular niche. However, the niche(s) in which MSCs reside in the fetal membranes, another rich source of MSCs, remains to be determined. The cell surface markers STRO-1 and 3G5 were previously employed to identify niches in a variety of tissues and here we use these markers to report the location of the MSC niche in the human decidua parietalis. The cultured decidua parietalis MSCs (DPMSCs) isolated from the choriodecidua component of the fetal membranes possessed stem cell-like properties such as adherence to plastic, colony forming ability, and multipotent differentiation potential. Fluorescence in situ hybridization analysis showed cultured DPMSCs were of maternal origin. Immunocytochemistry demonstrated that cultured DPMSCs stained positively with stem cell surface markers 3G5, CD105, CD106, STRO-1, CD146, CD49a, and α-SMA but were negative for hematopoietic markers (CD117, CD34) and vascular markers (CD34, von Willebrand factor [vWF]). Immunohistochemistry with antibodies to stem cell surface markers and the endothelial markers on term fetal membranes revealed a vascular niche for DPMSCs, which was confirmed by immunofluorescence analysis. Both STRO-1 and vWF fluorescence signals showed substantial overlap, while CD146 and vWF signals showed partial overlap. These observations were consistent with a vascular niche.

Placental CLIC3 is increased in fetal growth restriction and pre-eclampsia affected human pregnancies

Chloride intracellular channel (CLIC) proteins constitute a subgroup of the glutathione-S-transferase (GSTs) superfamily. In humans, the CLIC family of proteins consists of six members, designated CLIC 1-6, which have a conserved C-terminal 240 residue module and one major transmembrane domain. CLIC proteins regulate fundamental cellular processes including regulation of chloride ion concentration, stabilization of cell membrane potential, trans-epithelial transport, regulation of cell volume and stimulation of apoptotic processes in response to cellular stress. Previously, we described the expression profile of a member of the CLIC family of proteins, CLIC3, in human placentae and fetal membranes. In the current study, we determined CLIC3 expression in placentae from pregnancies complicated with either fetal growth restriction (FGR, n=19), pre-eclampsia (PE, n=16) or both FGR and PE combined (n=12) compared to gestation-matched controls (n=13) using real-time PCR and a CLIC3 specific immunoassay. Significantly increased CLIC3 mRNA and protein were detected in placental extracts from pregnancies with FGR, PE and PE with FGR compared to controls. Our results suggest that increased expression of CLIC3 may play a role in abnormal placental function associated with the human pregnancy disorders FGR and PE.

Calreticulin has opposing effects on the migration of human trophoblast and myometrial endothelial cells

Calreticulin is a calcium binding, endoplasmic reticulum resident protein best known for its roles in intracellular calcium homeostasis and the quality control processes of the endoplasmic reticulum. There is evidence for a range of activities for calreticulin outside the endoplasmic reticulum, including in the cytosol, on the surface of different cells types and in the extracellular matrix. Recent evidence indicates that human pregnancy is a condition of elevated circulating calreticulin. Calreticulin was increased in the plasma of women throughout pregnancy compared to the non-pregnant state. Calreticulin was also further increased during the hypertensive disorder of human pregnancy, pre-eclampsia. To clarify the roles of circulating calreticulin in pregnancy and pre-eclampsia, the aim of this study was to determine the effects of exogenous calreticulin on two cell types that are relevant to normal human pregnancy and to pre-eclampsia. Human primary myometrial microvascular endothelial cells (UtMVEC-Myo) and the human trophoblast cell line, HTR8/SVneo, were cultured with exogenous calreticulin at concentrations (2 μg/ml and 5 μg/ml) comparable to that measured in maternal blood. The higher concentration of calreticulin significantly increased the migration of the UtMVEC-Myo cells, but significantly reduced the migration of the HTR8/SVneo cells. In the presence of only FGF, FBS and antibiotics calreticulin at 5 μg/ml significantly reduced the number of UtMVEC-Myo cells during in vitro culture for 120 h. These results demonstrate that exogenous calreticulin can alter both HTR8/SVneo and UtMVEC-Myo cell functions in vitro at a (patho-) physiologically relevant concentration. Increased calreticulin may also contribute to altered functions of both cell types during pre-eclampsia.

154. EXTRACELLULAR CALRETICULIN ALTERS ENDOTHELIAL CELL AND TROPHOBLAST CELL FUNCTIONS IN VITRO CONSISTENT WITH PRE-ECLAMPSIA

Pre-eclampsia is a multisystem disorder of human pregnancy that involves abnormal placentation via insufficient trophoblast cell invasion of the maternal spiral arteries and widespread maternal endothelial cell dysfunction. Factors in plasma of pre-eclamptic women affect both trophoblast and endothelial cell functions during in vitro culture (1). The calcium-binding protein calreticulin is elevated in peripheral blood with pre-eclampsia compared to normotensive pregnancy (2). The aim of this study was to determine the effects of exogenous calreticulin at concentrations relevant to normotensive pregnancy (2 µg/mL) and to pre-eclampsia (5 µg/mL) on human trophoblast cell (HTR8) and microvascular endothelial cell (myometrial) numbers and migratory activity. Cell migration was measured by scratch assay; changes in cell number were measured by MTS assay (Promega). The results showed that calreticulin at 5µg/mL did not affect HTR8 cell number (control 68044+24542 cells, with calreticulin 72810 + 30673 cells, n = 3, P > 0.05) after 48 hours, but significantly inhibited migration of the cells by 48+11% compared to the control at 26 hours (n = 4, P < 0.02). Calreticulin at 5 µg/mL and under conditions that did not change cell number significantly increased migration of the myometrial endothelial cells by 39+7% (n = 4, P < 0.01) at 20 hours. Calreticulin at 5 µg/mL, however, significantly reduced endothelial cell numbers after 3–5 days (control 6213 + 1937 cells, with calreticulin 1937+728 cells, n = 6, P < 0.05). There was no significant change to the functions of either cell type with 2 µg/mL of calreticulin. In conclusion, exogenous calreticulin at a concentration consistent with that found in maternal blood with pre-eclampsia was shown to alter trophoblast and endothelial cell migratory activity and reduce endothelial cell numbers during in vitro culture. These results indicate that elevated circulating calreticulin may contribute to the cellular mechanisms that underlie the development of pre-eclampsia. (1) Harris et al, Reprod Sci, 2009, 16: 1082–90.(2) Gu et al, Molec Human Repro, 2008, 14: 309–15.

