Control of sodium excretion in human pregnancy

Nutraceuticals and Hypertensive Disorders in Pregnancy: The Available Clinical Evidence

The aim of the present critical review is to summarize the available clinical evidence supporting the use of some dietary supplements that have been shown to lower blood pressure in hypertensive pregnant women. A systematic search strategy was carried out to identify trials in MEDLINE (National Library of Medicine, Bethesda, Maryland, MD, USA; January 1980 to September 2019) and the Cochrane Register of Controlled Trials (The Cochrane Collaboration, Oxford, UK). The terms 'nutraceuticals', 'dietary supplements', 'pregnancy', 'pre-eclampsia', 'clinical trial', and 'human' were incorporated into an electronic search strategy. The references of the identified studies and review articles were reviewed to look for additional studies of interest. We preferably selected papers that reported recent comprehensive reviews or meta-analysis, or original clinical trials of substances with blood pressure-lowering or vascular protective effect in pregnancy. There is a relative body of evidence that supports the use of calcium, vitamin D, folic acid, and resveratrol in preventing the development of hypertensive disorders in pregnancy, and evidence supporting drug treatment too. Further clinical research is advisable to identify the dosage and timing of the supplementation, the group of women that might benefit the most from this approach, and the nutraceuticals with the best cost-effectiveness and risk-benefit ratio for widespread use in clinical practice.

Sodium Intake during Pregnancy, but Not Other Diet Recommendations Aimed at Preventing Cardiovascular Disease, Is Positively Related to Risk of Hypertensive Disorders of Pregnancy

BACKGROUND

The role of diet on hypertensive disorders of pregnancy (HDPs), including preeclampsia and gestational hypertension (GHTN), remains unclear.

OBJECTIVES

We evaluated whether adherence during pregnancy to dietary recommendations that reduce cardiovascular disease (CVD) in the general population is related to the risk of HDPs.

METHODS

We followed 66,651 singleton pregnancies from 62,774 women participating in the Danish National Birth Cohort. Diet was assessed during week of gestation 25 with an FFQ from which we created 2 dietary pattern scores: 1) AHA, based on the diet recommendations from the AHA 2020 Strategic Impact Goals; and 2) the Dietary Approaches to Stop Hypertension (DASH) diet. Cases of HDPs were identified through linkage with the Danish National Patient Registry. RRs and 95% CIs of HDPs were estimated by increasing quintiles of adherence to the AHA and DASH scores using log-Poisson regression models with generalized estimating equations-to account for repeated pregnancies per woman-while adjusting for potential confounders.

RESULTS

We identified 1809 cases of HDPs: n = 1310 preeclampsia (n = 300 severe preeclampsia) and n = 499 cases of GHTN. Greater adherence to AHA or DASH scores was not related to the risk of HDPs. However, when each component of the scores was separately evaluated, there were positive linear relations of sodium intake with HDPs (P-linearity < 0.01). Women with the highest sodium intake [median 3.70 g/d (range: 3.52, 7.52 g/d)] had 54% (95% CI:16%, 104%) higher risk of GHTN and 20% (95% CI:1%, 42%) higher risk of preeclampsia than women with the lowest intake [median 2.60 g/d (range: 0.83, 2.79 g/d)]. In addition, intake of whole grains was positively related to the risk of GHTN but not to preeclampsia ( P-heterogeneity = 0.002).

CONCLUSION

Sodium intake during pregnancy, but no other diet recommendations to prevent CVD among nonpregnant adults, is positively related to the occurrence of HDPs among pregnant Danish women.

Salt, aldosterone and extrarenal Na+ - sensitive responses in pregnancy

Outside of pregnancy excessive salt consumption is known to be harmful being linked to increased blood pressure and cardiovascular disease. However, pregnancy represents a major change to a woman's physiology resulting in an intimate adaptation to environmental conditions. It is now becoming apparent that salt is essential for a number of these changes during pregnancy including haematological, cardiac adaptations as well as directly influencing placental development and the uteroplacental immune environment. The present review discusses the important role that salt has during normal pregnancy and evidence will also be presented to show how the placenta may act as a salt sensing organ temporarily, yet substantially regulating maternal blood pressure.

