101
|
Abrams JM, Osborn JW. A role for benzamil-sensitive proteins of the central nervous system in the pathogenesis of salt-dependent hypertension. Clin Exp Pharmacol Physiol 2008; 35:687-94. [PMID: 18387084 DOI: 10.1111/j.1440-1681.2008.04929.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
1. Although increasing evidence suggests that salt-sensitive hypertension is a disorder of the central nervous system (CNS), little is known about the critical proteins (e.g. ion channels or exchangers) that play a role in the pathogenesis of the disease. 2. Central pathways involved in the regulation of arterial pressure have been investigated. In addition, systems such as the renin-angiotensin-aldosterone axis, initially characterized in the periphery, are present in the CNS and seem to play a role in the regulation of arterial pressure. 3. Central administration of amiloride, or its analogue benzamil hydrochloride, has been shown to attenuate several forms of salt-sensitive hypertension. In addition, intracerebroventricular (i.c.v.) benzamil effectively blocks pressor responses to acute osmotic stimuli, such as i.c.v. hypertonic saline. Amiloride or its analogues have been shown to interact with the brain renin-angiotensin-aldosterone system (RAAS) and to effect the expression of endogenous ouabain-like compounds. Alterations of brain RAAS function and/or endobain expression could play a role in the interaction between amiloride compounds and arterial pressure. Peripheral treatments with benzamil, even at higher doses than those given centrally, have little or no effect on arterial pressure. These data provide strong evidence that benzamil-sensitive proteins (BSPs) of the CNS play a role in cardiovascular responsiveness to sodium. 4. Mineralocorticoids have been linked to human hypertension; many patients with essential hypertension respond well to pharmacological agents antagonizing the mineralocorticoid receptor and certain genetic forms of hypertension are caused by chronically elevated levels of aldosterone. The deoxycorticosterone acetate (DOCA)-salt model of hypertension is a benzamil-sensitive model that incorporates several factors implicated in the aetiology of human disease, including mineralocorticoid action and increased dietary sodium. The DOCA-salt model is ideal for investigating the role of BSPs in the pathogenesis of hypertension, because mineralocorticoid action has been shown to modulate the activity of at least one benzamil-sensitive protein, namely the epithelial sodium channel. 5. Characterizing the BSPs involved in the pathogenesis of hypertension may provide a novel clinical target. Further studies are necessary to determine which BSPs are involved and where, in the nervous system, they are located.
Collapse
Affiliation(s)
- Joanna M Abrams
- Graduate Program in Neuroscience, Department of Integrative Biology and Physiology, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | | |
Collapse
|
102
|
Bagrov AY, Shapiro JI. Endogenous digitalis: pathophysiologic roles and therapeutic applications. NATURE CLINICAL PRACTICE. NEPHROLOGY 2008; 4:378-92. [PMID: 18542120 PMCID: PMC2574729 DOI: 10.1038/ncpneph0848] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2008] [Accepted: 04/29/2008] [Indexed: 12/22/2022]
Abstract
Endogenous digitalis-like factors, also called cardiotonic steroids, have been thought for nearly half a century to have important roles in health and disease. The endogenous cardiotonic steroids ouabain and marinobufagenin have been identified in humans, and an effector mechanism has been delineated by which these hormones signal through the sodium/potassium-transporting ATPase. These findings have increased interest in this field substantially. Although cardiotonic steroids were first considered important in the regulation of renal sodium transport and arterial pressure, subsequent work has implicated these hormones in the control of cell growth, apoptosis and fibrosis, among other processes. This Review focuses on the role of endogenous cardiotonic steroids in the pathophysiology of essential hypertension, congestive heart failure, end-stage renal disease and pre-eclampsia. We also discuss potential therapeutic strategies that have emerged as a result of the increased understanding of the regulation and actions of cardiotonic steroids.
