Expression of endothelial and inducible nitric oxide synthases and nitric oxide production in ovine placental and uterine tissues during late pregnancy

Nitric oxide synthase and its function in animal reproduction: an update

Nitric oxide (NO), a free radical labile gas, is involved in the regulation of various biological functions and physiological processes during animal reproduction. Recently, increasing evidence suggests that the biological role and chemical fate of NO is dependent on dynamic regulation of its biosynthetic enzyme, three distinct nitric oxide synthase (NOS) according to their structure, location and function. The impact of NOS isoforms on reproductive functions need to be timely elucidated. Here, we focus on and the basic background and latest studies on the development, structure, importance inhibitor, location pattern, complex functions. Moreover, we summarize the exactly mechanisms which involved some cell signal pathways in the regulation of NOS with cellular and molecular level in the animal reproduction. Therefore, this growing research area provides the new insight into the important role of NOS male and female reproduction system. It also provides the treatment evidence on targeting NOS of reproductive regulation and diseases.

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.

Modeling the Ruminant Placenta-Pathogen Interactions in Apicomplexan Parasites: Current and Future Perspectives

Neospora caninum and Toxoplasma gondii are one of the main concerns of the livestock sector as they cause important economic losses in ruminants due to the reproductive failure. It is well-known that the interaction of these parasites with the placenta determines the course of infection, leading to fetal death or parasite transmission to the offspring. However, to advance the development of effective vaccines and treatments, there are still important gaps on knowledge on the placental host-parasite interactions that need to be addressed. Ruminant animal models are still an indispensable tool for providing a global view of the pathogenesis, lesions, and immune responses, but their utilization embraces important economic and ethics restrictions. Alternative in vitro systems based on caruncular and trophoblast cells, the key cellular components of placentomes, have emerged in the last years, but their use can only offer a partial view of the processes triggered after infection as they cannot mimic the complex placental architecture and neglect the activity of resident immune cells. These drawbacks could be solved using placental explants, broadly employed in human medicine, and able to preserve its cellular architecture and function. Despite the availability of such materials is constrained by their short shelf-life, the development of adequate cryopreservation protocols could expand their use for research purposes. Herein, we review and discuss existing (and potential) in vivo, in vitro, and ex vivo ruminant placental models that have proven useful to unravel the pathogenic mechanisms and the host immune responses responsible for fetal death (or protection) caused by neosporosis and toxoplasmosis.

Loss of ITGB3 in ovine conceptuses decreases conceptus expression of NOS3 and SPP1: implications for the developing placental vasculature†

During the peri-implantation period of pregnancy in sheep, there is an initial period of loose apposition of the elongating conceptuses (embryos and associated placental membranes) to the endometrial luminal epithelium (LE) that is followed by adhesion of the conceptus trophectoderm to the endometrial LE for implantation. Integrins and maternal extracellular matrix (ECM) molecules are major contributors to stable adhesion at implantation, and the β3 integrin subunit (ITGB3) is implicated in the adhesion cascade for implantation in several species including the sheep. We blocked mRNA translation for trophectoderm-expressed ITGB3 by infusing morpholino antisense oligonucleotides into the uterine lumen of pregnant ewes on Day 9 to assess effects on conceptus elongation, and on Day 16 to assess effects on early placental development in sheep. Results indicate that sheep conceptuses elongate and implant to the uterine wall in the absence of ITGB3 expression by the conceptuses; however, loss of ITGB3 in conceptuses decreased the growth of embryos to Day 24 of gestation, and decreased expression of secreted phosphoprotein 1 (SPP1) and nitric oxide synthase 3 (NOS3). Abundant SPP1 was localized around the blood vessels in the placental allantoic membrane in normal sheep pregnancies. We hypothesize that NOS3 and SPP1 positively influence the development of the vasculature within the allantois, and that decreased expression of NOS3 and SPP1, in response to knockdown of ITGB3 in conceptuses, alters development of the vasculature in the allantois required to transport nutrients from the endometrium to support growth and development of the embryo.

Regulation of placental angiogenesis

Ample interest has been evoked in using placental angiogenesis as a target for the development of diagnosis tools and potential therapeutics for pregnancy complications based on the knowledge of placental angiogenesis in normal and aberrant pregnancies. Although these goals are still far from reach, one would expect that two complementary processes should be balanced for therapeutic angiogenesis to be successful in restoring a mature and functional vascular network in the placenta in any pregnancy complication: (i) pro-angiogenic stimulation of new vessel growth and (ii) anti-angiogenic inhibition of vessel overgrowth. As the best model of physiological angiogenesis, investigations of placental angiogenesis provide critical insights not only for better understanding of normal placental endothelial biology but also for the development of diagnosis tools for pregnancy complications. Such investigations will potentially identify novel pro-angiogenic factors for therapeutic intervention for tissue damage in various obstetric complications or heart failure or anti-angiogenic factors to target on cancer or vision loss in which circulation needs to be constrained. This review summarizes the genetic and molecular aspects of normal placental angiogenesis as well as the signaling mechanisms by which the dominant angiogenic factor vascular endothelial growth factor regulates placental angiogenesis with a focus on placental endothelial cells.

Oxytocin, its antagonist Atosiban, and preterm labor: a role for placental nitric oxide

OBJECTIVE

The aim of the present study was to understand the role played by Atosiban, an oxytocin receptor antagonist, on trophoblastic human cells, and the molecular bases of its efficacy and safety in the treatment of preterm labor. NO, peroxinitrite production and NOS expression have been evaluated on placenta obtained from term and preterm labors.

PATIENTS AND METHODS

We studied trophoblast cells isolated from selected placental tissue from 20 controls and 20 preterm patients after cesarean sections. Each sample was studied at basal state and after 2 hours incubation with oxytocin and Atosiban.

RESULTS

Significant variations of NO levels, peroxynitrite production and iNOS and eNOS expression both in the preterm, term samples and in each of the considered groups were observed. In the control group Atosiban re-established NO levels that were reduced after incubation with oxytocin, while in preterm samples NO levels were not only re-established but, after incubation with Atosiban, significantly increased compared to basal levels.

CONCLUSIONS

This confirms the beneficial role of Atosiban in prolonging the pregnancy of spontaneous labor at very early gestational periods. In conclusion, Atosiban might be an effective drug to prevent preterm labor, in the therapeutic approach to this pathology.

The l-arginine/nitric oxide pathway is impaired in overweight/obese pregnant women

OBJECTIVE

To evaluate the l-arginine/NO system and its role in insulin signaling and endothelial function during the pregnancy of women of different BMI categories.

STUDY DESIGN

Twelve women with BMI⩾25 were compared with 10 normal-weight women in a fasting condition after the infusion of l-arginine (20g in 3h) and after the evaluation of the flow-mediated vasodilation (FMD) of the brachial artery between the 9th-12th and 24th-27th weeks. Blood samples for insulin and nitrite/nitrate (NOx) were collected at baseline and after 1, 2 and 3h after initiating the infusion.

RESULTS

In both trimesters, the baseline NOx levels were similar among groups. In the 1st trimester of the lean women, there was a NOx increase in response to l-Arg (AUC: 1328; 3, 3173), which had increased by the 2nd trimester (AUC: 3884; 1905, 7686); in overweight/obese women, no responses to l-Arg were found in the 1st or 2nd trimesters. In the 1st trimester, the insulin levels were significantly reduced in both groups after l-Arg infusion. Although the insulin levels in all BMI categories were higher in the 2nd trimester, such levels during weeks 24-27 were suppressed only in normal-weight women after l-Arg infusion. The FMD was higher during both trimesters in the lean controls and was impaired in the overweight/obese subjects.

CONCLUSIONS

NO availability is impaired in overweight/obese women during pregnancy, which affects endothelial functioning and interferes with insulin regulation. These mechanisms could be involved in the development of hypertensive disorders and glucose intolerance in this population.

