Placental Blood Vessels Research Articles

Human cytomegalovirus protects endothelial cells from apoptosis induced by growth factor withdrawal.

The placental and umbilical blood vessel endothelia may play an important role in human cytomegalovirus (CMV) transmission and viral propagation in the fetus. We propose that CMV infection promotes endothelial cell viability for virus replication. Furthermore, we suggest that certain viral mechanisms are established to delay or inhibit the cellular response to undergo apoptosis. We have established a model of CMV infection in primary endothelial cells (HUVECs) in which productive infection with the endothelial-adapted strain of CMV, strain 4010, inhibits apoptosis induced by growth factor withdrawal. Apoptosis was measured by assessment of nuclear changes by TUNEL staining. Our results indicate that CMV infection at 48-96 h significantly protects the endothelial cell from apoptosis induced by growth factor withdrawal. We found that uninfected cells in the CMV-infected cell cultures, but not CMV-infected cells, were susceptible to apoptosis during growth factor withdrawal. Our studies examine the pro-apoptotic pathways that are inhibited and the anti-apoptotic pathways that are activated during CMV infection. The pro-apoptotic protein, caspase-3, is activated during growth factor withdrawal in mock-infected HUVECs, but activation is reduced in CMV-infected HUVECs. During infection, the CMV-encoded chemokine receptor US28 is expressed on the infected cell surface. Previously, we have shown that stimulation of US28 with the chemokine RANTES activates cellular proliferative responses in endothelial cells. It is likely, therefore, that US28 might activate anti-apoptotic mechanisms during CMV infection.

The assessment of placental blood vessels by three-dimensional power Doppler ultrasound.

This study was performed in order to compare the performance of classical two dimensional (2D) and three dimensional (3D) ultrasound, both with power Doppler technology, in the visualization of the placental vascular network during ongoing pregnancy. 15 pregnant volunteers in the third trimester of pregnancy were examined by 2D and 3D power Doppler ultrasound. The aim of the study was to follow the branching of the main stem vessel as far as possible distally in the placenta. In addition, we assessed the visualization rate of terminal parts of uteroplacental circulation, radial and spiral arteries. There was no difference in the visualization of primary placental stem vessels by 2D and 3D power Doppler. However, 3D power Doppler performs better distally, with statistically significant differences at the level of secondary stem (p = 0.03), and even more prominent differences at the level of tertiary stem vessels (p = 0.0008). There was no difference in the visualization rate of radial and spiral arteries (p > 0.05). We found 3D superior to 2D ultrasound with power Doppler technology in the determination of the distal vascular branches of the fetal placental blood vessels.

Choice of haemostasis parameters for monitoring of normal and complicated pregnancy

The concentrations of plasma proteins involved in the process of coagulation are changed during the normal pregnancy, disturbing the balance between procoagulant and anticoagulant system. These changes include the increased activity of coagulation factors, the increased fibrin production and suppression of fibrinolysis. In this way, the risk of loosing blood during pregnancy is reduced by physiological mechanisms, but the hazard of developing thrombosis is increased. Placental insufficiency may occur due to thrombosis of placental blood vessels, leading to repeated miscarriages, retardation of foetal growth, eclampsia, intrauterine foetal death and preterm birth. The causes of these incidents are the changes occurring within protein C coagulation system. The mutation in gene for factor V (so-called Factor V Leiden mutation), where the arginine 506 is replaced by glutamine, produces the mutated factor V having normal procoagulant activity but it is less responsive to APC. The condition characterized by poor anticoagulant response to APC is called the APC resistance. The aim of this study was to test the condition of coagulant, anticoagulant and fibrinolytic system in normal and complicated pregnancy as well as the function of protein C anticoagulant system in pregnancy of various gestation periods and APC resistance. The following parameters were measured for the evaluation of haemostasis system: prothrombin time, partial prothrombin time, fibrinogen, fibrin monomer, D-dimer antithrombin III, TAT complex, plasminogen, PAI, factor XIII, protein C protein S, Protein C Global and activated protein C. The testing was performed in pregnant women with normal and complicated pregnancy of various gestation periods. A special group consisted of pregnant women having two or more consecutive miscarriages. Commercial "Behring" tests based on spectrophotometric and coagulometric measure44 ments and ELISA method were used to determine the parameters of haemostasis. It was shown that fibrinogen fibrin monomer, TAT complex and PAI, as parameters of haemostasis, were good markers for the extent of hypercoagulable condition in pregnant women. In this study, significantly lower values of PC-NR and APC-NR were obtained in all three time periods in pregnant women with hypertension and repeated miscarriages in comparison to healthy controls, what verified that anticoagulant activity of activated protein C was significantly reduced during pregnancy, and especially in pregnancy associated with complications. The diagnostic value of haemostasis parameters as markers of thrombotic changes in pregnant women was tested by ROC analysis. According to the obtained results PC-NR and APC-NR showed satisfactory diagnostic accuracy as markers of thrombotic changes in pregnant women, more precisely, they were found to be good indicators of resistance to activated protein C in pregnancy.

