Maternal and fetal atrial natriuretic peptide levels at delivery from normal and growth retarded pregnancies

Significance of Atrial and Brain Natriuretic Peptide Measurements in Fetuses With Heart Failure

Fetal heart failure is mainly caused by congenital heart defect and arrhythmia. It is difficult to appropriately diagnose the severity of fetal heart failure simply by ultrasonography because the development of a fetal heart in fetoplacental circulation and how well the fetal myocardium can adapt to postnatal cardiopulmonary circulation are challenging to assess. In adult cardiology, natriuretic peptides (NPs) are the most useful biomarker of heart failure; however, studies investigating NP levels in the fetuses and amniotic fluid are quite limited. Furthermore, little is known about their production and metabolism. This review summarized the most relevant findings on NP levels in the umbilical cord blood and amniotic fluid. The findings can then extend their use as a diagnostic biomarker of heart failure in fetuses with congenital heart defect and/or arrhythmia.

ANP-stimulated Na+ secretion in the collecting duct prevents Na+ retention in the renal adaptation to acid load

We have recently reported that type A intercalated cells of the collecting duct secrete Na⁺ by a mechanism coupling the basolateral type 1 Na⁺-K⁺-2Cl^- cotransporter with apical type 2 H⁺-K⁺-ATPase (HKA2) functioning under its Na⁺/K⁺ exchange mode. The first aim of the present study was to evaluate whether this secretory pathway is a target of atrial natriuretic peptide (ANP). Despite hyperaldosteronemia, metabolic acidosis is not associated with Na⁺ retention. The second aim of the present study was to evaluate whether ANP-induced stimulation of Na⁺ secretion by type A intercalated cells might account for mineralocorticoid escape during metabolic acidosis. In Xenopus oocytes expressing HKA2, cGMP, the second messenger of ANP, increased the membrane expression, activity, and Na⁺-transporting rate of HKA2. Feeding mice with a NH₄Cl-enriched diet increased urinary excretion of aldosterone and induced a transient Na⁺ retention that reversed within 3 days. At that time, expression of ANP mRNA in the collecting duct and urinary excretion of cGMP were increased. Reversion of Na⁺ retention was prevented by treatment with an inhibitor of ANP receptors and was absent in HKA2-null mice. In conclusion, paracrine stimulation of HKA2 by ANP is responsible for the escape of the Na⁺-retaining effect of aldosterone during metabolic acidosis.

Plasma natriuretic peptide levels in fetuses with congenital heart defect and/or arrhythmia

OBJECTIVE

Diagnosing fetal heart failure remains challenging because it is difficult to know how well the fetal myocardium will perform as loading conditions change. In adult cardiology, natriuretic peptides (NPs) are established markers of heart failure. However, the number of studies investigating NP levels in fetuses is quite limited. The aim of this study was to evaluate the significance of plasma NP levels in the assessment of heart failure in fetuses with a congenital heart defect (CHD) and/or arrhythmia.

METHODS

This was a prospective observational study conducted at a tertiary pediatric cardiac center. A total of 129 singletons with CHD and/or arrhythmia and 127 controls were analyzed between 2012 and 2015. Umbilical cord plasma atrial NP, brain NP and N-terminal pro-brain NP levels at birth were compared with ultrasonography findings indicating fetal heart failure, such as cardiovascular profile (CVP) score and morphological characteristics.

RESULTS

Fetuses with CHD and/or arrhythmia had higher NP levels than did controls (P < 0.01). NP levels of fetuses with CHD and/or arrhythmia were correlated inversely with CVP score (P for trend < 0.01). No differences in NP levels were found in fetuses with CHD and/or arrhythmia and a CVP score of ≥ 8 in comparison to controls. Multivariate analysis showed that a CVP score of ≤ 5, tachy- or bradyarrhythmia at birth, preterm birth and umbilical artery pH < 7.15 were associated independently with high NP levels (P < 0.01). Among fetuses with a CVP score of ≤ 7, abnormal venous Doppler sonography findings were significantly more common and more severe in fetuses with tachy- or bradyarrhythmia than in those with CHD, and those with tachy- or bradyarrhythmia had higher NP levels than did those with CHD (P = 0.01). Fetuses with right-heart defect and moderate or severe tricuspid valve regurgitation had significantly higher NP levels than did fetuses with other types of CHD (P < 0.01).