Ovine uterine space restriction alters placental transferrin receptor and fetal iron status during late pregnancy

BACKGROUND

Fetal growth restriction is reported to be associated with impaired placental iron transport. Transferrin receptor (TfR) is a major placental iron transporter in humans but has not been studied in sheep. TfR is regulated by both iron and nitric oxide (NO), the molecule produced by endothelial nitric oxide synthase (eNOS). We hypothesized that limited placental development downregulates both placental TfR and eNOS expression, thereby lowering fetal tissue iron.

METHODS

An ovine surgical uterine space restriction (USR) model, combined with multifetal gestation, tested the extremes of uterine and placental adaptation. Blood, tissues, and placentomes from non-space restricted (NSR) singletons were compared with USR fetuses at gestational day (GD) 120 or 130.

RESULTS

When expressed proportionate to fetal weight, liver iron content did not differ, whereas renal iron was higher in USR vs. NSR fetuses. Renal TfR protein expression did not differ, but placental TfR expression was lower in USR fetuses at GD130. Placental levels of TfR correlated to eNOS. TfR was localized throughout the placentome, including the hemophagous zone, implicating a role for TfR in ovine placental iron transport.

CONCLUSION

Fetal iron was regulated in an organ-specific manner. In USR fetuses, NO-mediated placental adaptations may prevent the normal upregulation of placental TfR at GD130.

Signaling regulation of fetoplacental angiogenesis

During normal pregnancy, dramatically increased placental blood flow is critical for fetal growth and survival as well as neonatal birth weights and survivability. This increased blood flow results from angiogenesis, vasodilatation, and vascular remodeling. Locally produced growth factors including fibroblast growth factor 2 (FGF2) and vascular endothelial growth factor A (VEGFA) are key regulators of placental endothelial functions including cell proliferation, migration, and vasodilatation. However, the precise signaling mechanisms underlying such regulation in fetoplacental endothelium are less well defined, specifically with regard to the interactions amongst protein kinases (PKs), protein phosphatase, and nitric oxide (NO). Recently, we and other researchers have obtained solid evidence showing that different signaling mechanisms participate in FGF2- and VEGFA-regulated fetoplacental endothelial cell proliferation and migration as well as NO production. This review will briefly summarize currently available data on signaling mediating fetoplacental angiogenesis with a specific emphasis on PKs, ERK1/2, AKT1, and p38 MAPK and protein phosphatases, PPP2 and PPP3.

Role of nitric oxide in placental vascular development and function

Nitric oxide (NO) is one of the most pleiotropic signaling molecules at systemic and cellular levels, participating in vascular tone regulation, cellular respiration, proliferation, apoptosis and gene expression. Indeed NO actively participates in trophoblast invasion, placental development and represents the main vasodilator in this tissue. Despite the large number of studies addressing the role of NO in the placenta, its participation in placental vascular development and the effect of altered levels of NO on placental function remains to be clarified. This review draws a time-line of the participation of NO throughout placental vascular development, from the differentiation of vascular precursors to the consolidation of vascular function are considered. The influence of NO on cell types involved in the origin of the placental vasculature and the expression and function of the nitric oxide synthases (NOS) throughout pregnancy are described. The developmental processes involved in the placental vascular bed are considered, such as the participation of NO in placental vasculogenesis and angiogenesis through VEGF and Angiopoietin signaling molecules. The role of NO in vascular function once the placental vascular tree has developed, in normal pregnancy as well as in pregnancy-related diseases, is then discussed.

Shear stress regulation of nitric oxide production in uterine and placental artery endothelial cells: experimental studies and hemodynamic models of shear stresses on endothelial cells

Hemodynamic shear stress is the most powerful physiological regulator of endothelial Nitric Oxide Synthase (eNOS), leading to rapid rises in nitric oxide (NO). The substantial increases in uterine and placental blood flows throughout gestation rely heavily on the action of NO. We and others have investigated endothelial function in response to shear stress with cell culture models of shear stress. In order to apply the results of these studies more effectively, we need a more complete understanding of the origin and coupling of the hemodynamic forces and vascular tissue behavior. For example, equations commonly used to calculate in vivo shear stress incorporate assumptions of steady (non-pulsatile) blood flow and constant viscosity of blood (Newtonian fluid). Using computational models, we can estimate a waveform of shear stress over a cardiac cycle and the change in blood viscosity with shear rate and hematocrit levels, two variables that often change with size of vessel and location within a vascular tree. This review discusses hemodynamics as they apply to blood flow in vessels, in the hope that an integration of these fields can lead to improved in vitro shear stress experiments and understanding of NO production in uterine and placental vascular physiology during gestation.

Developmental programming: the concept, large animal models, and the key role of uteroplacental vascular development

Developmental programming refers to the programming of various bodily systems and processes by a stressor of the maternal system during pregnancy or during the neonatal period. Such stressors include nutritional stress, multiple pregnancy (i.e., increased numbers of fetuses in the gravid uterus), environmental stress (e.g., high environmental temperature, high altitude, prenatal steroid exposure), gynecological immaturity, and maternal or fetal genotype. Programming refers to impaired function of numerous bodily systems or processes, leading to poor growth, altered body composition, metabolic dysfunction, and poor productivity (e.g., poor growth, reproductive dysfunction) of the offspring throughout their lifespan and even across generations. A key component of developmental programming seems to be placental dysfunction, leading to altered fetal growth and development. We discuss various large animal models of developmental programming and how they have and will continue to contribute to our understanding of the mechanisms underlying altered placental function and developmental programming, and, further, how large animal models also will be critical to the identification and application of therapeutic strategies that will alleviate the negative consequences of developmental programming to improve offspring performance in livestock production and human medicine.

Effects of Pulsatile Shear Stress on Signaling Mechanisms Controlling Nitric Oxide Production, Endothelial Nitric Oxide Synthase Phosphorylation, and Expression in Ovine Fetoplacental Artery Endothelial Cells

During gestation, placental blood flow, endothelial nitric oxide (NO) production, and endothelial cell nitric oxide synthase (eNOS) expression are elevated dramatically. Shear stress can induce flow-mediated vasodilation, endothelial NO production, and eNOS expression. Both the activity and expression of eNOS are closely regulated because it is the rate-limiting enzyme essential for NO synthesis. The authors adapted CELLMAX artificial capillary modules to study the effects of pulsatile flow/shear stress on ovine fetoplacental artery endothelial (OFPAE) cell NO production, eNOS expression, and eNOS phosphorylation. This model allows for the adaptation of endothelial cells to low physiological flow environments and thus prolonged shear stresses. The cells were grown to confluence at 3 dynes/cm2, then were exposed to 10, 15, or 25 dynes/cm2 for up to 24 h and NO production, eNOS mRNA, and eNOS protein expression were elevated by shear stress in a graded fashion (p < .05). Production of NO by OFPAE cells exposed to pulsatile shear stress was de novo; i.e., inhibited by L-NMMA (N(G)-monomethyl-L-arginine) and reversed by excess NOS substrate L-arginine. Rises in NO production at 25 dynes/cm2 (8-fold) exceeded (p < .05) that seen for eNOS protein (3.6-fold) or eNOS mRNA (1.5-fold). Acute rises in NO production with shear stress occurred by eNOS activation, whereas prolonged NO rises were via elevations in both eNOS expression and enzyme activation. The authors therefore used Western analysis to investigate the signaling mechanisms underlying pulsatile shear stress-induced increases in eNOS phosphorylation and protein expression by "flow-adapted" OFPAE cells. Increasing shear stress from 3 to 15 dynes/cm2 very rapidly increased eNOS Ser1177, ERK1/2 (extracellular signal-regulated kinase 1 and 2) and Akt, but not p38 MAPK (p38 mitogen-activated protein kinase) phosphorylation by Western analysis. Phosphorylation of eNOS Ser1177 under shear stress was elevated by 20 min, a response that was blocked by PI-3K (phosphatidylinositol 3-kinase) inhibitors wortmannin and LY294002, but not the MEK (MAPK kinase) inhibitor UO126. Basic fibroblast growth factor (bFGF) enhanced eNOS protein levels in static culture via a MEK-mediated mechanism, but it could not further augment the elevated eNOS protein levels induced by 15 dynes/cm2 shear stress. Blocking of either signaling pathways or p38 MAPK did not change the shear stress-induced increase in eNOS protein levels. Therefore, shear stress induced rapid eNOS phosphorylation on Ser1177 in OFPAE cells through a PI-3K-dependent pathway. The bFGF-induced rise in eNOS protein levels in static culture was much less than those observed under flow and was blocked by inhibiting MEK. Prolonged shear stress-stimulated increases in eNOS protein levels were not affected by inhibition of MEK- or PI-3K-mediated pathways. In conclusion, pulsatile shear stress greatly induces NO production by OFPAE cells through the mechanisms of both PI-3K-mediated eNOS activation and elevations in eNOS protein levels; bFGF does not further stimulate eNOS expression under flow condition.

