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Jufar AH, Evans RG, May CN, Hood SG, Betrie AH, Trask‐Marino A, Bellomo R, Lankadeva YR. The effects of recruitment of renal functional reserve on renal cortical and medullary oxygenation in non-anesthetized sheep. Acta Physiol (Oxf) 2023; 237:e13919. [PMID: 36598336 PMCID: PMC10909474 DOI: 10.1111/apha.13919] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Revised: 11/18/2022] [Accepted: 01/02/2023] [Indexed: 01/05/2023]
Abstract
AIM Recruitment of renal functional reserve (RFR) with amino acid loading increases renal blood flow and glomerular filtration rate. However, its effects on renal cortical and medullary oxygenation have not been determined. Accordingly, we tested the effects of recruitment of RFR on renal cortical and medullary oxygenation in non-anesthetized sheep. METHODS Under general anesthesia, we instrumented 10 sheep to enable subsequent continuous measurements of systemic and renal hemodynamics, renal oxygen delivery and consumption, and cortical and medullary tissue oxygen tension (PO2 ). We then measured the effects of recruitment of RFR with an intravenous infusion of 500 ml of a clinically used amino acid solution (10% Synthamin® 17) in the non-anesthetized state. RESULTS Compared with baseline, Synthamin® 17 infusion significantly increased renal oxygen delivery mean ± SD maximum increase: (from 0.79 ± 0.17 to 1.06 ± 0.16 ml/kg/min, p < 0.001), renal oxygen consumption (from 0.08 ± 0.01 to 0.15 ± 0.02 ml/kg/min, p < 0.001), and glomerular filtration rate (+45.2 ± 2.7%, p < 0.001). Renal cortical tissue PO2 increased by a maximum of 26.4 ± 1.1% (p = 0.001) and medullary tissue PO2 increased by a maximum of 23.9 ± 2.8% (p = 0. 001). CONCLUSIONS In non-anesthetized healthy sheep, recruitment of RFR improved renal cortical and medullary oxygenation. These observations might have implications for the use of recruitment of RFR for diagnostic and therapeutic purposes.
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Affiliation(s)
- Alemayehu H. Jufar
- Pre‐Clinical Critical Care UnitFlorey Institute of Neuroscience and Mental Health, University of MelbourneMelbourneVictoriaAustralia
- Cardiovascular Disease Program, Department of PhysiologyBiomedicine Discovery Institute, Monash UniversityMelbourneVictoriaAustralia
| | - Roger G. Evans
- Pre‐Clinical Critical Care UnitFlorey Institute of Neuroscience and Mental Health, University of MelbourneMelbourneVictoriaAustralia
- Cardiovascular Disease Program, Department of PhysiologyBiomedicine Discovery Institute, Monash UniversityMelbourneVictoriaAustralia
| | - Clive N. May
- Pre‐Clinical Critical Care UnitFlorey Institute of Neuroscience and Mental Health, University of MelbourneMelbourneVictoriaAustralia
- Department of Critical CareMelbourne Medical School, University of MelbourneMelbourneVictoriaAustralia
| | - Sally G. Hood
- Pre‐Clinical Critical Care UnitFlorey Institute of Neuroscience and Mental Health, University of MelbourneMelbourneVictoriaAustralia
| | - Ashenafi H. Betrie
- Pre‐Clinical Critical Care UnitFlorey Institute of Neuroscience and Mental Health, University of MelbourneMelbourneVictoriaAustralia
- Melbourne Dementia Research CentreFlorey Institute of Neuroscience and Mental Health, The University of MelbourneMelbourneVictoriaAustralia
| | - Anton Trask‐Marino
- Pre‐Clinical Critical Care UnitFlorey Institute of Neuroscience and Mental Health, University of MelbourneMelbourneVictoriaAustralia
| | - Rinaldo Bellomo
- Pre‐Clinical Critical Care UnitFlorey Institute of Neuroscience and Mental Health, University of MelbourneMelbourneVictoriaAustralia
- Department of Critical CareMelbourne Medical School, University of MelbourneMelbourneVictoriaAustralia
| | - Yugeesh R. Lankadeva
- Pre‐Clinical Critical Care UnitFlorey Institute of Neuroscience and Mental Health, University of MelbourneMelbourneVictoriaAustralia
- Department of Critical CareMelbourne Medical School, University of MelbourneMelbourneVictoriaAustralia
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2
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Renal sympathetic activity: A key modulator of pressure natriuresis in hypertension. Biochem Pharmacol 2023; 208:115386. [PMID: 36535529 DOI: 10.1016/j.bcp.2022.115386] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Revised: 12/11/2022] [Accepted: 12/13/2022] [Indexed: 12/23/2022]
Abstract
Hypertension is a complex disorder ensuing necessarily from alterations in the pressure-natriuresis relationship, the main determinant of long-term control of blood pressure. This mechanism sets natriuresis to the level of blood pressure, so that increasing pressure translates into higher osmotically driven diuresis to reduce volemia and control blood pressure. External factors affecting the renal handling of sodium regulate the pressure-natriuresis relationship so that more or less natriuresis is attained for each level of blood pressure. Hypertension can thus only develop following primary alterations in the pressure to natriuresis balance, or by abnormal activity of the regulation network. On the other hand, increased sympathetic tone is a very frequent finding in most forms of hypertension, long regarded as a key element in the pathophysiological scenario. In this article, we critically analyze the interplay of the renal component of the sympathetic nervous system and the pressure-natriuresis mechanism in the development of hypertension. A special focus is placed on discussing recent findings supporting a role of baroreceptors as a component, along with the afference of reno-renal reflex, of the input to the nucleus tractus solitarius, the central structure governing the long-term regulation of renal sympathetic efferent tone.
