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Tin A, Köttgen A. Mendelian Randomization Analysis as a Tool to Gain Insights into Causes of Diseases: A Primer. J Am Soc Nephrol 2021; 32:2400-2407. [PMID: 34135084 PMCID: PMC8722812 DOI: 10.1681/asn.2020121760] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Accepted: 05/24/2021] [Indexed: 02/04/2023] Open
Abstract
Many Mendelian randomization (MR) studies have been published recently, with inferences on the causal relationships between risk factors and diseases that have potential implications for clinical research. In nephrology, MR methods have been applied to investigate potential causal relationships of traditional risk factors, lifestyle factors, and biomarkers from omics technologies with kidney function or CKD. This primer summarizes the basic concepts of MR studies, highlighting methods used in recent applications, and emphasizes key elements in conducting and reporting of MR studies that are important for interpreting the results.
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Affiliation(s)
- Adrienne Tin
- Department of Medicine, University of Mississippi Medical Center, Jackson, Mississippi
- Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland
| | - Anna Köttgen
- Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland
- Department of Data Driven Medicine, Institute of Genetic Epidemiology, Faculty of Medicine and Medical Center, University of Freiburg, Freiburg, Germany
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Richfield O, Cortez R, Navar LG. Simulations of Glomerular Shear and Hoop Stresses in Diabetes, Hypertension, and Reduced Renal Mass using a Network Model of a Rat Glomerulus. Physiol Rep 2021; 8:e14577. [PMID: 32951361 PMCID: PMC7507384 DOI: 10.14814/phy2.14577] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2020] [Revised: 08/18/2020] [Accepted: 08/19/2020] [Indexed: 12/15/2022] Open
Abstract
A novel anatomically accurate model of rat glomerular filtration is used to quantify shear stresses on the glomerular capillary endothelium and hoop stresses on the glomerular capillary walls. Plasma, erythrocyte volume, and plasma protein mass are distributed at network nodes using pressure differentials calculated taking into account volume loss to filtration, improving on previous models which only took into account blood apparent viscosity in calculating pressures throughout the network. Filtration is found to be heterogeneously distributed throughout the glomerular capillary network and is determined by concentration of plasma proteins and surface area of the filtering capillary segments. Hoop stress is primarily concentrated near the afferent arteriole, whereas shear stress is concentrated near the efferent arteriole. Using parameters from glomerular micropuncture studies, conditions of diabetes mellitus (DM), 5/6‐Nephrectomy (5/6‐Nx), and Angiotensin II‐induced hypertension (HTN) are simulated and compared to their own internal controls to assess the changes in mechanical stresses. Hoop stress is increased in all three conditions, while shear stress is increased in 5/6‐Nx, decreased in HTN, and maintained at control levels in DM by the hypertrophic response of the glomerular capillaries. The results indicate that these alterations in mechanical stresses and the consequent release of cytokines by or injury of the glomerular cells may play a significant role in the progression of glomerulopathy in these disease conditions.
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Affiliation(s)
- Owen Richfield
- Bioinnovation PhD Program, Tulane University, New Orleans, LA, USA.,Department of Physiology, Tulane School of Medicine, New Orleans, LA, USA
| | - Ricardo Cortez
- Department of Mathematics, Tulane University, New Orleans, LA, USA
| | - L Gabriel Navar
- Department of Physiology, Tulane School of Medicine, New Orleans, LA, USA
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3
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Kannenkeril D, Janka R, Bosch A, Jung S, Kolwelter J, Striepe K, Ott C, Martirosian P, Schiffer M, Uder M, Schmieder RE. Detection of Changes in Renal Blood Flow Using Arterial Spin Labeling MRI. Am J Nephrol 2021; 52:69-75. [PMID: 33677438 DOI: 10.1159/000513665] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Accepted: 12/07/2020] [Indexed: 11/19/2022]
Abstract
BACKGROUND Alteration in kidney perfusion is an early marker of renal damage. The purpose of this study was to evaluate if changes in renal blood flow (RBF) could be detected using MRI with arterial spin labeling (ASL) technique. METHODS RBF as assessed by cortical (CRBF), medullary, and total renal blood flow (TRBF) were measured by MRI with arterial spin labeling (ASL-MRI) using flow-sensitive alternating inversion recovery true fast imaging with steady-state precession sequence. In 11 normotensive healthy individuals (NT) and 11 hypertensive patients (HT), RBF was measured at baseline and after both feet were covered with cold ice packs (cold pressor test) that activates the sympathetic nervous system. In another experiment, RBF was measured in 10 patients with CKD before and after a pharmacological intervention. We compared RBF measurements between the 3 study populations. RESULTS A significant reduction in CRBF (p = 0.042) and a trend in TRBF (p = 0.053) were observed in response to the activation of the sympathetic nervous system. A trend toward reduction of CRBF (p = 0.051) and TRBF (p = 0.059) has been detected after pharmacological intervention. TRBF was significantly lower in patients with HT and CKD patients compared to NT individuals (NT vs. HT, p = 0.014; NT vs. CKD, p = 0.004). TRBF was lower in patients with CKD compared to HT (p = 0.047). CONCLUSION Our data indicate that both acute and short-term changes in RBF could be detected using ASL-MRI. We were able to detect differences in RBF between healthy and diseased individuals by needing only small sample size per group. Thus, ASL-MRI offers an advantage in conducting clinical trials compared to other technologies.
