Ouabain inhibits p38 activation in mice neutrophils.

Ouabain is a cardiac steroid hormone with immunomodulatory effects. It inhibits neutrophils migration induced by different stimuli, but little is known about the mechanisms involved in this effect. Thus, the aim of this study was to evaluate the ouabain effect on chemotactic signaling pathways in neutrophils. For that, mice neutrophils were isolated from bone marrow, treated with ouabain (1, 10, and 100 nM) for 2 h, submitted to transwell chemotaxis assay and flow cytometry analysis of Akt, ERK, JNK, and p38 phosphorylation induced by zymosan. Ouabain treatment (1, 10 and, 100 nM) reduces neutrophil chemotaxis induced by chemotactic peptide fMLP, but this substance did not inhibit Akt, ERK, and JNK activation induced by zymosan. However, ouabain (1 and 10 nM) reduced p38 phosphorylation in zymosan-stimulated neutrophils. These results suggest that ouabain may interfere in neutrophil migration through p38 MAPK inhibition.

Tamoxifen has an anti-manic effect but not protect the brain against oxidative stress in an animal model of mania induced by ouabain.

Studies have suggested the involvement of oxidative stress in the physiopathology of bipolar disorder. Preclinical data have shown that PKC inhibitors may act as mood-stabilizing agents and protect the brain in animal models of mania. The present study aimed to evaluate the effects of Lithium (Li) or tamoxifen (TMX) on behavioral changes and oxidative stress parameters in an animal model of mania induced by ouabain (OUA). Wistar rats received a single intracerebroventricular (ICV) injection of OUA or artificial cerebrospinal fluid (ACSF). From the day following ICV injection, the rats were treated for seven days with intraperitoneal injections of saline, Li or TMX twice a day. On the 7th day after OUA injection, locomotor activity was measured using the open-field test, and the oxidative stress parameters were evaluated in the hippocampus and frontal cortex of rats. The results showed that OUA induced hyperactivity in rats, which is considered a manic-like behavior. Also, OUA increased lipid peroxidation and oxidative damage to proteins, as well as causing alterations to antioxidant enzymes in the frontal cortex and hippocampus of rats. The Li or TMX treatment reversed the manic-like behavior induced by OUA. Besides, Li, but not TMX, reversed the oxidative damage caused by OUA. These results suggest that the manic-like effects induced by OUA and the antimanic effects of TMX seem not to be related to the oxidative stress.

Ouabain attenuates the oxidative stress induced by lipopolysaccharides in the cerebellum of rats.

Our study aimed to analyze the effect of ouabain administration on lipopolysaccharide (LPS)-induced changes in oxidative parameters, membrane lipid composition, and the activities of some important enzymes of the nervous system. The content of phospholipids, cholesterol, and gangliosides were analyzed in Wistar rats after intraperitoneal injection of ouabain (1.8 µg/kg), LPS (200 µg/kg), or saline. Oxidative parameters were also evaluated, including the activities of superoxide dismutase, catalase and glutathione peroxidase, the levels of glutathione and lipid peroxidation, as well as Na,K-ATPase activity and the level of glutamate transporter EAAT4. Administration of LPS resulted in increased oxidative stress, as evidenced by an increase in lipid peroxidation levels, glutathione peroxidase activity, decreased catalase activity and reduced glutathione levels. All changes recorded were attenuated by pretreatment with ouabain. Administration of ouabain plus LPS enhanced the total ganglioside content and EAAT4 levels, but failed to alter the Na,K-ATPase activity. Our data suggest a neuroprotective effect of ouabain against LPS-induced oxidative stress by promoting membrane lipid remodeling and increasing the expression of glutamate transporter EAAT4. Our results emphasize that the observed oxidative stress is not correlated with Na,K-ATPase, but with a possible ouabain-mediated effect on cellular signaling. The relevance of our results extends beyond LPS-induced changes in oxidative parameters, as nanomolar doses of ouabain might prove useful in neurodegenerative models. Further study of other cardenolides and related molecules, as well as the development of new molecules derived from ouabain, could also prove useful in the fight against the oxidative and/or general cell stress triggered by neuronal pathologies.

Evaluation of Se-phenyl-thiazolidine-4-carboselenoate protective activity against oxidative and behavioral stress in the maniac model induced by ouabain in male rats.