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3
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Jufar AH, May CN, Evans RG, Cochrane AD, Marino B, Hood SG, McCall PR, Bellomo R, Lankadeva YR. Influence of moderate-hypothermia on renal and cerebral haemodynamics and oxygenation during experimental cardiopulmonary bypass in sheep. Acta Physiol (Oxf) 2022; 236:e13860. [PMID: 35862484 DOI: 10.1111/apha.13860] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Revised: 07/11/2022] [Accepted: 07/18/2022] [Indexed: 11/01/2022]
Abstract
AIM Cardiac surgery requiring cardiopulmonary bypass (CPB) can result in renal and cerebral injury. Intra-operative tissue hypoxia could contribute to such organ injury. Hypothermia, however, may alleviate organ hypoxia. Therefore, we tested whether moderate-hypothermia (30o C) improves cerebral and renal tissue perfusion and oxygenation during ovine CPB. METHODS Ten sheep were studied while conscious, under stable anaesthesia and during 3 hours of CPB. In a randomised within-animal cross-over design, 5 sheep commenced CPB at a target body temperature of 30 o C (moderate-hypothermia). After 90 minutes, body temperature was increased to 36 o C (standard-procedure). The remaining 5 sheep were randomised to the opposite order of target body temperature. RESULTS Compared with the standard-procedure, moderately-hypothermic CPB reduced renal oxygen delivery (-34.8 ± 19.6%, P = 0.003) and renal oxygen consumption (-42.7 ± 35.2%, P = 0.04). Nevertheless, moderately-hypothermic CPB did not significantly alter either renal cortical or medullary tissue PO2 . Moderately-hypothermic CPB also did not significantly alter cerebral perfusion, cerebral tissue PO2 , or cerebral oxygen saturation compared with the standard-procedure. Compared with anaesthetised state, standard-procedure reduced renal medullary PO2 (-21.0 ± 13.8 mmHg, P = 0.014) and cerebral oxygen saturation (65.0 ± 7.0 to 55.4 ± 9.6%, P = 0.022) but did not significantly alter either renal cortical or cerebral PO2 . CONCLUSION Ovine experimental CPB leads to renal medullary tissue hypoxia. Moderately-hypothermic CPB did not improve cerebral or renal tissue oxygenation. In the kidney, this is probably because renal tissue oxygen consumption is matched by reduced renal oxygen delivery.
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Affiliation(s)
- Alemayehu H Jufar
- Pre-Clinical Critical Care Unit, Florey Institute of Neuroscience and Mental Health, University of Melbourne, Melbourne, Victoria, Australia.,Cardiovascular Disease Program, Biomedicine Discovery Institute and Department of Physiology, Monash University, Melbourne, Victoria, Australia
| | - Clive N May
- Pre-Clinical Critical Care Unit, Florey Institute of Neuroscience and Mental Health, University of Melbourne, Melbourne, Victoria, Australia.,Department of Critical Care, Melbourne Medical School, University of Melbourne, Victoria, Australia
| | - Roger G Evans
- Pre-Clinical Critical Care Unit, Florey Institute of Neuroscience and Mental Health, University of Melbourne, Melbourne, Victoria, Australia.,Cardiovascular Disease Program, Biomedicine Discovery Institute and Department of Physiology, Monash University, Melbourne, Victoria, Australia
| | - Andrew D Cochrane
- Department of Cardiothoracic Surgery, Monash Health and Department of Surgery (School of Clinical Sciences at Monash Health), Monash University, Melbourne, Victoria, Australia
| | - Bruno Marino
- Cellsaving and Perfusion Resources, Melbourne, Victoria, Australia
| | - Sally G Hood
- Pre-Clinical Critical Care Unit, Florey Institute of Neuroscience and Mental Health, University of Melbourne, Melbourne, Victoria, Australia
| | - Peter R McCall
- Department of Anaesthesia, Austin Health, Heidelberg, Victoria, Australia
| | - Rinaldo Bellomo
- Pre-Clinical Critical Care Unit, Florey Institute of Neuroscience and Mental Health, University of Melbourne, Melbourne, Victoria, Australia.,Department of Critical Care, Melbourne Medical School, University of Melbourne, Victoria, Australia
| | - Yugeesh R Lankadeva
- Pre-Clinical Critical Care Unit, Florey Institute of Neuroscience and Mental Health, University of Melbourne, Melbourne, Victoria, Australia.,Department of Critical Care, Melbourne Medical School, University of Melbourne, Victoria, Australia
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Sadowski J, Bądzyńska B. Altered renal medullary blood flow: A key factor or a parallel event in control of sodium excretion and blood pressure? Clin Exp Pharmacol Physiol 2020; 47:1323-1332. [PMID: 32163610 DOI: 10.1111/1440-1681.13303] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Revised: 03/03/2020] [Accepted: 03/09/2020] [Indexed: 11/29/2022]
Abstract
In the context of the ongoing debate on the mechanism of blood pressure (BP) regulation and pathophysiology of arterial hypertension ("renocentric" vs "neural" concepts), attention is focused on the putative regulatory role of changes in renal medullary blood flow (MBF). Experimental evidence is analysed with regard to the question whether an elevation of BP and renal perfusion pressure (RPP) is likely to increase MBF due to its impaired autoregulation. It is concluded that such increases have been clearly documented only in rats with extracellular fluid volume expansion. A possible translation of this finding to BP regulation in health and hypertension in humans may only be a matter of speculation. Within the "renocentric" theory, the key event leading to restoration of initial BP level is pressure natriuresis. Its relation to elevation of renal interstitial hydrostatic pressure and to the phenomenon of "wash-out" of renal medullary solutes by increasing MBF is discussed. We also assessed the validity of data supporting the putative mechanism of short-term restoration of elevated BP owing to the release of a vasodilator lipid (medullipin) by the medulla. The structure of the proposed medullary lipid is still undefined, and there is no sound evidence on its mediatory role in lowering elevated BP level. In conclusion, MBF change can hardly be regarded as a crucial event in the regulation of BP: it can be involved in the control of sodium excretion and BP only in some circumstances, although its contributory role cannot be excluded.
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Affiliation(s)
- Janusz Sadowski
- Department of Renal and Body Fluid Physiology, Mossakowski Medical Research Centre, Polish Academy of Sciences, Warsaw, Poland
| | - Bożena Bądzyńska
- Department of Renal and Body Fluid Physiology, Mossakowski Medical Research Centre, Polish Academy of Sciences, Warsaw, Poland
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Gardiner BS, Smith DW, Lee C, Ngo JP, Evans RG. Renal oxygenation: From data to insight. Acta Physiol (Oxf) 2020; 228:e13450. [PMID: 32012449 DOI: 10.1111/apha.13450] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2019] [Revised: 01/14/2020] [Accepted: 01/30/2020] [Indexed: 12/14/2022]
Abstract
Computational models have made a major contribution to the field of physiology. As the complexity of our understanding of biological systems expands, the need for computational methods only increases. But collaboration between experimental physiologists and computational modellers (ie theoretical physiologists) is not easy. One of the major challenges is to break down the barriers created by differences in vocabulary and approach between the two disciplines. In this review, we have two major aims. Firstly, we wish to contribute to the effort to break down these barriers and so encourage more interdisciplinary collaboration. So, we begin with a "primer" on the ways in which computational models can help us understand physiology and pathophysiology. Second, we aim to provide an update of recent efforts in one specific area of physiology, renal oxygenation. This work is shedding new light on the causes and consequences of renal hypoxia. But as importantly, computational modelling is providing direction for experimental physiologists working in the field of renal oxygenation by: (a) generating new hypotheses that can be tested in experimental studies, (b) allowing experiments that are technically unfeasible to be simulated in silico, or variables that cannot be measured experimentally to be estimated, and (c) providing a means by which the quality of experimental data can be assessed. Critically, based on our experience, we strongly believe that experimental and theoretical physiology should not be seen as separate exercises. Rather, they should be integrated to permit an iterative process between modelling and experimentation.