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The placenta may function as an extrarenal regulator of maternal blood pressure.

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Na⁺handling in pregnancy is completely different to the non-pregnant situation.

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Na⁺may actually lower blood pressure in pregnancy affected with pre-eclampsia.

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Aldosterone is an important regulator of placental and fetal development.

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Na⁺ may compensate for aldosterone deficiency in pregnancy.

Pregnancy as a critical window for blood pressure regulation in mother and child: programming and reprogramming

Pregnancy is a critical time for long-term blood pressure regulation in both mother and child. Pregnancies complicated by placental insufficiency, resulting in pre-eclampsia and intrauterine growth restriction, are associated with a threefold increased risk of the mother to develop hypertension later in life. In addition, these complications create an adverse intrauterine environment, which programmes the foetus and the second generation to develop hypertension in adult life. Female offspring born to a pregnancy complicated by placental insufficiency are at risk for pregnancy complications during their own pregnancies as well, resulting in a vicious circle with programmed risk for hypertension passing from generation to generation. Here, we review the epidemiology and mechanisms leading to the altered programming of blood pressure trajectories after pregnancies complicated by placental insufficiency. Although the underlying mechanisms leading to hypertension remain the subject of investigation, several abnormalities in angiotensin sensitivity, sodium handling, sympathetic activity, endothelial function and metabolic pathways are found in the mother after exposure to placental insufficiency. In the child, epigenetic modifications and disrupted organ development play a crucial role in programming of hypertension. We emphasize that pregnancy can be viewed as a window of opportunity to improve long-term cardiovascular health of both mother and child, and outline potential gains expected of improved preconceptional, perinatal and post-natal care to reduce the development of hypertension and the burden of cardiovascular disease later in life. Perinatal therapies aimed at reprogramming hypertension are a promising strategy to break the vicious circle of intergenerational programming of hypertension.

The role of the renin-angiotensin-aldosterone system in preeclampsia: genetic polymorphisms and microRNA

The compensatory alterations in the rennin-angiotensin-aldosterone system (RAAS) contribute to the salt-water balance and sufficient placental perfusion for the subsequent well-being of the mother and fetus during normal pregnancy and is characterized by an increase in almost all the components of RAAS. Preeclampsia, however, breaks homeostasis and leads to a disturbance of this delicate equilibrium in RAAS both for circulation and the uteroplacental unit. Despite being a major cause for maternal and neonatal morbidity and mortality, the pathogenesis of preeclampsia remains elusive, where RAAS has been long considered to be involved. Epidemiological studies have indicated that preeclampsia is a multifactorial disease with a strong familial predisposition regardless of variations in ethnic, socioeconomic, and geographic features. The heritable allelic variations, especially the genetic polymorphisms in RAAS, could be the foundation for the genetics of preeclampsia and hence are related to the development of preeclampsia. Furthermore, at a posttranscriptional level, miRNA can interact with the targeted site within the 3'-UTR of the RAAS gene and thereby might participate in the regulation of RAAS and the pathology of preeclampsia. In this review, we discuss the recent achievements of genetic polymorphisms, as well as the interactions between maternal and fetal genotypes, and miRNA posttranscriptional regulation associated with RAAS in preeclampsia. The results are controversial but utterly inspiring and attractive in terms of potential prognostic significance. Although many studies suggest positive associations with genetic mutations and increased risk for preeclampsia, more meticulously designed large-scale investigations are needed to avoid the interference from different variations.

Circulating lymphangiogenic factors in preeclampsia

BACKGROUND

Preeclampsia (PE), a human pregnancy-specific disorder is characterized by an anti-angiogenic state due to high levels of circulating soluble vascular endothelial growth factor 1 (sVEGFR-1). However, the role of lymphangiogenesis in PE has not been investigated. Recently, impaired vascular endothelial growth factor C (VEGF-C) (factor that regulates lymphangiogenesis) signaling has been implicated in the pathogenesis of interstitial edema and salt-sensitive hypertension. Therefore, we hypothesized that circulating VEGF-C and its circulating receptors (sVEGFR-2 and sVEGFR-3) may also be altered in PE and correlate with the severity of the phenotype.

