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American Journal of Physiology. Renal... Mar 2021Renal autoregulation is critical in maintaining stable renal blood flow (RBF) and glomerular filtration rate (GFR). Renal ischemia-reperfusion (IR)-induced kidney injury...
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. 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.
Topics: Animals; Arterioles; Blood Pressure; Glomerular Filtration Rate; Homeostasis; NADPH Oxidases; Rats; Reactive Oxygen Species; Renal Circulation; Renal Insufficiency, Chronic; Reperfusion Injury
PubMed: 33491564
DOI: 10.1152/ajprenal.00500.2020 -
Comprehensive Physiology Jan 2015Heat stress increases human morbidity and mortality compared to normothermic conditions. Many occupations, disease states, as well as stages of life are especially... (Review)
Review
Heat stress increases human morbidity and mortality compared to normothermic conditions. Many occupations, disease states, as well as stages of life are especially vulnerable to the stress imposed on the cardiovascular system during exposure to hot ambient conditions. This review focuses on the cardiovascular responses to heat stress that are necessary for heat dissipation. To accomplish this regulatory feat requires complex autonomic nervous system control of the heart and various vascular beds. For example, during heat stress cardiac output increases up to twofold, by increases in heart rate and an active maintenance of stroke volume via increases in inotropy in the presence of decreases in cardiac preload. Baroreflexes retain the ability to regulate blood pressure in many, but not all, heat stress conditions. Central hypovolemia is another cardiovascular challenge brought about by heat stress, which if added to a subsequent central volumetric stress, such as hemorrhage, can be problematic and potentially dangerous, as syncope and cardiovascular collapse may ensue. These combined stresses can compromise blood flow and oxygenation to important tissues such as the brain. It is notable that this compromised condition can occur at cardiac outputs that are adequate during normothermic conditions but are inadequate in heat because of the increased systemic vascular conductance associated with cutaneous vasodilation. Understanding the mechanisms within this complex regulatory system will allow for the development of treatment recommendations and countermeasures to reduce risks during the ever-increasing frequency of severe heat events that are predicted to occur.
Topics: Baroreflex; Cardiovascular System; Cerebrovascular Circulation; Heat Stress Disorders; Hemodynamics; Humans; Muscle, Skeletal; Renal Circulation; Splanchnic Circulation
PubMed: 25589263
DOI: 10.1002/cphy.c140015 -
Methods in Molecular Biology (Clifton,... 2021The kidney is a complex organ involved in the excretion of metabolic products as well as the regulation of body fluids, osmolarity, and homeostatic status. These...
The kidney is a complex organ involved in the excretion of metabolic products as well as the regulation of body fluids, osmolarity, and homeostatic status. These functions are influenced in large part by alterations in the regional distribution of blood flow between the renal cortex and medulla. Renal perfusion is therefore a key determinant of glomerular filtration. Therefore the quantification of regional renal perfusion could provide important insights into renal function and renal (patho)physiology. Arterial spin labeling (ASL) based perfusion MRI techniques, can offer a noninvasive and reproducible way of measuring renal perfusion in animal models. This chapter addresses the basic concept of ASL-MRI.This chapter is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers. This introduction chapter is complemented by two separate chapters describing the experimental procedure and data analysis.
Topics: Animals; Arteries; Biomarkers; Blood Flow Velocity; Contrast Media; Diffusion Magnetic Resonance Imaging; Humans; Image Enhancement; Image Processing, Computer-Assisted; Kidney; Monitoring, Physiologic; Perfusion; Renal Circulation; Software; Spin Labels
PubMed: 33476003
DOI: 10.1007/978-1-0716-0978-1_13 -
Medicina Intensiva Mar 2017Acute kidney injury (AKI) is a growing concern in Intensive Care Units. The advanced age of our patients, with the increase in associated morbidity and the complexity of... (Review)
Review
Acute kidney injury (AKI) is a growing concern in Intensive Care Units. The advanced age of our patients, with the increase in associated morbidity and the complexity of the treatments provided favor the development of AKI. Since no effective treatment for AKI is available, all efforts are aimed at prevention and early detection of the disorder in order to establish secondary preventive measures to impede AKI progression. In critical patients, the most frequent causes are sepsis and situations that result in renal hypoperfusion; preventive measures are therefore directed at securing hydration and correct hemodynamics through fluid perfusion and the use of inotropic or vasoactive drugs, according to the underlying disease condition. Apart from these circumstances, a number of situations could lead to AKI, related to the administration of nephrotoxic drugs, intra-tubular deposits, the administration of iodinated contrast media, liver failure and major surgery (mainly heart surgery). In these cases, in addition to hydration, there are other specific preventive measures adapted to each condition.
