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Leenen FHH, Wang HW, Hamlyn JM. Sodium pumps, ouabain and aldosterone in the brain: A neuromodulatory pathway underlying salt-sensitive hypertension and heart failure. Cell Calcium 2019; 86:102151. [PMID: 31954234 DOI: 10.1016/j.ceca.2019.102151] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2019] [Accepted: 12/15/2019] [Indexed: 02/08/2023]
Abstract
Accumulating evidence obtained over the last three decades has revealed a neuroendocrine system in the brain that mediates long term increases in blood pressure. The system involves distinct ion transport pathways including the alpha-2 isoform of the Na,K pump and epithelial sodium channels, as well as critical hormone elements such as angiotensin II, aldosterone, mineralocorticoid receptors and endogenous ouabain. Activation of this system either by circulating or central sodium ions and/or angiotensin II leads to a cascading sequence of events that begins in the hypothalamus and involves the participation of several brain nuclei including the subfornical organ, supraoptic and paraventricular nuclei and the rostral ventral medulla. Key events include heightened aldosterone synthesis and mineralocorticoid receptor activation, upregulation of epithelial sodium channels, augmented synthesis and secretion of endogenous ouabain from hypothalamic magnocellular neurons, and sustained increases in sympathetic outflow. The latter step depends upon increased production of angiotensin II and the primary amplification of angiotensin II type I receptor signaling from the paraventricular nucleus to the rostral ventral lateral medulla. The transmission of sympathetic traffic is secondarily amplified in the periphery by increased short- and long-term potentiation in sympathetic ganglia and by sustained actions of endogenous ouabain in the vascular wall that augment expression of sodium calcium exchange, increase cytosolic Ca2+ and heighten myogenic tone and contractility. Upregulation of this multi-amplifier system participates in forms of hypertension where salt, angiotensin and/or aldosterone are elevated and contributes to adverse outcomes in heart failure.
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Affiliation(s)
- Frans H H Leenen
- Brain and Heart Research Group, University of Ottawa Heart Institute, Ottawa, ON, Canada
| | - Hong-Wei Wang
- Brain and Heart Research Group, University of Ottawa Heart Institute, Ottawa, ON, Canada
| | - John M Hamlyn
- Department of Physiology, University of Maryland, Baltimore, MD, USA.
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Yamazato M, Nakamoto M, Sakima A, Yamazato Y, Takishita S, Ohya Y. Responsiveness of α2-adrenoceptor/I1-imidazoline receptor in the rostral ventrolateral medulla to cardiovascular regulation is enhanced in conscious spontaneously hypertensive rat. Clin Exp Hypertens 2018; 41:255-262. [PMID: 29764227 DOI: 10.1080/10641963.2018.1469641] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
Stimulation of α2-adrenoceptor/I1-imidazoline receptors in the rostral ventrolateral medulla decreases the blood pressure via sympathoinhibition. However, alteration of receptor responses in genetically hypertensive rats remains unclear. We examined cardiovascular responses of α2-adrenoceptor/I1-imidazoline receptor agonist and antagonists microinjected into the rostral ventrolateral medulla of conscious spontaneously hypertensive rats and normotensive Wistar Kyoto rats. Injection of 2-nmol clonidine-an α2-adrenoceptor/I1-imidazoline receptor agonist-unilaterally into the rostral ventrolateral medulla decreased the blood pressure, heart rate, and renal sympathetic nerve activity; the responses were significantly enhanced in spontaneously hypertensive rats than in Wistar Kyoto rats. Co-injection of 2-nmol 2-methoxyidazoxan (a selective α2-adrenoceptor antagonist) or 2-nmol efaroxan (an I1-receptor antagonist) with 2 nmol of clonidine attenuated the hypotensive and bradycardic effects of clonidine-only injection. Injection of 2-methoxyidazoxan alone increased the blood pressure and heart rate in spontaneously hypertensive rats, but not in Wistar Kyoto rats. These results suggest enhanced responsiveness of α2-adrenoceptor/I1-imidazoline receptors in the rostral ventrolateral medulla of spontaneously hypertensive rats.
