marinobufagenin and Hypertension

Significant hemodynamic changes ensue with aging, leading to an ever-growing epidemic of hypertension. Alterations in central arterial properties play a major role in these hemodynamic changes. These alterations are characterized by an initial decline in aortic distensibility and an increase of diastolic blood pressure, followed by a sharp increase in pulse wave velocity (PWV), and an increase in pulse pressure (PP) beyond the sixth decade. However, the trajectories of PWV and PP diverge with advancing age. There is an increased prevalence of salt-sensitive hypertension with advancing age that is, in part, mediated by marinobufagenin, an endogenous sodium pump ligand.

Topics: Age Factors; Aging; Arteries; Atrial Natriuretic Factor; Bufanolides; Hemodynamics; Humans; Hypertension; Ligands; Muscle, Smooth, Vascular; Myocytes, Smooth Muscle; Pulse Wave Analysis; Signal Transduction; Sodium Chloride, Dietary; Sodium-Potassium-Exchanging ATPase; Vascular Stiffness

Endogenous cardiotonic steroids (CTS), also called digitalis-like factors, are a group of steroid hormones linking high salt intake and elevated blood pressure and in part responsible for target organ damage in arterial hypertension. CTS act primarily through their ability to inhibit the ubiquitous transport enzyme sodium-potassium adenosine triphosphatase (Na⁺/K⁺-ATPase). A portion of Na⁺/K⁺-ATPase does not seem to actively "pump" sodium and potassium but is closely associated with other key signaling proteins. Plasma concentration and urine excretion of CTS are increased in experimental models with volume expansion and on a high salt diet. Elevated plasma concentration of marinobufagenin has been shown in volume-expanded states such as essential hypertension, primary aldosteronism, chronic renal failure, congestive heart failure and pregnancy. In experimental models marinobufagenin induces heart and kidney fibrosis to the same extent as observed in uremia. Neutralization of marinobufagenin with antibodies prevents such heart remodeling. Expanding our understanding of this new class of hormones may lead to development of novel and effective therapeutic strategies in hypertensive patients with renal and cardiovascular complications.

Topics: Animals; Blood Pressure; Bufanolides; Cardenolides; Cardiac Glycosides; Cardiotonic Agents; Humans; Hypertension; Kidney Diseases; Saponins; Sodium-Potassium-Exchanging ATPase; Ventricular Remodeling

In response to progressive nephron loss, volume and humoral signals in the circulation have increasing relevance. These signals, including plasma sodium, angiotensin II, and those related to volume status, activate a slow neuromodulatory pathway within the central nervous system (CNS). The slow CNS pathway includes specific receptors for angiotensin II, mineralocorticoids, and endogenous ouabain (EO). Stimulation of the pathway leads to elevated sympathetic nervous system activity (SNA) and increased circulating EO. The sustained elevation of circulating EO (or ouabain) stimulates central and peripheral mechanisms that amplify the impact of SNA on vascular tone. These include changes in synaptic plasticity in the brain and sympathetic ganglia that increase preganglionic tone and amplify ganglionic transmission, amplification of the impact of SNA on arterial tone in the vascular wall, and the reprogramming of calcium signaling proteins in arterial myocytes. These increase SNA, raise basal and evoked arterial tone, and elevate blood pressure (BP). In the setting of CKD, we suggest that sustained activation/elevation of the slow CNS pathway, plasma EO, and the cardiotonic steroid marinobufagenin, comprises a feed-forward system that raises BP and accelerates kidney and cardiac damage. Block of the slow CNS pathway and/or circulating EO and marinobufagenin may reduce BP and slow the progression to ESRD.

Topics: Bufanolides; Cardiac Glycosides; Disease Progression; Ganglia, Sympathetic; Humans; Hypertension; Kidney Failure, Chronic; Neuronal Plasticity; Ouabain; Renal Insufficiency, Chronic; Sympathetic Nervous System

Marinobufagenin (MBG), a steroid compound belonging to the bufadienolide cardiac inotropes, is a molecule enjoying a growing interest in the early diagnostic of volume expansion-mediated hypertensive states. This endogenous mammalian cardiotonic and natriuretic bufadienolide (characterized by vasoconstrictive activities) inhibits the α1 isoform of Na(+), K(+)-ATPase, implicating it in series of pathophysiological circumstances such as volume-expansion, essential hypertension and preeclampsia. Indeed, the enhanced production of MBG in preeclamptic patients has been confirmed in several studies, leading us to consider MBG as a biomarker for preeclampsia. The main source for MBG is located in the parotid and skin gland secretions of the toad Bufo marinus in which MBG is the major steroid cardiotonic component. This review emphasizes the key role of analytical development for dosage methods of MBG in biofluids, in the emergence of future perspectives in the diagnostic and therapeutic fields of preeclampsia (e.g. to investigate the biosynthetic origin of MBG and to better understand its implications).

Topics: Animals; Biomarkers; Bufanolides; Bufo marinus; Chromatography, High Pressure Liquid; Female; Humans; Hypertension; Immunoassay; Mass Spectrometry; Parotid Gland; Pre-Eclampsia; Pregnancy; Sebaceous Glands; Vasoconstriction; Vasoconstrictor Agents

The Na/K-ATPase was discovered as an energy transducing ion pump. A major difference between the Na/K-ATPase and other P-type ATPases is its ability to bind a group of chemicals called cardiotonic steroids (CTS). The plant-derived CTS such as digoxin are valuable drugs for the management of cardiac diseases, whereas ouabain and marinobufagenin (MBG) have been identified as a new class of endogenous hormones. Recent studies have demonstrated that the endogenous CTS are important regulators of renal Na(+) excretion and blood pressure. The Na/K-ATPase is not only an ion pump, but also an important receptor that can transduce the ligand-like effect of CTS on intracellular protein kinases and Ca(2+) signaling. Significantly, these CTS-provoked signaling events are capable of reducing the surface expression of apical NHE3 (Na/H exchanger isoform 3) and basolateral Na/K-ATPase in renal proximal tubular cells. These findings suggest that endogenous CTS may play an important role in regulation of tubular Na(+) excretion under physiological conditions; conversely, a defect at either the receptor level (Na/K-ATPase) or receptor-effector coupling would reduce the ability of renal proximal tubular cells to excrete Na(+), thus culminating/resulting in salt-sensitive hypertension.

Topics: Animals; Bufanolides; Calcium Signaling; Humans; Hypertension; Kidney Tubules, Proximal; Ouabain; Protein Kinases; Protein Transport; Sodium-Hydrogen Exchanger 3; Sodium-Hydrogen Exchangers; Sodium-Potassium-Exchanging ATPase

The bufadienolides are a group of steroid hormones that circulate in blood and are excreted in urine. They have the ability to inhibit the adenosine triphosphatase sodium-potassium pump (Na(+)-K(+)-ATPase), with predilection for its alpha1 isoform. This capability enables them to share with other cardiac glycosides the facility to cause an increase in sodium excretion, produce vasoconstriction resulting in hypertension, and act as cardiac inotropes. Bufadienolides have been implicated in instances of volume expansion-mediated hypertension, syndromes in which they are considered capable of causing a vascular leak, interfering with cellular proliferation, and inhibiting cellular maturation. An antagonist to the most well-studied bufadienolide, marinobufagenin, is resibufogenin, a compound that provides promise for the treatment of disorders in which excessive levels of marinobufagenin are present and are etiopathogenetic.

