Atrial natriuretic peptide and hemodynamic changes during normal human pregnancy

Hypertensive Disorders of Pregnancy and the Cardiovascular System: Causes, Consequences, Therapy, and Prevention

Hypertensive disorders of pregnancy continue to be significant contributors to adverse perinatal outcome and maternal mortality, as well as inducing life-long cardiovascular health impacts that are proportional to the severity and frequency of pregnancy complications. The placenta is the interface between the mother and fetus and its failure to undergo vascular maturation in tandem with maternal cardiovascular adaptation by the end of the first trimester predisposes to hypertensive disorders and fetal growth restriction. While primary failure of trophoblastic invasion with incomplete maternal spiral artery remodeling has been considered central to the pathogenesis of preeclampsia, cardiovascular risk factors associated with abnormal first trimester maternal blood pressure and cardiovascular adaptation produce identical placental pathology leading to hypertensive pregnancy disorders. Outside pregnancy blood pressure treatment thresholds are identified with the goal to prevent immediate risks from severe hypertension >160/100 mm Hg and long-term health impacts that arise from elevated blood pressures as low as 120/80 mm Hg. Until recently, the trend for less aggressive blood pressure management during pregnancy was driven by fear of inducing placental malperfusion without a clear clinical benefit. However, placental perfusion is not dependent on maternal perfusion pressure during the first trimester and risk-appropriate blood pressure normalization may provide the opportunity to protect from the placental maldevelopment that predisposes to hypertensive disorders of pregnancy. Recent randomized trials set the stage for more aggressive risk-appropriate blood pressure management that may offer a greater potential for prevention for hypertensive disorders of pregnancy. KEY POINTS: · Optimal management of maternal blood pressure to prevent preeclampsia and its risks is undefined.. · Early gestational rheological damage to the intervillous space predisposes to preeclampsia and FGR.. · First trimester blood pressure management may need to aim for normotension to prevent preeclampsia..

Stretch-induced compliance mechanism in pregnancy-induced cardiac hypertrophy and the impact of cardiovascular risk factors

Pressure overload-induced hypertrophy compromises cardiac stretch-induced compliance (SIC) after acute volume overload (AVO). We hypothesized that SIC could be enhanced by physiological hypertrophy induced by pregnancy's chronic volume overload. This study evaluated SIC-cardiac adaptation in pregnant women with or without cardiovascular risk (CVR) factors. Thirty-seven women (1st trimester, 1stT) and a separate group of 31 (3rd trimester, 3rdT) women [healthy or with CVR factors (obesity and/or hypertension and/or with gestational diabetes)] underwent echocardiography determination of left ventricular end-diastolic volume (LVEDV) and E/e' before (T0), immediately after (T1), and 15 min after (T2; SIC) AVO induced by passive leg elevation. Blood samples for NT-proBNP quantification were collected before and after the AVO. Acute leg elevation significantly increased inferior vena cava diameter and stroke volume from T0 to T1 in both 1stT and 3rdT, confirming AVO. LVEDV and E/e' also increased immediately after AVO (T1) in both 1stT and 3rdT. SIC adaptation (T2, 15 min after AVO) significantly decreased E/e' in both trimesters, with additional expansion of LVEDV only in the 1stT. NT-pro-BNP increased slightly after AVO but only in the 1stT. CVR factors, but not parity or age, significantly impacted SIC cardiac adaptation. A distinct functional response to SIC was observed between 1stT and 3rdT, which was influenced by CVR factors. The LV of 3rdT pregnant women was hypertrophied, showing a structural limitation to dilate with AVO, whereas the lower LV filling pressure values suggest increased diastolic compliance.NEW & NOTEWORTHY The sudden increase of volume overload triggers an acute myocardial stretch characterized by an immediate rise in contractility by the Frank-Starling mechanism, followed by a progressive increase known as the slow force response. The present study is the first to characterize echocardiographically the stretch-induced compliance (SIC) mechanism in the context of physiological hypertrophy induced by pregnancy. A distinct functional adaptation to SIC was observed between first and third trimesters, which was influenced by cardiovascular risk factors.

Prenatal arsenite exposure alters maternal cardiac remodeling during late pregnancy

Exposure to inorganic arsenic through drinking water is widespread and has been linked to many chronic diseases, including cardiovascular disease. Arsenic exposure has been shown to alter hypertrophic signaling in the adult heart, as well as in utero offspring development. However, the effect of arsenic on maternal cardiac remodeling during pregnancy has not been studied. As such, there is a need to understand how environmental exposure contributes to adverse pregnancy-related cardiovascular events. This study seeks to understand the impact of trivalent inorganic arsenic exposure during gestation on maternal cardiac remodeling in late pregnancy, as well as offspring outcomes. C57BL/6 J mice were exposed to 0 (control), 100 or 1000 μg/L sodium arsenite (NaAsO2) beginning at embryonic day (E) 2.5 and continuing through E17.5. Maternal heart function and size were assessed via transthoracic echocardiography, gravimetric measurement, and histology. Transcript levels of hypertrophic markers were probed via qRT-PCR and confirmed by western blot. Offspring outcomes were assessed through echocardiography and gravimetric measurement. We found that maternal heart size was smaller and transcript levels of Esr1 (estrogen receptor alpha), Pgrmc1 (progesterone receptor membrane component 1) and Pgrmc2 (progesterone receptor membrane component 2) reduced during late pregnancy with exposure to 1000 μg/L iAs vs. non-exposed pregnant controls. Both 100 and 1000 μg/L iAs also reduced transcription of Nppa (atrial natriuretic peptide). Akt protein expression was also significantly reduced after 1000 μg/L iAs exposure in the maternal heart with no change in activating phosphorylation. This significant abrogation of maternal cardiac hypertrophy suggests that arsenic exposure during pregnancy can potentially contribute to cardiovascular disease. Taken together, our findings further underscore the importance of reducing arsenic exposure during pregnancy and indicate that more research is needed to assess the impact of arsenic and other environmental exposures on the maternal heart and adverse pregnancy events.

Prenatal Arsenite Exposure Alters Maternal Cardiac Remodeling During Late Pregnancy

Exposure to inorganic arsenic through drinking water is widespread and has been linked to many chronic diseases, including cardiovascular disease. Arsenic exposure has been shown to alter hypertrophic signaling in the adult heart, as well as in-utero offspring development. However, the effect of arsenic on maternal cardiac remodeling during pregnancy has not been studied. As such, there is a need to understand how environmental exposure contributes to adverse pregnancy-related cardiovascular events. This study seeks to understand the impact of trivalent inorganic arsenic exposure during gestation on maternal cardiac remodeling in late pregnancy, as well as offspring outcomes. C57BL/6J mice were exposed to 0 (control), 100 or 1000 µg/L sodium arsenite (NaAsO 2 ) beginning at embryonic day (E) 2.5 and continuing through E17.5. Maternal heart function and size were assessed via transthoracic echocardiography, gravimetric measurement, and histology. Transcript levels of hypertrophic markers were probed via qRT-PCR and confirmed by western blot. Offspring outcomes were assessed through echocardiography and gravimetric measurement. We found that exposure to 1000 µg/L iAs abrogated normal physiologic growth of the maternal heart during late pregnancy and reduced transcript levels of estrogen receptor alpha (ERα), progesterone receptor membrane component 1 (Pgrmc1) and progesterone receptor membrane component 2 (Pgrmc2). Both 100 and 1000 µg/L iAs also reduced transcription of protein kinase B (Akt) and atrial natriuretic peptide (ANP). Akt protein expression was also significantly reduced after 1000 µg/L iAs exposure in the maternal heart with no change in activating phosphorylation. This significant abrogation of maternal cardiac hypertrophy suggests that arsenic exposure during pregnancy can potentially contribute to cardiovascular disease. Taken together, our findings further underscore the importance of reducing arsenic exposure during pregnancy and indicate that more research is needed to assess the impact of arsenic and other environmental exposures on the maternal heart and adverse pregnancy events.