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Affiliation(s)
- Masanobu Yamazato
- a Department of Cardiovascular Medicine, Nephrology and Neurology , Graduate School of Medicine, University of the Ryukyus , Nishihara-cho, Okinawa , Japan
| | - Minori Nakamoto
- a Department of Cardiovascular Medicine, Nephrology and Neurology , Graduate School of Medicine, University of the Ryukyus , Nishihara-cho, Okinawa , Japan
| | - Atsushi Sakima
- a Department of Cardiovascular Medicine, Nephrology and Neurology , Graduate School of Medicine, University of the Ryukyus , Nishihara-cho, Okinawa , Japan
| | - Yoriko Yamazato
- b Department of Infectious, Respiratory and Digestive Medicine, Faculty of Medicine , University of the Ryukyus , Nishihara-cho, Okinawa , Japan
| | - Shuichi Takishita
- a Department of Cardiovascular Medicine, Nephrology and Neurology , Graduate School of Medicine, University of the Ryukyus , Nishihara-cho, Okinawa , Japan
| | - Yusuke Ohya
- a Department of Cardiovascular Medicine, Nephrology and Neurology , Graduate School of Medicine, University of the Ryukyus , Nishihara-cho, Okinawa , Japan
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Iatrino R, Manunta P, Zagato L. Salt Sensitivity: Challenging and Controversial Phenotype of Primary Hypertension. Curr Hypertens Rep 2016; 18:70. [DOI: 10.1007/s11906-016-0677-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Fardin NM, Antonio EL, Montemor JAS, da Veiga GL, Tucci PJF, Campos RR. Digitoxin improves cardiovascular autonomic control in rats with heart failure. Can J Physiol Pharmacol 2016; 94:643-50. [DOI: 10.1139/cjpp-2015-0354] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The effects of chronic treatment with digitoxin on arterial baroreceptor sensitivity for heart rate (HR) and renal sympathetic nerve activity (rSNA) control, cardiopulmonary reflex, and autonomic HR control in an animal model of heart failure (HF) were evaluated. Wistar rats were treated with digitoxin, which was administered in their daily feed (1 mg/kg per day) for 60 days. The following 3 experimental groups were evaluated: sham, HF, and HF treated with digitoxin (HF + DIG). We observed an increase in rSNA in the HF group (190 ± 29 pps, n = 5) compared with the sham group (98 ± 14 pps, n = 5). Digitoxin treatment prevented an increase in rSNA (98 ± 14 pps, n = 7). Therefore, arterial baroreceptor sensitivity was decreased in the HF group (−1.24 ± 0.07 bpm/mm Hg, n = 8) compared with the sham group (−2.27 ± 0.23 bpm/mm Hg, n = 6). Digitoxin did not alter arterial baroreceptor sensitivity in the HF + DIG group. Finally, the HF group showed an increased low frequency band (LFb: 23 ± 5 ms2, n = 8) and a decreased high frequency band (HFb: 77 ± 5 ms2, n = 8) compared with the sham group (LFb: 14 ± 3 ms2; HFb: 86 ± 3 ms2, n = 9); the HF+DIG group exhibited normalized parameters (LFb: 15 ± 3 ms2; HFb: 85 ± 3 ms2, n = 9). In conclusion, the benefits of decreasing rSNA are not directly related to improvements in peripheral cardiovascular reflexes; such occurrences are due in part to changes in the central nuclei of the brain responsible for autonomic cardiovascular control.