Topics: Animals; Blood Volume; Bufanolides; Capillary Permeability; Cardiotonic Agents; Cytokines; Female; Heart Diseases; Humans; Hypertension; Molecular Structure; Pre-Eclampsia; Pregnancy; Renal Insufficiency, Chronic; Vascular Resistance; Vasoconstrictor Agents; Young Adult

Topics: Adrenal Cortex; Animals; Bufanolides; Cardiac Glycosides; Cardiotonic Agents; Digoxin; Homeostasis; Humans; Hypertension; Kidney Tubules, Proximal; Natriuresis; Ouabain; Sodium; Sodium-Potassium-Exchanging ATPase; Vasoconstrictor Agents

Cardiotonic steroids (CTS), long used to treat heart failure, are endogenously produced in mammals. Among them are the hydrophilic cardenolide ouabain and the more hydrophobic cardenolide digoxin, as well as the bufadienolides marinobufagenin and telecinobufagin. The physiological effects of endogenous ouabain on blood pressure and cardiac activity are consistent with the "Na(+)-lag" hypothesis. This hypothesis assumes that, in cardiac and arterial myocytes, a CTS-induced local increase of Na(+) concentration due to inhibition of Na(+)/K(+)-ATPase leads to an increase of intracellular Ca(2+) concentration ([Ca(2+)](i)) via a backward-running Na(+)/Ca(2+) exchanger. The increase in [Ca(2+)](i) then activates muscle contraction. The Na(+)-lag hypothesis may best explain short-term and inotropic actions of CTS. Yet all data on the CTS-induced alteration of gene expression are consistent with another hypothesis, based on the Na(+)/K(+)-ATPase "signalosome," that describes the interaction of cardiac glycosides with the Na(+) pump as machinery activating various signaling pathways via intramembrane and cytosolic protein-protein interactions. These pathways, which may be activated simultaneously or selectively, elevate [Ca(2+)](i), activate Src and the ERK1/2 kinase pathways, and activate phosphoinositide 3-kinase and protein kinase B (Akt), NF-kappaB, and reactive oxygen species. A recent development indicates that new pharmaceuticals with antihypertensive and anticancer activities may be found among CTS and their derivatives: the antihypertensive rostafuroxin suppresses Na(+) resorption and the Src-epidermal growth factor receptor-ERK pathway in kidney tubule cells. It may be the parent compound of a new principle of antihypertensive therapy. Bufalin and oleandrin or the cardenolide analog UNBS-1450 block tumor cell proliferation and induce apoptosis at low concentrations in tumors with constitutive activation of NF-kappaB.

Topics: Animals; Antihypertensive Agents; Antineoplastic Agents; Blood Pressure; Bufanolides; Calcium; Cardiac Glycosides; Cardiovascular System; Cell Death; Cell Proliferation; Diabetes Mellitus; Digoxin; Humans; Hypertension; Molecular Structure; Myocardial Contraction; Myocytes, Cardiac; Neoplasms; Ouabain; Sodium Chloride; Sodium-Potassium-Exchanging ATPase; Structure-Activity Relationship

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.. 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.. 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.

Topics: Blood Pressure; Brain; Bufanolides; Calmodulin-Binding Proteins; Cerebrospinal Fluid; Cytochrome P-450 Enzyme System; Endosomal Sorting Complexes Required for Transport; Enzyme Inhibitors; Epithelial Sodium Channels; Humans; Hypertension; Immediate-Early Proteins; Nedd4 Ubiquitin Protein Ligases; Ouabain; Protein Serine-Threonine Kinases; Receptor, Angiotensin, Type 1; Receptors, Angiotensin; Receptors, Mineralocorticoid; Receptors, Vasopressin; Renal Insufficiency; Renin-Angiotensin System; Sodium-Potassium-Exchanging ATPase; Sodium, Dietary; Transcription, Genetic; Ubiquitin-Protein Ligases; Vasoconstrictor Agents

Topics: Animals; Bufanolides; Cardenolides; Epithelial Sodium Channels; Humans; Hypertension; Kidney Tubules; Natriuretic Agents; Ouabain; Saponins; Sodium; Sodium Channels; Sodium-Potassium-Exchanging ATPase; Vascular Resistance

Topics: Animals; Bufanolides; Calcium; Cardenolides; Digoxin; Humans; Hypertension; Kidney; Natriuresis; Saponins; Sodium; Sodium-Potassium-Exchanging ATPase

Elevated arterial blood pressure is a common heritable susceptibility in the human population. The high penetrance of this trait in industrialized societies may be influenced by the interactions of environmental factors and common genetic variants. This review examines the role of the renal sodium pump (sodium, potassium-ATPase, NKA) in hypertension and its integration into mechanisms of body sodium balance. In particular, renal NKA provides an appealing target by which inherited factors caninfluence renal sodium reabsorption. Recent work has indicated how some such genetic mechanisms may function. In this paper, the capacity of renal NKA to integrate environmental and heritable factors to increase blood pressure are examined.

Topics: Absorption; Animals; Blood Pressure; Bufanolides; Cardiac Glycosides; Energy Metabolism; Humans; Hypertension; Kidney; Ouabain; Sodium; Sodium-Potassium-Exchanging ATPase

The cardiotonic steroid marinobufagenin (MBG) is increasingly suggested to be responsible for some of the cardiovascular injury that has been previously attributed to aldosterone. We examined the clinical correlates of circulating MBG concentrations in hypertensive patients and tested the hypothesis that MBG serves as a reliable diagnostic tool for detecting primary aldosteronism (PA).. Plasma MBG concentrations (mean: 0.51±0.25 nmol/l) were measured in the morning fasting samples in 20 patients with PA and 20 essential hypertensive (EH) controls matched for age, sex, body mass index, renal function, urinary sodium and intake of antihypertensive medication (mean age: 51.6 years; 52.2% women).. Overall, plasma MBG was directly correlated with plasma aldosterone, aldosterone to active renin ratio (AARR), diastolic blood pressure, mean carotid intima-media thickness, serum sodium, urinary protein to creatinine ratio and inversely with serum potassium levels. Plasma MBG levels were significantly higher in patients with PA compared to EH (mean: 0.68±0.12 versus 0.35±0.24 nmol/l; p<0.001). ROC analysis yielded a greater AUC for plasma MBG compared to the AARR, PAC and serum potassium levels for detecting PA. Youden's Index analyses yielded the optimal plasma MBG cut-off score for diagnosing PA at >0.49 nmol/l with specificity and sensitivity values of 0.85 and 0.95, respectively, which were higher than those at the optimum AARR cut-off at >3.32 ng/dl/µU/ml.. In a well-characterized cohort, values of plasma MBG were significantly related to clinical correlates of cardiovascular and renal disease. Plasma MBG emerged as a valuable alternative to the AARR for screening of PA.

Topics: Aldosterone; Blood Pressure; Bufanolides; Carotid Intima-Media Thickness; Essential Hypertension; Female; Follow-Up Studies; Humans; Hyperaldosteronism; Hypertension; Male; Middle Aged; Renin; Retrospective Studies; Treatment Outcome; Vasoconstrictor Agents

Systolic BP and large elastic artery stiffness both increase with age and are reduced by dietary sodium restriction. Production of the natriuretic hormone marinobufagenin, an endogenous α1 Na+,K+-ATPase inhibitor, is increased in salt-sensitive hypertension and contributes to the rise in systolic BP during sodium loading.. The hypothesis was that dietary sodium restriction performed in middle-aged/older adults (eight men and three women; 60 ± 2 years) with moderately elevated systolic BP (139 ± 2/83 ± 2 mmHg) would reduce urinary marinobufagenin excretion as well as systolic BP and aortic pulse-wave velocity (randomized, placebo-controlled, and crossover design). This study also explored the associations among marinobufagenin excretion with systolic BP and aortic pulse-wave velocity across conditions of 5 weeks of a low-sodium (77 ± 9 mmol/d) and 5 weeks of a normal-sodium (144 ± 7 mmol/d) diet.. Urinary marinobufagenin excretion (weekly measurements; 25.4 ± 1.8 versus 30.7 ± 2.1 pmol/kg per day), systolic BP (127 ± 3 versus 138 ± 5 mmHg), and aortic pulse-wave velocity (700 ± 40 versus 843 ± 36 cm/s) were lower during the low- versus normal-sodium condition (all P<0.05). Across all weeks, marinobufagenin excretion was related with systolic BP (slope=0.61, P<0.001) and sodium excretion (slope=0.46, P<0.001). These associations persisted during the normal- but not the low-sodium condition (both P<0.005). Marinobufagenin excretion also was associated with aortic pulse-wave velocity (slope=0.70, P=0.02) and endothelial cell expression of NAD(P)H oxidase-p47phox (slope=0.64, P=0.006).. These results show, for the first time in humans, that dietary sodium restriction reduces urinary marinobufagenin excretion and that urinary marinobufagenin excretion is positively associated with systolic BP, aortic stiffness (aortic pulse-wave velocity), and endothelial cell expression of the oxidant enzyme NAD(P)H oxidase. Importantly, marinobufagenin excretion is positively related to systolic BP over ranges of sodium intake typical of an American diet, extending previous observations in rodents and humans fed experimentally high-sodium diets.