Calreticulin in human pregnancy and pre-eclampsia

Pre-eclampsia is a disorder of human pregnancy that involves pregnancy-induced maternal hypertension and proteinuria. Evidence indicates that pre-eclampsia involves widespread activation of maternal endothelial cells. Calreticulin is a ubiquitously expressed, multi-functional protein that has been shown to have both pro- and anti-inflammatory effects on cultured endothelial cells in vitro and in whole animals. In order to clarify the role of this protein in normal human pregnancy and in pre-eclampsia, this study has measured expression of calreticulin in maternal blood and in placenta in patients with pre-eclampsia and in control pregnancies. There was a significant increase (approximately 5-fold) in calreticulin in plasma in term pregnant women compared with women who were not pregnant. There was no difference, however, in calreticulin in plasma from women who were sampled at first trimester, second trimester and at term. In addition, there was a significant increase (approximately 50%) in calreticulin in plasma from pre-eclamptic women compared to controls. Calreticulin mRNA and protein expression in placenta were not changed between pre-eclampsia and control pregnancies. These novel results indicate that calreticulin is increased in peripheral maternal blood early in pregnancy and remains elevated throughout normal gestation and that there is a further increase in calreticulin in pre-eclampsia.

204. Proteomic analysis of the effluent from perfused placental cotyledons identifies proteins associated with pre-eclampsia

Pre-eclampsia (PE) is proposed to involve maternal systemic endothelial cell dysfunction which may be caused by excessive shedding of syncytiotrophoblast microparticles (STBM) from the placenta into the maternal circulation. We have examined STBM harvested by perfusion of placental cotyledons from PE and gestation-matched control (GMC) pregnancies. Following proteomic analysis, the proteins Calreticulin, Chloride intracellular channel 3 (CLIC3), Valosin-containing protein (VCP), Protein disulfide-isomerase A3 (ERp57) and Protein kinase C inhibitor protein 1 (14–3-3) were identified as having increased expression in PE samples. This result suggests that there may be increased rate of release of these proteins from the placenta into the maternal circulation. The aims of this work are to measure the expression of these proteins in placental extracts and maternal plasma, and to compare expression between PE and GMC using western blots and/or ELISA with antibodies specific to each protein. Placental expression was confirmed for all five proteins, however, CLIC3 was the only protein significantly increased in the placenta in PE (17.858µg+1.62, n = 27, t-test P < 0.05) compared with GMC (10.478µg+0.76, n = 25). western blot determined there was a significant increase in calreticulin expression in plasma from PE women compared with GMC (as shown by Gu et al. 2008). Likewise, VCP was also increased in PE plasma (1810+280 density/0.25µl, n = 10) compared with GMC (884+260, n = 9). In contrast, the protein 14–3-3 was decreased in PE plasma (4 out of 27 PE plasma samples tested expressed 14–3-3) compared with GMC (10 out of 27 control plasma samples expressed 14–3-3). One of the western blots determined that there was a significant decrease in 14–3-3 expression in plasma from PE women (199.24+186 density/2.5µl, n = 10, un-paired t-test P < 0.05) compared with GMC (2174.91 ± 723.29, n = 11). Neither ERp57 nor CLIC3 was detected in maternal plasma. Those proteins found to be significantly different in PE compared with GMC may be involved in the pathophysiology of PE. These results demonstrate that proteomic analysis of the effluent from perfused placental cotyledons is a reliable screening method to successfully identify proteins that have altered expression with PE. (1) Gu et al. Mole. Human Repro. April 16 2008

Expression and cellular localisation of chloride intracellular channel 3 in human placenta and fetal membranes

Chloride channels regulate the movement of a major cellular anion and are involved in fundamental processes that are critical for cell viability. Regulation of intracellular chloride is achieved by multiple classes of channel proteins. One class of putative channels are the chloride intracellular channel (CLIC) family. Evidence suggests that several CLICs are expressed in human placenta, although their roles in this tissue are not certain. Northern blot analysis has shown that CLIC3 is highly expressed in placenta relative to other human tissues; however, its cellular distribution is not known. This study used microarray expression profiling to clarify which CLICs are expressed in human placenta and RT-PCR, Western blot and immunohistochemistry to determine the expression pattern of CLIC3 in human placenta and fetal membranes. Placentas and fetal membranes were obtained from term pregnancies after delivery and placental tissue was obtained from first trimester following either chorionic villous sampling or elective pregnancy termination. Trophoblast cells were isolated from first trimester and term placentas and placental endothelial cells were isolated from term placentas. Microarray expression profiling identified high expression of mRNA for CLICs 1, 3 and 4 in the isolated first trimester and term trophoblast cells. High mRNA expression in the isolated endothelial cells was also found for CLICs 1 and 4, but not CLIC3. Low expression was found for CLIC5 in all three types of isolated cells. RT-PCR confirmed that CLIC3 mRNA was expressed in trophoblast cells at both gestational ages, but was not present in endothelial cells. CLIC3 mRNA was also identified in whole placental extracts at both gestational ages and in term amnion and choriodecidua. Immunohistochemistry using a chicken anti-human CLIC3 antibody localised strong CLIC3-specific staining to the syncytiotrophoblast and villous cytotrophoblast cells in both first trimester and term placentas, and weaker staining in extravillous trophoblast cells in first trimester. In fetal membranes at term strong CLIC3-specific staining was localised to chorionic trophoblast cells, with weaker staining in amniotic epithelial and decidual cells. It was previously shown that chloride uptake was increased into cells that had been transfected with CLIC3. CLIC3 may facilitate chloride ion movement and the regulation of cellular processes associated with the movement of chloride in the placental and fetal membrane cells in which it is expressed.

Homeobox genes are differentially expressed in macrovascular human umbilical vein endothelial cells and microvascular placental endothelial cells

Angiogenesis is fundamental to normal placental development. Aberrant angiogenesis within the placental terminal villi is a characteristic of significant placental pathologies and includes structural and vascular abnormalities as well as altered endothelial cell function, which substantially impacts on maternal-fetal exchange. Homeobox gene transcription factors regulate vascular development in embryonic and adult tissues, but their role in the placental microvasculature is not well known. In this study, we isolated and enriched human placental microvascular endothelial cells (PLEC) by a perfusion-based method and compared homeobox gene expression between PLEC and macrovascular human umbilical vein endothelial cells (HUVEC). Reverse transcriptase PCR detected mRNA expression of homeobox genes DLX3, DLX4, MSX2, GAX and HLX1 in both PLEC and HUVEC. DLX4 and HLX1 have not been previously detected in PLEC and with the exception of GAX, none of these homeobox genes have been previously identified in HUVEC. There was lower expression of HLX1 mRNA in HUVEC compared with PLEC. Using real-time PCR analysis PLEC HLX1 mRNA expression relative to housekeeping gene GAPDH was 0.9+/-0.06 fold of the calibrator (n=6) versus 0.2+/-0.06 (n=6) for HUVEC, p<0.001. These data provided evidence of heterogeneity in homeobox gene expression between microvascular PLEC and macrovascular HUVEC that most likely reflects significant differences in endothelial cell function in the two different cellular environments.

