Renin and aldosterone response in human newborns to acute change in blood volume

Normative values of renin and aldosterone in clinically stable preterm neonates

BACKGROUND

There is a paucity of literature on the normative levels of plasma renin concentration (PRC) and serum aldosterone (SA) in premature neonates. This study aims to provide normative data on PRC and SA levels in preterm neonates in the first 2 weeks after birth and explore associations with maternal, perinatal, or postnatal factors.

METHODS

Neonates born at 26- to 34-week gestation were recruited from two neonatal intensive care units in Canada and Australia. The direct renin assay PRC and SA were analyzed on day 1 and days 14-21 after birth to compare across categorical variables and to produce normative values.

RESULTS

A total of 262 subjects were enrolled from the Canadian (29%) and Australian (71%) sites. The mean gestational age was 30 weeks, with a mean birth weight of 1457 g. The normative values of PRC and SA for neonates born between 26 + 0 and 29 + 6 weeks and 30 + 0 and 34 + 0 weeks of gestation were produced for day 1 and day 14-21 after birth. Both PRC and SA increased from day 1 to day 14-21. The more premature neonates reached a higher PRC on days 14-21 after birth but exhibited lower SA levels on day 1 after birth. When comparing gender, birth weight, and maternal risk factor categories, no statistical differences in PRC or SA were found. A small but significant decrease in PRC, but not SA, was noted for neonates with placental pathology.

CONCLUSIONS

This study produced normative values of PRA and SA in clinically stable preterm neonates that can be referenced for use in clinical practice. A higher resolution version of the Graphical abstract is available as Supplementary information.

Hormonal response to fluid administration in cardiac surgery patients

The effects of three different fluid regimes administered before surgery on stress-related hormones were studied in 36 patients undergoing elective aortocoronary bypass grafting. Low-dose Ringer's solution (10 ml/kg; low-dose crystalloid group [LDC]), high-dose Ringer's solution (20 ml/kg; high-dose crystalloid group [(HDC]). or a combination of Ringer's solution (10 ml/kg) with high-molecular weight hydroxyethylstarch (HES) (10 ml/kg) (crystalloid-HES group [C-HES]) were randomly administered prior to operation. Haemodynamic variables and plasma concentrations of ADH, ACTH, renin, aldosterone, cortisol and catecholamines were studied before volume load, before commencement of cardiopulmonary bypass (CPB), and immediately after weaning from CPB.

Cardiac index and stroke volume index in the C-HES group increased by 20% and 18% respectively, systemic vascular resistance decreased by 25% after volume infusion. This was associated with a decrease in the plasma concentrations of ADH, renin and aldosterone. In contrast to this, in the LDC and HDC groups, haemodynamic parameters remained almost unchanged after volume load. This was associated with an increase in aldosterone (LDC 20%; HDC 58%) and renin (LDC 110%; HDC 44%). In all groups, plasma concentrations of catecholamines increased progressively during the time of surgery and were not influenced by the nature or volume of fluid administered.

We conclude that the administration of a combination of crystalloid and colloid solutions during induction of anaesthesia effectively improves haemodynamics and attenuates the increase of the plasma levels of ADH, renin and aldosterone often associated with surgery.

The use of propranolol in the treatment of infantile haemangiomas: an update on potential mechanisms of action

Currently, propranolol is the preferred treatment for problematic proliferating infantile haemangiomas (IHs). The rapid action of propranolol has been shown to be especially dramatic in IHs involving dyspnoea, haemodynamic compromise, palpebral occlusion or ulceration. Another remarkable aspect of propranolol treatment revealed that the growth of the IHs was not only stabilized, but also that the improvement continued until complete involution was achieved, leading to a considerable shortening of the natural course of IH. However, the mechanisms underlying the effects of propranolol have not been fully elucidated. Recent studies have offered evidence of a variety of mechanisms. These include the promotion of pericyte-mediated vasoconstriction, the inhibition of vasculogenesis and catecholamine-induced angiogenesis, the disruption of haemodynamic force-induced cell survival, and the inactivation of the renin-angiotensin system. This review summarizes these mechanisms and the new concepts that are emerging in this area of research. Moreover, several molecular mechanisms by which propranolol may modify neovascularization in IH have also been proposed. The antihaemangioma effect of propranolol may not be attributable to a single mechanism, but rather to a combination of events that have not yet been elucidated or understood. Further studies are needed to evaluate and verify these mechanisms to gain a greater understanding of the effects of the intake of propranolol on haemangioma involution.