This study investigates Se-phenyl-thiazolidine-4-carboselenoate (Se-PTC) protective activity against oxidative and behavioral stress in the model of mania induced by ouabain (OUA) in male rats. The compound used was Se-PTC (50mg/kg) and the positive control LiCl (45mg/kg) was administered for intragastric route (i.g.) 30min prior to administration of OUA (10-5M). OUA was dissolved in artificial cerebrospinal fluid (aCSF) and administered at the 5µl through an intracerebroventricular (i.c.v) cannula. The pretreatment with Se-PTC was effective in preventing the increase in locomotor activity induced by OUA, however the positive control LiCl is capable to block crossing augmentation induced by OUA. Na+/K+-ATPase activity was significantly reduced in OUA group and the Se-PTC to normalize Na+/K+-ATPase activity. Pretreatment with Se-PTC protect against the increase in catalase activity and thiobarbituric acid reactive species (TBARS) content in the brain caused by OUA. Therefore, Se-PTC is effective against OUA-induced hyperactivity and alterations in brain oxidative status of rats.

The trophic effect of ouabain on retinal ganglion cells is mediated by IL-1ß and TNF-α.

Ouabain is a steroid hormone that binds to the enzyme Na(+), K(+) - ATPase and stimulates different intracellular pathways controlling growth, proliferation and cell survival. IL-1ß and TNF-α are pleiotropic molecules, conventionally regarded as pro-inflammatory cytokines with well-known effects in the immune system. In addition, IL-1ß and TNF-α also play important roles in the nervous system including neuroprotective effects. Previous data from our group showed that ouabain treatment is able to induce an increase in retinal ganglion cell survival kept in mixed retinal cell cultures. The aim of this work was to investigate if IL-1ß and TNF-α could be mediating the trophic effect of ouabain on retinal ganglion cells. Our results show that the trophic effect of ouabain on retinal ganglion cell was inhibited by either anti-IL-1ß or anti-TNF-α antibodies. In agreement, IL-1ß or TNF-α increased the retinal ganglion cells survival in a dose-dependent manner. Accordingly, ouabain treatment induces a temporal release of TNF-α and IL-1ß from retinal cell cultures. Interestingly, TNF-α and IL-1ß regulate each other intracellular levels. Our results suggest that ouabain treatment triggers the activation of TNF-α and IL-1ß signaling pathways leading to an increase in retinal ganglion cell survival.

Ouabain induces nitric oxide release by a PI3K/Akt-dependent pathway in isolated aortic rings from rats with heart failure.

BACKGROUND: Ouabain occurs in nanomolar concentrations in myocardial infarction and heart failure (HF). However, the effects of ouabain in vascular function in HF conditions were not investigated yet. Therefore, we analyzed the effects of acute administration of 3 nM ouabain in isolated aortic rings from rats with HF 4 weeks after myocardial infarction. METHODS AND RESULTS: Rats were submitted to sham operation or coronary artery occlusion. In HF rats, left ventricular positive and negative derivatives of intraventricular pressure reduced and left ventricular end diastolic pressure increased. Phenylephrine responses increased in HF rings when compared with controls. Ouabain incubation for 45 minutes reduced phenylephrine-induced contraction in both groups. Endothelial removal increased more phenylephrine response in ouabain-treated rings of sham rats. Ouabain potentiated the effect of L-NAME in both groups but more in sham rats. Wortmannin increased the phenylephrine response only in HF rings. The effect of tetraethylammonium was potentiated by ouabain only in HF rings. Ouabain increased phenylephrine-stimulated nitric oxide production in rings from both groups but increased the activation of Akt only in vessels from HF rats. CONCLUSIONS: Results demonstrate that low ouabain concentration can decrease vascular reactivity of aortic rings from HF rats. Ouabain was able to increase nitric oxide production in HF rats by triggering a signal transduction PI3K/Akt-dependent pathway and increasing an endothelium-hyperpolarizing factor release.

Signaling function of Na,K-ATPase induced by ouabain against LPS as an inflammation model in hippocampus.

