Transplacental passage and fetal secretion of aldosterone

Development of aldosterone biosynthesis during fetal and pediatric periods; Histological analysis of CYP11B2-positive cell distribution in the zona glomerulosa of human adrenal

The distribution of CYP11B2-positive or aldosterone producing adrenocortical cells in human fetuses and children and their age-dependent changes has not been studied. We aimed to explore the changes of aldosterone biosynthesis and age-related histological alterations of the zona glomerulosa in human adrenal gland during fetal and pediatric periods. We first reviewed 125 fetal and pediatric autopsy cases and retrieved 78 adrenals from 70 cases. CYP11B2 immunohistochemistry and quantitative image analysis of its results were performed in all adrenal glands. The ratio of the definitive zone (DZ) or zona glomerulosa (ZG) / the whole adrenocortical areas started to increase in the 2nd trimester, subsequently decreased in the 3rd, increased after birth, peaked in infancy, and then gradually decreased. The ratio of CYP11B2-positive / whole adrenocortical areas remained low during the fetal period but increased after birth, peaked at infancy, and then decreased. The ratio of CYP11B2-positive / DZ or ZG areas and CYP11B2-positive areas / depth of DZ or ZG demonstrated a distinctive bimodal pattern, with one peak in the fetal period and another in the neonatal period to infancy. This is the first study to perform quantitative analysis of the distribution of CYP11B2-positive cells, the histological DZ or ZG, and the development of aldosterone biosynthesis in human adrenal glands during fetal and pediatric periods.

Cardiovascular Health Starts in the Womb

Hypertension has largely been viewed as a disorder of adulthood. Historically, blood pressure (BP) was not routinely measured in children because hypertension was considered uncommon in childhood. It was not until the 1970s that it was apparent that in childhood BP levels were normally lower compared with those in adults, were related to age and growth, and that abnormal BP in children needed different definitions. Based on the distribution of BP levels in available child cohorts, the 95th percentile of BP levels became the definition of hypertension in children and adolescents-an epidemiological definition. Subsequent clinical and epidemiological research identified associated risk factors in childhood that linked abnormal BP in youth with hypertension in adulthood. In the 1980s, the Barker hypothesis, based on observations that low birth weight could be linked to cardiovascular disease in adulthood, promoted further research spanning epidemiological, clinical, and basic science on the childhood origins of hypertension. This review focuses on recent findings from both longitudinal maternal-child cohorts and experimental models that examine both maternal and offspring conditions associated with risks of subsequent cardiovascular disease.

Tissue concentration of aldosterone in fetal adrenals of intrauterine death cases

OBJECTIVES

Fetal adrenals are one of the main organs responsible for maturation and survival. Extant literature is not clear about whether second trimester fetal adrenals are capable of synthesizing secreting aldosterone.

METHODS

We have taken 20 adrenals from fetuses of intrauterine death cases. None of the fetuses had any external malformations and obstetric history was unremarkable. The organs were weighed and homogenized. The supernatant was used for aldosterone estimation by ELISA.

RESULTS

We consistently detected aldosterone in all the cases including second trimester. However, we did not see any correlation between aldosterone concentration and gestational age. It is striking to note that there are wide variations in the tissue levels of aldosterone across different gestational ages and also same period.

CONCLUSIONS

Tissue aldosterone levels in second trimester can be possibly induced by stress preceding intrauterine deaths. It is possible that functional status of adrenal is different in intrauterine death cases as opposed to elective abortions in second trimester.

The invention of aldosterone, how the past resurfaces in pediatric endocrinology

Sodium and water homeostasis are drastically modified at birth, in mammals, by the transition from aquatic life to terrestrial life. Accumulating evidence during the past ten years underscores the central role for the mineralocorticoid signaling pathway, in the fine regulation of this equilibrium, at this critical period of development. Interestingly, regarding evolution, while the mineralocorticoid receptor is expressed in fish, the appearance of its related ligand, aldosterone, coincides with terrestrial life, as it is first detected in lungfish and amphibian. Thus, aldosterone is likely one of the main hormones regulating the transition from an aquatic environment to an air environment. This review will focus on the different actors of the mineralocorticoid signaling pathway from aldosterone secretion in the adrenal gland, to mineralocorticoid receptor expression in the kidney, summarizing their regulation and roles throughout fetal and neonatal development, in the light of evolution.