CONCLUSIONS

Plasma NP levels in fetuses with CHD and/or arrhythmia are correlated with the severity of fetal heart failure. Elevated NP levels are attributed mainly to an increase in central venous pressure secondary to arrhythmia or atrioventricular valve regurgitation due to CHD, rather than to the morphological abnormality itself. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Copeptin: a marker for stress reaction in fetuses with intrauterine growth restriction

OBJECTIVE

To compare venous cord plasma concentrations of 4 vasoactive peptide precursors: carboxy-terminal proarginine vasopressin, CT-prondothelin (ET)-1, midregional proadrenomedullin, and MR-proatrial natriuretic peptide, between fetuses with intrauterine growth restriction and appropriate for gestational age controls.

STUDY DESIGN

Matched-pair analysis of 12 fetuses with significant intrauterine growth restriction and 42 healthy appropriate for gestational age control fetuses. All infants were singletons, delivered by elective section after 34 weeks and without chromosomal abnormalities.

RESULTS

Umbilical cord plasma copeptin levels (median [range]) were 4-fold higher in intrauterine growth restriction infants than in matched appropriate for gestational age controls: 23.2 (6.7-449) vs 5.1 (2.5-53) pmol/L (P < .001). Multivariate regression analysis revealed an association between copeptin and umbilical artery resistance index z-score (P = .034). The 3 other precursor peptides showed no changes.

CONCLUSION

High copeptin concentrations in the cord blood of intrauterine growth restriction newborns reflect a fetal stress response and support the fetal programming hypothesis.

Natriuretic peptide levels in intrauterine growth-restricted fetuses with absent and reversed end-diastolic flow of the umbilical artery in relation to ductus venosus flow velocities

OBJECTIVE

To determine if changes in natriuretic peptide levels [propeptide of atrial natriuretic peptide (proANP) and N-terminal propeptide of brain natriuretic peptide (NT-proBNP)] can be demonstrated in fetuses with serious growth restriction and Doppler ultrasonographic findings of hemodynamic compromise.

METHOD

Natriuretic peptides of the umbilical vein (proANP and NT-proBNP), arterial and venous blood gases, as well as lactate levels of the umbilical vein were determined in 38 appropriate for gestational age (AGA) fetuses, and 24 intrauterine growth-restricted (IUGR) fetuses with absent (zero-flow) and 17 IUGR fetuses with reversed end-diastolic flow (reverse-flow) of the umbilical artery.

RESULTS

A continuous increase in natriuretic peptides in the presence of progressive deterioration was shown. ANP concentrations were significantly lower in the AGA group (mean 818 fmol/mL; range 508-991 fmol/mL) than the zero-flow group (mean 19,680 fmol/mL; range 13,680-25,080 fmol/mL) and the reverse-flow group (mean 33,880 fmol/mL; range 24,365-41,786 fmol/mL). Significant differences were further demonstrated in BNP concentrations of the AGA group (mean 32 fmol/L; range 25-38 fmol/L), zero-flow group (mean 1191 fmol/L; range 908-1655 fmol/L), and reverse-flow group (mean 3063 fmol/L; range 1281-4968 fmol/L). Additionally, significant differences in lactate concentrations were observed for the three groups: AGA, 2.6 mmol/L (range 2-3 mmol/L); zero-flow group, 4.1 mmol/L (range 3.3-5 mmol/L); and reverse-flow group, 7.7 mmol/L (range 5.9-13.7 mmol/L). Increased ANP levels correlated with the arterial base excess and lactate concentrations, as well as with the flow velocities in the ductus venosus during atrial contraction (a-wave), and both ductus venosus indices (S-a)/D and (S-a)/V(mean). No correlations were established for BNP.

CONCLUSIONS

As components of a compensatory mechanism, natriuretic peptides exert an influence on the cardiovascular function of the fetus.

Control of the fetoplacental circulation

This year marks the 250th anniversary of the discovery by William Hunter of the existence of two distinct circulations within the human placenta. Until relatively recently the placenta has been viewed with “respect” – a passive structure which occasionally elicited fear and anxiety if implanted either too low or too deep. More recently our understanding of perinatal physiology, blood flow regulation and epidemiological data linking prenatal events with adult disease has created renewed interest in the placenta. This review will focus on the regulation of fetal blood flow in the placenta, the possible mechanisms whereby it may be deranged and why this might be relevant to adult disease.

Ultrasonographic and biochemical markers of human fetal cardiac dysfunction in placental insufficiency

BACKGROUND

Placental insufficiency may lead to fetal cardiovascular compromise. We sought to determine whether ultrasonographic parameters of fetal cardiovascular function correlate with umbilical arterial levels of biochemical markers of myocardial dysfunction and damage in placental insufficiency.

