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

Research progress of placental vascular pathophysiological changes in pregnancy-induced hypertension and gestational diabetes mellitus

The placenta is a vital organ for fetal development, providing the fetus with nutrients, oxygen, and other important factors. Placenta is rich in blood vessels. Abnormal placental vascular function and blood circulation may lead to insufficient blood supply to the fetus in the uterus, leading to serious consequences such as pregnancy complications, fetal distress and even stillbirth. Pregnancy-induced hypertension (PIH) and gestational diabetes mellitus (GDM) are common complications of pregnancy. Recent studies report that pregnancy complications are often accompanied by changes in placental vascular structure and function. What are the physiological characteristics of human placental blood vessels? What are the pathological changes in the state of PIH and GDM? What are the relationships between these pathological changes and the occurrence of these pregnancy complications? Answers to these questions not only increase the understanding of placental vascular characteristics, but also provide important information for revealing the pathological mechanism of PIH and GDM. This article will summarize the research on the pathological changes of placental blood vessels in PIH and GDM, hoping to further unravel the physiological and pathological characteristics of placental blood vessels in the state of PIH and GDM, provide information for guiding clinical treatment for PIH and GDM.

Novel insights for the role of nitric oxide in placental vascular function during and beyond pregnancy

More than 30 years have passed since endothelial nitric oxide synthesis was described using the umbilical artery and vein endothelium. That seminal report set the cornerstone for unveiling the molecular aspects of endothelial function. In parallel, the understanding of placental physiology has gained growing interest, due to its crucial role in intrauterine development, with considerable long-term health consequences. This review discusses the evidence for nitric oxide (NO) as a critical player of placental development and function, with a special focus on endothelial nitric oxide synthase (eNOS) vascular effects. Also, the regulation of eNOS-dependent vascular responses in normal pregnancy and pregnancy-related diseases and their impact on prenatal and postnatal vascular health are discussed. Recent and compelling evidence has reinforced that eNOS regulation results from a complex network of processes, with novel data concerning mechanisms such as mechano-sensing, epigenetic, posttranslational modifications, and the expression of NO- and l-arginine-related pathways. In this regard, most of these mechanisms are expressed in an arterial-venous-specific manner and reflect traits of the fetal systemic circulation. Several studies using umbilical endothelial cells are not aimed to understand placental function but general endothelial function, reinforcing the influence of the placenta on general knowledge in physiology.

The Bdkrb2 gene family provides a novel view of viviparity adaptation in Sebastes schlegelii

BACKGROUND

Black rockfish (Sebastes schlegelii) is a viviparous teleost. We proposed that the rockfish ovarian wall had a similar function to the uterus of mammals previously. In the present study, the well-developed vascular system was observed in the ovarian wall and the exterior surface of the egg membrane. In gestation, adaptation of the ovary vasculature to the rising needs of the embryos occurs through both vasodilation and neovascularization. Bdkrb2, encoding a receptor for bradykinin, plays a critical role in the control of vasodilatation by regulating nitric oxide production.

RESULTS

Eight Bdkrb2 genes were identified in the black rockfish genome. These genes were located on chromosome 14, which are arranged in a tandem array, forming a gene cluster spanning 50 kb. Protein structure prediction, phylogenetic analysis, and transcriptome analysis showed that eight Bdkrb2 genes evolved two kinds of protein structure and three types of tissue expression pattern. Overexpression of two Bdkrb2 genes in zebrafish indicated a role of them in blood vessel formation or remodeling, which is an important procedure for the viviparous rockfish getting prepared for fertilization and embryos implantation.

CONCLUSIONS

Our study characterizes eight Bdrkb2 genes in the black rockfish, which may contribute to preparation for fertilization and embryo implantation. This research provides a novel view of viviparity adaptation and lays the groundwork for future research into vascular regulation of ovarian tissue in the breeding cycle in black rockfish.

New views on endothelial dysfunction in gestational hypertension and potential therapy targets

The placenta has vital roles in metabolite exchange, fetal growth, and pre-eclampsia (PE). In this review, we discuss the pathogenesis of hypertension in pregnancy, focusing on four major theories to explain PE, discussing endothelial roles in those theories. We focus in particular on the roles of nitric oxide (NO) and prostacyclin (PGI₂) in placental endothelium, and propose new hypotheses for the influence and mechanisms of endothelial NO and PGI₂ signaling pathways in PE.

Vasomotor tone-associated factors and pregnancy outcomes of women who undergo in vitro fertilization

Vasomotor tone-associated factors play important roles in normal pregnancy, but their roles in the pregnancy outcome of women who undergo in vitro fertilization and embryo transfer (IVF-ET) remain unclear. A total of 82 infertile women who underwent successful IVF-ET were enrolled, including 18 pregnancy losses, 11 complications, and 53 normal deliveries. The serum NO and iNOS levels were significantly higher in the pregnancy loss group and significantly lower in the complication group than in the normal delivery group (p < 0.05). Significantly increased ET-1 and decreased PGI2 were found in both the pregnancy loss and complication groups compared with those in the normal delivery group (p < 0.05). NO, iNOS, and ET-1 are risk factors and PGI2 is a protective factor for pregnancy loss. ET-1 + PGI2 (AUC, 0.897; sensitivity, 90.6%; specificity, 83.3%) showed a relatively good predictive value for pregnancy loss following IVF-ET.