Maternal Nutritional and Water Homeostasis as a Presage of Fetal Birth Weight

Birth weight is a key determinant of perinatal outcomes which affect physical development and metabolic function. In this study, we evaluated the potential role of maternal body composition and nutritional status in programing fetal birth weight. This was a longitudinal study that included 29 pregnant women and their full-term newborns. Maternal dietary energy and fluid intake and body adipose tissue were assessed. In addition, we measured the serum content of copeptin, aldosterone, and angiotensin II in maternal and umbilical cord blood. The measurements were done across the three trimesters of pregnancy, on average, at 11.6 weeks, 18.3 weeks, and 30.2 weeks. Each newborn's birth weight was determined at the percentile line, using the World Health Organization (WHO) standards based on the gestational age, gender, and weight. We found no appreciable relation of fetal birth weight to the maternal dietary and fluid intakes, and the content of angiotensin II, aldosterone, or copeptin. However, birth weight correlated with increases in body adipose tissue in early pregnancy stages. Further, birth weight correlated positively with copeptin and adversely with angiotensin II in cord blood. We conclude that the present findings may be helpful in the assessment of a critical level of body adipose tissue in women of child-bearing age, above which the potential risk of macrosomia appears. The female population of child-bearing age needs a continual update on the nutritional knowledge to prevent modifiable maternal and fetal perinatal complications.

Prenatal diagnosis of Bartter syndrome: amniotic fluid aldosterone

OBJECTIVE

Bartter syndrome is a severe inherited tubulopathy characterized by postnatal salt wasting, severe polyuria, dehydration, failure to thrive and secondary hyperaldosteronism. Prenatally, the disease is usually discovered following the onset of severe polyhydramnios in the second trimester. We studied amniotic fluid aldosterone concentration in Bartter syndrome and in controls.

METHODS

Amniotic fluid aldosterone was assayed by radioimmunoassay. We undertook a retrospective case-control study based on 36 cases of prenatally suspected and postnatally confirmed Bartter syndrome (22 with identified mutations): and 72 gestational age matched controls presenting with polyhydramnios and 72 without polyhydramnios. Amniotic fluid aldosterone was compared between the three groups.

RESULTS

The median amniotic fluid aldosterone concentration in the Bartter syndrome group (90 pg/mL) was not different from that in the controls with polyhydramnios (90 pg/mL, P = 0.33) or without polyhydramnios (87 pg/mL, P = 0.41).

CONCLUSION

Amniotic fluid aldosterone assay cannot be used for prenatal diagnosis of Bartter syndrome. © 2015 John Wiley & Sons, Ltd.

Aldosterone biosynthesis in the human adrenal cortex and associated disorders

Aldosterone is one of the mineralocorticoids synthesized and secreted by the adrenal glands, and it plays pivotal roles in regulating extracellular fluid volume and blood pressure. Autonomous excessive aldosterone secretion resulting from adrenocortical diseases is known as primary aldosteronism, and it constitutes one of the most frequent causes of secondary hypertension. Therefore, it is important to understand the molecular mechanisms of aldosterone synthesis in both normal and pathological adrenal tissues. Various factors have been suggested to be involved in regulation of aldosterone biosynthesis, and several adrenocortical cell lines have been developed for use as in vitro models of adrenal aldosterone-producing cells, for analysis of the underlying molecular mechanisms. In this review, we summarize the available reports on the regulation of aldosterone biosynthesis in the normal adrenal cortex, in associated disorders, and in in vitro models.

100th anniversary of the discovery of the human adrenal fetal zone by Stella Starkel and Lesław Węgrzynowski: how far have we come?

Year 2010 marks a centennial anniversary of the description by Stella Starkel and Lesław Węgrzynowski, Polish students of the Faculty of Medicine, University of Lwów, the fetal zone of the human fetal adrenal gland. In 1911 both, Starkel and Węgrzynowski were graduated from the Faculty of Medicine of Lwow University. The paper appeared in the German Arch. Anat. Physiol. and its original title was "Beitrag zur Histologie der Nebeniere bei Feten und Kindern" ("Contribution to histology of adrenals of fetuses and children"). The studies were performed on 100 adrenal glands obtained from fetuses (from 6th month of gestation) and up to 5-year-old children. They described the fetal zone as a "medullary zone", also as "immature cortex", which undergoes involution in first years of life. To commemorate this discovery, this review aimed to present the most important achievements of studies on the development and involution of the human adrenal fetal zone.

