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      Renal Concentrating Defect in Protein Malnutrition: The Role of the Thick Ascending Limb of Henle and Inner Medullary Collecting Duct

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          Abstract

          The present study was carried out to examine the effect of chronic dietary protein restriction on renal water handling in the rat. During hypotonic saline infusion, the malnourished rats showed a lower free-water clearance, corrected by inulin clearance (7.2 ± 0.4%), than normal rats (13.6 ± 2.5%, p < 0.051), although the fractional distal delivery of sodium did not differ from normal. Throughout hypertonic saline diuresis the free-water reabsorption (TcC<sub>H2</sub>o) corrected by inulin clearance was lower in malnourished rats (6.62 ± 0.64%) than in control animals (9.25 ± 0.62, p < 0.05). Moreover, when Tc<sub>H2</sub>o was referred to the osmolar clearance, malnourished animals showed lower values than normal. These results suggest a defect in NaCl transport in the thick ascending limb of Henle. In vitro measurements of diffusional water permeability (P<sub>DW</sub>) in the inner medullary collecting duct (IMCD) obtained from malnourished rats showed an increase from 40.0 ± 5.4 × 10<sup>-5</sup> cm/s to 71.3 ± 5.4 × 10<sup>-5</sup> cm/s by adding maximum effective concentration (50 μU/ml) of arginine vasopressin (VP) to the bath. These values were not different from the P<sub>DW</sub> observed in the IMCD of normal rats. In another series of microperfusion experiments, the hydraulic conductivity in IMCD of malnourished rats measured also in the presence of maximum effective concentration of VP was 29.7 ± 3.4 × 10<sup>-6</sup> cm/atm/s, a mean value not significantly different from that observed in the IMCD of normal rats (35.2 ± 4.3 × 10<sup>-6</sup> cm/atm/s). However, the Lp stimulated by submaximum effective doses of VP (1 and 10 μU/ml) was significantly lower in the IMCD of malnourished than normal rats. These findings indicate that the concentration defect observed in malnourished rats was due to a defect in NaCl transport in the thick ascending limb of Henle, and a partial resistance of IMCD to VP-stimulated water permeability.

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          Author and article information

          Journal
          NEF
          Nephron
          10.1159/issn.1660-8151
          Nephron
          S. Karger AG
          1660-8151
          2235-3186
          1991
          1991
          11 December 2008
          : 57
          : 2
          : 156-163
          Affiliations
          Laboratório de Pesquisa Básica do Departamento de Clínica Médica da Faculdade de Medicina da Universidade de São Paulo, Brasil
          Article
          186243 Nephron 1991;57:156–163
          10.1159/000186243
          2020342
          © 1991 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
          Pages: 8
          Categories
          Original Paper

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