Expression patterns of endothelial and inducible nitric oxide isoforms in the porcine umbilical cord

Stable fetal-placental blood pressure and flow are extremely important in fetal growth and development. Uncontrolled and long-standing increased or decreased vascular blood pressure in the umbilical cord (UC) affects hyperaemia or ischaemia and consequently causes fetal death. Nitric oxide (NO) is one of the most active factors controlling blood flow through relaxation of the vascular smooth muscle. In this study, we investigated endothelial (eNOS) and inducible (iNOS) nitric oxide synthase expression and NADPH-diaphorase activity (NADPH-d) in the porcine UC at various stages of pregnancy. The UCs were collected from pigs on days 40, 60, 75 and 90 of pregnancy and postpartum. Western blot analysis as well as immunohistochemical staining revealed protein presence for eNOS and iNOS in the UC of the pig. The eNOS expression was maintained at a significantly higher level in all analysed days of pregnancy when compared with postnatal stage. Additionally, a significant protein increase for eNOS was observed in a periplacental part of UC on day 90. There were no obvious differences in iNOS protein level in UC samples derived from different stages of pregnancy. NADPH-diaphorase histochemical activity was correlated with NOS immunoreactivity during all analysed days of pregnancy. These results suggest that NOS isoforms are responsible for regulation of blood circulation in UC and immune responses.

Activation of multiple signaling pathways is critical for fibroblast growth factor 2- and vascular endothelial growth factor-stimulated ovine fetoplacental endothelial cell proliferation

Fibroblast growth factor-2 (FGF2) and vascular endothelial growth factor (VEGF) are two key regulators of placental angiogenesis. The potent vasodilator nitric oxide (NO) could also act as a key mediator of FGF2- and VEGF-induced angiogenesis. However, the postreceptor signaling pathways governing these FGF2- and VEGF-induced placental angiogenic responses are poorly understood. In this study, we assessed the role of endogenous NO, mitogen-activated protein kinase 3/1 (MAPK3/1), and v-akt murine thymoma viral oncogene homolog 1 (AKT1) in FGF2- and VEGF-stimulated proliferation of ovine fetoplacental endothelial (OFPAE) cells. Both FGF2 and VEGF time-dependently stimulated (P < 0.05) NO production and activated AKT1. Both FGF2- and VEGF-stimulated cell proliferation was dose-dependently inhibited (P < 0.05) by N(G)-monomethyl-L-arginine (L-NMMA; an NO synthase inhibitor), PD98059 (a selective MAPK3/1 kinase 1 and 2 [MAP2K1/2] inhibitor), or LY294002 (a selective phosphatidylinositol 3 kinase [PI3K] inhibitor) but not by phenyl-4,4,5,5 tetramethylimidazoline-1-oxyl 3-oxide (PTIO, a potent extracellular NO scavenger). At the maximal inhibitory dose without cytotoxicity, PD98059 and LY294002 completely inhibited VEGF-induced cell proliferation but only partially attenuated (P < 0.05) FGF2-induced cell proliferation. PD98059 and LY294002 also inhibited (P < 0.05) FGF2- and VEGF-induced phosphorylation of MAPK3/1 and AKT1, respectively. L-NMMA did not significantly affect FGF2- and VEGF-induced phosphorylation of either MAPK3/1 or AKT1. Thus, in OFPAE cells, both FGF2- and VEGF-stimulated cell proliferation is partly mediated via NO as an intracellular and downstream signal of MAPK3/1 and AKT1 activation. Moreover, activation of both MAP2K1/2/MAPK3/1 and PI3K/AKT1 pathways is critical for FGF2-stimulated cell proliferation, whereas activation of either one pathway is sufficient for mediating the VEGF-induced maximal cell proliferation, indicating that these two kinase pathways differentially mediate the FGF2- and VEGF-stimulated OFPAE cell proliferation.

Reduction of Maternal Adrenal Steroids Results in Increased VEGF Protein Without Increased eNOS in the Ovine Placenta

Fetal sheep studies have shown that reduced maternal cortisol or aldosterone levels alter placental morphology, with a reduction in placental blood flow. We have now tested the hypothesis that changes in placental morphology with relative adrenal hypoadrenalism are associated with changes in vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS). Four groups of late gestation pregnant ewes with singleton fetuses were studied; controls (intact adrenals), normal cortisol and aldosterone (ewes adrenalectomized and replaced with normal cortisol and aldosterone levels), low cortisol (ewes adrenalectomized and replaced with low cortisol levels), and low aldosterone (ewes adrenalectomized and replaced with low aldosterone levels). The placenta was categorized into A, B, C or D type placentomes. There were significantly more B and C type placentomes in the adrenalectomized groups than in controls. Overall, B types had more VEGF mRNA than A types. VEGF protein levels corresponding to a 23 kDa band were highest in low aldosterone animals in A and C type placentomes. VEGF protein levels corresponding to a 47 kDa band were higher in C type placentomes than A types; protein levels were also higher overall in low cortisol animals compared to controls. Fetoplacental eNOS protein levels were lower in the adrenalectomized groups than in controls. In conclusion, our results indicate that increases in cotyledonary VEGF(164) protein were associated with fetal tissue overgrowth in the placenta when the pregnancy-induced increase in adrenal steroids was prevented in the ewe. However, cotyledonary eNOS protein was suppressed with reduced maternal adrenal steroids, which is consistent with the reduced placental perfusion previously observed in this model.

Prostaglandins and reproduction in female farm animals

Prostaglandins impact on ovarian, uterine, placental, and pituitary function to regulate reproduction in female livestock. They play important roles in ovulation, luteal function, maternal recognition of pregnancy, implantation, maintenance of gestation, microbial-induced abortion, parturition, postpartum uterine and ovarian infections, and resumption of postpartum ovarian cyclicity. Prostaglandins have both positive and negative effects on reproduction; they are used to synchronize oestrus, terminate pseudopregnancy in mares, induce parturition, and treat retained placenta, luteinized cysts, pyometra, and chronic endometritis. Improved therapeutic uses for prostaglandins will be developed when we understand better their involvement in implantation, maintenance of luteal function, and establishment and maintenance of pregnancy.

Evidence for altered placental blood flow and vascularity in compromised pregnancies

The placenta is the organ that transports nutrients, respiratory gases, and wastes between the maternal and fetal systems. Consequently, placental blood flow and vascular development are essential components of normal placental function and are critical to fetal growth and development. Normal fetal growth and development are important to ensure optimum health of offspring throughout their subsequent life course. In numerous sheep models of compromised pregnancy, in which fetal or placental growth, or both, are impaired, utero-placental blood flows are reduced. In the models that have been evaluated, placental vascular development also is altered. Recent studies found that treatments designed to increase placental blood flow can 'rescue' fetal growth that was reduced due to low maternal dietary intake. Placental blood flow and vascular development are thus potential therapeutic targets in compromised pregnancies.