Aldosterone postnatally, but not at birth, is required for optimal induction of renal mineralocorticoid receptor expression and sodium reabsorption

Sodium wasting during the neonatal period is the consequence of a physiological aldosterone resistance, related to a low renal mineralocorticoid receptor (MR) expression at birth, both in humans and mice. To investigate whether aldosterone is involved in the neonatal regulation of MR expression, we compared aldosterone and corticosterone levels and renal MR expression by quantitative real-time PCR, between aldosterone synthase (AS) knockout, heterozygous, and wild type (WT) mice, at birth and postnatal d 8. Analysis of MR transcripts showed a similar expression profile in all genotypes, demonstrating that the lack of aldosterone does not modify either the low renal MR expression at birth or its postnatal induction. However, mRNA levels of the α-subunit of the epithelial sodium channel, a MR target gene, were significantly higher in WT compared with AS knockout mice, both at birth and postnatal d 8, despite high corticosterone levels in AS knockout mice, indicating that aldosterone is required for optimal renal induction of the epithelial sodium channel. Using organotypic cultures of newborn WT kidneys, we confirmed that aldosterone does not regulate MR expression at birth, but is instead capable of increasing MR expression in mature kidneys, unlike dexamethasone. In sum, we demonstrate both in vivo and in vitro, that, whereas aldosterone has no significant impact on renal MR expression at birth, it is crucial for optimal MR regulation in postnatal kidneys and for appropriate hydroelectrolytic balance. Understanding of MR-regulatory mechanisms could therefore lead to new therapeutic strategies for the management of sodium loss in preterms and neonates.

Development and function of the human fetal adrenal cortex: a key component in the feto-placental unit

Continuous efforts have been devoted to unraveling the biophysiology and development of the human fetal adrenal cortex, which is structurally and functionally unique from other species. It plays a pivotal role, mainly through steroidogenesis, in the regulation of intrauterine homeostasis and in fetal development and maturation. The steroidogenic activity is characterized by early transient cortisol biosynthesis, followed by its suppressed synthesis until late gestation, and extensive production of dehydroepiandrosterone and its sulfate, precursors of placental estrogen, during most of gestation. The gland rapidly grows through processes including cell proliferation and angiogenesis at the gland periphery, cellular migration, hypertrophy, and apoptosis. Recent studies employing modern technologies such as gene expression profiling and laser capture microdissection have revealed that development and/or function of the fetal adrenal cortex may be regulated by a panoply of molecules, including transcription factors, extracellular matrix components, locally produced growth factors, and placenta-derived CRH, in addition to the primary regulator, fetal pituitary ACTH. The role of the fetal adrenal cortex in human pregnancy and parturition appears highly complex, probably due to redundant and compensatory mechanisms regulating these events. Mounting evidence indicates that actions of hormones operating in the human feto-placental unit are likely mediated by mechanisms including target tissue responsiveness, local metabolism, and bioavailability, rather than changes only in circulating levels. Comprehensive study of such molecular mechanisms and the newly identified factors implicated in adrenal development should help crystallize our understanding of the development and physiology of the human fetal adrenal cortex.

Physiological partial aldosterone resistance in human newborns

In the neonatal period, the human kidney is characterized by an impaired ability to regulate water and sodium homeostasis, resembling partial aldosterone resistance. The aim of our study was to assess this hormonal insensitivity in newborn infants and to determine its relationship with neonatal sodium handling. We conducted a prospective study in 48 healthy newborns and their mothers. Aldosterone, renin, and electrolyte concentrations were measured in umbilical cords and in maternal plasma. Urinary aldosterone concentrations and sodium excretion were determined at urination within 24 h after birth. A significant difference was observed between aldosterone and renin levels in newborn infants compared with their mothers (817 +/- 73 versus 575 +/- 55 pg/mL and 79 +/- 10 versus 15 +/- 2 pg/mL, respectively, p < 0.001). This hyperactivation of the renin-angiotensin-aldosterone system was associated with hyponatremia and hyperkalemia in the newborn infants, and high urinary sodium loss, consistent with a partial aldosterone resistance at birth. Unlike plasma aldosterone, urinary aldosterone concentration was found highly correlated with plasma potassium concentrations, thus representing the best index for accurate evaluation of mineralocorticoid sensitivity. Our study represents a comprehensive characterization of the renin-aldosterone axis in newborn infants and provides evidence for physiologic partial aldosterone resistance in the neonatal period.