Investigating the Effects of Atrial Natriuretic Peptide on the Maternal Endothelium to Determine Potential Implications for Preeclampsia

Preeclampsia is associated with an increased lifelong risk of cardiovascular disease (CVD). It is not clear whether this is induced by persistent systemic organ and vascular damage following preeclampsia or due to a predisposition to both conditions that share cardiovascular pathophysiology. Common to both CVD and preeclampsia is the dysregulation of corin and its proteolytic product, atrial natriuretic peptide (ANP). ANP, a hypotensive hormone converted from pro-ANP by corin, is involved in blood pressure homeostasis. While corin is predominantly a cardiac enzyme, both corin and pro-ANP are significantly upregulated in the gravid uterus and dysregulated in preeclampsia. Relatively little is known about ANP function in the endothelium during a pregnancy complicated by preeclampsia. Here, we investigated the effect of ANP on endothelial cell proliferation and migration, markers of endothelial dysfunction, and receptor expression in omental arteries exposed to circulating preeclamptic toxins. ANP receptor expression is significantly upregulated in preeclamptic vasculature but not because of exposure to preeclampsia toxins tumour necrosis factor α or soluble fms-like tyrosine kinase-1. The supplementation of endothelial cells with ANP did not promote proliferation or migration, nor did ANP improve markers of endothelial dysfunction. The role of ANP in preeclampsia is unlikely to be via endothelial pathways.

Fetal growth restriction and neonatal-pediatric lung diseases: Vascular mechanistic links and therapeutic directions

Bronchopulmonary dysplasia (BPD) is the most common respiratory sequela of prematurity, and infants born with fetal growth restriction (FGR) are disproportionately represented in BPD statistics, as factors which affect somatic growth may also affect pulmonary growth. Effects of in-utero hypoxia underlying FGR on lung parenchymal architecture predisposing to BPD are well documented, but the pulmonary vascular constructs are not well appreciated. Disruption of angiogenesis during critical periods of lung growth impairs alveolarization, contributing to BPD pathogenesis. Pulmonary artery thickness/stiffness has been noted in FGR in the initial postnatal weeks, and also in well-grown infants with established BPD. The lack of waveform cushioning by the major arteries exposes the pulmonary resistance vessels to higher pulsatile stress, thereby accelerating microvascular disease. Reactive oxygen species, increased sympathetic activity and endothelial dysfunction are common mediators in FGR and BPD; each putative targets for prevention and/or therapeutics using interleukin (IL)-1 receptor antagonist (IL-1Ra), melatonin or inhibition of renin-angiotensin-aldosterone system. While BPD is the archetypal respiratory disease of infancy, effects of FGR on pulmonary function are long-term, extending well into childhood. This narrative links FGR in very/extremely preterm infants with BPD through the vascular affliction as a mechanistic and potentially, therapeutic pathway. Our objectives were to depict the burden of disease for FGR and BPD amongst preterm infants, portray vascular involvement in the placenta in FGR and BPD cohorts, provide high resolution vascular ultrasound information in both cohorts with a view to address therapeutic relevance, and lastly, link this information with paediatric age-group lung diseases.

Maternal plasma pro-atrial and C-type natriuretic peptide levels and their associations with cardiovascular and renal function in the second half of normal pregnancy: a longitudinal study

BACKGROUND

Physiological adaptation in pregnancy is characterized by remodeling of endocrine, cardiovascular and renal functions leading to fluid retention, volume expansion, altered cardiac loading conditions and hyperdynamic circulation. Natriuretic peptides have been used as biomarkers of cardiovascular function, but their associations with gestational age-related changes in maternal cardiac, endothelial and renal function have not been elucidated. The aim of this study was to establish longitudinal reference values for maternal plasma atrial natriuretic peptide (proANP) and C-type natriuretic peptide (CNP) and investigate their temporal association with cardiovascular and renal function in the second half of pregnancy.

METHODS

This study was a prospective longitudinal study of 53 low-risk pregnancies. Women were examined every 3-5 weeks during 22-40 weeks of gestation (252 observations). Fasting maternal blood samples were obtained to measure proANP, CNP, creatinine, cystatin C, uric acid, and fibrinogen levels. Cardiac function and systemic hemodynamics were assessed noninvasively by impedance cardiography (ICG) and vascular endothelial function by flow-mediated vasodilation of brachial artery (FMD).

RESULTS

The plasma proANP (R²adj = 0.79; P = 0.007), CNP (R2adj = 0.54; P = 0.005) decreased between 22 and 40 weeks. The creatinine (R²adj = 0.90; P < 0.001), cystatin C (R²adj = 0.93; P = < 0.001) and uric acid (R²adj = 0.83; P < 0.001) increased significantly, whereas the estimated glomerular filtration rate (R²adj = 0.93; P < 0.001) decreased with gestational age. The FMD did not change significantly but fibrinogen (R²adj = 0.79; P < 0.001) increased with advancing gestation. The maternal systemic vascular resistance index (R²adj = 0.50; P < 0.001) increased, stroke index (R²adj = 0.62; P < 0.001) decreased, whereas the cardiac index (R²adj = 0.62; P = 0.438) and thoracic fluid content (R²adj = 0.72; P = 0.132) did not change significantly with gestation. The proANP was associated with thoracic fluid content (R²adj = 0.74; P < 0.001) and fibrinogen (R²adj = 0.78; P = 0.034) but not with other variables of systemic hemodynamics, endothelial function, or renal function. The CNP was not associated significantly with parameters of cardiovascular or renal function.

CONCLUSION

Longitudinal reference values for maternal plasma proANP and CNP were established. These natriuretic peptides decreased slightly with advancing gestation, but they did not reflect the temporal physiological changes in maternal systemic hemodynamics, vascular endothelial function and renal function during the second half of pregnancy. The proANP correlated with the thoracic fluid content reflecting volume load in pregnancy.

Intensified hemodialysis for complicated pregnancy in a primigravida with advanced maternal age: a case report with literature review focusing on appropriate hemodialysis management during pregnancy

Background

Pregnancy in dialysis patients is rare but challenging both for nephrologists and obstetricians. Although intensified hemodialysis is effective to achieve favorable clinical outcomes in this clinical setting, the evidence concerning reliable parameters for the optimal dialysis prescription is scarce. Herein, we report a case of a primigravida with advanced maternal age who underwent a normal spontaneous vaginal delivery at full term managed by intensified hemodialysis, and discuss reliable indicators of the appropriate dialysis prescription.