Topics: Aged; Biomarkers; Blood Pressure; Bufanolides; Colorado; Cross-Over Studies; Diet, Sodium-Restricted; Double-Blind Method; Endothelial Cells; Female; Humans; Hypertension; Male; Middle Aged; NADPH Oxidases; Oxidative Stress; Pulse Wave Analysis; Time Factors; Treatment Outcome; Vascular Stiffness

Cardiotonic steroids, including marinobufagenin, are a group of new steroid hormones found in plasma and urine of patients with congestive heart failure, myocardial infarction, and chronic renal failure. In animal studies, partial nephrectomy induces marinobufagenin elevation, cardiac hypertrophy, and fibrosis. The objective of this study is to test the effect of renal ischemia on marinobufagenin levels in humans with renal artery stenosis (RAS). To test this, plasma marinobufagenin levels were measured in patients with RAS of the Prospective Randomized Study Comparing Renal Artery Stenting With or Without Distal Protection, non-RAS patient controls who were scheduled for coronary angiography, and normal healthy individuals. Marinobufagenin levels were significantly higher in patients with RAS compared with those of the other 2 groups. Multivariate analysis shows that occurrence of RAS is independently related to marinobufagenin levels. In addition, renal artery revascularization by stenting partially reversed marinobufagenin levels in the patients with RAS (0.77±0.06 nmol/L at baseline; 0.66±0.06 nmol/L at 24 hours; and 0.61±0.05 nmol/L at 1 month). In conclusion, we have found that marinobufagenin levels are increased in patients with RAS, whereas reversal of renal ischemia by stenting treatment reduces marinobufagenin levels. These results suggest that RAS-induced renal ischemia may be a major cause of marinobufagenin release.

Topics: Aged; Analysis of Variance; Bufanolides; Enzyme-Linked Immunosorbent Assay; Female; Glomerular Filtration Rate; Humans; Hypertension; Ischemia; Kidney; Logistic Models; Male; Middle Aged; Patient Selection; Prospective Studies; Renal Artery Obstruction; Stents

Factors that mediate increases in salt sensitivity of blood pressure with age remain to be clarified. The present study investigated 1) the effects of high-NaCl intake on two Na pump inhibitors, endogenous ouabain (EO) and marinobufagenin (MBG), in middle-aged and older normotensive Caucasian women; and 2) whether individual differences in EO and MBG are linked to variations in sodium excretion or salt sensitivity. A change from 6 days of a lower (0.7 mmol.kg(-1).day(-1))- to 6 days of a higher (4 mmol.kg(-1).day(-1))-NaCl diet elicited a sustained increase in MBG excretion that directly correlated with an increase in the fractional Na excretion and was inversely related to age and to an age-dependent increase in salt sensitivity. In contrast, EO excretion increased only transiently in response to NaCl loading and did not vary with age or correlate with fractional Na excretion or salt sensitivity. A positive correlation of both plasma and urine levels of EO and MBG during salt loading may indicate a casual link between two Na pump inhibitors in response to NaCl loading, as observed in animal models. A linear mixed-effects model demonstrated that age, dietary NaCl, renal MBG excretion, and body mass index were each independently associated with systolic blood pressure. Thus, a sustained increase in MBG in response to acutely elevated dietary NaCl is inversely linked to salt sensitivity in normotensive middle-aged and older women, and a relative failure of MBG elaboration by these older persons may be involved in the increased salt sensitivity with advancing age.

Topics: Adult; Age Factors; Aged; Aging; Blood Pressure; Body Mass Index; Bufanolides; Enzyme Inhibitors; Female; Humans; Hypertension; Linear Models; Middle Aged; Models, Biological; Natriuresis; Ouabain; Sodium Chloride, Dietary; Sodium-Potassium-Exchanging ATPase; Systole; Time Factors; Up-Regulation

Increased marinobufagenin (MBG) synthesis has been suggested in response to high dietary salt intake. The aim of this study was to determine the effects of short-term changes in sodium intake on plasma MBG levels in patients with primary salt-sensitive and salt-insensitive hypertension. In total, 51 patients with primary hypertension were evaluated during acute sodium restriction and sodium loading. Plasma or serum concentrations of MBG, natriuretic pro-peptides, aldosterone, sodium, potassium, as well as hematocrit (Hct) value, plasma renin activity (PRA) and urinary sodium and potassium excretion were measured. Ambulatory blood pressure monitoring (ABPM) and echocardiography were performed at baseline. In salt-sensitive patients with primary hypertension plasma MBG correlated positively with diastolic blood pressure (ABPM) and serum NT-proANP concentration at baseline and with serum NT-proANP concentration after dietary sodium restriction. In this subgroup plasma MBG concentration decreased during sodium restriction, and a parallel increase of PRA was observed. Acute salt loading further decreased plasma MBG concentration in salt-sensitive subjects in contrast to salt insensitive patients. No correlation was found between plasma MBG concentration and left ventricular mass index. In conclusion, in salt-sensitive hypertensive patients plasma MBG concentration correlates with 24-h diastolic blood pressure and dietary sodium restriction reduces plasma MBG levels. Decreased MBG secretion in response to acute salt loading may play an important role in the pathogenesis of salt sensitivity.

Topics: Adult; Aldosterone; Atrial Natriuretic Factor; Bufanolides; Female; Humans; Hypertension; Male; Middle Aged; Potassium; Renin; Sodium; Sodium, Dietary

Suppressed nighttime blood pressure dipping is associated with salt sensitivity and may increase the hemodynamic load on the microvasculature. The mechanism remains unknown whereby salt sensitivity may increase the cardiovascular risk of non-dippers. Marinobufagenin, a novel steroidal biomarker, is associated with salt sensitivity and other cardiovascular risk factors independent of blood pressure. The authors investigated whether microvascular function in non-dippers is associated with marinobufagenin. The authors included 220 dippers and 154 non-dippers (aged 20-30 years) from the African-PREDICT study, with complete 24-hour urinary marinobufagenin and sodium data. The authors determined dipping status using 24-hour blood pressure monitoring and defined nighttime non-dipping <10%. The authors measured microvascular reactivity as retinal artery dilation in response to light flicker provocation. Young healthy non-dippers and dippers presented with similar peak retinal artery dilation, urinary sodium, and MBG excretion (P > .05). However, only in non-dippers did peak retinal artery dilation relate negatively to marinobufagenin excretion after single (r = -0.20; P = .012), partial (r = -0.23; P = .004), and multivariate-adjusted regression analyses (Adj. R

Topics: Adult; Biomarkers; Blood Pressure; Blood Pressure Monitoring, Ambulatory; Bufanolides; Circadian Rhythm; Female; Humans; Hypertension; Male; Microcirculation; Sodium Chloride, Dietary; Young Adult

Endogenous cardiotonic steroid, marinobufagenin (MBG), induces Fli1-dependent tissue fibrosis. We hypothesized that an increase in MBG initiates the development of aortic fibrosis in salt-loaded rats with type 2 diabetes mellitus (DM2) via pressure-independent mechanism. DM2 was induced by a single intraperitoneal administration of 65 mg/kg streptozotocin to neonatal (4-5 days) male Wistar rats. Eight-week-old DM2 rats received water or 1.8% NaCl (DM-NaCl) solution for 4 weeks (n = 16); half of DM-NaCl rats were treated with anti-MBG monoclonal antibody (mAb) (DM-NaCl-AB) during week 4 of salt loading; control intact rats received water (n = 8/group). Blood pressure, MBG, erythrocyte Na/K-ATPase activity, aortic weights, levels of fibrosis markers (Fli1, protein kinase Cδ, transforming growth factor-β1, receptors of the transforming growth factor beta5, fibronectin, collagen-1), and sensitivity of the aortic explants to the vasorelaxant effect of sodium nitroprusside were assessed. No changes in systolic blood pressure were observed while erythrocyte Na/K-ATPase was inhibited by 30%, plasma MBG was doubled, and aortic markers of fibrosis became elevated in DM-NaCl rats versus control. Treatment of DM-NaCl rats with anti-MBG mAb activated Na/K-ATPase, prevented increases in aortic weights, and the levels of fibrosis markers returned to the control levels. The responsiveness of the aortic rings from DM-NaCl rats to the relaxant effect of sodium nitroprusside was reduced (half maximal effective concentration (EC50) = 29 nmol/L) versus control rings (EC50 = 7 nmol/L) and was restored by anti-MBG mAb (EC50 = 9 nmol/L). Our results suggest that in salt-loaded diabetic rats, MBG stimulates aortic collagen synthesis in a pressure-independent fashion and that 2 profibrotic mechanisms, Fli1 dependent and transforming growth factor-β dependent, underlie its effects.