Human Placental Vascular Reactivity in Health and Disease: Implications for the Treatment of Pre-eclampsia

Adequate development of the placenta is essential for optimal pregnancy outcome. Pre-eclampsia (PE) is increasingly recognized to be a consequence of placental dysfunction and can cause serious maternal and fetal complications during pregnancy. Furthermore, PE increases the risk of neonatal problems and has been shown to be a risk factor for cardiovascular disease of the mother later in life. Currently, there is no adequate treatment for PE, mainly because its multifactorial pathophysiology remains incompletely understood. It originates in early pregnancy with abnormal placentation and involves a cascade of dysregulated systems in the placental vasculature. To investigate therapeutic strategies it is essential to understand the regulation of vascular reactivity and remodeling of blood vessels in the placenta. Techniques using human tissue such as the ex vivo placental perfusion model provide insight in the vasoactive profile of the placenta, and are essential to study the effects of drugs on the fetal vasculature. This approach highlights the different pathways that are involved in the vascular regulation of the human placenta, changes that occur during PE and the importance of focusing on restoring these dysfunctional systems when studying treatment strategies for PE.

Malaria in pregnancy alters l-arginine bioavailability and placental vascular development

Reducing adverse birth outcomes due to malaria in pregnancy (MIP) is a global health priority. However, there are few safe and effective interventions. L-arginine is an essential amino acid in pregnancy and an immediate precursor in the biosynthesis of nitric oxide (NO), but there are limited data on the impact of MIP on NO biogenesis. We hypothesized that hypoarginemia contributes to the pathophysiology of MIP and that L-arginine supplementation would improve birth outcomes. In a prospective study of pregnant Malawian women, we show that MIP was associated with lower concentrations of L- arginine and higher concentrations of endogenous inhibitors of NO biosynthesis, asymmetric and symmetric dimethylarginine, which were associated with adverse birth outcomes. In a model of experimental MIP, L-arginine supplementation in dams improved birth outcomes (decreased stillbirth and increased birth weight) compared with controls. The mechanism of action was via normalized angiogenic pathways and enhanced placental vascular development, as visualized by placental microcomputerized tomography imaging. These data define a role for dysregulation of NO biosynthetic pathways in the pathogenesis of MIP and support the evaluation of interventions to enhance L-arginine bioavailability as strategies to improve birth outcomes.

What is precise pathophysiology in development of hypertension in pregnancy? Precision medicine requires precise physiology and pathophysiology

It is widely accepted that placental ischemia is central in the evolution of hypertension in pregnancy. Many studies and reviews have targeted placental ischemia to explain mechanisms for initiating pregnancy hypertension. The placenta is rich in blood vessels, which are the basis for developing placental ischemia. However, is the physiology of placental vessels the same as that of nonplacental vessels? What is the pathophysiology of placental vessels in development of pregnancy hypertension? This review aims to provide a comprehensive summary of special features of placental vascular regulations and the pathophysiological changes linked to preeclamptic conditions. Interestingly, some popular theories or accepted concepts could be based on our limited knowledge and evidence regarding placental vascular physiology, pharmacology and pathophysiology. New views raised could offer interesting ideas for future investigation of mechanisms as well as targets for pregnancy hypertension.

The fetal cerebral circulation: three decades of exploration by the LLU Center for Perinatal Biology

For more than three decades, research programs in the Center of Perinatal Biology have focused on the vascular biology of the fetal cerebral circulation. In the 1980s, research in the Center demonstrated that cerebral autoregulation operated over a narrower pressure range, and was more vulnerable to insults, in fetuses than in adults. Other studies were among the first to establish that compared to adult cerebral arteries, fetal cerebral arteries were more hydrated, contained smaller smooth muscle cells and less connective tissue, and had endothelium less capable of producing NO. Work in the 1990s revealed that pregnancy depressed reactivity to NO in extra-cerebral arteries, but elevated it in cerebral arteries through effects involving changes in cGMP metabolism. Comparative studies verified that fetal lamb cerebral arteries were an excellent model for cerebral arteries from human infants. Biochemical studies demonstrated that cGMP metabolism was dramatically upregulated, but that contraction was far more dependent on calcium influx, in fetal compared to adult cerebral arteries. Further studies established that chronic hypoxia accelerates functional maturation of fetal cerebral arteries, as indicated by increased contractile responses to adrenergic agonists and perivascular adrenergic nerves. In the 2000s, studies of signal transduction established age-dependent roles for PKG, PKC, PKA, ERK, ODC, IP3, myofilament calcium sensitivity, and many other mechanisms. These diverse studies clearly demonstrated that fetal cerebral arteries were functionally quite distinct compared to adult cerebral arteries. In the current decade, research in the Center has expanded to a more molecular focus on epigenetic mechanisms and their role in fetal vascular adaptation to chronic hypoxia, maternal drug abuse, and nutrient deprivation. Overall, the past three decades have transformed thinking about, and understanding of, the fetal cerebral circulation due in no small part to the sustained research efforts by faculty and staff in the Center for Perinatal Biology.