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Affiliation(s)
- Bruce S. Gardiner
- College of Science Health, Engineering and Education Murdoch University Perth Australia
- Faculty of Engineering and Mathematical Sciences The University of Western Australia Perth Australia
| | - David W. Smith
- Faculty of Engineering and Mathematical Sciences The University of Western Australia Perth Australia
| | - Chang‐Joon Lee
- College of Science Health, Engineering and Education Murdoch University Perth Australia
- Faculty of Engineering and Mathematical Sciences The University of Western Australia Perth Australia
| | - Jennifer P. Ngo
- Cardiovascular Disease Program Biomedicine Discovery Institute and Department of Physiology Monash University Melbourne Australia
- Department of Cardiac Physiology National Cerebral and Cardiovascular Research Center Osaka Japan
| | - Roger G. Evans
- Cardiovascular Disease Program Biomedicine Discovery Institute and Department of Physiology Monash University Melbourne Australia
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Strategies that improve renal medullary oxygenation during experimental cardiopulmonary bypass may mitigate postoperative acute kidney injury. Kidney Int 2019; 95:1338-1346. [DOI: 10.1016/j.kint.2019.01.032] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2018] [Revised: 01/23/2019] [Accepted: 01/24/2019] [Indexed: 02/07/2023]
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Urinary Oxygenation as a Surrogate Measure of Medullary Oxygenation During Angiotensin II Therapy in Septic Acute Kidney Injury. Crit Care Med 2017; 46:e41-e48. [PMID: 29077618 DOI: 10.1097/ccm.0000000000002797] [Citation(s) in RCA: 71] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
OBJECTIVES Angiotensin II is an emerging therapy for septic acute kidney injury, but it is unknown if its vasoconstrictor action induces renal hypoxia. We therefore examined the effects of angiotensin II on intrarenal PO2 in ovine sepsis. We also assessed the validity of urinary PO2 as a surrogate measure of medullary PO2. DESIGN Interventional study. SETTING Research Institute. SUBJECTS Sixteen adult Merino ewes (n = 8/group). INTERVENTIONS Sheep were instrumented with fiber-optic probes in the renal cortex, medulla, and within a bladder catheter to measure PO2. Conscious sheep were infused with Escherichia coli for 32 hours. At 24-30 hours, angiotensin II (0.5-33.0 ng/kg/min) or saline vehicle was infused. MEASUREMENTS AND MAIN RESULTS Septic acute kidney injury was characterized by hypotension and a 60% ± 6% decrease in creatinine clearance. During sepsis, medullary PO2 decreased from 36 ± 1 to 30 ± 3 mm Hg after 1 hour and to 20 ± 2 mm Hg after 24 hours; at these times, urinary PO2 was 42 ± 2, 34 ± 2, and 23 ± 2 mm Hg. Increases in urinary neutrophil gelatinase-associated lipocalin (12% ± 3%) and serum creatinine (60% ± 23%) were only detected at 8 and 24 hours, respectively. IV infusion of angiotensin II, at 24 hours of sepsis, restored arterial pressure and improved creatinine clearance, while not exacerbating medullary or urinary hypoxia. CONCLUSIONS In septic acute kidney injury, renal medullary and urinary hypoxia developed several hours before increases in currently used biomarkers. Angiotensin II transiently improved renal function without worsening medullary hypoxia. In septic acute kidney injury, angiotensin II appears to be a safe, effective therapy, and urinary PO2 may be used to detect medullary hypoxia.
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Cortical and Medullary Tissue Perfusion and Oxygenation in Experimental Septic Acute Kidney Injury. Crit Care Med 2015; 43:e431-9. [PMID: 26181218 DOI: 10.1097/ccm.0000000000001198] [Citation(s) in RCA: 84] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVES To determine whether there is a decrease in renal cortical or medullary perfusion and oxygenation in a conscious large animal model of hyperdynamic septic shock with acute kidney injury. DESIGN Interventional animal study. SETTING University-affiliated research institute. SUBJECTS Eight merino ewes. INTERVENTIONS Sheep were surgically instrumented with pulmonary and renal artery flow probes in the renal cortex and medulla, combination fiber-optic probes comprising a fluorescence optode to measure tissue PO2, and a laser-Doppler probe to assess tissue perfusion. Sepsis was induced by infusion of live Escherichia coli for 24 hours followed by 24-hour recovery. MEASUREMENTS AND MAIN RESULTS In unanesthetized normal sheep, resting levels of cortical and medullary tissue PO2 were 29.5 ± 4.4 and 29.1 ± 4.3 mm Hg, respectively. During infusion of E. coli, hyperdynamic sepsis developed with hypotension, tachycardia, increased cardiac output, increased renal blood flow, oliguria, decreased creatinine clearance, and increased serum creatinine. Renal oxygen delivery increased while renal oxygen consumption was unchanged. During sepsis, cortical tissue PO2 increased from 29.4 ± 4.3 to 36.3 ± 3.5 mm Hg (p < 0.001), whereas medullary oxygenation decreased from 29.6 ± 4.7 to 13.1 ± 2.7 mm Hg (p < 0.001). Cortical perfusion was not significantly changed, but medullary perfusion decreased (671 BPU [500-900 BPU] to 480 BPU [349-661 BPU]; geometric mean [95% CI]; p < 0.001). CONCLUSIONS In a large animal model of hyperdynamic sepsis, renal hyperemia was associated with preserved cortical oxygenation and perfusion, but decreased medullary oxygenation and perfusion. Medullary hypoxia due to intrarenal blood flow redistribution may be one of the factors causing acute kidney injury in sepsis.
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Abstract
Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.
