Elevation of nitrate levels in pregnant ewes and their fetuses

Evaluation of haemodynamic changes of uterine arteries using Doppler ultrasonography during different stages of pregnancy in Bos indicus cows

The objectives of the study were to evaluate haemodynamic changes and their relationships among ipsilateral (IPS) and contralateral (CONT) uterine arteries (UA) during different stages of pregnancy in Bos indicus cows. Multiparous pregnant cows (n = 40) having a gestation length 30.47 ± 0.54 (mean ± SD) days were randomly enrolled and subjected to Doppler ultrasonography sequentially at 1st, 2nd, 4th, 6th and 8th months of gestation. Blood flow indices including diameter of UA (mm), blood flow volume (BFVo, ml/min), blood flow velocity (BFVe, cm/s), time-averaged maximum velocity (TAMV, cm/s), pulsatility index (PI) and resistance index (RI) were recorded. Data were analysed with mixed models using the PROC MIXED procedures, and Pearson correlation coefficients were calculated using the PROC CORR statement in SAS. The final statistical models included the fixed effects of side of UA, gestation month and the interaction between side of UA and gestation month. Results revealed that the mean diameter of the UA (12.13 ± 0.22 vs. 10.09 ± 0.22), BFVo (1236.33 ± 0.55 vs. 770.41 ± 0.55), BFVe (17.18 ± 0.42 vs. 15.58 ± 0.42) and TAMV (17.11 ± 0.44 vs. 15.77 ± 0.44) was higher (p < .05) in IPS as compared to CONT side of the UA in cows. However, PI and RI did not differ between IPS and CON arteries of uterus in cows. A very high and positive correlation (r = .89; p < .05) existed between the diameter of UA and BFVo starting from 1st to 8th months of gestation in IPS as well as CONT sides of UA. Moreover, TAMV was highly and positively correlated (r = .91; p < .05) with BFVe throughout the gestation. In conclusion, these haemodynamic changes in the UA could be used as a valuable validity tool to differentiate the compromised pregnancy in Bos indicus cows.

Endotoxin-induced cerebral pathophysiology: differences between fetus and newborn

As the comparative pathophysiology of perinatal infection in the fetus and newborn is uncertain, this study contrasted the cerebral effects of endotoxemia in conscious fetal sheep and newborn lambs. Responses to intravenous bacterial endotoxin (lipopolysaccharide, LPS) or normal saline were studied on three consecutive days in fetal sheep (LPS 1 μg/kg, n = 5; normal saline n = 5) and newborn lambs (LPS 2 μg/kg, n = 10; normal saline n = 5). Cerebro-vascular function was assessed by monitoring cerebral blood flow (CBF) and cerebral vascular resistance (CVR) over 12 h each day, and inflammatory responses were assessed by plasma TNF alpha (TNF-α), nitrate and nitrite concentrations. Brain injury was quantified by counting both resting and active macrophages in the caudate nucleus and periventricular white matter (PVWM). An acute cerebral vasoconstriction (within 1 h of LPS injection) occurred in both the fetus (ΔCVR +53%) and newborn (ΔCVR +63%); subsequently prolonged cerebral vasodilatation occurred in the fetus (ΔCVR -33%) in association with double plasma nitrate/nitrite concentrations, but not in the newborn. Abundant infiltration of activated macrophages was observed in both CN and PVWM at each age, with the extent being 2-3 times greater in the fetus (P < 0.001). In conclusion, while the fetus and newborn experience a similar acute disruption of the cerebral circulation after LPS, the fetus suffers a more prolonged circulatory disruption, a greater infiltration of activated macrophages, and an exaggerated susceptibility to brain injury.

Effects of the Catechol and Methoxy Metabolites of 17β-Estradiol on Nitric Oxide Production by Ovine Uterine Artery Endothelial Cells

Nitric oxide (NO) production is essential to facilitate rises in uterine blood flow (UBF) during pregnancy. It has been proposed that the metabolites of E₂β, 2-hydroxyestradiol (2-OHE₂), 4-hydroxyestradiol (4-OHE₂), 2-methoxyestradiol (2-ME₂), and 4-methoxyestradiol (4-ME₂) play a role in mediating vasodilation and rises in UBF during pregnancy. We previously showed that the E₂β metabolites stimulate prostacyclin production in pregnancy-derived ovine uterine artery endothelial cells (P-UAECs); however, it is unknown whether the E₂β metabolites also induce NO production. Herein, UAECs derived from nonpregnant and pregnant ewes were used to test the hypothesis that E₂β metabolites stimulate NO production in a pregnancy-specific manner. Specific estrogen receptor (ER) and adrenergic receptor (AR) antagonists were used to determine the roles of ERs or ARs in E₂β metabolite-induced NO production. E₂β and its metabolites increased total nitric oxide metabolites (NOx) levels (NO₂ + NO₃) in P-UAECs, but not in NP-UAECs. Pretreatment with combined 1 µmol/L 1,3-bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy)phenol]-1H-pyrazole dihydrochloride (MPP; ER-α antagonist) and 1 µmol/L 4-[2-phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl]phenol (PHTPP; ER-β antagonist) inhibited the rises in NOx levels stimulated by E₂β and 2-ME₂, but had no effect on 2-OHE₂-, 4-OHE₂-, or 4-ME₂-stimulated rises in NOx levels. Pretreatment with yohimbine (α₂-AR antagonist) and propranolol (β_2,3-AR antagonist) inhibited the rises in NOx levels stimulated by 2-OHE₂, but not by E₂β, 4-OHE₂, 2-ME₂, or 4-ME₂. These data demonstrate that E₂β metabolites stimulate NO synthesis via ERs or ARs in UAECs in a pregnancy-specific manner, suggesting that these metabolites contribute to rises in vasodilation and UBF during pregnancy.

