Plasma renin activity in healthy children

Early-in-Life Serum Aldosterone Levels Could Predict Surgery in Patients with Obstructive Congenital Anomalies of the Kidney and Urinary Tract: A Pilot Study

The aim of the study was to evaluate whether serum aldosterone levels or plasmatic renin activity (PRA) measured early in life (1-3 months) could predict a future surgical intervention for obstructive congenital anomalies of kidney and urinary tract (CAKUT). Twenty babies aged 1-3 months of life with suspected obstructive CAKUT were prospectively enrolled. The patients underwent a 2-year follow-up and were classified as patients needing or not needing surgery. In all of the enrolled patients, PRA and serum aldosterone levels were measured at 1-3 months of life and were evaluated as predictors of surgery by receiver-operating characteristic (ROC) curve analysis. Patients undergoing surgery during follow-up showed significantly higher levels of aldosterone at 1-3 months of life compared to those who did not require surgery (p = 0.006). The ROC curve analysis of the aldosterone for obstructive CAKUT needing surgery showed an area under the ROC curve of 0.88 (95%CI = 0.71-0.95; p = 0.001). The aldosterone cut-off of 100 ng/dL presented 100% sensitivity and 64.3% specificity and predicted surgery in 100% of cases. The PRA at 1-3 months of life was not a predictor of surgery. In conclusion, serum aldosterone levels at 1-3 months could predict the need for surgery during obstructive CAKUT follow-up.

IgE-Mediated Systemic Anaphylaxis And Its Association With Gene Polymorphisms Of ACE, Angiotensinogen And Chymase

BACKGROUND

The renin-angiotensin system (RAS) protects the circulation against sudden falls in systemic blood pressure via generation of angiotensin II (AII). Previously, we demonstrated that patients with anaphylaxis involving airway angioedema and cardiovascular collapse (AACVS) had significantly increased "I" gene polymorphisms of the angiotensin-converting-enzymes (ACE). This is associated with lower serum ACE and AII levels and was not seen in anaphylaxis without collapse nor atopics and healthy controls.

OBJECTIVES

To examine the angiotensinogen (AGT-M235T) and chymase gene (CMA-1 A1903G) polymorphisms in these original subjects.

METHOD

122 patients with IgE-mediated anaphylaxis, 119 healthy controls and 52 atopics had polymorphisms of the AGT gene and chymase gene examined by polymerase chain reactions and gel electrophoresis. Their previous ACE genotypes were included for the analysis.

RESULTS

AGT-MM genes (associated with low AGT levels) were significantly increased in anaphylaxis (Terr's classification). When combined with ACE, anaphylaxis showed increased MM/II gene pairing (p<0.0013) consistent with lower RAS activity. For chymase, there was increased pairing of MM/AG (p<0.005) and AG/II and AG/ID (p<0.0073) for anaphylaxis consistent with lower RAS activity. A tri-allelic ensemble of the 6 commonest gene combinations for the healthy controls and anaphylaxis confirmed this difference (p=0.0001); for anaphylaxis, genes were predominately MM/AG/II or ID, while healthy controls were DD/MT/AG or GG patterns.

CONCLUSION

Our gene polymorphisms show lower RAS activity for anaphylaxis especially AACVS. Animal models of anaphylaxis are focused on endothelial nitric oxide (eNO) which is shown to be the mediator of fatal shock and prevented by eNO-blockade. The interaction of AII and eNO controls the microcirculation in man. High serum AII levels reduce eNO activity, so higher RAS-activity could protect against shock. Our data shows low RAS activity in anaphylaxis especially AACVS, suggesting the influence of these genes on shock are via AII levels and its effects on eNO.

Diagnostic Role of Renal Doppler Ultrasound and Plasma Renin Activity as Screening Tools for Renovascular Hypertension in Children

OBJECTIVES

The diagnostic role of an ultrasound (US) and plasma renin activity (PRA) combination is unknown, despite the usefulness of Doppler US as a screening tool for renovascular hypertension (RVHT). The purpose of this study was to evaluate the diagnostic usefulness of US for RVHT in children stratified according to PRA.

METHODS

We identified 336 children who underwent renal Doppler US examinations for hypertension and divided them into a high-renin group (n = 177) and a normal-renin group (n = 159) based on PRA and stratified them by age. The Doppler US findings were retrospectively reviewed, and computed tomographic angiography (CTA) for the same children was used as the reference standard.