The prevalence and risk factors of infantile haemangiomas: a case-control study in the Dutch population

Haemangiomas are considered to be the most common tumours of infancy. However, despite their frequent occurrence the aetiological determinants of their development remain unknown. Identifying these factors may provide insight on their pathogenesis. We performed cross-sectional screening for haemangiomas in newborns (0-16 months of age) in the general Dutch population. Haemangioma-specific and pregnancy-related data were collected in children with a haemangioma. These data were compared in a case-control design using multivariable logistic regression analysis. Among 2204 newborns, 219 (9.9%) had a haemangioma. The male-to-female ratio was 1:2. The majority of haemangiomas were located on the trunk (37%). The general practitioners or medical specialists were consulted in only a minority of cases (<7%). Amniocentesis [odds ratio (OR) 3.6, 95% confidence interval (CI) 1.11, 11.42], breech presentation [OR 2.3, 95% CI 1.14, 4.44], being first-born [OR 1.55, 95% CI 1.03, 2.33] and a birthweight ≤2500 g [OR 4.95, 95% CI 1.63, 15.05] were independent factors associated with the development of a haemangioma. Duration of pregnancy did not differ between study groups. Our study showed that the prevalence of a haemangioma is 9.9% in the general (Dutch) population. Four factors appear relevant in the development of haemangiomas. These factors may provide clues to its pathogenesis.

Expression of components of the renin-angiotensin system in proliferating infantile haemangioma may account for the propranolol-induced accelerated involution

Infantile haemangioma is a benign tumour of the microvasculature characterised by excessive proliferation of immature endothelial cells. It typically undergoes rapid proliferation during infancy followed by spontaneous slow involution during childhood often leaving a fibro-fatty residuum. In 2008, propranolol, a non-selective β-blocker, was serendipitously discovered to induce accelerated involution of a proliferating infantile haemangioma. However, the mechanism by which propranolol causes this dramatic effect is unclear. Using immunohistochemical staining, we show that the CD34+ endothelial progenitor cells of the microvessels in proliferating infantile haemangioma express angiotensin-converting enzyme and angiotensin II receptor-2, but not angiotensin II receptor-1. We have also shown using our in vitro explant model that the cells emanating from proliferating haemangioma biopsies form blast-like structures that proliferate in the presence of angiotensin II. We present here a plausible model involving the renin-angiotensin system that may account for the propranolol-induced accelerated involution of proliferating infantile haemangioma.

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.

Regulation of extracellular fluid volume in neonates

This review summarises mechanisms of control of extracellular fluid volume in the neonatal period. 'Normal' body fluid distribution and methods of its measurement are discussed as well as regulatory mechanisms with particular emphasis on hormonal and renal aspects.

Factors influencing plasma renin and renin substrate in premature infants

Concentrations of plasma renin (PRC) and plasma renin substrate (PRS) were measured during the first week of life in 52 infants born at less than 37 weeks' gestation (mean (SEM) gestation 30 (0.4) weeks, mean (SEM) birth weight 1.35 (0.08) kg). Both PRC (median 35, interquartiles 16.3, 94.5 ng/ml/hour) and PRS (median 2.3, interquartiles 1.3, 5.0 micrograms/ml) were raised compared with adults. The proportional rise in PRC was much greater than that in PRS, suggesting that PRS may be rate limiting in the generation of angiotensin I. Log10 PRC was inversely proportional to gestational age and a high urinary sodium loss was associated with a significantly raised log10 PRC. In hypoxaemic infants, there was a strong correlation between log10 PRS and haemoglobin concentration; this is a new observation in human infants but consistent with data available from other species.

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.

Changes in plasma concentrations of atrial natriuretic peptide during exchange transfusion in premature infants

Plasma concentrations of atrial natriuretic peptide (ANP) and hemodynamic parameters were investigated in five premature infants undergoing exchange transfusion. Baseline values of ANP were 51.7 +/- 21.2 fmol/ml. Volume depletion by withdrawal of 10 ml blood did not cause changes in systolic blood pressure (79.4 +/- 4.3 vs. 71.4 +/- 5.6 mmHg) and heart rate (115 +/- 5.2 vs. 115 +/- 2.4 b/min). ANP levels in plasma remained unaltered (53.4 +/- 24.9 fmol/ml). Replacement of 10 ml blood increased central venous pressure by 33% and ANP concentration in the plasma by nearly 30%, while heart rate and blood pressure remained unchanged. Our data indicate that the heart of the premature infant responded to acute blood replacement with increased ANP-release, while blood removal appeared not to influence hormone regulation.

Plasma renin activity in fetal disease

Fetal plasma renin activity (PRA) was measured in 42 pregnancies. Compared to control fetuses, PRA was elevated in three of four hypoxemic fetuses, in two of five with hydrops and in two of five with uropathies. PRA did not change with transfusion in seven alloimmunized fetuses. This study demonstrates PRA in human fetuses and suggests that the renin-angiotensin system can respond to stimuli in fetal life.