METHODS AND RESULTS

In 48 fetuses with placental insufficiency, umbilical artery blood was obtained at delivery for assessment of N-terminal peptide of proatrial natriuretic peptide (NT-proANP) and cardiac troponin-T (cTnT). Group 1 fetuses (n=12) had normal NT-proANP and cTnT serum concentrations. Group 2 fetuses (n=25) showed increased NT-proANP (>1145 pmol/L) and normal cTnT values. Group 3 fetuses (n=11) had increased NT-proANP and cTnT (>0.10 ng/mL) levels. The ultrasonographic parameters of fetal cardiovascular function were compared between the groups. Pulsatility indices for veins of the ductus venosus, left hepatic vein, and inferior vena cava correlated significantly with NT-proANP levels. In group 3, ductus venosus, left hepatic vein, and inferior vena cava pulsatility indices for veins were higher (P<0.01) than in groups 1 and 2. The proportion of left ventricular cardiac output of combined cardiac output was greater (P<0.05) and that of right ventricle was smaller (P<0.05) in group 3 than in group 2. In group 3, tricuspid regurgitation was noted most often (P<0.05), and right ventricular fractional shortening was less (P<0.01) than in group 2.

CONCLUSIONS

Pulsatility in human fetal systemic veins correlated significantly with the cardiac secretion of ANP. Fetuses with myocardial damage demonstrate increased systemic venous pressure, a change in the distribution of cardiac output toward the left ventricle, and a rise in right ventricular afterload.

Adrenomedullin in mammalian embryogenesis

Here are summarized data supporting that adrenomedullin (AM) is a multifunctional factor involved in the complex regulatory mechanisms of mammalian development. During rodent embryogenesis, AM is first expressed in the heart, followed by a broader but also defined spatio-temporal pattern of expression in vascular, neural, and skeletal-forming tissues as well as in the main embryonic internal organs. AM pattern of expression is suggestive of its involvement in the control of embryonic invasion, proliferation, and differentiation processes, probably through autocrine or paracrine modes of action. AM levels in fetoplacental tissues, uterus, maternal and umbilical plasma are highly increased during normal gestation. These findings in addition to other physiological and gene targeting studies support the importance of AM as a vasorelaxant factor implicated in the regulation of maternal vascular adaptation to pregnancy, as well as of fetal and fetoplacental circulations. AM is also present in amniotic fluid and milk, which is suggestive of additional functions in the maturation and immunological protection of the fetus. Altered expression of AM has been found in some gestational pathologies, although it is not yet clear whether this corresponds to causative or compensatory mechanisms. Future studies in regard to the distribution and expression levels of the molecules known to function as AM receptors, together with data on the action of complement factor H (an AM binding protein), may help to better define the roles of AM during embryonic development.

Atrial natriuretic factor in amniotic fluid and in maternal venous blood of pregnancies with fetal cardiac malformations and chromosomal abnormalities

OBJECTIVE

We evaluated the levels of atrial natriuretic factor (ANF) in amniotic fluid and in maternal venous blood in pregnancies with fetal cardiac malformations and chromosomal abnormalities.

METHOD

Between the 16th and 18th week of pregnancy, 151 women were divided into three groups. Group A included patients at lowest risk, carrying a fetus with a normally developing heart and normal karyotype (control group). Group B included women with a fetus suffering from cardiac malformations, with or without associated chromosomal abnormalities. Group C included women carrying a fetus affected with chromosomal abnormalities without congenital cardiopathies. ANF was evaluated by radioimmunoassay.

RESULTS

In maternal venous blood, the mean levels of ANF were 42.1, 53.1 and 38.7 pg/ml in groups A, B and C, respectively. In amniotic fluid, the mean levels of ANF were 34.2, 101.8 and 35.8 pg/ml in groups A, B and C, respectively. In group A (control group) there was no statistical difference in ANF levels across the gestational age range of 16-18 weeks, either in amniotic fluid or in maternal venous blood. A significant difference of ANF content in maternal venous blood was revealed in comparing group A with group B (p < 0.01), and group C with group B (p < 0.01). A statistically significant difference in ANF levels was also found in amniotic fluid between group A and group B (p < 0.01), and between group C and group B (p < 0.01). No statistically significant differences were found between group C and group A in comparing ANF levels in maternal venous blood and amniotic fluid.

CONCLUSION

ANF levels in amniotic fluid and in maternal venous blood are increased early in the case of fetuses with cardiac malformations, with or without associated karyotype alteration. Chromosomally abnormal fetuses without heart malformations have normal ANF levels. These results could be useful for elucidating fetal pathophysiology mechanisms.

Amniotic fluid nitric oxide and uteroplacental blood flow in pregnancy complicated by intrauterine growth retardation

OBJECTIVE

To examine the correlation between placental nitric oxide production and uteroplacental blood flow.