METHODS

We analyzed plasma levels of VEGF-C, sVEGFR-1, sVEGFR-2, and sVEGFR-3 in women with gestational hypertension (GHTN, n = 20), PE (n = 20), and normotensive pregnancies (NP, n = 20) in the third trimester and values were reported as mean ± SD in pg/mL.

RESULTS

As previously reported, sVEGFR-1 levels were significantly higher in subjects with PE (19,938 ± 12,973) than in GHTN (7156 ± 5432), p < 0.01 or NP (7760 ± 6018), p < 0.01. VEGF-C levels were lower in subjects with GHTN (676 ± 323) than in PE (1335 ± 625), p < 0.01, but not statistically different than in NP (971 ± 556), p = 0.11. There was a trend toward lower sVEGFR-2 in PE as compared to GHTN or NP. Interestingly, sVEGFR-3 was significantly lower in PE (54,371 ± 21,107) as compared to NP (83,709 ± 24,983), p < 0.01, but not different as compared to GHTN (54,642 ± 26,947). The ratio of sVEGFR-2 + sVEGFR-3/VEGF-C was dramatically lower during PE (57 ± 38) as compared to GHTN (113 ± 72), p < 0.01 or NP (133 ± 91), p < 0.01.

CONCLUSIONS

PE is characterized by circulating pro-lymphangiogenic state as evidenced by decreased sVEGFR-3, slightly decreased sVEGFR-2, increased VEGF-C, and a dramatically lower ratio of sVEGFR-2 + sVEGFR-3/VEGF-C. Our data suggest that the circulating pro-lymphangiogenic state during PE may be a compensatory response to edema and hypertension. Additional studies are needed to evaluate the clinical relevance of the altered lymphangiogenic signaling pathway during PE.

Longitudinal study of the renin angiotensin aldosterone system in purebred Spanish broodmares during pregnancy

During pregnancy, the coordinated interaction of the components of the renin-angiotensin-aldosterone system (RAAS) plays a vital role in accommodating the cardiovascular, haemodynamic and haematological needs imposed by foetal development and the placenta. This significantly influences the birth weight of the neonate and foetal viability. Although the evolution of each of the components of this system has been widely described in various species, it has not yet been clarified in the mare. Thus, the objectives of the present research were: 1) to establish reference values for renin (REN), angiotensin II (ANG-II) and aldosterone (ALD) concentrations in Spanish broodmares, and 2) to analyse the evolution of the aforementioned components during pregnancy. Thirty-one Purebred Spanish broodmares aged between 5 and 15 years old were studied for 11 months of pregnancy and compared to a control group composed of 11 non-pregnant Spanish mares. Morning venous blood samples were drawn on a monthly basis during pregnancy and pre-treated to prevent degradation until subsequent analysis. Serum REN, ANG-II and ALD concentrations were analysed by competitive immunoassay. This study found that pregnancy in Purebred Spanish broodmares is characterised by a gradual increase in REN concentrations, variable fluctuations in ALD concentrations, and no significant modifications in ANG-II concentrations. These results could provide potentially valuable information in understanding the physiological basis of the RAAS in mares, since we have been able to establish specific reference ranges for these components, as well as obtaining information on their evolution during pregnancy. As is often the case in other animal species, the increase in RAAS activity is a natural physiological process that occurs during pregnancy in Spanish broodmares. This may also be related to certain metabolic and hormone responses that contribute to the control of homeostasis in pregnant mares.