Topics: Animals; Aorta; Aortic Diseases; Blood Pressure; Bufanolides; Collagen; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Erythrocytes; Fibrosis; Hypertension; Male; Proto-Oncogene Protein c-fli-1; Rats, Wistar; Signal Transduction; Sodium Chloride; Sodium-Potassium-Exchanging ATPase; Transforming Growth Factor beta1; Vascular Remodeling; Vascular Stiffness

Background Elevated levels of an endogenous Na/K-ATPase inhibitor marinobufagenin accompany salt-sensitive hypertension and are implicated in cardiac fibrosis. Immunoneutralization of marinobufagenin reduces blood pressure in Dahl salt-sensitive (Dahl-S) rats. The effect of the anti-marinobufagenin monoclonal antibody on blood pressure, left ventricular (LV) and renal remodeling, and gene expression were investigated in hypertensive Dahl-S rats. Methods and Results Dahl-S rats were fed high NaCl (8%, HS; n=14) or low NaCl (0.1%, LS; n=14) diets for 8 weeks. Animals were administered control antibody (LS control antibody, LSC; HS control antibody, HSC; n=7 per group) or anti-marinobufagenin antibody once on week 7 of diet intervention (n=7 per group). Levels of marinobufagenin, LV, and kidney mRNAs and proteins implicated in profibrotic signaling were assessed. Systolic blood pressure was elevated (211±8 versus 133±3 mm Hg,

Topics: Animals; Blood Pressure; Blotting, Western; Bufanolides; Disease Models, Animal; Echocardiography; Enzyme Inhibitors; Gene Expression Regulation; Heart Ventricles; Hypertension; Male; Rats; Rats, Inbred Dahl; RNA; Transforming Growth Factor beta; Ventricular Remodeling

Marinobufagenin (MBG) is an endogenous cardiotonic steroid (CTS) that inhibits the Na+/K+-ATPase. Human MBG is significantly increased in end-stage renal disease and immunization against MBG attenuates cardiovascular fibrosis in a rat model of uremic cardiomyopathy. Mineralocorticoid antagonists (MRA) block MBG binding sites and decrease proteinuria in chronic kidney disease (CKD) patients. We therefore aimed to investigate the association of MBG and albuminuria, as a marker of renal damage, as well as MBG and decline of glomerular filtration rate (GFR).. The Graz endocrine causes of hypertension (GECOH) study is a single center study of adults routinely referred for screening of endocrine hypertension. Plasma MBG was measured by an enzyme-linked immunoassay, and in a post-hoc analysis, follow-up creatinine levels were obtained. Patients with proteinuria >3.5g/day at baseline were excluded from further evaluation.. We measured MBG concentrations in 40 hypertensive subjects and excluded one patient due to pre-existing proteinuria. Plasma MBG was significantly correlated with albuminuria (Spearman ρ = .357; p = .028) and proteinuria (ρ = .336; p = .039). In linear regression analysis, the association remained significant after adjustment for age, sex, and BMI (β = .306; p = .036), and for mean systolic blood pressure (β = .352; p = .034). In follow-up analyses (N = 30), MBG was significantly associated with decline in GFR after adjustment for time-to-follow-up (β = -.374; p = .042).. The findings suggest that MBG plasma concentrations were associated with albuminuria as well as decline in kidney function. Whether MBG predicts hard renal endpoints warrants further investigations.

Topics: Adult; Aged; Albuminuria; Animals; Biomarkers; Bufanolides; Cardiotonic Agents; Enzyme Inhibitors; Female; Follow-Up Studies; Glomerular Filtration Rate; Humans; Hypertension; Male; Middle Aged; Proteinuria; Rats; Renal Insufficiency, Chronic

The study addresses the association of marinobufagenin (MBG), a natriuretic and vasoconstrictor steroid, and Na/K-ATPase (NKA) activity with pressor response to salt-loading and arterial stiffness in resistant hypertension (RH). Thirty-four patients (18 males and 16 females; 56±8 years) with RH on a combined (lisnopril/amlodipine/hydrochlorothiazide) therapy and 11 healthy age-matched normotensive subjects (7 males and 4 females; 54±2 years) were enrolled in this study. Salt-loading was performed via intravenous infusion of 1000mL saline (0.9% NaCl) for 1h. Arterial stiffness was measured by Sphygmocor Px device with a calculation of pulse-wave velocity (PWV). Activity of NKA was measured in erythrocytes. We demonstrated that plasma levels of MBG and magnitude of NaCl-induced MBG-dependent NKA inhibition are associated with PWV, and that this association has gender- and age-specific fashion in RH patients.

Topics: Aging; Bufanolides; Cardiac Glycosides; Female; Humans; Hypertension; Male; Middle Aged; Pulse Wave Analysis; Sex Characteristics; Sodium Chloride; Vascular Resistance

We have investigated serum levels of immunoreactive marinobufagenin (MBG) in 16- to 20-week-old spontaneously hypertensive rats (SHRs)-A3 and in the normotensive Wistar-Kyoto (WKY) rat strain in the absence of salt loading, and we have investigated the genetic control of serum MBG.. We genotyped the F2 progeny of an SHR-A3×WKY intercross using a genome-wide panel of 253 single-nucleotide polymorphism markers that were dimorphic between SHR-A3 and WKY and measured serum MBG by ELISA. Serum MBG levels were lower in SHR-A3 than WKY rats (0.39±0.07 and 1.27±0.40 nmol/L, respectively), suggesting that MBG may not play a role in the markedly divergent blood pressure measured by telemetry in rats of these 2 strains (SHR-A3 and WKY, 198.3±4.43 and 116.8±1.51 mm Hg, respectively). The strain difference in serum MBG was investigated to determine whether genomic regions influencing MBG might be identified by genetic mapping. Quantitative trait locus mapping indicated a single locus influencing serum MBG in the region of chromosome 6q12. Homozygosity of WKY alleles at this locus was associated with increased serum MBG levels. We surveyed whole genome sequences from our SHR-A3 and WKY lines, seeking coding sequence variation between SHR-A3 and WKY within the mapped locus that might explain the inherited strain difference in serum MBG.. We identified amino acid substitution in the sterol transport protein Abcg5, present in SHR-A3, but absent in WKY, that is a potential mechanism influencing MBG levels.