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Affiliation(s)
- Dennis Kannenkeril
- Department of Nephrology and Hypertension, University Hospital Erlangen, Erlangen, Germany
| | - Rolf Janka
- Institute of Radiology, University Hospital Erlangen, Erlangen, Germany
| | - Agnes Bosch
- Department of Nephrology and Hypertension, University Hospital Erlangen, Erlangen, Germany
| | - Susanne Jung
- Department of Nephrology and Hypertension, University Hospital Erlangen, Erlangen, Germany
- Department of Cardiology, University Hospital Erlangen, Erlangen, Germany
| | - Julie Kolwelter
- Department of Nephrology and Hypertension, University Hospital Erlangen, Erlangen, Germany
- Department of Cardiology, University Hospital Erlangen, Erlangen, Germany
| | - Kristina Striepe
- Department of Nephrology and Hypertension, University Hospital Erlangen, Erlangen, Germany
| | - Christian Ott
- Department of Nephrology and Hypertension, University Hospital Erlangen, Erlangen, Germany
| | - Petros Martirosian
- Section on Experimental Radiology, University Hospital of Tübingen, Tübingen, Germany
| | - Mario Schiffer
- Department of Nephrology and Hypertension, University Hospital Erlangen, Erlangen, Germany
| | - Michael Uder
- Institute of Radiology, University Hospital Erlangen, Erlangen, Germany
| | - Roland E Schmieder
- Department of Nephrology and Hypertension, University Hospital Erlangen, Erlangen, Germany,
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Feng W, Remedies CE, Obi IE, Aldous SR, Meera SI, Sanders PW, Inscho EW, Guan Z. Restoration of afferent arteriolar autoregulatory behavior in ischemia-reperfusion injury in rat kidneys. Am J Physiol Renal Physiol 2021; 320:F429-F441. [PMID: 33491564 PMCID: PMC7988813 DOI: 10.1152/ajprenal.00500.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2020] [Revised: 12/23/2020] [Accepted: 01/12/2021] [Indexed: 12/11/2022] Open
Abstract
Renal autoregulation is critical in maintaining stable renal blood flow (RBF) and glomerular filtration rate (GFR). Renal ischemia-reperfusion (IR)-induced kidney injury is characterized by reduced RBF and GFR. The mechanisms contributing to renal microvascular dysfunction in IR have not been fully determined. We hypothesized that increased reactive oxygen species (ROS) contributed to impaired renal autoregulatory capability in IR rats. Afferent arteriolar autoregulatory behavior was assessed using the blood-perfused juxtamedullary nephron preparation. IR was induced by 60 min of bilateral renal artery occlusion followed by 24 h of reperfusion. Afferent arterioles from sham rats exhibited normal autoregulatory behavior. Stepwise increases in perfusion pressure caused pressure-dependent vasoconstriction to 65 ± 3% of baseline diameter (13.2 ± 0.4 μm) at 170 mmHg. In contrast, pressure-mediated vasoconstriction was markedly attenuated in IR rats. Baseline diameter averaged 11.7 ± 0.5 µm and remained between 90% and 101% of baseline over 65-170 mmHg, indicating impaired autoregulatory function. Acute antioxidant administration (tempol or apocynin) to IR kidneys for 20 min increased baseline diameter and improved autoregulatory capability, such that the pressure-diameter profiles were indistinguishable from those of sham kidneys. Furthermore, the addition of polyethylene glycol superoxide dismutase or polyethylene glycol-catalase to the perfusate blood also restored afferent arteriolar autoregulatory responsiveness in IR rats, indicating the involvement of superoxide and/or hydrogen peroxide. IR elevated mRNA expression of NADPH oxidase subunits and monocyte chemoattractant protein-1 in renal tissue homogenates, and this was prevented by tempol pretreatment. These results suggest that ROS accumulation, likely involving superoxide and/or hydrogen peroxide, impairs renal autoregulation in IR rats in a reversible fashion.NEW & NOTEWORTHY Renal ischemia-reperfusion (IR) leads to renal microvascular dysfunction manifested by impaired afferent arteriolar autoregulatory efficiency. Acute administration of scavengers of reactive oxygen species, polyethylene glycol-superoxide dismutase, or polyethylene glycol-catalase following renal IR restored afferent arteriolar autoregulatory capability in IR rats, indicating that renal IR led to reversible impairment of afferent arteriolar autoregulatory capability. Intervention with antioxidant treatment following IR may improve outcomes in patients by preserving renovascular autoregulatory function and potentially preventing the progression to chronic kidney disease after acute kidney injury.
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Affiliation(s)
- Wenguang Feng
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Colton E Remedies
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Ijeoma E Obi
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Stephen R Aldous
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Samia I Meera
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Paul W Sanders
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
- Department of Veterans Affairs Medical Center, Birmingham, Alabama
| | - Edward W Inscho
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Zhengrong Guan
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
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Yun D, Choi Y, Lee SP, Park KW, Koo BK, Kim HS, Kim DK, Joo KW, Kim YS, Han SS. Blood Pressure and Renal Progression in Patients Undergoing Percutaneous Coronary Intervention. Am J Hypertens 2020; 33:676-684. [PMID: 32179915 DOI: 10.1093/ajh/hpaa046] [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: 10/27/2019] [Revised: 02/28/2020] [Accepted: 03/12/2020] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND High blood pressure (BP) may impair renal function following percutaneous coronary intervention (PCI). However, the predictability of renal progression based on admission and discharge BP and BP threshold values remains unclear. METHODS A total of 8,176 adult patients who underwent PCI at Seoul National University Hospital from 2006 to 2016 were retrospectively analyzed. Renal progression was defined as a doubling of serum creatinine levels, ≥50% decrease of the estimated glomerular filtration rate, or development of end-stage renal disease. The risk of renal progression according to admission BP (any time) and discharge BP (8:00-10:00 am) was evaluated by multivariable Cox and additive generalized models with penalized splines. RESULTS During a median follow-up of 7 years (maximum: 13 years), 9.3% of patients (n = 758) reached renal progression. BP between admission and discharge showed a low correlation, and all BP parameters showed a nonlinear relationship with renal progression. Systolic BP at discharge (SBPd) was selected as the best predictor of renal progression because the delta for the Akaike information criterion from the baseline model to the model with BP parameters was the lowest. The risk of renal progression started to increase at SBPd ≥ 125 mm Hg. This increasing risk of renal progression with SBPd ≥ 125 mm Hg remained significant, despite adjusting for the competing risk of all-cause death. CONCLUSIONS High SBPd is associated with renal progression following PCI, particularly when it is ≥125 mm Hg. This can be used as a risk classification and potential target of renoprotective therapies.