Regulation of placental growth by aldosterone and cortisol

During pregnancy, trophoblasts grow to adapt the feto-maternal unit to fetal requirements. Aldosterone and cortisol levels increase, the latter being inactivated by a healthy placenta. By contrast, preeclamptic placental growth is reduced while aldosterone levels are low and placental cortisol tissue levels are high due to improper deactivation. Aldosterone acts as a growth factor in many tissues, whereas cortisol inhibits growth. We hypothesized that in preeclampsia low aldosterone and enhanced cortisol availability might mutually affect placental growth and function. Proliferation of cultured human trophoblasts was time- and dose-dependently increased with aldosterone (P < 0.04 to P < 0.0001) and inhibited by spironolactone and glucocorticoids (P < 0.01). Mineralo- and glucocorticoid receptor expression and activation upon agonist stimulation was verified by visualization of nuclear translocation of the receptors. Functional aldosterone deficiency simulated in pregnant mice by spironolactone treatment (15 μg/g body weight/day) led to a reduced fetal umbilical blood flow (P < 0.05). In rat (P < 0.05; R(2) = 0.2055) and human (X(2) = 3.85; P = 0.0249) pregnancy, placental size was positively related to plasma aldosterone. Autocrine production of these steroid hormones was excluded functionally and via the absence of specific enzymatic transcripts for CYP11B2 and CYP11B1. In conclusion, activation of mineralocorticoid receptors by maternal aldosterone appears to be required for trophoblast growth and a normal feto-placental function. Thus, low aldosterone levels and enhanced cortisol availability may be one explanation for the reduced placental size in preeclampsia and related disorders.

Hyperaldosteronism in pregnancy

Aldosterone is a key regulator of electrolyte and water homeostasis and plays a central role in blood pressure regulation. Hormonal changes during pregnancy, among them increased progesterone and aldosterone production, lead to the required plasma volume expansion of the maternal body as an accommodation mechanism for fetus growth. This review discusses the regulation of aldosterone production by aldosterone synthase (CYP11B2); the impact on aldosterone secretion due to the presence of a chimeric gene originating from a crossover between CYP11B1 and CYP11B2 in glucocorticoid remediable aldosteronism (GRA) — the inherited form of hypertension; enhanced aldosterone production in aldosterone-producing adenoma (APA); and idiopathic hyperaldosteronism (IHA). Features of hyperaldosteronism are also found in patients with apparent mineralocorticoid excess (AME), in which glucocorticoids exacerbate activation of the mineralocorticoid receptor (MR) because of a defect in the 11β-hydroxysteroid dehydrogenase type 2 enzyme. Regulation of aldosterone production and tissue-specific activation of the mineralocorticoid receptor are prerequisites for optimal control of body fluids and blood pressure during pregnancy and contribute largely to the wellbeing of the mother-to-be.

High aldosterone-to-renin variants of CYP11B2 and pregnancy outcome

BACKGROUND

Increased aldosterone concentrations and volume expansion of normal pregnancies are hallmarks of normal pregnancies and blunted in pre-eclampsia. Accordingly, we hypothesized an active mineralocorticoid system to protect from pre-eclampsia.

METHODS

In pregnant women (normotensive n = 44; pre-eclamptic n = 48), blood pressure, urinary tetrahydro-aldosterone excretion and activating polymorphisms (SF-1 site and intron 2) of the aldosterone synthase gene (CYP11B2) were determined; 185 non-pregnant normotensive individuals served as control. Amino acid-changing polymorphisms of the DNA- and agonist-binding regions of the mineralocorticoid receptor were evaluated by RT-PCR, SSCP and sequencing.

RESULTS

Urinary tetrahydro-aldosterone excretion was reduced in pre-eclampsia as compared to normal pregnancy (P < 0.05). It inversely correlated with blood pressure (r = 0.99, P < 0.04). Homozygosity for activating CYP11B2 polymorphisms was preferably present in normotensive as compared to pre-eclamptic pregnancies, identified (intron 2, P = 0.005; SF-1 site, P = 0.016). Two mutant haplotypes decreased the risk of developing pre-eclampsia (RR 0.16; CI 0.05-0.54; P < 0.001). In contrast, intron 2 wild type predisposed to pre-eclampsia (P < 0.0015). No functional mineralocorticoid receptor mutant has been observed.

CONCLUSIONS

High aldosterone availability is associated with lower maternal blood pressure. In line with this observation, gain-of-function variants of the CYP11B2 reduce the risk of developing pre-eclampsia. Mutants of the mineralocorticoid receptor cannot explain the frequent syndrome of pre-eclampsia.

Sodium balance in pregnancy

Sodium is the major cation in the extracellular fluid volume (ECFV) and as such, is the most important determinant of osmolality and of the volume of this fluid compartment. Hence any alteration in the control of body sodium will be reflected by changes in the ECFV, including the maternal plasma volume. There is no doubt that expansion of the plasma volume is a necessary and desirable event during pregnancy, influencing positively both maternal and fetal outcome. Therefore, studies of sodium balance in pregnancy provide important information relevant to both mother and fetus.