Topics: Animals; ATP Binding Cassette Transporter, Subfamily G, Member 5; Biomarkers; Blood Pressure; Bufanolides; Crosses, Genetic; Disease Models, Animal; Genetic Predisposition to Disease; Genome-Wide Association Study; Homozygote; Hypertension; Lipoproteins; Male; Phenotype; Polymorphism, Single Nucleotide; Quantitative Trait Loci; Rats, Inbred SHR; Rats, Inbred WKY

This investigation differentiates types of essential hypertension in a Georgian population as well as describes endogenous cardiotonic steroids in salt-sensitive and salt-resistant subjects. This case control study included 185 subjects: 94 cases with stage 1 essential hypertension (JNC7) naïve to antihypertensive treatment, and 91 controls. A salt-sensitivity test was used to dichotomize case and control groups into salt-sensitive and salt-resistant subgroups. Blood and urine samples were obtained to categorize participants as consuming high and low salt diets. Endogenous cardiotonic steroids, sodium and plasma-renin activity (PRA) were measured in both samples at the different sodium conditions. Determinants of circulating levels of endogenous sodium pump inhibitors were carried out using the ELISA and RIA methods; PRA was assessed by radioimmunoassay. Descriptive statistics were used to analyze the data. Differences in variables between sodium conditions were assessed using paired t-tests. Salt-sensitivity was found in 60.5% of the total population investigated, with a higher proportion in females. A statistically significant positive correlation was found between salt-sensitivity and age in females (r=0.262, p<0.01), and with 24-hour urine sodium concentration changes (r=0.334, p<0.01). A significant negative correlation was found between salt-sensitivity and PRA. At the high sodium condition, endogenous MBG and OU were high in salt-sensitive subjects compared to those who were salt-resistant. These compounds decreased with a low-salt diet in both salt-sensitive cases and controls but remained the same in salt-resistant individuals. The MBG and OU levels positively correlated with systolic blood pressure in salt-sensitive individuals but no variability was evident among salt-resistant subjects. Our results show that MBG and OU levels start to increase at the normotensive stage and sustained high concentrations can lead to elevated systolic blood pressure, a risk factor for arterial hypertension in salt-sensitive subjects.

Topics: Blood Pressure; Bufanolides; Cardiac Glycosides; Case-Control Studies; Female; Georgia (Republic); Humans; Hypertension; Male; Ouabain; Sex Factors; Sodium Chloride, Dietary

Salt-induced elevation of the endogenous digitalis like sodium pump ligand marinobufagenin (MBG) in the Dahl salt-sensitive rats resulted in elevated blood pressure (BP). Here, we tested, in humans, whether MBG levels are related to ambulatory 24-h BP (ABP), controlled long-term increase of salt-intake induces changes in MBG and any salt-induced change in MBG is related to salt sensitivity.. Thirty-nine healthy individuals (53 ± 11 years old; 20 men and 19 women) had a total daily NaCl intake of 50 mmol (low-salt) and 150 mmol (high-salt) for 4 weeks each, in a random order. ABP and MBG in plasma and urine were measured at baseline (unstandardized salt intake) and after high and low-salt intake.. At baseline, plasma MBG (P-MBG) was related to 24-h SBP (r = 0.43, P = 0.007) and DBP (r = 0.32, P = 0.047), whereas 24-h urinary excretion of MBG (UE-MBG) was related to 24-h DBP only (r = 0.42, P = 0.008). Sex-specific analyses revealed that these relationships were significant in men only. Compared with low-salt, high-salt diet increased P-MBG (P = 0.029), mainly driven by results in men. Male P-MBG responders vs. nonresponders (above vs. below median of high-salt induced P-MBG increase) had markedly enhanced SBP (10.4 ± 6.4 vs. 1.0 ± 6.0 mmHg; P = 0.003) and DBP (6.7 ± 5.0 vs. -0.6 ± 3.6 mmHg; P = 0.001) salt sensitivity.. In men, MBG increases with 24-h ABP, and similar to Dahl salt-sensitive rats, 4 weeks of high-salt induced MBG response is accompanied by marked salt sensitivity. However, these patterns seem to be sex-specific and are not observed in women.

Topics: Adult; Blood Pressure; Bufanolides; Female; Humans; Hypertension; Male; Middle Aged; Sex Factors; Sodium Chloride, Dietary; Sodium-Potassium-Exchanging ATPase

Previous studies from this laboratory have demonstrated that the bufodienolide, marinobufagenin, causes a syndrome in the pregnant rat that resembles human preeclampsia. Furthermore, marinobufagenin urinary excretion is elevated in approximately 85% of preeclamptic patients. Resibufagenin, an antagonist to marinobufagenin, completely prevents the syndrome (hypertension, proteinuria, and intrauterine growth restriction) if given from early pregnancy.. We investigated the effects of another bufodienolide, cinobufatalin, to determine if it, likewise, could induce the rat "preeclamptic" syndrome, which it did. We then examined whether resibufagenin could prevent the syndrome due to cinobufatalin.. Resibufagenin improved hypertension but not proteinuria, and did not prevent uterine growth restriction.. We conclude that more than one bufodienolide may induce the preeclamptic syndrome and that each may require a specific antagonist to prevent (or treat) the syndrome.

Topics: Animals; Bufanolides; Disease Models, Animal; Female; Fetal Growth Retardation; Hypertension; Pre-Eclampsia; Pregnancy; Proteinuria; Rats

Endogenous cardiotonic steroids, including marinobufagenin (MBG), stimulate vascular synthesis of collagen. Because mineralocorticoid antagonists competitively antagonize effect of cardiotonic steroids on the Na/K-ATPase, we hypothesized that spironolactone would reverse the profibrotic effects of MBG.. Experiment 1: Explants of thoracic aortae and aortic vascular smooth muscle cells from Wistar rats were cultured for 24 h in the presence of vehicle or MBG (100 nmol/l) with or without canrenone (10 μmol/l), an active metabolite of spironolactone. Experiment 2: In 16 patients (56 ± 2 years) with resistant hypertension on a combined (lisinopril/amlodipine/hydrochlorothiazide) therapy, we determined arterial pressure, pulse wave velocity, plasma MBG, and erythrocyte Na/K-ATPase before and 6 months after addition of placebo (n = 8) or spironolactone (50 mg/day; n = 8) to the therapy.. In rat aortic explants and in vascular smooth muscle cells, pretreatment with MBG resulted in a two-fold rise in collagen-1, and a marked reduction in the sensitivity of the aortic rings to the vasorelaxant effect of sodium nitroprusside following endothelin-1-induced constriction (EC50 = 480 ± 67 vs. 23 ± 3 nmol/l in vehicle-treated rings; P < 0.01). Canrenone blocked effects of MBG on collagen synthesis and restored sensitivity of vascular rings to sodium nitroprusside (EC50 = 17 ± 1 nmol/l). Resistant hypertension patients exhibited elevated plasma MBG (0.42 ± 0.07 vs. 0.24 ± 0.03 nmol/l; P = 0.01) and reduced Na/K-ATPase activity (1.9 ± 0.15 vs. 2.8 ± 0.2 μmol Pi/ml per h, P < 0.01) vs. seven healthy individuals. Six-month administration of spironolactone, unlike placebo treatment, was associated with a decrease in pulse wave velocity and arterial pressure, and with restoration of Na/K-ATPase activity in the presence of unchanged MBG levels.. MBG-induced vascular fibrosis is a likely target for spironolactone.

Topics: Animals; Aorta; Arterial Pressure; Bufanolides; Canrenone; Cells, Cultured; Collagen Type I; Endothelin-1; Erythrocytes; Female; Fibrosis; Humans; Hypertension; Male; Middle Aged; Mineralocorticoid Receptor Antagonists; Muscle, Smooth, Vascular; Myocytes, Smooth Muscle; Nitroprusside; Pulse Wave Analysis; Rats; Rats, Wistar; Sodium-Potassium-Exchanging ATPase; Spironolactone; Vasodilator Agents

We have shown that the ouabain-sensitive α2 Na,K-ATPase is required for adrenocorticotropic hormone (ACTH)-induced hypertension and gestational blood pressure regulation. It is therefore of interest to explore whether this binding site participates in the development of other forms of hypertension, such as deoxycorticosterone acetate (DOCA)-salt using mutant mice with altered sensitivity to ouabain.. Wild-type (α1 ouabain-resistant, α2 ouabain-sensitive: α(R/R)α2(S/S)), α1-resistant, α2-resistant (α1(R/R)α2(R/R)) and α1-sensitive, α2-resistant (α1(S/S)α2(R/R)) mice were uninephrectomized and implanted with DOCA pellets. The animals were given either tap water or 1% NaCl, and blood pressure was measured before and after DOCA.. DOCA-salt-treated α1(R/R)α2(R/R) mice developed hypertension to the same extent as α1(R/R)α2(S/S) mice (wild type), and the α1(S/S)α2(R/R) mice given DOCA-salt also showed no difference from the other two genotypes. The expression of the α1 isoform was not changed by DOCA-salt treatment in either α1(R/R)α2(S/S) or α1(R/R)α2(R/R) mice. However, the α2 subunit was expressed at substantially higher levels in the hearts of α1(R/R)α2(R/R) than α1(R/R)α2(S/S) mice, regardless of treatment. Plasma levels of ouabain did not change consistently, but those of marinobufagenin were modestly higher in DOCA-salt treated mice relatively to those without salt.. The ouabain-binding site of either the α1 or α2 Na,K-ATPase subunit does not play an essential role in the development of DOCA-salt hypertension in this mouse model. These findings indicate that the underlying mechanisms of hypertension induced by DOCA-salt treatment are different from those of ACTH-induced hypertension.