Exogenous Nitric Oxide Stimulates Cell Proliferation via Activation of a Mitogen-Activated Protein Kinase Pathway in Ovine Fetoplacental Artery Endothelial Cells1

Sodium nitroprusside (SNP), a nitric oxide (NO) donor and a nitrovasodilator drug used for patients with hypertensive crisis, has been shown to promote angiogenesis. However, direct evidence showing the involvement of NO in the SNP-induced angiogenesis is not available. Accordingly, we assessed whether NO generated from SNP-stimulated ovine fetoplacental artery endothelial (OFPAE) cell proliferation via activation of mitogen-activated protein kinase 3/1 (MAPK3/1, also termed ERK1/2). We observed that SNP dose dependently stimulated (P < 0.05) cell proliferation with a maximal effect at 1 microM and that SNP rapidly (<or=15 min) phosphorylated (P < 0.05) MAPK3/1 but not v-akt murine thymoma viral oncogene homolog 1 (AKT1). Treatment of cells with SNP caused a rapid increase in NO levels in media. These increased NO levels were inhibited (P < 0.05) by 2-phenyl-4,4,5,5 tetramethylimidazoline-1-oxyl 3-oxide (PTIO), a NO scavenger. The SNP-induced cell proliferation and MAPK3/1 phosphorylation were attenuated (P < 0.05) by both PTIO and PD98059, a specific mitogen-activated protein kinase kinase 1 and 2 (MAP2K1/2, also termed MEK1/2) inhibitor. Using a semiquantitative RT-PCR analysis, we also showed that up to 12 h of treatment, SNP and N(G)-monomethyl-L-arginine (L-NMMA, a NOS inhibitor) did not alter mRNA expression of VEGF, FGF2, and their major receptors in OFPAE cells. The SNP's stimulatory effects on OFPAE cell proliferation and MAPK3/1 activation were confirmed in a human placental artery endothelial (HPAE) cell line. These data indicate that exogenous NO generated from SNP is able to stimulate fetoplacental artery endothelial cell proliferation at least partly via activation of the MAP2K1/2/MAPK3/1 cascade. These data also suggest that SNP could potentially be used to modulate placental angiogenesis.

Is nitric oxide luteolytic or antiluteolytic?

Nitric oxide (NO) has been reported to be luteolytic based on treatment of cows in vivo with an inhibitor of nitric oxide synthase (NOS-produces NO), which delayed the decline in progesterone by two to three days [Jaroszewki J, Hansel, W. Intraluteal administration of a nitric oxide synthase blocker stimulates progesterone, oxytocin secretion and prolongs the life span of the bovine corpus luteum. Proc Soc Exptl Biol Med 2000;224:50-5; Skarzynski D, Jaroszewki J, Bah, M, et al. Administration of nitric oxide synthase inhibitor counteracts prostaglandin F(2alpha)-induced luteolysis in cattle. Biol Reprod 2003;68:1674-81]. The objective of this experiment was to determine the effect of a long acting NO donor or a NOS inhibitor infused chronically into the interstitial tissue of the ovarian vascular pedicle adjacent to the ovary with a corpus luteum on secretion of progesterone during the ovine estrous cycle. Ewes were treated either with Vehicle (N=5); Diethylenetriamine (DETA-control for DETA-NONOate; N=5); (Z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl) amino]diazen-1-ium-1,2-diolate (DETA-NONOate-long acting NO donor; N=6); or l-nitro-arginine methyl ester (l-NAME-NOS inhibitor; N=6) every 6 h from 24:00 h (0 h) on day 8 through 18:00 h on day 18 of the estrous cycle. Jugular venous blood was collected every 6h for analysis for progesterone and corpora lutea were collected at 18:00 h on day 18 and weighed. Weights of corpora lutea were heavier (P< or =0.05) in DETA-NONOate-treated ewes when compared to Vehicle, DETA, or l-NAME-treated ewes, which did not differ amongst each other (P> or =0.05). Profiles of progesterone in jugular venous blood on days 8-18 differed (P< or =0.05) in DETA-NONOate-treated ewes when compared to Vehicle, DETA, or l-NAME-treated ewes did not differ (P> or =0.05) amongst each other. It is concluded that NO is not luteolytic during the ovine estrous cycle, but may instead be antiluteolytic and prevent luteolysis.

In vivo progestin treatments inhibit nitric oxide and endothelin-1-induced bovine endometrial prostaglandin (PG) E (PGE) secretion in vitro

Synchronization of estrus with progestins in cows has been reported to inhibit nitric oxide (NO) and endothelin-1 (ET-1)-stimulated bovine luteal PGE secretion without affecting prostaglandin F2alpha (PGF2alpha) secretion in vitro [Weems YS, Randel RD, Tatman S, Lewis A, Neuendorff DA, Weems CW. Does estrous synchronization affect corpus luteum (CL) function? Prostaglandins Other Lipid Mediat 2004;74:45-59]. Two experiments were conducted to determine the effects of NO donors, endothelin-1 (ET-1), and NO synthase (NOS) inhibitors on bovine caruncular endometrial secretion of PGE and PGF2alpha in vitro. In Experiment 1, estrus was synchronized in Brahman cows with Synchromate-B ear implants, which contained the synthetic progestin norgestamet. Days 14-15 caruncular endometrial slices were weighed, diced, and incubated in vitro with treatments. Treatments (100 ng/ml) were: Vehicle (control), l-NAME (NOS inhibitor), l-NMMA (NOS inhibitor), DETA (control), DETA-NONOate (NO donor), sodium nitroprusside (NO donor), or ET-1. In Experiment 2, estrus was synchronized in Brahman cows with either Lutalyse (PGF2alpha) or a controlled intravaginal drug releasing device (CIDR-containing progesterone) or estrus was not synchronized. Days 14-15 caruncular endometrial slices were weighed, diced, and incubated in vitro with treatments. Treatments (100 ng/ml) were: vehicle, l-NAME, l-NMMA, DETA, DETA-NONOate, sodium nitroprusside, SNAP (NO donor) or ET-1. Tissues were incubated in M-199 for 1h without treatments and with treatments for 4 and 8h in both experiments. Media were analyzed for concentrations of PGE and PGF2alpha by radioimmunoassay (RIA). Hormone data in Experiments 1 and 2 were analyzed by 2x7 and 3x2x8 factorial design for ANOVA, respectively. Concentrations of PGE and PGF2alpha in media increased (P< or =0.05) from 4 to 8 h regardless of treatment group in Experiment 1, but did not differ (P> or =0.05) among treatments. In Experiment 2, concentrations of PGE and PGF2alpha increased (P< or =0.05) with time in all treatment groups of all three synchronization regimens. DETA-NONOate, SNAP, and sodium nitroprusside (NO donors) and ET-1 increased caruncular endometrial (P< or =0.05) secretion of PGE2 in unsynchronized and Lutalyse synchronized cows, but not when estrus was synchronized with a CIDR (P> or =0.05). No treatment increased (P> or =0.05) PGF2alpha in any synchronization regimen. It is concluded that norgestamet in Synchromate-B ear implants or progesterone in a CIDR alters NO or ET-1-induced secretion of PGE by bovine caruncular endometrium and could interfere with implantation by altering the PGE:PGF2alpha ratio resulting in increased embryonic losses during early pregnancy.

Polymorphisms of the Nos3 gene and unexplained late intrauterine fetal death

OBJECTIVE

Genetic polymorphisms associated with vascular diseases have been proposed to be involved in the pathogenesis of late unexplained intrauterine fetal death (IUFD). The Nos3 gene is known to regulate vascular tone via the endothelial nitric oxide synthase/nitric oxide pathway.

STUDY DESIGN

In a multicenter case-control study, we evaluated two Nos3 polymorphisms (exon 7 Glu298Asp and a 27bp-repeat in intron 4) in 92 women with IUFD and 92 healthy control women.