Renal response to an acute protein challenge in pregnant women with borderline hypertension

BACKGROUND

The renal reserve (RR), assessed after an oral protein challenge or the intravenous administration of amino acids, is still present in healthy pregnant women (NP), although resting glomerular filtration rate (GFR) and renal plasma flow (RPF) increase progressively throughout normal gestation. No studies have addressed this issue in hypertensive gravidas; the aim of this trial was to evaluate renal response to an acute protein load (PL) in NP and pregnant women with borderline hypertension (HP).

METHODS

Five NP, eight HP and eight healthy non-pregnant women (CG) were evaluated. After fasting overnight, all subjects received an oral water load (20 mL/kg of body weight), the urinary output was then replaced orally with equal volumes of water. After two 30 min periods, an 80 g PL was provided. Creatinine clearance (CCr) was measured every 30 min from 1 h before and for 4 h following PL. Participants remained recumbent during the study, bladder emptiness was assessed by ultrasound immediately after each micturition. Baseline CCr was taken as the average of two 30 min periods before PL and peak Ccr as the maximal CCr recorded thereafter.

RESULTS

The groups were similar with regard to age, weight or gestation age. Baseline CCr (NP: 118.5+/-6.0, HP: 127.4+/-6.7 and CG: 99.8+/-2.9 mL/min, P=0.004 (CG vs NP and HP), increased after PL to NP: 223.5+/-9.8 to HP: 178.5+/-13 and to CG: 149.1+/-4.0 mL/min, P<0.0004 (CG vs HP, CG vs NP and NP vs HP)). Peak minus baseline CCr was 97.3+/-10.1; 46.3+/-12.7 and 48.3+/-4.8 for NP, HP and CG, respectively (P<0.006 HP vs CG and NP). The peak CCr was obtained significantly earlier in both pregnant groups (Period 3) compared with the healthy non-pregnant women (Period 5) (P=0.02). The fractional proximal reabsorption of sodium (FPRNa+) at peak CCr was similar in the groups (NP: 0.74+/-0.01 HP: 0.78+/-0.02 and CG: 0.74+/-0.03, P=not significant (NS)) as was the distal delivery of sodium (DDNa+) (NP: 5.8+/-0.5; HP: 4.1+/-0.5 and CG: 4.3+/-0.4 meq/min, P=NS). Fractional excretion of urea (%) increased from 91.4+/-5.5 to 105.5+/-9.8%; 80.7+/-8.0 to 97.3+/-9.8; and 44.4+/-7.8 to 86.0+/-7.1 in NP, HP and CG, respectively (P=NS). There was a trend towards a poorer maternal and fetal outcome in the HP group.

CONCLUSION

Mid-term borderline HP failed to increase CCr as much as NP did after a protein challenge, suggesting altered functional response of the nephron or lessened sensitivity of renal vasculature to additional vasodilator stimuli. These results support the interest of additional prospective studies with a larger number of patients to confirm these findings and evaluate the value of RR tests as predictors of outcome of pregnancies at risk.

Preeclampsia: a renal perspective

Preeclampsia is a syndrome that affects 5% of all pregnancies, producing substantial maternal and perinatal morbidity and mortality. The aim of this review is to summarize our current understanding of the pathogenesis of preeclampsia with special emphasis on the recent discovery that circulating anti-angiogenic proteins of placental origin may play an important role in the pathogenesis of proteinuria and hypertension of preeclampsia.

Evidence for compromised aldosterone synthase enzyme activity in preeclampsia

BACKGROUND

In normal pregnancy, an increased aldosterone (Aldo) concentration coincides with volume expansion. In preeclampsia, Aldo levels are low despite intravascular volume depletion. The present investigation aimed to characterize the compromised Aldo synthesis in preeclampsia, and to identify the molecular basis hereof.

METHODS

We recruited 66 pregnant women (24 uneventful, 42 preeclamptic). Genomic DNA was isolated from peripheral blood leukocytes. Urine samples were obtained for gas chromatography-mass spectroscopic measurements of steroid hormones reflecting apparent Aldo synthase (CYP11B2) and 11-hydroxylase (CYP11B1) activities. Polymerase chain reaction (PCR)-based screening for CYP11B2 mutations was performed by SSCP, restriction analysis, and sequencing.