RESULTS

In the high-renin group, 36 patients had positive Doppler US findings that were confirmed by CTA in 32 cases. The sensitivity and specificity values for Doppler US in the high-renin group were 84.2% and 93.6%, respectively. In the normal-renin group, 10 patients had positive Doppler US findings; these positive findings were confirmed by CTA in 9 cases. The sensitivity and specificity values for US in the normal-renin group were 100.0% and 100.0%. There were anatomic variations (n = 3) and segmental artery stenosis (n = 2) among the cases with false-negative US findings, which were confirmed by CTA.

CONCLUSIONS

If patients have high PRA, a Doppler US examination should be performed with caution to avoid false-negative detection. If patients have normal PRA, renal Doppler US might be adequate for diagnosis of RVHT to avoid unnecessary CTA.

Does Extremely Low Birth Weight Predispose to Low-Renin Hypertension?

Low birth weight and prematurity are risk factors for hypertension in adulthood. Few studies in preterm or full-term born children reported on plasma renin activity (PRA). We tested the hypothesis that renin might modulate the incidence of hypertension associated with prematurity. We enrolled 93 prematurely born children with birth weight <1000 g and 87 healthy controls born at term, who were all examined at ≈11 years. Renal length and glomerular filtration rate derived from serum cystatin C were 0.28 cm (95% confidence interval, 0.09–0.47) and 11.5 mL/min per 1.73 m 2 (6.4–16.6) lower in cases, whereas their systolic/diastolic blood pressure (BP) was 7.5 mm Hg (4.8–10.3)/4.0 mm Hg (2.1–5.8) higher ( P <0.001 for all). The odds of having systolic prehypertension or systolic hypertension associated with extreme low birth weight were 6.43 (2.52–16.4; P <0.001) and 10.9 (2.46–48.4; P =0.002). Twenty-four hours of urinary sodium excretion was similar in cases and controls (102.1 versus 106.8 mmol; P =0.47). Sodium load per nephron was estimated as sodium excretion divided by kidney length (mmol/cm). PRA was 0.54 ng/mL per hour (0.23–0.85; P =0.001) lower in cases. PRA, systolic BP, and sodium load were available in 43 cases and 56 controls. PRA decreased with systolic BP (slope −0.022 ng/mL per hour/ − mm Hg ; P =0.048), but was unrelated to sodium load (slope +0.13 mmol/cm − mm Hg ; P =0.54). The slope of PRA on systolic BP was similar ( P =0.17) in cases and controls. In conclusion, extremely low birth weight predisposes young adolescents to low-renin hypertension, but does not affect the inverse association between PRA and BP.

Clinical Trial Registration—

URL: https://www.clinicaltrials.gov . Unique identifier: NCT02147457.

The effect of puberty on diurnal sodium regulation

The aim of this study was to investigate the impact of sex and puberty stage on circadian changes in sodium excretion, sodium-regulating hormones, and hemodynamics. Thirty-nine healthy volunteers (9 prepuberty boys, 10 prepuberty girls, 10 puberty boys, and 10 puberty girls) were included. They all underwent a 24-h circadian in-patient study under standardized conditions regarding activity, diet, and fluid intake. Blood samples were drawn every 4 h, and the urine was collected in fractions. Blood pressure and heart rate were noninvasively monitored. Atrial natriuretic peptide (ANP), angiotensin II, aldosterone, and renin were measured in blood. Children in puberty had lower plasma levels of renin (P<0.05) and angiotensin II (P<0.05) and a 26% reduction in filtered sodium without changes in sodium excretion compared with prepuberty children. A circadian rhythm in sodium excretion, the renin-angiotensin system, ANP, and blood pressure was found with a midnight ANP peak (P<0.001), a nighttime decrease in hemodynamic parameters (P<0.001), an increase in plasma renin (P<0.001) and angiotensin II (P<0.001), and a decrease in sodium excretion (P<0.001) mainly on the basis of increased sodium reabsorption (P<0.001). The timing of the changes did not depend on sex or puberty group. There is a circadian rhythm of sodium excretion and sodium regulation in 7- to 15-yr-old children. This rhythm is similar in boys and girls. As an important new finding, puberty changes the plasma levels of renin and angiotensin II without changing the amount of sodium excreted or the day to night sodium excretion ratio.