BACKGROUND: Ouabain (OUA) is a newly recognized hormone that is synthesized in the adrenal cortex and hypothalamus. Low doses of OUA can activate a signaling pathway by interaction with Na,K-ATPase, which is protective against a number of insults. OUA has central and peripheral anti-inflammatory effects. Lipopolysaccharide (LPS), via toll-like receptor 4 activation, is a widely used model to induce systemic inflammation. This study used a low OUA dose to evaluate its effects on inflammation induced by LPS injection in rats. METHODS: Adult male Wistar rats received acute intraperitoneal (ip) OUA (1.8 µg/kg) or saline 20 minutes before LPS (200 µg/kg, ip) or saline injection. Some of the animals had their femoral artery catheterized in order to assess arterial blood pressure values before and after OUA administration. Na,K-ATPase activity, cytokine mRNA levels, apoptosis-related proteins, NF-κB activation brain-derived neurotrophic factor BDNF, corticosterone and TNF-α levels were measured. RESULTS: OUA pretreatment decreased mRNA levels of the pro-inflammatory cytokines, inducible nitric oxide synthase (iNOS) and IL-1ß, which are activated by LPS in the hippocampus, but with no effect on serum measures of these factors. None of these OUA effects were linked to Na,K-ATPase activity. The involvement of the inflammatory transcription factor NF-κB in the OUA effect was indicated by its prevention of LPS-induced nuclear translocation of the NF-κB subunit, RELA (p65), as well as the decreased cytosol levels of the NF-κB inhibitor, IKB, in the hippocampus. OUA pretreatment reversed the LPS-induced glial fibrillary acidic protein (GFAP) activation and associated inflammation in the dentate gyrus. OUA also prevented LPS-induced increases in the hippocampal Bax/Bcl2 ratio suggesting an anti-apoptotic action in the brain. CONCLUSION: Our results suggest that a low dose of OUA has an important anti-inflammatory effect in the rat hippocampus. This effect was associated with decreased GFAP induction by LPS in the dentate gyrus, a brain area linked to adult neurogenesis.

Immunomodulatory activity of ouabain in Leishmania leishmania amazonensis-infected Swiss mice.

Ouabain is a cardiotonic steroid identified as an endogenous substance of human plasma, being produced by the adrenal, pituitary, and hypothalamus. Despite the studies demonstrating the ability of ouabain to modulate inflammation and other aspects of the immune response, the effects of this substance in Leishmaniasis is unknown. The purpose of this work was to understand the immunomodulatory activity of ouabain in experimental Leishmaniasis in Swiss mice. It was demonstrated that ouabain reduced total cell numbers in the peritoneal cavity as a reflex of the inhibition of neutrophil migration induced by Leishmania (L.) Amazonensis. Furthermore, ouabain reduced TNF-α and IFN-γ levels, without cytotoxicity against peritoneal macrophages. These data showed the anti-inflammatory role of ouabain in the early events of the immune response triggered by Leishmania (L.) Amazonensis infection in murine model.

Decreased BDNF levels in amygdala and hippocampus after intracerebroventricular administration of ouabain / Diminuição dos níveis de BDNF em amígdala e hipocampo após a administração intracerebroventricular de ouabaína

OBJECTIVE: The present study aims to investigate the effects of ouabain intracerebroventricular injection on BDNF levels in the amygdala and hippocampus of Wistar rats.METHODS: Animals received a single intracerebroventricular injection of ouabain (10-3 and 10-2 M) or artificial cerebrospinal fluid and immediately, 1h, 24h, or seven days after injection, BDNF levels were measured in the rat's amygdala and hippocampus by sandwich-ELISA (n = 8 animals per group).RESULTS: When evaluated immediately, 3h, or 24h after injection, ouabain in doses of 10-2 and 10-3 M does not alter BDNF levels in the amygdala and hippocampus. However, when evaluated seven days after injection, ouabain in 10-2 and 10-3 M, showed a significant reduction in BDNF levels in both brain regions evaluated.DISCUSSION: In conclusion, we propose that the ouabain decreased BDNF levels in the hippocampus and amygdala when assessed seven days after administration, supporting the Na/K ATPase hypothesis for bipolar illness.

OBJETIVO: O presente estudo tem como objetivo investigar os efeitos da injeção intracerebroventricular de ouabaína sobre os níveis de BDNF na amígdala e no hipocampo de ratos Wistar.MÉTODOS: Os animais receberam uma única injeção intracerebroventricular de ouabaína (10-3 and 10-2 M) ou fluido cerebroespinhal artificial e, imediatamente, 3h, 24h ou sete dias após a injeção, os níveis de BDNF foram mensurados na amígdala e hipocampo dos ratos por ELISA sandwich (n = 8 animais por grupo).RESULTADOS: Quando avaliados imediatamente após a injeção, 3h ou 24h, ouabaína nas doses 10-2 e 10-3 M não alterou os níveis de BDNF em ambas as estruturas avaliadas. Entretanto, quando avaliados sete dias após a injeção, ouabaína nas doses 10-2 e 10-3 M mostrou uma significante redução nos níveis de BDNF em amígdala e hipocampo.CONCLUSÃO: Em conclusão, propõe-se que a administração de ouabaína diminuiu os níveis de BDNF em amígdala e hipocampo quando avaliados sete dias após a injeção, suportando a hipótese da participação da Na/K ATPase no transtorno bipolar.