Case presentation

A 39-year-old primigravida with end-stage renal disease was referred to our department for hemodialysis management during pregnancy. She had a history of multiple gynecologic disorders, including cervical dysplasia, right tubal ectopic pregnancy and spontaneous abortion; consequently, she conceived through in vitro fertilization and embryo transfer. After pregnancy was confirmed, an intensified hemodialysis schedule with weekly duration of 36 hours was employed to prevent volume overload and the accumulation of hyperosmotic substances. Utilizing maternal blood pressure, plasma atrial natriuretic peptide levels and fetal development as indicators of volume status, we incremented her dry weight by 300–400 g per week in the first and second trimester and 100–200 g per week in the third trimester, respectively. Serum urea nitrogen levels were persistently maintained below 50 mg/dL. Throughout pregnancy, fetal growth and development were within normal limits. At 38 weeks and 3 days of gestation, she delivered a healthy child vaginally without complications. To date, the child’s development has been normal, both physically and mentally.

Conclusions

Pregnancy in dialysis patients with advanced age that leads to a normal childbirth is exceptionally rare. Our case is the hemodialysis patient with the most advanced age who achieves a normal spontaneous vaginal delivery at full term. Considering that cardiovascular system and endogenous metabolism dynamically alter during pregnancy, various clinical parameters should be closely monitored to modify dialysis settings accordingly. Of note, our case suggests that plasma atrial natriuretic peptide level is a useful parameter for the appropriate dry weight. Intensified hemodialysis is an effective and reliable measure that can achieve normal pregnancy in dialysis patients, even in a primigravida with advanced maternal age.

Neural control of blood pressure during pregnancy in humans

PURPOSE

Previous microneurographic studies found that muscle sympathetic nerve activity (MSNA) increased in normotensive pregnant women and was even greater in women with gestational hypertension and preeclampsia during the third trimester. It is possible that sympathetic activation during the latter months of normal pregnancy helps return arterial pressure to non-pregnant levels. However, when the increase in sympathetic activity is excessive, hypertension ensues. The key question that must be addressed is whether sympathetic activation develops early during pregnancy and remains high throughout gestation, or whether this sympathetic overactivity only occurs at term, providing the substrate for preeclampsia and other pregnancy-associated cardiovascular complications.

METHODS

This was a literature review of autonomic neural control during pregnancy.

RESULTS

Recent work from our laboratory and other laboratories showed that in healthy women resting MSNA increased in early pregnancy, increased further in late pregnancy, and returned to the pre-pregnancy levels shortly after delivery. We found that women who exhibited excessive sympathetic activation during the first trimester, before any clinical signs and symptoms appeared, developed gestational hypertension at term. We also found that the level of corin, an atrial natriuretic peptide-converting enzyme, was increased in the maternal circulation, especially during late pregnancy, as a homeostatic response to elevated sympathetic activity.

CONCLUSION

These findings provide important insight into the neural mechanisms underlying hypertensive disorders during pregnancy. With this knowledge, early prevention or treatment targeted to the appropriate pathophysiology may be initiated, which may reduce maternal and fetal death or morbidity, as well as cardiovascular risks in women later in life.

Placental histopathology in preterm fetal growth restriction

AIMS

Approximately 6-9% pregnancies are affected by fetal growth restriction (FGR). Placental alterations related to utero-placental insufficiency in FGR may induce placental vascular remodelling to the detriment of the fetus. The objective of this article was to study histopathological features of placentae in a cohort of preterm growth-restricted infants in comparison to a cohort of preterm appropriately grown infants.

METHODS

In a cohort of 40 preterm infants of 28-32 weeks' gestation, placental histopathology was evaluated by a histopathologist, who was blinded to the identity of the grouping. Twenty infants had FGR, while 20 were appropriate for gestational age (AGA). Predefined histopathological characteristics were assessed based on the Amsterdam Placental Workshop Group Consensus Statement.

RESULTS

The gestational age and birthweight of the FGR and AGA cohorts were 29.8 ± 1.3 versus 30 ± 0.9 weeks, P = 0.78 and 923 ± 168 versus 1403 ± 237 g, <0.001, respectively. Maternal vascular malperfusion, accelerated villous maturation and fetal vascular malperfusion were features that were significantly more common in FGR placentae.

CONCLUSION

Based on the results of the present study, specific placental histopathological changes may be present in FGR placentae, which may reflect the effects of utero-placental insufficiency.

Vascular changes in fetal growth restriction: clinical relevance and future therapeutics

Fetal growth restriction (FGR) affects about 5-10% pregnancies and is associated with poorer outcomes in the perinatal period. Additionally, long standing epidemiological data support its association with chronic diseases such as hypertension and diabetes. Cardiac and vascular adaptations in response to chronic hypoxemia due to utero-placental insufficiency are hallmarks of fetal adaptations. Investigators have attempted to identify these changes in the placenta at the microscopic and molecular level. The ex vivo dual perfusion model of the placenta enables the study of placental haemodynamics in growth-restricted pregnancies. Persistent arterial abnormalities (thickness and stiffness) noted on vascular ultrasound during fetal life through to the young-adult age group for those affected by FGR, seem to be a plausible link between in utero events and chronic circulatory diseases. Using these, this review reflects current thought on vascular maladaptive changes in the FGR cohorts and the role in investigating current and future therapeutics.

Developmental origins of pregnancy-induced cardiac changes: establishment of a novel model using the atrial natriuretic peptide gene-disrupted mice

Pregnancy evokes many challenges on the maternal cardiovascular system that may unmask predispositions for future disease. This is particularly evident for women who develop pregnancy-related disorders, for example, pre-eclampsia and gestational diabetes or hypertension. Such pregnancy-related syndromes increase the risk for cardiovascular disease (CVD) postpartum. As a result, pregnancy has been termed as a cardiovascular stress test and an indicator or marker to predict the development of CVD later in life. In addition, pregnancy-related disorders impact the development of offspring also placing them at a higher risk for disease. Utilizing pregnancy as a physiological stressor, the current investigation sought to determine whether the cardiovascular system of offspring exposed to gestational hypertension in utero would respond adversely to the stress of pregnancy. Heterozygous atrial natriuretic peptide gene-disrupted (ANP^+/-) offspring were generated by either crossing male wildtype ANP^+/+ with female knockout ANP^-/- to produce ANP^+/-KO mice or crossing female wildtype ANP^+/+ with male knockout ANP^-/- to produce ANP^+/-WT mice. To study the cardiovascular stress induced by pregnancy, female ANP^+/-WT and ANP^+/-KO mice were mated with male wildtype ANP^+/+ mice to initiate pregnancy. Cardiac size and molecular expression of the renin-angiotensin (RAS) and natriuretic peptide systems (NPS) were compared between offspring groups. Our data demonstrate that gestational hypertension and lack of maternal ANP did not significantly impact the progression and regression of pregnancy-induced cardiac hypertrophy over gestation and postpartum in ANP^+/- offspring. Additionally, the molecular cardiac expression of the RAS and NPS did not differ between offspring groups. Future investigation should assess potential differences in cardiac function and the impact of fetal-programming on offspring cardiovascular adaptations during pregnancy in more severe models of pregnancy-related hypertensive syndrome such as angiotensin II or isoproterenol infusion.