Neonatal renal physiology

The renal system plays a tremendous role in growth and development of infants and children. The kidney itself also undergoes a maturation process as it transitions from the fetal to the extrauterine environment. Renal function continues to undergo further adaptive changes in the neonatal period. It is important for the clinician caring for neonates to be aware of the expected fluid shifts, electrolyte handling, and renal functional capacity as these "normal" changes will become quite relevant when medical or surgical pathology is present. The preterm neonates are especially vulnerable due to their functionally immature kidneys. Renal function in the preterm neonate is not only immature at birth but there is a significant delay in the renal function to achieve its full capacity. This review highlights the physiologic adaptations of the kidney and its effects on the body during the neonatal period.

Relationships between renin, aldosterone, and 24-hour ambulatory blood pressure in obese adolescents

Renin-angiotensin system (RAS) activation and abnormalities of ambulatory blood pressure (ABP) are present in obesity, but relationships between components of the RAS and ABP have not been defined in the young. Anthropometric measurements and 24-h ABP were obtained on 30 obese adolescents with and without type 2 diabetes mellitus. Plasma renin activity (PRA), aldosterone, and other cardiovascular risk factors were measured. Median PRA levels were 2.5 [interquartile range (IQR), 1.7-4.1] ng/mL/h and were higher in the diabetic subjects compared with the nondiabetics. Females had significantly higher PRA than males 3.2 (IQR, 2-4.8) versus 1.8 (IQR, 1.1-2.9) ng/mL/h (p = 0.04) and were more obese. BMI Z score and PRA were significantly correlated (rho = 0.46, p < 0.001). PRA inversely correlated with 24-h systolic ABP (rho = -0.46, p = 0.02) and strongly with 24-h pulse pressure (rho = -0.61, p = 0.001). Aldosterone levels were also correlated with 24-h pulse pressure (rho = -0.46, p = 0.02). In multivariate models, lower PRA was independently associated with 24-h systolic blood pressure. In this study, PRA was positively correlated with BMI, but the relationships between components of the RAS and ABP were inverse. Further studies are needed to define the pathophysiologic relationship between RAS components and blood pressure regulation in obese youth.

Nitric oxide and angiotensin II regulation of renal hemodynamics in the developing piglet

We have previously shown that nitric oxide (NO) is a more important intrarenal vasodilator in the developing animal compared with the adult. The interaction between NO and the renin angiotensin system in the developing kidney is not known. The purpose of this study was to determine the role of NO and angiotensin II in the regulation of developing renal function. We examined the effects of the inhibition of intrarenal NO synthesis with N-nitro-L-arginine methyl ester (L-NAME), 3 micro g/kg/min, intrarenally, administered after intrarenal infusion of either saline or an angiotensin II AT1 receptor antagonist [ATX (A-81988), 0.4 micro g/kg/min] in piglets, age 3 wk, and adult pigs. The developing piglet demonstrated significantly greater renal responses to L-NAME alone. Intrarenal NO synthesis inhibition after saline preinfusion decreased renal blood flow (RBF) in the piglet 29% compared with the adult pig 9%, but only in the piglet decreased GFR 31%, and increased plasma renin activity 57%. Intrarenal infusion of ATX significantly increased RBF in the piglet, 23%, although not altering RBF in the adult. The renal responses to L-NAME were significantly attenuated by ATX preinfusion in both age groups. After ATX pretreatment, L-NAME in piglets decreased RBF 14%, and abolished the change in GFR, whereas in adult pigs decreased RBF only 5%.

IN CONCLUSION

1) angiotensin II may be a more important vasoconstrictor in the developing kidney and 2) NO is a more important regulator of renal function in the developing kidney through modulation of the renin angiotensin system.

Developmental consequences of the renin-angiotensin system

Molecular, cellular, and physiological studies indicate that the renin-angiotensin system (RAS) is highly expressed during early kidney development. We propose that a major function of the RAS during early embryonic development is the modulation of growth processes that lead the primitive kidney into a properly differentiated and architecturally organized organ suited for independent extrauterine life. As development progresses, the RAS acquires new and overlapping functions such as the endocrine and paracrine regulation of blood pressure and renal hemodynamics. Disease states in adult mammals often result in expression of RAS genes and phenotypic changes resembling the embryonic pattern, emphasizing the importance of undertaking developmental studies. Because of their importance in health and disease, the immediate challenge is to identify the mechanisms that regulate the unique development of the RAS and its role(s) in normal and abnormal growth processes.

