Article

Chronic ouabain treatment induces vasa recta endothelial dysfunction in the rat

Department of Medicine, UMMS, Baltimore, MD 21201, USA.
American journal of physiology. Renal physiology (Impact Factor: 3.3). 11/2008; 296(1):F98-F106. DOI: 10.1152/ajprenal.90429.2008
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ABSTRACT Descending vasa recta (DVR) are 15-microm vessels that perfuse the renal medulla. Ouabain has been shown to augment DVR endothelial cytoplasmic Ca(2+) ([Ca(2+)](CYT)) signaling. In this study, we examined the expression of the ouabain-sensitive Na-K-ATPase alpha2 subunit in the rat renal vasculature and tested effects of acute ouabain exposure and chronic ouabain treatment on DVR. Immunostaining with antibodies directed against the alpha2 subunit verified its expression in both DVR pericytes and endothelium. Acute application of ouabain (100 or 500 nM) augmented the DVR nitric oxide generation stimulated by acetylcholine (ACh; 10 microM). At a concentration of 1 mM, ouabain constricted microperfused DVR, whereas at 100 nM, it was without effect. Acute ouabain (100 nM) did not augment constriction by angiotensin II (0.5 or 10 nM), whereas l-nitroarginine methyl ester-induced contraction of DVR was slightly enhanced. Ouabain-hypertensive (OH) rats were generated by chronic ouabain treatment (30 microg.kg(-1).day(-1), 5 wk). The acute endothelial [Ca(2+)](CYT) elevation by ouabain (100 nM) was absent in DVR endothelia of OH rats. The [Ca(2+)](CYT) response to 10 nM ACh was also eliminated, whereas the response to 10 microM ACh was not. The endothelial [Ca(2+)](CYT) response to bradykinin (100 nM) was significantly attenuated. We conclude that endothelial responses may offset the ability of acute ouabain exposure to enhance DVR vasoconstriction. Chronic exposure to ouabain, in vivo, leads to hypertension and DVR endothelial dysfunction, manifested as reduced [Ca(2+)](CYT) responses to both ouabain- and endothelium-dependent vasodilators.