RESULTS

The investigated Nos3 polymorphisms were not associated with the occurrence of IUFD. In the subgroup of pregnancies affected by IUFD, women with at least one mutant allele of the Nos3 intron 4 polymorphism were diagnosed with IUFD at a significantly earlier gestational age (31.8 [standard deviation (S.D.) = 4.9] weeks versus 34.6 [S.D. = 4.8] weeks, p = 0.02) and showed a significantly reduced birth weight (2113 g [S.D. = 1028] versus 1571 g [S.D. = 568], p = 0.03).

CONCLUSION

We are the first to report on Nos3 polymorphisms and IUFD. While not being associated with the incidence of IUFD overall, the intron 4 Nos3 polymorphism might modulate the timing of IUFD in affected pregnancies.

Angiotensin II Elevates Nitric Oxide Synthase 3 Expression and Nitric Oxide Production Via a Mitogen-Activated Protein Kinase Cascade in Ovine Fetoplacental Artery Endothelial Cells1

Normal pregnancy is associated with high angiotensin II (ANG II) concentrations in the maternal and fetal circulation. These high levels of ANG II may promote production vasodilators such as nitric oxide (NO). ANG II receptors are expressed in ovine fetoplacental artery endothelial (OFPAE) cells and mediate ANG II-stimulated OFPAE cell proliferation. Herein, we tested whether ANG II stimulated NO synthase 3 (NOS3, also known as eNOS) expression and total NO (NO(x)) production via activation of mitogen-activated protein kinase 3/1 (MAPK3/1, also known as ERK1/2) in OFPAE cells. ANG II elevated (P < 0.05) eNOS protein, but not mRNA levels with a maximum effect at 10 nM. ANG II also dose dependently increased (P < 0.05) NO(x) production with a maximal effect at doses of 1-100 nM. Activation of ERK1/2 by ANG II was determined by immunocytochemistry and Western blot analysis. ANG II rapidly induced positive staining for phosphorylated ERK1/2, appearing in cytosol after 1-5 min of ANG II treatment, accumulating in nuclei after 10 min, and disappearing at 15 min. ANG II increased (P < 0.05) phosphorylated ERK1/2 protein levels. Activation of ERK1/2 was confirmed by an immunocomplex kinase assay using ELK1 as a substrate. PD98059 significantly inhibited ANG II-induced ERK1/2 activation, and the ANG II-elevated eNOS protein levels but only partially reduced ANG II-increased NO(x) production. Thus, in OFPAE cells, the ANG II increased NO(x) production is associated with elevated eNOS protein expression, which is mediated at least in part via activation of the mitogen-activated protein kinase kinase1 and kinase2 (MAP2K1 and MAP2K2, known also as MEK1/2)/ERK1/2 cascade. Together with our previous observation that ANG II stimulates OFPAE cell proliferation, these data suggest that ANG II is a key regulator for both vasodilation and angiogenesis in the ovine fetoplacenta.

Circulating levels of nitric oxide and vascular endothelial growth factor throughout ovine pregnancy

Nitric oxide (NO) production has been shown to increase uterine blood flow and be elevated in ewes carrying multiple fetuses during late gestation. Vascular endothelial growth factor (VEGF) has been reported to increase eNOS expression and NO production in endothelial cell cultures. As angiogenesis and vasodilatation of the uterine and placental vascular beds are important at all stages of pregnancy, it is important to understand how VEGF and NO change throughout gestation in circulation. Therefore the objectives of the current study were to evaluate the systemic levels of VEGF and NO metabolite (NOx) throughout ovine gestation and to determine if there was an effect of sheep carrying singletons versus multiple fetuses. NOx and VEGF concentrations were analysed in systemic blood from pregnant ewes starting on day 27 of pregnancy and at multiple intermittent intervals throughout pregnancy until term. Blood samples from non-pregnant and postpartum ewes were also analysed. NOx concentrations in maternal blood expressed a biphasic pattern with NOx concentrations increasing (P < 0.05) over non-pregnant values on days 40-69 of gestation, returning to non-pregnant concentrations from days 70-100, and again increasing (P < 0.05) until term. Postpartum NOx concentrations were similar to non-pregnant values. While ewes carrying multiple fetuses had increased (P < 0.05) concentrations of NOx on days 60-69, there were no differences in NOx concentrations in ewes carrying singletons or multiples from day 70-99 of gestation. Starting on day 100 and continuing throughout the duration of pregnancy, ewes carrying multiple fetuses had increased (P < 0.05) concentrations of NOx compared to ewes carrying singletons. Concentrations of VEGF showed a different pattern from NOx with VEGF decreasing (P < 0.05) from day 20-69 of pregnancy compared to non-pregnant ewes. Concentrations of VEGF returned to non-pregnant levels by day 70 and remained constant throughout the duration of pregnancy. On days 20-39, ewes carrying singleton fetuses had an increased VEGF concentration (P < 0.05), whereas ewes carrying multiple fetuses demonstrated elevated VEGF concentrations from day 90-109 of gestation. Concentrations from non-pregnant and postpartum ewes did not differ (P > 0.1). While there was no effect of fetal number on circulating VEGF concentrations, circulating levels of NOx were substantially increased (P < 0.05) in ewes carrying multiple fetuses, compared to ewes carrying singletons. The pattern of the rise in NOx in circulating plasma was not directly associated with changes in VEGF regardless of the number of fetuses present. However, circulating concentrations of NOx and VEGF appear to, respectively, follow patterns of uterine blood flow and angiogenesis of the uterus. An understanding of these circulatory patterns may have important implications for fetal size, birth weight and fetal/developmental origins of adult disease.

Angiotensin II regulation of ovine fetoplacental artery endothelial functions: interactions with nitric oxide

During normal pregnancy, elevated angiotensin II (Ang II) concentrations in the maternal and fetal circulations are associated with dramatic increases in placental angiogenesis and blood flow. Much is known about a local renin-angiotensin system within the uteroplacental vasculature. However, the roles of Ang II in regulating fetoplacental vascular functions are less well defined. In the fetal placenta, the overall in vivo vasoconstrictor responses of the blood vessels to Ang II infusion is thought to be less than that in its maternal counterpart, even though infused Ang II induces vasoconstriction. Recent data from our laboratories suggest that Ang II stimulates cell proliferation and increases endothelial nitric oxide synthase (eNOS) and production of nitric oxide (NO) in ovine fetoplacental artery endothelial cells. These data imply that elevations of the known vasoconstrictor Ang II in the fetal circulation may indeed play a role in the marked increases in fetoplacental angiogenesis and that Ang II-elevated endothelial NO production may partly attenuate Ang II-induced vasoconstriction on vascular smooth muscle. Together with both of these processes, the high levels of Ang II in the fetal circulation may serve to modulate overall fetoplacental vascular resistance. In this article, we review currently available data on the expression of Ang II receptors in the ovine fetal placenta with particular emphasis on the effects of Ang II on ovine fetoplacental endothelium. The potential cellular mechanisms underlying the regulation of Ang II on endothelial growth and vasodilator production are discussed.

