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      Renal Hemodynamics during Development of Hypertension in Young Spontaneously Hypertensive Rats

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          Abstract

          Background/Aims: Cross-transplantation studies between animals with genetic hypertension and normotensive animals indicate a key role of the kidney in development of hypertension, and studies in young spontaneously hypertensive rats (SHR) have shown reduced glomerular filtration rate (GFR) and renal blood flow (RBF) for a short period at the age of 4–6 weeks during blood pressure increase. We tested the hypothesis that a decline in GFR during development of hypertension in SHR might be more pronounced in juxtamedullary cortex than other cortical zones. Methods: By use of the aprotinin method, total and zonal cortical GFR was measured in anaesthetized Wistar-Kyoto (WKY) rats and SHR at the ages of 2, 4, 6, 8 and 10 weeks. RBF was measured by a transit time flowmeter. Results: Body and kidney weights in SHR and WKY were not significantly different in any age group (p >0.05). Mean arterial blood pressure (MAP) was not different at the age of 2 weeks (79 ± 6 mm Hg in SHR and 74 ± 5 mm Hg in WKY, p > 0.05), but was significantly higher in 4-week-old SHR (104 ± 1 mm Hg) compared to 4-week-old WKY (77 ± 3 mm Hg) (p < 0.01). The difference in blood pressure increased with age from 4 to 10 weeks. RBF, total GFR, and outer, middle, and inner cortical GFR increased with age but were not different in SHR and WKY in any age group (p >0.05). Renal vascular resistance was increased from 4 weeks of age in SHR (21.5 ± 1.8), significantly higher than WKY (14.4 ± 0.9 mm Hg·ml<sup>–1</sup>·min·g) (p < 0.01) and stayed at higher values in older age groups (p ≤ 0.01). Conclusion: RBF, total and zonal GFR are not significantly different in anaesthetized SHR compared to WKY at ages from 2 to 10 weeks and GFR in juxtamedullary cortex is not decreased in SHR during onset of hypertension. The results from the present study indicate that development of hypertension cannot be explained by a temporary decline in RBF or total or zonal GFR.

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          Renal Hemodynamics in Young and Old Spontaneously Hypertensive Rats during Intrarenal Infusion of Arginine Vasopressin

          Background/Aims: To gain insight into the effect of arginine vasopressin (AVP) on renal hemodynamics in hypertensive rats, we investigated the vasoconstrictive response to AVP on total renal blood flow (RBF) and total and zonal glomerular filtration rate (GFR) in young and old spontaneously hypertensive rats (SHR). A hypothesis of increased AVP sensitivity in the juxtamedullary cortex of SHR was tested. Methods: Total RBF and total and zonal GFR were studied in 10- and 40-week-old SHR and normotensive Wistar-Kyoto rats (WKY). RBF was recorded by a flowmeter before infusion of AVP and immediately after injection of a bolus dose of 10 ng AVP. Whole kidney GFR and its intracortical distribution was measured by the tubular uptake of 125 I- and 131 I-labelled aprotinin before and during a continuous infusion of AVP 5 ng/min. Ligand binding measurements of preglomerular V 1a receptors were performed in young and old rats. Results: RBF decreased by 43 ± 3% in 10-week SHR (9.2 ± 0.5 vs. 5.2 ± 0.3 ml·min –1 ·g –1 ), significantly more than 10-week WKY where RBF decreased by 35 ± 3% (9.6 ± 0.7 vs. 6.5 ± 0.5 ml·min –1 ·g –1 ) (p 0.05). GFR decreased by 6 ± 3% (1.03 ± 0.04 vs. 0.96 ± 0.04 ml·min –1 ·g –1 , p –1 ·g –1 , p > 0.10). GFR decreased by 11 ± 10% in 40-week SHR and by 4 ± 4% in 40-week WKY (p > 0.05). AVP infusion significantly increased filtration fraction in all groups except 40-week SHR, indicating that AVP has the strongest vasoconstrictive effect on postglomerular vessels. The intrarenal distribution of GFR was unchanged in the normotensive and hypertensive groups. V 1a receptor density was upregulated in young SHR compared to young WKY (p 1a receptors.
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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
            28 November 2002
            : 25
            : 5
            : 322-328
            Affiliations
            aRenal Research Group, Institute of Medicine, and bDepartment of Physiology, University of Bergen, Norway
            Article
            66792 Kidney Blood Press Res 2002;25:322–328
            10.1159/000066792
            12435879
            © 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.

            Page count
            Figures: 6, Tables: 1, References: 39, Pages: 7
            Product
            Self URI (application/pdf): https://www.karger.com/Article/Pdf/66792
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            Original Paper

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