Collapse
Affiliation(s)
- Alexei Y Bagrov
- Hypertension Unit at Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, NIH, Baltimore 21224, MD, USA.
| | | |
Collapse
|
103
|
Schoner W, Scheiner-Bobis G. Role of endogenous cardiotonic steroids in sodium homeostasis. Nephrol Dial Transplant 2008; 23:2723-9. [PMID: 18556748 DOI: 10.1093/ndt/gfn325] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
|
104
|
Abstract
PURPOSE OF REVIEW To integrate recent studies showing that abnormal Na transport in the central nervous system plays a pivotal role in genetic models of salt-sensitive hypertension. RECENT FINDINGS Na transport-regulating mechanisms classically considered to reflect renal control of the blood pressure, i.e. aldosterone-mineralocorticoid receptors-epithelial sodium channels-Na/K-ATPase, have now been demonstrated to be present in the central nervous system contributing to regulation of cerebrospinal fluid [Na] by the choroid plexus and to neuronal responsiveness to cerebrospinal fluid/brain [Na]. Dysfunction of either or both can activate central nervous system pathways involving 'ouabain' and angiotensin type 1 receptor stimulation. The latter causes sympathetic hyperactivity and adrenal release of marinobufagenin - a digitalis-like inhibitor of the alpha1 Na/K-ATPase isoform - both contributing to hypertension on high salt intake. Conversely, specific central nervous system blockade of mineralocorticoid receptors or epithelial sodium channels prevents the development of hypertension on high salt intake, irrespective of the presence of a 'salt-sensitive kidney'. Variants in the coding regions of some of the genes involved in Na transport have been identified, but sodium sensitivity may be mainly determined by abnormal regulation of expression, pointing to primary abnormalities in regulation of transcription. SUMMARY Looking beyond the kidney is providing new insights into mechanisms contributing to salt-sensitive hypertension, which will help to dissect the genetic factors involved and to discover novel strategies to prevent and treat salt-sensitive hypertension.
Collapse
Affiliation(s)
- Bing S Huang
- Hypertension Unit, University of Ottawa Heart Institute, Ontario, Canada
| | | | | |
Collapse
|
105
|
Van Huysse JW. Endogenous brain Na pumps, brain ouabain-like substance and the alpha2 isoform in salt-dependent hypertension. ACTA ACUST UNITED AC 2007; 14:213-20. [PMID: 17980562 DOI: 10.1016/j.pathophys.2007.09.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2007] [Revised: 08/09/2007] [Accepted: 08/25/2007] [Indexed: 11/24/2022]
Abstract
An endogenous ouabain-like substance (OLS) plays a critical role in the etiology of experimental models of human hypertension induced by a high salt diet. Early on, evidence for a role of this Na, K-ATPase inhibitor in blood pressure regulation was provided mainly by correlations of blood pressure with the levels of circulating Na, K-ATPase inhibitor. However, over the past decade, numerous studies have shown that endogenous Na pump inhibitors in the brain mediate salt-dependent hypertension in a variety of experimental models, including Dahl salt-sensitive (Dahl-S) and spontaneously hypertensive (SHR) rats on a high-salt diet. Other forms of hypertension that are known to be mediated by endogenous ouabain-like substances include steroid/salt- (e.g., DOCA-salt) and ACTH-induced hypertension. Even when exogenous ouabain is peripherally administered and/or the plasma ouabain/OLS level is increased in rats, the resulting hypertension is of CNS origin. After peripheral ouabain administration, ouabain levels increase in the plasma and the inhibitor subsequently accumulates in the brain. The ensuing hypertension is abolished by the intracerebroventricular (icv) administration of an anti-ouabain antibody (but not by the same antibody dose given iv), by discrete excitotoxic lesions in the brain or by ganglionic blockade, demonstrating that the response is neurally mediated. The pressor response to stimuli that increase the brain OLS (high salt diet, icv sodium) or to icv ouabain is abolished by icv losartan, demonstrating that the brain OLS activates the brain renin-angiotensin system (RAS) downstream. There are three isoforms of the catalytic alpha subunit of the Na, K-ATPase in the brain and cardiovascular system (alpha1, alpha2 and alpha3), but it is not known which brain isoform(s) mediate the hypertensive effects of circulating/CNS ouabain. Preliminary studies in gene-targeted mice suggest that the alpha2 isoform plays a critical role.