Increased adrenomedullin protein content and mRNA expression in human fetal membranes but not placental tissue in pre-eclampsia

The relationship between Pre-eclampsia (PE) and placental production of Adrenomedullin (AdM) is not completely understood. This study measured placental and fetal membrane AdM protein concentrations by specific radioimmunoassay and mRNA expression by Northern blot analysis in samples obtained at either term or preterm gestation from women either in labour or not in labour. Samples were obtained from women with normotensive and pre-eclamptic pregnancies. There were significant increases in immunoreactive AdM protein concentration (pg/mg DNA) in choriodecidua and amnion of women with PE compared to normal pregnancy for the preterm not-in-labour group (choriodecidua: control 124 +/- 16, n = 10, PE 361 +/- 35, n = 10; amnion: control 94 +/- 12, n = 10, PE 153 +/- 19, n = 10) and for the term not-in-labour (choriodecidua: control 128 +/- 17, n = 14, PE 459 +/- 51, n = 8; amnion: control 112 +/- 15, n = 14, PE 253 +/- 57, n = 8) and in-labour (choriodecidua: control 531 +/- 74, n = 14, PE 881 +/- 188, n = 8; amnion: control 545 +/- 84, n = 14, PE 1008 +/- 230, n = 8) groups. AdM mRNA relative abundance was greater in preterm, not-in-labour choriodecidual samples in PE, but not in amnion. In addition, this study observed labour-associated increases in choriodecidual and amniotic irAdM in term pre-eclamptic and control patients. However, there were no significant changes in AdM protein or mRNA expressions between any of the groups for placental tissue. These results suggest that fetal membranes, but not placental, production of AdM is increased at the post-translational level during PE in preterm and term tissues and at the pre-translational level during PE in preterm tissues. Fetal membranes, AdM may play an important role in the regulation of feto-placental hemodynamics and fetal physiology during pre-eclampsia.

Fetal growth restriction is associated with increased apoptosis in the chorionic trophoblast cells of human fetal membranes

The aim of the study was to determine the incidence and spatial distribution of apoptotic cell in fetal membranes obtained from human pregnancies complicated with fetal growth restriction (FGR) for which there was no established cause. Fetal membrane samples from normal (n=10) and FGR-affected (n=10) pregnancies were collected and stored following delivery. The incidence of apoptosis and the number of apoptotic cells in normal and FGR-affected fetal membranes were determined using immunohistochemistry and a monoclonal antibody for neo-epitope of cytokeratin-18, M30. The level of apoptotic proteins in FGR-fetal membranes compared to the normal tissue was determined using Western immunoblotting analysis. Multiple labeling of trophoblast cells using immunofluorescence markers was used to investigate regional differences in localization of apoptotic cells between normal and FGR-affected fetal membranes. Apoptosis was detected in both normal and FGR-affected fetal membranes. However, quantitative analysis of apoptotic cells by immunohistochemistry showed a significant increase in FGR-affected fetal membranes compared to normal (p<0.005). Furthermore, it was observed that apoptotic cells were predominantly localized to chorio-decidual layer of the fetal membrane. By using semi-quantitative analysis of Western immunoblotting, a significant increase in the levels of the apoptotic marker proteins poly-ribo (ADP) polymerase (PARP) and the neo-epitope of cytokeratin-18 were observed in FGR-affected fetal membranes compared to normal (p<0.005). Immunofluorescence studies further confirmed the restriction of the apoptotic cells to the chorionic trophoblast cells in FGR-affected fetal membranes. Our results document for the first time an increased incidence of apoptosis in FGR-affected fetal membranes, with the apoptotic cells restricted primarily to the chorionic trophoblast layer of the fetal membranes. Increased apoptosis in FGR-affected fetal membranes may impair functions of the fetal membranes that are important for normal fetal development and growth. Elucidation of the molecular mechanisms involved in the control of apoptosis in the chorionic trophoblast layer in the FGR-affected fetal membranes may provide further insights into the etiology of FGR.

Increased biological oxidation and reduced anti-oxidant enzyme activity in pre-eclamptic placentae

Oxidative stress occurs when cellular levels of reactive oxygen species exceed anti-oxidant capabilities and has been implicated in the pathogenesis of pre-eclampsia. In this study we have examined the tissue levels of endogenous anti-oxidant proteins (superoxide dismutase, glutathione peroxidase, thioredoxin reductase and thioredoxin) and the level of lipid and protein oxidation in placental samples from normal and pre-eclamptic pregnancies. Pre-eclamptic tissue homogenates demonstrated significantly increased levels of lipid peroxidation (20.68 +/- 7.811 microM protein versus 5.33 +/- 4.03 microM/mg protein, P < 0.001) and a trended increase in protein carbonyl concentration (248.1 +/- 97.71 units/mg protein versus 209.7 +/- 82.6 U/mg protein) when compared to controls. The levels and activities of the anti-oxidant proteins superoxide dismutase (2.48 +/- 0.6 U/mg protein versus 2.02 +/- 0.51 U/mg protein, P <0.02), thioredoxin reductase (19.25 +/- 9.81 U/mg protein versus 13.02 +/- 5.66 U/mg protein,P = 0.02), thioredoxin (107.00 +/- 18.11 ng/mg protein versus 91.12 +/- 21.18 ng/mg protein, P = 0.02) and glutathione peroxidase (17.33 +/- 6.63 mmol/min/mg protein versus 11.50 +/- 3.11 mmol/min/mg, P < 0.02) were all found to be significantly reduced when comparing pre-eclamptic placental tissue homogenates to gestational age-matched control placentae from non-pre-eclamptic pregnancies. The results of this study demonstrate a decreased enzymatic anti-oxidant capacity and increased oxidation in placental tissue from pre-eclamptic women, which may contribute to the pathogenesis of this complex disorder.

Expression of GLUT12 in the fetal membranes of the human placenta

The aim of this study was to characterize the expression of the novel glucose transporter GLUT12 in the fetal membranes of the human placenta. RT-PCR and Western blotting of extracts of amnion and choriodecidua from four normal term placentas identified GLUT12 mRNA and protein expression. In all four samples the signals for GLUT12 were markedly stronger in the choriodecidua than in the amnion, whereas the signals for GLUT1, a glucose transporter know to be expressed in fetal membranes, were similar for the two tissues. In further studies, paraffin sections of fetal membranes were analyzed by immunohistochemistry with GLUT12 and GLUT1-specific polyclonal antibodies. GLUT12 immunoreactivity was localized predominantly to the trophoblast cells in the chorion and to a lesser extent to decidual cells and to epithelial and fibroblast cells of the amnion. GLUT1 was localized to chorionic trophoblast cells and amniotic epithelial and fibroblast cells. GLUT12 expression was predominantly cytoplasmic, whereas GLUT1 was associated with the membrane of the cells. These results show that GLUT12 is expressed in cells of human fetal membranes and suggest that GLUT12 may play a role in the facilitation of glucose transport into these cells.