Influence of upright activity on plasma renin activity and aldosterone concentration in children

Plasma renin activity (PRA) and plasma aldosterone concentration (PAC) were measured in 156 healthy infants and children under basal conditions of normal diet and recumbency. PRA and PAC were also evaluated during and after stimulation of the renin-angiotension-aldosterone system by postural change. Basal values of PRA significantly declined with increasing age. Postural change by standing up resulted in an increase of PRA and PAC in all age groups. The increment of PRA but not of PAC was greater in older than in younger children. Neither the basal nor the stimulated levels of PRA and PAC were influenced by sex, body weight, body surface area, serum sodium, serum potassium, creatinine, and 24-h urine secretion of sodium and potassium. Both PRA and PAC returned to the basal levels within 60 min after resuming recumbent posture.

Age-related changes in the renin-aldosterone system. Physiological effects and clinical implications

Age-related changes in the renin-aldosterone system in normal humans are well documented. The most pronounced changes are observed at the extremes of life: plasma renin activity and plasma aldosterone levels are highest in the newborn, and lowest in the elderly population. There is a close temporal and directional relationship between the age-related decrease in plasma renin activity and the age-related decrease in plasma aldosterone. The renin-aldosterone system is also influenced by sex and race. The activation of the renin-aldosterone system in newborns and infants probably represents an important physiological mechanism designed to maintain positive sodium balance. The decreases in plasma renin activity and plasma aldosterone levels observed in elderly persons are usually only modest, and are not associated with clinical alterations in fluid or electrolyte metabolism. The superimposition of a disease process, or the injudicious prescription of a drug, inhibiting renin release or angiotensin II production, could theoretically facilitate sodium wasting in newborns or infants, or precipitate hyporeninaemic hypoaldosteronism in older adults. The primary clinical importance of age-related changes in the renin-aldosterone system relates to its impact on the proper classification of an individual's renin-aldosterone profile when attempting to diagnose a clinical condition (e.g. low, normal or high renin hypertension). This is particularly true for newborns, infants and children to age 4, and for adults entering the sixth decade of life.

Renovascular hypertension in children

Renal arteriography remains the only study to identify and define correctly both location and extent of renal artery stenosis. Because other studies do not adequately identify all children who have renal artery disease, it is reasonable to perform renal arteriography in those children with severe hypertension who do not have another readily identifiable cause for their hypertension. On the other hand, in children with less profound elevation of blood pressure in whom there is no other definable cause, it is possible to defer renal angiography. In these children with mild or moderate hypertension, studies such as the captopril 99mTc-DTPA scan or intravenous digital subtraction angiography may identify those for whom arteriography is more likely to have abnormal results.

The renin-angiotensin system and blood pressure regulation during infancy and childhood

The renin-angiotensin system plays multiple roles in the maintenance of normal blood pressure and renal function. The balance and integration of these roles change during development in ways that we do not yet fully understand. This article reviews the ways in which the renin-angiotensin system maintains normal cardiovascular homeostasis during development and its participation in physiologic and biochemical events.

Severe tubular resistance to aldosterone in a child with familial juvenile nephronophthisis

A 9.5-year-old girl, whose early symptoms were polyuria and growth retardation, is described. During the progression of her disease, hyperkalaemia developed out of proportion to the degree of renal insufficiency. Her fractional excretion of sodium increased from 3.3% to 35%, and her fractional excretion of potassium decreased from 55% to 22%. The plasma aldosterone level and plasma renin activity (PRA) were very high--290 ng/ml and 100 ng/dl per hour, respectively (normal range for this age 2.6-20.8 ng/ml and 1.2-2.7 ng/ml per hour, respectively). In an attempt to reduce these hormone levels, an acute and sustained saline load, captopril and peritoneal dialysis were used. Only the sustained saline load normalized the PRA, and only peritoneal dialysis sufficiently suppressed the plasma aldosterone level. Successful renal transplantation normalized both plasma aldosterone and PRA. This girl presents the unusual occurrence of pseudohypoaldosteronism type I, during the course of familial juvenile nephronophthisis.