Hypertensive effects of the iv administration of picomoles of ouabain.

Ouabain, an endogenous digitalis compound, has been detected in nanomolar concentrations in the plasma of several mammals and is associated with the development of hypertension. In addition, plasma ouabain is increased in several hypertension models, and the acute or chronic administration of ouabain increases blood pressure in rodents. These results suggest a possible association between ouabain and the genesis or development and maintenance of arterial hypertension. One explanation for this association is that ouabain binds to the α-subunit of the Na(+) pump, inhibiting its activity. Inhibition of this pump increases intracellular Na(+), which reduces the activity of the sarcolemmal Na(+)/Ca(2+) exchanger and thereby reduces Ca(2+) extrusion. Consequently, intracellular Ca(2+) increases and is taken up by the sarcoplasmic reticulum, which, upon activation, releases more calcium and increases the vascular smooth muscle tone. In fact, acute treatment with ouabain enhances the vascular reactivity to vasopressor agents, increases the release of norepinephrine from the perivascular adrenergic nerve endings and promotes increases in the activity of endothelial angiotensin-converting enzyme and the local synthesis of angiotensin II in the tail vascular bed. Additionally, the hypertension induced by ouabain has been associated with central mechanisms that increase sympathetic tone, subsequent to the activation of the cerebral renin-angiotensin system. Thus, the association with peripheral mechanisms and central mechanisms, mainly involving the renin-angiotensin system, may contribute to the acute effects of ouabain-induced elevation of arterial blood pressure.

Hypertensive effects of the iv administration of picomoles of ouabain

Ouabain, an endogenous digitalis compound, has been detected in nanomolar concentrations in the plasma of several mammals and is associated with the development of hypertension. In addition, plasma ouabain is increased in several hypertension models, and the acute or chronic administration of ouabain increases blood pressure in rodents. These results suggest a possible association between ouabain and the genesis or development and maintenance of arterial hypertension. One explanation for this association is that ouabain binds to the α-subunit of the Na+ pump, inhibiting its activity. Inhibition of this pump increases intracellular Na+, which reduces the activity of the sarcolemmal Na+/Ca2+ exchanger and thereby reduces Ca2+ extrusion. Consequently, intracellular Ca2+ increases and is taken up by the sarcoplasmic reticulum, which, upon activation, releases more calcium and increases the vascular smooth muscle tone. In fact, acute treatment with ouabain enhances the vascular reactivity to vasopressor agents, increases the release of norepinephrine from the perivascular adrenergic nerve endings and promotes increases in the activity of endothelial angiotensin-converting enzyme and the local synthesis of angiotensin II in the tail vascular bed. Additionally, the hypertension induced by ouabain has been associated with central mechanisms that increase sympathetic tone, subsequent to the activation of the cerebral renin-angiotensin system. Thus, the association with peripheral mechanisms and central mechanisms, mainly involving the renin-angiotensin system, may contribute to the acute effects of ouabain-induced elevation of arterial blood pressure.

Evaluation of citrate synthase activity in brain of rats submitted to an animal model of mania induced by ouabain.

Bipolar disorder (BD) is a psychiatric disorder characterized by alternating episodes of mania and depression. The intracerebroventricular (i.c.v) administration of ouabain (a Na(+)/K(+)-ATPase inhibitor) in rats has been used as an animal model of mania, because present face, construct and predictive validities. Several studies strongly suggest that mitochondrial dysfunction play a central role in the pathophysiology of BD. Citrate synthase (CS) is an enzyme localized in the mitochondrial matrix and represents one of the most important steps of Krebs cycle. The aim of this study was to investigate CS activity in brain of rats after the administration of ouabain. Adult male Wistar rats received a single i.c.v. administration of ouabain (10(-2) and 10(-3) M) or vehicle (control group). Locomotor activity was measured using the open field task. CS activity was measured in the brain of rats immediately (1 h) and 7 days after ouabain administration. Our results showed that spontaneous locomotion was increased 1 h after ouabain administration, and that the hyperlocomotion persists 7 days after the administration. Moreover, CS activity was inhibited immediately after the administration of ouabain in the prefrontal cortex at the doses of 10(-3) and 10(-2) M. This inhibition remains by 7 days after the administration of ouabain. On the other hand, it was not observed any difference in CS activity in the hippocampus and striatum. Considering that inhibition of CS activity may reflect a mitochondrial dysfunction, it is tempting to speculate that the reduction of brain energy metabolism might be related to the pathophysiology of BD.