Differential vasodilation of human placental and myometrial arteries related to myofilament Ca(2+)-desensitization and the expression of Hsp20 but not MYPT1

Endothelial-dependent regulation of vascular tone occurs in part via protein kinase G1α-mediated changes in smooth muscle myofilament sensitivity to Ca(2+). Tissue-specific differences in PKG-dependent relaxation have been attributed to altered expression of myofilament-associated proteins that are substrates for PKG binding. These include the alternative splicing of the myosin targeting subunit (MYPT1) of myosin light chain phosphatase to yield leucine zipper positive (LZ(+)) and negative (LZ(-)) isovariants, with the former being required for PKG-mediated relaxation, and/or altered expressions of telokin, vasodilator-stimulated phosphoprotein (VASP) or heat shock protein Hsp20. During human pregnancy the uterine and placental circulations remain distinct entities and, as such, their mechanisms of vascular tone regulation may differ. Indeed, the sensitivity of myometrial arteries to endothelial-dependent agonists has been suggested to be greater than that of placental arteries. We tested the hypothesis that this was related to tissue-specific changes in PKG-mediated myofilament Ca(2+)-desensitization and/or the expressions of PKG-interacting myofilament-associated proteins. Permeabilized human placental and myometrial arteries were constricted with maximal activating Ca(2+) (pCa 4.5), or sub-maximal Ca(2+) (pCa 6.7) and the thrombane mimetic U46619, and exposed to 8-Br-cGMP. In each case, relaxation was significantly greater in myometrial arteries (e.g. relaxation in pCa 4.5 to 8-Br-cGMP was 49 ± 9.7%, n = 7) than placental arteries (relaxation of 23 ± 6.6%, n = 6, P < 0.05). MYPT1 protein levels, or MYPT1 LZ(+)/LZ(-) mRNA ratios, were similar for both artery types. Of other proteins examined, only Hsp20 expression was significantly elevated in myometrial arteries than placental arteries. These results demonstrate that the reduced human placental artery relaxation to PKG stimulation lies partly at the level of myofilament (de)activation and may be related to a lower expression of Hsp20 than in myometrial arteries.

[Fetal cerebral-umbilical Doppler ratio in prediction of fetal distress in patients with preeclampsia]

BACKGROUND/AIM

The use of color Doppler ultrasonography provides noninvasive observation, confirmation and quantification of pathophysiological processes in fetoplacental circulation in pregnant patients. By blood vessel mapping and the obtained waves spectral analysis it is posible to evaluate vascular resistency of the fetus blood vessels. The aim of the study was to evaluate cerebral-umbilical pulsatility index ratio in fetal circulation in prediction of fetal distress in patients with preeclampsia.

METHODS

By measurement of pulsatility indices in medial cerebral and umbilical arteries in 400 patients with uncomplicated pregnancy, normal values were calculated for fetuses from 15-40 weeks. In our study group 70 patients with preeclampsia were included. Cerebral-umbilical (C/U) ratio was calculated after pulsatility indices in medial cerebral artery and umbilical artery determining by the spectral Doppler analysis of flow velocity waveforms in these vessels. Fetal outcome was analyzed by measurement of the Apgar score at the 5th minute and fetal pH at birth.

RESULTS

The mean C/U ratio values in the third trimester of normal pregnancy were between 1.8 and 1.9. The mean C/U ratio values in the patients complicated with preeclampsia were significantly lower comparing to normal pregnancies (ANOVA, p < 0.05). The mean 5th minute Apgar score in the study group was 6.35 +/- 1.58, and the mean fetal pH at birth was 7.16 +/- 0.15. Linear regression test showed a highly significant correlation between low C/U ratio and fetal pH at birth in patients with preeclampsia (r = 0.49, p < 0.01).

CONCLUSION

The C/U ratio values obtained from spectral Doppler analysis in fetal vessels showed a highly significant correlation with fetal pH at birth in the patients with preeclampsia. The results of our study confirmed the reliability of C/U ratio in estimation of fetal condition in preeclamptic patients. Very low C/U ratio values in patients with preeclampsia indicate that in these fetuses fetal acidosis and fetal distress may be expected.