Consensus Document of the Italian Association of Hospital Cardiologists (ANMCO), Italian Society of Pediatric Cardiology (SICP), and Italian Society of Gynaecologists and Obstetrics (SIGO): pregnancy and congenital heart diseases

The success of cardiac surgery over the past 50 years has increased numbers and median age of survivors with congenital heart disease (CHD). Adults now represent two-thirds of patients with CHD; in the USA alone the number is estimated to exceed 1 million. In this population, many affected women reach reproductive age and wish to have children. While in many CHD patients pregnancy can be accomplished successfully, some special situations with complex anatomy, iatrogenic or residual pathology are associated with an increased risk of severe maternal and fetal complications. Pre-conception counselling allows women to come to truly informed choices. Risk stratification tools can also help high-risk women to eventually renounce to pregnancy and to adopt safe contraception options. Once pregnant, women identified as intermediate or high risk should receive multidisciplinary care involving a cardiologist, an obstetrician and an anesthesiologist with specific expertise in managing this peculiar medical challenge. This document is intended to provide cardiologists working in hospitals where an Obstetrics and Gynecology Department is available with a streamlined and practical tool, useful for them to select the best management strategies to deal with a woman affected by CHD who desires to plan pregnancy or is already pregnant.

PLASMA CONCENTRATIONS AND CORRELATIONS OF NATRIURETIC PEPTIDES AND OXYTOCIN DURING LABOR AND EARLY POSTPARTUM PERIOD

Context

Natriuretic peptides (NP) and oxytocin (OT) play an important role in cardiovascular and hydro-electrolytic homeostasis. Changes in NP levels and their roles in cardiovascular adaptations in pregnancy and labor have not been clear.

Objective

The present study aimed to investigate the changes and correlations in plasma levels of atrial natriuretic peptide (ANP), C-type natriuretic peptide (CNP), B-type natriuretic peptide (BNP) and OT during labor and the postpartum period.

Study design

Blood samples were collected from 29 healthy pregnant women in the active phase of spontaneous labor, 15 minutes after delivery and 3 hours postpartum. Plasma levels of OT and the stable N-terminal fragments of NPs (NT-proANP, NT-proCNP, NT-proBNP) were measured using enzyme or electrochemiluminescence immunoassays.

Results

The plasma levels of NT-proANP and NT-proCNP significantly decrease 3 hours postpartum compared to the active phase of labor and to 15 minutes after delivery. The plasma NT-proBNP levels significantly higher after delivery and 3 hours postpartum compared to the active phase of labor. A significant correlation exists between OT and NT-proANP levels during the active phase of labor and 15 minutes after delivery.

Conclusions

The data show that during labor and postpartum, the plasma concentrations of the NPs change differently. Elevations in NT- proBNP after delivery suggest that BNP may be involved in postpartum adaptations. The correlations between OT and ANP levels indicate that OT may be partly responsible for the increased levels of ANP and may have a role in the modification of the cardiovascular system.

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.

Kv5, Kv6, Kv8, and Kv9 subunits: No simple silent bystanders

Members of the electrically silent voltage-gated K(+) (Kv) subfamilies (Kv5, Kv6, Kv8, and Kv9, collectively identified as electrically silent voltage-gated K(+) channel [KvS] subunits) do not form functional homotetrameric channels but assemble with Kv2 subunits into heterotetrameric Kv2/KvS channels with unique biophysical properties. Unlike the ubiquitously expressed Kv2 subunits, KvS subunits show a more restricted expression. This raises the possibility that Kv2/KvS heterotetramers have tissue-specific functions, making them potential targets for the development of novel therapeutic strategies. Here, I provide an overview of the expression of KvS subunits in different tissues and discuss their proposed role in various physiological and pathophysiological processes. This overview demonstrates the importance of KvS subunits and Kv2/KvS heterotetramers in vivo and the importance of considering KvS subunits and Kv2/KvS heterotetramers in the development of novel treatments.

Dysregulated flow-mediated vasodilatation in the human placenta in fetal growth restriction

Increased vascular resistance and reduced fetoplacental blood flow are putative aetiologies in the pathogenesis of fetal growth restriction (FGR); however, the regulating sites and mechanisms remain unclear. We hypothesised that placental vessels dictate fetoplacental resistance and in FGR exhibit endothelial dysfunction and reduced flow-mediated vasodilatation (FMVD). Resistance was measured in normal pregnancies (n = 10) and FGR (n = 10) both in vivo by umbilical artery Doppler velocimetry and ex vivo by dual placental perfusion. Ex vivo FMVD is the reduction in fetal-side inflow hydrostatic pressure (FIHP) following increased flow rate. Results demonstrated a significant correlation between vascular resistance measured in vivo and ex vivo in normal pregnancy, but not in FGR. In perfused FGR placentas, vascular resistance was significantly elevated compared to normal placentas (58 ± 7.7 mmHg and 36.8 ± 4.5 mmHg, respectively; 8 ml min⁻¹; means ± SEM; P < 0.0001) and FMVD was severely reduced (3.9 ± 1.3% and 9.1 ± 1.2%, respectively). In normal pregnancies only, the highest level of ex vivo FMVD was associated with the lowest in vivo resistance. Inhibition of NO synthesis during perfusion (100 μm l-NNA) moderately elevated FIHP in the normal group, but substantially in the FGR group. Human placenta artery endothelial cells from FGR groups exhibited increased shear stress-induced NO generation, iNOS expression and eNOS expression compared with normal groups. In conclusion, fetoplacental resistance is determined by placental vessels, and is increased in FGR. The latter also exhibit reduced FMVD, but with a partial compensatory increased NO generation capacity. The data support our hypothesis, which highlights the importance of FMVD regulation in normal and dysfunctional placentation.

Low-dose oral or non-oral hormone therapy: effects on C-reactive protein and atrial natriuretic peptide in menopause

OBJECTIVE

To assess the effects of oral low-dose and non-oral hormone therapy (HT) on ultra-sensitive C-reactive protein (CRP), atrial natriuretic peptide (ANP), and cardiovascular risk factors in postmenopause.

METHODS

In this randomized, cross-over study, 44 recently postmenopausal women, with no clinical evidence of cardiovascular disease, received oral low-dose HT (estradiol 1 mg + drospirenone 2 mg/day) for 3 months. Forty-two patients received non-oral, conventional HT (1.5 mg/day percutaneous 17β-estradiol gel or equivalent for nasal route) for 3 months followed by 200 mg/day micronized progesterone by the vaginal route (14 days during each menstrual period). After 3 months, patients were crossed over without washout. Post-HT vs. pre-HT measures were determined: lipids, glucose, body mass index, waist circumference, fibrinogen, CRP-stratified levels, and ANP levels. The study was registered at clinical trials.gov (NCT01432028).

RESULTS

The mean age was 51 ± 3 years and the mean time since the menopause was 22 ± 10 months. CRP-stratified high levels decreased in a higher number of non-oral HT patients, who moved to intermediate and low levels (p = 0.02). No effect of HT was observed on ANP levels (baseline 67.4 (18.4-104.5), low-dose oral 43.5 (14.4-95.9), non-oral 39.8 (15.5-67.5) pg/ml). Markers of endothelial function did not worsen with either low-dose oral or non-oral HT: von Willebrand factor (baseline 118 ± 37%, low-dose oral 119 ± 38%, non-oral 108 ± 3%, p < 0.01), fibrinogen (baseline 356 ± 58 mg/dl; low-dose oral 343 ± 77 mg/dl; non-oral 326 ± 71 mg/dl, p < 0.01).

CONCLUSIONS

Low-dose oral and non-oral HT for 6 months had neutral or beneficial effects in recently postmenopausal women with no clinical evidence of cardiovascular disease.