In-vitro evidence of autocrine secretion of vascular endothelial growth factor by endothelial cells from human placental blood vessels.

Vascular endothelial growth factor (VEGF), a highly specific mitogen for vascular endothelial cells, is involved in placental vascular growth and remodelling. The aim of this study was to investigate whether placental endothelial cells secrete VEGF in an autocrine manner and if this secretion is correlated with endothelial cell growth. Blood vessels, excised from the apical surface of three human placentae, were sectioned into 40 fragments per placenta and cultured in fibrin gel matrix for 27 days. Immunohistochemical detection of placental endothelial cells was performed by positive staining with anti-human factor VIII-associated antigen and negative staining with anti-human alpha-actin and desmin. To investigate the production and autocrine action of VEGF, VEGF concentrations in culture media were measured and the effect of an anti-VEGF neutralizing antibody on endothelial cell growth was observed. The results demonstrate that soluble VEGF is secreted by placental endothelial cells reaching a plateau from day 24 (68.74 +/- 7.52 pg/ml) to day 27 (67.20 +/- 6.28 pg/ml). Furthermore, VEGF concentrations in media collected on days 6, 12, 18, 21 and 27 of culture were found to be directly correlated to the sprouting parameter of endothelial cells, as calculated by image analysis on the same day ( P < 0.001, r (2) = 0.95 ). The use of 10 and 100 ng/ml of a neutralizing antibody against human VEGF suppressed cell proliferation, compared to that observed in the untreated controls, by 74.8 +/- 7.3 and 89.4 +/- 3.9% respectively. In conclusion, this study reports the first evidence of autocrine secretion of VEGF by human placental endothelial cells and demonstrates the involvement of VEGF in endothelial cell growth within a fibrin gel culture.

The three-dimensional feto-maternal vascular interrelationship during early bovine placental development: a scanning electron microscopical study.

Both the fetal and maternal microvasculature of bovine placentomes was examined by scanning electron microscopy of vascular casts. So far the development of the vascular architecture of the bovine placentome in early gestation has only been studied 2-dimensionally due to technical difficulties arising from the fragility of the early placental blood vessels. Repeated experiments led to the selection of the microvascular corrosion casts presented here. The vasculature of the maternal compartment is supplied by large caruncular stalk or spiral arteries, which release short maternal stem arteries. In the 3rd month of gestation, these arteries branch into several arterioles at their base, thus providing the vascular framework for the lower part of the septal walls of the primary crypts. In the 4th month, due to progressive longitudinal growth of the stem arteries, branching into arterioles occurs not only at the base, but over the whole length of the stem arteries. These arterioles supply the capillary complexes of the septa which resemble the major part of the septal vasculature and face the secondary crypts. Further indentation results in the formation of tertiary crypt capillary complexes, encircling the earlier secondary unit. From the 6th month of gestation the architecture resembles the fully developed maternal placenta with stem arteries running directly to the fetal side to branch into 4 to 6 arterioles, which turn back to enter secondary and tertiary septa. Maternal venules, collecting the blood from the capillary bed of secondary and tertiary septa, converge onto stem veins leaving the caruncle via branches of the uterine vein. The fetal part of the placentome is supplied by the cotyledonary arteries, which branch into fetal stem arteries that are the tributary to single villous trees. Over their whole course towards the maternal side, these give off arterioles entering secondary villi. The tertiary or terminal villous vasculature consists of capillaries, which are organised in serial capillary loops. This system is progressively elaborated in the course of gestation. In the 4th month there are only finger-like loops, whereas from the 6th month large fan-like structures can be observed. In early gestation the maternal and fetal blood vessels meet predominantly in a countercurrent fashion, changing to the less efficient crosscurrent exchange when the tertiary unit develops. These results indicate the development of a highly elaborated fetomaternal villous-crypt exchange system, already established in the 1st half of gestation, thus meeting the increasing needs of the fetus.