Collapse
Affiliation(s)
- James W Van Huysse
- University of Ottawa Heart Institute and Departments of Medicine and Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario, Canada K1Y 4W7
| |
Collapse
|
106
|
Osborn JW, Collister JP, Guzman P. Effect of peripheral sympathetic nerve dysfunction on salt sensitivity of arterial pressure. Clin Exp Pharmacol Physiol 2007; 35:273-9. [PMID: 17973927 DOI: 10.1111/j.1440-1681.2007.04827.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
1. Dysregulation of peripheral sympathetic pathways contributes to some forms of salt-dependent hypertension. However, at the present time it is not known whether salt-induced activation of sympathetic nerves or loss of normal sympathoinhibitory responses to salt-induced volume expansion contributes to neurogenic salt-dependent hypertension. The present study was performed to the test the hypothesis that loss of peripheral sympathetic nerve function results in salt-dependent hypertension. 2. The effect of three pharmacological interventions of sympathetic nerve function on the long-term salt-sensitivity of mean arterial pressure (MAP) were measured: (i) blockade of ganglionic transmission with hexamethonium (HEX; n = 5); (ii) destruction of sympathetic nerve terminals with guanethidine (GUAN; n = 7); and (iii) alpha-adrenoceptor blockade with two specific antagonists, namely prazosin (PRAZ; n = 7) and terazosin (TERAZ; n = 8). 3. Mean arterial pressure and heart rate were measured 24 h/day by radiotelemetry in conscious rats during 5 days of normal and 7 days of high (HNa) dietary sodium intake. Despite marked increases in both sodium and water intake during 7 days of the HNa diet, no statistically significant changes in MAP were observed in HEX, GUAN, PRAZ or TERAZ groups. 4. We conclude that loss of peripheral sympathetic neural pathways alone does not cause salt-dependent hypertension in the rat.
Collapse
Affiliation(s)
- John W Osborn
- Departments of Integrative Biology and Physiology, University of Minnesota, Minneapolis, Minnesota 55105, USA.
| | | | | |
Collapse
|
107
|
Fedorova OV, Zhuravin IA, Agalakova NI, Yamova LA, Talan MI, Lakatta EG, Bagrov AY. Intrahippocampal microinjection of an exquisitely low dose of ouabain mimics NaCl loading and stimulates a bufadienolide Na/K-ATPase inhibitor. J Hypertens 2007; 25:1834-44. [PMID: 17762648 DOI: 10.1097/hjh.0b013e328200497a] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
BACKGROUND Brain endogenous ouabain (EOU) raises blood pressure (BP) via an angiotensin II (ATII)-sensitive pathway in NaCl-loaded Dahl salt-sensitive rats (DSS). Brain EOU activates central and adrenocortical renin-angiotensin systems, and stimulates marinobufagenin, a vasoconstrictor and natriuretic inhibitor of sodium pump. METHODS We studied effects of acute NaCl loading (17 mmol/kg NaCl, intraperitoneally) on levels of EOU and marinobufagenin in several brain areas in DSS. We then studied effects of intrahippocampal administration of very-low-dose ouabain (60 pg) on EOU, marinobufagenin, BP, sodium excretion, and sodium-pump activity in the aorta and renal medulla in the absence and presence of anti-marinobufagenin and anti-ouabain antibodies, and losartan. RESULTS NaCl loading of DSS induced transient increases of EOU in the hippocampus and amygdala (15 min; 300%), supraoptical nucleus of hypothalamus (SON) (30 min, 230%) and pituitary (30 min; 85%), and ATII elevation in the SON (30 min). Intrahippocampal administration of ouabain (60 pg) stimulated ATII in the SON, produced natriuresis, 40 mmHg rise in BP, inhibition of sodium-pump in the renal medulla (19.6%) and aorta (25%), and a two-fold increase in renal marinobufagenin excretion. Pretreatment of rats with anti-marinobufagenin antibody prevented ouabain-induced pressor and natriuretic responses and sodium-pump inhibition. Pressor responses to ouabain were also prevented by losartan (intravenously) and by administration of anti-ouabain antibody into the SON. CONCLUSIONS NaCl loading of DSS induces a cascade of events, triggered by brain EOU and ATII. Intrahippocampal administration of a low-dose ouabain mimics effects of NaCl loading and stimulates marinobufagenin, which produces natriuresis, and inhibits the vascular sodium-pump, inducing an increase in BP.