Topics: Animals; Binding Sites; Blood Pressure; Bufanolides; Desoxycorticosterone; Digoxin; Hypertension; Immunoglobulin Fab Fragments; Mice; Myocardial Contraction; Ouabain; Sodium Chloride; Sodium-Potassium-Exchanging ATPase

Levels of marinobufagenin (MBG), an endogenous bufadienolide Na/K-ATPase (NKA) inhibitor, increase in preeclampsia and in NaCl-sensitive hypertension.. We tested a 3E9 monoclonal anti-MBG antibody (mAb) for the ability to lower blood pressure (BP) in NaCl-sensitive hypertension and to reverse the preeclampsia-induced inhibition of erythrocyte NKA. Measurements of MBG were performed via immunoassay based on 4G4 anti-MBG mAb.. In hypertensive Dahl-S rats, intraperitoneal administration of 50 microg/kg 3E9 mAb lowered BP by 32 mmHg and activated the Na/K-pump in the thoracic aorta by 51%. NaCl supplementation of pregnant rats (n = 16) produced a 37 mmHg increase in BP, a 3.5-fold rise in MBG excretion, and a 25% inhibition of the Na/K-pump in the thoracic aorta, compared with pregnant rats on a normal NaCl intake. In eight pregnant hypertensive rats, 3E9 mAb reduced the BP (21 mmHg) and restored the vascular Na/K-pump. In 14 patients with preeclampsia (mean BP, 126 +/- 3 mmHg; 26.9 +/- 1.4 years; gestational age, 37 +/- 0.8 weeks), plasma MBG was increased three-fold and erythrocyte NKA was inhibited compared with that of 12 normotensive pregnant women (mean BP, 71 +/- 3 mmHg) (1.5 +/- 0.1 vs. 3.1 +/- 0.2 micromol Pi/ml/h, respectively; P < 0.01). Ex-vivo 3E9 mAb restored NKA activity in erythrocytes from patients with preeclampsia. As compared with 3E9 mAb, Digibind, an affinity-purified antidigoxin antibody, was less active with respect to lowering BP in both hypertensive models and to restoration of NKA from erythrocytes from patients with preeclampsia.. Anti-MBG mAbs may be a useful tool in studies of MBG in vitro and in vivo and may offer treatment of preeclampsia.

Topics: Adult; Animals; Antibodies, Monoclonal; Blood Pressure; Bufanolides; Digoxin; Disease Models, Animal; Female; Humans; Hypertension; Immunoglobulin Fab Fragments; Pre-Eclampsia; Pregnancy; Pregnancy Trimester, Third; Pregnancy, Animal; Rats; Rats, Inbred Dahl; Sensitivity and Specificity; Sodium Chloride, Dietary; Sodium-Potassium-Exchanging ATPase

Marinobufagenin and telecinobufagin have been identified as digitalis-like factors in mammals. In toads, marinobufagenin-related compounds, such as marinobufotoxin (MBT), have been isolated in some tissues but not in mammals, and its biological action has not been elucidated. Herein, we aimed to explore the possible production and/or secretion of MBT and the biological action in rats. First, the MBT in culture supernatant of the adrenocortical-originated cell line Y-1 was analyzed by high-performance liquid chromatography and sensitive ELISA for marinobufagenin-like immunoreactivity. Moreover, the structural information was obtained by mass spectrometry. To determine the biological action, MBT (9.6 and 0.96 microg/kg per day) was intraperitoneally infused via an osmotic minipump for 1 week. Blood pressure and renal excretion of marinobufagenin-like immunoreactivity were measured. Marinobufagenin-like immunoreactivity was found in Y-1 cell culture media, and the concentration increased until 24 hours. The structural analysis suggested that marinobufagenin-like immunoreactivities were marinobufagenin and MBT, and tandem mass spectrum analysis revealed them with the specific daughter ions. The highest sensitive ELISA-positive peak of marinobufagenin-like immunoreactivity in the media was MBT. Continuous administration of MBT in rats for 1 week significantly increased systolic blood pressure and renal excretion of marinobufagenin-like immunoreactivity compared with control rats (135+/-3.0 versus 126+/-2.0 mm Hg and 1.41+/-0.286 versus 0.34+/-0.064 ng/day, respectively). These data suggest that MBT, arginine-suberoyl ester of marinobufagenin, can be a novel digitalis-like factor with hypertensive action and is secreted from the adrenocortical cells.

Topics: Adrenal Cortex; Animals; Antibodies, Monoclonal; Antibody Specificity; Blood Pressure; Bufanolides; Cardanolides; Cardenolides; Cell Line; Chromatography, High Pressure Liquid; Drug Administration Schedule; Enzyme-Linked Immunosorbent Assay; Hypertension; Injections, Intraperitoneal; Male; Mass Spectrometry; Rats; Rats, Wistar; Saponins

The study of the pathogenesis of preeclampsia has been hampered by a relative dearth of animal models. We developed a rat model of preeclampsia in which the excretion of a circulating inhibitor of Na/K ATPase, marinobufagenin (MBG), is elevated. These animals develop hypertension, proteinuria, and intrauterine growth restriction. The administration of a congener of MBG, resibufogenin (RBG), reduces blood pressure to normal in these animals, as is the case when given to pregnant animals rendered hypertensive by the administration of MBG. Studies of Na/K ATPase inhibition by MBG and RBG reveal that these agents are equally effective as inhibitors of the enzyme.

Topics: Animals; Blood Pressure; Bufanolides; Disease Models, Animal; Enzyme Inhibitors; Female; Humans; Hypertension; Isoenzymes; Molecular Structure; Ouabain; Pre-Eclampsia; Pregnancy; Rats; Sodium-Potassium-Exchanging ATPase

Topics: Animals; Blood Pressure; Bufanolides; Enzyme Inhibitors; Heart Atria; Humans; Hypertension; Mice; Natriuresis; Natriuretic Agents; Peptides; Plasma; Sodium-Potassium-Exchanging ATPase

Although obstructive sleep apnea (OSA) is an independent risk factor for hypertension, the underlying mechanisms are not clearly understood. Apnea and hypopnea episodes during sleep lead to sympathoactivation, decrease plasma pH, and predispose to sodium and volume retention. We hypothesized that, the latter could stimulate digitalis-like natriuretic/vasopressor hormones, endogenous ouabain (EO) and marinobufagenin (MBG). Overnight polysomnography (Embletta) and 24 hrs blood pressure monitoring (SpaceLab 90207) was conducted in 52 consecutive patients with OSA (51 +/- 8 years; 40 males, 12 females) and in 48 age-matched hypertensive subjects without OSA. According to the polysomnography data, 17 patients had a mild degree of OSA (apnea/hypopnea index (AHI) 5-15), 17 patients-moderate (AHI 15-30) and 18 -severe OSA (AHI >30). Levels of MBG excretion co-varied with OSA severity (0.5 +/- 0.1, 0.9 +/- 0.04 and 1.2 +/- 0.06 nmoles per 24 hrs, respectively), while excretion of EO did not differ in patients with different degrees of OSA severity. Our observations suggest that MBG may be involved in the pathogenesis of hypertension in OSA, and may be a marker of OSA severity.