288.Labour-associated changes in human fetal membranes and placental adrenomedullin mRNA expression

We have recently shown that total adrenomedullin (AdM) concentrations are elevated in choriodecidual and amniotic tissues, but not in placental, in response to human labour at term and pre-term (1). Therefore, the present study was designed to determine whether AdM mRNA expression was increased with labour in term and pre-term samples by using Northern Blot Analysis. Placentas were collected either at elective caesarean section (not-in-labour, NIL), after normal vaginal deliveries and at caesarean section during labour (in-labour, IL) from women with singleton pregnancies at term (>36 weeks gestation, 39.2 � 0.2) or pre-term (between 24 to 36 weeks gestation, 32 � 0.4), but with otherwise uneventful antenatal courses. There were significant labour-induced increases in AdM mRNA expressions in amnion and choriodecidua in both groups, pre-term and term (see table in PDF file). No difference was found in those who had vaginal deliveries with those who had caesarean sections after the commencement of labour at pre-term. Amongst term samples in labour all subjects were delivered vaginally uneventfully, except two cases where forceps were used in the third stage of labour. AdM mRNA levels are increased in association with both term and pre-term labour, both in amnion and choriodecidua. We postulate that increased production of AdM by fetal membranes in association with labour may be involved in fetal and/or maternal adaptations to labour. For example, AdM may compensate for local-acting vasoconstrictor substances that are increased during labour, or it may act on the fetal lung in preparation for extra-uterine life. (1) Al-Ghafra A, Gude NM, Brennecke SP, King RG (2003) Labour-associated changes in adrenomedullin content in human placenta and fetal membranes. Clin. Sci. 105, 419–423.

Labour-associated changes in adrenomedullin content in human placenta and fetal membranes

The aim of the present study was to determine the effects of labour and mode of delivery on human placental and fetal membrane content of adrenomedullin (AdM). Placentas and fetal membranes were collected either at term or pre-term gestation from women either in labour or not in labour, and AdM was measured in tissue extracts by specific RIA. There were significant increases in AdM concentrations in amnion and choriodecidua for the in-labour group compared with the not-in-labour group for both pre-term and term gestations. There was no difference in AdM concentration in placental tissue between labour groups. This study provides evidence that fetal membrane AdM is increased in amniotic and choriodecidual tissues in response to labour, and suggests that it may play a role during human labour.

GLUT12 expression in human placenta in first trimester and term

The aim of this study was to characterize the expression of a novel glucose transporter protein GLUT12 in human placenta. GLUT12 mRNA expression was identified by RT-PCR in extracts from five normal term placentae and in extracts from cultured cells of the JAR, JEG-3 and HTR-8Svneo cell lines. In further studies, paraffin sections of first trimester tissue from chorionic villus sampling and term tissue obtained after delivery were analysed by immunohistology with a GLUT12 specific polyclonal antibody. GLUT12 immunoreactivity was expressed predominantly in the syncytiotrophoblast and in extra-villous trophoblast cells in first trimester tissues at 10, 11 and 12 weeks' gestation. In term tissue, however, GLUT12 staining was not detected in syncytiotrophoblast and was found predominantly in villous vascular smooth muscle cells and villous stromal cells. These results suggest that there is a dynamic spatial and temporal expression pattern for the novel glucose transporter GLUT12 in human placenta.

Placental glucose transport and utilisation is altered at term in insulin-treated, gestational-diabetic patients

AIMS/HYPOTHESIS

We have previously shown that placentae from patients with gestational diabetes mellitus who did not receive insulin had lower glucose transport and utilisation than non-diabetic control subjects. To assess the placental glucose handling characteristics of women with gestational diabetes mellitus receiving insulin, we examined glucose transport and utilisation in placentae from three groups of women after term delivery: those with gestational diabetes mellitus and receiving insulin (n = 9, insulin group); those with gestational diabetes mellitus and not receiving insulin (n = 10, no insulin group); and those with normal, non-diabetic pregnancies (n = 9, control group).

METHODS

Dual perfusion of an isolated placental lobule was done using maternal glucose concentrations of 4, 8, 16 and 24 mmol/l. Glucose and L-lactate concentrations in the maternal and fetal effluents were measured. Direct glucose transfer from the maternal to the fetal effluent was measured using 14C-D-glucose. Mean rates in micromol ming(-1) (wet tissue) at maternal glucose concentration of 8 mmol/l are shown.

RESULTS

Glucose uptake from the maternal perfusate (insulin group 0.57, no insulin group 0.30) and net glucose transfer to the fetal effluent (insulin group 0.41, no insulin group 0.20) both increased in the placentae of women receiving insulin compared with the diabetic group not receiving insulin. Both groups of patients had lower placental glucose utilisation than the control group (insulin group 0.16, no insulin group 0.10, control group 0.25).

CONCLUSION/INTERPRETATION

These results suggest that materno-fetal glucose transport increases in the placentae of women with gestational diabetes mellitus who receive insulin compared with those women who do not receive insulin.

The effect of vascular coiling on venous perfusion during experimental umbilical cord encirclement

OBJECTIVE

The aim of these studies was to compare venous perfusion in umbilical cords subjected to a standardized tight encirclement force. Comparisons were made between cords from normal pregnancies and those complicated by gestational diabetes mellitus and intrauterine growth restriction.

STUDY DESIGN

The cannulated cord segment was wrapped around a plastic container, which in turn was attached with nylon string to a hanging graduated measuring cylinder in which known volumes of water could be applied for weight. The cord was perfused with Krebs solution to a constant venous perfusion pressure of 40 mm Hg. Weights of 100-g increments were applied until total cessation of venous perfusion was observed. The weight, length, number of vascular coils, and degree of hydration were recorded for each cord. The coiling index was defined as the number of vascular coils per 10 cm of cord.

RESULTS

Regression analysis of 34 cords (normal, n = 16; gestational diabetes mellitus, n = 12; intrauterine growth restriction, n = 6) identified a significant inverse correlation (P =.0003, Spearman rank correlation) between coiling index and the minimum weight required to occlude venous perfusion. Cords from pregnancies complicated by intrauterine growth restriction displayed a higher frequency of vascular coiling and were more easily occluded (median weight, 350 g) than were cords from pregnancies complicated by gestational diabetes mellitus, which were less coiled and tended to resist occlusion (median weight, 1100 g).

CONCLUSION

During experimental cord encirclement there was a significant inverse relationship between vascular coiling and susceptibility to cord venous occlusion when traction was applied to the encirclement.

Relative abundance of placental pro-atrial natriuretic factor mRNA in normal pregnancy and pre-eclampsia

Atrial natriuretic factor (ANF), produced by cytotrophoblast cells of the human placenta, may be involved in the regulation of uteroplacental blood flow. Pre-eclampsia is associated with maternal hypertension and reduced uteroplacental perfusion. The relationship between pre-eclampsia and placental production of ANF is not known. This study measured pro-ANF mRNA levels by Northern blot analysis in placentae delivered by caesarean section at preterm and term gestations from women with normotensive and pre-eclamptic pregnancies and found no significant difference between pre-eclampsia and normal pregnancy at either gestation. This result suggests that placental production of ANF is not altered at the pretranslational level during pre-eclampsia.

