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      Nephron Endowment and Renal Filtration Surface Area in Young Spontaneously Hypertensive Rats

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          Abstract

          Background/Aims: A reduction in nephron endowment leading to reduced renal filtration surface area has been implicated in the development of hypertension. The aim of this study was to compare glomerular (and thereby nephron) number and renal filtration surface area in young Wistar-Kyoto rats (WKY) with young spontaneously hypertensive rats (SHR), prior to the development of hypertension in this model. Methods: Using unbiased stereological methods the number and size of glomeruli, as well as total renal filtration surface area were determined in perfusion-fixed kidneys of 4-week-old WKY and SHR. Results: At 4 weeks of age, in weight-matched animals, there was no significant difference in the number of glomeruli in the kidneys of SHR compared to WKY (28,620 ± 1,643 and 25,670 ± 1,263 glomeruli/kidney, respectively). Similarly, there was no difference in mean glomerular volume (SHR: 4.70 ± 0.31 × 10<sup>–4</sup> mm<sup>3</sup>; WKY: 4.28 ± 0.20 × 10<sup>–4</sup> mm<sup>3</sup>). Surprisingly, total renal filtration surface area was significantly greater in SHR than WKY (3,867 ± 116 and 3,176 ± 83 mm<sup>2</sup>, respectively). Conclusion: The renal abnormality underlying the development of hypertension in the SHR is not due to inborn deficits in nephron endowment and/or filtration surface area.

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          The quantitative development of glomerular capillaries in rats with special reference to unbiased stereological estimates of their number and sizes.

          The kidneys of 14 female Wistar rats from 5 days to 18 months postnatally have been perfusion-fixed to study the development of glomerular capillaries using design-based stereological techniques. This report uses a topological definition of a capillary structural unit which forms the basis for the estimation of the number of glomerular capillaries using histological sections. The number of mature glomeruli is about 27,500 for all animals older than 5 days, whereas the 5-day-old animals have 21,100 mature glomeruli. Postnatally, the mean glomerular volume increases rapidly for the first 2 months after which it increases at a much slower rate. At first there is a rapid increase in total number, length, and surface area of glomerular capillaries with age; after 2 months the increase is rather moderate. The rapid growth of glomerular capillaries is anisomorphic, and the restrained growth is roughly isomorphic. The mean length of glomerular capillaries is nearly constant at 56 microns in mature and immature rats. The cross-sectional area rises only twofold from the most immature to the oldest rats. Using an approximation of the geometric factor in the law of Poiseuille, a decreasing resistance of glomerular capillaries with age is obtained. This is in agreement with the falling resistance of maturing renal vasculature and the increasing single-nephron glomerular filtration rate. When taking into account the constant mean capillary length and moderate increase in cross-sectional area of glomerular capillaries in growing rats, it appears that the branching of capillaries, forming a complicated network of serial and parallel connections, seems to be the structural basis for normal glomerular capillary growth.
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            Blood Pressure and Indices of Glomerular Filtration Area in Hypertensive and Normotensive Prague Rats

            The involvement of the kidney in the pathogenesis of hypertension has long been recognised, although the specific renal mechanisms underlying this phenomenon are still unknown. A current hypothesis attributes hypertension to a reduction in glomerular filtration area by glomerular loss. The present study analyses the relationship between glomerular number and volume and conscious systolic blood pressure (SBP) in 4- to 53-week-old hypertensive (PHR) and normotensive (PNR) rats of the Prague strain. Adult PHRs had higher SBP, were larger and had larger kidneys than PNRs, but 20% fewer glomeruli. A significant negative correlation between SBP and glomerular number was found in PHR males, but not in PHR females or PNRs. There was no correlation at all between glomerular volume and SBP and, in young animals, both SBP and glomerular number were higher in PHRs than in PNRs. In addition, in adult PHRs, glomerular volume and SBP were higher in males than in females. In summary, a generally valid, causal relationship linking raised blood pressure to decreased glomerular number or volume could not be demonstrated in the Prague rat model of genetically determined hypertension. The nature of the renal mechanism(s) determining the hypertension in this model remains unknown.
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              Author and article information

              Journal
              KBR
              Kidney Blood Press Res
              10.1159/issn.1420-4096
              Kidney and Blood Pressure Research
              S. Karger AG
              1420-4096
              1423-0143
              2002
              2002
              06 February 2002
              : 25
              : 1
              : 20-26
              Affiliations
              Department of Anatomy and Cell Biology, Monash University, Clayton, Melbourne, Vic., Australia
              Article
              49431 Kidney Blood Press Res 2002;25:20–26
              10.1159/000049431
              11834873
              9b03bc3f-21ba-4caa-b742-9c2a30e76964
              © 2002 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.

              History
              Page count
              Figures: 2, Tables: 1, References: 33, Pages: 7
              Categories
              Original Paper

              Cardiovascular Medicine,Nephrology
              Filtration surface area,SHR,Glomerulus,Nephron,Stereology,Kidney,Hypertension

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