Uteroplacental circulation and fetal vascular function and development

Although blood flow in the placental vasculature is governed by the same physiological forces of shear, pressure and resistance as in other organs, it is also uniquely specialized on the maternal and fetal sides. At the materno-fetal interface, the independent uteroplacental and umbilicoplacental circulations must coordinate sufficiently to supply the fetus with the nutrients and substrates it needs to grow and develop. Uterine arterial flow must increase dramatically to accommodate the growing fetus. Recent evidence delineates the hormonal and endothelial mechanisms by which maternal vessels dilate and remodel during pregnancy. The umbilical circulation is established de novo during embryonic development but blood does not flow through the placenta until late in the first trimester. The umbilical circulation operates in the interest of maintaining fetal oxygenation over the course of pregnancy, and is affected differently by mechanical and chemical regulators of vascular tone compared to other organs. The processes that match placental vascular growth and fetal tissue growth are not understood, but studies of compromised pregnancies provide clues. The subtle changes that cause the failure of the normally regulated vascular processes during pregnancy have not been thoroughly identified. Likewise, practical and effective therapeutic strategies to reverse detrimental placental perfusion patterns have yet to be investigated.

The renal circulation in normal pregnancy and preeclampsia: is there a place for relaxin?

During the first trimester of human pregnancy, the maternal systemic circulation undergoes remarkable vasodilation. The kidneys participate in this vasodilatory response resulting in marked increases in renal plasma flow (RPF) and glomerular filtration rate (GFR). Comparable circulatory adaptations are observed in conscious gravid rats. Administration of the corpus luteal hormone relaxin (RLN) to nonpregnant rats and humans elicits vasodilatory changes like those of pregnancy. Systemic and renal vasodilation are compromised in midterm pregnant rats by neutralization or elimination of circulating RLN and in women conceiving with donor eggs who lack a corpus luteum and circulating RLN. Although RLN exerts both rapid (minutes) and sustained (hours to days) vasodilatory actions through different molecular mechanisms, a final common pathway is endothelial nitric oxide. In preeclampsia (PE), maternal systemic and renal vasoconstriction leads to hypertension and modest reduction in GFR exceeding that of RPF. Elevated level of circulating soluble vascular endothelial growth factor receptor-1 arising from the placenta is implicated in the hypertension and disruption of glomerular fenestrae and barrier function, the former causing reduced Kf and the latter proteinuria. Additional pathogenic factors are discussed. Last, potential clinical ramifications include RLN replacement in women conceiving with donor eggs and its therapeutic use in PE. Another goal has been to apply knowledge gained from investigating circulatory adaptations in pregnancy toward identifying and developing novel therapeutic strategies for renal and cardiovascular disease in the nonpregnant population. So far, one candidate to emerge is RLN and its potential therapeutic use in heart failure.

Gestational hypertension in atrial natriuretic peptide knockout mice and the developmental origins of salt-sensitivity and cardiac hypertrophy

OBJECTIVE

To determine the effect of gestational hypertension on the developmental origins of blood pressure (BP), altered kidney gene expression, salt-sensitivity and cardiac hypertrophy (CH) in adult offspring.

METHODS

Female mice lacking atrial natriuretic peptide (ANP-/-) were used as a model of gestational hypertension. Heterozygous ANP+/- offspring was bred from crossing either ANP+/+ females with ANP-/- males yielding ANP+/-(WT) offspring, or from ANP-/- females with ANP+/+ males yielding ANP+/-(KO) offspring. Maternal BP during pregnancy was measured using radiotelemetry. At 14weeks of age, offspring BP, gene and protein expression were measured in the kidney with real-time quantitative PCR, receptor binding assay and ELISA.

RESULTS

ANP+/-(KO) offspring exhibited normal BP at 14weeks of age, but displayed significant CH (P<0.001) as compared to ANP+/-(WT) offspring. ANP+/-(KO) offspring exhibited significantly increased gene expression of natriuretic peptide receptor A (NPR-A) (P<0.001) and radioligand binding studies demonstrated significantly reduced NPR-C binding (P=0.01) in the kidney. Treatment with high salt diet increased BP (P<0.01) and caused LV hypertrophy (P<0.001) and interstitial myocardial fibrosis only in ANP+/-(WT) and not ANP+/-(KO) offspring, suggesting gestational hypertension programs the offspring to show resistance to salt-induced hypertension and LV remodeling. Our data demonstrate that altered maternal environments can determine the salt-sensitive phenotype of offspring.

Maternal plasma concentrations of sST2 and angiogenic/anti-angiogenic factors in preeclampsia

OBJECTIVES

Angiogenic/anti-angiogenic factors have emerged as one of the promising biomarkers for the prediction of preeclampsia. Since not all patients with preeclampsia can be identified by these analytes, the search for additional biomarkers continues. The soluble form of ST2 (sST2), a protein capable of binding to interleukin (IL)-33 and thus contributing to a Th1-biased immune response, has been reported to be elevated in maternal plasma of women with preeclampsia. The aims of this study were to examine: (1) differences in maternal plasma concentrations of sST2 and IL-33 between women diagnosed with preeclampsia and those having uncomplicated pregnancies; (2) the relationship between sST2, umbilical and uterine artery Doppler velocimetry, and the severity of preeclampsia; and (3) the performance of sST2 and angiogenic/anti-angiogenic factors in identifying patients with preeclampsia at the time of diagnosis.

METHODS

This cross-sectional study included women with preeclampsia (n = 106) and women with an uncomplicated pregnancy (n = 131). Plasma concentrations of sST2, IL-33, soluble vascular endothelial growth factor receptor (sVEGFR)-1, soluble endoglin (sEng) and placental growth factor (PlGF) were determined by enzyme linked immune sorbent assay. Area under the receiver operating characteristic curve (AUC) for the identification of preeclampsia was examined for each analyte.

RESULTS

(1) Patients with preeclampsia had a higher mean plasma concentrations of sST2 than those with an uncomplicated pregnancy (p < 0.0001), while no significant difference in the mean plasma concentration of IL-33 between the two groups was observed; (2) the magnitude of this difference was greater in early-onset, compared to late-onset disease, and in severe compared to mild preeclampsia; (3) sST2 plasma concentrations did not correlate with the results of uterine or umbilical artery Doppler velocimetry (p = 0.7 and p = 1, respectively) among women with preeclampsia; (4) sST2 correlated positively with plasma concentrations of sVEGFR1-1 and sEng (Spearman's Rho = 0.72 and 0.63; each p < 0.0001), and negatively with PlGF (Spearman's Rho = -0.56, p < 0.0001); and (5) while the AUC achieved by sST2 and angiogenic/anti-angiogenic factors in identifying women with preeclampsia at the time of diagnosis were non-significantly different prior to term (<37 weeks of gestation), thereafter the AUC achieved by sST2 was significantly less than that achieved by angiogenic/anti-angiogenic factors.

CONCLUSIONS

Preeclampsia is associated with increased maternal plasma concentrations of sST2. The findings that sST2 concentrations do not correlate with uterine or umbilical artery Doppler velocimetry in women with preeclampsia suggest that elevated maternal plasma sST2 concentrations in preeclampsia are not related to the increased impedance to flow in the utero-placental circulation. The performance of sST2 in identifying preeclampsia at the time of diagnosis prior to 37 weeks of gestation was comparable to that of angiogenic/anti-angiogenic factors. It remains to be elucidated if an elevation of maternal plasma sST2 concentrations in pregnancy is specific to preeclampsia.

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.

