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Sparks MA, Dilmen E, Ralph DL, Rianto F, Hoang TA, Hollis A, Diaz EJ, Adhikari R, Chew G, Petretto EG, Gurley SB, McDonough AA, Coffman TM. Vascular control of kidney epithelial transporters. Am J Physiol Renal Physiol 2021; 320:F1080-F1092. [PMID: 33969697 PMCID: PMC8285646 DOI: 10.1152/ajprenal.00084.2021] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Revised: 04/23/2021] [Accepted: 05/05/2021] [Indexed: 01/03/2023] Open
Abstract
A major pathway in hypertension pathogenesis involves direct activation of ANG II type 1 (AT1) receptors in the kidney, stimulating Na+ reabsorption. AT1 receptors in tubular epithelia control expression and stimulation of Na+ transporters and channels. Recently, we found reduced blood pressure and enhanced natriuresis in mice with cell-specific deletion of AT1 receptors in smooth muscle (SMKO mice). Although impaired vasoconstriction and preserved renal blood flow might contribute to exaggerated urinary Na+ excretion in SMKO mice, we considered whether alterations in Na+ transporter expression might also play a role; therefore, we carried out proteomic analysis of key Na+ transporters and associated proteins. Here, we show that levels of Na+-K+-2Cl- cotransporter isoform 2 (NKCC2) and Na+/H+ exchanger isoform 3 (NHE3) are reduced at baseline in SMKO mice, accompanied by attenuated natriuretic and diuretic responses to furosemide. During ANG II hypertension, we found widespread remodeling of transporter expression in wild-type mice with significant increases in the levels of total NaCl cotransporter, phosphorylated NaCl cotransporter (Ser71), and phosphorylated NKCC2, along with the cleaved, activated forms of the α- and γ-epithelial Na+ channel. However, the increases in α- and γ-epithelial Na+ channel with ANG II were substantially attenuated in SMKO mice. This was accompanied by a reduced natriuretic response to amiloride. Thus, enhanced urinary Na+ excretion observed after cell-specific deletion of AT1 receptors from smooth muscle cells is associated with altered Na+ transporter abundance across epithelia in multiple nephron segments. These findings suggest a system of vascular-epithelial in the kidney, modulating the expression of Na+ transporters and contributing to the regulation of pressure natriuresis.NEW & NOTEWORTHY The use of drugs to block the renin-angiotensin system to reduce blood pressure is common. However, the precise mechanism for how these medications control blood pressure is incompletely understood. Here, we show that mice lacking angiotensin receptors specifically in smooth muscle cells lead to alternation in tubular transporter amount and function. Thus, demonstrating the importance of vascular-tubular cross talk in the control of blood pressure.
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Affiliation(s)
- Matthew A Sparks
- Division of Nephrology, Department of Medicine, Duke University School of Medicine, Durham, North Carolina
- Renal Section, Durham Veterans Affairs Health Care System, Durham, North Carolina
| | - Emre Dilmen
- Division of Nephrology, Department of Medicine, Duke University School of Medicine, Durham, North Carolina
| | - Donna L Ralph
- Department of Physiology and Neuroscience, Keck School of Medicine of the University of Southern California, Los Angeles, California
| | - Fitra Rianto
- Division of Nephrology, Department of Medicine, Duke University School of Medicine, Durham, North Carolina
| | - Thien A Hoang
- Division of Nephrology, Department of Medicine, Duke University School of Medicine, Durham, North Carolina
| | - Alison Hollis