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Affiliation(s)
- Mattias Carlström
- Department of Medicine, Division of Nephrology and Hypertension and Hypertension, Kidney and Vascular Research Center, Georgetown University, Washington, District of Columbia; Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden; and Department of Cell Biology and Physiology, UNC Kidney Center, and McAllister Heart Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
| | - Christopher S Wilcox
- Department of Medicine, Division of Nephrology and Hypertension and Hypertension, Kidney and Vascular Research Center, Georgetown University, Washington, District of Columbia; Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden; and Department of Cell Biology and Physiology, UNC Kidney Center, and McAllister Heart Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
| | - William J Arendshorst
- Department of Medicine, Division of Nephrology and Hypertension and Hypertension, Kidney and Vascular Research Center, Georgetown University, Washington, District of Columbia; Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden; and Department of Cell Biology and Physiology, UNC Kidney Center, and McAllister Heart Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
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Abdelkader A, Ho J, Ow CPC, Eppel GA, Rajapakse NW, Schlaich MP, Evans RG. Renal oxygenation in acute renal ischemia-reperfusion injury. Am J Physiol Renal Physiol 2014; 306:F1026-38. [PMID: 24598805 DOI: 10.1152/ajprenal.00281.2013] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Tissue hypoxia has been demonstrated, in both the renal cortex and medulla, during the acute phase of reperfusion after ischemia induced by occlusion of the aorta upstream from the kidney. However, there are also recent clinical observations indicating relatively well preserved oxygenation in the nonfunctional transplanted kidney. To test whether severe acute kidney injury can occur in the absence of widespread renal tissue hypoxia, we measured cortical and inner medullary tissue Po2 as well as total renal O2 delivery (Do2) and O2 consumption (Vo2) during the first 2 h of reperfusion after 60 min of occlusion of the renal artery in anesthetized rats. To perform this experiment, we used a new method for measuring kidney Do2 and Vo2 that relies on implantation of fluorescence optodes in the femoral artery and renal vein. We were unable to detect reductions in renal cortical or inner medullary tissue Po2 during reperfusion after ischemia localized to the kidney. This is likely explained by the observation that Vo2 (-57%) was reduced by at least as much as Do2 (-45%), due to a large reduction in glomerular filtration (-94%). However, localized tissue hypoxia, as evidence by pimonidazole adduct immunohistochemistry, was detected in kidneys subjected to ischemia and reperfusion, particularly in, but not exclusive to, the outer medulla. Thus, cellular hypoxia, particularly in the outer medulla, may still be present during reperfusion even when reductions in tissue Po2 are not detected in the cortex or inner medulla.
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Affiliation(s)
- Amany Abdelkader
- Dept. of Physiology, PO Box 13F, Monash Univ., Victoria 3800, Australia.
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Kennedy‐Lydon TM, Crawford C, Wildman SSP, Peppiatt‐Wildman CM. Renal pericytes: regulators of medullary blood flow. Acta Physiol (Oxf) 2013; 207:212-25. [PMID: 23126245 PMCID: PMC3561688 DOI: 10.1111/apha.12026] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2012] [Revised: 07/03/2012] [Accepted: 09/27/2012] [Indexed: 01/29/2023]
Abstract
Regulation of medullary blood flow (MBF) is essential in maintaining normal kidney function. Blood flow to the medulla is supplied by the descending vasa recta (DVR), which arise from the efferent arterioles of juxtamedullary glomeruli. DVR are composed of a continuous endothelium, intercalated with smooth muscle-like cells called pericytes. Pericytes have been shown to alter the diameter of isolated and in situ DVR in response to vasoactive stimuli that are transmitted via a network of autocrine and paracrine signalling pathways. Vasoactive stimuli can be released by neighbouring tubular epithelial, endothelial, red blood cells and neuronal cells in response to changes in NaCl transport and oxygen tension. The experimentally described sensitivity of pericytes to these stimuli strongly suggests their leading role in the phenomenon of MBF autoregulation. Because the debate on autoregulation of MBF fervently continues, we discuss the evidence favouring a physiological role for pericytes in the regulation of MBF and describe their potential role in tubulo-vascular cross-talk in this region of the kidney. Our review also considers current methods used to explore pericyte activity and function in the renal medulla.
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Affiliation(s)
| | - C. Crawford
- Medway School of Pharmacy The Universities of Kent and Greenwich at Medway Kent UK
| | - S. S. P. Wildman
- Medway School of Pharmacy The Universities of Kent and Greenwich at Medway Kent UK
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Damkjaer M, Vafaee M, Braad PE, Petersen H, Høilund-Carlsen PF, Bie P. Renal cortical and medullary blood flow during modest saline loading in humans. Acta Physiol (Oxf) 2012; 205:472-83. [PMID: 22433079 DOI: 10.1111/j.1748-1716.2012.02436.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2011] [Revised: 01/05/2012] [Accepted: 03/13/2012] [Indexed: 02/02/2023]
Abstract
AIM Renal medullary blood flow (RMBF) is considered an important element of sodium homeostasis, but the experimental evidence is incongruent. Studies in anaesthetized animals generally support the concept in contrast to measurements in conscious animals. We hypothesized that saline-induced natriuresis is associated with changes in RMBF in humans. METHODS After 4 days of low-sodium diet, healthy men were subjected to slow intravenous saline loading (12 μmol kg(-1) min(-1)) for 4 h. Renal medullary and cortical blood flow was determined by positron emission tomography with H(2)(15)O before and after saline infusion using two independent imaging processing methods. One based on a previously published algorithm (voxel peeling) and a novel method based on contrast-enhanced computed tomography (CT). Blood pressure was measured oscillometrically every 10 min. Cardiac output, heart rate and total peripheral resistance were recorded continuously. RESULTS Saline loading increased the urinary sodium excretion by 3.6-fold (21-76 μmol min(-1) , P < 0.01). The RMBF was 2.6 ± 0.2 mL g(-1) tissue min(-1) before and 2.7 ± 0.1 mL g(-1) tissue min(-1) after saline (n.s.). Cortical blood flow was 3.6 ± 0.1 before and 3.4 ± 0.2 after saline (n.s.). Mean arterial blood pressure did not change measurably (90 vs. 90 mmHg). Bland-Altman analysis suggested agreement between results obtained with voxel peeling (2.6 ± 0.2 mL g(-1) tissue min(-1)) and contrast-enhanced CT (2.0 ± 0.1 mL g(-1) tissue min(-1)). CONCLUSION In normal humans, changes in RMBF are not necessarily involved in the natriuretic response to modest saline loading. This result is in line with data from conscious rodents.
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Affiliation(s)
- M. Damkjaer
- Institute of Molecular Medicine; University of Southern Denmark; Odense; Denmark
| | - M. Vafaee
- Department of Neuroscience and Pharmacology; Faculty of Health Sciences; University of Copenhagen; Copenhagen; Denmark
| | - P. E. Braad
- Department of Nuclear Medicine; Odense University Hospital; Odense; Denmark
| | - H. Petersen
- Department of Nuclear Medicine; Odense University Hospital; Odense; Denmark
| | | | - P. Bie
- Institute of Molecular Medicine; University of Southern Denmark; Odense; Denmark
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Eppel GA, Head GA, Denton KM, Evans RG. Effects of tempol and candesartan on neural control of the kidney. Auton Neurosci 2012; 168:48-57. [PMID: 22336580 DOI: 10.1016/j.autneu.2012.01.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2011] [Revised: 01/21/2012] [Accepted: 01/22/2012] [Indexed: 02/07/2023]
Abstract
We compared the effects of tempol (300 μmol kg(-1) plus 300 μmol kg(-1) h(-1), n=14) and candesartan (10 μg kg(-1) plus 10 μg kg(-1) h(-1), n=14) on renal haemodynamics, excretory function, and responses to electrical stimulation of the renal nerves (RNS) in lean and obese rabbits under pentobarbitone anaesthesia. Depressor responses to tempol (-16 ± 2 mmHg) and candesartan (-12 ± 1 mmHg) were similar. Candesartan, but not tempol, significantly increased basal renal blood flow (RBF; +36 ± 7%). Tempol, but not candesartan, significantly reduced glomerular filtration rate (GFR; -30 ± 10%) and sodium excretion (U(Na)V; -44 ± 14%). RNS induced frequency-dependent reductions in RBF (-20 ± 3% at 1 Hz), GFR (-28 ± 6% at 1 Hz) and U(Na)V (-55 ± 6% at 1 Hz). Candesartan blunted these responses. Tempol did not significantly alter RBF and GFR responses to RNS but blunted the U(Na)V response. Responses to RNS, and the effects of tempol and candesartan, were similar in lean compared with obese rabbits. Unlike candesartan, tempol did not induce renal vasodilatation, maintain GFR and U(Na)V during reductions in arterial pressure, or blunt neurally-mediated vasoconstriction. In conclusion, unlike the AT(1)-receptor antagonist candesartan, tempol does not blunt the effects of RNS on renal haemodynamic function. Furthermore, under the current experimental conditions superoxide appears to make little contribution to the actions of endogenous angiotensin II on baseline renal haemodynamics or excretory function, or their responses to RNS.