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Affiliation(s)
- Núbia Mantovan Fardin
- Cardiovascular Division, Department of Physiology, Universidade Federal de São Paulo, Escola Paulista de Medicina, Rua Botucatu, 862, CEP 04023-060, São Paulo, SP, Brazil
| | - Ednei Luiz Antonio
- Cardiology Division, Department of Medicine, Universidade Federal de São Paulo, São Paulo, SP, Brazil
| | | | - Glaucia Luciano da Veiga
- Cardiovascular Division, Department of Physiology, Universidade Federal de São Paulo, Escola Paulista de Medicina, Rua Botucatu, 862, CEP 04023-060, São Paulo, SP, Brazil
| | - Paulo José Ferreira Tucci
- Cardiology Division, Department of Medicine, Universidade Federal de São Paulo, São Paulo, SP, Brazil
| | - Ruy R. Campos
- Cardiovascular Division, Department of Physiology, Universidade Federal de São Paulo, Escola Paulista de Medicina, Rua Botucatu, 862, CEP 04023-060, São Paulo, SP, Brazil
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Activation of mineralocorticoid receptors in the rostral ventrolateral medulla is involved in hypertensive mechanisms in stroke-prone spontaneously hypertensive rats. Hypertens Res 2012; 35:470-6. [DOI: 10.1038/hr.2011.220] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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Padilha A, Salaices M, Vassallo D, Batista P, Siman F. Hypertensive effects of the iv administration of picomoles of ouabain. Braz J Med Biol Res 2011; 44:933-8. [DOI: 10.1590/s0100-879x2011007500103] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2011] [Accepted: 07/20/2011] [Indexed: 12/20/2022] Open
Affiliation(s)
| | | | - D.V. Vassallo
- Universidade Federal do Espírito Santo, Brasil; Escola Superior de Ciências da Santa Casa de Misericórdia de Vitória, Brasil
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Leenen FH. The central role of the brain aldosterone–“ouabain” pathway in salt-sensitive hypertension. Biochim Biophys Acta Mol Basis Dis 2010; 1802:1132-9. [DOI: 10.1016/j.bbadis.2010.03.004] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2009] [Revised: 03/02/2010] [Accepted: 03/07/2010] [Indexed: 11/29/2022]
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Westcott KV, Huang BS, Leenen FH. Brain renin–angiotensin–aldosterone system and ventricular remodeling after myocardial infarct: a reviewThis article is one of a selection of papers published in a special issue on Advances in Cardiovascular Research. Can J Physiol Pharmacol 2009; 87:979-88. [DOI: 10.1139/y09-067] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
After a myocardial infarct (MI), a variety of mechanisms contribute to progressive cardiac remodeling and dysfunction. Progressive activation of central sympathoexcitatory pathways appears to depend on a neuromodulatory pathway, involving local production of aldosterone and release of endogenous ouabain-like compounds (‘ouabain’) possibly from magnocellular neurons in the supraoptic and paraventricular nuclei. ‘Ouabain’ may lower the membrane potential of neurons and thereby enhance activity of angiotensinergic pathways. These central pathways appear to coordinate progressive activation of several peripheral mechanisms such as sympathetic tone and circulating and cardiac renin–angiotensin–aldosterone system (RAAS). Central blockade of aldosterone production, mineralocorticoid receptors, ‘ouabain’ activity, or AT1 receptors similarly prevents activation of these peripheral mechanisms. Cardiac remodeling after MI involves progressive left ventricular dilation, fibrosis, and decrease in contractile performance. Central blockade of this neuromodulatory pathway causes a marked attenuation of the remodeling and dysfunction, presumably by inhibiting increases in (cardiac) sympathetic activity and RAAS. At the cellular level, these systems may contribute to the cardiac remodeling by activating proinflammatory cytokines and cardiac myocyte apoptosis. New therapeutic approaches, specifically preventing activation of this brain neuromodulatory pathway, may lead to more optimal and specific approaches to the prevention of heart failure after MI.
