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      Effect of Chronic Renal Failure on Arginase and Argininosuccinate Synthetase Expression

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          Abstract

          Background: L-arginine ( L-arg) participates in numerous biological functions including urea and nitric oxide synthesis. Sources of L-arg include dietary proteins and endogenous synthesis by argininosuccinate synthetase and argininosuccinate lyase. L-arg is converted to urea by arginase I in the liver and arginase II in the kidney. Normally, the liver fully consumes L-arg for urea generation and does not contribute to its circulating pool. Instead, much of the circulating L-arg is produced by the kidney. If true, plasma L-arg should be severely reduced in chronic renal failure (CRF); however, plasma L-arg is frequently unchanged in CRF. We hypothesized that preservation of plasma L-arg in CRF may be, partly, due to downregulation/inhibition of arginase. Methods: Argininosuccinate synthetase, arginase I and II protein abundance and activity were measured in the liver and kidneys of rats 6 weeks after 5/6 nephrectomy or sham operation. In addition, arginase activity was measured in the presence of different urea concentrations to simulate azotemia in vitro. Results: Arginases I and II protein abundance as well as arginase activity in the liver, measured in the physiological buffer, were similar among the CRF and control groups. However, in vitro experiments simulating a uremic milieu revealed a marked concentration-dependent inhibition of arginase activity by urea in the tissue lysates. CRF had no significant effect on argininosuccinate synthetase abundance in the kidney, liver, spleen or intestine. Conclusions: Although CRF does not change the abundance or intrinsic properties of arginase, the inherent rise in urea concentration inhibits its enzymatic activity. The latter, in turn, attenuates L-arg catabolism and urea production and, thereby, mitigates the fall in plasma L-arg.

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          Most cited references 10

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          Amino acid metabolism in exercising man.

           P. Felig,  J. Wahren (1971)
          Arterial concentration and net exchange across the leg and splanchnic bed of 19 amino acids were determined in healthy, postabsorptive subjects in the resting state and after 10 and 40 min of exercise on a bicycle ergometer at work intensities of 400, 800, and 1200 kg-m/min. Arterio-portal venous differences were measured in five subjects undergoing elective cholecystectomy. In the resting state significant net release from the leg was noted for 13 amino acids, and significant splanchnic uptake was observed for 10 amino acids. Peripheral release and splanchnic uptake of alanine exceeded that of all other amino acids, accounting for 35-40% of total net amino acid exchange. Alanine and other amino acids were released in small amounts (relative to net splanchnic uptake) by the extrahepatic splanchnic tissues drained by the portal vein. During exercise arterial ananine rose 20-25% with mild exertion and 60-96% at the heavier work loads. Both at rest and during exercise a direct correlation was observed between arterial alanine and arterial pyruvate levels. Net amino acid release across the exercising leg was consistently observed at all levels of work intensity only for alanine. Estimated leg alanine output increased above resting levels in proportion to the work load. Splanchnic alanine uptake during exercise exceeded that of all other amino acids and increased by 15-20% during mild and moderate exercise, primarily as a consequence of augmented fractional extraction of alanine. For all other amino acids, there was no change in arterial concentration during mild exercise. At heavier work loads, increases of 8-35% were noted for isoleucine, leucine, methionine, tyrosine, and phenylalanine, which were attributable to altered splanchnic exchange rather than augmented peripheral release. The data suggest that (a) synthesis of alanine in muscle, presumably by transamination of glucose-derived pyruvate, is increased in exercise probably as a consequence of increased availability of pyruvate and amino groups; (b) circulating alanine serves an important carrier function in the transport of amino groups from peripheral muscle to the liver, particularly during exercise; (c) a glucose-alanine cycle exists whereby alanine, synthesized in muscle, is taken up by the liver and its glucose-derived carbon skeleton is reconverted to glucose.
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            Renal metabolism of amino acids and ammonia in subjects with normal renal function and in patients with chronic renal insufficiency.