Vasodilator factors in the systemic and local adaptations to pregnancy

We postulate that an orchestrated network composed of various vasodilatory systems participates in the systemic and local hemodynamic adaptations in pregnancy. The temporal patterns of increase in the circulating and urinary levels of five vasodilator factors/systems, prostacyclin, nitric oxide, kallikrein, angiotensin-(1-7) and VEGF, in normal pregnant women and animals, as well as the changes observed in preeclamptic pregnancies support their functional role in maintaining normotension by opposing the vasoconstrictor systems. In addition, the expression of these vasodilators in the different trophoblastic subtypes in various species supports their role in the transformation of the uterine arteries. Moreover, their expression in the fetal endothelium and in the syncytiotrophoblast in humans, rats and guinea-pigs, favour their participation in maintaining the uteroplacental circulation. The findings that sustain the functional associations of the various vasodilators, and their participation by endocrine, paracrine and autocrine regulation of the systemic and local vasoactive changes of pregnancy are abundant and compelling. However, further elucidation of the role of the various players is hampered by methodological problems. Among these difficulties is the complexity of the interactions between the different factors, the likelihood that experimental alterations induced in one system may be compensated by the other players of the network, and the possibility that data obtained by manipulating single factors in vitro or in animal studies may be difficult to translate to the human. In addition, the impossibility of sampling the uteroplacental interface along normal pregnancy precludes obtaining longitudinal profiles of the various players. Nevertheless, the possibility of improving maternal blood pressure regulation, trophoblast invasion and uteroplacental flow by enhancing vasodilation (e.g. L-arginine, NO donors, VEGF transfection) deserves unravelling the intricate association of vasoactive factors and the systemic and local adaptations to pregnancy.

Hemodynamic Adaptation during Pregnancy in Chronic Hypertension

OBJECTIVE

To assess hemodynamic and NT-proANP changes in women with chronic hypertension during pregnancy.

METHODS

Stroke volume index (SI), heart rate (HR), cardiac output index (CI), systemic vascular resistance index (SVRI), pulse wave velocity (PWV), and left cardiac work index (LCWI) were measured using whole-body impedance cardiography. Systolic blood pressure (SAP), mean arterial pressure (MAP), diastolic blood pressure (DAP), and pulse pressure (PP) were also measured. Arterial compliance was defined as the SI-to-PP ratio (SI/PP). Hemodynamic parameters and NT-proANP concentrations were assessed during the early and late second trimester, the third trimester, and after delivery in 20 women with essential hypertension and 30 normotensive women.

RESULTS

Arterial blood pressure, SVRI, and PWV remained higher during the whole study period in chronic hypertensive compared with healthy pregnancies. In the early second trimester, women with chronic hypertension had significantly lower SI and NT-proANP concentrations than did normotensive women.

CONCLUSION

The hemodynamics of chronic hypertension during pregnancy are characterized by persistent high vascular resistance. Lower SI and NT-proANP values found in chronic hypertensive pregnancies during the early second trimester may suggest a reduced intravascular volume increase during pregnancy.

Effect of posture on creatinine clearance in late pregnancy and after pregnancy

AIM

To assess creatinine clearance that indicates glomerular filtration rate (GFR) and to demonstrate the effect of posture on creatinine clearance in late pregnancy compared to the non-pregnant state.

METHODS

Twenty-six healthy pregnant women aged 19-30 years were studied for two sessions, first in their third trimester of pregnancy and then in a non-pregnant state at 6-12 weeks after delivery. In both sessions, creatinine clearance was assessed at three periods: the 24-h baseline, and at the end of 2-h sitting and 2-h lying (in left lateral decubitus position) periods. Urine and blood samples were collected for creatinine clearance measurement.

RESULTS

The results showed that the 24-h creatinine clearance in late pregnancy was 28.3% higher than that in the non-pregnant state (122.6 +/- 26.2 vs 95.3 +/- 15.1 mL/min per 1.73 m2, P < 0.001). In late pregnancy, after 2-h sitting, creatinine clearance decreased significantly (10%) compared to the 24-h baseline (122.6 +/- 26.2 vs 110.4 +/- 28.6 mL/min per 1.73 m2, P < 0.001). Creatinine clearance rose back to the high baseline level after the pregnant woman laid in left lateral decubitus for 2 h. The decrease in creatinine clearance during prolonged sitting was not seen in the non-pregnant state. At any posture, the creatinine clearance was always higher in the pregnant state than in the non-pregnant.

CONCLUSIONS

This study showed that creatinine clearance in late pregnancy was much higher than in the non-pregnant state, and was affected by sitting for up to 2 h. It might be wise for women to lay down in the left lateral decubitus position for a while after many hours of sitting when pregnancy is approaching its term.

Role of relaxin in maternal renal vasodilation of pregnancy

The remarkable hemodynamic changes of normal pregnancy are briefly reviewed. In addition, new findings and current concepts related to the underlying hormonal and molecular mechanisms are presented. Finally, work that is in progress as well as future directions is briefly discussed.

Mechanisms of renal vasodilation and hyperfiltration during pregnancy: current perspectives and potential implications for preeclampsia

A thorough understanding of the renal and cardiovascular adaptations to normal gestation is essential for proper diagnosis and management of hypertensive disorders and renal diseases during pregnancy. Here, we briefly review the renal hemodynamic changes of normal pregnancy. In addition, we present new findings and current concepts related to the underlying hormonal and molecular mechanisms. Finally, we speculate on the potential contribution of these insights from normal pregnancy to the pathogenesis of preeclampsia.

Vasoactive mediators and retinopathy during type 1 diabetic pregnancy

PURPOSE

To evaluate the role of various vasoactive hormones in the evolution of diabetic retinopathy during pregnancy and postpartum.

METHODS

Retinopathy was graded from fundus photographs of 45 pregnant women with type 1 diabetes and seven pregnant women without diabetes in a prospective study. Markers of renin-angiotensin-system (RAS), plasma renin activity (PRA), angiotensin II (AngII), aldosterone, natriuretic peptides (ANP, BNP, CNP) and adreonomedullin (AM) were measured during the first and third trimesters and at 3 months postpartum. The women with diabetes were grouped by progression of retinopathy during pregnancy and postpartum.

RESULTS

Levels of PRA (p = 0.001) and ANP (p = 0.03) were significantly lower in diabetes than in non-diabetes subjects throughout pregnancy and postpartum. No significant differences appeared in levels of AngII, aldosterone, AM, BNP or CNP between the two groups. In multivariate logistic regression analyses with retinopathy progression by the third trimester as the dependent variable, only duration of diabetes qualified in the model (p = 0.027, R = 0.227, Exp(B) = 1.28).

CONCLUSIONS

Diabetic pregnancy is associated with lower levels of PRA and ANP compared to non-diabetic pregnancy. Lowered RAS activity may contribute to the hyperdynamic blood flow and progression of DR during diabetic pregnancy. Within the power of this study no clear associations between the vasoactive hormones and progression of retinopathy could be detected.