Mechanisms of Renal Vasodilation and Hyperfiltration During Pregnancy

Glomerular filtration rate (GFR) and renal plasma flow (RPF) increase by 40-65% and 50-85%, respectively, during normal pregnancy in women. Studies using the gravid rat as a model have greatly enhanced our understanding of mechanisms underlying these remarkable changes in the renal circulation during gestation. Hyperfiltration appears to be almost completely due to the increase in RPF, the latter attributable to profound reductions in both the renal afferent and efferent arteriolar resistances. The major pregnancy hormone involved is relaxin. The mediators downstream from relaxin include endothelin (ET) and nitric oxide (NO). New evidence indicates that relaxin increases vascular gelatinase activity during pregnancy, thereby converting big ET to ET(1-32), which leads to renal vasodilation, hyperfiltration, and reduced myogenic reactivity of small renal arteries via the endothelial ET(B) receptor and NO. Whether the chronic volume expansion characteristic of pregnancy contributes to the maintenance of gestational renal changes requires further investigation. Additional studies are also needed to further delineate the molecular basis of these mechanisms and, importantly, to investigate whether they apply to women.

2.45 GHz microwave irradiation-induced oxidative stress affects implantation or pregnancy in mice, Mus musculus

The present experiment was designed to study the 2.45 GHz low-level microwave (MW) irradiation-induced stress response and its effect on implantation or pregnancy in female mice. Twelve-week-old mice were exposed to MW radiation (continuous wave for 2 h/day for 45 days, frequency 2.45 GHz, power density=0.033549 mW/cm(2), and specific absorption rate=0.023023 W/kg). At the end of a total of 45 days of exposure, mice were sacrificed, implantation sites were monitored, blood was processed to study stress parameters (hemoglobin, RBC and WBC count, and neutrophil/lymphocyte (N/L) ratio), the brain was processed for comet assay, and plasma was used for nitric oxide (NO), progesterone and estradiol estimation. Reactive oxygen species (ROS) and the activities of ROS-scavenging enzymes- superoxide dismutase, catalase, and glutathione peroxidase-were determined in the liver, kidney and ovary. We observed that implantation sites were affected significantly in MW-irradiated mice as compared to control. Further, in addition to a significant increase in ROS, hemoglobin (p<0.001), RBC and WBC counts (p<0.001), N/L ratio (p<0.01), DNA damage (p<0.001) in brain cells, and plasma estradiol concentration (p<0.05), a significant decrease was observed in NO level (p<0.05) and antioxidant enzyme activities of MW-exposed mice. Our findings led us to conclude that a low level of MW irradiation-induced oxidative stress not only suppresses implantation, but it may also lead to deformity of the embryo in case pregnancy continues. We also suggest that MW radiation-induced oxidative stress by increasing ROS production in the body may lead to DNA strand breakage in the brain cells and implantation failure/resorption or abnormal pregnancy in mice.

Emerging role of relaxin in the maternal adaptations to normal pregnancy: implications for preeclampsia

Relaxin is an approximately 6-kilodalton peptide hormone secreted by the corpus luteum, and circulates in the maternal blood during pregnancy. Relaxin administration to awake, chronically instrumented, nonpregnant rats mimics the vasodilatory phenomena of pregnancy. Furthermore, immunoneutralization of relaxin or its elimination from the circulation during midterm pregnancy in awake rats prevents maternal systemic and renal vasodilation, and the increase in global arterial compliance. Human investigation, albeit limited through 2010, also reveals vasodilatory effects of relaxin in the nonpregnant condition and observations consistent with a role for relaxin in gestational renal hyperfiltration. Evidence suggests that the vasodilatory responses of relaxin are mediated by its major receptor, the relaxin/insulin-like family peptide 1 receptor, RFXP1. The molecular mechanisms of relaxin vasodilation depend on the duration of hormone exposure (ie, there are rapid and sustained vasodilatory responses). Newly emerging data support the role of Gα(i/o) protein coupling to phosphatidylinositol-3 kinase/Akt (protein kinase B)-dependent phosphorylation and activation of endothelial nitric oxide synthase in the rapid vasodilatory responses of relaxin. Sustained vasodilatory responses critically depend on vascular endothelial and placental growth factors, and increases in arterial gelatinase(s) activity. Gelatinases hydrolyze big endothelin (ET) at a gly-leu bond to form ET(1-32), which activates the endothelial ET(B)/nitric oxide vasodilatory pathway. Although the relevance of relaxin biology to preeclampsia is largely speculative at this time, there are potential tantalizing links that are discussed in the context of our current understanding of the etiology and pathophysiology of the disease.