RESULTS

CYP11B1 activity was unaltered, but reduction of mean tetrahydro (TH)-Aldo excretion by a factor of 3.9 indicated a diminished CYP11B2 activity in preeclampsia. Accordingly, the ratios of (TH-11-dehydrocorticosterone [A]+TH-corticosterone [B]+5alpha-THB) to (TH-cortisone +TH-cortisol [F]+5alpha-THF) and of 18-OH-THA to THAldo were increased in preeclampsia 2.6- and 15.2-fold, respectively, indicating reduced Aldo synthesis due to diminished methyl oxidase (MO) activity. A lower percentage of women with normal pregnancies had CYP11B2 mutations when compared to preeclamptic women (P < 0.05). Eight polymorphisms were detected, two of which were non-amino acid conserving. Of those, the mutation V386A, earlier found to jeopardize MO activity, was exclusively observed in preeclampsia (0% vs. 17%; P < 0.05).

CONCLUSION

Aldo deficiency due to a compromised MO step of Aldo synthesis favors extracellular volume depletion, and may account for an increased risk of placental hypoperfusion and consecutive development of preeclampsia. The sole presence of mutation V386A in preeclamptic mothers may identify a subgroup with an increased risk to develop preeclampsia during pregnancy.

Induction of intrauterine growth restriction with a low-sodium diet fed to pregnant rats

OBJECTIVE

A low-sodium diet fed to female rats before mating through parturition leads to pups of lower weight. We characterized the effect of low dietary sodium during the last week of gestation (after fetal organogenesis) on fetal and maternal homeostasis.

STUDY DESIGN

Pregnant Sprague-Dawley rats were randomly assigned to a control group or to a group fed a low-sodium diet from gestational days 15 through 22. Systolic blood pressures were measured throughout pregnancy. On day 22 plasma volume was measured and blood samples were taken for electrolyte and hormonal measurements. Fetal and placental weights were also determined.

RESULTS

Plasma renin activity and aldosterone level were significantly higher in the experimental group than in the control group. Plasma volume was significantly lower in pregnant rats receiving a low-sodium than in those receiving a control diet. Rats receiving a low-sodium diet had pups of lower weight and length (4.45 +/- 0.22 g, 3.90 +/- 0.06 cm) than pups of the control group (5.21 +/- 0.12 g, 4.10 +/- 0.02 cm). Pups born to mothers with low-sodium diets recuperated from intrauterine growth restriction by 14 days after birth.

CONCLUSION

These data indicate that a low-sodium diet given to pregnant rats for the last 7 days of gestation leads to reduced plasma volume expansion and fetal growth restriction. This could prove to be a simple animal model for studying the relationship between maternal plasma volume and fetal growth.

Effects of gestation on enzymes controlling aldosterone synthesis in the rat adrenal

In the present study, the effects of gestation on various enzymes implicated in corticosteroid synthesis were evaluated in adrenal zona glomerulosa and zona fasciculata-reticularis of the Sprague-Dawley rat. The activity and expression of cholesterol side-chain cleavage cytochrome P450, 11beta-hydroxylase cytochrome P450, and aldosterone synthase cytochrome P450 (P450aldo) were analyzed. Plasma aldosterone levels were increased significantly at 22 days gestation (n = 10) and fell below the nonpregnant levels at 18-36 h postpartum (n = 11). The activity and expression of 11beta-hydroxylase cytochrome P450 and cholesterol side-chain cleavage cytochrome P450 were not modified by gestation. P450aldo activity increased at 14 days gestation (n = 4) and returned to the prepregnancy level at 2 weeks postpartum (n = 5). As shown by Northern blot analysis (n = 3), P450aldo messenger RNA increased significantly at 22 days gestation and decreased 18-36 h postpartum. We clearly demonstrated that elevated plasma aldosterone levels during pregnancy are associated with augmented activity and messenger RNA levels of P450aldo in the zona glomerulosa.