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Affiliation(s)
- Donghwan Yun
- Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea
| | - Yunhee Choi
- Division of Medical Statistics, Medical Research Collaborating Center, Seoul National University College of Medicine, Seoul, Korea
| | - Seung-Pyo Lee
- Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea
- Department of Internal Medicine and Cardiovascular Center, Seoul National University Hospital, Seoul, Korea
| | - Kyung Woo Park
- Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea
- Department of Internal Medicine and Cardiovascular Center, Seoul National University Hospital, Seoul, Korea
| | - Bon-Kwon Koo
- Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea
- Department of Internal Medicine and Cardiovascular Center, Seoul National University Hospital, Seoul, Korea
| | - Hyo-Soo Kim
- Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea
- Department of Internal Medicine and Cardiovascular Center, Seoul National University Hospital, Seoul, Korea
| | - Dong Ki Kim
- Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea
- Division of Nephrology, Seoul National University Hospital, Seoul, Korea
| | - Kwon Wook Joo
- Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea
- Division of Nephrology, Seoul National University Hospital, Seoul, Korea
| | - Yon Su Kim
- Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea
- Division of Nephrology, Seoul National University Hospital, Seoul, Korea
| | - Seung Seok Han
- Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea
- Division of Nephrology, Seoul National University Hospital, Seoul, Korea
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Guan Z, Makled MN, Inscho EW. Purinoceptors, renal microvascular function and hypertension. Physiol Res 2020; 69:353-369. [PMID: 32301620 DOI: 10.33549/physiolres.934463] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Proper renal blood flow (RBF) and glomerular filtration rate (GFR) are critical for maintaining normal blood pressure, kidney function and water and electrolyte homeostasis. The renal microvasculature expresses a multitude of receptors mediating vasodilation and vasoconstriction, which can influence glomerular blood flow and capillary pressure. Despite this, RBF and GFR remain quite stable when arterial pressure fluctuates because of the autoregulatory mechanism. ATP and adenosine participate in autoregulatory control of RBF and GFR via activation of two different purinoceptor families (P1 and P2). Purinoceptors are widely expressed in renal microvasculature and tubules. Emerging data show altered purinoceptor signaling in hypertension-associated kidney injury, diabetic nephropathy, sepsis, ischemia-reperfusion induced acute kidney injury and polycystic kidney disease. In this brief review, we highlight recent studies and new insights on purinoceptors regulating renal microvascular function and renal hemodynamics. We also address the mechanisms underlying renal microvascular injury and impaired renal autoregulation, focusing on purinoceptor signaling and hypertension-induced renal microvascular dysfunction. Interested readers are directed to several excellent and comprehensive reviews that recently covered the topics of renal autoregulation, and nucleotides in kidney function under physiological and pathophysiological conditions (Inscho 2009, Navar et al. 2008, Carlstrom et al. 2015, Vallon et al. 2020).
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Affiliation(s)
- Z Guan
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, South Birmingham, USA.
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Vallon V, Unwin R, Inscho EW, Leipziger J, Kishore BK. Extracellular Nucleotides and P2 Receptors in Renal Function. Physiol Rev 2019; 100:211-269. [PMID: 31437091 DOI: 10.1152/physrev.00038.2018] [Citation(s) in RCA: 58] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The understanding of the nucleotide/P2 receptor system in the regulation of renal hemodynamics and transport function has grown exponentially over the last 20 yr. This review attempts to integrate the available data while also identifying areas of missing information. First, the determinants of nucleotide concentrations in the interstitial and tubular fluids of the kidney are described, including mechanisms of cellular release of nucleotides and their extracellular breakdown. Then the renal cell membrane expression of P2X and P2Y receptors is discussed in the context of their effects on renal vascular and tubular functions. Attention is paid to effects on the cortical vasculature and intraglomerular structures, autoregulation of renal blood flow, tubuloglomerular feedback, and the control of medullary blood flow. The role of the nucleotide/P2 receptor system in the autocrine/paracrine regulation of sodium and fluid transport in the tubular and collecting duct system is outlined together with its role in integrative sodium and fluid homeostasis and blood pressure control. The final section summarizes the rapidly growing evidence indicating a prominent role of the extracellular nucleotide/P2 receptor system in the pathophysiology of the kidney and aims to identify potential therapeutic opportunities, including hypertension, lithium-induced nephropathy, polycystic kidney disease, and kidney inflammation. We are only beginning to unravel the distinct physiological and pathophysiological influences of the extracellular nucleotide/P2 receptor system and the associated therapeutic perspectives.
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Affiliation(s)
- Volker Vallon
- Departments of Medicine and Pharmacology, University of California San Diego & VA San Diego Healthcare System, San Diego, California; Centre for Nephrology, Division of Medicine, University College London, London, United Kingdom; IMED ECD CVRM R&D, AstraZeneca, Gothenburg, Sweden; Department of Medicine, Division of Nephrology, The University of Alabama at Birmingham, Birmingham, Alabama; Department of Biomedicine/Physiology, Aarhus University, Aarhus, Denmark; Departments of Internal Medicine and Nutrition and Integrative Physiology, and Center on Aging, University of Utah Health & Nephrology Research, VA Salt Lake City Healthcare System, Salt Lake City, Utah
| | - Robert Unwin
- Departments of Medicine and Pharmacology, University of California San Diego & VA San Diego Healthcare System, San Diego, California; Centre for Nephrology, Division of Medicine, University College London, London, United Kingdom; IMED ECD CVRM R&D, AstraZeneca, Gothenburg, Sweden; Department of Medicine, Division of Nephrology, The University of Alabama at Birmingham, Birmingham, Alabama; Department of Biomedicine/Physiology, Aarhus University, Aarhus, Denmark; Departments of Internal Medicine and Nutrition and Integrative Physiology, and Center on Aging, University of Utah Health & Nephrology Research, VA Salt Lake City Healthcare System, Salt Lake City, Utah
| | - Edward W Inscho