Thrombophilia, Thrombosis and Pregnancy

The risk of venous thromboembolism (VTE) in pregnancy is 0.05-1.8%, six times greater than in the non-pregnant state, and pulmonary embolism remains the most common cause of maternal death. Maternal age, previous history of VTE, Caesarean section and the presence of thrombophilia, significantly increase the risk of VTE. Acquired or hereditary thrombophilia occur in almost two-thirds of women presenting with recurrent miscarriages, pre-eclampsia, intrauterine growth restriction, abruptio placentae, or stillbirth, which are associated with microvascular thrombosis in placental blood vessels. Women with VTE during pregnancy and especially those with thrombophilia require individualized management, based on the type of defect, the family history and the presence of additional risk factors. These factors are important in determining the dose and duration of antithrombotic therapy during pregnancy and the puerperium, and the thromboprophylactic strategy for future pregnancies. Oral anticoagulants are now seldom used during pregnancy because of their significant side effects. Low-molecular-weight heparins (LMWHs) are increasingly replacing unfractionated heparin in the prevention and treatment of VTE during pregnancy. LMWHs have also been shown to be effective in improving the outcome of pregnancy in women with previous obstetric complications.

Thrombophilia and its treatment in pregnancy.

Pulmonary embolism is the most common cause of maternal death during pregnancy and the puerperium in the industrialized world. The risk of venous thromboembolism (VTE) in pregnancy is 0.05%-1.8%, 6 times greater than in the non-pregnant state. The risk is increased in women over 35 years and those with obesity, previous VTE, operative delivery, or underlying thrombophilia. Women presenting with recurrent miscarriages, preeclampsia, intrauterine growth restriction, abruptio placentae, or stillbirth (all associated with microvascular thrombosis in placental blood vessels) have high incidence (65%) of thrombophilia. About 70% of the women who present with VTE during pregnancy are carriers of hereditary or acquired thrombophilia. Treatment of women with VTE during pregnancy, and especially those with thrombophilia, requires individualized dosing and duration of antithrombotic therapy and the formulation of thromboprophylactic strategies for future pregnancies. Warfarin is contraindicated during the first trimester due to fetotoxicity; unfractionated heparin (UFH) is associated with practical disadvantages and the risk of heparin-induced thrombocytopenia (HIT) and osteoporosis with long-term use. Low molecular weight heparins (LMWHs) are convenient to use, do not cross the placenta, carry a lower risk of HIT and osteoporosis, and are safe and effective. LMWHs are replacing UFH as the anticoagulant of choice during pregnancy and improve pregnancy outcome in women with a history of obstetric complications and confirmed thrombophilia.

Fetal Placental Vascular Responses to Corticotropin-Releasing Hormone in Vitro. Effects of Variation in Oxygen Tension

In this study, using the human placenta perfused in vitro with Krebs' bicarbonate solution, we have examined the effects of changes in oxygen tension on the vasoreactivity of fetal placental blood vessels to corticotropin releasing hormone (CRH). Vasodilatory responses to human synthetic CRH were measured during sub-maximal vasoconstriction of the fetal placental circulation with prostaglandin F2α(PGF2α) (1–100μm). Decreases in fetal placental arterial perfusion pressure (FAP) were obtained with CRH under conditions of high oxygen or low oxygen tension, ≥450mmHg and ≤50mmHg, respectively. Secretion of CRH into the maternal and fetal placental circulations was measured during changes in oxygen tension in normal placentae and placentae from abnormal pregnancies complicated by pre-eclampsia.The change from high to low oxygen perfusion resulted in a small increase in the basal perfusion pressure (21±3.6 to 28.3±2.6mmHg; (P≤ 0.001, Student's paired t -test). During high oxygen perfusion, CRH (0.3–3000p m) caused a concentrationdependent reduction of the PGF2αinduced increase in FAP. However, during low oxygen perfusion, the vasodilatory effects of CRH were completely inhibited (P≤ 0.05, regression analysis, ANOVA). The effect of the NO synthase inhibitor l -nitro-ω-arginine methyl ester (l -NAME, 1–100μm), on basal FAP during high and low oxygen conditions was also established. Low oxygen perfusion significantly attenuated l -NAME-induced increases in perfusion pressure (P≤ 0.05, regression analysis, ANOVA). Low oxygen perfusion was associated with an increase in CRH secretion into the maternal but not fetal circulation. CRH release into either the maternal or fetal circulations of abnormal placentae were not significantly different from normal controlsIn conclusion CRH-induced vasodilatation of the fetal placental vasculature in vitro is inhibited during low oxygen perfusion. This effect may be related to reduced NO production. Reduced CRH induced vasodilation is associated with increased secretion of the CRH into the maternal but not fetal circulation.