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Affiliation(s)
- Gabriela A Eppel
- Department of Physiology, Monash University, Melbourne, Australia
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Evans RG, Eppel GA, Michaels S, Burke SL, Nematbakhsh M, Head GA, Carroll JF, O'Connor PM. Multiple mechanisms act to maintain kidney oxygenation during renal ischemia in anesthetized rabbits. Am J Physiol Renal Physiol 2010; 298:F1235-43. [PMID: 20200093 DOI: 10.1152/ajprenal.00647.2009] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We examined the mechanisms that maintain stable renal tissue PO(2) during moderate renal ischemia, when changes in renal oxygen delivery (DO(2)) and consumption (VO(2)) are mismatched. When renal artery pressure (RAP) was reduced progressively from 80 to 40 mmHg, VO(2) (-38 ± 7%) was reduced more than DO(2) (-26 ± 4%). Electrical stimulation of the renal nerves (RNS) reduced DO(2) (-49 ± 4% at 2 Hz) more than VO(2) (-30 ± 7% at 2 Hz). Renal arterial infusion of angiotensin II reduced DO(2) (-38 ± 3%) but not VO(2) (+10 ± 10%). Despite mismatched changes in DO(2) and VO(2), renal tissue PO(2) remained remarkably stable at ≥40 mmHg RAP, during RNS at ≤2 Hz, and during angiotensin II infusion. The ratio of sodium reabsorption to VO(2) was reduced by all three ischemic stimuli. None of the stimuli significantly altered the gradients in PCO(2) or pH across the kidney. Fractional oxygen extraction increased and renal venous PO(2) fell during 2-Hz RNS and angiotensin II infusion, but not when RAP was reduced to 40 mmHg. Thus reduced renal VO(2) can help prevent tissue hypoxia during mild renal ischemia, but when renal VO(2) is reduced less than DO(2), other mechanisms prevent a fall in renal PO(2). These mechanisms do not include increased efficiency of renal oxygen utilization for sodium reabsorption or reduced washout of carbon dioxide from the kidney, leading to increased oxygen extraction. However, increased oxygen extraction could be driven by altered countercurrent exchange of carbon dioxide and/or oxygen between renal arteries and veins.
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Affiliation(s)
- Roger G Evans
- Dept. of Physiology, PO Box 13F, Monash Univ., Victoria 3800, Australia.
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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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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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Eppel GA, Ventura S, Evans RG. Regional vascular responses to ATP and ATP analogues in the rabbit kidney in vivo: roles for adenosine receptors and prostanoids. Br J Pharmacol 2006; 149:523-31. [PMID: 16981003 PMCID: PMC2014670 DOI: 10.1038/sj.bjp.0706901] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
BACKGROUND AND PURPOSE Our knowledge of the effects of P2-receptor activation on renal vascular tone comes mostly from in vitro models. We aimed to characterise the pharmacology of ATP in the renal circulation in vivo. EXPERIMENTAL APPROACH In pentobarbitone anaesthetized rabbits, we examined total renal and medullary vascular responses to ATP (0.2 and 0.8 mg kg(-1)), beta, gamma-methylene ATP (beta, gamma-mATP, 7 and 170 microg kg(-1)), alpha, beta-mATP (0.2 and 2 microg kg(-1)) and adenosine (2 and 6 microg kg(-1)) using transit-time ultrasound and laser Doppler flowmetry, respectively. We also determined whether adenosine receptors, NO or prostanoids contribute to the actions of the purinoceptor agonists. KEY RESULTS Renal arterial boluses of ATP, beta,gamma-mATP, and adenosine produced biphasic changes; ischaemia followed by hyperaemia, in total renal and medullary blood flow. alpha,beta-mATP induced only ischaemia. The adenosine receptor antagonist 8-(p-sulphophenyl)theophylline reduced the responses to adenosine and the hyperaemic responses to ATP and beta,gamma-mATP only. NO synthase inhibition (Nomega-nitro-L-arginine) did not significantly alter responses to the P2 receptor agonists. Subsequent cyclooxygenase inhibition (ibuprofen) reduced the ATP- and beta, gamma-mATP-induced increases in renal blood flow. All other responses remained unchanged. CONCLUSIONS AND IMPLICATIONS In the rabbit kidney in vivo, alpha, beta-mATP sensitive receptors mediate vasoconstriction. beta,gamma-mATP and ATP induce vasodilation at least partly through adenosine receptors. ATP induced renal vasodilatation is independent of NO and partly dependent on prostanoids in the bulk of the kidney, but not in the vasculature controlling medullary blood flow.
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Affiliation(s)
- G A Eppel
- Department of Physiology, Monash University, Melbourne, Victoria, Australia.