- Departments of Medicine and Pharmacology, University of California San Diego & VA San Diego Healthcare System, San Diego, California; Centre for Nephrology, Division of Medicine, University College London, London, United Kingdom; IMED ECD CVRM R&D, AstraZeneca, Gothenburg, Sweden; Department of Medicine, Division of Nephrology, The University of Alabama at Birmingham, Birmingham, Alabama; Department of Biomedicine/Physiology, Aarhus University, Aarhus, Denmark; Departments of Internal Medicine and Nutrition and Integrative Physiology, and Center on Aging, University of Utah Health & Nephrology Research, VA Salt Lake City Healthcare System, Salt Lake City, Utah
| | - Jens Leipziger
- Departments of Medicine and Pharmacology, University of California San Diego & VA San Diego Healthcare System, San Diego, California; Centre for Nephrology, Division of Medicine, University College London, London, United Kingdom; IMED ECD CVRM R&D, AstraZeneca, Gothenburg, Sweden; Department of Medicine, Division of Nephrology, The University of Alabama at Birmingham, Birmingham, Alabama; Department of Biomedicine/Physiology, Aarhus University, Aarhus, Denmark; Departments of Internal Medicine and Nutrition and Integrative Physiology, and Center on Aging, University of Utah Health & Nephrology Research, VA Salt Lake City Healthcare System, Salt Lake City, Utah
| | - Bellamkonda K Kishore
- Departments of Medicine and Pharmacology, University of California San Diego & VA San Diego Healthcare System, San Diego, California; Centre for Nephrology, Division of Medicine, University College London, London, United Kingdom; IMED ECD CVRM R&D, AstraZeneca, Gothenburg, Sweden; Department of Medicine, Division of Nephrology, The University of Alabama at Birmingham, Birmingham, Alabama; Department of Biomedicine/Physiology, Aarhus University, Aarhus, Denmark; Departments of Internal Medicine and Nutrition and Integrative Physiology, and Center on Aging, University of Utah Health & Nephrology Research, VA Salt Lake City Healthcare System, Salt Lake City, Utah
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Abstract
The myogenic response is a key autoregulatory mechanism in the mammalian kidney. Triggered by blood pressure perturbations, it is well established that the myogenic response is initiated in the renal afferent arteriole and mediated by alterations in muscle tone and vascular diameter that counterbalance hemodynamic perturbations. The entire process involves several subcellular, cellular, and vascular mechanisms whose interactions remain poorly understood. Here, we model and investigate the myogenic response of a multicellular segment of an afferent arteriole. Extending existing work, we focus on providing an accurate—but still computationally tractable—representation of the coupling among the involved levels. For individual muscle cells, we include detailed Ca2+ signaling, transmembrane transport of ions, kinetics of myosin light chain phosphorylation, and contraction mechanics. Intercellular interactions are mediated by gap junctions between muscle or endothelial cells. Additional interactions are mediated by hemodynamics. Simulations of time-independent pressure changes reveal regular vasoresponses throughout the model segment and stabilization of a physiological range of blood pressures (80–180 mmHg) in agreement with other modeling and experimental studies that assess steady autoregulation. Simulations of time-dependent perturbations reveal irregular vasoresponses and complex dynamics that may contribute to the complexity of dynamic autoregulation observed in vivo. The ability of the developed model to represent the myogenic response in a multiscale and realistic fashion, under feasible computational load, suggests that it can be incorporated as a key component into larger models of integrated renal hemodynamic regulation.
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Guan Z, Wang F, Cui X, Inscho EW. Mechanisms of sphingosine-1-phosphate-mediated vasoconstriction of rat afferent arterioles. Acta Physiol (Oxf) 2018. [PMID: 28640982 DOI: 10.1111/apha.12913] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
AIM Sphingosine-1-phosphate (S1P) influences resistance vessel function and is implicated in renal pathological processes. Previous studies revealed that S1P evoked potent vasoconstriction of the pre-glomerular microvasculature, but the underlying mechanisms remain incompletely defined. We postulated that S1P-mediated pre-glomerular microvascular vasoconstriction involves activation of voltage-dependent L-type calcium channels (L-VDCC) and the rho/rho kinase pathway. METHODS Afferent arteriolar reactivity was assessed in vitro using the blood-perfused rat juxtamedullary nephron preparation, and diameter was measured during exposure to physiological and pharmacological agents. RESULTS Exogenous S1P (10-9 -10-5 mol L-1 ) evoked concentration-dependent vasoconstriction of afferent arterioles. Superfusion with nifedipine, a L-VDCC blocker, increased arteriolar diameter by 39 ± 18% of baseline and significantly attenuated the S1P-induced vasoconstriction. Superfusion with the rho kinase inhibitor, Y-27632, increased diameter by 60 ± 12% of baseline and also significantly blunted vasoconstriction by S1P. Combined nifedipine and Y-27632 treatment significantly inhibited S1P-induced vasoconstriction over the entire concentration range tested. In contrast, depletion of intracellular Ca2+ stores with the Ca2+ -ATPase inhibitors, thapsigargin or cyclopiazonic acid, did not alter the S1P-mediated vasoconstrictor profile. Scavenging reactive oxygen species (ROS) or inhibition of nicotinamide adenine dinucleotide phosphate oxidase activity significantly attenuated S1P-mediated vasoconstriction. CONCLUSION Exogenous S1P elicits potent vasoconstriction of rat afferent arterioles. These data also demonstrate that S1P-mediated pre-glomerular vasoconstriction involves activation of L-VDCC, the rho/rho kinase pathway and ROS. Mobilization of Ca2+ from intracellular stores is not required for S1P-mediated vasoconstriction. These studies reveal a potential role for S1P in the modulation of renal microvascular tone.
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Affiliation(s)
- Z. Guan
- Division of Nephrology; Department of Medicine; University of Alabama at Birmingham; Birmingham AL USA
| | - F. Wang
- Department of Biostatistics; Ryals School of Public Health; University of Alabama at Birmingham; Birmingham AL USA
| | - X. Cui
- Department of Biostatistics; Ryals School of Public Health; University of Alabama at Birmingham; Birmingham AL USA
| | - E. W. Inscho
- Division of Nephrology; Department of Medicine; University of Alabama at Birmingham; Birmingham AL USA
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Abstract
Clinicians make frequent treatment decisions regarding acute blood pressure reduction for the critically ill. Key to the decision making process is a balance between reducing arterial wall stress and maintaining perfusion to vital organs. In this article, we review the physiological considerations underlying acute blood pressure management, including the concept of cerebral autoregulation and its adaptations to chronic hypertension. We then discuss available pharmacological interventions suited for reducing blood pressure acutely. We also discuss specific blood pressure targets in common critical illnesses and consider future directions in this therapeutic area.