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.

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.

Evolution of oxidative/nitrosative stress biomarkers during an open-field vaccination procedure in sheep: effect of melatonin

Melatonin has been shown to exert immunomodularory properties with broad application in veterinary medicine. In previous work we have described that subcutaneous coadministration of melatonin to seeps vaccinated against two stumps of A1 and C strains of Dichelobacter nodosus enhanced both the antibody titer and serum IgG levels to A1 and C strains of D. nodosus compared to vaccinated animals not treated with melatonin. Following a similar protocol here we have investigated the effect of a higher dose of melatonin (36mg/animal) in the improvement of the immune response and in the possible oxidative/nitrosative stress produced during the immunization protocol. Our results show that footrot vaccine application induced nitrosative but not oxidative stress at 42 days post-vaccination, which was neutralized by melatonin administration. On the other hand, melatonin improved the immune response with respect to our previous data increasing the time of permanence of antibodies in serum, opening new perspectives for melatonin as prophylactic drug.

Increased nitrite reductase activity of fetal versus adult ovine hemoglobin

Growing evidence indicates that nitrite, NO2-, serves as a circulating reservoir of nitric oxide (NO) bioactivity that is activated during physiological and pathological hypoxia. One of the intravascular mechanisms for nitrite conversion to NO is a chemical nitrite reductase activity of deoxyhemoglobin. The rate of NO production from this reaction is increased when hemoglobin is in the R conformation. Because the mammalian fetus exists in a low-oxygen environment compared with the adult and is exposed to episodes of severe ischemia during the normal birthing process, and because fetal hemoglobin assumes the R conformation more readily than adult hemoglobin, we hypothesized that nitrite reduction to NO may be enhanced in the fetal circulation. We found that the reaction was faster for fetal than maternal hemoglobin or blood and that the reactions were fastest at 50-80% oxygen saturation, consistent with an R-state catalysis that is predominant for fetal hemoglobin. Nitrite concentrations were similar in blood taken from chronically instrumented normoxic ewes and their fetuses but were elevated in response to chronic hypoxia. The findings suggest an augmented nitrite reductase activity of fetal hemoglobin and that the production of nitrite may participate in the regulation of vascular NO homeostasis in the fetus.

Circulating calcitonin gene-related peptide and its placental origins in normotensive and preeclamptic pregnancies

OBJECTIVE

The present study was designed to determine plasma calcitonin gene-related peptide concentration in both maternal and fetal circulations in normotensive and pre-eclamptic pregnancies and investigate whether placenta is 1 of its origins.

STUDY DESIGN

Maternal blood, cord blood, and villous tissue were collected from women in normotensive pregnancies and complicated with pre-eclampsia. Calcitonin gene-related peptide concentrations were determined by radioimmunoassay. Cellular localizations of calcitonin gene-related peptide messenger ribonucleic acid and protein expressions in placental villi were determined by in situ hybridization and immunohistochemistry.

RESULTS

The following results were reached: (1) maternal plasma calcitonin gene-related peptide concentrations increased with advancing gestation but fell after delivery; (2) both maternal and cord plasma calcitonin gene-related peptide concentrations were positively correlated with the infant birth weights; (3) compared with normotensive pregnancies, calcitonin gene-related peptide levels in both maternal and cord plasma decreased in pregnancies with pre-eclampsia; (4) in normotensive pregnancies, the plasma calcitonin gene-related peptide of the umbilical vein was higher than the umbilical artery, but no significant differences between vein and artery in pre-eclampsia; (5) calcitonin gene-related peptide messenger ribonucleic acid and protein were expressed by syncytiotrophoblast cells and villous vascular endothelial cells in normotensive pregnancies, but only weak or absent staining was observed in pre-eclamptic placentas; and (6) calcitonin gene-related peptide is secreted by villous tissue in explant culture in a time-dependent manner, but less calcitonin gene-related peptide was produced by villous tissues from patients with pre-eclampsia.

CONCLUSION

Calcitonin gene-related peptide may play potential roles in maternal hemodynamic adaptation and fetal growth. Decreased circulating calcitonin gene-related peptide levels may be involved in maternal-fetal pathophysiology of pre-eclampsia. It is novel that placenta villous tissues might be one of the potential sources of calcitonin gene-related peptide during pregnancy.

Umbilical vein plasma concentrations of asymmetrical dimethylarginine are increased in male but not female neonates delivered preterm: a pilot study

BACKGROUND

Infants born term have substantially elevated plasma concentrations of the endogenous nitric oxide synthase antagonist asymmetrical dimethylarginine (ADMA) that normalize with growth. The plasma levels of ADMA in preterm newborns are unknown.

SUBJECTS AND METHODS

Plasma concentrations of ADMA, symmetrical dimethylarginine (SDMA) and L-arginine were analyzed from venous umbilical cord blood samples of 19 preterm and 21 term infants by high performance liquid chromatography.

RESULTS

Male preterm newborns (n=11) had higher ADMA (median [95% confidence interval (CI)]: 1.90 [1.73-2.10] micromol/l) than females born preterm (n=8; 1.57 [1.24-1.69] micromol/l; p<0.005). In term born males (n=10) and females (n=11) ADMA was significantly lower than in preterm male infants (all p<0.005), and without sex differences. SDMA and L-arginine concentrations were comparable between all groups. ADMA correlated inversely with body weight in male preterm newborns (r=-0.67; p<0.03).