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Eppel GA, Ventura S, Denton KM, Evans RG. Lack of contribution of P2X receptors to neurally mediated vasoconstriction in the rabbit kidney in vivo. Acta Physiol (Oxf) 2006; 186:197-207. [PMID: 16497199 DOI: 10.1111/j.1748-1716.2006.01526.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: 11/28/2022]
Abstract
AIM The contribution of adenosine triphosphate (ATP) to the neural control of regional renal perfusion in vivo remains unknown. We therefore examined whether P2X receptors mediate renal vascular responses to electrical stimulation of the renal nerves (RNS) in pentobarbitone anaesthetized rabbits. METHODS Responses to RNS were tested before and during renal arterial infusion of alpha,beta-methylene ATP (alpha,beta-mATP, 7-56 microg kg(-1) min(-1)) to desensitize P2X1 receptors. RNS consisted of 3 min trains at graded frequencies and short trains of RNS (4-32 pulses). RESULTS Three-minute trains of RNS reduced renal blood flow (RBF), cortical laser Doppler flux (CLDF), and medullary LDF (MLDF) by -90 +/- 3%, -89 +/- 3% and -31 +/- 11%, respectively, at 4 Hz. MLDF was reduced less than CLDF or RBF. During short train RNS, RBF, CLDF and MLDF were reduced by -22 +/- 2%, -15 +/- 2% and -12 +/- 2%, respectively, for 32 s at 1 Hz. CLDF and MLDF were reduced to a similar extent. Infusion of alpha,beta-mATP induced transient reductions in RBF, CLDF and MLDF, but within 5 min these variables had recovered to control levels. Vascular responses to RNS were not significantly altered by alpha,beta-mATP treatment. CONCLUSIONS In the rabbit kidney in vivo, alpha,beta-mATP-sensitive receptors mediate vasoconstriction and reduce perfusion in both cortical and medullary vascular beds. However, these receptors do not mediate neurally induced reductions in renal perfusion.
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Affiliation(s)
- G A Eppel
- Department of Physiology, Monash University, Melbourne, Vic., Australia.
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Evans RG, Majid DSA, Eppel GA. Mechanisms mediating pressure natriuresis: what we know and what we need to find out. Clin Exp Pharmacol Physiol 2006; 32:400-9. [PMID: 15854149 DOI: 10.1111/j.1440-1681.2005.04202.x] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
1. It is well established that pressure natriuresis plays a key role in long-term blood pressure regulation, but our understanding of the mechanisms underlying this process is incomplete. 2. Pressure natriuresis is chiefly mediated by inhibition of tubular sodium reabsorption, because both total renal blood flow and glomerular filtration rate are efficiently autoregulated. Inhibition of active sodium transport within both the proximal and distal tubules likely makes a contribution. Increased renal interstitial hydrostatic pressure (RIHP) likely inhibits sodium reabsorption by altering passive diffusion through paracellular pathways in 'leaky' tubular elements. 3. Nitric oxide and products of cytochrome P450-dependent arachidonic acid metabolism are key signalling mechanisms in pressure natriuresis, although their precise roles remain to be determined. 4. The key unresolved question is, how is increased renal artery pressure 'sensed' by the kidney? One proposal rests on the notion that blood flow in the renal medulla is poorly autoregulated, so that increased renal artery pressure leads to increased renal medullary blood flow (MBF), which, in turn, leads to increased RIHP. An alternative proposal is that the process of autoregulation of renal blood flow leads to increased shear stress in the preglomerular vasculature and, so, release of nitric oxide and perhaps products of cytochrome P450-dependent arachidonic acid metabolism, which, in turn, drive the cascade of events that inhibit sodium reabsorption. 5. Central to the arguments underlying these opposing hypotheses is the extent to which MBF is autoregulated. This remains highly controversial, largely because of the limitations of presently available methods for measurement of MBF.
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Affiliation(s)
- Roger G Evans
- Department of Physiology, Monash University, Melbourne, Victoria, Australia.
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O'Connor PM, Kett MM, Anderson WP, Evans RG. Renal medullary tissue oxygenation is dependent on both cortical and medullary blood flow. Am J Physiol Renal Physiol 2005; 290:F688-94. [PMID: 16219913 DOI: 10.1152/ajprenal.00275.2005] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The aim of the current study was to determine whether renal medullary oxygenation is independent of the level of cortical blood flow by testing responses to stimuli that selectively reduce blood flow in either the cortex or medulla. In anesthetized rabbits, renal arterial infusion of [Phe(2),Ile(3),Orn(8)]-vasopressin selectively reduced medullary perfusion and Po(2) (-54 +/- 24 and -50 +/- 10%, respectively) but did not significantly affect cortical perfusion or tissue oxygenation. In contrast, stimulation of the renal nerves resulted in renal cortical ischemia with reductions in total renal blood flow (-76 +/- 3% at 4 Hz), cortical perfusion (-57 +/- 17%), and cortical Po(2) (-44 +/- 12%). Medullary tissue Po(2) was reduced by -70 +/- 5% at 4 Hz, despite medullary perfusion being unaffected and distal tubular sodium reabsorption being reduced (by -83.3 +/- 1.2% from baseline). In anesthetized rats, in which renal perfusion pressure was maintained with an aortic constrictor, intravenous infusion of ANG II (0.5-5 microg. kg(-1).min(-1)) dose dependently reduced cortical perfusion (up to -65 +/- 3%; P < 0.001) and cortical Po(2) (up to -57 +/- 4%; P < 0.05). However, medullary perfusion was only significantly reduced at the highest dose (5 microg. kg(-1).min(-1); by 29 +/- 6%). Medullary perfusion was not reduced by 1 microg. kg(-1).min(-1) ANG II, but medullary Po(2) was significantly reduced (-12 +/- 4%). Thus, although cortical and medullary blood flow may be independently regulated, medullary oxygenation may be compromised during moderate to severe cortical ischemia even when medullary blood flow is maintained.
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Affiliation(s)
- Paul M O'Connor
- Dept. of Physiology, Medical College of Wisconsin, 8071 Watertown Plank Road, Milwaukee, WI 53266, USA.
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Eppel GA, Luff SE, Denton KM, Evans RG. Type 1 neuropeptide Y receptors and alpha1-adrenoceptors in the neural control of regional renal perfusion. Am J Physiol Regul Integr Comp Physiol 2005; 290:R331-40. [PMID: 16195497 DOI: 10.1152/ajpregu.00317.2005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The aim of this study was to determine the contribution of neuropeptide Y (NPY) Y1 receptors in neurally mediated reductions in renal medullary perfusion. In pentobarbital sodium-anesthetized rabbits, electrical stimulation of the renal nerves (RNS, 0.5-16 Hz) decreased renal perfusion in a frequency-dependent manner. Under control conditions, 4 Hz reduced cortical and medullary perfusion by -85 +/- 3% and -43 +/- 7%, whereas 8 Hz reduced them by -93 +/- 2% and -73 +/- 4%, respectively. After Y1 receptor antagonism with BIBO3304TF (0.1 mg/kg plus 0.2 mg x kg x (-1) x h(-1)), RNS reduced perfusion less (by -65 +/- 9% and -12 +/- 8% at 4 Hz) x alpha1-Adrenoceptor antagonism with prazosin (0.2 mg/kg plus 0.2 mg kg(-1)h(-1)) also inhibited RNS-induced reductions in renal perfusion (-80 +/- 4% and -37 +/- 10% reductions in the cortex and medulla, respectively, at 8 Hz). When given after BIBO3304TF treatment, prazosin inhibited RNS-induced reductions in cortical and medullary perfusion more profoundly (-57 +/- 12% and -25 +/- 9% reductions, respectively, at 8 Hz) x Y1 receptor- and alpha1-adrenoceptor-blockade were confirmed by testing vascular responses to renal arterial NPY and phenylephrine boluses. NPY-positive immunolabeling was observed around interlobular arteries, afferent and efferent arterioles, and in the outer medulla. In conclusion, Y1 receptors and alpha1-adrenoceptors contribute to RNS-induced vasoconstriction in the vessels that control both cortical and medullary perfusion. Consistent with this, NPY immunostaining was associated with blood vessels that control perfusion in both regions. There also seems to be an interaction between Y1 receptors and alpha1-adrenoceptor-mediated neurotransmission in the control of renal perfusion.