PARTICIPANTS

Thirty-one pregnant women with fetuses with intrauterine growth retardation and 27 normal pregnancies as controls.

DESIGN

Correlation between amniotic fluid measurements of nitrite metabolite in the third trimester and flow velocimetry waveforms recorded from uterine, umbilical and fetal middle cerebral arteries. Intrauterine growth retarded pregnancies were compared with controls.

MAIN OUTCOME MEASURES

Concentrations of nitric oxide metabolites (NO2- and NO3-) in amniotic fluid were correlated with flow velocimetry waveforms findings by the determination of correlation coefficient.

RESULTS

Overall median nitrite values in amniotic fluid were higher (P < 0.01) in intrauterine growth retarded patients (median 8.6 micromol/mg creatinine) than in controls (5.6 micromol/mg creatinine). Pathologic uterine flow velocimetry waveforms in uterine artery (-2SD) were observed in 12 women of the intrauterine growth retarded group, and the concentration of amniotic fluid nitrite was significantly lower (P < 0.01) in these patients (median 4.45 micromol/mg creatinine) than in those with normal flow velocity waveforms (median 11.43 micromol/mg creatinine). A significant negative correlation was observed between nitrite concentrations and uterine artery resistance index, umbilical artery pulsatility index and umbilical artery pulsatility index:middle cerebral artery pulsatility index ratio.

CONCLUSIONS

We conclude that placental nitric oxide is significantly associated with uteroplacental blood flow and may be important in maintaining adequate uteroplacental perfusion in intrauterine growth retarded pregnancies.

Nitric oxide concentrations are increased in the feto-placental circulation in intrauterine growth restriction

The aim of this study was to measure plasma concentrations of total nitrites, as an index of nitric oxide (NO) synthesis, in the fetal circulation of normal pregnancies and in pregnancies complicated by intrauterine growth restriction. Plasma was prepared from umbilical venous blood collected from 13 placentae from normal pregnancies complicated by intrauterine growth restriction. Plasma NO concentrations were determined using the Greiss reaction by measuring combined oxidation products of NO, plasma nitrite (NO2-) and nitrate (NO3-) after reduction with nitrate reductase. Significantly higher NO2-concentrations were found in umbilical venous plasma in the group complicated by intrauterine growth restriction compared to the control group (65.6 mumol/1, P < 0.001. These results support the hypothesis that increased NO production may be a compensatory response to improve blood flow in the placenta and/or may play a role in limiting platelet adhesion and aggregation.

The relationship between uterine artery Doppler velocimetry and umbilical venous adenosine levels in pregnancies complicated by preeclampsia

OBJECTIVE

The aim of this study was to evaluate the relationship between uteroplacental circulatory insufficiency and the fetoplacental release of adenosine in pregnancies complicated by preeclampsia.

STUDY DESIGN

We performed uterine artery Doppler velocimetry and calculated the pulsatility index of the uterine artery, to detect uteroplacental circulatory insufficiency, immediately before cordocentesis in 39 pregnant women complicated by preeclampsia. Umbilical venous blood obtained by cordocentesis was then analyzed for blood gases, pH, and plasma adenosine levels. Increased plasma adenosine was taken to signal its increased release from the placenta and fetus relative to its rate of disappearance.

RESULTS

The mean umbilical venous plasma adenosine level in the abnormal pulsatility index group was 1.78 +/- 0.17 mumol/L (mean +/- SEM, n = 25), significantly higher than in the normal pulsatility index group 0.58 +/- 0.14 mumol/L (n = 14, p < 0.001). Furthermore, in the abnormal pulsatility index group the elevation of plasma adenosine levels in the umbilical vein was found even in normoxic fetuses.

CONCLUSION

Fetal plasma adenosine increases before uteroplacental circulatory insufficiency becomes severe enough to cause generalized fetal hypoxemia. We postulate that enhanced adenosine formation in the fetus, umbilical cord vessels, and particularly the placenta may, at least in part, contribute to control and maintenance of placental blood flow.

Use of cordocentesis in the management of preterm or growth-restricted fetuses with abnormal monitoring

The dilemma of when to deliver preterm or growth-restricted fetuses with abnormal monitoring is faced by all those treating such patients. Current noninvasive tests for fetal well-being have relatively high false-positive rates. Cordocentesis allows the clinician to directly analyze fetal blood and determine whether the fetus is truly in distress, is suffering from aneuploidy, or is plagued by infection. However, with improved neonatal care, otherwise normal infants of birth weight greater than 1500 gm have very low morbidity and mortality rates and any delay in delivery offered by cordocentesis is probably not justified. It is in the fetus whose estimated weight is below 1500 gm that cordocentesis should be used. If the results are normal, expectant management and the administration of corticosteroids will allow for pulmonary maturation and a more favorable outcome.

