Water Balance and ‘Salt Wasting' in the First Year of Life: The Role of Aldosterone-Signaling Defects

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Abstract

In newborns and infants, dehydration and salt wasting represent a relatively common cause of admission to hospital and may result in life-threatening complications. Kidneys are responsible for electrolyte homoeostasis, but neonatal kidneys show low glomerular filtration rate and immaturity of the distal nephron, leading to reduced ability to concentrate urine. High extrarenal fluid losses often contribute to the increased occurrence of electrolyte disorders. Aldosterone is essential for sodium retention in the kidney, salivary glands, sweat glands and colon. A partial and transient aldosterone resistance is present in newborns and infants, thus reducing the capability of maintaining sodium balance in specific pathological conditions. The present review examines the mechanisms making infants more susceptible to salt wasting. Peculiar aspects of renal physiology in the first year of life and management of electrolyte disorders (i.e. sodium and potassium) are considered. Finally, inherited disorders associated with neonatal salt wasting are examined in detail.

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Most cited references 57

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Epithelial sodium channel (ENaC) family: Phylogeny, structure-function, tissue distribution, and associated inherited diseases.

Israel Hanukoglu, Aaron Hanukoglu (2016)

The epithelial sodium channel (ENaC) is composed of three homologous subunits and allows the flow of Na(+) ions across high resistance epithelia, maintaining body salt and water homeostasis. ENaC dependent reabsorption of Na(+) in the kidney tubules regulates extracellular fluid (ECF) volume and blood pressure by modulating osmolarity. In multi-ciliated cells, ENaC is located in cilia and plays an essential role in the regulation of epithelial surface liquid volume necessary for cilial transport of mucus and gametes in the respiratory and reproductive tracts respectively. The subunits that form ENaC (named as alpha, beta, gamma and delta, encoded by genes SCNN1A, SCNN1B, SCNN1G, and SCNN1D) are members of the ENaC/Degenerin superfamily. The earliest appearance of ENaC orthologs is in the genomes of the most ancient vertebrate taxon, Cyclostomata (jawless vertebrates) including lampreys, followed by earliest representatives of Gnathostomata (jawed vertebrates) including cartilaginous sharks. Among Euteleostomi (bony vertebrates), Actinopterygii (ray finned-fishes) branch has lost ENaC genes. Yet, most animals in the Sarcopterygii (lobe-finned fish) branch including Tetrapoda, amphibians and amniotes (lizards, crocodiles, birds, and mammals), have four ENaC paralogs. We compared the sequences of ENaC orthologs from 20 species and established criteria for the identification of ENaC orthologs and paralogs, and their distinction from other members of the ENaC/Degenerin superfamily, especially ASIC family. Differences between ENaCs and ASICs are summarized in view of their physiological functions and tissue distributions. Structural motifs that are conserved throughout vertebrate ENaCs are highlighted. We also present a comparative overview of the genotype-phenotype relationships in inherited diseases associated with ENaC mutations, including multisystem pseudohypoaldosteronism (PHA1B), Liddle syndrome, cystic fibrosis-like disease and essential hypertension.

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Mutations in subunits of the epithelial sodium channel cause salt wasting with hyperkalaemic acidosis, pseudohypoaldosteronism type 1.

S Gründer, Mohit Mathew, I Hanukoglu … (1996)

Autosomal recessive pseudohypoaldosteronism type I is a rare life-threatening disease characterized by severe neonatal salt wasting, hyperkalaemia, metabolic acidosis, and unresponsiveness to mineralocorticoid hormones. Investigation of affected offspring of consanguineous union reveals mutations in either the alpha or beta subunits of the amiloride-sensitive epithelial sodium channel in five kindreds. These mutations are homozygous in affected subjects, co-segregate with the disease, and introduce frameshift, premature termination or missense mutations that result in loss of channel activity. These findings demonstrate the molecular basis and explain the pathophysiology of this disease.

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Epithelial Sodium Transport and Its Control by Aldosterone: The Story of Our Internal Environment Revisited

Bernard C. Rossier, Michael E. Baker, Romain A. Studer (2015)

Transcription and translation require a high concentration of potassium across the entire tree of life. The conservation of a high intracellular potassium was an absolute requirement for the evolution of life on Earth. This was achieved by the interplay of P- and V-ATPases that can set up electrochemical gradients across the cell membrane, an energetically costly process requiring the synthesis of ATP by F-ATPases. In animals, the control of an extracellular compartment was achieved by the emergence of multicellular organisms able to produce tight epithelial barriers creating a stable extracellular milieu. Finally, the adaptation to a terrestrian environment was achieved by the evolution of distinct regulatory pathways allowing salt and water conservation. In this review we emphasize the critical and dual role of Na + -K + -ATPase in the control of the ionic composition of the extracellular fluid and the renin-angiotensin-aldosterone system (RAAS) in salt and water conservation in vertebrates. The action of aldosterone on transepithelial sodium transport by activation of the epithelial sodium channel (ENaC) at the apical membrane and that of Na + -K + -ATPase at the basolateral membrane may have evolved in lungfish before the emergence of tetrapods. Finally, we discuss the implication of RAAS in the origin of the present pandemia of hypertension and its associated cardiovascular diseases.

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Author and article information

Journal

Journal ID (publisher-id): HRP

Journal ID (nlm-ta): Horm Res Paediatr

Journal ID (doi): 10.1159/issn.1663-2818

Title: Hormone Research in Paediatrics

Publisher: S. Karger AG

ISSN (Print): 1663-2818

ISSN (Electronic): 1663-2826

Publication date Subscription-year: 2016

Publication date (Print): October 2016

Publication date (Electronic): 07 September 2016

Volume: 86

Issue: 3

Pages: 143-153

Affiliations

^aUnit of Endocrinology and Diabetes, ‘Bambino Gesù' Children's Hospital, and ^bMolecular Endocrinology Unit, ‘Bambino Gesù' Children's Hospital-Tor Vergata University, Rome, Italy; ^cDepartment of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden

Author notes

*Carla Bizzarri, MD, ‘Bambino Gesù' Children's Hospital, Piazza S. Onofrio 4, IT-00165 Rome (Italy), E-Mail carla.bizzarri@opbg.net

Article

Publisher ID: 449057 Other ID: Horm Res Paediatr 2016;86:143-153

DOI: 10.1159/000449057

PubMed ID: 27598420

SO-VID: 7d9bf091-3187-4f1a-90d6-50a1ab1c3e61

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Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

History

Date received : 19 April 2016

Date accepted : 10 August 2016

Page count

Figures: 3, Tables: 1, References: 70, Pages: 11

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Water Balance and ‘Salt Wasting' in the First Year of Life: The Role of Aldosterone-Signaling Defects

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Karger: Endocrinology

Most cited references 57

Epithelial sodium channel (ENaC) family: Phylogeny, structure-function, tissue distribution, and associated inherited diseases.

Mutations in subunits of the epithelial sodium channel cause salt wasting with hyperkalaemic acidosis, pseudohypoaldosteronism type 1.

Epithelial Sodium Transport and Its Control by Aldosterone: The Story of Our Internal Environment Revisited

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Cited by 13

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