Uterine blood flow responses to ICI 182 780 in ovariectomized oestradiol-17beta-treated, intact follicular and pregnant sheep

Oestrogen dramatically increases uterine blood flow (UBF) in ovariectomized (Ovx) ewes. Both the follicular phase and pregnancy are normal physiological states with elevated levels of circulating oestrogen. ICI 182 780 is a pure steroidal oestrogen receptor (ER) antagonist that blocks oestrogenic actions in oestrogen-responsive tissue. We hypothesized that an ER-mediated mechanism is responsible for in vivo rises in UBF in physiological states of high oestrogen. The purpose of the study was to examine the effect of an ER antagonist on exogenous and endogenous oestradiol-17beta (E2beta)-mediated elevations in UBF. Sheep were surgically instrumented with bilateral uterine artery blood flow transducers, and uterine and femoral artery catheters. Ovx animals (n = 8) were infused with vehicle (35% ethanol) or ICI 182 780 (0.1-3.0 microg min(-1)) into one uterine artery for 10 min before and 50 min after E2beta was given (1 microg kg(-1) I.V. bolus) and UBF was recorded for an additional hour. Intact, cycling sheep were synchronized to the follicular phase using progesterone, prostaglandin F2alpha(PGF2alpha) and pregnant mare serum gonadotrophin (PMSG). When peri-ovulatory rises in UBF reached near peak levels, ICI 182 780 (1 or 2 microg (ml uterine blood flow)-1) was infused unilaterally (n = 4 sheep). Ewes in the last stages of pregnancy (late pregnant ewes) were also given ICI 182 780 (0.23-2.0 microg (ml uterine blood flow)-1; 60 min infusion) into one uterine artery (n = 8 sheep). In Ovx sheep, local infusion of ICI 182 780 did not alter systemic cardiovascular parameters, such as mean arterial blood pressure or heart rate; however, it maximally decreased ipsilateral, but not contralateral, UBF vasodilatory responses to exogenous E2beta by approximately 55-60% (P < 0.01). In two models of elevated endogenous E2beta, local ICI 182 780 infusion inhibited the elevated UBF seen in follicular phase and late pregnant ewes in a time-dependent manner by approximately 60% and 37%, respectively; ipsilateral >> contralateral effects (P < 0.01). In late pregnant sheep ICI 182 780 also mildly and acutely (for 5-30 min) elevated mean arterial pressure and heart rate (P < 0.05). We conclude that exogenous E2beta-induced increases in UBF in the Ovx animal and endogenous E2beta-mediated elevations of UBF during the follicular phase and late pregnancy are partially mediated by ER-dependent mechanisms.

Expression, localization, and function of MRP5 (ABCC5), a transporter for cyclic nucleotides, in human placenta and cultured human trophoblasts: effects of gestational age and cellular differentiation

The placenta functions both as site for nutrition and protection of the fetus. Transport proteins, including members of the multidrug resistance protein (MRP)/ABCC subfamily, have been recognized to contribute to the latter function. MRP5 (ABCC5) was identified as transmembrane transport protein for cyclic nucleotides, especially 3',5'-cyclic GMP (cGMP), indicating an additional role in signal transduction and a potential role in placenta development. We therefore studied expression, localization, and function of MRP5 in placenta of different gestational ages. Quantitative real-time polymerase chain reaction revealed expression of MRP5 in all 60 samples from pre-term and term placenta, with a decreasing mean expression with gestational age (MRP5/18S-ratio x 1000; < 32 weeks: 2.91 +/- 0.73, n = 15; 32 to 37 weeks: 2.10 +/- 0.87, n = 15; > 37 weeks: 0.46 +/- 0.08, n = 30; P < 0.01). Immunofluorescence microscopy with an anti-MRP5 antibody indicated localization of MRP5 preferentially in the basal membrane of syncytiotrophoblasts and in and around fetal vessels. ATP-dependent [(3)H]cGMP transport as evidence for MRP5 function could be demonstrated in isolated basal membrane vesicles. Moreover, the influence of cellular differentiation on MRP5 expression was studied in isolated trophoblasts, revealing an increase of the MRP5 expression in parallel with the hCG production (MRP5/18S-ratio x 1000 was 2.4 +/- 0.5 at day 5 of culture and 1.45 +/- 0.5 at day 0 of culture, n = 3 preparations, significant difference with P < 0.05). In conclusion, MRP5 expression depends on gestational age and varies throughout the differentiation process. In view of the important role of cGMP for cellular differentiation, MRP5 may play a role in placental development in context with a specific need for cellular cGMP export.

IGF-I, 17beta-estradiol and progesterone in SHR and in rats treated with L-NAME: fetal-placental development

METHODS

The relationship between progesterone (P4), 17beta-estradiol, insulin-like growth factor (IGF-I) and embryonic and fetal development, were examined. Female Sprague Dawley rats were divided into two groups: control untreated (n=60) and treated (n=63) with L-NAME (N(omega)-nitro-L-arginine methyl ester), 15 mg/day in drinking water from the first day after mating to day 18 of gestation. A further group was formed (n=63) of spontaneously hypertensive rats (SHR). Mean systolic blood pressure was recorded daily. On days 6, 11 and 18 of pregnancy, the number of sites of implantation, litter and placenta weight was examined. In addition, serum levels of P4, 17beta-estradiol and IGF-I were determined.

RESULTS

Systolic blood pressure (SBP) (mmHg) increased significantly in L-NAME and SHR rats over the course of the experiment. On day 6 of pregnancy, in the L-NAME group the number of implantation sites, levels of IGF-I and 17beta-estradiol were significantly lower than in the control group. In SHR, only the concentration of IGF-I was low (p<0.05). In contrast, on day 11 of pregnancy no variation was found in the parameters under study. On day 18 of gestation, a significant decrease in litter and placenta weight, concentration of P4 and IGF-I was observed in the experimental groups.

CONCLUSION

The data further suggest that nitric oxide might regulate IGF-I production, indicating that growth factors may play an important role in fetal-placental development.

Effects of estrous synchronization on response to nitric oxide donors, nitric oxide synthase inhibitors, and endothelin-1 in vitro

Two experiments were conducted to determine the effects of nitric oxide (NO) donors, endothelin-(ET-1), and NO synthase (NOS) inhibitors on bovine luteal function in vitro. In experiment 1, estrus in Brahman cows was synchronized with Synchro-Mate-B (SMB) and day-13-14 corpora luteal slices were weighed, diced and incubated in vitro. Treatments (100 ng/ml) were: vehicle, N[see symbol in text]-nitro-L-arginine-L-methyl ester (L-NAME), N(G)-monomethyl-L-arginine acetate (L-NMMA), diethylenetriamine (DETA), DETA-NONOate, sodium nitroprusside (SNP), or ET-1. In experiment 2, estrus was synchronized with Lutalyse, a Controlled Intravaginal Progesterone Releasing Device (CIDR), or cows were not synchronized. Corpora lutea were collected, weighed, and luteal slices were weighed, diced and incubated in vitro with treatments. Treatments (100ng/ml) were: vehicle, L- NAME, L-NMMA, DETA, DETA-NONOate, sodium nitroprusside, S-nitroso-N-acetylpenicillamine (SNAP) or endothelin-1. Tissues were incubated in M- 199 for 1 h without treatments and for 4 and 8 h in both experiments with treatments in both experiments. Media were analyzed for progesterone, prostaglandins E2 and F2alpha (PGE2, PGF2alpha) by radioimmunoassay (RIA). Hormone data in experiments 1 and 2 were analyzed by 2 x 7 and 3 x 2 x 8 factorial design for analysis of variance (ANOVA), respectively. Luteal weights in experiment 2 were analyzed by a one-way ANOVA. Concentrations of progesterone in media were similar (P > or = 0.05) among treatments within experiments. Concentrations of PGE2 in media in experiment 1 were undetectable in 90 and 57% of the samples at 4 and 8 h, respectively. PGF2alpha increased (P < or = 0.05) with time, but did not differ (P > or = 0.05) among treatments. Secretion of PGF2alpha was not affected by treatments (P > or = 0.05). In experiment 2, luteal weights of the induced estrous cycle were decreased (P < or = 0.05) by Lutalyse. Concentrations of PGE2 and PGF2alpha increased (P < or = 0.05) with time in control of all three synchronization regimens. DETA-NONOate, SNAP, sodium nitroprusside (NO donors) and ET-1 increased (P < or = 0.05) PGE2 except in the CIDR synchronized group (P > or = 0.05). No treatment increased (P > or = 0.05) PGF2alpha in any synchronization regimen. It is concluded that either SMB containing norgestomet or a CIDR containing progesterone alters luteal secretion of PGE2, Lutalyse lowers luteal weights in the induced estrous cycle, and NO or ET-1 given alone are not luteolytic agents. It is suggested that NO and ET-1 could have indirect antiluteolytic/luteotropic effects via increasing PGE2 secretion by luteal tissue rather than being luteolytic.