Topics: Adult; Blood Pressure Determination; Bufanolides; Female; Humans; Hypertension; Male; Middle Aged; Ouabain; Polysomnography; Sleep Apnea, Obstructive

NaCl loading of Dahl salt-sensitive rats (DS) stimulates marinobufagenin (MBG), an alpha1 Na/K-ATPase (NKA) isoform ligand. Cardiac function depends on NKA, which is regulated in part by endogenous digitalis-like ligands. Our goal was to study whether changes occur in MBG and endogenous ouabain (EO) production during cardiac remodelling in hypertensive DS, and whether these are associated with changes in myocardial NKA isoforms and sensitivity to MBG and ouabain.. Changes in MBG and EO levels, changes in myocardial NKA isoform composition, and sensitivity to endogenous ligands during development of cardiac hypertrophy and the transition to heart failure were studied in DS rats with an 8% NaCl intake.. The animals developed compensated left ventricular hypertrophy after 4 weeks, which progressed to heart failure at 9-12 weeks. The hypertrophic stage was associated with increased plasma MBG levels (mean +/- SEM of 1.22 +/- 0.22 versus 0.31 +/- 0.03 nmol/l; P < 0.01), increased sensitivity of NKA to MBG, and an increased abundance of alpha1 NKA. Plasma levels of EO did not change, and the sensitivity of NKA to ouabain decreased. The transition to heart failure was accompanied by a decrease in alpha1 NKA, a reduction in plasma MBG, and decreased sensitivity of NKA to MBG. In addition, an increased abundance of ouabain-sensitive alpha3 NKA, a three-fold rise in plasma EO (1.01 +/- 0.13 versus 0.27 +/- 0.06 nmol/l), and a seven-fold increase in the ouabain sensitivity of NKA compared with controls were observed.. During cardiac hypertrophy and the transition to heart failure, a shift in endogenous NKA ligands production is linked to a shift in myocardial NKA isoforms.

Topics: Animals; Bufanolides; Cardiac Output, Low; Cardiomegaly; Enzyme Inhibitors; Hypertension; Isoenzymes; Ligands; Male; Ouabain; Rats; Rats, Inbred Dahl; Sodium Chloride; Sodium-Potassium-Exchanging ATPase

Individuals who eat salty diets and who are "salt-sensitive" tend to have increased left ventricular mass, independent of blood pressure; this phenomenon awaits an explanation. It is clear that local up-regulation of angiotensin II (AngII) production and activity play a key role in the induction of left ventricular hypertrophy (LVH). Recent evidence suggests that a healthy coronary microvascular endothelium opposes this effect by serving as a paracrine source of nitric oxide (NO), a natural antagonist of AngII activity, and that up-regulation of this mechanism can account for the protective role of bradykinin with respect to LVH. The coronary microvasculature also possesses NAD(P)H oxidase activity that can generate superoxide, inimical to the bioactivity of endothelial NO. There is now good reason to believe that the triterpenoid marinobufagenin (MBG), a selective inhibitor of the alpha-1 isoform of the sodium pump, mediates the impact of salty diets on blood pressure;production of MBG by the adrenal cortex is boosted when salt-sensitive animals are fed salty diets. It is hypothesized that coronary microvascular endothelium expresses the alpha-1 isoform of the sodium pump, and that MBG thus can target this endothelium. If that is the case, MBG would be expected to decrease membrane potential in these cells;as a consequence, superoxide production would be up-regulated, NO synthase activity would be down-regulated, and myocardial NO bioactivity would thus be suppressed. This would offer a satisfying explanation for the impact of salt and salt-sensitivity on risk for LVH. If expression of the alpha-1 isoform of the sodium pump is a more general property of vascular endothelium, MBG may suppress NO bioactivity in other regions of the vascular tree, thereby contributing to other adverse effects elicited by salty diets: reduced arterial compliance, medial hypertrophy, impaired endothelium-dependent vasodilation, hypertensive/diabetic glomerulopathy, increased risk for stroke, and hypertension.

Topics: Angiotensin II; Animals; Blood Pressure; Bufanolides; Endothelium, Vascular; Humans; Hypertension; Hypertrophy, Left Ventricular; Microcirculation; Models, Biological; Models, Theoretical; Nitric Oxide; Sodium Chloride, Dietary; Vasoconstrictor Agents

Marinobufagenin (MBG), an endogenous ligand of alpha-1 Na/K-ATPase, becomes elevated and contributes to hypertension in NaCl-loaded Dahl-S rats (DS). Protein kinase C (PKC) phosphorylates alpha-1 Na/K-ATPase and increases its MBG sensitivity. Cicletanine, an antihypertensive compound with PKC-inhibitory activity, reverses MBG-induced Na/K-ATPase inhibition and vasoconstriction. We hypothesized that increased PKC levels in sodium-loaded hypertensive DS would sensitize alpha-1 Na/K-ATPase to MBG and that PKC inhibition by cicletanine would produce an opposite effect. We studied the effects of cicletanine on systolic blood pressure, left ventricular PKC isoforms, cardiac alpha-1 Na/K-ATPase levels, and sensitivity to MBG in hypertensive DS. Seven DS received 50 mg x kg(-1) x d(-1) cicletanine, and 7 DS received vehicle during 4 weeks of an 8% NaCl diet. Vehicle-treated rats exhibited an increase in blood pressure, left ventricular mass, MBG excretion (74+/-11 vs 9+/-1 pmol/24 h, P<0.01), myocardial alpha-1 Na/K-ATPase protein, and PKC beta2 and delta. The sensitivity of Na/K-ATPase to MBG was enhanced at the level of high-affinity binding sites (IC50, 0.8 vs 4.4 nmol/L, P<0.01). Cicletanine-treated rats exhibited a 56-mm Hg reduction in blood pressure (P<0.01) and a 30% reduction in left ventricular weight, whereas cardiac alpha-1 Na/K-ATPase protein and MBG levels were unchanged. In cicletanine-treated rats, PKC beta2 was not increased, the sensitivity of Na/K-ATPase to MBG was decreased (IC50=20 micromol/L), and phorbol diacetate-induced alpha-1 Na/K-ATPase phosphorylation was reduced versus vehicle-treated rats. In vitro cicletanine treatment of sarcolemma from vehicle-treated rats also desensitized Na/K-ATPase to MBG, indicating that this effect was not solely attributable to a reduction in blood pressure. Thus, PKC-induced phosphorylation of cardiac alpha-1 Na/K-ATPase is a likely target for cicletanine treatment.

Topics: Animals; Antihypertensive Agents; Binding Sites; Blood Pressure; Bufanolides; Enzyme Inhibitors; Heart Ventricles; Hypertension; Hypertrophy, Left Ventricular; Kidney; Protein Kinase C; Protein Kinase C beta; Pyridines; Rats; Rats, Inbred Dahl; Sarcolemma; Sodium-Potassium-Exchanging ATPase

Digitalis-like sodium pump ligands (SPLs) effect natriuresis via inhibition of renal tubular Na(+),K(+)-ATPase but may induce vasoconstriction. The present study investigated the potential roles of 2 putative endogenous SPLs, an ouabain-like compound (OLC) and an alpha(1) Na(+),K(+)-ATPase inhibitor, marinobufagenin (MBG), in regulating natriuresis and blood pressure (BP) responses to sustained and acute NaCl loading in Dahl salt-sensitive rats (DS).. During 4 weeks of an 8% NaCl diet, DS exhibited a progressive increase in MBG renal excretion (66 +/-13 pmol/24 hours at week 4 versus 11 +/- 1 pmol/24 hours at baseline, n=48), which paralleled an increase in systolic BP (174 +/- 10 mm Hg at week 4 versus 110 +/- 2 mm Hg at baseline). By contrast, OLC excretion peaked at week 1 and returned to baseline levels. Administration of an anti-MBG, but not anti-ouabain antibody, to DS after 3 weeks of a high NaCl diet lowered BP (139 +/- 7 versus 175 +/- 5 mm Hg, P<0.001, n=5). Acute NaCl loading (2 hours) of DS (n=5) increased MBG and OLC excretion and natriuresis. Pretreatment of acutely NaCl-loaded DS with an anti-MBG antibody (n=5) reduced the excretion of sodium and MBG but not that of OLC. An anti-ouabain antibody (n=5) reduced sodium excretion and both OLC and MBG.. An initial transient stimulation of OLC induced by NaCl loading of DS precedes an MBG response. A sustained increase in MBG production in DS contributes to the chronic BP elevation induced by a sustained high NaCl intake.