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Casare FAM, Thieme K, Costa-Pessoa JM, Rossoni LV, Couto GK, Fernandes FB, Casarini DE, Oliveira-Souza M. Renovascular remodeling and renal injury after extended angiotensin II infusion. Am J Physiol Renal Physiol 2016; 310:F1295-307. [PMID: 26962104 DOI: 10.1152/ajprenal.00471.2015] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2015] [Accepted: 03/05/2016] [Indexed: 11/22/2022] Open
Abstract
Chronic angiotensin II (ANG II) infusion for 1 or 2 wk leads to progressive hypertension and induces inward hypertrophic remodeling in preglomerular vessels, which is associated with increased renal vascular resistance (RVR) and decreased glomerular perfusion. Considering the ability of preglomerular vessels to exhibit adaptive responses, the present study was performed to evaluate glomerular perfusion and renal function after 6 wk of ANG II infusion. To address this study, male Wistar rats were submitted to sham surgery (control) or osmotic minipump insertion (ANG II 200 ng·kg(-1)·min(-1), 42 days). A group of animals was treated or cotreated with losartan (10 mg·kg(-1)·day(-1)), an AT1 receptor antagonist, between days 28 and 42 Chronic ANG II infusion increased systolic blood pressure to 185 ± 4 compared with 108 ± 2 mmHg in control rats. Concomitantly, ANG II-induced hypertension increased intrarenal ANG II level and consequently, preglomerular and glomerular injury. Under this condition, ANG II enhanced the total renal plasma flow (RPF), glomerular filtration rate (GFR), urine flow and induced pressure natriuresis. These changes were accompanied by lower RVR and enlargement of the lumen of interlobular arteries and afferent arterioles, consistent with impairment of renal autoregulatory capability and outward preglomerular remodeling. The glomerular injury culminated with podocyte effacement, albuminuria, tubulointerstitial macrophage infiltration and intrarenal extracellular matrix accumulation. Losartan attenuated most of the effects of ANG II. Our findings provide new information regarding the contribution of ANG II infusion over 2 wk to renal hemodynamics and function via the AT1 receptor.
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Affiliation(s)
| | - Karina Thieme
- Laboratory of Cellular and Molecular Endocrinology, Medical School, University of Sao Paulo, Sao Paulo, Brazil; and
| | - Juliana Martins Costa-Pessoa
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil
| | - Luciana Venturini Rossoni
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil
| | - Gisele Kruger Couto
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil
| | | | - Dulce Elena Casarini
- Division of Nephrology, Department of Medicine, Federal University of Sao Paulo, Sao Paulo, Brazil
| | - Maria Oliveira-Souza
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil;
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Cheng HM, Hoe SZ. Students′ convoluted trouble with renal autoregulation: A teaching note for students and physiology educators. BLDE UNIVERSITY JOURNAL OF HEALTH SCIENCES 2016. [DOI: 10.4103/2456-1975.183281] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
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Guan Z, Singletary ST, Cha H, Van Beusecum JP, Cook AK, Pollock JS, Pollock DM, Inscho EW. Pentosan polysulfate preserves renal microvascular P2X1 receptor reactivity and autoregulatory behavior in DOCA-salt hypertensive rats. Am J Physiol Renal Physiol 2015; 310:F456-65. [PMID: 26697978 DOI: 10.1152/ajprenal.00110.2015] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2015] [Accepted: 12/21/2015] [Indexed: 01/06/2023] Open
Abstract
Inflammation contributes to ANG II-associated impairment of renal autoregulation and microvascular P2X1 receptor signaling, but its role in renal autoregulation in mineralocorticoid-induced hypertension is unknown. Autoregulatory behavior was assessed using the blood-perfused juxtamedullary nephron preparation. Hypertension was induced in uninephrectomized control rats (UNx) by subcutaneous implantation of a DOCA pellet plus administration of 1% NaCl in the drinking water (DOCA-salt) for 3 wk. DOCA-salt rats developed hypertension that was unaltered by anti-inflammatory treatment with pentosan polysulfate (DOCA-salt+PPS) but was suppressed with "triple therapy" (hydrochlorothiazide, hydralazine, and reserpine; DOCA-salt+TTx). Baseline arteriolar diameters were similar across all groups. UNx rats exhibited pressure-dependent vasoconstriction with diameters declining to 69 ± 2% of control at 170 mmHg, indicating intact autoregulation. DOCA-salt treatment significantly blunted this pressure-mediated vasoconstriction. Diameters remained between 91 ± 4 and 98 ± 3% of control over 65-170 mmHg, indicating impaired autoregulation. In contrast, pressure-mediated vasoconstriction was preserved in DOCA-salt+PPS and DOCA-salt+TTx rats, reaching 77 ± 7 and 75 ± 3% of control at 170 mmHg, respectively. ATP is required for autoregulation via P2X1 receptor activation. ATP- and β,γ-methylene ATP (P2X1 receptor agonist)-mediated vasoconstriction were markedly attenuated in DOCA-salt rats compared with UNx (P < 0.05), but significantly improved by PPS or TTx (P < 0.05 vs. DOCA-salt) treatment. Arteriolar responses to adenosine and UTP (P2Y2 receptor agonist) were unaffected by DOCA-salt treatment. PPS and TTx significantly reduced MCP-1 and protein excretion in DOCA-salt rats. These results support the hypothesis that hypertension triggers inflammatory cascades but anti-inflammatory treatment preserves renal autoregulation in DOCA-salt rats, most likely by normalizing renal microvascular reactivity to P2X1 receptor activation.