Differential expression of the vascular endothelial growth factor-receptor system in the gravid uterus of yorkshire and Meishan pigs

Litter size in the pig is limited by uterine capacity, which is dependent on uterine size, placental size, and vascularity. Placentae of U.S. pig breeds, such as the Yorkshire, exhibit marked growth from mid to late gestation, increasing their surface area of endometrial attachment. In contrast, placentae of the prolific Chinese Meishan pig exhibit little growth from mid to late gestation; instead, they exhibit a marked and progressive increase in the density of placental blood vessels. Vascular endothelial growth factor (VEGF) is a potent angiogenic and permeability-enhancing factor that is produced and secreted by placentae of several species, including the pig. The activity of VEGF is mediated through two specific receptors (VEGF-R1 and VEGF-R2), both of which are expressed by placental and endometrial tissues in pigs and are thought to play a role in mediating increased vascularization and/or permeability at the fetal-maternal interface. The objectives of the present study were to determine concentrations of VEGF in fetal blood and placental fluids as well as placental and adjacent endometrial mRNA expression of VEGF, VEGF-R1, and VEGF-R2 on Days 30, 50, 70, 90, and 110 of gestation in Yorkshire and Meishan pigs. Day 90 Meishan conceptuses exhibited marked increases (P < 0.05) in placental VEGF mRNA expression as well as fetal blood and allantoic fluid concentrations of VEGF, which remained elevated through Day 110. In contrast, Yorkshire conceptuses failed to exhibit increases in placental VEGF mRNA expression or concentrations of VEGF in fetal blood or allantoic fluid until Day 110. Receptor mRNA expression patterns differed between Meishan and Yorkshire conceptuses, but no difference was found in their expression levels. Placental efficiency (fetal weight/placental weight) was higher (P < 0.05) on Days 90 and 110 in Meishan than in Yorkshire conceptuses. The earlier increase in VEGF protein and mRNA expression in the Meishan versus the Yorkshire conceptus may explain the previously reported increased vascularity and increased placental efficiency of this breed compared the Yorkshire breed.

Developmental changes in nitric oxide synthesis in the ovine placenta

Nitric oxide (NO), synthesized from l-arginine by NO synthase (NOS), is a key regulator of placental angiogenesis and growth during pregnancy. However, little is known about placental NO synthesis associated with ovine conceptus development. This study was conducted to test the hypothesis that placental NO synthesis is greatest during early gestation. Columbia cross-bred ewes were hysterectomized on Days 30, 40, 60, 80, 100, 120, or 140 of gestation (n = 4 per day) to obtain placentomes, intercotyledonary placenta, and intercaruncular endometrium. Tissues were analyzed for constitutive NOS (cNOS) and inducible NOS (iNOS) activities, NO synthesis, tetrahydrobiopterin (BH4) and NADPH (essential cofactors for NOS), and GTP-cyclohydrolase I (GTP-CH, a rate-controlling enzyme in de novo synthesis of BH4) activity using radiochemical and chromatographic methods. Marked changes in NO synthesis, cNOS and iNOS activities, GTP-CH activity, and concentrations of BH4 and NADPH occurred in all placental and endometrial tissues between Days 30 and 140 of gestation. NO synthesis peaked on Day 60 of gestation in both intercotyledonary placenta and placentomes and on Days 40-60 in intercaruncular endometrium. NO synthesis in placentomes increased 100% between Days 80 and 100 of gestation, when placental and uterine blood flows increase continuously. In all placental and endometrial tissues, NO synthesis was positively correlated with total NOS activity, GTP-CH activity, and concentrations of BH4 and NADPH. Importantly, these results indicate a high degree of metabolic coordination among the several integrated pathways that support high rates of NO synthesis in the conceptus and uterus and establish a new base of information for future studies to define the roles of NO in fetal-placental growth and development.

Expression of endothelial and inducible nitric oxide synthases is modulated in the endometrium of cyclic and early pregnant mares

The expression of the endothelial and inducible nitric oxide synthases (eNOS and iNOS, respectively) was examined in the endometrium of cyclic and pregnant mares by real-time polymerase chain reaction and immunohistology. The concentration of eNOS mRNA varied throughout the oestrous cycle, with significantly higher transcripts on Day 5 of the oestrous cycle (P < 0.05), whereas iNOS transcription did not change significantly over time (P > 0.05). In early pregnant mares both eNOS and iNOS mRNA increased between Days 12 and 15 (P < 0.05). In cyclic mares, eNOS protein was detected immunocytochemically in endometrial epithelia, the basement membrane, the endothelial layer and smooth muscle cells of the vasculature. Using immunocytochemical methods, iNOS protein was undetectable in the endometrium of cyclic mares but could be demonstrated in pregnant mares. Endometrial epithelia of pregnant mares were immunopositive for both proteins with a more intense labelling for iNOS. Thus, the present study describes for the first time the modulation and spatial distribution of eNOS and iNOS expression during the oestrous cycle and early pregnancy, suggesting that ovarian steroids are differently involved in the regulation of each NOS. Localisation of eNOS protein in endometrial epithelia and various vascular components indicates that this isoform may be involved in the regulation of endometrial cyclicity. The presence and increase of both forms of NOS during early gestation suggest a role for them in the control of endometrial vascular bed and glandular activity to provide a suitable microenvironment for successful pregnancy.

Mechanisms of shear stress-induced endothelial nitric-oxide synthase phosphorylation and expression in ovine fetoplacental artery endothelial cells

Placental blood flow, nitric-oxide (NO) levels, and endothelial NO synthase (eNOS) expression increase during human and ovine pregnancy. Shear stress stimulates NO production and eNOS expression in ovine fetoplacental artery endothelial (OFPAE) cells. Because eNOS is the rate-limiting enzyme essential for NO synthesis, its activity and expression are both closely regulated. We investigated signaling mechanisms underlying pulsatile shear stress-induced increases in eNOS phosphorylation and protein expression by OFPAE cells. The OFPAE cells were cultured at 3 dynes/cm2 shear stress, then exposed to 15 dynes/cm2 shear stress. Western blot analysis for phosphorylated ERK1/2, Akt, p38 mitogen activated protein kinase (MAPK), and eNOS showed that shear stress rapidly increased phosphorylation of ERK1/2 and Akt but not of p38 MAPK. Phosphorylation of eNOS Ser1177 under shear stress was elevated by 20 min, a response that was blocked by the phosphatidyl inositol-3-kinase (PI-3K)-inhibitors wortmannin and LY294002 but not by the mitogen activated protein kinase kinase (MEK)-inhibitor UO126. Basic fibroblast growth factor (bFGF) enhanced eNOS protein levels in static culture via a MEK-mediated mechanism, but it could not further augment the elevated eNOS protein levels otherwise induced by the 15 dynes/cm2 shear stress. Blockade of either signaling pathway changed the shear stress-induced increase in eNOS protein levels. In conclusion, shear stress induced rapid eNOS phosphorylation on Ser1177 in OFPAE cells through a PI-3K-dependent pathway. The bFGF-induced rise in eNOS protein levels in static culture was much less than those observed under flow and was blocked by inhibition of MEK. Prolonged shear stress-stimulated increases in eNOS protein were not affected by inhibition of MEK- or PI-3K-mediated pathways.