CONCLUSION

Male neonates delivered preterm have significantly higher umbilical cord venous plasma concentrations of ADMA compared to female neonates and infants born term. The sex difference and the time course of elevated ADMA may play a role in development and warrant further investigation.

Expression of phosphodiesterase 5 in maternal and fetal sheep

OBJECTIVE

Ovine pregnancy is associated with elevated levels of nitric oxide. Nitric oxide stimulates cyclic guanosine monophosphate (cGMP), which results in vascular smooth muscle relaxation/vasodilation. Phosphodiesterase type 5 regulates cGMP in the urogenital track. The present study was designed to determine message expression of phosphodiesterase type 5 in the myometrium, uterine vessels, and placentome of the sheep and phosphodiesterase type 5 protein expression in the maternal and fetal placentome.

STUDY DESIGN

Tissue was collected from 5 nonpregnant and 5 pregnant anesthetized animals (gestational day = 134 +/- 4) and frozen at -80 degrees C. Optimized reverse transcription-polymerase chain reaction was performed on all tissues, and immunohistochemistry was performed on the placentome only.

RESULTS

Phosphodiesterase type 5 messenger ribonucleic acid levels were significantly higher in the myometrium and placentome, compared with the maternal blood vessels. Phosphodiesterase type 5 protein was immuno-localized to the vascular smooth muscle of the maternal vessels, stroma, and placental capsule only.

CONCLUSION

Although phosphodiesterase type 5 messenger ribonucleic acid was present in the fetal placenta, phosphodiesterase type 5 protein was expressed only in maternally derived placental tissue. This suggests that regulation of cGMP levels and vascular tone in the umbilical circulation differs from the uterine circulation.

Effects of nitric oxide and prostacyclin on hemodynamic response by big endothelin-1 in near term fetal sheep

AIMS

To measure plasma concentrations of endothelin (ET)-1, NO metabolites (nitrate/nitrite; NOx) and 6-keto PGF1 alpha (PGF1 alpha) in maternal and fetal sheep blood, and to evaluate the effects of big ET-1 on hemodynamic response, blood gases and NO and 6-keto PGF1 alpha production in near term fetal sheep.

METHODS

Hemodynamic parameters were measured during infusion of big ET-1 into the carotid vein in chronically catheterized fetal sheep on day 125 of gestation. Fetal arterial blood samples were obtained for ET-1, PGF1 alpha) and nitrate/nitrite (NOx) measurements.

RESULTS

ET-1, NOx and PGF1 alpha plasma concentrations were all significantly higher in fetal compared with the maternal plasma. Big ET-1 significantly decreased fetal systolic and diastolic blood pressure and significantly increased fetal heart rate. Big ET-1 stimulated plasma PGF1 alpha), but not NOx , concentration.

CONCLUSIONS

Circulatory regulating factors in the fetus were up-regulated. The effects of ET-1 on fetal hemodynamic response may be mediated via prostacyclin, but not via the NO pathway.

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.

An overview of endothelium-derived hyperpolarising factor (EDHF) in normal and compromised pregnancies

Normal pregnancy is associated with decreased peripheral vascular resistance, although the mechanisms are poorly understood. Pre-eclampsia is characterised by increased vessel resistance and a decreased relaxant capacity, contributing to the associated hypertension, multi-organ damage and intra-uterine growth restriction. An endothelium-derived vasoactive substance-endothelium-derived hyperpolarising factor may be responsible for the physiological changes in the maternal vasculature. This is a review of the current understanding of the complexities of vessel behaviour. Evidence is reviewed to support the possible contribution of endothelium-derived hyperpolarising factor to the compromised vascular state in pre-eclampsia. This is an important area of research which may help to understand further the pathogenesis of this specific pregnancy related disease, that contributes greatly to maternal and fetal morbidity and mortality.

Nitric oxide synthase activity in human trophoblast, term placenta and pregnant myometrium

To investigate the possible role of nitric oxide (NO) produced locally or intramurally in the quiescence of the pregnant myometrium, nitric oxide synthase (NOS) activity was measured in samples from first trimester (villous, and non villous-trophoblast), term placenta and pregnant myometrium. Trophoblast tissue was obtained from psychosocial termination of pregnancy (9-12 weeks' gestation) whereas placenta and myometrium, from the same patient, at deliveries by Caesarean section. NOS activity was measured in both cytosolic and particulate fractions by the formation of 14C-citrulline from 14C-arginine. Western immunoblotting was used to identify the endothelial NOS (eNOS) and neuronal (nNOS) isoforms. The activity of NOS in particulate fractions from all preparations was considerably higher than the cytosolic fractions. Activity in all fractions except the myometrium was highly Ca-dependent. More than 50% of particulate NOS from the myometrium was Ca-independent. NOS activity was highest in the villous trophoblast and there was a significant difference between the villous and non-villous trophoblast. In placenta and myometrium, NOS was 2-4 fold and 20-28-fold lower than the villous trophoblast, respectively. Western blot analysis showed clearly eNOS in the particulate fraction and a weak eNOS band in the cytosolic fractions, whereas nNOS was not detectable in any of the fractions. In view of the marginal activity of NOS in the myometrium, NO produced by the trophoblast and placenta could play a significant role in maintaining uterine quiescence by paracrine effect.

