1
|
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.
Collapse
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
| |
Collapse
|
2
|
Zhang Z, Payne K, Pallone TL. Adaptive responses of rat descending vasa recta to ischemia. Am J Physiol Renal Physiol 2018; 314:F373-F380. [PMID: 28814437 DOI: 10.1152/ajprenal.00062.2017] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
tested whether rat descending vasa recta (DVR) undergo regulatory adaptations after the kidney is exposed to ischemia. Left kidneys (LK) were subjected to 30-min renal artery cross clamp. After 48 h, the postischemic LK and contralateral right kidney (RK) were harvested for study. When compared with DVR isolated from either sham-operated LK or the contralateral RK, postischemic LK DVR markedly increased their NO generation. The selective inducible NOS (iNOS) inhibitor 1400W blocked the NO response. Immunoblots from outer medullary homogenates showed a parallel 2.6-fold increase in iNOS expression ( P = 0.01). Microperfused postischemic LK DVR exposed to angiotensin II (ANG II, 10 nM), constricted less than those from the contralateral RK, and constricted more when exposed to 1400W (10 µM). Resting membrane potentials of pericytes from postischemic LK DVR pericytes were hyperpolarized relative to contralateral RK pericytes (62.0 ± 1.6 vs. 51.8 ± 2.2 mV, respectively, P < 0.05) or those from sham-operated LK (54.9 ± 2.1 mV, P < 0.05). Blockade of NO generation with 1400W did not repolarize postischemic pericytes (62.5 ± 1.4 vs. 61.1 ± 3.4 mV); however, control pericytes were hyperpolarized by exposure to NO donation from S-nitroso- N-acetyl- dl-penicillamine (51.5 ± 2.9 to 62.1 ± 1.4 mV, P < 0.05). We conclude that postischemic adaptations intrinsic to the DVR wall occur after ischemia. A rise in 1400W sensitive NO generation and iNOS expression occurs that is associated with diminished contractile responses to ANG II. Pericyte hyperpolarization occurs that is not explained by the rise in ambient NO generation within the DVR wall.
Collapse
Affiliation(s)
- Zhong Zhang
- Division of Nephrology, Department of Medicine, University of Maryland School of Medicine , Baltimore, Maryland
| | - Kristie Payne
- Division of Nephrology, Department of Medicine, University of Maryland School of Medicine , Baltimore, Maryland
| | - Thomas L Pallone
- Division of Nephrology, Department of Medicine, University of Maryland School of Medicine , Baltimore, Maryland.,Baltimore Veterans Administration Medical Center , Baltimore, Maryland
| |
Collapse
|
3
|
Sgouralis I, Evans RG, Layton AT. Renal medullary and urinary oxygen tension during cardiopulmonary bypass in the rat. MATHEMATICAL MEDICINE AND BIOLOGY-A JOURNAL OF THE IMA 2017; 34:313-333. [PMID: 27281792 DOI: 10.1093/imammb/dqw010] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2016] [Accepted: 05/11/2016] [Indexed: 02/07/2023]
Abstract
Renal hypoxia could result from a mismatch in renal oxygen supply and demand, particularly in the renal medulla. Medullary hypoxic damage is believed to give rise to acute kidney injury, which is a prevalent complication of cardiac surgery performed on cardiopulmonary bypass (CPB). To determine the mechanisms that could lead to medullary hypoxia during CPB in the rat kidney, we developed a mathematical model which incorporates (i) autoregulation of renal blood flow and glomerular filtration rate, (ii) detailed oxygen transport and utilization in the renal medulla and (iii) oxygen transport along the ureter. Within the outer medulla, the lowest interstitial tissue P$_{\rm O2}$, which is an indicator of renal hypoxia, is predicted near the thick ascending limbs. Interstitial tissue P$_{\rm O2}$ exhibits a general decrease along the inner medullary axis, but urine P$_{\rm O2}$ increases significantly along the ureter. Thus, bladder urinary P$_{\rm O2}$ is predicted to be substantially higher than medullary P$_{\rm O2}$. The model is used to identify the phase of cardiac surgery performed on CPB that is associated with the highest risk for hypoxic kidney injury. Simulation results indicate that the outer medulla's vulnerability to hypoxic injury depends, in part, on the extent to which medullary blood flow is autoregulated. With imperfect medullary blood flow autoregulation, the model predicts that the rewarming phase of CPB, in which medullary blood flow is low but medullary oxygen consumption remains high, is the phase in which the kidney is most likely to suffer hypoxic injury.