Intracerebroventricular ouabain administration induces oxidative stress in the rat brain.

Intracerebroventricular (ICV) injection of ouabain (a potent Na(+)/K(+)-ATPase inhibitor) in rats resulted in manic-like effects. There is an emerging body of data indicating that major neuropsychiatric disorders, such as bipolar disorder and schizophrenia, are associated with increased oxidative stress. In this study, we investigated the effects of ICV ouabain injection on oxidative stress parameters in total tissue of rat brain. Our findings demonstrated that ICV injection increased thiobarbituric acid reactive species levels and protein carbonyl generation in the prefrontal cortex and hippocampus of rats. Moreover, the activity of the antioxidants enzymes catalase and superoxide dismutase was altered in several areas of the rat brain and cerebrospinal fluid of ICV ouabain-subjected rats. These results showed that Na(+)/K(+)-ATPase inhibition can lead to oxidative stress in the brain of rats.

Chronic ouabain treatment exacerbates blood pressure elevation in spontaneously hypertensive rats: the role of vascular mechanisms.

OBJECTIVE: Hypertensive rats are more sensitive to the pressor effects of acute ouabain than normotensive rats. We analyzed the effect of chronic ouabain (approximately 8.0 microg/day, 5 weeks) treatment on the blood pressure of spontaneously hypertensive rats (SHRs) and Wistar-Kyoto rats and the contribution of vascular mechanisms. METHODS: Responses to acetylcholine and phenylephrine were analyzed in isolated tail arteries. Protein expression of endothelial nitric oxide synthase and cyclooxygenase-2 (COX-2) were also investigated. RESULTS: Ouabain treatment enhanced blood pressure only in SHRs. The pD2 for acetylcholine was decreased in arteries from SHRs compared with Wistar-Kyoto rats, and ouabain did not change this parameter. However, ouabain was able to increase the pD2 to phenylephrine in SHRs. Nitric oxide synthase inhibition with NG-nitro-L-arginine methyl ester or potassium channel blockade by tetraetylamonium increased the response to phenylephrine in SHRs, with a smaller increase in response observed in ouabain-treated SHRs. In addition, indomethacin (a COX inhibitor) and ridogrel (a thromboxane A2 synthase inhibitor and prostaglandin H2/thromboxane A2 receptor antagonist) decreased contraction to phenylephrine in tail rings from ouabain-treated SHRs. Protein expression of endothelial nitric oxide synthase was unaltered following ouabain treatment in SHRs, whereas COX-2 expression was increased. CONCLUSION: Chronic ouabain treatment further increases the raised blood pressure of SHRs. This appears to involve a vascular mechanism, related to a reduced vasodilator influence of nitric oxide and endothelium-derived hyperpolarizing factor and increased production of vasoconstrictor prostanoids by COX-2. These data suggest that the increased plasma levels of ouabain could play an important role in the maintenance of hypertension and the impairment of endothelial function.

Intracerebroventricular administration of ouabain to rats changes the expression of NMDA receptor subunits in cerebral cortex and hippocampus.

Ouabain exerts neurotoxic action and activates the population of NMDA receptors. Herein the effect of ouabain on the expression of NMDA subunits was evaluated. Adult Wistar rats were administered intracerebroventricularly with 0.1, 10 and 100 nmol ouabain or saline solution (control). Two days later, membranes of cerebral cortex and hippocampus were isolated. Western blots with antibodies for the NMDA receptor subunits: NR1; NR2A; NR2B; NR2C and NR2D were carried out. In cerebral cortex, NR2D subunit increased 30% with 10 nmol ouabain dose. With 100 nmol ouabain, NR1 and NR2D subunits enhanced 40 and 20%, respectively. In hippocampus, with the dose of 0.1 nmol ouabain, NR1 subunit enhanced roughly 50% whereas NR2B subunit decreased 30%. After administration of 10 nmol ouabain dose, NR2A, NR2B and NR2C subunits decreased 40, 50 and 30%, respectively. With the dose of 100 nmol of ouabain, NR1, NR2A and NR2B subunits diminished 10-20%. It is concluded that ouabain administration led to a differential regulation in the expression of NMDA subunits. These results may be correlated with the modulatory action of ouabain on NMDA receptor.