Vesicoureteric reflux and renal injury

Renal injury associated with the intrarenal reflux (IRR) of urine that is either infected, under high pressure, or both, is a major cause of severe hypertension during childhood and adolescence and of chronic renal insufficiency in patients less than 30 years of age. Many, but not all, adolescent and adult patients with reflux nephropathy (RN) give a history of urinary tract infection (UTI) or unexplained fevers in infancy or early childhood, when the kidney is thought to be at greatest risk of injury. Although vesicoureteric reflux (VUR) is observed more commonly in infants than children with UTI, it is rare in uninfected patients at any age and should never be considered a normal finding during human development. Renal scarring may not be obvious in radiographic or radionuclear studies to medical management alone, no definite benefit of one over the other was observed, regardless of the grade of VUR. Moreover, progressive renal injury in scarred kidneys has been noted even after VUR had been corrected, when infection had been prevented, and while hypertension had been controlled satisfactorily. Focal glomerular sclerosis, a lesion found in patients with proteinuria and RN, has been identified not only in scarred kidneys, but also may be seen in contralateral, unscarred kidneys without VUR, which might suggest a humoral factor or, perhaps, a hyperfiltration phenomenon. RN is one of the most frequent causes of end-stage renal disease (ESRD) in children, adolescents, and young adults, which is potentially preventable. However, prevention will depend on early identification of patients at risk--infants and young children after the first UTI and siblings of patients with VUR--aggressive and effective treatment of UTI, minimizing intravesical pressure, and education of patients, parents, and physicians.

Inadequacy of captopril challenge test for diagnosing renovascular hypertension in children and adolescents

A captopril challenge test (CCT) for renovascular disease in adults was described recently. We used it in 20 consecutive, untreated hypertensive children and adolescents. All had a normal urinalysis and glomerular filtration rate and non-diagnostic renal sonograms or intravenous urograms. Plasma renin activity (PRA) was measured before and 1 h after administration of captopril (0.76 +/- 0.17 mg/kg). The CCT was positive in 10 patients. Renal arteriograms were performed in 7 patients with a positive CCT and in 2 with a negative CCT. Renovascular disease was found in 4 patients, 1 of whom had a negative CCT. The PRA response to captopril was the same in patients with true- and the false-positive tests. The predictive value of the positive test was 43%. In conclusion, we did not find the CCT, as described for adults, to be of value in children and adolescents.

Management of severe hypertension in childhood Takayasu's arteritis

Six children presented with severe hypertension caused by Takayasu's arteritis (TA), of whom four had bilateral renal artery narrowing and two coarctation syndrome. Two presented with hypertensive encephalopathy and four with congestive cardiac failure. All had a strongly positive skin reactions to purified protein derivative of mycobacterium tuberculosis. Bilateral renal arterial bypass grafts performed in two children resulted in prolonged normalization of their blood pressures, but the grafts clotted 12-18 months later. Primary renal autotransplantation was unsuccessful in two children, one with bilateral renal arterial narrowing and iliac vessel involvement and one with a long coarctation. Secondary renal autotransplantation was successful in a third child with localized aortitis. A successful aortic patch graft was performed in one child with coarctation of the aorta. Angiotensin-converting-enzyme inhibitors should be used with caution in treating the hypertension caused by TA, since bilateral renal arterial narrowing is common and their administration may result in renal insufficiency. The long-term prognosis is guarded in severely hypertensive children with extensive vascular disease due to TA.

Molecular and cellular aspects of renin during kidney ontogeny

The activity of the renin-angiotensin system is subjected to remarkable developmental changes. Circulating as well as renal concentrations of renin are high in early life, decreasing progressively as maturation evolves. This review summarizes the current molecular framework underlying those changes during kidney development. Evidence is presented demonstrating that expression of the renin gene is developmentally regulated. Renin messenger ribonucleic acid (mRNA) levels are higher in fetuses and newborns than in adult mammals. As maturation progresses, the distribution of renin and its mRNA shifts from large intrarenal arteries in the fetus to the classic juxtaglomerular localization in the adult. Potential explanations for these changes as well as the cytosolic events mediating renin release and gene expression are discussed. Evidence is also presented demonstrating that under diverse physiologic and pathologic conditions the adult kidney vasculature has the capability to recruit renin gene expressing and/or containing cells. Throughout, an effort has been made to identify gaps in our knowledge. Not without bias, we hope that future research in this area will lead to a better understanding of the biology of renin in the developing as well as the adult individual.