Effects of human pregnancy on fluid regulation responses to short-term exercise

This study tested the hypothesis that human pregnancy alters fluid and electrolyte regulation responses to acute short-term exercise. Responses of 22 healthy pregnant women (PG; gestational age, 37.0 +/- 0.2 wk) and 17 nonpregnant controls (CG) were compared at rest and during cycling at 70 and 110% of the ventilatory threshold (VT). At rest, ANG II concentration was significantly (P < 0.05) higher in PG vs. CG, whereas plasma osmolality and concentrations of AVP, sodium, and potassium were significantly lower. Atrial natriuretic peptide concentration at rest was similar between groups. ANG II and AVP concentrations increased significantly from rest to 110% VT in CG only, whereas increases in atrial natriuretic peptide concentration were similar between groups. Increases in osmolality, and total protein and albumin concentrations from rest to both work rates were similar between the two groups. PG and CG exhibited similar shifts in fluid during acute short-term exercise, but the increases in ANG II and AVP were absent and attenuated, respectively, during pregnancy. This was attributed to the significantly augmented fluid volume state already present at rest in late gestation.

Circadian rhythm of ANP, aldosterone and PRA in normotensive IUGR

OBJECTIVE

Atrial natriuretic peptide (ANP) increases are reported during normal pregnancy, but the relation to arterial pressure and the renin-angiotensin system is debatable. We assessed whether normotensive pregnancies with intrauterine growth retardation (IUGR) present an alteration of maternal ANP levels.

DESIGN

A total of 11 pregnant women with IUGR, in the absence of any other maternal or fetal pathology, entered the study during the third trimester. They were compared with 12 healthy pregnant women of similar age and characteristics. We monitored all subjects for blood pressure (BP), ANP, aldosterone and plasma renin activity (PRA), under the same conditions for 24 h. All subjects were submitted to the same regimen of life; with homogeneous dark : light periods, salt intake and meal times.

METHODS

BP was monitored at 20 min intervals for 24 h and blood tests performed at six time points during the 24 h. EDTA plasma samples were immediately centrifuged. Hormone assays were performed by radioimmunoassay. Koch's nonparametric two-way analysis of variance (ANOVA) was used to compare the hormone time-dependent profiles in the two groups. Circadian rhythms were assessed by cosinor analysis.

RESULTS

The IUGR group was characterized by higher ANP values compared to normal pregnancy, (205 +/- 24 versus 146 +/- 21 pg/ml: P < 0.05) but not significant differences were shown for PRA, aldosterone and BP circadian rhythms.

CONCLUSIONS

This study shows higher ANP values in human pregnancy complicated by IUGR, with presence of normal BP, aldosterone and PRA profiles.

Vasoactive mediator release by fetal endothelial cells in intrauterine growth restriction and preeclampsia

OBJECTIVE

Preeclampsia and fetal growth restriction are associated with poor placental perfusion, which may be accompanied by a compensatory release of vasoactive substances in the fetoplacental circuit. This study examines the effects of preeclampsia and fetal growth restriction on nitric oxide and prostacyclin signaling pathways in fetal endothelial cells.

STUDY DESIGN

Human umbilical vein endothelial cells from 30 control pregnancies, 18 pregnancies with preeclampsia, and 9 pregnancies with intrauterine growth restriction were cultured. Intracellular cyclic guanosine monophosphate accumulation and 6-keto-prostaglandin F1alpha production were determined.

RESULTS

Intracellular accumulation of cyclic guanosine monophosphate was significantly higher in the preeclampsia group and lower in the growth restriction group than in the control group (9.8, 1.8, and 3.9 pmol/microg protein for 5 minutes, respectively), whereas 6-keto-prostaglandin F1alpha production was not significantly different in the 3 groups.

CONCLUSION

The data suggest that the fetoplacental vascular response to preeclampsia is to increase production of cyclic guanosine monophosphate, perhaps to maintain vessel dilatation and maximum flow through placental villi. In fetal growth restriction the umbilical vein endothelial cells do not or cannot respond to chronic hypoxia by increasing cyclic guanosine monophosphate, which may lead to fetoplacental vasoconstriction.

Differential alterations in responsiveness in particulate and soluble guanylate cyclases in pregnant guinea pig myometrium

OBJECTIVE

The mechanism underlying myometrial quiescence during pregnancy is unknown. Our group has previously shown that during pregnancy myometrial cyclic guanosine monophosphate content rises to several hundred times the nonpregnant levels, only to abruptly decline days before the onset of labor. Cyclic guanosine monophosphate plays an integral role in the relaxation of smooth muscle. The aim of this investigation was therefore to determine the effects of pregnancy on both soluble and particulate guanylate cyclase enzymatic activities and messenger ribonucleic acid expressions.

STUDY DESIGN

Myometrium was obtained from randomly cycling adult nonpregnant guinea pigs and near-term (50-60 days' gestation) pregnant guinea pigs of similar chronologic age. Subcellular fractions were prepared by differential ultracentrifugation. Guanylate cyclase activity was determined by the conversion of guanosine triphosphate to cyclic guanosine monophosphate under basal or stimulated conditions in either the soluble guanylate cyclase or particulate guanylate cyclase fraction. A nitric oxide donor, S-nitroso- N-penacillamine, was used to activate soluble guanylate cyclase (n = 10 animals in each group). Several natriuretic peptides (atrial natriuretic peptide, brain natriuretic peptide, and C-type natriuretic peptide) and uroguanylin were used to stimulate the different particulate guanylate cyclase isoforms guanylate cyclase A, guanylate cyclase B, and guanylate cyclase C, respectively, in pregnant (n = 8) and nonpregnant (n = 6) animals. Cyclic guanosine monophosphate content was measured by radioimmunoassay, and enzymatic activity was expressed as picomoles of cyclic guanosine monophosphate per milligram of protein per minute. Total guanylate cyclase represented the sum of soluble guanylate cyclase and particulate guanylate cyclase activities for a tissue. To investigate whether the observed changes in guanylate cyclase activity were paralleled by changes in receptor expression, messenger ribonucleic acid levels of the genes for guanylate cyclase A and guanylate cyclase B isoforms were quantified by ribonuclease protection assay (n = 5 animals in each group).

RESULTS

Under basal conditions particulate guanylate cyclase represented 78% (nonpregnant state) to 88% (during pregnancy) of the total guanylate cyclase activity in the guinea pig myometrium. Pregnancy further reduced myometrial soluble guanylate cyclase (both basal and stimulated by nitric oxide) relative to the nonpregnant state. Pregnancy selectively increased atrial natriuretic peptide-stimulated particulate guanylate cyclase activity (attributed to guanylate cyclase A), although it did not change basal myometrial particulate guanylate cyclase activity in general. Guanylate cyclase B (particulate guanylate cyclase stimulated by C-type natriuretic peptide) and guanylate cyclase C (particulate guanylate cyclase stimulated by uroguanylin) activities were unaltered by pregnancy. The selective increase in responsiveness of particulate guanylate cyclase to atrial natriuretic peptide during pregnancy was not paralleled by an increased in level of messenger ribonucleic acid for the gene for guanylate cyclase A.

CONCLUSION

Pregnancy reduced the in vitro responsiveness of the myometrial soluble guanylate cyclase to nitric oxide while increasing the responsiveness of the particulate isoform to atrial natriuretic peptide and brain natriuretic peptide through a mechanism independent of any change in receptor expression.