The effect of a mast cell degranulating agent on vascular resistance in the human placental vascular bed and on the tone of isolated placental vessels

The objective of this study is to investigate the effect of a mast cell degranulating agent, compound 48/80, on vascular resistance in the perfused human placenta and on the tone of isolated human chorionic vessels. Human placenta was obtained from term nonlaboring women undergoing cesarean delivery. Placental vascular bed perfusion pressure and isometric tension for segments of chorionic plate artery and vein were obtained in response to potassium chloride, compound 48/80, a mast cell stabilizer (cromolyn), and thromboxane A2 mimetic (U46619). Compound 48/80 significantly increased perfusion pressure in isolated human placental cotyledons. This effect was significantly potentiated further after induction of active vascular tone by thromboxane A2 mimetic U46619. Cromolyn significantly attenuated responses to compound 48/80 in these preparations. Compound 48/80 also significantly increased tone in isolated human chorionic artery and vein rings, and responses were abolished by cromolyn. In conclusion, degranulation of placental and intravascular mast cells by compound 48/80 leads to the release of vasoconstrictive substances. This could impair placental blood flow and result in growth restriction in fetuses of women with type l hypersensitivity reactions.

Sphingosine-1-Phosphate Acts via Rho-Associated Kinase and Nitric Oxide to Regulate Human Placental Vascular Tone1

Sphingosine-1-phosphate (S1P), a bioactive lipid released from activated platelets, has been demonstrated in animal models to regulate vascular tone through receptor-mediated activation of Rho-associated kinase 1 and nitric oxide synthase 3. The role of S1P in regulation of human vascular tone (particularly during pregnancy, with its unique vascular adaptations and localized platelet activation) is unknown. We hypothesized that S1P would constrict small placental arteries through activation of Rho-associated kinases with modulation by nitric oxide. Reverse transcription-polymerase chain reaction of chorionic plate artery preparations detected mRNAs encoding all five receptors for S1P, and S1P induced dose-dependent vasoconstriction of both chorionic plate and stem villous isobarically mounted arteries, which at 10 micromol/L was 32.9% +/- 3.86% (mean +/- SEM) and 34.6% +/- 7.01%, respectively. In stem villous arteries, S1P-induced vasoconstriction was enhanced significantly following inhibition of nitric oxide synthases with N(G)-nitro-L-arginine methyl ester (100 micromol/L, 52.6% +/- 6.28%, P < 0.05). The S1P-induced vasoconstriction was reversed by Y27632, an inhibitor of Rho-associated kinases (10 micromol/L) in both chorionic plate (to 14.9% +/- 4.95%) and stem villous arteries (to 2.71% +/- 6.13%). The S1P added to alpha-toxin-permeabilized, isometrically mounted chorionic plate arteries bathed in submaximal Ca(2+)-activating solution induced Ca(2+)-sensitization of constriction, which was 47.7% +/- 10.0% of that occurring to maximal Ca(2+)-activating solution. This was reduced by Y27632 to 18.4% +/- 18.4%. Interestingly, S1P-induced vasoconstriction occurred in all isobarically mounted arteries but was inconsistent in isometrically mounted chorionic plate arteries. In summary, S1P-induced vasoconstriction in human placental arteries is mediated by increased Ca(2+)-sensitization through activation of Rho-associated kinases, and this vasoconstriction also is modulated by nitric oxide. Identification of these actions of S1P in the placental vasculature is important for understanding both normal and potentially abnormal vascular adaptations with pregnancy.

Expression of nitric oxide synthase isoforms and detection of nitric oxide in rat placenta

Nitric oxide (NO) production in the rat placenta was monitored and quantified by electron paramagnetic resonance (EPR) spectroscopy with hemoglobin and an Fe-N-(dithiocarboxy)sarcosine (DTCS) complex as NO-trapping reagents. Expression of nitric oxide synthase (NOS) isoforms was also examined by quantitative RT-PCR analysis. The EPR spectrum of the placenta with hemoglobin trapping showed a three-line hyperfine structure (g = 2.008 and a = 1.66-mT). The EPR signal was diminished after the placenta was homogenized or the NOS inhibitor L-NAME was administered to pregnant rats. Therefore, the specific signal was definitely identified as being derived from endogenous NO spin-trapped by hemoglobin, and the EPR spectrum showed that the NO adduct existed as a pentacoordinate alpha-NO heme species. The EPR spectrum of the placenta with Fe-DTCS trapping showed a triplet signal (g = 2.038) derived from an NO-Fe-DTCS complex. The height of the triplet signal did not vary significantly with gestational stage during the last few days of gestation. At the gestational stages examined, the level of NOS II mRNA expression was significantly higher than that of NOS III mRNA. NOS II expression in term (day 21.5) placenta was significantly increased compared with that in preterm (day 19.5) placenta (P < 0.01, n = 4 or 5). These results suggest that NOS II is the predominant producer of NO in the placenta and that NOS II-generated NO plays significant roles in the maintenance of placental functions immediately before birth.