Induction of Placental Heme Oxygenase-1 Is Protective Against TNFα-induced Cytotoxicity and Promotes Vessel Relaxation

Pregnancy is characterized by an inflammatory-like process and this may be exacerbated in preeclampsia. The heme oxygenase (HO) enzymes generate carbon monoxide (CO) that induces blood vessel relaxation and biliverdin that acts as an endogenous antioxidant. We examined the expression and localization of HO-1 and HO-2 in normal and preeclamptic placenta using reverse transcription polymerase chain reaction (RT-PCR), RNase protection assay, immunoblotting and immunohistochemistry. In addition, the effect of HO activation on tumor necrosis factor-alpha (TNFalpha) induced placental damage and on feto-placental circulation was studied. We provide the first evidence for the role of HO as an endogenous placental factor involved with cytoprotection and placental blood vessel relaxation. HO-1 was significantly higher at term, compared with first trimester placentae indicating its role in placental vascular development and regulation. HO-1 predominantly localized in the extravascular connective tissue that forms the perivascular contractile sheath around the developing blood vessels. HO-2 was localized in the capillaries, as well as the villous stroma, with weak staining of trophoblast. Induction of HO-1 caused a significant attenuation of TNFalpha-mediated cellular damage in placental villous explants, as assessed by lactate dehydrogenase leakage (p < 0.01). HO-1 protein was significantly reduced in placentae from pregnancies complicated with preeclampsia, compared with gestationally matched normal pregnancies. This suggests that the impairment of HO-1 activation may compromise the compensatory mechanism and predispose the placenta to cellular injury and subsequent maternal endothelial cell activation. Isometric contractility studies showed that hemin reduced vascular tension by 61% in U46619-preconstricted placental arteries. Hemin-induced vessel relaxation and CO production was inhibited by HO inhibitor, tin protoporphyrin IX. Our findings establish HO-1 as an endogenous system that offers protection against cytotoxic damage in the placenta, identifies the HO-CO pathway to regulate feto-placental circulation and provides a new approach to study the disease of preeclampsia.

Chimaeric and constitutive DNA fingerprints in the common marmoset (Callithrix jacchus)

Marmosets normally produce dizygotic twins sharing placental blood vessels and exchanging bone marrow cells. Each individual is therefore likely to be a blood chimaera. To date, marmosets had only been DNA fingerprinted using blood samples and probes 33.6 and 33.15, resulting in highly similar fingerprints among litter mates and little variation between other individuals, thereby limiting this method's use for individual identification and parentage testing. In this study, novel probes were applied to detect greater polymorphism and to produce individual-specific DNA fingerprints. As expected, blood DNA profiles of twins and triplets were virtually identical, confirming chimaerism in this tissue and identifying litter mates. Furthermore, these profiles were sufficiently variable to distinguish between sibs from different litters and between all other individuals. To produce individual-specific DNA fingerprints, the use of DNA extracted from tissues poor in leukocytes was essential. The findings demonstrate that, despite extensive blood chimaerism, marmoset colonies can be effectively DNA fingerprinted for indicidual identification, zygosity testing, and relationship studies.

The development of the endotheliochorial mink placenta: light microscopy and scanning electron microscopical morphometry of maternal vascular casts.