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Affiliation(s)
- Zhengrong Guan
- Department of Physiology, Georgia Regents University, Augusta, Georgia; Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; and
| | - Sean T Singletary
- Department of Physiology, Georgia Regents University, Augusta, Georgia
| | - Haword Cha
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; and School of Natural Sciences, University of California, Merced, California
| | - Justin P Van Beusecum
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; and
| | - Anthony K Cook
- Department of Physiology, Georgia Regents University, Augusta, Georgia; Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; and
| | - Jennifer S Pollock
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; and
| | - David M Pollock
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; and
| | - Edward W Inscho
- Department of Physiology, Georgia Regents University, Augusta, Georgia; Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; and
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14
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Fellner RC, Guan Z, Cook AK, Pollock DM, Inscho EW. Endothelin contributes to blunted renal autoregulation observed with a high-salt diet. Am J Physiol Renal Physiol 2015; 309:F687-96. [PMID: 26246513 DOI: 10.1152/ajprenal.00641.2014] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Accepted: 07/29/2015] [Indexed: 01/03/2023] Open
Abstract
Autoregulation of renal blood flow (RBF) is an essential function of the renal microcirculation that has been previously shown to be blunted by excessive dietary salt. Endogenous endothelin 1 (ET-1) is increased following a high-salt (HS) diet and contributes to the control of RBF but the differential effects of ET-1 on renal microvessel autoregulation in response to HS remain to be established. We hypothesized that a HS diet increases endothelin receptor activation in normal Sprague-Dawley rats and blunts autoregulation of RBF. The role of ET-1 in the blunted autoregulation produced by a HS diet was assessed in vitro and in vivo using the blood-perfused juxtamedullary nephron preparation and anesthetized rats, respectively. Using highly selective antagonists, we observed that blockade of either ETA or ETB receptors was sufficient to restore normal autoregulatory behavior in afferent arterioles from HS-fed rats. Additionally, normal autoregulatory behavior was restored in vivo in HS-fed rats by simultaneous ETA and ETB receptor blockade, whereas blockade of ETB receptors alone showed significant improvement of normal autoregulation of RBF. Consistent with this observation, autoregulation of RBF in ETB receptor-deficient rats fed HS was similar to both ETB-deficient rats and transgenic control rats on normal-salt diets. These data support the hypothesis that endogenous ET-1, working through ETB and possibly ETA receptors, contributes to the blunted renal autoregulatory behavior in rats fed a HS diet.
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Affiliation(s)
- Robert C Fellner
- Department of Physiology, Medical College of Georgia, Georgia Regents University, Augusta, Georgia
| | - Zhengrong Guan
- Department of Physiology, Medical College of Georgia, Georgia Regents University, Augusta, Georgia; Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Anthony K Cook
- Department of Physiology, Medical College of Georgia, Georgia Regents University, Augusta, Georgia; Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - David M Pollock
- Section of Experimental Medicine, Department of Medicine, Medical College of Georgia, Georgia Regents University, Augusta, Georgia; and Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
| | - Edward W Inscho
- Department of Physiology, Medical College of Georgia, Georgia Regents University, Augusta, Georgia; Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
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15
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Abstract
PURPOSE OF REVIEW The purpose of this review is to provide an update on the current knowledge regarding the role of the intrarenal rennin-angiotensin system (RAS) in the regulation of glomerular function including glomerular dynamics and filtration rate, glomerular permeability and structural alterations during chronic increases in intrarenal angiotensin (Ang) II. RECENT FINDINGS Recent studies have continued to delineate the complex interactions among the various RAS components that participate in regulating glomerular function. Although Ang II acting on AT1 receptors remains as the predominant influence on glomerular dynamics, some of these effects are indirectly mediated by Ang II modulating the sensitivity of the macula densa tubuloglomerular feedback mechanism as well as the more recently described feedback mechanism from the connecting tubule. Interestingly, the actions of Ang II on these systems cause opposite effects on glomerular function demonstrating the complexities associated with the influences of Ang II on glomerular function. When chronically elevated, Ang II also stimulates and/or interacts with other factors, including reactive oxygen species, cytokines and growth factors and other hormones or paracrine agents, to elicit structural alterations. SUMMARY Recent studies have provided further evidence for the presence of many components of the RAS in glomerular structures, which supports the importance of locally produced angiotensin peptides to regulate glomerular haemodynamics, filtration rate and macromolecular permeability and contribute to fibrosis and glomerular injury when inappropriately augmented.
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16
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Ren Y, D'Ambrosio MA, Garvin JL, Peterson EL, Carretero OA. Mechanism of impaired afferent arteriole myogenic response in Dahl salt-sensitive rats: role of 20-HETE. Am J Physiol Renal Physiol 2014; 307:F533-8. [PMID: 24990891 DOI: 10.1152/ajprenal.00283.2014] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The afferent arteriole (Af-Art) controls glomerular capillary pressure, an important determinant of glomerular injury. Af-Art myogenic response is mediated by ATP, and ATP signaling is in turn mediated by 20-HETE. Dahl salt-sensitive rats (Dahl SS) have decreased renal 20-HETE production. We hypothesized that Dahl SS have an impaired myogenic response and constrictor response to ATP, due to decreased 20-HETE. Af-Arts from Dahl SS or Dahl salt-resistant rats (Dahl SR) were microdissected and perfused. When myogenic response was induced by increasing Af-Art perfusion pressure from 60 to 140 mmHg, luminal Af-Art diameter decreased in Dahl SR but not in Dahl SS (-3.1 ± 0.8 vs. 0.5 ± 0.8 μm, P < 0.01). The 20-HETE antagonist 20-HEDE (10(-6) M) blocked the myogenic response in Dahl SR but had no effect in Dahl SS. Addition of a subconstrictor concentration of 20-HETE (but not a subconstrictor concentration of norepinephrine) restored the myogenic response in Dahl SS. We then perfused Af-Arts at 60 mmHg and tested the effects of the ATP analog α,β-methylene-ATP (10(-6) M). Maximum ATP-induced constriction was attenuated in Dahl SS compared with Dahl SR (1.5 ± 0.5 vs. 7.4 ± 0.8 μm, P < 0.001). 20-HEDE attenuated ATP-induced Af-Art constriction in Dahl SR but not in Dahl SS, and consequently, ATP-induced constriction was no longer different between strains. In conclusion, Dahl SS have an impaired myogenic response and ATP-induced Af-Art constriction due to a decrease in Af-Art 20-HETE. The impaired myogenic responses may contribute to the nephrosclerosis that develops in Dahl SS.