Effects of gestational diabetes on human placental glucose uptake, transfer, and utilisation

AIMS/HYPOTHESIS

Gestational diabetes is associated with complications for the offspring before, during and after delivery. Poor maternal glucose control, however, is a weak predictor of these complications. Given its position at the interface of the maternal and fetal circulations, the placenta possibly plays a crucial part in protecting the fetus from adverse effects from the maternal diabetic milieu. We hypothesised that gestational diabetes may result in changes in placental function, particularly with respect to the uptake, transfer, and/or utilisation of glucose. We aimed to examine glucose transport and utilisation in intact human placental lobules from women with gestational diabetes and those from normal pregnancies.

METHOD

Dual perfusion of an isolated placental lobule was done on placentae from diet treated gestational diabetic (n = 7) and normal pregnant patients (n = 9) using maternal glucose concentrations of 4, 8, 16 and 24 mmol/l in random order over a 4-h experiment. Results were expressed in micromol x min(-1) x g(-1).

RESULTS

D-glucose uptake from the maternal circulation (control 0.492 vs gestational diabetes mellitus 0.248, at 8 mmol/l maternal glucose), D-glucose utilisation by the placenta (0.255 vs 0.129), D-glucose transfer to the fetal circulation (direct 0.979 vs 0.402; net transfer 0.269 vs 0.118) and L-lactate maternal release into both the fetal (0.052 vs 0.042) and maternal (0.255 vs 0.129) circulation were significantly reduced during in vitro perfusion of placentae from patients with gestational diabetic pregnancies. Transfer of 3H-L-glucose also significantly reduced in the diabetic group (8.1% vs 2.6%).

CONCLUSION/INTERPRETATION

These results suggest that placental transport and metabolism of D-glucose is altered during gestational diabetes.

Magnesium regulates hypoxia-stimulated apoptosis in the human placenta

Apoptosis (programmed cell death) in the human placenta is likely to play a major role in determining the structure and function of that organ. Fetal growth restriction (FGR) has been shown to be associated with increased levels of placental apoptosis. Altered regulation of apoptosis may play an important pathophysiological role in FGR. As reduced placental perfusion and reduced oxygenation are features of FGR, one aim of this study was to determine the effects of hypoxia on apoptotic activity, as assessed by DNA laddering, of placental tissue in vitro. In addition, levels of placental apoptosis may be affected by pharmacological agents routinely used in obstetric patient management. Thus an additional aim of this study was to determine the effects of several relevant pharmacological agents on the levels of DNA laddering during in vitro incubation of human placentae under hypoxic conditions. Incubation of normal placental explant tissue at 37 degrees C for 1-2 h under hypoxic conditions significantly increased placental DNA laddering compared with that in non-incubated tissue, whereas levels of DNA laddering during incubation for up to 2 h under normoxic conditions were not significantly higher than those in non-incubated tissue. The DNA laddering activity of placental explants after 2 h of incubation under hypoxic conditions was significantly increased with increased concentrations of magnesium, but remained unchanged by the inclusion of pethidine, aspirin, nifedipine, dexamethasone, heparin or indomethacin in the incubation mixture. These results suggest that hypoxia may stimulate apoptotic activity in cultured human placental tissues, and that hypoxia-stimulated placental apoptosis may be further increased by increasing the extracellular magnesium concentration.

Human placental nitric oxide synthase activity is not altered in diabetes

Endothelial nitric oxide synthase (NOS) protein and mRNA have been identified and calcium-dependent NOS activity has been measured in human placentae during normal pregnancy. Recently, mRNA and protein for the inducible isoform of NOS have been detected in placentae of women with gestational diabetes. The aim of this study was to determine whether calcium-independent (ciNOS) and/or total (tNOS) NOS activities were increased in placentae obtained after vaginal delivery or Caesarean section from women assigned to the following groups according to standard obstetric criteria: gestational diabetes, diabetes before pregnancy and non-diabetic controls. tNOS and ciNOS were assessed by measuring the conversion of [3H]L-arginine to [3H]L-citrulline in the three groups. Michaelis-Menten constants (Km) and maximum velocities of reaction (Vmax) were calculated using Lineweaver-Burk analysis for tNOS. There were no significant differences in either ciNOS, Vmax or Km values between any of the three groups (normal, ciNOS 12.7+/-1.6%, Vmax 16.6+/-3.3 pmol.min-1.mg-1 protein, Km 15.30+/-2.6 micromol/l; gestational diabetes, ciNOS 15.4+/-1.4%, Vmax 14.8+/-5.2 pmol.min-1. mg-1 protein, Km 10.5+/-1.7 micromol/l; diabetes before pregnancy, ciNOS 13.4+/-1.1%, Vmax 14.9+/-3.4 pmol.min-1.mg-1 protein, Km 17. 7+/-2.2 micromol/l). The presence of macrosomia did not affect tNOS activity in those with diabetes before pregnancy, and glycosylated haemoglobin levels measured between weeks 27 and 39 were not correlated with ciNOS activity. The results from the present study do not provide evidence for increased placental tNOS or ciNOS activities in pregnancies complicated by gestational diabetes or diabetes present before pregnancy.

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.

Effects of ATP, ADP, thrombin, vasopressin and U46619 on human placental nitric oxide synthase activity

The human placenta contains nitric oxide synthase (NOS) activity, which had been previously found to be localized in the syncytiotrophoblast and the endothelial cells of stem villous vessels. Nitric oxide produced by the syncytiotrophoblast could affect maternal platelet aggregation. The aim of the present study was to examine the effects of substances known to cause platelet aggregation (arginine vasopressin (AVP), the thromboxane A2 mimetic U46619, adenosine diphosphate (ADP) and thrombin) on NOS activity of human placental explants in vitro. Placentae were obtained at term from women with obstetrically uncomplicated deliveries. NOS activity was measured in explants by determining the conversion of [3H]L-arginine to [3H]L-citrulline during 60 min incubations. Either the presence of N-omega-L-arginine or the omission of calcium (in the presence of EDTA) significantly inhibited NOS activity. Adenosine triphosphate (ATP) at concentrations of 100-1000 microM significantly stimulated NOS activity, and was used as a positive control. ADP at a concentration of 1000 microM was found to significantly stimulate NOS activity, however, the other platelet aggregating substances investigated, thrombin (0.1, 10 U/ml), AVP (1, 10, 20 microM) and U46619 (3, 30, 300 nM), had no significant effect on NOS activity. These results show that ATP and ADP can stimulate human placental NOS activity, but provide no evidence that platelet aggregating agents other than ADP can affect the production of NO.