Intraventricular haemorrhage and the renin-angiotensin-aldosterone system in very low birthweight infants

Blood volume, plasma renin activity (PRA) and urine aldosterone excretion (UAE) were measured in ten very low birthweight infants who had a Grade 3 or 4 intraventricular haemorrhage (IVH) during the first 2 days after birth. Mean (range) birthweight was 950 (630-1500) g and gestational age was 27 (23-31) weeks. Nine infants were receiving assisted ventilation and one was breathing spontaneously. Eight IVH occurred on the first postnatal day and two on the second; seven were symptomatic and three asymptomatic. PRA was significantly higher than control values on Day 1 only; median 244 (range 91-654) ng/ml per h vs. 64 (4-259) ng/ml per h (P less than 0.01). Infants with symptomatic IVH in the preceding 8 h (n = 6) all had PRA greater than 300 ng/ml per h; none of these infants had received transfusions or volume expansion between IVH and PRA measurement. PRA was less than 100 ng/ml per h in the three infants with asymptomatic IVH and one infant with greater than 24 h interval between IVH and PRA measurement; three of these four had received transfusions prior to PRA measurement. UAE was not significantly different from control values on either Day 1 or Day 2. Blood volume at 22 +/- 3 h postnatal age ranged from 75 to 107 ml/kg. There was an inverse logarithmic correlation between PRA and blood volume (r = 0.883; P less than 0.005), with PRA values exceeding 300 ng/ml per h when blood volume was less than 90 ml/kg. UAE did not correlate with either PRA or blood volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma aldosterone and renin activity

Eight infants had paired measurements of plasma aldosterone and plasma renin activity while being treated for congestive heart failure. There is parallelism with aldosterone and renin activity in the presence of a hyperactive renin-angiotensin-aldosterone system. Six patients had plasma renin activity and plasma aldosterone measured after commencing captopril and we have shown biochemical blockade of the renin-angiotensin-aldosterone system.

Urinary sodium excretion and the renin-aldosterone system in new-born calves

Urinary Na+ and K+ excretion, plasma aldosterone levels (PAL) and plasma renin activity (PRA) were measured in three groups of four 3-day-old calves infused with aldosterone, ethacrynic acid and hydrochlorothiazide or with vehicle. Aldosterone infusion (16.7 micrograms/kg body wt. given by rapid injection, followed by the infusion of 33.3 micrograms/kg body wt. during 6 h) decreased urinary Na+ concentration and excretion during the 6 h period of infusion. This effect disappeared during the following 18 h. Ethacrynic acid (2 mg/kg body wt. by rapid injection, followed by the infusion of 1.5 mg/kg body wt..h during 6 h) and hydrochlorothiazide (8 mg/kg body wt. by rapid injection, followed by the infusion of 6 mg/kg body wt..h during 6 h) increased urinary volume and urinary excretion of Na+, but decreased urinary K+ concentration without affecting urinary K+ excretion during the 6 h period of infusion. During the same time, the plasma Na+ concentration decreased, PRA increased rapidly and was followed by a significant rise in PAL. These results demonstrate that in very young healthy calves, the renal tubules are able to respond to aldosterone. The renin-aldosterone system is also operative in these animals since it responds to Na+ depletion induced by the combination of diuretics and inhibitors of tubular Na+ reabsorption.

The effect of dopamine administration on the activity of the renin-angiotensin-aldosterone system in sick preterm infants

Nine premature infants with birth weight of 1150 to 2500 g and gestational age of 28 to 35 weeks were given dopamine in a dose of 2-4 micrograms/kg/min to treat cardiopulmonary distress. In addition to monitoring of blood gases, blood pressure, acid-base balance, urine flow and urinary sodium excretion, plasma renin activity (PRA) and plasma aldosterone concentration (PA) was also determined prior to and during dopamine therapy. The dopamine-induced increase in urine flow and urinary sodium excretion was associated with a significant increase of PRA from 18.2 +/- 5.1 ng/ml/h to 33.0 +/- 5.6 ng/ml/h (P less than 0.025), while PA and blood pressure remained unaltered by dopamine administration. It is suggested that the angiotensin II-stimulated aldosterone production is overridden by the inhibitory effect of dopamine.

Aldosterone concentrations in dehydrated infants

The mean serum aldosterone concentration of 37 infants with acute gastroenteritis and dehydration was markedly elevated on admission (mean +/- SE 94.3 +/- 12.1 ng/ml) and approximated to normal values (18.2 +/- 3.7 ng/ml) following recovery from the acute disease (t=3.56 p less than 0.005). Serum aldosterone levels were significantly positively correlated with the percent weight loss (r=0.41, p less than 0.05) and with the blood urea nitrogen levels (r=0.55, p less than 0.001). There was no correlation between either serum sodium levels or blood osmolarity and aldosterone concentrations. Serum potassium levels were positively correlated with aldosterone levels (r=0.53, p less than 0.001). These findings indicate that small infants when dehydrated respond appropriately with elevated aldosterone levels. The amount of body fluid depletion and hyperkalemia are the major factors determining the amount of aldosterone response.

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.

Renin-angiotensin-aldosterone system

There is increased activity of the renin, angiotensin, aldosterone (RAA) system in infancy and childhood. An inverse relationship between plasma renin, aldosterone and age has been demonstrated. In childhood hypertension due to renovascular disease or pyelonephritic scarring peripheral plasma renin is increased. Renal vein renin measurements in children with renal hypertension have proved valuable in predicting surgical curability of the underlying lesion. The upper limit of normal for the renal venous renin ratio in normotensive children without renal disease is 1.5. Pharmacological blockade of the RAA system has a place in diagnosis and treatment of hypertensive children. The plasma renin aldosterone profile is diagnostically useful in the investigation of salt-wasting disease and can easily distinguish between aldosterone biosynthetic defects and pseudohypoaldosteronism.