Topics: Acute Kidney Injury; Contrast Media; Critical Care; Diuretics; Fenoldopam; Fluid Therapy; Hemodynamics; Humans; Intensive Care Units; Liver Failure; Postoperative Complications; Renal Circulation; Rhabdomyolysis; Risk Factors; Secondary Prevention; Sepsis; Vasoconstrictor Agents
PubMed: 28190602
DOI: 10.1016/j.medin.2016.12.004 -
American Journal of Physiology. Renal... May 2015It has been long known that the kidney plays an essential role in the control of body fluids and blood pressure and that impairment of renal function may lead to the... (Review)
Review
It has been long known that the kidney plays an essential role in the control of body fluids and blood pressure and that impairment of renal function may lead to the development of diseases such as hypertension (Guyton AC, Coleman TG, Granger Annu Rev Physiol 34: 13-46, 1972). In this review, we highlight recent advances in our understanding of renal hemodynamics, obtained from experimental and theoretical studies. Some of these studies were published in response to a recent Call for Papers of this journal: Renal Hemodynamics: Integrating with the Nephron and Beyond.
Topics: Animals; Computer Simulation; Hemodynamics; Homeostasis; Humans; Hypertension; Kidney; Kidney Diseases; Models, Animal; Models, Cardiovascular; Oxygen; Renal Circulation; Renin-Angiotensin System
PubMed: 25715984
DOI: 10.1152/ajprenal.00008.2015 -
American Journal of Kidney Diseases :... Oct 2023Recent advances in multiparametric magnetic resonance imaging (MRI) allow multiple quantitative measures to assess kidney morphology, tissue microstructure, oxygenation,...
Recent advances in multiparametric magnetic resonance imaging (MRI) allow multiple quantitative measures to assess kidney morphology, tissue microstructure, oxygenation, kidney blood flow, and perfusion to be collected in a single scan session. Animal and clinical studies have investigated the relationship between the different MRI measures and biological processes, although their interpretation can be complex due to variations in study design and generally small participant numbers. However, emerging themes include the apparent diffusion coefficient derived from diffusion-weighted imaging, T and T mapping parameters, and cortical perfusion being consistently associated with kidney damage and predicting kidney function decline. Blood oxygen level-dependent (BOLD) MRI has shown inconsistent associations with kidney damage markers but has been predictive of kidney function decline in several studies. Therefore, multiparametric MRI of the kidneys has the potential to address the limitations of existing diagnostic methods to provide a noninvasive, noncontrast, and radiation-free method to assess whole kidney structure and function. Barriers to be overcome to facilitate widespread clinical application include improved understanding of biological factors that impact MRI measures, development of a larger evidence base for clinical utility, standardization of MRI protocols, automation of data analysis, determining optimal combination of MRI measures, and health economic evaluation.
Topics: Animals; Humans; Oxygen; Kidney; Magnetic Resonance Imaging; Kidney Diseases; Renal Circulation
PubMed: 37187282
DOI: 10.1053/j.ajkd.2023.02.007 -
Diagnostic and Interventional Radiology... 2016Over the last decade, exponential advances in computed tomography (CT) technology have resulted in improved spatial and temporal resolution. Faster image acquisition... (Review)
Review
Over the last decade, exponential advances in computed tomography (CT) technology have resulted in improved spatial and temporal resolution. Faster image acquisition enabled renal CT angiography to become a viable and effective noninvasive alternative in diagnosing renal vascular pathologies. However, with these advances, new challenges in contrast media administration have emerged. Poor synchronization between scanner and contrast media administration have reduced the consistency in image quality with poor spatial and contrast resolution. Comprehensive understanding of contrast media dynamics is essential in the design and implementation of contrast administration and image acquisition protocols. This review includes an overview of the parameters affecting renal artery opacification and current protocol strategies to achieve optimal image quality during renal CT angiography with iodinated contrast media, with current safety issues highlighted.
Topics: Computed Tomography Angiography; Contrast Media; Dose-Response Relationship, Drug; Humans; Image Interpretation, Computer-Assisted; Kidney; Radiographic Image Enhancement; Radiologists; Renal Artery; Renal Circulation
PubMed: 26728701
DOI: 10.5152/dir.2015.15219 -
Nephron 2023Alterations of renal hemodynamics play an essential role in renal homeostasis and kidney diseases. Recent data indicated that semaphorin 3C (SEMA3C), a secreted...
BACKGROUND
Alterations of renal hemodynamics play an essential role in renal homeostasis and kidney diseases. Recent data indicated that semaphorin 3C (SEMA3C), a secreted glycoprotein involved in vessel development, can modulate renal vascular permeability in acute kidney injury, but whether and how it might impact systemic and renal hemodynamics is unknown.
OBJECTIVES
The objective of the study was to explore the effect of SEMA3C on systemic and renal hemodynamics.
METHODS
SEMA3C recombinant protein was administered intravenously in two-month-old wild-type mice, and the variations of mean arterial pressure, heart rate, renal blood flow, and renal vascular resistance were measured and analyzed.