- Division of Nephrology, Department of Medicine, Duke University School of Medicine, Durham, North Carolina
| | - Edward J Diaz
- Division of Nephrology, Department of Medicine, Duke University School of Medicine, Durham, North Carolina
| | - Rishav Adhikari
- Division of Nephrology, Department of Medicine, Duke University School of Medicine, Durham, North Carolina
| | - Gabriel Chew
- Program in Cardiovascular and Metabolic Disorders, Duke-NUS Medical School, Singapore
| | - Enrico G Petretto
- Program in Cardiovascular and Metabolic Disorders, Duke-NUS Medical School, Singapore
| | - Susan B Gurley
- Division of Nephrology and Hypertension, Oregon Health & Science University, Portland, Oregon
| | - Alicia A McDonough
- Department of Physiology and Neuroscience, Keck School of Medicine of the University of Southern California, Los Angeles, California
| | - Thomas M Coffman
- Division of Nephrology, Department of Medicine, Duke University School of Medicine, Durham, North Carolina
- Renal Section, Durham Veterans Affairs Health Care System, Durham, North Carolina
- Program in Cardiovascular and Metabolic Disorders, Duke-NUS Medical School, Singapore
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Rademaker MT, Scott NJA, Koh CY, Kini RM, Richards AM. Natriuretic peptide analogues with distinct vasodilatory or renal activity: integrated effects in health and experimental heart failure. Cardiovasc Res 2020; 117:508-519. [PMID: 32167565 DOI: 10.1093/cvr/cvaa052] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/21/2019] [Revised: 02/02/2020] [Accepted: 03/11/2020] [Indexed: 11/12/2022] Open
Abstract
AIMS Management of acute decompensated heart failure (ADHF) requires disparate treatments depending on the state of systemic/peripheral perfusion and the presence/absence of expanded body-fluid volumes. There is an unmet need for therapeutics that differentially treat each aspect. Atrial natriuretic peptide (ANP) plays an important role in blood pressure and volume regulation. We investigate for the first time the integrated haemodynamic, endocrine and renal effects of human ANP analogues, modified for exclusive vasodilatory (ANP-DRD) or diuretic (ANP-DGD) activities, in normal health and experimental ADHF. METHODS AND RESULTS We compared the effects of incremental infusions of ANP analogues ANP-DRD and ANP-DGD with native ANP, in normal (n = 8) and ADHF (n = 8) sheep. ANP-DRD administration increased plasma cyclic guanosine monophosphate (cGMP) in association with dose-dependent reductions in arterial pressure in normal and heart failure (HF) sheep similarly to ANP responses. In contrast to ANP, which in HF produced a diuresis/natriuresis, this analogue was without significant renal effect. Conversely, ANP-DGD induced marked stepwise increases in urinary cGMP, urine volume, and sodium excretion in HF comparable to ANP, but without accompanying vasodilatory effects. All peptides increased packed cell volume relative to control in both states, and in HF, decreased left atrial pressure. In response to ANP-DRD-induced blood pressure reductions, plasma renin activity rose compared to control only during the high dose in normals, and not at all in HF-suggesting relative renin inhibition, with no increase in aldosterone in either state, whereas renin and aldosterone were both significantly reduced by ANP-DGD in HF. CONCLUSION These ANP analogues exhibit distinct vasodilatory (ANP-DRD) and diuretic/natriuretic (ANP-DGD) activities, and therefore have the potential to provide precision therapy for ADHF patients with differing pathophysiological derangement of pressure-volume homeostasis.