Postnatal development of renal function during the first year of life

Several aspects of renal function vary considerably during the 1st year of life and differ markedly from the equivalent values in the adult. Glomerular filtration rate (GFR) increases little, prior to the time an infant reaches a conceptional age of 34 weeks, the point in renal development from which the absolute GFR (ml/min) increases gradually to mature values when linear growth is completed during adolescence. GFR corrected for body size is not comparable with adult normal values until after 12 months of age; therefore, whether GFR is estimated from Scr or measured by timed urine collection, there is no easily recalled range of normal values for infants. One must know the changes in the renal function of normal infants that take place following birth during the 1st year of life. Despite several attempts to do so, renal function during the 1st year of life cannot be assessed from urine flow rate. A urine flow rate of less than 1 ml/kg per hour may be normal and appropriate and may not be harmful either to preterm or full-term infants with normal GFR. Impaired concentrating ability of the neonatal kidney is probably of no clinical significance in all but the most extreme circumstances and is not a major factor in an infant becoming dehydrated, developing hypernatremia or being at greater risk of acute renal injury. Acid-base status in infants must be interpreted appropriately to know when alkali therapy should be introduced to avoid growth failure secondary to true metabolic acidosis. When plasma renin activity is measured in the infant with renal failure of hypertension, one must compare the result with the normal range of values related to postnatal age of normal infants.

Hypodipsic hypernatremia associated with absence of septum lucidum and olfactory dysfunction

A case of hypodipsic hypernatremia in a 16-month-old Japanese boy is reported. Partial antidiuretic hormone deficiency was present. Computed tomography of the brain revealed absence of septum lucidum. No ophthalmological abnormality could be found. He had hyposmia, which has not been reported previously in association with hypernatremia due to hypodipsia. Forced fluid administration and nasal 1-deamino-8-d-arginine vasopressin treatment could maintain serum electrolyte levels within normal ranges. However, episodes of hypernatremia could not be completely avoided while he was treated with 1-deamino-8-d-arginine vasopressin and ad libitum oral fluid.

Type 4 renal tubular acidosis (sub-type 2) associated with idiopathic interstitial nephritis

An 18-month-old girl presenting with anorexia and failure to thrive, was referred for adenoidectomy. Arterial hypertension was discovered on physical examination. Laboratory results revealed hyperkalaemic, hyperchloraemic, metabolic acidosis, with slight azotemia. Urinary aldosterone excretion and plasma renin were decreased. Renal biopsy showed idiopathic interstitial nephritis. The diagnosis of type 4 renal tubular acidosis, sub-type 2, i.e. primary hyporeninaemic secondary hypoaldosteronism was proposed. According to our knowledge, this disease has not previously been reported in young children, but is well known in azotaemic adults. We therefore propose the inclusion of this uncommon renal disease in the differential diagnosis of failure to thrive in childhood.

The renin-angiotensin-aldosterone system in infancy and childhood in basal conditions and after stimulation

Plasma renin activity (PRA), aldosterone (PA), sodium and potassium concentration were measured in 107 healthy infants and children under basal conditions of normal diet and recumbency. Urinary aldosterone (UAldo), sodium and potassium were also measured (n = 51). A significant (P less than 0.001) age-related decrease in PRA (r = -0.67), PA (r = -0.67), UAldo (r = -0.56) was observed, with a striking scatter of values especially in infancy. The reninangiotensin-aldosterone system (RAAS) was also studied after stimulation by standardised sodium restriction during 4 days, followed by acute postural change (n = 40). After salt restriction a rise of PRA and UAldo was noted, but a rise in PA could not be demonstrated in children aged 0-6 months. The influence of postural change on the RAAS seems more important in older children. The reported values not only in basal but also in stimulated conditions allow study of the RAAS in diseases such as salt loss and hypertension.

Plasma and adrenal aldosterone levels in premature mice at birth and during neonatal development

The concentrations of aldosterone in the plasma and adrenal glands, the concentrations of sodium and potassium in the plasma and the hematocrit were estimated from birth to day 6 after birth in premature mice removed by Caesarean section on day 19 of pregnancy in comparison with newborn mice delivered spontaneously vaginally on day 20 of pregnancy. In premature mice, the plasma aldosterone concentrations increased twice: at birth after reanimation, then at 6 h after birth. The first increase at birth resulted probably from ACTH stimulation. Several factors could be involved in the peak at 6 h after birth: ACTH stimulation, the decrease in the level of sodium in the plasma and the increase in the hematocrit due to kidney immaturity of premature mice. The results suggest that the renin-angiotensin-aldosterone system is able to respond to stimulations in the first 6 h after birth in premature mice. The rise in the level of plasma aldosterone which has been found at birth in newborns delivered spontaneously vaginally on day 20 of pregnancy (control animals) did not result from variations of plasma electrolytes, plasma volume and ACTH; this rise has been induced by labor of the parturition which caused the aldosterone release from adrenal glands.