Developmental and functional biology of the primate fetal adrenal cortex

The unique characteristics of the primate (particularly human) fetal adrenal were first realized in the early 1900s when its morphology was examined in detail and compared with that of other species. The unusual architecture of the human fetal adrenal cortex, with its unique and disproportionately enlarged fetal zone, its compact definitive zone, and its dramatic remodeling soon after birth captured the interest of developmental anatomists. Many detailed anatomical studies describing the morphology of the developing human fetal adrenal were reported between 1920 and 1960, and these morphological descriptions have not changed significantly. More recently, it has become clear that fetal adrenal cortical growth involves cellular hypertrophy, hyperplasia, apoptosis, and migration and is best described by the migration theory, i.e. cells proliferate in the periphery, migrate centripetally, differentiate during their migration to form the functional cortical zones, and then likely undergo apoptosis in the center of the cortex. Consistent with this model, cells of intermediate phenotype, arranged in columnar cords typical of migration, have been identified between the definitive and fetal zones. This cortical area has been referred to as the transitional zone and, based on the expression of steroidogenic enzymes, we consider it to be a functionally distinct cortical zone. Elegant experiments during the 1950s and 1960s demonstrated the central role of the primate fetal adrenal cortex in establishing the estrogenic milieu of pregnancy. Those findings were among the first indications of the function and physiological role of the human fetal adrenal cortex and led Diczfalusy and co-workers to propose the concept of the feto-placental unit, in which DHEA-S produced by the fetal adrenal cortex is used by the placenta for estrogen synthesis. Tissue and cell culture techniques, together with improved steroid assays, revealed that the fetal zone is the primary source of DHEA-S, and that its steroidogenic activity is regulated by ACTH. In recent years, function of the human and rhesus monkey fetal adrenal cortical zones has been reexamined by assessing the localization and ontogeny of steroidogenic enzyme expression. The primate fetal adrenal cortex is composed of three functionally distinct zones: 1) the fetal zone, which throughout gestation does not express 3 beta HSD but does express P450scc and P450c17 required for DHEA-S synthesis; 2) the transitional zone, which early in gestation is functionally identical to the fetal zone but late in gestation (after 25-30 weeks) expresses 3 beta HSD, P450scc, and P450c17, and therefore is the likely site of glucocorticoid synthesis, and 3) the definitive zone, which lacks P450c17 throughout gestation but late in gestation (after 22-24 weeks) expresses 3 beta HSD and P450scc, and therefore is the likely site of mineralocorticoid synthesis. Indirect evidence, based on effects of P450c21 deficiency and maternal estriol concentrations, indicate that the fetal adrenal cortex produces cortisol and DHEA-S early in gestation (6-12 weeks). However, controversy exists as to whether cortisol is produced de novo or derived from the metabolism of progesterone, as data regarding the expression of 3 beta HSD in the fetal adrenal cortex early in gestation are conflicting. During the 1960s, Liggins and colleagues demonstrated that in the sheep, cortisol secreted by the fetal adrenal cortex late in gestation regulates maturation of the fetus and initiates the cascade of events leading to parturition. Those pioneering discoveries provided insight into the mechanism underlying the timing of parturition and therefore were of particular interest to obstetricians and perinatologists confronted with the problems of preterm labor. However, although cortisol emanating from the fetal adrenal cortex promotes fetal maturation in primates as it does in sheep, its role in the regulation of primate parturition, unlike that in sheep

Hypertensive cardiomegaly caused by an aldosterone-secreting adenoma in a newborn

A case of primary hyperaldosteronism and cardiomegaly due to a unilateral adrenal adenoma in a newborn is presented. Some peculiarities, most likely in relation to the onset of the disease during fetal life were evident: plasma cortisol was slightly increased before surgery, plasma renin activity was elevated 9 months after surgery and mineralcorticoid receptors remained suppressed 4 months after surgery. Unilateral adrenalectomy reversed both hypertension and cardiomegaly. We speculate that cardiomegaly was related to both hyperaldosteronism and hypertension and that individual factors are involved in the pathogenesis of cardiomegaly in hyperaldosteronism.

