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      Disorders of Salt and Water Balance in Children

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          Abstract

          Background: In past decades, our understanding of the vasopressin-mediated renal concentration mechanism has improved considerably due to the discovery of new endocrine-related neurotransmitters and the elucidation of the roles of crucial molecular players in this process. The identification of disease-causing genes in hereditary disorders of water balance has been extremely helpful in identifying these pivotal molecules. Acquired diseases, however, are the most frequent causes of impaired water homeostasis. Diagnosis: The clinical and biochemical diagnosis of hormonal deficit is confirmed by standard laboratory tests, but recent advances in imaging techniques have shed new light on the pathophysiology of many of these diseases. Management: Magnetic resonance imaging (MRI) permits identification of the posterior pituitary in vivo and can clearly delineate the shape, size and enhancement pattern of the pituitary stalk, as well as its functional integrity. Thickening of the pituitary stalk is a common finding on MRI scans in several pituitary stalk pathologies, but it is not specific to any single pathological subtype. However, biopsy of an enlarged pituitary stalk should be reserved for selected patients with hypothalamic-pituitary mass or with progressive thickening of the pituitary stalk.

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          Most cited references 14

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          Urinary excretion of aquaporin-2 in patients with diabetes insipidus.

          Urine-concentrating ability is regulated by vasopressin. Recently, the specific water-channel protein of the renal collecting duct, known as aquaporin-2, was cloned. However, it is not certain whether this molecule is responsive to vasopressin. We measured the urinary excretion of aquaporin-2 and its response to vasopressin in 11 normal subjects and 9 patients with central or nephrogenic diabetes insipidus. The urine samples were collected during periods of dehydration and hydration and after the administration of vasopressin. Urine samples were analyzed for aquaporin-2 by the Western blot assay and immunogold labeling, and the amount of aquaporin-2 was determined by radioimmunoassay. Aquaporin-2 was detectable in the urine in both soluble and membrane-bound forms. In the five normal subjects tested, the mean (+/- SE) urinary excretion of aquaporin-2 was 11.2 +/- 2.2 pmol per milligram of creatinine after a period of dehydration, and it decreased to 3.9 +/- 1.9 pmol per milligram of creatinine (P = 0.03) during the second hour after a period of hydration. In the six other normal subjects, an infusion of desmopressin (1-desamino-8-D-arginine vasopressin) increased the urinary excretion of aquaporin-2 from 0.8 +/- 0.3 to 11.2 +/- 1.6 pmol per milligram of creatinine (P < 0.001). The five patients with central diabetes insipidus also had increases in urinary excretion of aquaporin-2 in response to the administration of vasopressin, but the four patients with X-linked or non-X-linked nephrogenic diabetes insipidus did not. Aquaporin-2 is detectable in the urine, and changes in the urinary excretion of this protein can be used as an index of the action of vasopressin on the kidney.
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            Central diabetes insipidus in children and young adults.

            Central diabetes insipidus is rare in children and young adults, and up to 50 percent of cases are idiopathic. The clinical presentation and the long-term course of this disorder are largely undefined. We studied all 79 patients with central diabetes insipidus who were seen at four pediatric endocrinology units between 1970 and 1996. There were 37 male and 42 female patients whose median age at diagnosis was 7.0 years (range, 0.1 to 24.8). All patients underwent magnetic resonance imaging (MRI) and periodic studies of anterior pituitary function. The median duration of follow-up was 7.6 years (range, 1.6 to 26.2). The causes of the central diabetes insipidus were Langerhans-cell histiocytosis in 12 patients, an intracranial tumor in 18 patients, a skull fracture in 2 patients, and autoimmune polyendocrinopathy in 1 patient; 5 patients had familial disease. The cause was considered to be idiopathic in 41 patients (52 percent). In 74 patients (94 percent) the posterior pituitary was not hyperintense on the first MRI scan obtained, and 29 patients (37 percent) had thickening of the pituitary stalk. Eighteen patients had changes in the thickness of the pituitary stalk over time, ranging from normalization (six patients) or a decrease in thickness (one patient) to further thickening (seven patients) or thickening of a previously normal stalk (four patients). Anterior pituitary hormone deficiencies, primarily growth hormone deficiency, were documented in 48 patients (61 percent) a median of 0.6 year (range, 0.1 to 18.0) after the onset of central diabetes insipidus. Most children and young adults with acquired central diabetes insipidus have abnormal findings on MRI scans of the head, which may change over time, and at least half have anterior pituitary hormone deficiencies during follow-up.
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              The importance of aquaporin water channel protein structures.

              The history of the water channel and recent structural and functional analyses of aquaporins are reviewed. These ubiquitous channels are important for bacteria, plants and animals, exhibit a pronounced sequence homology and share functional as well as structural similarities. Aquaporins allow water or small specific solutes to pass unhindered, but block the passage of ions to prevent dissipation of the transmembrane potential. Besides advances in structure determination, recent experiments suggest that many of these channels are regulated by pH variations, phosphorylation and binding of auxiliary proteins.
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                Author and article information

                Journal
                HRE
                Horm Res Paediatr
                10.1159/issn.1663-2818
                Hormone Research in Paediatrics
                S. Karger AG
                978-3-8055-8255-1
                978-3-318-01446-4
                1663-2818
                1663-2826
                2007
                February 2007
                15 February 2007
                : 67
                : Suppl 1
                : 71-76
                Affiliations
                Department of Pediatrics, IRCCS G. Gaslini, University of Genova, Genova, Italy
                Article
                97556 Horm Res 2007;67:71–76
                10.1159/000097556
                © 2007 S. Karger AG, Basel

                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.

                Page count
                Figures: 2, Tables: 1, References: 25, Pages: 6
                Categories
                Pediatric Workshop 2

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