Importance of plasma angiotensin concentrations in a comparative study of responses to angiotensin in the maturing newborn lamb

Plasma angiotensin concentrations were measured in a longitudinal study of the vascular, renal, and adrenal responses to infusions of angiotensin II (AII) in the maturing newborn lamb. Basal plasma concentrations of angiotensin increased with age and correlated with the rising arterial pressure that occurred with maturation. However, age was a stronger determinant of arterial pressure than was plasma angiotensin concentration. For any given dose of AII per kilogram of body weight, the actual plasma angiotensin concentration achieved increased as the lambs matured and gained weight. Therefore, a comparative study of biologic responses to AII in maturing animals must be based on actual plasma angiotensin concentrations achieved rather than on dose of AII infused per kilogram of body weight. When analyzed on the basis of actual plasma angiotensin concentration, the increase in arterial pressure and the suppression of plasma renin activity in response to increasing plasma angiotensin concentrations did not differ significantly as the lambs matured. However, the increment in plasma aldosterone concentrations in response to increasing plasma angiotensin concentrations was diminished in immature lambs (less than 18 days) when compared to the aldosterone responses in the same lambs at older ages.

Ontogeny of blood pressure and the renin-angiotensin-aldosterone system. Sequential studies in the newborn lamb

To test the hypothesis that the rise in arterial pressure occurring with maturation is due to an increase in the vascular responsiveness to angiotensin II, sequential cumulative doses of angiotensin II were infused intravenously into chronically catheterized newborn lambs maintained on a constant, weight-adjusted sodium intake from birth to 8 weeks of age. Basal mean arterial pressure correlated with both age and weight, but age was a stronger determinant of mean arterial pressure than was weight. No change in the mean arterial pressure response to angiotensin II occurred with maturation. Basal plasma renin activity and plasma aldosterone concentrations were low and did not change significantly with age. Therefore, in the newborn lamb in the sodium replete state, age is a better determinant of arterial pressure than is weight. However, an age-related change in vasoconstrictor responsiveness to angiotensin II does not occur and, therefore, cannot account for the rise in arterial pressure that is observed with maturation.

Sodium, potassium and age: possible determinants of plasma renin activity and aldosterone during childhood (age 4-16)

The renin-angiotensin-aldosterone system was studied in fifty healthy children aged 4-16 years under normal sodium and potassium intake. The plasma renin activity (PRA) and plasma aldosterone (PA) decreased with age: r = -0.30, P less than 0.05 for plasma renin activity and r = -0.33, P less than 0.05 for plasma aldosterone. Significant negative correlation was obtained between plasma renin activity and the 24-h urinary sodium excretion; r = -0.40, P less than 0.01. This relationship remained significant when the daily urinary sodium excretion was corrected for 1.73 m2 body surface area (BSA); r = -0.40, P less than 0.01. Using the multivariance analysis, plotting the plasma renin activity against the two combined parameters (24-h urinary sodium excretion and age), no improvement was obtained (r = 0.38, P greater than 0.05). This finding suggests that during childhood, sodium rather than age has a major modulatory role on plasma renin activity. With advancing age the plasma aldosterone showed a significant positive correlation coefficient with plasma renin activity(r = 0.29, P less than 0.05). Multivariance analysis between plasma aldosterone and the two combined parameters, Plasma renin activity and age, significantly improved the correlation coefficient (r = 0.42, P less than 0.05) suggesting that both plasma renin activity and age play a dominant modulatory role in the control of plasma aldosterone during childhood. Neither 24-h urinary sodium excretion, nor 24-h urinary potassium excretion, improved the multiple correlation coefficient with plasma aldosterone when added to plasma renin activity and age.