Is ANP responsible for the hemoconcentration in preeclampsia?

A hypothesis is presented that high plasma concentration of alpha-human Atrial Natriuretic Peptide (ANP) might be responsible for hemoconcentration of preeclampsia (PE), mediated by increased diuresis and shift of fluid to the interstitium. ANP is known as a peptide regulating blood volume by diuresis and natriuresis, and perhaps through increased permeability in vessels. Moreover ANP is an antagonist to the renin-angiotensin-aldosterone (RAA) system, especially when this system is activated quantitatively as in pregnancy or qualitatively as in PE.

Mechanisms regulating renal sodium excretion during development

The present review focuses on the ontogeny of mechanisms involved in renal sodium excretion during renal maturation. The effect of birth on renal excretion of sodium and the role played by the different tubular segments in the regulation of sodium excretion during maturation are discussed. The influence of circulating catecholamines and renal sympathetic innervation in regulating sodium excretion during renal development is reviewed. The effects of aldosterone, atrial natriuretic factor, and prostaglandins on sodium regulation during renal maturation are discussed. Special emphasis is given to the potential role of glucocorticoids in modulating sodium excretion early in life.

Aldosterone and corticosterone in amniotic fluid during various stages of pregnancy

Concentrations of unconjugated aldosterone and corticosterone were measured in amniotic fluid (AF) at different stages of pregnancy. AT 9-20 weeks gestation the mean AF level of aldosterone was 14.4+/0.7 ng/dl, and of corticosterone 82.9 +/- 6.4 ng/dl. Both showed the same pattern during pregnancy, with a rise in AF levels in the last few weeks. At 28-40 weeks gestation the mean AF aldosterone level was 25.5 +/- 2.0 ng/dl and the mean AF corticosterone was 218.3 +/- 26.6 ng/dl.

Simultaneous determination of seven unconjugated steroids in maternal venous and umbilical arterial and venous serum in elective and emergency cesarean section at term

In order to assess specific gluco- and mineralocorticoid functions in both mother and fetoplacental unit in relation to the presence or absence of labor, serum levels of unconjugated aldosterone (A), corticosterone (B), deoxycorticosterone (DOC), progesterone (P), 17-hydroxyprogesterone (17-OHP), cortisol (F), and cortisone (E) were determined simultaneously. These levels were determined by specific radioimmunoassays in two groups of 24 paired maternal venous and umbilical arterial and venous samples obtained at term delivery by either elective (Group I, N = 8) or emergency (Group II, N = 8) cesarean section. In Group II, after spontaneous labor, mean maternal serum levels of all steroids investigated exceeded those found in Group I (not in labor). These increases were most pronounced (p less than 0.005) in F (74%) and DOC (106%) levels demonstrating stimulation of both the glucocorticoid (cortisol)--and the mineralocorticoid (aldosterone)--producing pathways of the maternal adrenals by spontaneous labor. Arteriovenous differences in umbilical steroid levels revealed in both groups the placental origin of P, 17-OHP, and E (p less than 0.05 to 0.005), with greater (more negative) mean AV differences after labor (Group II). The negative AV difference of DOC, B, A, and F found in Group I, however, decreased after labor and became even positive in the cases of B and F, reflecting the close relationship between spontaneous labor and the fetal adrenal's active production not only of the glucocorticoids B and F, but also, to a lesser extent, of the mineralocorticoids DOC and aldosterone.