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Affiliation(s)
- YiLin Ren
- Hypertension and Vascular Research Division, Department of Internal Medicine, Henry Ford Hospital, Detroit, Michigan
| | - Martin A D'Ambrosio
- Hypertension and Vascular Research Division, Department of Internal Medicine, Henry Ford Hospital, Detroit, Michigan
| | - Jeffrey L Garvin
- Hypertension and Vascular Research Division, Department of Internal Medicine, Henry Ford Hospital, Detroit, Michigan; Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio; and
| | - Edward L Peterson
- Department of Public Health Sciences, Henry Ford Hospital, Detroit, Michigan
| | - Oscar A Carretero
- Hypertension and Vascular Research Division, Department of Internal Medicine, Henry Ford Hospital, Detroit, Michigan;
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17
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Burnstock G, Evans LC, Bailey MA. Purinergic signalling in the kidney in health and disease. Purinergic Signal 2014; 10:71-101. [PMID: 24265071 PMCID: PMC3944043 DOI: 10.1007/s11302-013-9400-5] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Accepted: 10/24/2013] [Indexed: 12/21/2022] Open
Abstract
The involvement of purinergic signalling in kidney physiology and pathophysiology is rapidly gaining recognition and this is a comprehensive review of early and recent publications in the field. Purinergic signalling involvement is described in several important intrarenal regulatory mechanisms, including tuboglomerular feedback, the autoregulatory response of the glomerular and extraglomerular microcirculation and the control of renin release. Furthermore, purinergic signalling influences water and electrolyte transport in all segments of the renal tubule. Reports about purine- and pyrimidine-mediated actions in diseases of the kidney, including polycystic kidney disease, nephritis, diabetes, hypertension and nephrotoxicant injury are covered and possible purinergic therapeutic strategies discussed.
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Affiliation(s)
- Geoffrey Burnstock
- Autonomic Neuroscience Centre, University College Medical School, Rowland Hill Street, London, NW3 2PF, UK,
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18
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Nagasawa T, Imig JD. Afferent Arteriolar Responses to β,γ-methylene ATP and 20-HETE are not Blocked by ENaC Inhibition. Physiol Rep 2013; 1:e00082. [PMID: 24159379 PMCID: PMC3804346 DOI: 10.1002/phy2.82] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Afferent arteriolar myogenic and tubuloglomerular feedback responses are critical for the proper maintenance of renal hemodynamics and water and electrolyte homeostasis. Adenosine triphosphate (ATP) P2X receptor activation and 20-hydroxyeicosatetraenoic acids (20-HETE) have been implicated in afferent arteriolar autoregulatory responses. Besides these two participants, members of the degenerin/epithelial Na+ channel (DEG/ENaC) family have been demonstrated to play a pivotal role in the afferent arteriolar myogenic response. The aim of this study was to determine if ENaC contributes to P2X receptor- or 20-HETE-mediated afferent arteriolar vasoconstriction. As previously demonstrated, afferent arteriolar diameter responses to increasing perfusion pressure from 100 to 160 mmHg were abolished by ENaC inhibitors amiloride or benzamil. Afferent arteriolar diameter decreased by 29% under control conditions and by 1% and 5% in the presence of amiloride or benzamil, respectively. The P2X receptor agonist β,γ-methylene ATP decreased afferent arteriolar diameter by 3 ± 1%, 7 ± 1%, 12 ± 2%, and 17 ± 3% in response to 0.1, 1, 10, and 100 μmol/L, respectively. ENaC inhibition did not alter the afferent arteriolar vasoconstrictor response to the P2X receptor agonist β,γ-methylene ATP. Like P2X receptor activation, 20-HETE dose-dependently decreased afferent arteriolar diameter and this vasoconstrictor response was not altered by the presence of ENaC inhibitors amiloride or benzamil. These results suggest that DEG/ENaC channels are required for afferent arteriolar autoregulatory responses; however, DEG/ENaC channels do not contribute to P2X receptor- or 20-HETE-mediated afferent arteriolar vasoconstriction.
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Affiliation(s)
- Tasuku Nagasawa
- Department of Pharmacology & Toxicology and Cardiovascular Center, Medical College of Wisconsin, Milwaukee, WI, USA
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19
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Abstract
PURPOSE OF REVIEW Despite apparent blood pressure (BP) control and renin-angiotensin system (RAS) blockade, the chronic kidney disease (CKD) outcomes have been suboptimal. Accordingly, this review is addressed to renal microvascular and autoregulatory impairments that underlie the enhanced dynamic glomerular BP transmission in CKD progression. RECENT FINDINGS Clinical data suggest that failure to achieve adequate 24-h BP control is likely contributing to the suboptimal outcomes in CKD. Whereas evidence continues to accumulate regarding the importance of preglomerular autoregulatory impairment to the dynamic glomerular BP transmission, emerging data indicate that nitric oxide-mediated efferent vasodilation may play an important role in mitigating the consequences of glomerular hypertension. By contrast, the vasoconstrictor effects of angiotensin II are expected to potentially reduce glomerular barotrauma and possibly enhance ischemic injury. When adequate BP measurement methods are used, the evidence for BP-independent injury initiating mechanisms is considerably weaker and the renoprotection by RAS blockade largely parallels its antihypertensive effectiveness. SUMMARY Adequate 24-h BP control presently offers the most feasible intervention for reducing glomerular BP transmission and improving suboptimal outcomes in CKD. Investigations addressed to improving myogenic autoregulation and/or enhancing nitric oxide-mediated efferent dilation in addition to the more downstream mediators may provide additional future therapeutic targets.
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20
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Albers DJ, Hripcsak G, Schmidt M. Population physiology: leveraging electronic health record data to understand human endocrine dynamics. PLoS One 2012; 7:e48058. [PMID: 23272040 PMCID: PMC3522687 DOI: 10.1371/journal.pone.0048058] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2011] [Accepted: 09/25/2012] [Indexed: 11/19/2022] Open
Abstract
Studying physiology and pathophysiology over a broad population for long periods of time is difficult primarily because collecting human physiologic data can be intrusive, dangerous, and expensive. One solution is to use data that have been collected for a different purpose. Electronic health record (EHR) data promise to support the development and testing of mechanistic physiologic models on diverse populations and allow correlation with clinical outcomes, but limitations in the data have thus far thwarted such use. For example, using uncontrolled population-scale EHR data to verify the outcome of time dependent behavior of mechanistic, constructive models can be difficult because: (i) aggregation of the population can obscure or generate a signal, (ii) there is often no control population with a well understood health state, and (iii) diversity in how the population is measured can make the data difficult to fit into conventional analysis techniques. This paper shows that it is possible to use EHR data to test a physiological model for a population and over long time scales. Specifically, a methodology is developed and demonstrated for testing a mechanistic, time-dependent, physiological model of serum glucose dynamics with uncontrolled, population-scale, physiological patient data extracted from an EHR repository. It is shown that there is no observable daily variation the normalized mean glucose for any EHR subpopulations. In contrast, a derived value, daily variation in nonlinear correlation quantified by the time-delayed mutual information (TDMI), did reveal the intuitively expected diurnal variation in glucose levels amongst a random population of humans. Moreover, in a population of continuously (tube) fed patients, there was no observable TDMI-based diurnal signal. These TDMI-based signals, via a glucose insulin model, were then connected with human feeding patterns. In particular, a constructive physiological model was shown to correctly predict the difference between the general uncontrolled population and a subpopulation whose feeding was controlled.