Renin and angiotensin levels in children

Plasma renin activity, plasma renin concentration, and angiotensin II levels were measured in 63 normal children aged between 2 months and 12 years. The results showed that the high levels of renin and angiotensin II present in infancy remained above adult levels throughout the first decade of life but that there was a decline with age. Boys less than 8 years old had lower plasma renin activity and angiotensin II levels than girls of a similar age; this may be due to a relative substrate deficiency. Serum urea levels were inversely correlated with plasma renin activity in both sexes. A significant inverse relationship was found between both plasma renin activity and angiotensin II, and serum sodium in the girls; a similar, although not statistically significant, relationship was seen with plasma renin activity in the boys. An inverse correlation was found between plasma renin concentration and diastolic blood pressure for the group as a whole.

Changes in ventricular size and plasma renin activity after cardiac surgery in children

Plasma renin activity and one-dimensional echocardiographic measurements of the left atrium and left ventricle as well as function indices were studied repeatedly in 20 children with various cardiopathies (ages: 9 months to 15 years) before and after corrective surgery. Nine children had tetralogy of Fallot, four had pulmonary stenosis, four had rheumatic heart disease, two had ventricular septal defect, and one had atrial septal defect. Plasma renin activity was normal preoperatively, but increased significantly immediately after surgery, was still significantly higher on the 12th postoperative day and returned to normal six to eight weeks after surgery. Patients with tetralogy of Fallot and pulmonary stenosis had higher plasma renin activity values than the others. There was a positive correlation between plasma renin activity and postoperative percentage change of the left ventricular dimension. In patients with tetralogy of Fallot and pulmonary stenosis, this meant that plasma renin activity became normal when the preoperatively small left ventricle reached its normal dimension. This adjustment occurred slowly over a period of two months. In rheumatic heart disease and left-to-right shunt lesions, plasma renin activities became normal when the preoperatively dilated left ventricle decreased in size towards normal values; the plasma renin activities of these patients had reached normal levels by the fifth postoperative day. The renin secretion is modulated by various factors: of these, ventricular size and pulmonary venous return seem to be of importance.

Micro determination of plasma renin activity in normal infants and children of capillary and venous blood

Plasma renin activity (PRA) has been measured by microassay on capillary and venous blood sampled simultaneously in 21 subjects; there is no significant difference between these two groups of PRA values. PRA values in normal infants, children and adults have been measured with this microassay and the results are similar to those previously published by authors using different radioimmunological assays.

Role of the renin-angiotensin-aldosterone system in hypertensive children with coarctation of the aorta

To investigate the role of the renin-angiotensin-aldosterone system as a cause of hypertension, 20 hypertensive patients with coarctation of the aorta were studied during normal and low sodium intake and after diuresis with flurosemide. Eight patients with essential hypertension and 13 control subjects were similarly studied. Plasma renin activity values in patients with coarctation were similar to those in patients with essential hypertension and in control patients during normal and low sodium diets. However, after the administration of furosemide, plasma renin activity values were significantly higher in the patients with coarctation than in the other two groups (P less than 0.005 and less than 0.01, respectively). The values for urinary aldosterone, plasma volume and extracell fluid volume (bromide space) were increased in patients with coarctation during both normal and low sodium intake. These renin and aldosterone responses and body fluid spaces in patients with coarctation suggest that their hypertension resembles a one-kidney Goldblatt model. The data help to better define the role of the renin-angiotensin-aldosterone system in the hypertension of coarctation and thus may help guide the clinician in therapeutic interventions.

Hyperreninemia and secondary hyperaldosteronism in pheochromocytomas

Foremost in the differential diagnosis of hypertension is the identification of surgically correctable lesions. Increased plasma renin activity in a hypertensive patient suggests the presence of a renovascular or renal etiology. We have recently seen two adolescent patients whose hyperreninemia was cuased by a pheochromocytoma. Secondary hyperaldosteronism was an associated finding.

Immunoreactive urinary prostaglandins A and E in neonates, children, and adults

Urinary prostaglandins were measured by radioimmunoassay in neonates (31-35 weeks gestational age), children (4-15 years) and adults (24-36 years). Neonates showed significantly lower levels of both iPGE and iPGA compared to children (p less than 0.01) and adults (p less than 0.01). Children also had significantly lower levels than adults (p less than 0.01). Since urinary prostaglandins reflect intrarenal levels of prostaglandins, the results support other studies that suggest prostaglandins may play a role in controlling renal blood flow in infants.