Behaviour of plasma renin activity and aldosterone during the first 72 h of life

Plasma renin activity (PRA) and plasma aldosterone concentrations (PAC) were determined in fifty normal newborns during the first 72 h of life. PRA was elevated in all cases and tends to increase from the first (6.79 +/- 0.69SE ng/ml/h) to the third day of life (8.24 +/- 0.96SE ng/ml/h). PAC was also elevated and rose from 24.06 +/- 3.23SE ng/dl on the first day to 39.20 +/- 4.25SE ng/dl on the third day. No significant correlation was observed between PRA and PAC. Serum sodium was within the normal range, whereas serum potassium was slightly elevated during the first 48 h of life. The physiological significance of the high levels of PRA and PAC in newborns is not clear at present. Many factors may be involved in the increased activation of the renin-angiotensin-aldosterone system: low blood pressure, hypersensitivity of the macula densa to catecholamines, relative insensitivity of the immature kidney to aldosterone, hyperkalaemia and other control mechanisms for aldosterone secretion all of which probably operate simultaneously during the first days of life.

Plasma renin and aldosterone in pregnancy complicated by adrenal insufficiency

Serial measurements of plasma renin and plasma aldosterone were made throughout pregnancy in two women with adrenal insufficiency. The values were compared with levels obtained in eight normal primigravidae. Aldosterone levels were low or undetectable in adrenal insufficiency and plasma renin levels were grossly elevated in one patient with adrenal insufficiency but within the normal range in the other.

Aldosterone and sodium HOMEOSTASIS in preterm infants

A specific mass spectrometric method was used for tetrahydroaldosterone determination in urine of preterm infants (26-34 weeks gestational age) up to 9 weeks of age. Hyponatraemia during the first 2 weeks of life was associated with an excretion of tetrahydroaldosterone (5-50 mug/24 h) comparable with full-term infants. Excretion of tetrahydroaldosterone was significantly elevated in all infants studied during the third week of life (80-350 mug/24 h) and this was associated with establishment of positive sodium balance. The excretion of tetrahydro aldosterone remained high for 2 or 3 weeks. The results are discussed in relation to the development of renal tubules and control mechanism for sodium homeostasis.

Plasma renin activity and aldosterone concentration in children

Using semi-micro methods, plasma renin activity (PRA) and plasma aldosterone concentration (PA) were measured concurrently in 79 healthy children aged 1 month to 15 years to establish a reference range. PRA and PA varied inversely with age. Eleven children with renal hypertension had higher PRA and PA than age-matched controls. In contrast, PRA was much greater in 38 saline-depleted children. PA was not uniformly increased in this group and was within the normal range in children with adrenal diseases compared with the high values seen in other salt-wasting states. The findings emphasise the need to relate data from patients to age-matched control values before attempting interpretation and suggest that sodium depletion is a more potent stimulator of renin-aldosterone release than renovascular disease or renal scarring in children. Plasma renin-aldosterone profiles were also valuable in discriminating between renal and adrenal causes of salt loss in childhood.

Plasma aldosterone, cortisol and corticosterone concentrations in the new-born guinea-pig

1. Plasma aldosterone concentrations have been measured by radio-immunoassay in the new-born and adult guinea-pig and related to plasma cortisol and corticosterone concentrations.2. Plasma aldosterone concentrations were high in the hours immediately after birth with peak values of 552 pg/ml. at between 6 and 24 hr of age. Adult male plasma concentrations were 72 pg/ml. in plasma taken by cardiac puncture and 126 pg/ml. when measured in blood taken from an indwelling arterial catheter.3. The major plasma glucocorticoid was cortisol and earlier reports of values above 1 mug/ml. were confirmed by more exacting column chromatography with Sephadex LH 20.4. There was no constant relation between aldosterone and glucocorticoid concentrations in the animals studied, either new-born or adult.5. Plasma cortisol: corticosterone ratios were not constant but varied considerably. In the adult a sevenfold rise in plasma cortisol concentration occurred under certain conditions without any change in plasma corticosterone concentrations.