Reduction of placental nitric oxide synthase activity in pre-eclampsia

1. The role of the potent vasodilator nitric oxide in the pathogenesis of pre-eclampsia is unclear. We have tested the hypothesis that placental activity of the enzyme which synthesizes nitric oxide (nitric oxide synthase) is reduced in pre-eclampsia. 2. Placentae were obtained after vaginal delivery or Caesarean section from women who had been assigned to the following groups according to standard obstetric criteria: term non-pre-eclamptic control, term pre-eclamptic, preterm non-pre-eclamptic control and preterm pre-eclamptic. Nitric oxide synthase activity of placental tissue homogenates was assessed by measuring conversion of [3H]L-arginine into [3H]L-citrulline in the presence of NADPH, FAD, tetrahydrobiopterin, calmodulin, CaCl2, magnesium acetate and a range of L-arginine concentrations. Michaelis Menton constants (K(m)) amd maximum velocities of reaction (Vmax) were calculated using Lineweaver-Burk analysis. 3. Vmax was significantly reduced in both term and preterm pre-eclamptic placentae compared with placentae from corresponding gestation-matched controls. There were no significant differences in the K(m) values for nitric oxide synthase between any of the four groups, nor were Vmax or K(m) values significantly influenced by mode of delivery. 4. These results provide evidence that human placental nitric oxide synthase activity is significantly reduced in pre-eclampsia. Such a reduction was evident at both term and preterm gestations. Reduced placental nitric oxide synthase activity may have an adverse effect on placental haemodynamic function in pre-eclampsia, and could be involved in the pathogenesis of this important and common obstetric complication.

Endothelins-1, 2 and 3 are released in vitro from the human bilaterally perfused placenta

Immunoreactive-endothelin (ir-ET) has previously been detected in human fetal effluents from in vitro perfused placentae. To date however, because of a lack of radio-immunoassay specificity, the ET isoforms in fetal effluents had not been determined, nor had placental maternal effluents been examined for ETs. The aim of this study was to identify the isoforms of ET released into the maternal and fetal circulations of the human in vitro bilaterally perfused placenta. Both circulations of placentae, obtained after normal vaginal delivery, were perfused with a modified Krebs solution and maternal and fetal effluents from the start of the second hour of perfusion were collected, extracted on Scp-pak C18 cartridges, concentrated by vacuum evaporation and separated by reverse-phase HPLC separation. HPLC fractions were measured by ET-RIA and compared to known synthetic standards. Maternal and fetal effluents contained ET-1 (natural and oxidised ET-1), ET-2 and ET-3 (n = 5). Maternal and fetal release of ET-1 was 2.2 +/- 0.7 and 1.4 +/- 0.1 fmol/min/g wet weight of tissue respectively, ET-2 was 0.4 +/- 0.2 and 0.5 +/- 0.2 and fmol/min/g respectively, and ET-3 was 0.5 +/- 0.2 and 0.7 +/- 0.4 fmol/min/g respectively. There were no significant differences between the release of either ET-1, ET-2 or ET-3 in the maternal or fetal circulations. In conclusion, this study indicated that ET-1, ET-2 and ET-3 were all released into both the maternal and fetal effluents from the in vitro perfused human placenta.

Alpha-atrial natriuretic peptide-induced attenuation of vasoconstriction in the fetal circulation of the human isolated perfused placenta

In order to examine the effect of alpha-ANP on fetal placental vascular tone, single placental lobules were bilaterally perfused and fetal inflow pressure recorded. The placental vasculature was sub-maximally pre-constricted by infusion of the nitric oxide synthase inhibitor N omega-nitro-L-arginine (NOLA) or the thromboxane A2-mimetic U46619. In the presence of continuous infusion of 59.3 mumol/l NOLA, producing a mean pressure increase of 43.7 +/- 1.7 mmHg (n = 8, mean +/- SEM), alpha-ANP (10.7 to 325 nmol/l) produced significant pressure decreases (P < 0.05). In separate experiments (U46619 was either infused at concentrations (4.8 to 21.4 nmol/l) to produce a mean pressure increase (50.1 +/- 2.6 mmHg, n = 10) similar to that produced by NOLA infusion or was infused at a concentration (28.5 nmol/l) that produced a significantly higher pressure increase (104 +/- 15 mmHg), infusion of 1 mumol/l alpha-ANP significantly reduced perfusion pressure. However, 100 nmol/l alpha-ANP or less had no significant effect (n = 4-7). These results indicate that alpha-ANP attenuates NOLA-induced and U46619-induced vasoconstriction in the human placenta, but at concentrations higher than those in fetal or maternal plasma.

Atrial natriuretic factor production by the human placenta

Atrial natriuretic factor (ANF), a 28 amino acid peptide, is primarily produced and secreted by cardiac atrial myocytes to modulate cardiovascular and renal functions. Although ANF is also produced in tissues other than the heart, it remains uncertain whether the peptide is synthesised by human placentae. We provide here evidence from in vitro studies suggesting de novo production of ANF by the human placenta. Placental tissues were collected from normal term pregnancies by elective Cesarean section and acid extracted for ANF radioimmunoassay. The level of placental immunoreactive (ir) ANF was 186 +/- 33 pg/gm wet tissues (mean +/- SE, n = 6). Perfusates from in vitro perfusion of the fetoplacental compartment of placental lobules yielded 26 +/- 6 pg/min/gm wet tissue (n = 3) of irANF. Furthermore, pro-ANF mRNA signals were localised by colorimetric in situ hybridization in a subpopulation of placental cytotrophoblast-like cells, but not in syncytiotrophoblasts nor in chorionic cells of placental sections. Northern blot analysis of placental tissue extracts showed a single band of pro-ANF mRNA signals (-0.85 Kb) similar in size to that found in the rat heart. Our findings suggest that ANF is expressed and produced by a small population of human placental cytotrophoblast-like cells. The possibility that placental ANF may be secreted locally or into the fetoplacental circulation to exert paracrine, autocrine or both effects now needs to be considered.

Calcium dependence of alpha-aminoisobutyric acid transfer in human bilaterally perfused placental lobules

Human isolated bilaterally perfused placental lobules were employed to study the Ca++ dependence of materno-fetal transfer of the non-metabolisable amino acid, alpha-aminoisobutyric acid (AIB). Bilateral perfusion with Ca(++)-free Krebs' solution containing 2 mmol/l EDTA for 60 min resulted in a significant reduction in materno-fetal AIB transfer compared to controls perfused with normal Krebs' solution. However, bilateral perfusion with Krebs' solution containing: 2.5 mmol/l Ca++ and 2 mmol/l EDTA; 3.8 mmol/l Ca++ with no EDTA; or Ca(++)-free Krebs' solution alone did not produce significantly different materno-fetal AIB transfer compared to placentae perfused with normal Krebs' solution. The reduction in AIB transfer during perfusion with Ca(++)-free Krebs' solution with EDTA was partially restored with subsequent reperfusion with normal Krebs' solution for 90 min. These results suggest that AIB transfer in human perfused placental lobules is at least partially Ca(++)-dependent.