Possible mechanisms underlying pregnancy-induced changes in uterine artery endothelial function

The last 10 years has seen a dramatic increase in our understanding of the mechanisms underlying the pregnancy-specific adaptation in cardiovascular function in general and the dramatic changes that occur in uterine artery endothelium in particular to support the growing fetus. The importance of these changes is clear from a number of studies linking restriction of uterine blood flow (UBF) and/or endothelial dysfunction and clinical conditions such as intrauterine growth retardation (IUGR) and/or preeclampsia in both humans and animal models; these topics are covered only briefly here. The recent developments that prompts this review are twofold. The first is advances in an understanding of the cell signaling processes that regulate endothelial nitric oxide synthase (eNOS) in particular (Govers R and Rabelink TJ. Am J Physiol Renal Physiol 280: F193-F206, 2001). The second is the emerging picture that uterine artery (UA) endothelial cell production of nitric oxide (NO) as well as prostacyclin (PGI2) may be as much a consequence of cellular reprogramming at the level of cell signaling as due to tonic stimuli inducing changes in the level of expression of eNOS or the enzymes of the PGI2 biosynthetic pathway (cPLA2, COX-1, PGIS). In reviewing just how we came to this conclusion and outlining the implications of such a finding, we draw mostly on data from ovine or human studies, with reference to other species only where directly relevant.

Plasma adrenomedullin levels in pregnancies with appropriate for gestational age and small for gestational age infants

AIMS

To evaluate whether maternal and fetal plasma adrenomedullin levels in pregnancies with small for gestational age (SGA) infants are different from those in pregnancies with appropriate for gestational age (AGA) infants.

METHODS

Maternal and fetal circulating adrenomedullin levels were compared between 62 pregnancies with AGA (43 delivered vaginally and 19 delivered by elective cesarean section) and 28 pregnancies with SGA (20 delivered vaginally and 8 delivered by elective cesarean section) at birth. Plasma adrenomedullin levels were measured from maternal and cord venous blood samples using a radioimmunoassay. Umbilical artery blood pH was also measured.

RESULTS

There were no significant differences for maternal total adrenomedullin levels, mature adrenomedullin levels, and its ratio among the groups. There were also no significant differences for fetal total adrenomedullin levels, mature adrenomedullin levels, and its ratio among the groups. In the AGA group delivered vaginally, fetal mature/total adrenomedullin ratio (mean +/- standard error, 16.6 +/- 0.7%) was significantly higher than the maternal ratio (13.8 +/- 0.6%) (p < 0.05). In the SGA group delivered vaginally, fetal mature/total adrenomedullin ratio (18.5 +/- 1.0%) was also significantly higher than the maternal ratio (14.5 +/- 0.6%) (p < 0.05). There was no significant difference in umbilical artery blood pH among the groups.

CONCLUSIONS

These results suggest that maternal and fetal plasma circulating adrenomedullin levels may play a role in maternal and fetal cardiovascular adaptation during delivery in pregnancies with both AGA and SGA infants.

Pregnancy enhances endothelium-dependent relaxation of ovine uterine artery: role of NO and intracellular Ca(2+)

The present study tested the hypothesis that the pregnancy-associated increase in endothelium-dependent relaxation of the uterine artery was mediated primarily by an increase in nitric oxide (NO) release, resulting in a reduction in smooth muscle intracellular Ca(2+) concentration ([Ca(2+)](i)). Uterine arteries obtained from nonpregnant and near-term (140 days gestation) pregnant sheep were used. The Ca(2+) ionophore A23187 induced endothelium-dependent relaxations in both nonpregnant and pregnant uterine arteries, with an increased relaxation in the pregnant tissue. In contrast, endothelium-independent relaxations induced by sodium nitroprusside were the same in nonpregnant and pregnant arteries. In addition, removal of the endothelium significantly increased noradrenaline-induced contractions in pregnant, but not nonpregnant, uterine arteries. In accordance, pregnancy increased both basal and A23187-stimulated NO releases in the uterine artery. Simultaneous measurement of tension and [Ca(2+)](i) in the smooth muscle demonstrated a linear correlation with the slope of unity between A23187-induced relaxation and the reduction of [Ca(2+)](i) in both nonpregnant and pregnant uterine arteries. The A23187-induced reduction of [Ca(2+)](i) was significantly enhanced in pregnant, compared with nonpregnant, uterine arteries. The results indicate that pregnancy increases NO release, which, through decreasing [Ca(2+)](i) in the smooth muscle, accounts for the increased endothelium-dependent relaxation of the uterine artery. Signal transduction pathways distal to NO production are not changed by pregnancy.

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.

Physiologic role of nitric oxide in the maintenance of uterine quiescence in nonpregnant and pregnant sheep

OBJECTIVE

This study evaluated the role of nitric oxide in the maintenance of uterine quiescence in nonpregnant and pregnant ewes.