Collapse
Affiliation(s)
- Olga V Fedorova
- Laboratory of Cardiovascular Science, National Institute on Aging, NIH, Baltimore, Maryland 21224, USA
| | | | | | | | | | | | | |
Collapse
|
108
|
Brinks V, H. van der Mark M, de Kloet ER, S. Oitzl M. Differential MR/GR activation in mice results in emotional states beneficial or impairing for cognition. Neural Plast 2007; 2007:90163. [PMID: 17710249 PMCID: PMC1940328 DOI: 10.1155/2007/90163] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2006] [Revised: 02/01/2007] [Accepted: 02/05/2007] [Indexed: 11/17/2022] Open
Abstract
Corticosteroids regulate stress response and influence emotion, learning, and memory via two receptors in the brain, the high-affinity mineralocorticoid (MR) and low-affinity glucocorticoid receptor (GR). We test the hypothesis that MR- and GR-mediated effects interact in emotion and cognition when a novel situation is encountered that is relevant for a learning process. By adrenalectomy and additional constant corticosterone supplement we obtained four groups of male C57BL/6J mice with differential chronic MR and GR activations. Using a hole board task, we found that mice with continuous predominant MR and moderate GR activations were fast learners that displayed low anxiety and arousal together with high directed explorative behavior. Progressive corticosterone concentrations with predominant action via GR induced strong emotional arousal at the expense of cognitive performance. These findings underline the importance of a balanced MR/GR system for emotional and cognitive functioning that is critical for mental health.
Collapse
Affiliation(s)
- Vera Brinks
- Gorlaeus Lab, Division of Medical Pharmacology, LACDR/LUMC, Leiden University, Einsteinweg 55, 2300 Leiden, The Netherlands
- *Vera Brinks:
| | - Maaike H. van der Mark
- Gorlaeus Lab, Division of Medical Pharmacology, LACDR/LUMC, Leiden University, Einsteinweg 55, 2300 Leiden, The Netherlands
| | - E. Ron de Kloet
- Gorlaeus Lab, Division of Medical Pharmacology, LACDR/LUMC, Leiden University, Einsteinweg 55, 2300 Leiden, The Netherlands
| | - Melly S. Oitzl
- Gorlaeus Lab, Division of Medical Pharmacology, LACDR/LUMC, Leiden University, Einsteinweg 55, 2300 Leiden, The Netherlands
| |
Collapse
|
109
|
Millar ID, Bruce JIE, Brown PD. Ion channel diversity, channel expression and function in the choroid plexuses. Cerebrospinal Fluid Res 2007; 4:8. [PMID: 17883837 PMCID: PMC2072944 DOI: 10.1186/1743-8454-4-8] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2007] [Accepted: 09/20/2007] [Indexed: 12/11/2022] Open
Abstract
Knowledge of the diversity of ion channel form and function has increased enormously over the last 25 years. The initial impetus in channel discovery came with the introduction of the patch clamp method in 1981. Functional data from patch clamp experiments have subsequently been augmented by molecular studies which have determined channel structures. Thus the introduction of patch clamp methods to study ion channel expression in the choroid plexus represents an important step forward in our knowledge understanding of the process of CSF secretion. Two K+ conductances have been identified in the choroid plexus: Kv1 channel subunits mediate outward currents at depolarising potentials; Kir 7.1 carries an inward-rectifying conductance at hyperpolarising potentials. Both K+ channels are localised at the apical membrane where they may contribute to maintenance of the membrane potential while allowing the recycling of K+ pumped in by Na+-K+ ATPase. Two anion conductances have been identified in choroid plexus. Both have significant HCO3- permeability, and may play a role in CSF secretion. One conductance exhibits inward-rectification and is regulated by cyclic AMP. The other is carried by an outward-rectifying channel, which is activated by increases in cell volume. The molecular identity of the anion channels is not known, nor is it clear whether they are expressed in the apical or basolateral membrane. Recent molecular evidence indicates that choroid plexus also expresses the non-selective cation channels such as transient receptor potential channels (TRPV4 and TRPM3) and purinoceptor type 2 (P2X) receptor operated channels. In conclusion, good progress has been made in identifying the channels expressed in the choroid plexus, but determining the precise roles of these channels in CSF secretion remains a challenge for the future.