Regulation of human placental fetal vessel tone: role of nitric oxide

Factors affecting fetal vessel resistance have been studied in vitro in bilaterally perfused lobules of human placentae. Potent and efficacious constrictors in this preparation (in order of potency) include endothelin-1 > the thromboxane mimetic U46619 > endothelin-3 > prostaglandin F2 alpha. Inhibitors of eicosanoid synthesis did not affect fetal vessel basal perfusion pressure, nor did they potentiate the effects of the vasoconstrictor U46619. In contrast, the nitric oxide inhibitors N omega-nitro-L-arginine (NOLA), haemoglobin and methylene blue all increased fetal vessel basal perfusion pressure and also increased U46619-induced constriction. Similarly, NOLA markedly potentiated the constrictor effects of endothelin-1, angiotensin II, 5-hydroxytryptamine and bradykinin. These studies therefore provide evidence that NO is important in the maintenance of low basal fetal vessel impedance and also reduces the effects of a number of vasoconstrictor autacoids. Nitric oxide synthase (NOS) activity of human placental homogenates has been measured and shown to be mainly calcium-dependent. Human placental NOS activity was not affected by labour state but was reduced in pre-eclampsia. No evidence was found that in pre-eclampsia raised concentrations of the endogenous NOS inhibitor asymmetric dimethylarginine were responsible for the reduced placental NOS activity. Hence, these studies provide evidence that NO is an important endogenous dilator of the fetal vessels of the human placenta and that reduced NOS activity could contribute to the pathogenesis and/or effects of pre-eclampsia.

Human placental and fetal membrane nitric oxide synthase activity before, during and after labour at term

The aim of this study was to determine whether any labour-associated changes in nitric oxide synthase (NOS) activity occur in human placenta and fetal membranes. NOS activity in amnion, choriodecidua, and placenta obtained from women before (at Caesarean section, not in labour), during (at Caesarean section, in labour) and after (spontaneous onset labour, normal vaginal delivery) labour was assessed by measuring conversion of radio-labelled L-arginine to L-citrulline. NOS activity, as judged by its inhibition by the specific NOS inhibitor N omega-nitro-L-arginine, was present in placental and amnionic tissues, but not in choriodecidual tissue specimens. Activity detected in choriodecidua was significantly blocked during incubation with a high concentration of valine, suggesting that L-arginine was being consumed by reactions other than NOS under the experimental conditions in that tissue. There were no significant differences among the labour groups in either amnion or placental NOS activities measured in the presence of 1 microM L-arginine. Amnion NOS activity was significantly less than that in placenta. Placental V(max) and Km values (determined after removal of endogenous L-arginine) did not differ significantly among the different labour groups.

Effect of asymmetric dimethyl arginine on nitric oxide synthase activity in normal and pre-eclamptic placentae

An endogenous inhibitor of nitric oxide synthase (NOS), NG,NG dimethylarginine (asymmetric dimethylarginine, ADMA), which is present in human plasma and urine, has been reported to be elevated in the plasma of women with pre-eclampsia. As ADMA inhibition may contribute to reduced placental NOS activity observed in pre-eclampsia, the aim of this study was to compare the effects of ADMA on placental NOS activity from pre-eclamptic and normal pregnancies (gestational ages 38.4 +/- 0.9 and 38.3 +/- 0.3 weeks respectively). NOS activity was determined by measuring the conversion of [3H]L-arginine to [3H]L-citrulline in homogenates of normal and pre-eclamptic placentae in the absence and presence of increasing concentrations of ADMA (1-100 microM). The IC50 for ADMA for the pre-eclamptic placentae (22.1 +/- 2.1 microM, n = 6) was not significantly different from that for the normal placentae (18.8 +/- 1.4 microM, n = 6). When ADMA and L-arginine in homogenates was removed by ion exchange chromatography and exogenous L-arginine replaced (32 microM), the IC50 for the pre-eclamptic placentae (19.5 +/- 1.8 microM, n = 6) was not significantly different than that for the normal placentae (20.9 +/- 1.0 microM, n = 6), and NOS activity in the absence of endogenous and exogenous ADMA was still reduced in pre-eclamptic placentae. These results provide no evidence that the sensitivity of placental NOS to ADMA is affected by pre-eclampsia, or that placental ADMA contributes to the reduction of placental NOS in pre-eclampsia.

Evidence for inhibition by endothelium-derived relaxing factor of thromboxane A2 receptor-mediated vasoconstriction in the fetal vessels of the human perfused placenta

Three inhibitors of the release or effects of endothelium-derived relaxing factor (EDRF), N-nitro-L-arginine, methylene blue and oxyhemoglobin, caused further increases in perfusion pressure during vascular constriction with submaximal concentrations of the thromboxane A2-mimetic, U46619 in fetal vessels of human placental lobules perfused in vitro. The results suggest the EDRF, released during constriction of fetal placental vessels in response to thromboxane A2 receptor stimulation, attenuates the vasoconstrictor response. Hence, impairment of EDRF release or function could contribute to the reduced placental blood flow observed in various disease states associated with increased thromboxane A2 production such as pre-eclampsia.

Endothelin: release by and potent constrictor effect on the fetal vessels of human perfused placental lobules

Human placental lobules were bilaterally perfused with a modified Krebs solution at constant flow rates of 5 mL min-1, and fetal inflow perfusion pressure was recorded. The effect of infusions of endothelin-1 and endothelin-3 (ET-1 and ET-3) on the perfusion pressure was assessed and compared with that for the thromboxane A2-mimetic U46619 and prostaglandin F2 alpha (PGF2 alpha). All substances caused significant increases in pressure, ET-1 being the most potent, followed in order by U46619, ET-3 and PGF2 alpha. In addition, ET-like immunoreactivity was identified in the fetal effluent of placental lobules during 4 h of basal perfusion. The mean ET-1 equivalent immunoreactivity at 1 h of perfusion was 0.6 +/- 0.2 fmol min-1 g-1 of wet lobule weight for 10 placentae. These data suggest that human fetal placental endothelial cells are capable of synthesizing ETs and that ETs are potent constrictors of the fetal placental vessels. Thus, endothelins may play a role in the control of fetal vascular tone in the human placenta in normal and/or pathological conditions.

Human placental acetylcholine

The human placenta contains both acetylcholine (ACh) and choline acetyltransferase, and in vitro bilaterally perfused placental lobules release ACh. The function of this placental cholinergic system has not yet been clearly defined, although changes occur in it during parturition and it may be linked to placental prostaglandin generation at this time. It has also been suggested that ACh may regulate placental amino-acid transport and/or blood flow. It has been found that ACh release from fetal vessels of bilaterally perfused placental lobules is reduced during preeclampsia but is not necessarily correlated with any change in perfusion pressure or materno-fetal transfer of the nonmetabolizable amino acid alpha-aminoisobutyric acid. However, a correlation has been found between releases from human placental explants of ACh (when inhibited by (2-benzoylethyl)trimethylammonium or vesamicol) and of prostaglandins E2 and F2 alpha. Thus, although the evidence for a role of ACh in the control of placental amino-acid transfer or vascular tone is not conclusive, inhibition of the human placental cholinergic system has been shown to be associated with reduced output of prostaglandins from this tissue.