STUDY DESIGN

Sixteen ovariectomized nonpregnant and 10 pregnant (115 days' gestation) chronically instrumented ewes were studied. Uterine contractility was assessed by electromyography and intrauterine pressure recordings. Nitric oxide synthase inhibition was induced with nitro-L -arginine methyl ester or aminoguanidine (4. 5 mg/kg per hour) given during estrogen replacement with 17beta-estradiol (100 microg/d) or in late gestation. In the pregnant group we evaluated the ability of nitric oxide synthase inhibition to alter the responsiveness to oxytocin-induced uterine contractility. Blood pressure and common internal iliac artery blood flow were assessed to confirm nitric oxide synthase inhibition. In addition, the effects of the nitric oxide donor nitroglycerin and the cyclooxygenase inhibitor indomethacin were studied in nonpregnant sheep. The effect of nitric oxide in vitro on myometrial spontaneous and induced contractions was also studied.

RESULTS

In nonpregnant estrogen-replaced sheep, nitric oxide synthase inhibition and nitroglycerin administration did not alter uterine contractility, despite significant changes in blood pressure. In contrast, indomethacin decreased electromyographic results to 70% of baseline after 1 hour and 47% after 2 hours. In pregnant ewes nitric oxide synthase inhibition failed to alter uterine contractility in response to oxytocin. These findings are in contrast to results of the in vitro study in which nitric oxide was shown to relax sheep myometrium.

CONCLUSION

The absence of significant effects of nitric oxide synthase inhibition and nitric oxide donors on uterine contractility in vivo suggests that nitric oxide does not play a physiologic role in the regulation of uterine contractility in nonpregnant or pregnant ewes.

Evidence of a nonendothelial source of nitric oxide in the isolated perfused hindlimb vasculature of the pregnant rat

OBJECTIVE

This study was undertaken to further elucidate the roles of the vascular endothelium and nitric oxide (NO) in the regulation of vascular tone and constrictor responsiveness in pregnancy.

METHODS

The perfusion pressure-flow relationship was measured in isolated, perfused, norepinephrine-constricted (1) endothelium-intact, (2) endothelium-denuded, and (3) N omega-nitro-L-arginine methyl ester (L-NAME)-treated hindlimbs from nonpregnant and term-pregnant rates.

RESULTS

Baseline perfusion pressure at a flow rate of 2 mL/min was similar (approximately 20 min Hg) in all hindlimbs. Norepinephrine (0.5 muM) increased perfusion pressure in both nonpregnant (+21.6 +/- 2.4 mm Hg) and pregnant (+13.6 +/- 0.9 mm Hg) endothelium-intact rat hindlimbs. In nonpregnant rat hindlimbs, endothelium removal and L-NAME increased norepinephrine vasoconstriction similarly (+44.3 +/- 4.0 mm Hg and +46.4 +/- 8.6 mm Hg, respectively). In pregnant-rat hindlimbs, L-NAME increased norepinephrine vasoconstriction by 43.5 +/- 10.8 mm Hg, similar to that in nonpregnant-rat hindlimbs, but endothelium removal only increased norepinephrine vasoconstriction by 28.0 +/- 2.2 mm Hg. Perfusion pressure increased linearly as the flow rate was increased from 2 to 4 mL/min, and the slope of the regression line of the endothelium-intact pregnant-rat hindlimbs (7.0 +/- 0.6) was slightly, but not significantly, lower than that of the nonpregnant-rat hindlimbs (9.6 +/- 0.9). Endothelium removal increased the slopes of the regression lines, but that of pregnant-rat hindlimbs (12.8 +/- 1.6) was significantly lower (p < or = 0.05) than that of the nonpregnant-rat hindlimbs (23.8 +/- 1.8). L-NAME caused a similar increase in the pressure-flow slopes of nonpregnant-rat (36.5 +/- 3.4) and pregnant-rat (32.1 +/- 5.3) hindlimbs.

CONCLUSIONS

These results suggest that nonendothelial nitric oxide production may be increased in the hindlimb resistance vasculature of the pregnant rat, which may play a role in the normal pregnancy blunting of constrictor responsiveness and reduction of vascular resistance.

Production and excretion of nitrate by human newborn infants: neonates are not little adults

Endothelium-derived relaxing factor, identified as nitric oxide or its adducts, is metabolized to nitrate and excreted in the urine. Since blood pressures are lower in newborn infants compared to adults, we hypothesized that newborn infants would have increased excretion of nitrate on the day of birth. Neonatal urine was collected before 24 h of age when exogenous intake of nitrate was low. Two different analytical methods showed that nitrate accounted for >99% of nitrogen oxides in urine of healthy neonates and adults. The absolute micromolar concentration of nitrate in urine from infants was significantly below that of adults. When nitrate content was standardized for the reduced renal function in the newborn infant (creatinine content) and body mass (kilogram weight), the concentration of nitrate in neonatal urine was significantly higher than that of adults. Nitrate concentrations in the urine of prematurely born infants were twice that of nitrate measured in urine from term infants. These findings suggested that nitric oxide is produced in larger intravascular quantities in newborn infants versus adults. Thus, we postulated that nitric oxide released from a nitrosothiol would be metabolized to nitrate more readily by neonatal erythrocytes compared to red blood cells obtained from adults. Neonatal erythrocytes, suspended at concentrations of 8, 12, or 16 g per deciliter of hemoglobin, produced 1.7- to 2.1-fold more nitrate than equivalent hemoglobin concentrations of adult erythrocytes that were each incubated with S-nitroso-N-acetylpenicillamine (100 microM) over a 2-h period. Taken together, the studies of urinary nitrate in newborn infants and the ability of neonatal erythrocytes to generate nitrate are consistent with a robust production of nitric oxide immediately after birth.