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Affiliation(s)
- Miriam T Rademaker
- Department of Medicine, Christchurch Heart Institute, University of Otago-Christchurch, PO Box 4345, Christchurch 8011, New Zealand
| | - Nicola J A Scott
- Department of Medicine, Christchurch Heart Institute, University of Otago-Christchurch, PO Box 4345, Christchurch 8011, New Zealand
| | - Cho Yeow Koh
- Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119228, Singapore
| | - R Manjunatha Kini
- Department of Biological Science, Faculty of Science, National University of Singapore, Singapore 119228, Singapore
| | - A Mark Richards
- Department of Medicine, Christchurch Heart Institute, University of Otago-Christchurch, PO Box 4345, Christchurch 8011, New Zealand.,Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119228, Singapore.,Cardiovascular Research Institute, National University Health Systems, Centre for Translational Medicine, Medical Drive, Singapore 117599, Singapore
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Gonzalez-Vicente A, Saez F, Monzon CM, Asirwatham J, Garvin JL. Thick Ascending Limb Sodium Transport in the Pathogenesis of Hypertension. Physiol Rev 2019; 99:235-309. [PMID: 30354966 DOI: 10.1152/physrev.00055.2017] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The thick ascending limb plays a key role in maintaining water and electrolyte balance. The importance of this segment in regulating blood pressure is evidenced by the effect of loop diuretics or local genetic defects on this parameter. Hormones and factors produced by thick ascending limbs have both autocrine and paracrine effects, which can extend prohypertensive signaling to other structures of the nephron. In this review, we discuss the role of the thick ascending limb in the development of hypertension, not as a sole participant, but one that works within the rich biological context of the renal medulla. We first provide an overview of the basic physiology of the segment and the anatomical considerations necessary to understand its relationship with other renal structures. We explore the physiopathological changes in thick ascending limbs occurring in both genetic and induced animal models of hypertension. We then discuss the racial differences and genetic defects that affect blood pressure in humans through changes in thick ascending limb transport rates. Throughout the text, we scrutinize methodologies and discuss the limitations of research techniques that, when overlooked, can lead investigators to make erroneous conclusions. Thus, in addition to advancing an understanding of the basic mechanisms of physiology, the ultimate goal of this work is to understand our research tools, to make better use of them, and to contextualize research data. Future advances in renal hypertension research will require not only collection of new experimental data, but also integration of our current knowledge.
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Affiliation(s)
| | - Fara Saez
- Department of Physiology and Biophysics, Case Western Reserve University , Cleveland, Ohio
| | - Casandra M Monzon
- Department of Physiology and Biophysics, Case Western Reserve University , Cleveland, Ohio
| | - Jessica Asirwatham
- Department of Physiology and Biophysics, Case Western Reserve University , Cleveland, Ohio
| | - Jeffrey L Garvin
- Department of Physiology and Biophysics, Case Western Reserve University , Cleveland, Ohio
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Emans TW, Janssen BJ, Pinkham MI, Ow CPC, Evans RG, Joles JA, Malpas SC, Krediet CTP, Koeners MP. Exogenous and endogenous angiotensin-II decrease renal cortical oxygen tension in conscious rats by limiting renal blood flow. J Physiol 2016; 594:6287-6300. [PMID: 27426098 PMCID: PMC5088249 DOI: 10.1113/jp270731] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Accepted: 07/08/2016] [Indexed: 01/08/2023] Open
Abstract
KEY POINTS Our understanding of the mechanisms underlying the role of hypoxia in the initiation and progression of renal disease remains rudimentary. We have developed a method that allows wireless measurement of renal tissue oxygen tension in unrestrained rats. This method provides stable and continuous measurements of cortical tissue oxygen tension (PO2) for more than 2 weeks and can reproducibly detect acute changes in cortical oxygenation. Exogenous angiotensin-II reduced renal cortical tissue PO2 more than equi-pressor doses of phenylephrine, probably because it reduced renal oxygen delivery more than did phenylephrine. Activation of the endogenous renin-angiotensin system in transgenic Cyp1a1Ren2 rats reduced cortical tissue PO2; in this model renal hypoxia precedes the development of structural pathology and can be reversed acutely by an angiotensin-II receptor type 1 antagonist. Angiotensin-II promotes renal hypoxia, which may in turn contribute to its pathological effects during development of chronic kidney disease. ABSTRACT We hypothesised that both exogenous and endogenous angiotensin-II (AngII) can decrease the partial pressure of oxygen (PO2) in the renal cortex of unrestrained rats, which might in turn contribute to the progression of chronic kidney disease. Rats were instrumented with telemeters equipped with a carbon paste electrode for continuous measurement of renal cortical tissue PO2. The method reproducibly detected acute changes in cortical oxygenation induced by systemic hyperoxia and hypoxia. In conscious rats, renal cortical PO2 was dose-dependently reduced by intravenous AngII. Reductions in PO2 were significantly greater than those induced by equi-pressor doses of phenylephrine. In anaesthetised rats, renal oxygen consumption was not affected, and filtration fraction was increased only in the AngII infused animals. Oxygen delivery decreased by 50% after infusion of AngII and renal blood flow (RBF) fell by 3.3 ml min-1 . Equi-pressor infusion of phenylephrine did not significantly reduce RBF or renal oxygen delivery. Activation of the endogenous renin-angiotensin system in Cyp1a1Ren2 transgenic rats reduced cortical tissue PO2. This could be reversed within minutes by pharmacological angiotensin-II receptor type 1 (AT1 R) blockade. Thus AngII is an important modulator of renal cortical oxygenation via AT1 receptors. AngII had a greater influence on cortical oxygenation than did phenylephrine. This phenomenon appears to be attributable to the profound impact of AngII on renal oxygen delivery. We conclude that the ability of AngII to promote renal cortical hypoxia may contribute to its influence on initiation and progression of chronic kidney disease.