Effects of pulsatile shear stress on nitric oxide production and endothelial cell nitric oxide synthase expression by ovine fetoplacental artery endothelial cells

Placental blood flow, endothelial nitric oxide (NO) production, and endothelial cell nitric oxide synthase (eNOS) expression increase during pregnancy. Shear stress, the frictional force exerted on endothelial cells by blood flow, stimulates vessel dilation, endothelial NO production, and eNOS expression. In order to study the effects of pulsatile flow/shear stress, we adapted Cellco CELLMAX artificial capillary modules to study ovine fetoplacental artery endothelial (OFPAE) cells for NO production and eNOS expression. OFPAE cells were grown in the artificial capillary modules at 3 dynes/cm2. Confluent cells were then exposed to 10, 15, or 25 dynes/cm2 for up to 24 h. NO production by OFPAE cells exposed to pulsatile shear stress was inhibited to nondetectable levels by the NOS inhibitor l-NMMA and reversed by excess NOS substrate l-arginine. NO production and expression of eNOS mRNA and protein by OFPAE cells were elevated by shear stress in a graded fashion (P < 0.05). The rise in NO production with 25 dynes/cm2 shear stress (8-fold) was greater (P < 0.05) than that observed for eNOS protein (3.6-fold) or eNOS mRNA (1.5-fold). The acute shear stress-induced rise in NO production by OFPAE cells was via eNOS activation, whereas the prolonged NO rise occurred by elevations in both eNOS expression and enzyme activation. Thus, elevations of placental blood flow and physiologic shear stress may be partly responsible for the increases in placental arterial endothelial eNOS expression and NO production during pregnancy.

Enhanced umbilical blood flow during acute hypoxemia after chronic umbilical cord compression: a role for nitric oxide

BACKGROUND

The continuing incidence of intrapartum morbidity may be partly due to antenatal compromise, which influences the fetal defense to labor and delivery. We have shown that antenatal exposure of the ovine fetus to partial compression of the umbilical cord suppresses femoral vasoconstriction during subsequent acute hypoxemia through elevated nitric oxide (NO) activity. This study investigated whether elevated NO activity in cord-compressed fetuses enhanced the vasodilator response to hypoxemia in circulations in which blood flow is known to increase during acute hypoxemia, such as the umbilical vascular bed.

METHODS AND RESULTS

Fifteen fetal sheep were chronically instrumented between 117 and 120 days of gestation with vascular catheters and an umbilical flow probe. In 8 of these fetuses, umbilical blood flow was reduced by 30% for 3 days between 125 and 128 days. The remaining 7 fetuses acted as sham-operated controls. Between 2 and 7 days after umbilical cord/sham compression, fetuses were exposed to 2 episodes of acute hypoxemia, on separate days, during infusion with either saline or treatment with a combination of NG-nitro-l-arginine methyl ester and sodium nitroprusside. The data show that umbilical cord compression significantly enhances the umbilical hyperemia through NO-dependent mechanisms during a subsequent episode of acute hypoxemia.

CONCLUSIONS

Increased fetal NO activity after chronic cord compression has opposing effects in circulations that either constrict or dilate during subsequent acute hypoxemia. The data imply that antenatal compromise switches the fetal strategy to withstand episodes of subsequent acute hypoxemia of the type that may occur during labor and delivery from a reliance on vasoconstrictor mechanisms to those promoting NO-dependent vasodilation.

Inhibition of nitric oxide enhances ovine lentivirus replication in monocyte-derived macrophages

Ovine lentivirus (OvLV) also known as maedi-visna virus, infects and replicates primarily in macrophages. This investigation examined the role of nitric oxide in the replication of OvLV in cultured macrophages. Peripheral blood mononuclear cells were collected from OvLV-free sheep and cultured in Teflon coated flasks at a high concentration of lamb serum. The cells were subsequently infected with OvLV strain 85/34. OvLV replication was assessed under different experimental treatments by comparison of reverse transcriptase (RT) activity in culture supernatant. Cultures that were treated with exogenous nitric oxide via S-nitroso-acetylpenicillamine did not have altered levels of RT activity compared to cultures treated with the inactive control compound, acetylpenicillamine. However, blockage of nitric oxide production by treatment with aminoguanidine, a competitive inhibitor of inducible nitric oxide synthase (iNOS), led to a significant rise in RT activity. This rise in RT activity was partially reversed in aminoguanidine treated cultures by L-arginine, the normal substrate for iNOS. Finally, the number of viral antigen producing cells was also quantified after aminoguanidine treatment and found to be significantly higher than untreated cultures. Collectively, these results indicate that nitric oxide is a negative regulator of OvLV replication in macrophages.

Adverse intrauterine conditions diminish the fetal defense against acute hypoxia by increasing nitric oxide activity

BACKGROUND

The incidence of perinatal morbidity arising from birth hypoxia or asphyxia has not changed significantly in recent years despite marked improvements in labor management. Perinatal mortality in these circumstances may therefore reflect antenatal compromise and subsequent alteration of the fetal capacity to respond to episodes of hypoxia that may occur during labor. Hence, we have investigated the effects of fetal pre-exposure to a period of adverse intrauterine conditions on the mechanisms mediating the fetal defense response to a subsequent episode of acute hypoxia in sheep.

METHODS AND RESULTS

Sixteen fetal sheep were chronically instrumented at 118+/-2 days for recording of blood pressure, heart rate, and femoral and umbilical blood flows. In 8 of these fetuses, umbilical blood flow was reduced by 30% for 3 days (between days 125 and 128). The remaining 8 fetuses acted as sham-operated controls. Between 2 and 7 days after umbilical cord/sham compression, all fetuses were exposed to 2 episodes of acute hypoxemia on separate days during infusion with either saline or treatment with a combination of N(G)-nitro-L-arginine methyl ester and sodium nitroprusside. We show that previous fetal exposure to a period of adverse intrauterine conditions, such as that induced by compression of the umbilical cord, elevates nitric oxide activity and results in a markedly diminished cardiovascular defense response to subsequent acute hypoxia.

CONCLUSIONS

The data imply that pre-exposure to adverse antenatal conditions may render the fetus more susceptible to the acute hypoxia or asphyxia that can accompany relatively uncomplicated labor and delivery.

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.

Endothelial vasodilator production by uterine and systemic arteries. VI. Ovarian and pregnancy effects on eNOS and NO(x)

Normal pregnancy and the follicular phase of the ovarian cycle are both estrogen-dominated physiological states that are characterized by elevations in uterine blood flow and endothelial nitric oxide synthase (eNOS) protein expression in the uterine artery (UA) endothelium. It is unknown if elevations in mRNA level account for the changes in protein or eNOS activity. We tested the hypothesis that pregnancy and the follicular phase are associated with increases in eNOS mRNA and the consequent elevated expression of eNOS protein results in increased circulating nitric oxide (NO) levels. UA were obtained from pregnant (PREG; n = 8; 110-130 days gestation; term = 145 +/- 3 days), nonpregnant luteal (LUT; n = 6), nonpregnant follicular (FOL; n = 6), and nonpregnant ovariectomized (OVEX; n = 6) sheep. Circulating NO levels were analyzed as total NO(2)-NO(3) (NO(x)). Western analysis performed on UA endothelial-isolated proteins demonstrated that eNOS protein levels were OVEX = LUT < or = FOL < PREG (P < 0.05), whereas eNOS mRNA expression (RT-PCR) in UA endothelial cells obtained by limited collagenase digestion was OVEX < LUT < FOL < PREG (P < 0.05). Pregnancy dramatically elevated eNOS protein (4.1- to 6.9-fold) and mRNA (2.4- to 6.9-fold) over LUT controls (P < 0.01). Circulating NO(x) levels were not altered by ovariectomy or the ovarian cycle but were elevated from 4.4 +/- 1.1 microM in LUT to 12 +/- 4, 22 +/- 3, and 41 +/- 3 microM at 110, 120, and 130 days gestation (P < 0.01). Systemic NO(x) levels in singleton (12.5 +/- 1.6 microM) were less (P < 0.01) than in multiple (twin 27.6 +/- 6.5 microM; triplet = 46 +/- 10 microM) pregnancies. Therefore, the follicular phase and, to a much greater extent, pregnancy are associated with elevations in UA endothelium-derived eNOS expression, although significant increases in systemic NO(x) levels were only observed in the PREG group (multiple > singleton). Thus, although UA endothelial increases in eNOS protein and mRNA levels are associated with high estrogen states, increases in local UA NO production may require additional eNOS protein activation to play its important role in the maintenance of uterine blood flow in pregnancy.