Chronic ouabain treatment enhances cardiac myosin ATPase activity in rats.

1. Chronic ouabain administration increases blood pressure and produces a positive inotropic effect. However, the temporal changes capable of affecting both arterial and ventricular pressures and myosin ATPase activity during the induced hypertension have not been determined. 2. The aim of the present study was to investigate the time-course of the induction of hypertension to define when changes occur in Wistar rats treated with 25 mg/kg per day, s.c., ouabain for 3, 7, 15 or 30 days. 3. In anaesthetized rats, diastolic blood pressure increased after 7 days treatment with ouabain and after 15 and 30 days treatment, increases were observed in systolic blood pressure, left ventricular systolic pressure and myosin ATPase activity. After 15 days treatment, heart rate (HR) also increased, but after 30 days treatment HR returned to control levels. However, only after 30 days treatment did the left ventricular positive and negative first derivatives of intraventricular pressure (dP/dt(max) and dP/dt(min), respectively) increase. Increased arterial and left ventricular systolic pressures and myosin ATPase activity observed after 15 days treatment maintained similar levels as those after 30 days treatment. 4. The results suggest that changes in arterial and left ventricular pressures, HR and myosin ATPase activity induced by chronic ouabain treatment are time dependent, increasing after 15 days treatment. After 30 days treatment, the increase in systolic and diastolic arterial and ventricular pressures remained stable, as did inotropism. Normalization of HR after 30 days treatment suggests that during the period from Day 16 to Day 30 ouabain-induced hypertension is dependent, at least in part, on increased sympathetic activity.

Ouabain at nanomolar concentration promotes synthesis and release of angiotensin II from the endothelium of the tail vascular bed of spontaneously hypertensive rats.

The effects of 1 nM ouabain (OUA) on the contractile actions of phenylephrine (PHE, 0.001-100 microg) and functional activity of the sodium pump (NKA) in isolated-perfused tail vascular beds from WKY and SHR were investigated. In preparations from SHR, perfusion with OUA in the presence of endothelium (E+) increased the sensitivity (pED50) of PHE (before: 2.14 +/- 0.06 versus after: 2.47 +/- 0.07; P < 0.05) without altering the maximal response (Emax). After endothelial damage, OUA reduced the Emax of PHE in SHR (before: 350 +/- 29 versus after: 293 +/- 25 mm Hg; P < 0.05). In SHR/E+, pretreatment with losartan (10 microM) or enalaprilat (1 microM) prevented the increased sensitivity to PHE induced by OUA. OUA increased NKA activity in SHR/E+ (before: 45 +/- 6 versus after: 58 +/- 5%, P < 0.05). Losartan (10 mg/Kg, i.v.) also abolished the increment in systolic and diastolic blood pressure induced by OUA (0.18 microg/Kg, i.v.) in anesthetized SHR. OUA did not alter the actions of PHE in either anesthetized WKY rats or vascular preparations. Results suggest that 1 nM OUA increased the vascular reactivity to PHE only in SHR/E+. This effect is mediated by OUA-induced activation of endothelial angiotensin converting enzyme that promotes the local formation of angiotensin II, which sensitizes the vascular smooth muscle to the actions of PHE.

Effects of small doses of ouabain on the arterial blood pressure of anesthetized hypertensive and normotensive rats