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Affiliation(s)
- Tonja W Emans
- Nephrology and Hypertension, University Medical Centre Utrecht, Utrecht, The Netherlands.,Internal Medicine-Nephrology, Academic Medical Centre at the University of Amsterdam, The Netherlands
| | - Ben J Janssen
- Department of Pharmacology and Toxicology, Maastricht University, Maastricht, The Netherlands
| | | | - Connie P C Ow
- Cardiovascular Disease Program, Biosciences Discovery Institute and Department of Physiology, Monash University, Melbourne, Australia
| | - Roger G Evans
- Cardiovascular Disease Program, Biosciences Discovery Institute and Department of Physiology, Monash University, Melbourne, Australia
| | - Jaap A Joles
- Nephrology and Hypertension, University Medical Centre Utrecht, Utrecht, The Netherlands
| | - Simon C Malpas
- Department of Physiology, University of Auckland, Auckland, New Zealand.,Millar Inc, Auckland, New Zealand
| | - C T Paul Krediet
- Internal Medicine-Nephrology, Academic Medical Centre at the University of Amsterdam, The Netherlands
| | - Maarten P Koeners
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK.
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Optimizing inhibition of the renin-angiotensin system in hypertension. J Hypertens 2016; 34:838-41. [PMID: 27027379 DOI: 10.1097/hjh.0000000000000895] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Ford Versypt AN, Makrides E, Arciero JC, Ellwein L, Layton AT. Bifurcation study of blood flow control in the kidney. Math Biosci 2015; 263:169-79. [PMID: 25747903 PMCID: PMC4768488 DOI: 10.1016/j.mbs.2015.02.015] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2014] [Revised: 02/25/2015] [Accepted: 02/26/2015] [Indexed: 11/15/2022]
Abstract
Renal blood flow is maintained within a narrow window by a set of intrinsic autoregulatory mechanisms. Here, a mathematical model of renal hemodynamics control in the rat kidney is used to understand the interactions between two major renal autoregulatory mechanisms: the myogenic response and tubuloglomerular feedback. A bifurcation analysis of the model equations is performed to assess the effects of the delay and sensitivity of the feedback system and the time constants governing the response of vessel diameter and smooth muscle tone. The results of the bifurcation analysis are verified using numerical simulations of the full nonlinear model. Both the analytical and numerical results predict the generation of limit cycle oscillations under certain physiologically relevant conditions, as observed in vivo.