Collapse
Affiliation(s)
- Ioannis Sgouralis
- National Institute for Mathematical and Biological Synthesis, NIMBioS, Knoxville, TN 37996, USA
| | - Roger G Evans
- Cardiovascular Disease Program, Bioscience Discovery Institute and Department of Physiology, Monash University, Monash, Clayton, VIC 3800, Australia
| | - Anita T Layton
- Department of Mathematics, Duke University, Duke, Durham, NC 27708, USA
| |
Collapse
|
4
|
Ngo JP, Ow CP, Gardiner BS, Kar S, Pearson JT, Smith DW, Evans RG. Diffusive shunting of gases and other molecules in the renal vasculature: physiological and evolutionary significance. Am J Physiol Regul Integr Comp Physiol 2016; 311:R797-R810. [DOI: 10.1152/ajpregu.00246.2016] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2016] [Accepted: 07/27/2016] [Indexed: 01/22/2023]
Abstract
Countercurrent systems have evolved in a variety of biological systems that allow transfer of heat, gases, and solutes. For example, in the renal medulla, the countercurrent arrangement of vascular and tubular elements facilitates the trapping of urea and other solutes in the inner medulla, which in turn enables the formation of concentrated urine. Arteries and veins in the cortex are also arranged in a countercurrent fashion, as are descending and ascending vasa recta in the medulla. For countercurrent diffusion to occur, barriers to diffusion must be small. This appears to be characteristic of larger vessels in the renal cortex. There must also be gradients in the concentration of molecules between afferent and efferent vessels, with the transport of molecules possible in either direction. Such gradients exist for oxygen in both the cortex and medulla, but there is little evidence that large gradients exist for other molecules such as carbon dioxide, nitric oxide, superoxide, hydrogen sulfide, and ammonia. There is some experimental evidence for arterial-to-venous (AV) oxygen shunting. Mathematical models also provide evidence for oxygen shunting in both the cortex and medulla. However, the quantitative significance of AV oxygen shunting remains a matter of controversy. Thus, whereas the countercurrent arrangement of vasa recta in the medulla appears to have evolved as a consequence of the evolution of Henle’s loop, the evolutionary significance of the intimate countercurrent arrangement of blood vessels in the renal cortex remains an enigma.
Collapse
Affiliation(s)
- Jennifer P. Ngo
- Cardiovascular Disease Program, Biosciences Discovery Institute and Department of Physiology and
| | - Connie P.C. Ow
- Cardiovascular Disease Program, Biosciences Discovery Institute and Department of Physiology and
| | - Bruce S. Gardiner
- School of Engineering and Information Technology, Murdoch University, Perth, Western Australia
| | - Saptarshi Kar
- School of Computer Science and Software Engineering, The University of Western Australia, Perth, Australia; and
| | - James T. Pearson
- Cardiovascular Disease Program, Biosciences Discovery Institute and Department of Physiology and
- Monash Biomedical Imaging Facility, Monash University, Melbourne, Australia
- Department of Cardiac Physiology, National Cerebral and Cardiovascular Center Research Institute, Osaka, Japan
| | - David W. Smith
- School of Computer Science and Software Engineering, The University of Western Australia, Perth, Australia; and
| | - Roger G. Evans
- Cardiovascular Disease Program, Biosciences Discovery Institute and Department of Physiology and
| |
Collapse
|
5
|
Abstract
Mathematical modeling techniques have been useful in providing insights into biological systems, including the kidney. This article considers some of the mathematical models that concern urea transport in the kidney. Modeling simulations have been conducted to investigate, in the context of urea cycling and urine concentration, the effects of hypothetical active urea secretion into pars recta. Simulation results suggest that active urea secretion induces a "urea-selective" improvement in urine concentrating ability. Mathematical models have also been built to study the implications of the highly structured organization of tubules and vessels in the renal medulla on urea sequestration and cycling. The goal of this article is to show how physiological problems can be formulated and studied mathematically, and how such models may provide insights into renal functions.