Short communication: the effect of mode of delivery on contractile function of placental arteries in vitro

This study was designed to determine the effect of the mode of delivery on the in vitro assessment of placental blood vessel function. Twenty-two subjects with uncomplicated pregnancies, normal antenatal Doppler flow velocity waveforms and normal birth weights were recruited for the study. The 11 subjects who were delivered by elective caesarean section were matched with 11 controls, who had uncomplicated labours and spontaneous vaginal delivery. Two tertiary chorionic plate arteries were dissected free 1 h after delivery and mounted in a myograph. Cumulative concentration response curves were constructed to the thromboxane A2 analogue U46619, prostaglandin F2 alpha and angiotensin II. After a period of 12 h a further two vessels were mounted and a concentration response curve to U46619 was repeated to determine whether a delay of several hours after delivery would have an effect on the responses of these vessels. These placental arteries constrict to U46619, prostaglandin F2 alpha and angiotensin II in a dose-dependent manner. There was no statistical difference in the maximum contractile responses or pD2 values between the different modes of delivery. A delay in dissection of up to 12 h had no effect on the maximum response or pD2 with U46619. Therefore, contractile function of placental arteries is unaffected by mode of delivery or a delay in dissection.

Atrial natriuretic peptide counteracts the vasoconstrictor effects of 5-hydroxytryptamine, U46619 and endothelin-1 in the human umbilical artery

A role for atrial natriuretic peptide (ANP) in maintaining low vascular resistance within the fetoplacental circulation was investigated using isolated strips of human umbilical artery (HUA). Physiological levels of ANP significantly reduced the isometric contractile response of the HUA to U46619 (a stable thromboxane A2 mimetic), to 5-hydroxytryptamine and to endothelin-1, though no effect on agonist sensitivity could be demonstrated. These data suggest that ANP may modify vascular tone in vivo thereby counterbalancing several humoral factors which act to increase vascular resistance within the fetoplacental circulation.

Atrial natriuretic factor concentration in normal, growth-retarded, anemic, and hydropic fetuses

OBJECTIVE

Our purpose was to establish a reference range with gestation for plasma concentrations of atrial natriuretic factor in fetal blood and to examine whether the concentration is altered in fetal anemia, acidemia, or hydrops.

STUDY DESIGN

Atrial natriuretic factor was measured in umbilical venous blood taken by cordocentesis from pregnancies complicated by red blood cell isoimmunization (n = 17), intrauterine growth retardation (n = 12), and hydrops fetalis (n = 20) and from controls (n = 66). Additionally, maternal blood atrial natriuretic factor concentration was measured in 40 uncomplicated pregnancies.

RESULTS

In the control group detectable levels were found from 16 weeks onward, and the fetal plasma atrial natriuretic factor concentration did not change with gestation. In anemic, acidemic, and hydropic fetuses the concentration was higher than in controls.

CONCLUSION

Fetuses are capable of producing atrial natriuretic factor under physiologic conditions, and the concentration is increased appropriately in pathologic states.

Fetal vascular atrial natriuretic peptide receptors in human placenta: alteration in intrauterine growth retardation and preeclampsia

OBJECTIVE

Our purpose was to quantify fetoplacental vascular atrial natriuretic peptide receptor subtypes in human pregnancies complicated by intrauterine growth retardation or preeclampsia and to relate these parameters to the fetoplacental vascular impedance as assessed by Doppler velocimetry.

STUDY DESIGN

Guanylate cyclase-coupled and uncoupled receptors were quantified by radioligand-binding methods in membrane fractions prepared from primary and secondary stem villous vessels. Data for 16 abnormal pregnancies delivered preterm were compared with that for six gestationally matched preterm controls.

RESULTS

The number of guanylate cyclase-coupled receptors was significantly (p < 0.001) greater in pregnancies complicated by intrauterine growth retardation or preeclampsia irrespective of normal or abnormal umbilical artery Doppler blood flow velocity pattern. The number of guanylate cyclase-uncoupled receptors was unaltered.

CONCLUSIONS

Because fetal plasma atrial natriuretic peptide concentration is normal or elevated in intrauterine growth retardation and preeclampsia, these data suggest that atrial natriuretic peptide-mediated fetoplacental vasodilation is augmented in these disorders even in the presence of increased vascular resistance within the fetoplacental unit.