Ouabain increases vascular resistance and may induce hypertension by inhibiting the Na+ pump. The effects of 0.18 and 18 æg/kg, and 1.8 mg/kg ouabain pretreatment on the phenylephrine (PHE; 0.1, 0.25 and 0.5 æg, in bolus)-evoked pressor responses were investigated using anesthetized normotensive (control and uninephrectomized) and hypertensive (1K1C and DOCA-salt treated) rats. Treatment with 18 æg/kg ouabain increased systolic and diastolic blood pressure in all groups studied. However, the magnitude of this increase was larger for the hypertensive 1K1C and DOCA-salt rats than for normotensive animals, while the pressor effect of 0.18 æg/kg ouabain was greater only in DOCA-salt rats. A very large dose (1.8 mg/kg) produced toxic effects on the normotensive control but not on uninephrectomized or 1K1C rats. Rat tail vascular beds were perfused to analyze the effects of 10 nM ouabain on the pressor response to PHE. In all animals, 10 nM ouabain increased the PHE pressor response, but this increase was larger in hypertensive DOCA-salt rats than in normotensive and 1K1C rats. Results suggested that a) increases in diastolic blood pressure induced by 18 æg/kg ouabain were larger in hypertensive than normotensive rats; b) in DOCA-salt rats, smaller ouabain doses had a stronger effect than in other groups; c) hypertensive and uninephrectomized rats were less sensitive to toxic doses of ouabain, and d) after treatment with 10 nM ouabain isolated tail vascular beds from DOCA-salt rats were more sensitive to the pressor effect of PHE than those from normotensive and 1K1C hypertensive rats. These data suggest that very small doses of ouabain, which might produce nanomolar plasma concentrations, enhance pressor reactivity in DOCA-salt hypertensive rats, supporting the idea that endogenous ouabain may contribute to the increase and maintenance of vascular tone in hypertension

Effects of small doses of ouabain on the arterial blood pressure of anesthetized hypertensive and normotensive rats.

Ouabain increases vascular resistance and may induce hypertension by inhibiting the Na+ pump. The effects of 0.18 and 18 microg/kg, and 1.8 mg/kg ouabain pretreatment on the phenylephrine (PHE; 0.1, 0.25 and 0.5 microg, in bolus)-evoked pressor responses were investigated using anesthetized normotensive (control and uninephrectomized) and hypertensive (1K1C and DOCA-salt treated) rats. Treatment with 18 microg/kg ouabain increased systolic and diastolic blood pressure in all groups studied. However, the magnitude of this increase was larger for the hypertensive 1K1C and DOCA-salt rats than for normotensive animals, while the pressor effect of 0.18 microg/kg ouabain was greater only in DOCA-salt rats. A very large dose (1.8 mg/kg) produced toxic effects on the normotensive control but not on uninephrectomized or 1K1C rats. Rat tail vascular beds were perfused to analyze the effects of 10 nM ouabain on the pressor response to PHE. In all animals, 10 nM ouabain increased the PHE pressor response, but this increase was larger in hypertensive DOCA-salt rats than in normotensive and 1K1C rats. Results suggested that a) increases in diastolic blood pressure induced by 18 microg/kg ouabain were larger in hypertensive than normotensive rats; b) in DOCA-salt rats, smaller ouabain doses had a stronger effect than in other groups; c) hypertensive and uninephrectomized rats were less sensitive to toxic doses of ouabain, and d) after treatment with 10 nM ouabain isolated tail vascular beds from DOCA-salt rats were more sensitive to the pressor effect of PHE than those from normotensive and 1K1C hypertensive rats. These data suggest that very small doses of ouabain, which might produce nanomolar plasma concentrations, enhance pressor reactivity in DOCA-salt hypertensive rats, supporting the idea that endogenous ouabain may contribute to the increase and maintenance of vascular tone in hypertension.

[The role of adenosine on the anti-arrhythmic action of digitalis glycosides]. / Papel de la adenosina sobre la acción antiarrítmica de los digitálicos.

UNLABELLED: The action of adenosine on atrial functional refractory period, as well as on its ability to interrupt atrial flutter is similar to that of digitalis. The latter suggests the possible existence of an adenilic component to digitalis action. To test this possibility, we measured the plasma concentrations of adenosine after ouabain infusion in dogs, and we investigated the effect of digitalis on atrial refractory period and on flutter in conditions of cholinergic inhibition and purinergic blockade. Ouabain was administered until ventricular fibrillation was induced. Blood was obtained from both the coronary sinus and the femoral vein, and adenosine was measured by liquid chromatography. The refractory period was measured by applying an extra stimulus at variable intervals following a train of 10 basic beats. Flutter was induced by stimulation of the posterior internodal pathway. RESULTS: The concentration of adenosine in plasma collected from the coronary sinus increased by more than 100%; the effect of digitalis on atrial refractory period was independent of cholinergic blockade, but it was inhibited by aminophylline; the ability of digitalis to interrupt flutter was modified by aminophylline. CONCLUSION: The antiarrhythmic action of digitalis seems to include an adenilic component, that results from the liberation of adenosine in the heart.