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Affiliation(s)
- D J Albers
- Department of Biomedical Informatics, Columbia University, New York, New York, United States of America.
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21
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Guan Z, Fuller BS, Yamamoto T, Cook AK, Pollock JS, Inscho EW. Pentosan polysulfate treatment preserves renal autoregulation in ANG II-infused hypertensive rats via normalization of P2X1 receptor activation. Am J Physiol Renal Physiol 2010; 298:F1276-84. [PMID: 20200092 DOI: 10.1152/ajprenal.00743.2009] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Inflammatory factors are elevated in animal and human subjects with hypertension and renal injury. We hypothesized that inflammation contributes to hypertension-induced renal injury by impairing autoregulation and microvascular reactivity to P2X(1) receptor activation. Studies were conducted in vitro using the blood-perfused juxtamedullary nephron preparation. Rats receiving ANG II (60 ng/min) infusion were treated with the anti-inflammatory agent pentosan polysulfate (PPS) for 14 days. The magnitude and progression of hypertension were similar in ANG II and ANG II+PPS-treated rats (169 ± 5 vs. 172 ± 2 mmHg). Afferent arterioles from control rats exhibited normal autoregulatory behavior with diameter decreasing from 18.4 ± 1.6 to 11.4 ± 1.7 μm when perfusion pressure was increased from 70 to 160 mmHg. In contrast, pressure-mediated vasoconstriction was markedly attenuated in ANG II-treated rats, and diameter remained essentially unchanged over the range of perfusion pressures. However, ANG II-treated rats receiving PPS exhibited normal autoregulatory behavior compared with ANG II alone rats. Arteriolar reactivity to ATP and β,γ-methylene ATP was significantly reduced in ANG II hypertensive rats compared with controls. Interestingly, PPS treatment preserved normal reactivity to P2 and P2X(1) receptor agonists despite the persistent hypertension. The maximal vasoconstriction was 79 ± 3 and 81 ± 2% of the control diameter for ATP and β,γ-methylene ATP, respectively, similar to responses in control rats. PPS treatment significantly reduced α-smooth muscle actin staining in afferent arterioles and plasma transforming growth factor-β1 concentration in ANG II-treated rats. In conclusion, PPS normalizes autoregulation without altering ANG II-induced hypertension, suggesting that inflammatory processes reduce P2X(1) receptor reactivity and thereby impair autoregulatory behavior in ANG II hypertensive rats.
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Affiliation(s)
- Zhengrong Guan
- Dept. of Physiology, Medical College of Georgia, 1120 15th St., Augusta, GA 30912, USA
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22
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Corriden R, Insel PA. Basal release of ATP: an autocrine-paracrine mechanism for cell regulation. Sci Signal 2010; 3:re1. [PMID: 20068232 DOI: 10.1126/scisignal.3104re1] [Citation(s) in RCA: 263] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Cells release adenosine triphosphate (ATP), which activates plasma membrane-localized P2X and P2Y receptors and thereby modulates cellular function in an autocrine or paracrine manner. Release of ATP and the subsequent activation of P2 receptors help establish the basal level of activation (sometimes termed "the set point") for signal transduction pathways and regulate a wide array of responses that include tissue blood flow, ion transport, cell volume regulation, neuronal signaling, and host-pathogen interactions. Basal release and autocrine or paracrine responses to ATP are multifunctional, evolutionarily conserved, and provide an economical means for the modulation of cell, tissue, and organismal biology.
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Affiliation(s)
- Ross Corriden
- Departments of Pharmacology and Medicine, University of California, San Diego, La Jolla, CA 92093, USA
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Seeliger E, Wronski T, Ladwig M, Dobrowolski L, Vogel T, Godes M, Persson PB, Flemming B. The renin-angiotensin system and the third mechanism of renal blood flow autoregulation. Am J Physiol Renal Physiol 2009; 296:F1334-45. [DOI: 10.1152/ajprenal.90476.2008] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Autoregulation of renal blood flow comprises three mechanisms: the myogenic response (MR), the tubuloglomerular feedback (TGF), and a third mechanism (3M). The nature of 3M is unknown; it may be related to hypotensive resetting of autoregulation that probably relies on pressure-dependent stimulation of the renin-angiotensin system (RAS). Thus we used a normotensive angiotensin II clamp in anesthetized rats and studied autoregulation 1) by slow ramp-shaped reductions in renal perfusion pressure (RPP) followed by ramp-shaped RPP restorations and 2) by means of the step response technique: after 30 s of either total or partial suprarenal aortic occlusion, a step increase in RPP was made and the response of renal vascular conductance analyzed to assess the mechanisms' strength and initial direction (vasodilation or constriction). The angiotensin clamp abolished the resetting of autoregulation during ramp-shaped RPP changes. Under control conditions, the initial TGF response was dilatory after total occlusions but constrictive after partial occlusions. The initial 3M response presented a mirror image to the TGF: it was constrictive after total but dilatory after partial occlusions. The angiotensin clamp suppressed the TGF and turned the initial 3M response following total occlusions into dilation. We conclude that 1) pressure-dependent RAS stimulation is a major cause behind hypotensive resetting of autoregulation, 2) TGF sensitivity strongly depends on pressure-dependent changes in RAS activity, 3) the 3M is modulated, but not mediated, by the RAS, and 4) the 3M acts as a counterbalance to the TGF and might possibly be related to the recently described connecting tubule glomerular feedback.
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