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Affiliation(s)
- Katherine V. Westcott
- Hypertension Unit, University of Ottawa Heart Institute, 40 Ruskin Street, Ottawa, ON K1Y 4W7, Canada
| | - Bing S. Huang
- Hypertension Unit, University of Ottawa Heart Institute, 40 Ruskin Street, Ottawa, ON K1Y 4W7, Canada
| | - Frans H.H. Leenen
- Hypertension Unit, University of Ottawa Heart Institute, 40 Ruskin Street, Ottawa, ON K1Y 4W7, Canada
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Ramesh ST, Asad M, Dhamanigi SS, Prasad VS. Effect of central administration of ondansetron, a 5-hydroxytryptamine-3 receptor antagonist on gastric and duodenal ulcers. Fundam Clin Pharmacol 2009; 23:303-9. [DOI: 10.1111/j.1472-8206.2009.00668.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Huang BS, Leenen FHH. The brain renin-angiotensin-aldosterone system: A major mechanism for sympathetic hyperactivity and left ventricular remodeling and dysfunction after myocardial infarction. Curr Heart Fail Rep 2009; 6:81-8. [DOI: 10.1007/s11897-009-0013-9] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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Kent MAH, Huang BS, Van Huysse JW, Leenen FHH. Brain Na+,K+-ATPase isozyme activity and protein expression in ouabain-induced hypertension. Brain Res 2004; 1018:171-80. [PMID: 15276875 DOI: 10.1016/j.brainres.2004.05.059] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/25/2004] [Indexed: 10/26/2022]
Abstract
In normotensive rats, chronic infusion of exogenous ouabain causes hypertension involving central mechanisms. To determine whether ouabain-induced hypertension is associated with specific changes in brain Na+,K+-ATPase activity and expression, we assessed brain Na+,K+-ATPase isozyme activity and protein expression in rats treated with ouabain (50 microg/day s.c. or 10 microg/day i.c.v. for 14 days). Resting mean arterial pressure (MAP) was higher in s.c.- and i.c.v.-ouabain-treated animals vs. control (124+/-2 vs. 105+/-2 and 130+/-2 vs. 109+/-2, respectively, p<0.01). Ouabain infused s.c. or i.c.v. for 14 days had no effect on Na+,K+-ATPase isozyme activity in hypothalamic, pontine/medullary or cortical microsomes. However, the percent increase in total Na+,K+-ATPase activity produced in vitro by antibody Fab fragments that bind ouabain with high affinity (Digibind) was two-fold greater in s.c.- and i.c.v.-ouabain-treated rats vs. control, but only in hypothalamic microsomes. Thus, ouabain infused s.c. or i.c.v. does appear to directly inhibit Na+,K+-ATPase activity in the hypothalamus. On the other hand, in the hypothalamus, s.c.- and i.c.v.-ouabain infusions tended to increase alpha3 (by 30-44%), but had no effect on alpha1 or alpha2 Na+,K+-ATPase isozyme protein expression. In addition, ouabain was found to partially dissociate from the Na+,K+-ATPase enzyme following sample processing. Thus, the inability to detect a decrease in enzyme activity in the hypothalamus in response to ouabain may be due, in part, to an increase in enzyme expression and the dissociation of ouabain during sample processing.
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Affiliation(s)
- Mary-Anne H Kent
- Hypertension Unit, University of Ottawa Heart Institute, 40 Ruskin Street, Ottawa, Ontario, Canada K1Y 4W7
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Pullen MA, Brooks DP, Edwards RM. Characterization of the neutralizing activity of digoxin-specific Fab toward ouabain-like steroids. J Pharmacol Exp Ther 2004; 310:319-25. [PMID: 14982968 DOI: 10.1124/jpet.104.065250] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Digoxin-specific Fab (Digibind) is a mixture of antidigoxin Fab fragments prepared from sheep sera and is used as a treatment for digoxin poisoning. Digoxin-specific Fab has been shown to neutralize an endogenous Na+/K+ ATPase inhibitor (endogenous digoxin-like Na+/K+ ATPase regulatory factor; EDLF) in rats and humans and to lower blood pressure. Although the exact structure of EDLF is unknown, compounds identical to or structurally related to ouabain, bufalin, and marinobufagenin have been detected in mammalian plasma. In this study, some structural characteristics of EDLF were inferred from the ability of digoxin-specific Fab to neutralize the Na+/K+ ATPase inhibitory activity of several known cardenolides and bufodienolides. Additional structural information was obtained from [3H]ouabain binding and enzyme-linked immunosorbent assay experiments. Digoxin-specific Fab had the ability to interact to some extent with all of the cardenolides and bufodienolides tested. However, digoxin-specific Fab was more than 20-fold more potent in neutralizing ouabain and bufalin than marinobufagenin. The antihypertensive effect of digoxin-specific Fab seen in preeclampsia and animal models of hypertension may therefore be due to a molecule identical to or structurally similar to ouabain or bufalin.