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Rajapakse NW, Sampson AK, Eppel GA, Evans RG. Angiotensin II and nitric oxide in neural control of intrarenal blood flow. Am J Physiol Regul Integr Comp Physiol 2005; 289:R745-54. [PMID: 15890788 DOI: 10.1152/ajpregu.00477.2004] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We investigated the roles of the renin-angiotensin system and the significance of interactions between angiotensin II and nitric oxide, in responses of regional kidney perfusion to electrical renal nerve stimulation (RNS) in pentobarbital sodium-anesthetized rabbits. Under control conditions, RNS (0.5–8 Hz) reduced total renal blood flow (RBF; −89 ± 3% at 8 Hz) and cortical perfusion (CBF; −90 ± 2% at 8 Hz) more than medullary perfusion (MBF; −55 ± 5% at 8 Hz). Angiotensin II type 1 (AT1)-receptor antagonism (candesartan) blunted RNS-induced reductions in RBF ( P = 0.03), CBF ( P = 0.007), and MBF ( P = 0.04), particularly at 4 and 8 Hz. Nitric oxide synthase inhibition with NG-nitro-l-arginine (l-NNA) enhanced RBF ( P = 0.003), CBF ( P = 0.001), and MBF ( P = 0.03) responses to RNS, particularly at frequencies of 2 Hz and less. After candesartan pretreatment, l-NNA significantly enhanced RNS-induced reductions in RBF ( P = 0.04) and CBF ( P = 0.007) but not MBF ( P = 0.66). Renal arterial infusion of angiotensin II (5 ng·kg−1·min−1) selectively enhanced responses of MBF to RNS in l-NNA-pretreated but not in vehicle-pretreated rabbits. In contrast, greater doses of angiotensin II (5–15 ng·kg−1·min−1) blunted responses of MBF to RNS in rabbits with intact nitric oxide synthase. These results suggest that endogenous angiotensin II enhances, whereas nitric oxide blunts, neurally mediated vasoconstriction in the renal cortical and medullary circulations. In the renal medulla, but not the cortex, angiotensin II also appears to be able to blunt neurally mediated vasoconstriction.
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Affiliation(s)
- Niwanthi W Rajapakse
- Dept. of Physiology, PO Box 13F, Monash University, Melbourne, Victoria 3800, Australia
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Ichai C, Giunti C. [On which renal haemodynamic and renal function parameters can we act to protect the kidney?]. ANNALES FRANCAISES D'ANESTHESIE ET DE REANIMATION 2005; 24:148-60. [PMID: 15737501 DOI: 10.1016/j.annfar.2004.12.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/01/2023]
Affiliation(s)
- C Ichai
- Département d'anesthésie-réanimation Est, service de réanimation CHU de Nice, hôpital Saint-Roch, 5, rue Pierre-Dévoluy, 06006 Nice cedex 1, France.
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Denton KM, Shweta A, Finkelstein L, Flower RL, Evans RG. Effect of endothelin-1 on regional kidney blood flow and renal arteriole calibre in rabbits. Clin Exp Pharmacol Physiol 2005; 31:494-501. [PMID: 15298540 DOI: 10.1111/j.1440-1681.2004.04036.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
1. Medullary blood flow (MBF) is important in the long-term control of arterial pressure. However, it is unclear which vascular elements regulate MBF. 2. Exogenous endothelin (ET)-1 decreases cortical more than medullary blood flow. We hypothesized that ET-1 would therefore constrict afferent (AA) and efferent arterioles (EA) of juxtamedullary glomeruli less than those of cortical glomeruli. 3. Mean arterial pressure, renal blood flow and cortical (CBF) and medullary (MBF) blood flow, via laser-Doppler flowmetry, were measured before and after intrarenal ET-1 (2 ng/kg per min; n = 6) or vehicle (n = 6) in anaesthetized rabbits. Kidneys were perfusion fixed, vascular casts formed, lumen diameters measured via scanning electron microscopy and relative resistance calculated. 4. Mean arterial pressure was not significantly affected by ET-1 infusion. Cortical glomerular arteriole lumen diameters were significantly reduced in the ET-1-infused group (AA approximately 30%, EA approximately 18%; PA < 0.01), compatible with the decrease in CBF (42 +/- 3%; PGT < 0.01). Juxtamedullary arteriole lumen diameters were also significantly reduced in the ET-1-infused group (AA approximately 34%, EA approximately 21%; PA < 0.01); however, MBF did not decrease. 5. In conclusion, our data suggest that juxtamedullary arterioles are not of primary importance in the regulation of MBF because, despite reductions in juxtamedullary arteriole diameters in response to ET-1, MBF was not decreased.
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Affiliation(s)
- Kate M Denton
- Department of Physiology, Monash University, Melbourne, Victoria, Australia.
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Guild SJ, Malpas SC, Eppel GA, Nguang SK, Evans RG. Effect of renal perfusion pressure on responses of intrarenal blood flow to renal nerve stimulation in rabbits. Clin Exp Pharmacol Physiol 2004; 31:35-45. [PMID: 14756682 DOI: 10.1111/j.1440-1681.2004.03947.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
1. We investigated how sympathetic nerve activity and renal perfusion pressure (RPP) interact in controlling renal haemodynamics in pentobarbitone-anaesthetized rabbits. 2. Renal blood flow (RBF) was reduced by electrical renal nerve stimulation (0.5-8 Hz), with RPP set using an extracorporeal circuit to 65, 100 and 135 mmHg. 3. Responses of RBF and cortical laser Doppler flux to renal nerve stimulation were blunted by increased RPP. For example, 4 Hz stimulation reduced RBF by 68 +/- 7% with baseline perfusion pressure approximately 65 mmHg, but only by 22 +/- 3% at approximately 135 mmHg. Medullary laser Doppler flux was less responsive than cortical laser Doppler flux to renal nerve stimulation and its response was not dependent on perfusion pressure. 4. When perfusion pressure was clamped at its baseline level during renal nerve stimulation, responses of RBF and cortical laser Doppler flux, but not medullary laser Doppler flux, were still blunted with increased baseline perfusion pressure. 5. A frequency rich stimulus was applied to assess the effects of perfusion pressure on dynamic neural control of RBF. Renal blood flow responded similarly at each level of perfusion pressure, as a low-pass filter with a pure time delay. 6. Our results suggest that, in the rabbit extracorporeal circuit model, increased RPP blunts the ability of steady state renal nerve stimulation to reduce cortical, but not medullary perfusion. However, in this model the level of RPP appears to have little impact on dynamic neural control of RBF.