Analysis of the responses of the fetal vessels of human perfused placental lobules to acute infusions of arachidonic acid

The vasodilatory response to arachidonic acid by the fetal vessels of human perfused placental lobules, in which tone had been increased by infusion of the thromboxane A2 mimetic U46619, was significantly reduced in the presence of the prostacyclin (PGI2) synthetase inhibitor tranylcypromine compared with saline infusion controls. HPLC analysis of the fetal effluent from human perfused placental lobules, in which radiolabelled arachidonic acid had been infused, identified two peaks of activity. The first peak displayed an elution profile similar to that of a 6-keto-PGF1 alpha standard; the presence of 6-keto-PGF1 alpha in this peak was confirmed by RIA. The second peak had an elution profile similar to that of an arachidonic acid standard. These results suggest that the vasodilatory response to the fetal vessels of human perfused placental lobules to acute infusions of arachidonic acid is mediated, at least in part, by the synthesis of PGI2. These data are consistent with the hypothesis that PGI2 may be involved in the maintenance of low vascular resistance of the fetal placenta in utero.

Effects of opioids on acetylcholine output of perfused human placental cotyleda

(1) Output of acetylcholine (ACh) from fetal vessels of Krebs-perfused human placental cotyleda was estimated by bioassay using the rat stomach strip. (2) Infusion of high concentrations of the opioids pethidine, morphine or ethylketocyclazocine, but not [D-Ala2]-methionine enkephalinamide (0.1-300 mumol/l), reduced ACh output. Fifty per cent inhibition of output occurred in the presence of concentrations of greater than or equal to 300 mumol/l (morphine and ethylketocyclazocine) and 338 (317, 353; 95 per cent c.l., n = 6) mumol/l (pethidine). (3) ACh output was inhibited by infusion of 100 mumol/l naloxone or 10 mumol/l naltrexone, but was not affected by lower concentrations of either antagonist. (4) These results suggest that the therapeutic concentrations of morphine and pethidine likely to occur in vivo would not affect placental ACh output into fetal vessels. The finding that high concentrations of synthetic opioids or opioid antagonists were required to inhibit output suggests that they may not be acting specifically, and provides no evidence for the hypothesis that endogenous opioids play a role in control of ACh release into fetal vessels of human placentae.

Changes in the biological activity of autacoids during passage through the human perfused fetoplacental lobule

Changes in the biological activities of a number of autacoids after a single passage through the human perfused fetoplacental lobule have been assessed by bioassay, whilst recording fetal vascular resistance. Bradykinin did not affect vascular resistance, but its biological activity on the superfused bioassay tissues fell by approximately 98%, whereas des-Asp1-angiotensin I activity increased at least 80-fold and the vascular resistance rose. All these effects were inhibited by captopril. Angiotensin II increased vascular resistance but its activity on the bioassay tissues was not changed. 5-Hydroxytryptamine activity was reduced by 67-90% and resistance to flow was not affected. The activities of prostaglandins D2, E2, and F2 alpha were slightly reduced. Prostaglandins D2 and F2 alpha caused vasoconstriction, their maximum effects being greater than those of either of the angiotensins. The TxA2-mimetic U46619 was approximately 90 times more potent than PGF2 alpha, as a vasoconstrictor, but the maximal effects were comparable. Thus, autacoid activity can be reduced, augmented or not affected during passage through the human perfused fetal placental vasculature.

Acetylcholine output and foetal vascular resistance of human perfused placental cotyleda

The foetal villous vessels of single cotyleda of human placentae have been perfused with a constant flow of Krebs solution, recording inflow pressure and passing the venous perfusate in cascade over guinea-pig ileum and rat stomach strip preparations in vitro. Each cotyledon released for at least 4 h a substance that was probably acetylcholine. The perfusate caused contractions of both preparations which were inhibited by atropine or hyoscine and potentiated by physostigmine. Contractile activity was destroyed after incubation at 37 degrees C of perfusate with acetylcholinesterase but not with acetylcholinesterase plus physostigmine. When the perfusion temperature was lowered to 34 degrees C or below, acetylcholine output was reduced, the extent depending on the fall in temperature. No change in resistance of the villous vessels occurred during the changes in temperature or in the presence at 37 degrees C of atropine, hyoscine, hexamethonium, (+)-tubocurarine, hemicholinium-3 or bretylium. Submaximal vasoconstrictor responses of the villous vessels to the thromboxane A2-mimetic U46619 were not affected by reduction of the perfusion temperature to 30 degrees C, which lowered acetylcholine-like output by approximately 70%. Responses to U46619, at 37 degrees C, were unchanged during the presence of atropine or hyoscine. Acetylcholine is released into the foetal circulation of the human placenta but no evidence could be obtained that it affects villous vascular smooth muscle tone or vasoconstrictor responses.

Characterization of thromboxane A2 receptors in the human fetal placental vessels and umbilical vein

An in vitro examination has been made of the thromboxane A2 receptors in human fetal placental villous vessels and umbilical veins utilizing the TxA2 agonist U46619 and its competitive antagonist AH22921. U46619 was a potent constrictor of both preparations. The EC50 were 25.3 nmol/l (s.e.m. = 2.5, n = 8) for causing constriction of perfused villous vessels and 22 nmol/l (s.e.m. = 5, n = 17) for contraction of the venous longitudinal strip. AH22921 competitively antagonized responses to U46619 in both preparations. The pA2 values were not significantly different and their 95% confidence limits, obtained for its ability to antagonize responses to U46619 in villous vessels and the umbilical vein, were 8.0 (7.3-8.8) and 7.1 (6.3-7.9) respectively. It is concluded that TxA2 receptors in both the human fetal placental villous vessels and umbilical vein may be similar. They also may be similar to those in human platelets and pulmonary blood vessels.

Effects of vasoactive autacoids on the human umbilical-fetal placental vasculature

Studies have been made of the effects of autacoids on vascular tone of the human perfused fetal umbilical vein and placental lobule. The thromboxane A2 (TxA2)-mimetic substance U46619, 5-hydroxytryptamine and bradykinin were powerful constrictors of the vein. Prostaglandins E2 (PGE2), F2 alpha (PGF2 alpha), adrenaline, noradrenaline, histamine and angiotensin II were much less potent. Venoconstriction caused by U46619, bradykinin and 5-hydroxytryptamine was reduced during inhibition of phospholipase A2 with mepacrine. Responses to U46619 were also reduced after inhibition of cyclo-oxygenase with indomethacin whereas those to bradykinin and 5-hydroxytryptamine were potentiated. In the placenta U46619 was the most potent vasoconstrictor, bradykinin, 5-hydroxytryptamine, angiotensin II, PGE2 and PGF2 alpha being 10-100 times less active. Responses to U46619 were reduced by either mepacrine or indomethacin. Arachidonic acid caused umbilical venoconstriction but vasodilatation in the placenta. Both effects were reduced by indomethacin. Prostacyclin (PGI2) caused vasodilatation in both preparations. It is suggested that TxA2 in the placenta and TxA2, 5-hydroxytryptamine and bradykinin in the umbilical vein could contribute to control of vascular smooth muscle tone. Their vasoconstrictor effects are partly indirect and affected by the concomitant local release of eicosanoids. The results add support to previous conclusions that these autacoids may normally have important influences on blood flow in the fetal extra-corporeal circulation. Agents inhibiting their synthesis, eg non-steroidal anti-inflammatory agents, should only be prescribed during pregnancy with these facts in mind.