Effect of nitric oxide synthase inhibition on the uterine vasculature of the late-pregnant ewe

OBJECTIVES

We studied the role of nitric oxide in the maintenance of uterine vascular tone during pregnancy.

STUDY DESIGN

Late-pregnant ewes were instrumented with ultrasonographic flow probes on the left and right main uterine arteries. A catheter was passed retrogradely into 1 uterine artery from a tributary. In 14 animals nitric oxide synthase inhibitor (N omega-nitro-L-arginine methyl ester; L-NAME) was infused at 2 or 20 mg/kg during a 1-minute period into either the main left or right uterine artery.

RESULTS

The nitric oxide synthase inhibitor (20 mg/kg), infused into 1 uterine artery, significantly decreased uterine blood flow (P <.001) bilaterally, increased (P <.05) mean arterial pressure, and decreased heart rate (P <.05). The compound (when infused at 2 mg/kg) also significantly (P <.05) decreased uterine blood flow in the artery ipsilateral to, but not contralateral to, the infusion, with no change in mean arterial pressure and a decrease (P <.05) in heart rate.

CONCLUSION

During ovine pregnancy, endogenous nitric oxide production contributes to uterine vasodilatation.

Endothelial nitric oxide release in isolated perfused ovine uterine arteries: effect of pregnancy

The present study was designed to determine the release of endothelial nitric oxide, measured as combined nitric oxide, nitrite and nitrate (NOx), in isolated perfused uterine arteries obtained from nonpregnant and pregnant sheep. Noradrenaline produced concentration-dependent increases in perfusion pressure in both nonpregnant and pregnant uterine arteries with pD2 values of 5.1+/-0.07 and 4.6+/-0.04, respectively. The maximum responses were 300.8+/-8.8 mmHg for nonpregnant arteries and 86.9+/-1.3 mmHg for pregnant ones. N(G)-nitro-L-arginine increased noradrenaline-mediated maximum response in the pregnant (86.9+/-1.3 to 144.6+/-5.1 mmHg), but not in the nonpregnant, uterine arteries. The basal level of NOx was significantly higher in pregnant than in nonpregnant uterine arteries (346.1+/-63.2 vs. 86.0+/-20.6 pmol/ml). The calcium ionophore A23187 and adenosine triphosphate produced concentration-dependent increases in NOx release in both nonpregnant and pregnant arteries. Compared to the nonpregnant tissue, the agonist-induced increase in NOx release was significantly enhanced in the pregnant uterine artery. In accordance, endothelial NO synthase protein expression in pregnant uterine artery was 197% of that in nonpregnant artery. These data indicate that in the uterine artery, pregnancy increases both basal and agonist-induced release of endothelial nitric oxide, which is likely to play a key role in attenuated vascular reactivity of the uterine artery to vasoconstrictors during the course of pregnancy.

Long-term high-altitude hypoxia increases plasma nitrate levels in pregnant ewes and their fetuses

OBJECTIVE

The study was designed to determine whether moderate chronic hypoxia changes plasma nitrate concentrations in nonpregnant and pregnant, near-term ewes and their fetuses.

STUDY DESIGN

Pregnant ewes were put into either a normoxic control group or a chronically hypoxic group maintained at high altitude (3820 m, PaO 2 60 mm Hg) from day 30 of gestation. On day 140 blood samples were collected from the maternal jugular vein and from the fetal umbilical artery and vein. Blood samples were also obtained from normoxic nonpregnant adult ewes and nonpregnant adult ewes exposed to high-altitude hypoxia for 110 days. Plasma nitrate concentrations were determined through chemiluminescence assay.

RESULTS

Within normoxic groups plasma nitrate concentrations of pregnant, near-term ewes were significantly elevated compared with those of nonpregnant ewes (17.4 +/- 0.3 vs 6.8 +/- 0.4 micromol/L, P <.0001). Fetal umbilical arterial and venous plasma nitrate concentrations did not differ from each other in the normoxic group (44.7 +/- 4.2 and 44.0 +/- 4.3 micromol/L, respectively) but were significantly higher than those of their mothers (P <.0001). Compared with normoxic groups, pregnant ewes with chronic hypoxia showed significantly increased plasma nitrate concentrations (30.9 +/- 1.8 micromol/L, P <.001), as did their fetuses (arterial 146.1 +/- 14.7 micromol/L, venous 154.5 +/- 14.6 micromol/L, P <.0001), but nonpregnant ewes with chronic hypoxia did not (7.5 +/- 0.3 micromol/L, P >.05).