Endothelium-derived nitric oxide synthase protein expression in ovine placental arteries

During the third trimester, fetoplacental and uterine blood flows increase dramatically to meet the high metabolic demands of the growing fetus. We hypothesized that the expression of endothelial nitric oxide synthase (eNOS) in fetoplacental artery endothelium and the concentrations of nitric oxide (NO) and cyclic GMP (cGMP) in amniotic fluid (AF) are increased during the third trimester of ovine gestation. Placental arteries and AF were collected from ewes at 110, 120, 130, and 142 days of gestation (n = 24; mean +/- SEM term = 145 +/- 3 days). Expression of eNOS protein was measured in intact and denuded placental arteries and in endothelium-derived protein by Western analysis and confirmed by immunohistochemistry. Concentrations of NO (nitrates plus nitrites) and cGMP were determined in AF. Placental artery eNOS protein expression was localized to the endothelium, where it was markedly greater than in vascular smooth muscle. Placental artery endothelium-derived eNOS expression and AF cGMP concentrations were similar at 110 and 120 days of gestation; however, both peaked at 130 days at levels two- to threefold above baseline (P < 0.05) before returning to baseline at 142 days of pregnancy. The AF NO (nitrates plus nitrites) levels, however, increased progressively between 120 days of gestation and term (P < 0.05). We concluded that endothelium-derived placental artery eNOS levels, AF NO (nitrates plus nitrites), and AF cGMP were markedly increased during the third trimester, thus supporting a role for NO-mediated elevations in cGMP in the control of fetoplacental blood flow.

Heme oxygenase activity in term human placenta

Carbon monoxide (CO) is a novel gaseous chemical messenger, formed during heme oxygenase (HO)-catalysed oxidation of heme. CO is proposed to play a key role(s) in cell function in many organ systems, including vasodilator action in the cardiovascular system. Recently, it has been demonstrated that there is expression of HO protein in the human placenta and this appears to have a regulatory role in placental perfusion. The objective of the present study was to determine HO enzymatic activity in vitro in five different regions of term human placenta. HO activity was determined in the microsomal fraction of tissue homogenate by measuring the rate of formation of CO from heme, using a gas-chromatographic method. HO activity, expressed as nmol CO formed/g tissue wet weight/h, was higher (P< 0.05) in the chorionic plate, chorionic villi, basal plate and chorio-decidua compared with the amnion. The finding that HO enzymatic activity is present in different regions of term human placenta supports the concept that the heme-CO (HO) pathway plays a complementary role with the L -arginine-nitric oxide (nitric oxide synthase) pathway in the regulation of placental haemodynamics.

Maternal and fetal serum nitric oxide (NO) concentrations in normal pregnancy, pre-eclampsia and eclampsia

OBJECTIVES

To measure the maternal and fetal serum concentrations of total nitrites and nitrates (as an index of nitric oxide production) in normal pregnancy, pre-eclampsia and eclampsia.

DESIGN

Three groups of women were studied cross-sectionally: late pregnant women with pre-eclampsia and eclampsia (n=31); normal late pregnant women (n=32); and age-matched healthy non-pregnant women (n=21). Venous blood samples were collected from all women and both maternal and umbilical venous samples were collected from pregnant women.

METHODS

Blood samples were assayed for nitric oxide (NO) production by Greiss reaction which measures the combined oxidation products of NO (total nitrites and nitrates).

RESULTS

There was a significant increase in serum total nitrites and nitrates concentrations in normal pregnant women than in the serum of age-matched normal non-pregnant women (P<0.0001). Significantly higher total nitrites and nitrates levels were found in the maternal sera of the pre-eclamptic and eclamptic women compared with those of normal pregnant women (P<0.0001). Also, fetal blood levels of total nitrites and nitrates were significantly increased in pre-eclampsia and eclampsia compared with those of normal pregnancy (P<0.0001).

CONCLUSIONS

(1) Serum nitric oxide (NO) production is increased in normal pregnancy than in the normal non-pregnancy. (2) Maternal and fetal serum NO levels are increased significantly in pre-eclampsia and eclampsia, which possibly represents a compensatory/protective mechanism to maintain blood flow and limit platelets aggregation in the fetal-maternal circulations. (3) The increase in NO production is directly related to the severity of pre-eclampsia; this would be of diagnostic significance for the prediction of the severity of this syndrome.

The role of nitro-reduction and nitric oxide in the toxicity of chloramphenicol

Recent work on the toxicology of chloramphenicol suggests that its propensity to cause damage to the blood forming organs may be related to its potential for nitro-reduction and the subsequent production of nitric oxide. In this study both aerobic and anaerobic nitro-reduction of chloramphenicol by human foetal and neonatal liver results in the production of the amine derivative. However intermediates of the reaction nitroso- or glutathionesulphinamido-chloramphenicol could not be detected by hplc. Perfusion of chloramphenicol through isolated lobules of human placentae caused a decrease in blood pressure at a time which coincided with a peak of nitric oxide production. However, although the pressure drop could be reversed by an inhibitor of nitric oxide synthetase, the nitric oxide profile remained the same. These observations suggest that involvement of the para-nitro group of chloramphenicol could cause both hemotoxicity and hypotension in susceptible individuals.