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    • "Ouabain also stimulated the release of acetylcholine [42]–[43] and natriuretic peptides [44]. It has been proposed that ouabain-induced endothelial dysfunction could represent a crucial step in the evolution of ouabain-induced hypertension [39]. We confirmed the downregulation of nitric oxide synthase 1 and 3 gene expression in the aorta, which is a standard response to high salt intake; however, the unchanged expression of nitric oxide synthase genes in the mesenteric arteries and the normal plasma levels of cGMP suggest that there was no significant widespread damaging effect of ouabain on the endothelium. "
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    ABSTRACT: Ouabain is a cardiac glycoside produced in the adrenal glands and hypothalamus. It affects the function of all cells by binding to Na+/K+-ATPase. Several lines of evidence suggest that endogenous ouabain could be involved in the pathogenesis of essential (particularly, salt-sensitive) hypertension. However, information regarding the postulated hypertensive effect of the long-term administration of low-dose exogenous ouabain is inconsistent. This study was designed to help settle this controversy through the use of telemetric monitoring of arterial blood pressure and to elucidate the ouabain-induced alterations that could either promote or prevent hypertension. Ouabain (63 and 324 µg/kg/day) was administered subcutaneously to male Wistar rats. Radiotelemetry was used to monitor blood pressure, heart rate and measures of cardiovascular variability and baroreflex sensitivity. The continuous administration of ouabain for 3 months did not elevate arterial blood pressure. The low-frequency power of systolic pressure variability, urinary excretion of catecholamines, and cardiovascular response to restraint stress and a high-salt diet as well as the responsiveness to α1-adrenergic stimulation were all unaltered by ouabain administration, suggesting that the activity of the sympathetic nervous system was not increased. However, surrogate indices of cardiac vagal nerve activity based on heart rate variability were elevated. Molecular remodeling in mesenteric arteries that could support the development of hypertension (increased expression of the genes for the Na+/Ca2+ exchanger and Na+/K+-ATPase α2 isoform) was not evident. Instead, the plasma level of vasodilatory calcitonin gene-related peptide (CGRP) significantly rose from 55 (11, SD) in the control group to 89 (20, SD) pg/ml in the ouabain-treated rats (PTukey's = 18.10-5). These data show that long-term administration of exogenous ouabain does not necessarily cause hypertension in rodents. The augmented parasympathetic activity and elevated plasma level of CGRP could be linked to the missing hypertensive effect of ouabain administration.
    PLoS ONE 10/2014; 9(10):e108909. DOI:10.1371/journal.pone.0108909 · 3.23 Impact Factor
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    • "Ouabain also reduces nitric oxide signaling in the kidney [62], and shifts the pressure-natriuresis relationship rightward [40]. Thus, the combination of the vasopressor and renal effects of elevated circulating EO is expected to maintain a large portion of the elevated BP in Ang II hypertension. "
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    ABSTRACT: Central nervous system (CNS) administration of angiotensin II (Ang II) raises blood pressure (BP). The rise in BP reflects increased sympathetic outflow and a slower neuromodulatory pressor mechanism mediated by CNS mineralocorticoid receptors (MR). We investigated the hypothesis that the sustained phase of hypertension is associated also with elevated circulating levels of endogenous ouabain (EO), and chronic stimulation of arterial calcium transport proteins including the sodium-calcium exchanger (NCX1), the type 6 canonical transient receptor potential protein (TRPC6), and the sarcoplasmic reticulum calcium ATPase (SERCA2). Wistar rats received a chronic intra-cerebroventricular infusion of vehicle (C) or Ang II (A, 2.5 ng/min, for 14 days) alone or combined with the MR blocker, eplerenone (A+E, 5 µg/day), or the aldosterone synthase inhibitor, FAD286 (A+F, 25 µg/day). Conscious mean BP increased (P<0.05) in A (123±4 mm Hg) vs all other groups. Blood, pituitary and adrenal samples were taken for EO radioimmunoassay (RIA), and aortas for NCX1, TRPC6 and SERCA2 immunoblotting. Central infusion of Ang II raised plasma EO (0.58±0.08 vs C 0.34±0.07 nM (P<0.05), but not in A + E and A + F groups as confirmed by off-line liquid chromatography (LC)-RIA and LC-multistage mass spectrometry. Two novel isomers of EO were elevated by Ang II; the second less polar isomer increased >50-fold in the A+F group. Central Ang II increased arterial expression of NCX1, TRPC6 and SERCA2 (2.6, 1.75 and 3.7-fold, respectively; P<0.01)) but not when co-infused with E or F. Adrenal and pituitary EO were unchanged. We conclude that brain Ang II activates a CNS-humoral axis involving plasma EO. The elevated EO reprograms peripheral ion transport pathways known to control arterial Na+ and Ca2+ homeostasis; this increases contractility and augments sympathetic effects. The new axis likely contributes to the chronic pressor effect of brain Ang II.
    PLoS ONE 10/2014; 9(10):e108916. DOI:10.1371/journal.pone.0108916 · 3.23 Impact Factor
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    • "Além do mais, recentemente, Cao et al. (2009) demonstraram que o tratamento crônico com ouabaína por 5 semanas promove disfunção endotelial na " vasa recta " de rins de ratos. Estes resultados sugerem que a exposição crônica à ouabaína poderia promover uma redução do fluxo sanguíneo medular, geralmente associado com retenção de sódio e hipertensão (Cao et al., 2009). O grupo da Dra. "
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    ABSTRACT: Na+K+-ATPase (NKA) is an integral membrane protein that participates in transport mechanisms along renal tubules for sodium reabsorption and other substrates. Its known that ouabain (OUA) administration, a NKA inhibitor, induces hypertension in Wistar rats. However, the role of kidneys in this model of hypertension is not elucidated. So, the aim of this study was to evaluate the possibles alterations in renal function induced by chronic treatment with OUA by 5 or 20 weeks. Chronic treatment with OUA induced hypertension in a similar magnitude in both experimental groups. Moreover, OUA administration was able to increase water intake, urinary flow, and protein expression of 1 isoform of NKA. However, OUA treatment did not alter significantly the glomerular filtration rate, likewise the fractional excretion of Na+ and K+. In summary, chronic OUA treatment induces mild hypertension independent of the period of administration, but the kidneys dont play an important role in the hypertensive process in this model of hypertension. A Na+K+-ATPase (NKA) é uma proteína de membrana que participa de mecanismos de transporte nos túbulos renais para a reabsorção de sódio e outros substratos. Sabe-se que a administração de ouabaína (OUA), um inibidor da NKA, induz hipertensão arterial em ratos. No entanto, o papel dos rins nesse modelo de hipertensão não está bem elucidado. Desta forma, o objetivo do presente estudo foi avaliar as possíveis alterações na função renal induzidas pelo tratamento crônico com OUA por 5 ou 20 semanas. Sendo assim, foi observado que o tratamento com OUA promoveu hipertensão de mesma magnitude nos dois grupos avaliados. Além disso, a administração de OUA induziu o aumento da ingestão de água, do fluxo urinário e da expressão protéica da isoforma 1 da NKA. Porém, não foi capaz de alterar de maneira significativa o ritmo de filtração glomerular, assim como a fração de excreção de Na+ e K+. Pode-se concluir que, o tratamento crônico com OUA induz hipertensão, porém parece que os rins não contribuem de forma importante para o processo hipertensivo neste modelo de hipertensão.
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