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Affiliation(s)
- Ashlee N Ford Versypt
- School of Chemical Engineering, Oklahoma State University, Stillwater, OK 74078, USA
| | - Elizabeth Makrides
- Division of Applied Mathematics, Brown University, Providence, RI 02912, USA.
| | - Julia C Arciero
- Department of Mathematical Sciences, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202, USA
| | - Laura Ellwein
- Department of Mathematics and Applied Mathematics, Virginia Commonwealth University, Richmond, VA 23284, USA
| | - Anita T Layton
- Department of Mathematics, Duke University, Durham, NC 27708, USA
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Ito S. In Vitro Study of the Juxtaglomerular Apparatus and Its Implications in the Chronic Kidney Disease. Hypertension 2015; 65:970-5. [DOI: 10.1161/hypertensionaha.114.04365] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2014] [Accepted: 01/09/2015] [Indexed: 11/16/2022]
Affiliation(s)
- Sadayoshi Ito
- From the Division of Nephrology, Endocrinology and Vascular Medicine, Department of Medicine, Tohoku University School of Medicine, Sendai, Japan
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8
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Ito S. [111th Scientific Meeting of the Japanese Society of Internal Medicine Presidential Lecture; Evolution and diseases]. ACTA ACUST UNITED AC 2014; 103:2029-39. [PMID: 27522751 DOI: 10.2169/naika.103.2029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Affiliation(s)
- Sadayoshi Ito
- From the Division of Nephrology, Endocrinology, and Vascular Medicine, Department of Medicine, Tohoku University School of Medicine, Sendai, Miyagi, Japan
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10
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Navar LG, Arendshorst WJ, Pallone TL, Inscho EW, Imig JD, Bell PD. The Renal Microcirculation. Compr Physiol 2008. [DOI: 10.1002/cphy.cp020413] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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11
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Navar LG, Arendshorst WJ, Pallone TL, Inscho EW, Imig JD, Bell PD. The Renal Microcirculation. Microcirculation 2008. [DOI: 10.1016/b978-0-12-374530-9.00015-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
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12
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Morgan TK, Montgomery K, Mason V, West RB, Wang L, van de Rijn M, Higgins JP. Upregulation of histidine decarboxylase expression in superficial cortical nephrons during pregnancy in mice and women. Kidney Int 2006; 70:306-14. [PMID: 16760908 DOI: 10.1038/sj.ki.5001553] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Mechanisms regulating pregnancy-induced changes in renal function are incompletely understood. Few candidate genes have been identified and data suggest that alternate mechanisms remain to be elucidated. Our objective was to screen thousands of genes expressed in kidneys from mice throughout gestation to identify possible key regulators of renal function during pregnancy. Mouse complementary DNA microarrays were used to screen for differences in expression during pregnancy in C57BL/6 mice. Interesting candidate genes whose expression varied with pregnancy were further analyzed by reverse transcription-PCR and Northern blot. Expression was localized by in situ hybridization and immunohistochemistry. Follow-up immunohistochemical analyses in archival human kidney sections from the fetus, non-pregnant, and pregnant women were also performed. Histidine decarboxylase (HDC), the enzyme that synthesizes histamine, was markedly upregulated in the mouse kidney during pregnancy. HDC expression localized to proximal tubule cells of fetal and adult mice. Females showed strong expression in the juxtamedullary zone before pregnancy and upregulation in the superficial cortical zone (SCZ) by mid-gestation. Histamine colocalized with HDC. Male mice showed only low HDC expression. Similar expression patterns were observed in human kidneys. Our results show that HDC expression and histamine production are increased in the SCZ during pregnancy. If histamine acts as a vasodilator, we speculate that increasing production in the SCZ may increase renal blood flow to this zone and recruit superficial cortical nephrons during pregnancy.
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Affiliation(s)
- T K Morgan
- Department of Pathology, Stanford University Medical Center, Stanford, California, USA.