Management of complicated preeclampsia

The complicated preeclamptic patient represents a challenge for the clinician faced with her antepartum or postpartum care. The most serious sequelae of preeclampsia account for a significant portion of maternal morbidity and mortality. Severe preeclampsia also results in an appreciable portion of perinatal morbidity and mortality. In this review, developing trends in the treatment of severe preeclampsia are discussed. Expectant treatment of the patient remote from term, anesthesia choices, and delivery route are reviewed. Developing trends in the pharmacological approach to complicated preeclampsia are discussed. New concepts in the treatment of cerebrovascular preeclampsia and hepatic rupture are outlined and reviewed.

Heme oxygenase and nitric oxide synthase in the placenta of the guinea-pig during gestation

Nitric oxide (NO) and carbon monoxide (CO) are novel gaseous chemical messengers that play key roles in cell function and cell-cell communication in many organ systems, including the cardiovascular system. Although the presence of NO synthase (NOS) in the placenta and its role in the regulation of fetoplacental and uteroplacental blood flow are well established, little is known about placental expression and activity of heme oxygenase (HO), the enzyme that catalyses the oxidation of heme to CO, biliverdin and iron, during gestation. The objectives of this study were to elucidate the localization of HO-1 and HO-2 isoforms relative to NOS III protein, and to determine the enzymatic activity of HO in the placenta of the guinea-pig during gestation. Placentae were obtained from pregnant guinea-pigs at gestational day (GD) 34, 50, 62 and full term (term, about GD 68). Immunohistochemical localization of HO-1, HO-2 and NOS III protein was conducted using selective polyclonal antibodies. HO activity was determined by using a gas chromatographic method to measure the rate of formation of CO from heme. Faint staining for HO-1 was observed in the adventitial layer of larger fetal blood vessels of the placenta at GD 34. The intensity of this staining was higher at GD 50 and GD 62, and decreased at full term. Similar areas in serial sections of placentae obtained at these selected times during gestation exhibited lower staining intensity when incubated with anti-HO-2 antiserum. Placental HO activity was significantly increased (P<0.05) at GD 62 compared with GD 34, GD 50 and full term. NOS III (endothelial constitutive NOS) staining was highest at GD 34, decreasing thereafter, and was localized mostly to trophoblast lining maternal channels. The data demonstrate that, in the guinea-pig, placental HO and NOS differ in tissue localization during the second half of gestation, with expression of HO protein and its catalytic activity being higher during near-term pregnancy. In a preliminary immunohistochemical investigation of the full-term human placenta, HO-1 protein was localized primarily in the adventitial region of fetal blood vessels of stem chorionic villi. In view of the vasodilator action of CO and NO, the HO and NOS systems may play key roles in the regulation of placental haemodynamics.

Cellular localization of AT1 receptor mRNA and protein in normal placenta and its reduced expression in intrauterine growth restriction. Angiotensin II stimulates the release of vasorelaxants

Angiotensin II (ANG II) is a potent vasoconstrictor and growth promoter. Quantitative receptor autoradiography using the nonselective radioligand [125I]ANG II and subtype-selective competing compounds demonstrated the presence of both ANG II receptor (AT)1 and AT2 receptor recognition sites. In addition, a relatively small population of apparently non-AT1/non-AT2 sites was identified that may represent a novel high affinity ANG II recognition site in human placenta. Using placental membrane preparations, the AT2 receptor antagonist PD123177 failed to compete for [3H]ANG II binding at relevant concentrations, whereas the AT1 receptor antagonist losartan competed in a monophasic manner for all the specific binding, suggesting that the non-AT1/non-AT2 recognition site identified using autoradiography may be a cytosolic binding site. AT1 receptor binding was significantly reduced (P < 0. 02) in intraeuterine growth restriction (IUGR) pregnancies. Western blot analysis confirmed this showing a reduction in AT1 receptor protein. In situ hybridization and immunocytochemistry revealed that AT1 receptor mRNA and protein were localized throughout pregnancy in the cytotrophoblast, syncytiotrophoblast, and extravillous trophoblast, as well as in or around the blood vessels of placental villi. The intensity of the hybridization signal for AT1 receptor mRNA over the syncytium was reduced in IUGR. ANG II evoked a rapid and concentration-dependent release of NO in first trimester cytotrophoblast-like cells that was abolished by the inclusion of the competitive NOS inhibitor NG-monomethyl-L-arginine. Neither losartan nor PD123177 alone significantly inhibited ANG II-evoked NO release, and when cells were stimulated with ANG II in the presence of losartan (10 microM) and PD123177 (10 microM) in combination, NO release was significantly inhibited (P < 0.05). These observations also suggest, for the first time, the existence of a cross-talk between AT1 or AT2 receptors in trophoblast and that the reduction in placental AT1 receptors in IUGR may, in part, account for poor placental function in this disorder.