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Affiliation(s)
- Sarah-Jane Guild
- Circulatory Control Laboratory, Department of Physiology, University of Auckland, PB 92019, Auckland, New Zealand.
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Bergström G, Evans RG. Mechanisms underlying the antihypertensive functions of the renal medulla. ACTA ACUST UNITED AC 2004; 181:475-86. [PMID: 15283761 DOI: 10.1111/j.1365-201x.2004.01321.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
There is good evidence that the renal medulla plays a pivotal role in long-term regulation of blood pressure. 'Renal medullary' blood pressure regulating systems have been postulated to involve both exocrine (pressure natriuresis/diuresis) and endocrine [renal medullary depressor hormone (RMDH)] functions. However, recent studies indicate that pressure diuresis/natriuresis dominates the antihypertensive renal response to increased renal perfusion pressure, suggesting little physiological role for a putative RMDH in compensatory responses to acutely increased blood pressure. The medullary circulation appears to play a key role in mediating pressure diuresis, although the precise mechanisms involved remain controversial. Counter-regulatory vasodilator mechanisms (e.g. nitric oxide), at least partly mediated through cross-talk between the vasculature and the tubular epithelium, protect the medullary circulation from the vasoconstrictor effects of hormonal factors such as angiotensin II. These mechanisms also appear to contribute to compensatory responses to increased salt intake in salt-resistant individuals. Failure of these mechanisms predisposes the organism towards the development of hypertension, appears to underlie the development of some forms of experimental hypertension, and may even contribute to the pathogenesis of essential hypertension.
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Affiliation(s)
- G Bergström
- Department of Clinical Physiology, Cardiovascular Institute, Göteborg University, Göteborg, Sweden
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Eppel GA, Lee LL, Evans RG. α-Adrenoceptor subtypes mediating regional kidney blood flow responses to renal nerve stimulation. Auton Neurosci 2004; 112:15-24. [PMID: 15233926 DOI: 10.1016/j.autneu.2004.03.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2003] [Revised: 02/13/2004] [Accepted: 03/01/2004] [Indexed: 11/25/2022]
Abstract
The mechanisms underlying the relative insensitivity of the renal medullary circulation to renal sympathetic nerve stimulation (RNS) remain unknown. Therefore, we tested the effects of systemic alpha(1)- and alpha(2)-adrenoceptor blockade on responses to electrical RNS in pentobarbitone anaesthetized rabbits. Renal blood flow (RBF), cortical laser Doppler flux (CLDF), and to a lesser extent medullary LDF (MLDF) were reduced by RNS in a frequency-dependent manner. Prazosin decreased responses of RBF and CLDF, but not MLDF, to RNS. For example, during the control period 4 Hz stimulation reduced RBF, CLDF and MLDF by 85+/-3%, 89+/-2%, and 20+/-12%, respectively, but after prazosin, corresponding responses were 39+/-3%, 42+/-5% and 28+/-7%, respectively. Prazosin markedly blunted pressor and renal vasoconstrictor responses to intravenous phenylephrine, without altering pressor responses to intravenous xylazine. Rauwolscine enhanced renal vasoconstrictor responses to RNS, although this was statistically significant for RBF and CLDF but not MLDF. For example, during the control period 2 Hz stimulation reduced RBF, CLDF and MLDF by 63+/-7%, 58+/-7%, and 29+/-17%, respectively, and after rauwolscine, corresponding responses were 83+/-4%, 87+/-1%, and 53+/-12%, respectively. Rauwolscine markedly blunted renal vasoconstrictor responses to renal arterial guanabenz, but not phenylephrine. These data suggest that alpha(1)-adrenoceptors contribute to RNS-induced vasoconstriction in the renal cortex, but contribute less in vascular elements controlling medullary perfusion. Activation of alpha(2)-adrenoceptors appears to blunt RNS-induced renal vasoconstriction, but this mechanism does not underlie the relative insensitivity of medullary perfusion to RNS.
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Affiliation(s)
- Gabriela A Eppel
- Department of Physiology, Monash University, P.O. Box 13F, Melbourne, Victoria 3800, Australia.
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Duke LM, Eppel GA, Widdop RE, Evans RG. Disparate roles of AT2 receptors in the renal cortical and medullary circulations of anesthetized rabbits. Hypertension 2003; 42:200-5. [PMID: 12847115 DOI: 10.1161/01.hyp.0000083341.64034.00] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The contributions of angiotensin II type 1 (AT1) and type 2 (AT2) receptors to the control of regional kidney blood flow were determined in pentobarbital-anesthetized rabbits. Intravenous candesartan (AT1 antagonist; 10 microg/kg plus 10 microg x kg(-1) x h(-1)) reduced mean arterial pressure (12%) and increased total renal blood flow (29%) and cortical laser-Doppler flux (18%) but not medullary laser-Doppler flux. Neither intravenous PD123319 (AT2 antagonist; 1 mg/kg plus 1 mg x kg(-1) x h(-1)) nor saline vehicle significantly affected these variables, and the responses to candesartan plus PD123319 were indistinguishable from those of candesartan alone. In vehicle-treated rabbits, renal-arterial infusions of angiotensin II (1 to 25 ng x kg(-1) x min(-1)) and angiotensin III (5 to 125 ng x kg(-1) x min(-1)) dose-dependently reduced renal blood flow (up to 51%) and cortical laser-Doppler flux (up to 50%) but did not significantly affect medullary laser-Doppler flux or arterial pressure. Angiotensin(1-7) (20 to 500 ng x kg(-1) x min(-1)) had similar effects but of lesser magnitude. CGP42112A (20 to 500 ng x kg(-1) x min(-1)) did not significantly affect these variables. After PD123319 administration, angiotensin II and angiotensin III dose-dependently increased medullary laser-Doppler flux (up to 84%), and reductions in renal blood flow in response to angiotensin II were enhanced. Candesartan abolished renal hemodynamic responses to the angiotensin peptides, even when given in combination with PD123319. We conclude that AT2 receptor activation counteracts AT1-mediated vasoconstriction in the renal cortex but also counteracts AT1-mediated vasodilatation in vascular elements controlling medullary perfusion. These mechanisms might have an important effect on the control of medullary perfusion under conditions of activation of the renin-angiotensin system.
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Affiliation(s)
- Lisa M Duke
- Department of Physiology, PO Box 13F, Monash University, Victoria 3800, Australia.
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