Postantal Development of Renin-Angiotensin-Aldosterone System, RAAS, in Relation to Electrolyte Balance in Premature Infants

Abstract

Summarycharacteristic for hypoaldosteronism, it is tempting to postulate a causal relationship between physiologic hyponatremia and the In an attempt to provide information about the role of RAAS in function of renin-angiotensin-aldoster~ne system (RAAS) in low development of late hyponatremia in low-birthweight neonates, birthweight neonate.simultaneous measurement of plasma renin activity, (PRA),In an attempt to obtain information about the role of RAAS in plasma aldosterone concentration (PA), and urinary aldosterone development of hyponatremia, the present study was undertaken excretion (UAE) was made using RIA methods along with deter-to determine the postnatal changes of plasma renin activity (PRA), mination Na and weekly to the 6th week of life' plasma aldosterone concentration (PA), and urinary aldosterone Seven healthy male infants with mean birthweight of 1580 g, range: excretion (UAE) in relation to the electrolyte balance in premature 1160-1850 g, and mean gestational age of 31 weeks, range: 30-32 infants during the first 6 weeks of life. weeks, were selected for the study.Due to the increased urinary Na loss, negative Na balance developed in the first 2 weeks followed by positive balance there- MATERIALS A N D METHODSafter. PRA, PA, and UAE increased tremendously from the initially high values of 18.2 f 4-1 ng/ml/hr, 1.7 f 0.5 and 2.6The studies were performed on seven healthy male appropriate f 0.4 %/day, mean and SEM, to their maximum of 78.6 18e1 for dates premature infants. The mean birthweight and the gesng/ml/hr, P < 0.01,6-8 f 3.7 ng/ml, P < 0-05, and 26.4 f 2.9 tational age of the infants was 1580 g and 31 weeks with the day, P < 0.01, in the 3rd week, respectively. Later on, gradual ranges of 1160-1850 g and 30-32 weeks, respectively. The mothers declines occurred, however, PRA, PA, and UAE remained highly were on normal diet without diuretic therapy, none had a history elevated even at the 6th week with values of 45.5 +-15 ng/ml/hr, of renal disease or previous toxemia of pregnancy. All undenvent 1.6 f 0.5 ng/ml, and 14.5 + 1.4 &day, respectively. uncomplicated vaginal delivery. Gestational age was assessed It is suggested that late h~ponatremia of Premature infants is primarily from the mothers menstrual history, but was confirmed due to tubular unresponsiveness to aldosterone and not to in&-by physical examination of the infant. The l-min Apgar score was quate response of RAAS to stimulation. more than 7 and the perinatal course remained uneventful in each case. SpeculationThe infants were fed appropriate cow's milk formulas ("RobCbi A") by a round the clock feeding pattern at 2-hourly intervals The initially high urinary sodium excretion in premature infants until they weighed about 1500 g and 3-hourly intervals, thereafter. is coupled with low urinary potassium excretion indicating limited The formula contained 71 calories, 2.1 g protein, 3.4 g fat, 8.0 g renal sodium reabsorption in exchange for potassium. Later on, sugar, and 0.5 g minerals in 100 ml. Food intake was gradually progre...

Adrenocortical Steroids in Small-for-Gestational-Age Term Infants during the Early Neonatal Period1,2

“…It has been shown that the renin-angiotensin-aldosterone system is highly active during the neonatal period, particularly in premature infants (l9,20). Our data on high aldosterone levels in SGA infants also suggest an activation of this system, whereas in two other studies (7,8), limited to the 2nd day, and to the 7th day of life, respectively, no difference was found between SGA and AGA infants. Sulyok et al (8), however, described a tendency to higher plasma renin activity and urinary aldosterone excretion in intrauterine growth-retarded neonates.…”

“…Only few and contradictory results on corticosteroid levels in SGA infants have been reported (4)(5)(6), partly combining data from infants born by various modes of delivery, or infants at various postnatal and gestational ages. Because of the amount of blood necessary for the determination of corticosteroids, these studies were limited to single steroids such as cortisol (5) or aldosterone (7,8). For the same reason, longitudinal studies throughout the early neonatal period are not available.…”

Action of Atrial Natriuretic Peptide in the Immature Ovine Kidney

“…This suggests that the inability to retain a normal percentage of the dietary salt intake is somehow related to the level of immaturity of the kidney. One suggestion has been that the immature kidney is relatively insensitive to the sodium-retaining effect of the endogenous aldosterone (4). However, it has been shown that one feature of the defect is that a larger than normal percentage of the renal filtrate is delivered to the distal tubule, suggesting that too little filtrate is reabsorbed in the proximal tubule (2).…”

Heparin-Induced Hyperkalemia in an Extremely-Low-Birth-Weight Infant: A Case Report

“…Only a slight increase in the plasma K+ level independently promoted aldosterone secretion in a K+-loading study of adults (6). No associations between spot plasma K+ levels and urinary or plasma aldosterone levels have been reported in infants (14,15,16,17). However, from these results, it is not clear whether normokalemia suppressed the plasma aldosterone or hypoaldosteronism caused the hyperkalemia.…”