Nitric oxide in preeclampsia: lack of evidence for decreased production

The purpose of our study was to determine the involvement of the L-arginine-NO system in preeclampsia. We studied 26 patients with preeclampsia and 27 normotensive pregnancies. Maternal and cord plasma, urine and amniotic fluid were assayed for nitric oxide metabolites (nitrite and nitrate) using the Griess reaction. Sections of placenta and fetal membranes were immunostained with polyclonal anti-endothelial and anti-neuronal nitric oxide synthase antibodies. The concentration of nitrate in the amniotic fluid of preeclamptic patients (median 10.3 mumol/mg creatinine) was significantly higher (P < 0.001) than in the normotensive group (5.6 mumol/mg creatinine). Nitrate concentrations in maternal and cord plasma and in urine were similar in the two groups. Endothelial cells of the villi of preeclamptic placentas showed a higher positivity in endothelial nitric oxide synthase immunostaining with respect to normotensive controls. Our results indicate that feto-placental NO production is not reduced in preeclampsia. In contrast, the increased concentrations of NO metabolites in amniotic fluid and the positive immunostaining of endothelial nitric oxide synthase in the placental villi suggest that the placental L-arginine-NO system is up-regulated in preeclampsia.

Prolonged reduction of high blood pressure with human nitric oxide synthase gene delivery

Endothelium-derived nitric oxide (NO) in peripheral vessels has been shown to modulate vascular resistance and blood pressure. We explored the effect of a continuous supply of human endothelial NO synthase (eNOS) on the blood pressure of spontaneously hypertensive rats (SHR) by somatic gene delivery. A DNA construct containing the human eNOS gene fused to the cytomegalovirus promoter/enhancer was injected into SHR through the tail vein. A single injection of the naked eNOS plasmid DNA caused a significant reduction of systemic blood pressure for 5 to 6 weeks in SHR, and the effect continued for up to 10 to 12 weeks after a second injection. The differences were significant from 2 to 12 weeks postinjections (n=6, P<.01). In a separate experiment, L-arginine, the substrate of eNOS, was supplied in drinking water at a concentration of 7.5 g/L for 11 weeks after eNOS gene delivery. A maximal blood pressure reduction of 21 mm Hg in SHR was observed with eNOS DNA compared with that of control SHR injected with vector DNA (181.9+/-1.46 versus 202.7+/-2.79 mm Hg, mean+/-SEM, n=6, P<.01). Human eNOS gene delivery induces significant increases in urinary and aortic cGMP levels and urinary and serum nitrite/nitrate content (P<.05), while no significant differences in body weight, heart rate, water intake, food consumption, or urine excretion were observed. These results indicate that somatic delivery of the human eNOS gene induces a prolonged reduction of high blood pressure and raises the potential of using eNOS gene therapy for hypertension and cardiovascular diseases.

Activation and dimerization of type III nitric oxide synthase by submicromolar concentrations of tetrahydrobiopterin in microsomal preparations from human primordial placenta

We have found in a previous study that 5-50 microM tetrahydrobiopterin (BH4) stimulated 1.2-2.5-fold Ca(2+)-dependent nitric-oxide synthase (NOS) activity in homogenates prepared from primordial human placentae. Now we report on the dramatic, about sixfold, activating effect of BH4 on this activity measured in microsomal preparations. Firstly, both in the absence and presence of BH4, arginine bound to kinetically homogeneous sites, with no significant change between the apparent KM values for arginine (3.12 +/- 1.99 microM and 2.06 +/- 1.13 microM in the absence and presence of 50 microM BH4 respectively, mean +/- s.d., n = 3). On the other hand, the Vmax values measured in different pools of placenta tissue varied between 2.5-7.55 (no BH4 added) and 13.3-58.5 (with BH4 added) pmol/min/mg protein. Secondly, the microsomal preparations responded sensitively to BH4 addition. A dose-response study indicated that as low as 79 nM final BH4 concentration stimulated NOS activity half-maximally, and 1 microM BH4 resulted in an almost maximal effect. Thirdly, immunoblot analysis combined with laser densitometric evaluation demonstrated that BH4 efficiently promoted the aggregation of microsomal NOS type III isozyme into a protein having the characteristics (electrophoretic mobility, resistance of SDS) of the dimeric form. Half-maximal dimerizing activity was reached at 148 +/- 33 nM BH4 (mean +/- s.d., n = 3), whereas 1 microM BH4 led to almost, maximal aggregation of monomers. This is the first time that BH4-induced dimerization of a NOS type III isoform has been demonstrated. Considering that human placenta predominantly expresses NOS type III isoform and BH4 concentration in this tissue is 207 +/- 87 nM, the present results strongly suggest that the dimerizing effect of BH4 is a crucial physiological mechanism for the assembly of active Ca(2+)-dependent NOS in the human primordial placenta.