Collapse
Affiliation(s)
- Ian D Millar
- Faculty of Life Sciences, Core Technology Facility, University of Manchester, Manchester M13 9NT, UK
| | - Jason IE Bruce
- Faculty of Life Sciences, Core Technology Facility, University of Manchester, Manchester M13 9NT, UK
| | - Peter D Brown
- Faculty of Life Sciences, Core Technology Facility, University of Manchester, Manchester M13 9NT, UK
| |
Collapse
|
110
|
Fronius M, Clauss WG. Mechano-sensitivity of ENaC: may the (shear) force be with you. Pflugers Arch 2007; 455:775-85. [PMID: 17874325 DOI: 10.1007/s00424-007-0332-1] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2007] [Accepted: 08/03/2007] [Indexed: 10/22/2022]
Abstract
The epithelial Na+ channel (ENaC) is the rate-limiting step for Na+ absorption in various vertebrate epithelia and deeply enmeshed in the control of salt and water homeostasis. The phylogenetic relationship of ENaC molecules to mechano-sensitive Degenerins from Caenorhabditis elegans indicates that ENaC might be mechano-sensitive as well. Primarily, it was suggested that ENaC might be activated by membrane stretch. However, this issue still remains to be clarified because controversial results were published. Recent publications indicate that shear stress represents an adequate stimulus, activating ENaC via increasing the single-channel open probability. Basing on the experimental evidence published within the past years and integrating this knowledge into a model related to the mechano-sensitive receptor complex known from C. elegans, we introduce a putative mechanism concerning the mechano-sensitivity of ENaC. We suggest that mechano-sensitive ENaC activation represents a nonhormonal regulatory mechanism. This feature could be of considerable physiological significance because many Na+-absorbing epithelia are exposed to shear forces. Furthermore, it may explain the wide distribution of ENaC proteins in nonepithelial tissues. Nevertheless, it remains a challenge for future studies to explore the mechanism how ENaC is controlled by mechanical forces and shear stress in particular.
Collapse
Affiliation(s)
- Martin Fronius
- Institute of Animal Physiology, Justus-Liebig-University Giessen, Wartweg 95, 35392, Giessen, Germany.
| | | |
Collapse
|
111
|
Giraldez T, Afonso-Oramas D, Cruz-Muros I, Garcia-Marin V, Pagel P, González-Hernández T, Alvarez de la Rosa D. Cloning and functional expression of a new epithelial sodium channel delta subunit isoform differentially expressed in neurons of the human and monkey telencephalon. J Neurochem 2007; 102:1304-15. [PMID: 17472699 DOI: 10.1111/j.1471-4159.2007.04622.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Epithelial sodium channel (ENaC) is a member of the ENaC/degenerin family of amiloride-sensitive, non-voltage gated sodium ion channels. ENaC alpha, beta and gamma subunits are abundantly expressed in epithelial tissues, where they have been well characterized. An ENaC delta subunit has also been described in the human nervous system, although its histological distribution pattern remains unexplored. We have now isolated a novel ENaC delta isoform (delta2) from human brain and studied the expression pattern of both the known (delta1) and the new (delta2) isoforms in the human and monkey telencephalon. ENaC delta2 is produced by a combination of alternative transcription start sites, a frame shift in exon 3 and alternative splicing of exon 4. It forms functional amiloride-sensitive sodium channels when co-expressed with ENaC beta and gamma accessory subunits. Comparison with the classical ENaC channel (alphabetagamma) indicates that the interaction between delta2, beta and gamma is functionally inefficient. Both ENaC delta isoforms are widely expressed in pyramidal cells of the human and monkey cerebral cortex and in different neuronal populations of telencephalic subcortical nuclei, but double-labelling experiments demonstrated a low level of co-localization between isoforms (5-8%), suggesting specific functional roles for each of them.
Collapse
Affiliation(s)
- Teresa Giraldez
- Unidad de Farmacología, Universidad de La Laguna, La Laguna, Tenerife, Spain.