CONCLUSIONS

We conclude that (1) production of endogenous nitric oxide is increased by pregnancy in sheep and is higher in the fetus than in the mother, and (2) moderate chronic hypoxia selectively augments nitric oxide production in the pregnant ewe's circulation and, even more profoundly, in the fetal lamb's circulation.

Major vasodilator role for nitric oxide in the gastrointestinal circulation of the mid-gestation fetal lamb

As nitric oxide (NO) may be a particularly important vasodilator in early life, we investigated its role in the regulation of the gastrointestinal (GI) circulation at mid-gestation. Cardiac output and GI blood flow were measured by the radioactive microsphere technique in eight chronically instrumented and unanesthetized mid-gestation fetal sheep. Mean arterial pressure (MAP), heart rate, blood flow, oxygen delivery, and vascular resistance were determined before and after infusion of the specific NO synthase inhibitor, Nomega-nitro-L-arginine (L-NNA) at doses of 10 and 25 mg/kg. In response to L-NNA infusion, MAP increased (p < 0.01) and combined ventricular output decreased (p < 0.001). GI blood flow and oxygen delivery decreased and vascular resistance increased in the stomach and all segments of the small and large intestine (all p < 0.001). The greatest reduction in blood flow was in the small intestine (p < 0.01) and the basal differential pattern of small intestinal blood flow exceeding large intestinal flow was completely abolished. These changes were much greater than those previously described in late-gestation fetuses. Our results suggest that, at mid-gestation, NO plays a major role in the regulation of blood flow and vascular tone across all segments of the fetal GI tract, with its effects being more pronounced than later in development.

Role of nitric oxide on the central hemodynamic response to acute volume expansion in the pregnant rat

OBJECTIVES

Our hypothesis was that during pregnancy nitric oxide acts as mediator in the hemodynamic response to volume expansion.

STUDY DESIGN

The study was performed on 12 rats on days 19 to 20 of pregnancy. Six rats were injected intravenously with hexamethonium bromide plus the inhibitor of nitric oxide synthase L-nitro-arginine methyl ester. For a control group, six rats were injected with hexamethonium bromide plus the L-nitro-arginine methyl ester vehicle. A volume expansion (1.2% body weight) was performed in both groups by intravenous infusion of bovine albumin (6%) solution.

RESULTS

In the control group volume expansion induced a hyperdynamic circulation characterized by increased cardiac output, decreased total vascular resistance, and no change in arterial pressure; however, in the study group volume expansion induced a pressor response without hyperdynamic circulation.

CONCLUSION

During pregnancy volume expansion induces a hyperdynamic circulatory state possibly mediated by nitric oxide release. A defect in the release of nitric oxide may be responsible for an inadequate hemodynamic response to volume expansion.

Plasma concentrations of asymmetric dimethylarginine, a natural inhibitor of nitric oxide synthase, in normal pregnancy and preeclampsia

OBJECTIVE

We investigated the change in the plasma concentration of asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthase, in early-, mid-, and late-gestation normotensive pregnancies and in gestational age-matched preeclamptic pregnancies and compared the observed changes with changes in blood pressure.

STUDY DESIGN

Blood pressure and peripheral plasma asymmetric dimethylarginine concentrations were measured in 20 nonpregnant and 145 pregnant women (33 first-trimester, 50 second-trimester, and 44 third-trimester normotensive pregnancies and 18 third-trimester pregnancies complicated by preeclampsia). In 23 normotensive pregnancies serial plasma asymmetric dimethylarginine concentrations were measured. Statistical analysis was by analysis of variance and linear regression.

RESULTS

The blood pressures recorded throughout normal pregnancy were significantly lower than in nonpregnant subjects (p < 0.0001). The mean systolic, diastolic, and average blood pressures were significantly higher in the second-trimester groups than in the first-trimester groups, whereas in the third trimester average and diastolic blood pressures were significantly higher than in the second trimester. The mean (+/-SD) systolic and diastolic blood pressures in third-trimester preeclamptic patients was 157.7 +/- 11.2 and 110.9 +/- 8.5 mm Hg. The mean plasma asymmetric dimethylarginine concentration in nonpregnant women was 0.82 +/- 0.31 micromol/L (significantly higher than in normotensive pregnancy, p < 0.0001). The plasma asymmetric dimethylarginine concentration was also significantly higher in second-trimester than in first-trimester normotensive groups (respectively, 0.52 +/- 0.20 micromol/L and 0.40 +/- 0.15 micromol/L, p = 0.001) and was higher in third-trimester normotensive pregnancy 0.56 +/- 0.23 micromol/L than it was in the second trimester. The asymmetric dimethylarginine concentration in third-trimester preeclamptic patients was 1.17 +/- 0.42 micromol/L (p < 0.0001 vs normotensive third-trimester subjects).

CONCLUSIONS

It is well recognized that blood pressure falls in early normal pregnancy and rises again toward term. These studies show that the early fall in blood pressure is accompanied by a significant fall in the plasma asymmetric dimethylarginine concentration. Later in pregnancy circulating concentrations increase and, when pregnancy is complicated by preeclampsia, concentrations are higher than in the nonpregnant state. Our data support a role for both asymmetric dimethylarginine and nitric oxide in the changes in blood pressure seen in both normal and preeclamptic pregnancy.