RESULTS
Acute administration of SEMA3C induced (i) systemic hemodynamic changes, including mean arterial pressure decrease and heart rate augmentation; (ii) renal hemodynamic changes, including reduced vascular resistance and elevated renal blood flow. Continuous perfusion of SEMA3C had no significant effect on systemic or renal hemodynamics.
CONCLUSION
SEMA3C is a potent vasodilator affecting both systemic and renal hemodynamics in mice.
Topics: Mice; Animals; Hemodynamics; Kidney; Vascular Resistance; Heart Rate; Renal Circulation; Semaphorins
PubMed: 36580904
DOI: 10.1159/000528259 -
Hypertension Research : Official... Oct 2023The aim of the present study was to assess the autoregulatory capacity of renal blood flow (RBF) and of the pressure-natriuresis characteristics in the early phase of...
The aim of the present study was to assess the autoregulatory capacity of renal blood flow (RBF) and of the pressure-natriuresis characteristics in the early phase of heart failure (HF) in rats, normotensive and with angiotensin II (ANG II)-dependent hypertension. Ren-2 transgenic rats (TGR) were employed as a model of ANG II-dependent hypertension. HF was induced by creating the aorto-caval fistula (ACF). One week after ACF creation or sham-operation, the animals were prepared for studies evaluating in vivo RBF autoregulatory capacity and the pressure-natriuresis characteristics after stepwise changes in renal arterial pressure (RAP) induced by aortic clamping. In ACF TGR the basal mean arterial pressure, RBF, urine flow (UF), and absolute sodium excretion (UV) were all significantly lower tha n in sham-operated TGR. In the latter, reductions in renal arterial pressure (RAP) significantly decreased RBF whereas in ACF TGR they did not change. Stepwise reductions in RAP resulted in marked decreases in UF and UV in sham-operated as well as in ACF TGR, however, these decreases were significantly greater in the former. Our data show that compared with sham-operated TGR, ACF TGR displayed well-maintained RBF autoregulatory capacity and improved slope of the pressure-natriuresis relationship. Thus, even though in the very early HF stage renal dysfunction was demonstrable, in the HF model of ANG II-dependent hypertensive rat such dysfunction and the subsequent HF decompensation cannot be simply ascribed to impaired renal autoregulation and pressure-natriuresis relationship.
Topics: Rats; Animals; Angiotensin II; Natriuresis; Hypertension; Kidney; Blood Pressure; Rats, Transgenic; Renal Circulation; Heart Failure; Sodium; Homeostasis
PubMed: 37592042
DOI: 10.1038/s41440-023-01401-z -
British Journal of Anaesthesia Aug 2020Anaesthesia-induced changes in renal perfusion are dependent on the choice of anaesthetic agent. However, the effects of varying inspired oxygen fraction (FiO) on renal...
BACKGROUND
Anaesthesia-induced changes in renal perfusion are dependent on the choice of anaesthetic agent. However, the effects of varying inspired oxygen fraction (FiO) on renal perfusion and oxygenation during TIVA (propofol + fentanyl) or volatile anaesthesia (VA; isoflurane) are unknown.
METHODS
In 16 Merino ewes, we surgically implanted a renal artery flow probe and laser-Doppler and oxygen-sensing probes in the renal medulla and cortex. We compared the systemic and renal effects of graded alterations in FiO (0.21, 0.40, 0.60, and 1.0) during TIVA or VA and compared the changes with those in the non-anaesthetised state.
RESULTS
Compared with the non-anaesthetised state, TIVA and VA decreased renal blood flow (-50% vs -75%), renal oxygen delivery (-50% vs -80%), and renal cortical (-40% vs -60%) and medullary perfusion (-50% vs -75%). At an FiO of 0.21, both anaesthetic regimens induced similar reductions in cortical (-58 vs -65%) and medullary (-37% vs -38%) oxygenation. At higher concentrations of FiO, renal blood flow and renal tissue perfusion were not changed, but intrarenal oxygenation improved similarly under TIVA and VA. In particular, at an FiO of ≥0.40 and ≤0.60, cortical and medullary oxygen tension were similar to the non-anaesthetised state.
CONCLUSIONS
Irrespective of FiO, TIVA decreased renal and intrarenal perfusion less than VA, but at low FiO concentrations both led to equivalent reductions in renal cortical and medullary oxygenation. However, with FiO between 0.40 and 0.60 during TIVA or VA, both cortical and medullary oxygenation was maintained at normal physiological levels.
Topics: Anesthetics, Inhalation; Anesthetics, Intravenous; Animals; Female; Fentanyl; Hemodynamics; Isoflurane; Models, Animal; Oxygen; Propofol; Renal Circulation; Sheep
PubMed: 32563492
DOI: 10.1016/j.bja.2020.03.033