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De Luca Sarobe V, Nowicki S, Carranza A, Levin G, Barontini M, Arrizurieta E, Ibarra FR. Low sodium intake induces an increase in renal monoamine oxidase activity in the rat. Involvement of an angiotensin II dependent mechanism. ACTA ACUST UNITED AC 2006; 185:161-7. [PMID: 16168010 DOI: 10.1111/j.1365-201x.2005.01473.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
AIMS The interplay between natriuretic dopamine and antinatriuretic angiotensin II represents an important mechanism for the regulation of renal sodium and water excretion. Monoamine oxidase is the main metabolizing pathway for dopamine in the renal cortex. In this study, we have analysed the effect of low sodium feeding and AT1 receptor blockade on renal dopamine metabolism by monoamine oxidase. METHODS Four groups of rats were studied: 1, normal salt diet (NS); 2, low salt diet (LS); 3, NS receiving Losartan (Los, specific AT1 receptor antagonist, 20 mg kg(-1) bwt day(-1), NS + Los); 4, LS receiving Los (LS + Los). RESULTS Urinary dopamine excretion was lower in LS than in NS rats (543 +/- 32 vs. 680 +/- 34 ng day(-1) 100 g(-1) bwt, P < 0.05). When treated with Los, DOPAC excretion and urinary DOPAC/dopamine ratio fell significantly in the LS + Los group as compared with the LS group (1199 +/- 328 vs. 3081 +/- 681 ng day(-1) 100 g(-1) bwt and 1.90 +/- 0.5 vs. 5.7 +/- 1.2, respectively, both P < 0.02). Losartan increased hydroelectrolyte excretion in the LS group. No changes were found in the NS + Los group. Aromatic L-amino acid decarboxylase activity in cortex was similar in NS and LS rats. Instead, monoamine oxidase activity was higher in cortical homogenates from LS rats (in nmol mg tissue(-1) h(-1): NS 7.66 +/- 0.52; LS 9.82 +/- 0.59, P < 0.05) and this difference was abolished in LS + Los rats (7.34 +/- 0.49 nmol mg tissue(-1) h(-1), P < 0.01, vs. LS). CONCLUSIONS We have concluded that low levels of dopamine in the urine of LS rats are because of an increase in the activity of renal monoamine oxidase and that angiotensin II mediates this increase through stimulation of AT1 receptors.
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Affiliation(s)
- V De Luca Sarobe
- Instituto de Investigaciones Médicas A. Lanari, University of Buenos Aires, Buenos Aires, Argentina
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Heller J, Trebicka J, Shiozawa T, Schepke M, Neef M, Hennenberg M, Sauerbruch T. Vascular, hemodynamic and renal effects of low-dose losartan in rats with secondary biliary cirrhosis. Liver Int 2005; 25:657-66. [PMID: 15910503 DOI: 10.1111/j.1478-3231.2005.01053.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
BACKGROUND In cirrhosis, splanchnic and systemic vasodilatation induce a hyperdynamic circulatory dysfunction, portal hypertension and renal sodium retention. This vasodilatation is in part because of an impaired vascular response to alpha1-adrenoceptor agonists. Recently, the angiotensin II type 1-receptor antagonist losartan has been shown to attenuate portal hypertension. We hypothesized that losartan decreases portal pressure by counteracting the impaired vascular responsive to alpha1-adrenoceptor agonists. METHODS We studied, in rats with secondary biliary cirrhosis and sham-operated rats, the effect of 0.5 and 10 mg losartan/kg x day on aortic responsiveness to alpha1-adrenoceptor stimulation with methoxamine and angiotensin II (myograph), splanchnic and systemic hemodynamics (colored microspheres), plasma noradrenaline levels and kidney function. RESULTS In cirrhotic rats, 10 mg losartan/kg x day completely inhibited aortic contractility to angiotensin II, decreased vascular resistance and arterial pressure and induced renal failure. In contrast, 0.5 mg losartan/kg x day only partially inhibited aortic contractility to angiotensin II, but improved aortic contractility to methoxamine, increased splanchnic and systemic vascular resistance, decreased portal pressure, decreased plasma norepinephrine levels and induced natriuresis. CONCLUSIONS In cirrhotic rats, losartan at a very low dose increases splanchnic vascular resistance, decreases portal pressure and improves kidney function, possibly by an increased vascular responsiveness to alpha1-adrenoceptor agonists.