Plasma aldosterone concentration at delivery and during the newborn period

Aldosterone concentrations in plasma of women on normal sodium intake undergoing cesarean section were 3.7+/-1.4 ng/100 ml (mean+/-1 SD). These values were significantly lower (P < 0.001) than those observed in mothers on normal sodium diet, delivered by the vaginal route (14.9+/-7.0 ng/100 ml). A significant elevation (P < 0.001) of the concentrations was found if the mothers had been on sodium restriction and/or diuretics (44.9+/-24.2 ng/100 ml). In supine position, adult nonpregnant subjects have aldosterone concentrations in plasma of 1.7+/-1.4 ng/100 ml on normal sodium intake and of 16.7+/-8.1 ng/100 ml on low sodium diet.Simultaneous determinations of aldosterone levels in cord blood showed that cord values were significantly higher than those of the corresponding mother (P < 0.01 by paired t test). However, values in cord blood of infants born to mothers on a normal sodium intake were significantly lower (P < 0.005) than those of infants whose mothers had required low sodium diet and/or diuretics during their pregnancy. Aldosterone concentrations in plasma of infants 1-72 hr of age and born to mothers on normal sodium intake were 25.9+/-11.7 ng/100 ml (mean +/-1 SD). These values were significantly lower (P < 0.005) than those of infants born to mothers on restricted sodium intake with or without diuretics (80.3+/-54.4 ng/100 ml). The concentrations at birth were not significantly different from those observed during the first 3 days of life (P > 0.6).

The regulation of aldosterone secretion in anephric man

The regulation of aldosterone secretion in anephric man was investigated in studies on nephrectomized patients who were being intermittently hemodialyzed while awaiting renal transplantation. The effects of supine and upright posture on the concentration of plasma aldosterone on the 1st day postdialysis and on a 3rd or 4th day postdialysis were compared to the effects of postural variation in normal subjects who were on a low sodium intake and on a high sodium intake. In contrast with the normal subjects who exhibited higher concentrations of plasma aldosterone after 2 hr of upright posture than in the supine position and low concentrations of plasma aldosterone on a high sodium intake, the anephric patients showed less consistent variations in plasma aldosterone due to changes in posture and exhibited higher concentrations of plasma aldosterone on the 3rd or 4th day postdialysis, despite an increase in body weight, than on the 1st day postdialysis. The increase in the concentration of plasma aldosterone in the anephric patients between the 1st day postdialysis and the 3rd or 4th day postdialysis indicates that aldosterone secretion is not responding primarily, in this situation, to volume-related stimuli. There was a high degree of correlation between the concentration of plasma aldosterone and the corresponding levels of serum potassium concentration, which also rose significantly between the 1st day postdialysis and the 3rd or 4th day postdialysis. Furthermore, when potassium accumulation between dialyses was prevented in three of these patients, the concentration of plasma aldosterone fell to minimally detectable levels. The results of these studies suggest that the primary regulator of aldosterone secretion in the absence of the kidneys is potassium.

Renin, angiotensin and aldosterone in human pregnancy and the menstrual cycle

Aldosterone secretion is frequently, although not invariably, increased above the normal non-pregnant range in normal pregnancy. Substantial increases in plasma aldosterone concentration have also been demonstrated as early as the sixteenth week. In pregnancy, aldosterone secretion rate responds in the usual way to changes in sodium intake.

Plasma renin concentration is frequently, but not invariably, raised above the normal non-pregnant range. Plasma renin-substrate is consistently raised in pregnancy. Plasma angiotensin II has also been shown usually to be raised in a series of pregnant women.

A significant positive correlation has been shown between the maternal plasma aldosterone concentration and the product of the concurrent plasma renin and renin-substrate concentrations. This suggests that the increased plasma aldosterone in pregnancy is the consequence of an increase in circulating angiotensin II, which in turn is related to the level of both renin and its substrate in maternal blood. For these reasons, estimations of renin activity in pregnancy are of dubious value.

The increased renin, angiotensin and aldosterone concentrations may represent a tendency to maternal sodium depletion, probably mainly a consequence of the increased glomerular filtration rate. It is possible that the nausea and other symptoms of early pregnancy may be a consequence of this tendency to sodium depletion, with its attendant hormonal changes. In ‘pre-eclampsia’, renin and aldosterone values are generally slightly lower than in normal pregnancy. Human chorion can apparently synthesize renin independently of the kidney. The physiological significance of this remains at present obscure, but it seems unlikely that this source contributes much, if at all, to the often elevated maternal plasma renin.

Plasma renin, renin-activity and angiotensin II concentrations, and aldosterone secretion are increased in the luteal phase of the menstrual cycle.