Molecular mechanism of cGMP-mediated smooth muscle relaxation

Contraction and relaxation of smooth muscle is a tightly regulated process involving numerous endogenous substances and their intracellular second messengers. We examine the key role of cyclic guanosine monophosphate (cGMP) in mediating smooth muscle relaxation. We briefly review the current art regarding cGMP generation and degradation, while focusing on the recent identification of the molecular mechanisms underlying cGMP-mediated smooth muscle relaxation. cGMP-induced SM relaxation is mediated mainly by cGMP-dependent protein kinase activation. It involves several molecular events culminating in a reduction in intracellular Ca(2+) concentration and a decrease in the sensitivity of the contractile system to Ca(2+). We propose that the cGMP-induced decrease in Ca(2+) sensitivity is a strategic way to achieve "active relaxation" of the smooth muscle. In summary, we present compelling evidence supporting a key role for cGMP as a mediator of smooth muscle relaxation in physiological and pharmacological settings.

Relationship of systemic hemodynamics, left ventricular structure and function, and plasma natriuretic peptide concentrations during pregnancy complicated by preeclampsia

OBJECTIVE

This study was done to evaluate left ventricular structure and function among pregnant patients with preeclampsia and compare them with those of normotensive pregnant and nonpregnant subjects. It also tested the hypothesis that abnormalities in left ventricular structure and function are associated with elevated plasma levels of natriuretic peptides.

STUDY DESIGN

The study compared 75 pregnant women (n = 40 with preeclampsia; n = 35 normotensive pregnant women) and 10 nonpregnant normotensive control subjects undergoing an echocardiographic and biohumoral (renin activity and aldosterone, atrial natriuretic peptide, and brain natriuretic peptide concentrations) evaluation. The statistical analysis was carried out by analysis of variance, and significance was set at P <.05.

RESULTS

Comparison of pregnant patients with preeclampsia versus both normotensive pregnant women and nonpregnant women showed significant increases in left ventricular mass and left ventricular endsystolic and end-diastolic volumes and significant reductions in left ventricular ejection fraction and percentage of fractional shortening. These changes coincided with increases in plasma levels of atrial natriuretic peptide and brain natriuretic peptide that were linearly related to the left ventricular structural and functional changes observed in patients with preeclampsia.

CONCLUSION

Pregnant patients with preeclampsia showed adaptation to the increase in systemic blood pressure, with significant modification of left ventricular structure and function related to the plasma levels of both atrial natriuretic peptide and brain natriuretic peptide. A simple evaluation of plasma natriuretic peptide concentrations could help to discriminate patients with preeclampsia who have a condition of mild left ventricular overload.

Brain natriuretic peptide (BNP) and cyclic guanosine monophosphate (cGMP) levels in normal pregnancy and preeclampsia

OBJECTIVE

Our purpose was to evaluate plasma levels of brain natriuretic peptide (pBNP) and cyclic guanosine monophosphate (pcGMP) in preeclamptic patients and controls.

STUDY DESIGN

Blood samples were obtained from 35 patients with preeclampsia and from the same women during the subsequent puerperal period. The control group consisted of normotensive pregnant women, matched with the patients for age, gestational age, and parity. The concentrations of pBNP and pcGMP were determined by the RIA method. Statistical analysis was performed using the Mann-Whitney's U test.

RESULTS

The pBNP level in the preeclampsia group was significantly increased, to 7-fold that of the control group. The pcGMP level was 50% higher in the preeclampsia group than in the control group, but this was not significant. Both the pBNP level and the pcGMP level in the puerperal period did not significantly differ between the patients and the controls.

CONCLUSION

The pBNP concentrations increased in the preeclamptic women, and then these compensations were normalized in the puerperal period.

Effect of ovariectomy and estrogen replacement on cardiovascular disease in heart failure-prone SHHF/Mcc- fa cp rats

The importance of endogenous and exogenous estrogen levels to the development of cardiovascular disease in women in controversial. The purpose of our study was to examine the effect of estrogen on the development of hypertension, cardiac hypertrophy, ventricular function, and gene expression for atrial natriuretic peptide (ANP) and components of the renin angiotensin system in spontaneously hypertensive heart failure rats (SHHF/Mcc- facp). Development of hypertension was prevented in 3-month-old ovariectomized rats receiving subcutaneous 17 beta -estradiol implants (EST) compared to ovariectomized (OVX) and controls (CON). EST had the least left ventricular hypertrophy, CON were intermediate, and OVX had the most (P<0.05), correlating well with systolic blood pressure. OVX had significantly lower percentage V(1)myosin isoform compared to EST and CON, indicating reversion to a more immature phenotype associated with hypertrophy. Similarly, OVX had decreased percentage left ventricular shortening fraction by echocardiography compared to EST and CON. These changes were not accompanied by alterations in plasma ANP, or in expression of mRNA for left ventricular ANP, renal renin, or hepatic angiotensinogen. Serum angiotensin converting enzyme activity was lower in EST compared to CON or OVX. When 17 beta -estradiol was given to 17-month-old rats that had naturally ceased estrous cycling, there was no effect on hypertension, progression of cardiac functional decline, or survival. In conclusion, estradiol treatment given prior to the development of hypertension in SHHF prevented left ventricular hypertrophy and hypertension. Development of congestive heart failure was not delayed if 17 beta -estradiol was begun in the post-menopausal period. Effectiveness of estrogen therapy may depend on age or whether hypertension is already established at the time treatment is begun.

Plasma and 24-h NO(x) and cGMP during normal pregnancy and preeclampsia in women on a reduced NO(x) diet

We tested the hypothesis that nitric oxide (NO) biosynthesis increases during normal human pregnancy and decreases in preeclampsia. The major metabolites of NO, nitrate and nitrite (NO(x)), were measured in both the plasma and 24-h urine of women subjected to a reduced NO(x) diet. In this way, the plasma and urinary levels mainly reflected endogenous production rather than dietary intake. Moreover, we assessed cGMP, a second messenger of NO, in the same samples. Both NO(x) and cGMP assays were validated in our laboratory. We first conducted a cross-sectional study of nonpregnant women (n = 15), normal pregnant women in the first (n = 9), second (n = 17) and third (n = 22) trimesters, as well as women with preeclampsia (n = 15) and transient hypertension of pregnancy (n = 7). We also performed a serial study in the same women (n = 9) before, during, and after pregnancy. Taken together, the results of the two investigations suggested marked increases in cGMP production especially during the first trimester when the maternal circulation is rapidly vasodilating. In contrast, whole body NO production as estimated by the plasma level and urinary excretion of NO(x) was not elevated during the first trimester. Finally, unequivocal demonstration of reduced NO biosynthesis in preeclampsia was not forthcoming.

Physiology and pathophysiology of blood volume regulation

Adequate cardiac output and tissue perfusion is dependent on intravascular blood volume and its adequate return to the heart. Considering the overall functions of the cardiovascular system in ensuring appropriate flow to the peripheral microcirculation, it is not surprising that conflicts of interest may occur when an organism is exposed to stresses. Of particular importance are the stresses in which there are increased oxygen demands, decreased oxygen availability and concomitant requirements for thermoregulation. When there is depletion of intravascular blood volume, the splanchnic circulation is in effect an "autologous blood bank" for maintaining venous return until trans-capillary refill and haemodilution occurs. With the acute haematological stress response centralisation of blood, secondary contraction of the venous capacitance occurs, as seen with acute hypoxia. This results in overfilling of the heart, activation of atrial volume receptors, release of atrial natriuretic peptide and subsequent reduction of the plasma volume by rapid shifting of plasma into the lymphatic capacitance (via spleen) and transcapillary efflux throughout the circulation. In this overview the physiology and pathophysiology of blood volume, red cell mass and plasma volume regulation is reviewed.