Collapse
Affiliation(s)
- Anita T Layton
- Department of Mathematics, Duke University, Durham, NC, USA,
| |
Collapse
|
6
|
Fry BC, Layton AT. Oxygen transport in a cross section of the rat inner medulla: impact of heterogeneous distribution of nephrons and vessels. Math Biosci 2014; 258:68-76. [PMID: 25260928 DOI: 10.1016/j.mbs.2014.09.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2014] [Revised: 09/04/2014] [Accepted: 09/05/2014] [Indexed: 11/18/2022]
Abstract
We have developed a highly detailed mathematical model of oxygen transport in a cross section of the upper inner medulla of the rat kidney. The model is used to study the impact of the structured organization of nephrons and vessels revealed in anatomic studies, in which descending vasa recta are found to lie distant from clusters of collecting ducts. Specifically, we formulated a two-dimensional oxygen transport model, in which the positions and physical dimensions of renal tubules and vessels are based on an image obtained by immunochemical techniques (T. Pannabecker and W. Dantzler, Three-dimensional architecture of inner medullary vasa recta, Am. J. Physiol. Renal Physiol. 290 (2006) F1355-F1366). The model represents oxygen diffusion through interstitium and other renal structures, oxygen consumption by the Na(+)/K(+)-ATPase activities of the collecting ducts, and basal metabolic consumption. Model simulations yield marked variations in interstitial PO2, which can be attributed, in large part, to the heterogeneities in the position and physical dimensions of the collecting ducts. Further, results of a sensitivity study suggest that medullary oxygenation is highly sensitive to medullary blood flow, and that, at high active consumption rates, localized patches of tissue may be vulnerable to hypoxic injury.
Collapse
Affiliation(s)
- Brendan C Fry
- Department of Mathematics, Duke University, Durham, NC 27708-0320, USA.
| | - Anita T Layton
- Department of Mathematics, Duke University, Durham, NC 27708-0320, USA
| |
Collapse
|
7
|
Evans RG, Ince C, Joles JA, Smith DW, May CN, O'Connor PM, Gardiner BS. Haemodynamic influences on kidney oxygenation: Clinical implications of integrative physiology. Clin Exp Pharmacol Physiol 2013; 40:106-22. [DOI: 10.1111/1440-1681.12031] [Citation(s) in RCA: 178] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2012] [Revised: 10/21/2012] [Accepted: 11/15/2012] [Indexed: 01/08/2023]
Affiliation(s)
- Roger G Evans
- Department of Physiology; Monash University; Melbourne; Victoria; Australia
| | - Can Ince
- Department of Translational Physiology; Academic Medical Center; University of Amsterdam; Amsterdam; The Netherlands
| | - Jaap A Joles
- Department of Nephrology and Hypertension; University Medical Center; Utrecht; The Netherlands
| | - David W Smith
- School of Computer Science and Software Engineering; The University of Western Australia; Perth; Western Australia; Australia
| | - Clive N May
- Florey Institute of Neuroscience and Mental Health; University of Melbourne; Melbourne; Victoria; Australia
| | - Paul M O'Connor
- Department of Physiology; Georgia Health Sciences University; Augusta; GA; USA
| | - Bruce S Gardiner
- School of Computer Science and Software Engineering; The University of Western Australia; Perth; Western Australia; Australia
| |
Collapse
|
8
|
|