The development of the mink endotheliochorial placenta has been studied by means of light microscopy and scanning electron microscopy of maternal vascular corrosion casts. The placental blood vessels of three groups of mink, representing early, intermediate and near-term gestational ages were either perfusion fixed for histology, or instilled with liquid plastic in order to prepare vascular casts, which were examined qualitatively and/or quantitatively. The maternal component of the placental vascular system evolves from preimplantation blood vessels between the endometrial glands, into which the initial feto-maternal contact is made. The influence of highly invasive syncytiotrophoblast provokes a transition of the maternal capillaries into extensively anastomosing sinusoids with a subsequent modification of their endothelial cells into large cells with luminal protrusions. Three-dimensionally, the sinusoids are arranged as vascular crypts. This implies a villous-crypt type of interdigitation for the mink, but since the fetal capillaries surround the maternal sinusoids as a dense network a labyrinth is formed. The vascular crypts are supplied by very short arterioles, branching from maternal stem arteries, which arise from branches of the uterine artery and move straight to the surface of the endometrium. Venous outlets of the sinusoids converge onto venules and large stem veins in the deepest portion of the endometrium. This architectural pattern persists until term. Morphometry was used to confirm the qualitative observations in vascular casts. The diameter of maternal vascular crypts significantly increased from 137.3+/-21.9 microm in early gestation up to 217.8+/-80.9 microm in the intermediate stage and 431.8+/-119.5 microm near-term, when compared to the paraplacental zone in early gestation (82.2+/-19.5 microm). The capillary or sinusoidal diameter also increased significantly from intermediate stage (42.9+/-11.8 microm) to near term (60.1+/-16.7 microm), whereas the difference in the paraplacental zone (7.3+/-2.1 microm) and early gestation (13.0+/-3.2 microm) was not statistically significant.

Disturbed Nitric Oxide/Endothelin-1 Equilibrium in Cultured Human Placental Endotheliocytes in Preeclampsia

Several observations suggest that endothelial cell dysfunction is a central pathophysiologic event of preeclampsia. Endothelin-1 (ET-1) is a vasoconstrictor peptide of the endotheliocyte and is increased in the sera of preeclamptic patients. The aim of this study was to investigate the possible regulatory mechanisms between ET-1 and nitric oxide (NO) production in cultured placental endotheliocytes. We report that endothelial cells of arterial placental blood vessels show a dysfunctional mechanism of negative feedback regulation of ET-1 production by cGMP or insufficient NO release in response to a stimulus in the form of an increasing ET-1 concentration.

The elastic fiber system in the human placenta with special reference to elastic type blood vessels

Generally, elastic fibers are part of a so-called elastic fiber system. This system includes elastin (a homogenous component), elaunin (elastin connected to microfibrils) and oxytalan fibers. Recently, we have demonstrated elastic tissue fibers as an essential component of the perivascular contractile sheath (PVCS) also in human placental stem villi. In fetal placental blood vessels, the findings about elastic tissue fibers are contradictory and no information exists about oxytalan fibers in the human placenta. Therefore, we reinvestigated the distribution of the elastic fiber system in the blood vessels of the umbilical cord, chorionic plate and stem villi. Using unfixed orcein-stained cryostal sections of term placentae, we have found a well developed elastic fiber system in fetal blood vessels. It is not possible to discriminate between arteries and veins by morphological criteria and/or the distribution of elastic fibers. After oxidation with peracetic acid additional orcein-stained fibers, were detected in Wharton's jelly and in the placental stroma. The high amount of elastic fibers throughout umbilical and placental blood vessels makes it reasonable to postulate the existence of elastic type blood vessels. Nevertheless, the great range of distribution varieties and the differing amount of elastic fibers in the blood vessels of all investigated placentae was striking. Within stem villi, there exists a longitudinal and circular vascular (inner) and a longitudinal extravascular (outer=PVCS) elastic fiber system. These two systems are ‘connected’ with the smooth muscle cells in both systems, thus forming two contractile myofibroelastic subsystems of a large overall placental myofibroelastic fiber system, in which tightly regulated cellmatrix interactions exists.

The impact of either a Meishan or Yorkshire uterus on Meishan or Yorkshire fetal and placental development to days 70, 90, and 110 of gestation.