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Affiliation(s)
- Mark A Pullen
- Department of Renal Biology, GlaxoSmithKline Pharmaceuticals, King of Prussia, Pennsylvania, USA.
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Yamazato M, Sakima A, Nakazato J, Sesoko S, Muratani H, Fukiyama K. Hypotensive and sedative effects of clonidine injected into the rostral ventrolateral medulla of conscious rats. Am J Physiol Regul Integr Comp Physiol 2001; 281:R1868-76. [PMID: 11705772 DOI: 10.1152/ajpregu.2001.281.6.r1868] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We examined the effects of clonidine injected unilaterally into the rostral ventrolateral medulla (RVLM) of conscious, unrestrained rats. We also examined whether the local alpha(2)-adrenoceptor mechanism contributed to the action of clonidine injected into the RVLM. Injection of clonidine but not vehicle solution significantly decreased the mean arterial pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA) in conscious, unrestrained rats as well as in propofol-anesthetized rats. The frequency of natural behavior was significantly lower after clonidine injection than after vehicle injection. The depressor and sympathoinhibitory responses were significantly larger in the propofol-anesthetized rats than in the conscious rats. Coinjection of a selective alpha(2)-adrenoceptor antagonist, 2-methoxyidazoxan, with clonidine into the RVLM significantly attenuated the depressor, bradycardiac, sympathoinhibitory, and sedative effects of clonidine injected alone. In conclusion, clonidine injected into the RVLM decreased MAP, HR, and RSNA and caused sedation in conscious, unrestrained rats. The action of clonidine in the RVLM was at least partly mediated by alpha(2)-adrenoceptor mechanisms.
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Affiliation(s)
- M Yamazato
- Third Department of Internal Medicine, University of the Ryukyus School of Medicine, 207 Uehara, Okinawa 903-0215, Japan.
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Cargnelli G, Trevisi L, Debetto P, Luciani S, Bova S. Effect of long-term ouabain treatment on contractile responses of rat aortae. J Cardiovasc Pharmacol 2000; 35:538-42. [PMID: 10774782 DOI: 10.1097/00005344-200004000-00004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Male Sprague-Dawley rats were infused with 50 microg/kg/day of ouabain for 4 weeks to address the question whether prolonged exposure to the drug affects blood pressure, the in vitro contractile responses to agonists and high K+ of their aortae, and the influence of endothelium on these responses. Systolic blood pressure was not affected by ouabain treatment. The responsiveness of endothelium-intact aortae from ouabain-treated rats to endothelin-1 increased, that to phenylephrine decreased, and that to high K+ was unchanged, as compared with control. The responses of endothelium-free aortae to endothelin-1, phenylephrine, and high K+ were lower in ouabain-treated than in control rats. The removal of endothelium increased the response to phenylephrine and decreased that to high K+ in either control or ouabain-treated rat aortae, whereas it did not affect the response to endothelin-1 in control rat aortae and decreased it in ouabain-treated rat aortae. The response to caffeine was unaffected by either ouabain treatment or endothelium removal. Thus rat ouabain long-term treatment induces opposing effects on the responsiveness of their intact aortae to an alpha-adrenergic agonist and endothelin-1. If these effects observed in the ex vivo experiments occur also in vivo on rat microvasculature, they could balance out and contribute to the lack of effect on systolic blood pressure of prolonged ouabain treatment.