            The net renal metabolism of amino acids and ammonia in the post absorptive state was evaluated in subjects with normal renal function and in patients with chronic renal insufficiency by measuring renal uptake and release, and urinary excretion of free amino acids and ammonia. In normal subjects the kidney extracts glutamine, proline, citrulline, and phenylalanine and releases serine, arginine, taurine, threonine, tyrosine, ornithine, lysine, and perhaps alanine. The renal uptake of amino acids from arterial blood occurs by way of plasma only, whereas approximately a half of amino acid release takes place by way of blood cells. Glycine is taken up from arterial plasma, while similar amounts of this amino acid are released by way of blood cells. In the same subjects total renal ammonia production can be largely accounted for by glutamine extracted. In patients with chronic renal insufficiency (a) the renal uptake of phenylalanine and the release of taurine and ornithine disappear; (b) the uptake of glutamine and proline, and the release of serine and threonine are reduced by 80--90%; (c) the uptake of citrulline and the release of alanine, arginine, tyrosine, and lysine are reduced by 60--70%; (d) no exchange of glycine is detectable either by way of plasma or by way of blood cells; (e) exchange of any other amino acid via blood cells disappears, and (f) total renal ammonia production is reduced and not more than 35% of such production can be accounted for by glutamine extracted, so that alternative precursors must be used. A 140% excess of nitrogen release found in the same patients suggests an intrarenal protein and peptide breakdown, which eventually provides free amino acids for ammonia production.
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              Role of increased oxygen free radical activity in the pathogenesis of uremic hypertension.

               Y. Ding,  F Oveisi,  N. Vaziri (1998)
              Earlier studies have demonstrated increased oxygen free radical (OFR) activity, diminished antioxidant capacity and reduced OFR-inactivating enzymes in chronic renal failure (CRF). Via inactivation of nitric oxide (NO), oxidation of arachidonic acid and a direct vasoconstrictive action, OFR can potentially raise blood pressure (BP). This study was designed to test the hypothesis that increased OFR activity may contribute to CRF hypertension. Four weeks after 5/6 nephrectomy rats were treated for two weeks with either lazaroid, a potent antioxidant and lipid peroxidation inhibitor (CRF-LZ group), or vehicle alone (CRF group) by daily gastric gavage. The control group was sham operated and placebo treated. The CRF group exhibited significant increases in BP and plasma lipid peroxidation product, malondialdehyde (MDA), indicating enhanced OFR activity. This was accompanied by decreased urinary nitrate/nitrite (NOx) excretion suggesting depressed NO production. LZ therapy normalized plasma MDA and significantly ameliorated CRF-induced hypertension. Both MDA and blood pressure (BP) rose to values seen in the untreated CRF group within two weeks after termination of LZ therapy. Intravenous administration of the hydroxyl radical scavenger, dimethylthiourea (DMTU), significantly lowered BP and raised urinary NOx excretion. However, no discernible effects were found with either superoxide dismutase or catalase (superoxide and H2O2 quenchers). The results suggest that increased OFR activity is, in part, responsible for CRF-associated HTN. The study further points to hydroxyl radicals as the major source of OFR in CRF animals. If substantiated in humans, antioxidant therapy becomes a logical adjunct in the management of CRF.
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                Author and article information

                Journal
                AJN
                Am J Nephrol
                10.1159/issn.0250-8095
                American Journal of Nephrology
                S. Karger AG
                0250-8095
                1421-9670
                2006
                July 2006
                19 July 2006
                : 26
                : 3
                : 310-318
                Affiliations
                Division of Nephrology and Hypertension, University of California, Irvine, Calif., USA
                Article
                94344 Am J Nephrol 2006;26:310–318
                10.1159/000094344
                16809898
                © 2006 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: 8, Tables: 1, References: 31, Pages: 9
                Product
                Self URI (application/pdf): https://www.karger.com/Article/Pdf/94344
                Categories
                Original Report: Laboratory Investigation

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