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Affiliation(s)
- Jörg Heller
- Department of Internal Medicine I, University of Bonn, Bonn, Germany.
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Roald AB, Tenstad O, Aukland K. The effect of AVP-V receptor stimulation on local GFR in the rat kidney. ACTA PHYSIOLOGICA SCANDINAVICA 2004; 182:197-204. [PMID: 15450116 DOI: 10.1111/j.1365-201x.2004.01352.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/30/2023]
Abstract
AIM Arginine vasopressin (AVP) might influence urinary concentration ability by altering the intrarenal distribution of glomerular filtration rate (GFR). METHODS To study this possibility we have measured the intracortical distribution of GFR following acute AVP-V1 receptor stimulation in anaesthetized female Sprague-Dawley (SPD) rats during euvolemia and water diuresis by the aprotinin method, allowing two consecutive measurements of zonal GFR in the same kidney. RESULTS Acute i.v. bolus injection of 50 ng V1 receptor agonist ([Phe2, Ile3, Orn8]-vasopressin) followed by a continuous infusion of 5 ng min(-1) in euvolemic rats reduced GFR by 25% in outer cortex (OC), 20% in middle cortex (MC) and 19% in inner cortex (IC) relative to vehicle infusion (all P < 0.05). In water diuretic rats V1 receptor agonist reduced GFR by 22% in OC, 10% in MC and 11% in IC relative to vehicle infusion (P < 0.05). GFR decreased slightly more in OC than in MC and IC in both euvolemic and water diuretic rats (P < 0.05) indicating a distribution of GFR towards MC and IC. Acute infusion of the selective non-peptide V1 receptor antagonist OPC-21268 in euvolemic rats reduced GFR by 14% in OC, 13% in MC and 11% in IC relative to vehicle infusion (P < 0.05), with no significant difference between the layers. CONCLUSIONS The change in distribution of GFR not only between OC and IC, but also between OC and MC suggests that the afferent/efferent arterioles and not the medullary vasa recta is the main site of resistance change. We conclude that acute i.v. infusion of V1 receptor agonist in high doses reduces GFR more in superficial than in deep cortex in both euvolemic and water diuretic rats and that this may be of some importance for water conservation, adding to the V2- receptor effect on water permeability of the collecting ducts.
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Affiliation(s)
- A B Roald
- Department of Biomedicine, University of Bergen, Bergen, Norway
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Baran D, Tenstad O, Aukland K. Aprotinin uptake in the proximal tubules in the rat kidney I. Length of proximal tubular uptake segment. J Struct Biol 2003; 142:402-8. [PMID: 12781667 DOI: 10.1016/s1047-8477(03)00070-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Aprotinin (Ap), a basic polypeptide with a molecular weight of 6500, is filtered at the glomerular membrane without steric restriction and is completely absorbed by the proximal tubule cells. Here Ap is broken down to amino acids, but no breakdown products enter the peritubular circulation during the first 20 min following an intravenous injection. These properties have recently been exploited for measurement of local glomerular filtration rate, based on the assumption that the proximal tubular uptake site is located at the level of the filtering glomerulus. To evaluate that assumption we have now made serial autoradiographs of the rat kidney 20 min after intravenous injection of 2-750 microg of 125I-Aprotinin. With all doses the percent 125I-containing proximal tubular transections were about 50 in the outer and middle cortex and 35 in the inner third. We interpret these numbers to mean that all filtered Ap is taken up in the first two thirds of the proximal convoluted tubular length and does not reach the pars recta. Since the proximal tubule on average is located more superficial than its glomerulus, measurement of local Ap uptake will tend to overestimate glomerular filtration rate in outer layers of the cortex. Quantitative estimate of this "displacement" will be presented in a companion article.
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Affiliation(s)
- Dadash Baran
- Department of Physiology, University of Bergen, Cionas Liesvei 91, Norway.
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