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Affiliation(s)
- G Cargnelli
- Department of Pharmacology, University of Padova, Italy
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15
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Huang BS, Yuan B, Leenen FHH. Chronic blockade of brain "ouabain" prevents sympathetic hyper-reactivity and impairment of acute baroreflex resetting in rats with congestive heart failure. Can J Physiol Pharmacol 1999. [DOI: 10.1139/y99-115] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In rats with congestive heart failure (CHF) post myocardial infarction (MI) acute blockade of brain "ouabain" reverses sympathetic hyperactivity and chronic blockade prevents the desensitization of baroreflex function. This study was conducted to determine: i) if chronic blockade of brain "ouabain" maintains normal sympathetic reactivity; andii) if acute baroreflex resetting (another parameter of baroreflex function) also becomes impaired, and if so, does brain "ouabain" contribute to impairment in acute baroreflex resetting. CHF post MI was induced by acute coronary artery ligation in Wistar rats. Animals were treated with 200 µg·day-1 i.c.v. or i.v. Fab fragments (which bind brain "ouabain" with high affinity), or treated with 200 µg·day-1 i.c.v. gamma-globulins (control group). The length of treatment was 0.5-8 weeks or 4-8 weeks post MI. At 8 weeks mean arterial pressure (MAP), central venous pressure (CVP), heart rate (HR), and renal sympathetic nerve activity (RSNA) were recorded in concious rats at rest and in response to: i) air-jet stress, ii) i.c.v. guanabenz (an α2-adrenoceptor agonist), and iii) a 30 min i.v. infusion of nitroprusside (NP). Excitatory responses to air stress and inhibitory responses to guanabenz of MAP, HR, and RSNA were significantly enhanced in rats with CHF versus the sham-operated treated group. This enhancement was prevented in the CHF group treated with i.c.v., but not i.v., Fab. Nitroprusside induced a sustained decrease in MAP (~ 25 mmHg) and a transient decrease in CVP. Heart rate and RSNA increased significantly within 1 min of beginning the infusion. The peak increases as well as the product of changes in MAP-HR and RSNA-HR were significantly smaller in rats with CHF treated with gamma-globulins versus sham rats and versus CHF rats treated with i.c.v. Fab. In sham-operated rats and CHF rats treated with i.c.v. Fab, RSNA and HR began to decrease within 3-4 min of beginning the NP infusion and had returned to baseline by 20 min. In contrast, RSNA and HR remained increased throughout the infusion in the CHF rats treated with gamma-globulins. These data indicate that in rats with CHF acute resetting of the arterial baroreflex in response to a lower BP becomes impaired, and chronic blockade of brain "ouabain" prevents both this change in baroreflex resetting as well as sympathetic hyperactivity.Key words: heart failure, acute baroreflex resetting, sympathetic hyperactivity, nitroprusside.
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Bagrov YY, Dmitrieva NI, Manusova NB, Zvartau EE, Patkina NA, Bagrov AY. Involvement of endogenous digitalis-like factors in voluntary selection of alcohol by rats. Life Sci 1999; 64:PL219-25. [PMID: 10350362 DOI: 10.1016/s0024-3205(99)00131-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
This study tested the hypothesis that endogenous digitalis-like factor (DLF) is involved in the development of alcohol dependence in rats. In 33 male Wistar rats in conditioned place preference (CPP) experiment, ethanol evoked increase in time spent in the ethanol-associated compartment (702+/-82 in ethanol-treated vs. 426+/-86 sec in the controls). Digoxin pretreatment (125 microg/kg, i/p) did not affect the time spent in the water-associated compartment (476+/-80 sec), but prevented the acquisition of ethanol CPP (385+/-112 sec in ethanol-paired side, P<0.05). In a two bottle choice test, where rats (n=6 per group) chose between drinking water and 9% ethanol, immunization against two putative DLFs, marinobufagenin and ouabain (MBG and OLC) resulted in a 60% increase of ethanol consumption. Acute intragastric administration of 9% ethanol to the rats was associated with increased OLC in cerebrospinal fluid, and stimulated urinary excretion of MBG and OLC. Thus, in rats, digoxin, which mimics the effects of DLFs, suppresses the free choice of alcohol, while immunization against DLFs is associated with alcohol seeking behavior.