Straightbred Yorkshire (Y) conceptuses are larger than straightbred Meishan (M) conceptuses throughout gestation and at farrowing. In contrast, when Y and M conceptuses were gestated together in Y recipient females, the birth weight of M pigs was similar to that of their Y littermates. Even though placentae of M pigs remained markedly smaller than placentae of Y littermates, they were significantly more vascular. The objective of this study was to compare and contrast the changes in Y and M conceptus growth and placental-endometrial vascularity throughout late gestation in Y or M uteri. Gravid uteri were recovered at slaughter from M and Y females that were gestating either M or Y conceptuses on d 70, 90, or 110 of gestation. Uterine and conceptus measurements were recorded, and a section of the intact endometrial-placental attachment site for each conceptus was fixed, embedded, and later evaluated for placental and endometrial vascular density. Placental surface area and weight were greater (P < .001) when M or Y conceptuses were recovered from Y uteri compared with M uteri on each day of gestation examined. Further, by d 110, the surface area of Y placentae was greater (P < .001) than that of M placentae, regardless of uterine type in which they were gestated. The vascular density of M placentae and adjacent endometrium doubled (P < .05) between d 70 and 110 of gestation (3.0 and 2.5 vs 6.0 and 5.1%, respectively), with no significant increase in placental surface area. In contrast, the surface area of Y placentae doubled in size (P < .001) between d 90 and 110 of gestation, but placental and adjacent endometrial vascular density remained relatively constant, averaging 3.2 and 3.8%, respectively. These data are consistent with the premise that placental size is largely determined by the uterus in which a conceptus is gestated until approximately d 90. After d 90, fetal breed-specific mechanisms maintain optimal fetal growth. Between d 90 and term, M fetal growth depends on progressive increases in placental blood vessel density and requires no increase in placental size. In contrast, Y conceptuses seem to rely exclusively on placental growth to increase placental-endometrial surface area for nutrient exchange.

Immunohistochemical analysis of globulin and complements in blood vessels of placental villi during pregnancy induced hypertension

The changes of globulin and complements in placental villi blood vessels were immunohistochemically studied in pregnancy induced hypertension patients and normal pregnant patients by a randomized, double-blind approach. The immunostaining of IgG, IgE, C3, C4, and 5-HT was seen in the villous blood vessels and the helicine arteries of pregnancy induced hypertensive placental villi. The strong positive rates were 100%, 90%, 100%, 100% and 90% in serious pregnancy induced hypertensive patients, accompanied by aggregation of mastocytes and vasculopathy of villous blood vessels and the helicine arteries. It is concluded that the immuno-pathological damage took place in the villous blood vessels and helicine arteries, resulting in vasculopathy and villous regressive changes and that the immunological factors were closely related to pregnancy induced hypertension.

High and low molecular weight kininogen and plasma prekallikrein/plasma kallikrein in villous capillaries of human term placenta

This study examined the expression and presence of components of the kallikrein-kinin system in human term placenta. Immunohistochemical studies localized H-kininogen and plasma prekallikrein/plasma kallikrein to endothelial cells of placental villous capillaries. In larger placental blood vessels and umbilical cord, neither kininogens nor kallikreins were detected. High (H) and low (L) molecular weight kininogen, plasma prekallikrein and plasma kallikrein were detected by Western blot analysis in human term placenta and in maternal and fetal blood, whereas tissue kallikrein was not. Furthermore, mRNA of plasma prekallikrein was detected by reverse transcriptase-polymerase chain reaction (RT-PCR) in placental homogenates, while mRNA of H-kininogen, L-kininogen and tissue kallikrein was not. Because H-kininogen and plasma prekallikrein circulate in a complexed form, we suggest that endothelial cells bind kininogen and plasma prekallikrein in which they are secreted by the fetal liver from fetal blood. The co-localization of kininogen and plasma prekallikrein/plasma kallikrein suggests that kinins could be generated locally in placental capillaries. When released, they may play a role in regulating placental blood flow and transplacental transport of substrates and metabolites.