Effects of maturation on cyclic GMP metabolism in ovine carotid arteries

Previous studies suggest that elevated basal levels of cGMP in newborn arteries may help explain why vascular resistance is lower in newborns than adults. To explore the reasons why basal cGMP is higher in neonatal arteries, the present studies examined rates of cGMP synthesis and degradation in newborn and adult ovine common carotid arteries. The measurements were performed in both intact and homogenized arteries, and results were normalized relative to cell water to estimate intracellular concentrations and minimize errors due to compositional differences between newborn and adult arteries. Steady state levels of cGMP measured under baseline conditions averaged 0.11 +/- 0.02 microM in adult arteries and 0.59 +/- 0.11 microM in newborn arteries. These resting cGMP levels were unaffected by endothelium removal. Under baseline conditions, steady state rates of cGMP synthesis (mumol of cGMP/L of cell water/min) were higher in newborn (0.31 +/- 0.06) than in adult (0.15 +/- 0.04) arteries. Maximal rates of cGMP degradation (mumol of cGMP/L of cell water/min) measured in artery homogenates were also much higher in preparations of newborn (106 +/- 6) than of adult (78 +/- 6) arteries. Together, these data suggest that the reason resting cGMP concentrations were higher in newborn than in adult arteries was due at least in part to a higher basal rate of cGMP synthesis in the newborn. Estimates of apparent Km values for PDE were also greater in newborn (2.9 microM) than in adult (1.5 microM) preparations, suggesting that age-related differences in the Km for PDE may also contribute to the elevated basal concentration of cGMP observed in the newborn.

Nitric oxide synthase in human placenta and umbilical cord from normal, intrauterine growth-retarded and pre-eclamptic pregnancies

1. It has been suggested that a deficiency of nitric oxide (NO) may explain many of the pathophysiological features of pre-eclampsia (PE) and intra-uterine (foetal) growth retardation (IUGR). To elucidate further the role of NO in the pathophysiology of pregnancy we have determined the relative amount and activity of NO synthase (NOS) in first trimester and normal-term placental tissues, as well as in the placenta and umbilical cord in pregnancies complicated by PE and IUGR, using NG-nitro-L-[2,3,4,5(-3)H]-arginine ([3H]-L-NOARG) binding, quantitative in vitro autoradiography, [3H]-arginine to [3H]-citrulline conversion and Western blotting. 2. Specific, high affinity (KD = 38 nM) [3H]-L-NOARG binding was demonstrated in the villous trophoblast of normal-term placentae. Binding was calcium-independent, stereoselective and exhibited a rank order of inhibition by NOS inhibitors and substrate (L-NOARG > or = L-NMMA > or = 7-NI > L-NAME > L-Arg > or = L-NIO > ADMA). 3. [3H]-L-NOARG binding density and NOS activity were both significantly greater in placental tissues from first trimester and PE or IUGR complicated pregnancies compared to normal-term placentae. 4. Western blotting, using an endothelial NOS peptide antiserum, demonstrated a approximately 140 KDa protein band in placental extracts and indicated that the amount of immunoreactive material was significantly greater in first trimester compared to normal-term placentae. 5. Specific [3H]-L-NOARG binding was also localized to the endothelial lining of umbilical arteries and veins, binding density being greater in the artery than the vein. [3H]-L-NOARG binding to the umbilical artery endothelium was significantly lower in PE and IUGR complicated pregnancies compared to normal-term controls. 6. The role of trophoblast-derived NO in human placental pathophysiology remains to be established, but differences in the amount of placental [3H]-L-NOARG binding, NOS activity and immunoreactive material indicate that expression of NOS in the villous trophoblast falls during pregnancy. Conversely, the apparent reduction in NOS in the umbilical artery endothelium in PE and IUGR complicated pregnancies may be indicative of endothelial dysfunction.

Nitric oxide synthase activities in placental tissue from normotensive, pre-eclamptic and growth retarded pregnancies

OBJECTIVE

To measure nitric oxide synthase activity in tissues from the placenta, placental bed and umbilical cord at delivery in normal and complicated pregnancies.

DESIGN

A prospective blinded study.

SETTING

The obstetric departments of three London teaching hospitals.

SUBJECTS

Samples of whole placenta, dissected stem villous arteries, umbilical cord vessels and the placental bed of the uterus were collected at delivery and assayed for nitric oxide synthase activity. Samples of placenta were taken from ten normotensive, six pre-eclamptic and eight growth retarded pregnancies, and stem villous arteries from a further seven normotensive pregnancies.

RESULTS

There was minimal placental bed nitric oxide synthase activity in each group. Placental villous homogenates from pregnancies complicated by pre-eclampsia and fetal growth retardation had significantly lower activities of nitric oxide synthase than those from normotensive women with appropriately grown babies. There were no significant differences in calcium dependent or calcium independent nitric oxide synthase activities in the umbilical vein and artery in the normal or in the pre-eclamptic groups. However, there was significantly more calcium dependent than calcium independent nitric oxide synthase in the umbilical veins in all groups.

CONCLUSIONS

Local nitric oxide production in the placental bed of the uterus is unlikely to contribute substantially to the low resting vascular tone in the uteroplacental circulation. However, a relative deficiency of placental nitric oxide in pregnancies complicated by fetal growth retardation and pre-eclampsia may contribute to the development of the high impedance fetoplacental circulation found in these conditions.