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Affiliation(s)
- Y Y Bagrov
- Laboratory of Membrane Barrier Functions, Sechenov Institute of Evolutionary Physiology and Biochemistry, St. Petersburg, Russia
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Blaustein MP, Juhaszova M, Golovina VA. The cellular mechanism of action of cardiotonic steroids: a new hypothesis. Clin Exp Hypertens 1998; 20:691-703. [PMID: 9682925 DOI: 10.3109/10641969809053247] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Arterial smooth muscle (ASM) contraction is triggered by agonist-evoked Ca2+ mobilization from sarcoplasmic reticulum (SR). The amount of Ca2+ released, and thus, the magnitude of the contractions, depends directly on SR Ca2+ content. Na+ pump inhibition by cardiotonic steroids (CTS) indirectly increases the Ca2+ content of the SR and, thus, contractility. This sequence of events does not, however, account for the multiple Na+ pump alpha subunit isoforms with different affinities for Na+ and for CTS, nor does it explain the cardiotonic and vasotonic effects of low doses of CTS that do not elevate cytosolic Na+ or Ca2+. We show that the Na+ pump high ouabain affinity (alpha3) isoform and the plasmalemmal (PM) Na/Ca exchanger are confined to PM domains that overlie junctional SR in ASM, while low ouabain affinity alpha1 and the PM Ca2+ pump are uniformly distributed in the PM. Thus, low doses of CTS, including an endogenous ouabain-like compound, influence cytosolic Na+ and (indirectly) Ca2+ concentrations only in the cytoplasmic clefts between the PM and junctional SR (a functional unit we call the "plasmerosome"). In turn, this modulates the Ca2+ content of the junctional SR and cell responsiveness.
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Affiliation(s)
- M P Blaustein
- Department of Physiology, University of Maryland School of Medicine, Baltimore 21201, USA
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Van Huysse JW, Leenen FH. Role of endogenous brain "ouabain" in the sympathoexcitatory and pressor effects of sodium. Clin Exp Hypertens 1998; 20:657-67. [PMID: 9682921 DOI: 10.3109/10641969809053243] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Endogenous cardiac glycoside inhibitors of the Na, K-ATPase (called "ouabain" here) with structures similar to plant ouabain have been isolated in several tissues, including the adrenal cortex and the brain. Recent studies have demonstrated that "ouabain" in the anteroventral third ventricle (AV3V) region of the hypothalamus mediates the sympathoexcitatory and pressor responses to a high sodium diet in Dahl salt-sensitive (Dahl-S) and spontaneously hypertensive (SHR) rats. Although the mechanisms regulating the biosynthesis, release and deactivation of CNS "ouabain" remain unknown, the discovery of the importance of brain "ouabain" in cardiovascular regulation creates a novel path for the development of antihypertensive pharmacopeia.
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Affiliation(s)
- J W Van Huysse
- Department of Medicine, University of Ottawa Heart Institute, Ontario
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Abstract
Accumulated evidence has suggested that several sodium pump inhibitors, similar to cardiotonic steroids, are present in the human body. Ouabain-like factor, the most appealing candidate, has been found to be increased with high sodium intake and hypervolaemia, and in essential hypertension, mineralocorticoid hypertension, and pregnancy-induced hypertension. Furthermore, blocking the action of ouabain-like factor with digibind or a novel anti-ouabain agent lowers blood pressure in several models of hypertension. Several important questions remain, however, before it can be concluded that ouabain-like factor is indeed involved in the regulation of sodium homeostasis and blood pressure.
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Affiliation(s)
- A Goto
- Second Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Japan.
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