| | | | | | | | | | | | | |
Collapse
|
112
|
|
113
|
ENaC Proteins in Vascular Smooth Muscle Mechanotransduction. CURRENT TOPICS IN MEMBRANES 2007; 59:127-53. [DOI: 10.1016/s1063-5823(06)59006-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/05/2023]
|
114
|
Praetorius J. Water and solute secretion by the choroid plexus. Pflugers Arch 2006; 454:1-18. [PMID: 17120021 DOI: 10.1007/s00424-006-0170-6] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2006] [Accepted: 09/12/2006] [Indexed: 12/23/2022]
Abstract
The cerebrospinal fluid (CSF) provides mechanical and chemical protection of the brain and spinal cord. This review focusses on the contribution of the choroid plexus epithelium to the water and salt homeostasis of the CSF, i.e. the secretory processes involved in CSF formation. The choroid plexus epithelium is situated in the ventricular system and is believed to be the major site of CSF production. Numerous studies have identified transport processes involved in this secretion, and recently, the underlying molecular background for some of the mechanisms have emerged. The nascent CSF consists mainly of NaCl and NaHCO(3), and the production rate is strictly coupled to the rate of Na(+) secretion. In contrast to other secreting epithelia, Na(+) is actively pumped across the luminal surface by the Na(+),K(+)-ATPase with possible contributions by other Na(+) transporters, e.g. the luminal Na(+),K(+),2Cl(-) cotransporter. The Cl(-) and HCO(3) (-) ions are likely transported by a luminal cAMP activated inward rectified anion conductance, although the responsible proteins have not been identified. Whereas Cl(-) most likely enters the cells through anion exchange, the functional as well as the molecular basis for the basolateral Na(+) entry are not yet well-defined. Water molecules follow across the epithelium mainly through the water channel, AQP1, driven by the created ionic gradient. In this article, the implications of the recent findings for the current model of CSF secretion are discussed. Finally, the clinical implications and the prospects of future advances in understanding CSF production are briefly outlined.
Collapse
Affiliation(s)
- Jeppe Praetorius
- The Water and Salt Research Center & Institute of Anatomy, University of Aarhus, Wilhelm Meyers Allé, 8000 Aarhus, Denmark.
| |
Collapse
|
115
|
Huang BS, Cheung WJ, Wang H, Tan J, White RA, Leenen FHH. Activation of brain renin-angiotensin-aldosterone system by central sodium in Wistar rats. Am J Physiol Heart Circ Physiol 2006; 291:H1109-17. [PMID: 16603700 DOI: 10.1152/ajpheart.00024.2006] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Functional studies indicate that the sympathoexcitatory and pressor responses to an increase in cerebrospinal fluid (CSF) [Na+] by central infusion of Na+-rich artificial cerebrospinal fluid (aCSF) in Wistar rats are mediated in the brain by mineralocorticoid receptor (MR) activation, ouabain-like compounds (OLC), and AT1-receptor stimulation. In the present study, we examined whether increasing CSF [Na+] by intracerebroventricular infusion of Na+-rich aCSF activates MR and thereby increases OLC and components of the renin-angiotensin system in the brain. Male Wistar rats received via osmotic minipump an intracerebroventricular infusion of aCSF or Na+-rich aCSF, in some groups combined with intracerebroventricular infusion of spironolactone (100 ng/h), antibody Fab fragments (to bind OLC), or as control gamma-globulins. After 2 wk of infusion, resting blood pressure and heart rate were recorded, OLC and aldosterone content in the hypothalamus were assessed by a specific ELISA or radioimmunoassay, and angiotensin-converting enzyme (ACE) and AT1-receptor binding densities in various brain nuclei were measured by autoradiography using 125I-labeled 351 A and 125I-labeled ANG II. When compared with intracerebroventricular aCSF, intracerebroventricular Na+-rich aCSF increased CSF [Na+] by approximately 5 mmol/l, mean arterial pressure by approximately 20 mmHg, heart rate by approximately 65 beats/min, and hypothalamic content of OLC by 50% and of aldosterone by 33%. Intracerebroventricular spironolactone did not affect CSF [Na+] but blocked the Na+-rich aCSF-induced increases in blood pressure and heart rate and OLC content. Intracerebroventricular Na+-rich aCSF increased ACE and AT1-receptor-binding densities in several brain nuclei, and Fab fragments blocked these increases. These data indicate that in Wistar rats, a chronic increase in CSF [Na+] may increase hypothalamic aldosterone and activate CNS pathways involving MR, and OLC, leading to increases in AT1-receptor and ACE densities in brain areas involved in cardiovascular regulation and hypertension.
Collapse
Affiliation(s)
- Bing S Huang
- Hypertension Unit, University of Ottawa Heart Institute, H360, 40 Ruskin St., Ottawa, Ontario, Canada K1Y 4W7
| | | | | | | | | | | |
Collapse
|