Characteristics of ANP-binding sites in the adrenal capsules of term-pregnant rats

Significant increases of circulatory volume and plasma aldosterone levels are observed in pregnancy. We investigated whether a decrease of atrial natriuretic peptide (ANP) receptors in the adrenal zona glomerulosa (ZG) could explain the marked elevation of plasma aldosterone occurring during pregnancy. 125I-ANP binding was measured in competition experiments using rANP(1-28), ANP(4-23), a truncated analog which has high specificity for the ANP-C receptor, or a combination of both. Western blot experiments were also performed with an investigation into the effect of ANP on aldosterone secretion in adrenal capsule suspensions. 125I-ANP binding on adrenal ZG membranes was displaced by ANP(1-28) with an affinity (Kd) of 313 +/- 39 and 323 +/- 60 pM (NS) for pregnant and non-pregnant rats, respectively. The density of sites (Bmax) decreased slightly but not significantly during pregnancy. Displacement experiments with ANP(4-23) demonstrated a Bmax of 137 and 134 fmol/mg of proteins (NS) for pregnant and non pregnant rats, respectively. Studies were performed to block the ANP-C site. Displacing the remaining 125I-ANP binding with ANP(1-28) led to an affinity constant and receptor density which were not significantly different between the two groups of rats. The results obtained with Western blots showed a single band of 123 kDa with no significant variations in ANP-R1 receptors in the ZG during gestation. The sensitivity of potassium-, ACTH- or angiotensin II-stimulated aldosterone secretion to ANP was not altered by gestation. These data show that the apparent hyperaldosteronism found in normal term-pregnant rats is not the consequence of modifications in the affinity, number and properties of ANP receptor types or in the sensitivity of the aldosterone response to ANP.

The effect of pregnancy on renal function: physiology and pathophysiology

Marked changes in renal function occur with pregnancy. We present a summary of these changes in this review and give insight into possible mechanisms if they are known. Controversies exist regarding the therapy of pregnancy-induced hypertension and asymptomatic and recurrent bacteriuria. The current views on these topics are given. Specific renal diseases are summarized, including transplantation, and optimum management strategies and maternal and fetal prognosis during pregnancy are given.

Plasma atrial natriuretic factor and urinary excretion of a ouabain displacing factor and dopamine in normotensive pregnant women before and after delivery

Estimation of urinary excretion of a ouabain displacing factor and dopamine was carried out immediately before delivery, and 7 days and 70 to 90 days after delivery in 12 normotensive pregnant women. Simultaneous estimation of plasma 99-126 atrial natriuretic factor, plasma renin activity, and plasma aldosterone were also undertaken. The data were compared with those obtained in a group of nonpregnant normotensive women (n = 14) and a group of pregnant normotensive women in the early phase of the third trimester (n = 14). Urinary ouabain displacing factor and dopamine levels were significantly higher in the early phase of the third trimester, as compared with nonpregnant women. But immediately before delivery, ouabain displacing factor excretion had fallen below nonpregnant values and dopamine excretion had dropped to control values. Both remained low after delivery. Plasma atrial natriuretic factor was higher in pregnant women, as compared with nonpregnant controls and remained high just before delivery and 7 and 70 to 90 days after delivery. Plasma renin activity and plasma aldosterone levels were higher during pregnancy and had fallen to nonpregnant values 7 days post partum. This drop in plasma renin activity and aldosterone by 7 days post partum, in contrast with the unchanged high values of atrial natriuretic factor, may contribute to negative sodium balance after delivery. It is concluded that there is considerable discrepancy in natriuretic and antinatriuretic factors before and after delivery.

Pregnancy-induced hypertension: current concepts

This brief review outlines current concepts concerning the aetiology and pathophysiology of pregnancy-induced hypertension and, based upon these concepts, presents a plan of intensive care management for the severe forms of this condition.

Volume homeostasis in normal and hypertensive human pregnancy

In this chapter are outlined the many factors involved in the regulation of sodium and volume homeostasis in normal human pregnancy and their interrelationships. New developments concerning the role of sodium/potassium ATPase, atrial natriuretic peptide, arginine vasopressin and angiotensin II as regulatory forces are outlined, together with a review of earlier work. Abnormalities found in women with, or destined for, PAH are described and their significance is discussed.