The effect of mode of delivery on contractile function of placental arteries in vitro

This study was designed to determine the effect of the mode of delivery on the in vitro assessment of placental blood vessel function. Twenty-two subjects with uncomplicated pregnancies, normal antenatal Doppler flow velocity waveforms and normal birth weights were recruited for the study. The 11 subjects who were delivered by elective caesarean section were matched with 11 controls, who had uncomplicated labours and spontaneous vaginal delivery. Two tertiary chorionic plate arteries were dissected free 1 h after delivery and mounted in a myograph. Cumulative concentration response curves were constructed to the thromboxane A 2 analogue U46619, prostaglandin F 2α and angiotensin II. After a period of 12 h a further two vessels were mounted and a concentration response curve to U46619 was repeated to determine whether a delay of several hours after delivery would have an effect on the responses of these vessels. These placental arteries constrict to U46619, prostaglandin F 2α and angiotensin II in a dose-dependent manner. There was no statistical difference in the maximum contractile responses or pD 2 values between the different modes of delivery. A delay in dissection of up to 12 h had no effect on the maximum response or pD 2 with U46619. Therefore, contractile function of placental arteries is by mode of delivery or a delay in dissection.

Endothelin‐induced contractions in human placental blood vessels are enhanced in intrauterine growth retardation, and modulated by agents that regulate levels of intracellular calcium.

Endothelin-1 (ET-1) is a strongly vasoactive polypeptide that may be involved in the regulation of the uteroplacental blood flow. In the present study we have examined the contractile response to ET-1 in human placental arteries in the presence of several agents that interfere with storage of intracellular calcium, e.g. caffeine, ryanodine and thapsigargin. We have also compared the contractile response to ET-1 in normal pregnancies with that of patients with foetal intrauterine growth retardation (IUGR), a condition with reduced uteroplacental blood flow. We found that the response to ET-1 in the placental arteries from women with normal pregnancies was reduced by 20% in the absence of extracellular calcium. Caffeine relaxed the basal tone of the vessels and reduced the contractile response to ET-1 by 51%. Nifedipine in addition to caffeine resulted in a reduction of 70%. Ryanodine also reduced the tone. Thapsigargin had no effect on the placental arteries at lower concentrations, but gave a progressive and slow contraction at 10(-6) M. The ET-1 induced contraction in placental arteries from IUGR patients was 67% more potent than in placental arteries from women with normal pregnancies, 129% as compared with 77% of the maximal K(+)-induced contraction. We conclude that the ET-1-induced contractile response in the human placental artery is dependent on influx of extracellular calcium as well as mobilization of calcium from intracellular stores. An increased sensitivity to ET-1 in placental arteries may contribute to the reduced uteroplacental blood flow in intrauterine growth retardation.

STUDIES ON PREGNANCY HYPERTENSION AND IUGR‐SFD EFFECTS OF DRUGS ON THE BLOOD VESSELS IN THE PLACENTA OF PREGNANT SHRSP

1. Based upon our previous work, we came to the conclusion that a decrease in placental blood volume was a possible factor behind intrauterine growth retardation (IUGR) in pregnancy-induced hypertension. 2. In a second study, we used an image analysis system to measure cross-sectional areas and wall thicknesses of central blood vessels of the spiral artery, the so-called 'central artery'. 3. It was thought that one of the more basic factors behind IUGR in pregnancy-induced hypertension might possibly be narrowings and spasms of the maternal placental blood vessels. 4. In this study, we found that the three drugs we used (MgSO4 center dot 7H2O, Solcoseryl and KCl) all resulted in an enlargement of the cross-sectional areas of the maternal blood vessels, and that MgSO4 center dot 7H2O, in particular, also relaxed maternal blood vessel spasms in SHRSP placenta.

Can meconium in the amniotic fluid injure the fetal brain?

To determine if meconium in the amniotic fluid (AF) can cause cerebral palsy by stimulating umbilical and placental blood vessels to constrict. Brain injury patterns were analyzed in 43 children whose exposure to meconium in the AF was their only identified risk for quadriplegic cerebral palsy. The times their injuries occurred were established by following lymphocyte counts in their blood after birth. All 43 had cerebral cortical and subcortical brain damage of the type produced by late gestational ischemia and hypoxemia. The time between the onset of injury and birth ranged from 2-38 hours. The neonates were severely acidotic at birth when birth occurred within 12-14 hours after ischemia and hypoxemia began. Thereafter, the acidosis receded as the time between its start and birth increased, presumably because vasoconstriction had ended. Severe acidosis did not recede in nine children whose cerebral palsy was due to disorders that kept them hypoxemic until birth. Meconium in the AF may sometimes initiate vasoconstriction that leads to ischemic, hypoxemic cerebral palsy.