Topics: Adrenal Glands; Animals; Antibodies; Blood Pressure; Bufanolides; Cardenolides; Digoxin; Enzyme Inhibitors; Hypertension; Ligands; Male; Models, Animal; Natriuresis; Pituitary Gland; Potassium; Rats; Rats, Inbred Dahl; Saponins; Sodium; Sodium Chloride; Sodium Chloride, Dietary; Sodium-Potassium-Exchanging ATPase; Vasoconstrictor Agents

Dahl salt-sensitive rats (DS), which have a mutation in the alpha-1 subunit of Na(+)/K(+)-ATPase, exhibit impaired pressure natriuresis and on a high-salt diet, retain Na(+) and exhibit increased blood pressure. Recently, we have shown that mammalian tissues contain a bufadienolide Na(+)/K(+)-ATPase inhibitory factor, marinobufagenin (MBG), that exhibits greater affinity for the alpha-1 than alpha-3 sodium pump isoform. The present study investigated the possible role of MBG in hypertension in DS on a high NaCl intake. Eight DS and 8 Dahl salt-resistant rats (DR) were placed on an 8% NaCl diet. Within 2 weeks, systolic blood pressure increased in DS (162+/-9 mm Hg at week 2 versus 110+/-2 mm Hg in baseline, P<0.01), and increased less in DR (124+/-3 mm Hg at week 2 versus 112+/-2 mm Hg in baseline). Renal excretion of MBG increased 4-fold (38.9+/-7.6 pmol versus 9.1+/-1.3 pmol in baseline, P<0.01) in DS, but by only 25% in DR (13.2+/-0.9 pmol versus 10.3+/-0.7 pmol in baseline). Excretion of endogenous ouabain did not change in either strain. MBG-immunoreactive material was purified from the urine of hypertensive DS by means of 2 steps of reverse-phase high performance liquid chromatography (HPLC) and compared with plant ouabain and amphibian MBG for its ability to inhibit the Na(+)/K(+)-ATPase from rat kidney (which expresses only alpha-1 Na(+)/K(+)-ATPase isoform). Unlike ouabain (IC(50)=248 micromol/L), serially diluted, HPLC-purified MBG immunoreactivity from DS and authentic MBG potently inhibited rat kidney Na(+)/K(+)-ATPase (IC(50)=70 and 78 nmol/L, respectively). Our results suggest that an alpha-1 Na(+)/K(+)-ATPase ligand, MBG, is elaborated to promote natriuresis in hypertensive DS. MBG acts as a selective inhibitor of the ouabain-resistant alpha-1 Na(+)/K(+)-ATPase subunit, ie, the major sodium pump isoform of the kidneys, as would be expected of a putative natriuretic hormone.

Topics: Animals; Blood Pressure; Bufanolides; Chromatography, High Pressure Liquid; Enzyme Inhibitors; Hypertension; Isoenzymes; Kidney; Natriuresis; Ouabain; Rats; Rats, Inbred Dahl; Sodium; Sodium Chloride; Sodium-Potassium-Exchanging ATPase; Sodium, Dietary

Our study investigated the hypothesis that the combination of a high NaCl diet and social isolation stress would increase systolic blood pressure (SBP) and endogenous sodium pump ligands (SPL), ouabainlike compound (OLC), and marinobufagenin (MBG). Excretion of MBG and OLC, SBP, and organ weights were studied in four groups (n = 8) of male Fisher 344 x Norwegian brown rats: controls, socially isolated (Iso), 4% NaCl diet (Salt), and the combination of Salt and Iso (Iso+Salt). In Salt, MBG excretion increased by 78% (P < 0.01), whereas SBP and OLC remained unchanged. In Iso, SBP and MBG did not change, but OLC peaked on day 1. In the Iso+Salt, SBP increased by 9 mmHg, MBG excretion increased (42.0 +/- 7.6 vs. 10.0 +/- 1.5 pmol/24 h, P < 0.01), whereas OLC peaked at day 1 (25.0 +/- 2.5 vs. 10.0 +/- 2.0 pmol/24 h, P < 0.01) and remained elevated. Heart and kidney weights were increased in Salt and Iso+Salt. Aortic weights were increased in Iso and Iso+Salt. Thus a high NaCl intake stimulates MBG excretion, whereas isolation stress stimulates OLC. The combination of Salt and Iso is accompanied by marked stimulation of both SPL.

Topics: Animals; Bufanolides; Cardenolides; Digoxin; Drinking; Eating; Hypertension; Male; Natriuresis; Organ Size; Rats; Rats, Inbred BN; Rats, Inbred F344; Saponins; Social Isolation; Sodium Chloride, Dietary; Sodium-Potassium-Exchanging ATPase; Stress, Psychological; Urine

Previous studies have shown that high end-tidal CO2 (PetCO2) is a marker for sodium sensitivity of blood pressure (BP) in White Americans, and that the BP of African Americans is more sensitive to high sodium intake than that of whites. The present study tested the hypothesis that resting PetCO2 is higher in normotensive African Americans than in whites. Resting end-tidal CO2 of 395 white and 125 African American participants in the Baltimore Longitudinal Study on Aging was monitored for 20 min with a respiratory gas monitor, and BP and heart rate were recorded every 5 min by oscillometric methodology. Twenty-four-hour urinary excretion of a circulating sodium pump inhibitor marinobufagenin-like compound (MBG), which increases when plasma volume is expanded, was also analyzed by fluoroimmunoassay in racial groups. Mean resting PetCO2 of African American men was higher than that of white men (38.1+/-0.5 v 36.4+/-0.3 mm Hg), and resting PetCO2 of African American women was higher than that of white women (37.7+/-0.3 v 36.2+/-0.3 mm Hg). The differences were not significant in either men or women less than 50 years old, but were substantial in both men and women more than 50 years. Twenty-four-hour urinary excretion of MBG was higher in white (2.7+/-0.2 pmol) than in African American (2.1+/-0.2 pmol) participants, and high PetCO2 was a significant independent predictor of high MBG excretion in African Americans. These data are consistent with the hypothesis that the higher resting PetCO2 in African Americans plays a role in slower urinary excretion of sodium, greater BP sensitivity to high sodium intake, and increased prevalence of chronic hypertension.

Topics: Age Distribution; Black People; Blood Pressure; Blood Volume; Bufanolides; Carbon Dioxide; Female; Humans; Hypertension; Male; Middle Aged; Regression Analysis; Sex Distribution; Sodium; Sodium-Potassium-Exchanging ATPase; White People

Recently, an endogenous digitalis-like factor (EDLF) was shown to be stimulated in corticotropin (ACTH) hypertension in the rat. We have shown that mammalian plasma contains a vasoconstrictor Na,K-ATPase inhibitor, which cross-reacts with an antibody to amphibian EDLF, marinobufagenin. In the present experiment, the effect of 8 days of intramuscular ACTH treatment (0.5 mg/kg/day) of male Fisher 344 x NB rats on blood pressure, plasma ouabain-like and marinobufagenin-like immunoreactivity, and on the activity of Na,K-ATPase in aortic sarcolemma were studied. The ACTH treatment for 8 days resulted in increased systolic blood pressure (151 +/- 12.4 v 121 +/- 4.0 mm Hg, P < .01), inhibition of Na,K-ATPase in aortic sarcolemma (2.99 +/- 0.35 v 5.43 +/- 0.17 micromol ADP/mg(prot)/h), and increases in plasma concentration of marinobufagenin-like (0.44 +/- 0.06 v 0.21 +/- 0.05 nmol/L), but not ouabain-like (0.09 +/- 0.01 v 0.10 +/- 0.04 nmol/L) immunoreactivity. In dissociation enhanced lanthanide fluoroimmunoassay (DELFIA), serial dilutions of plasma from ACTH-treated rats extracted with 25% and 80% acetonitrile, respectively, demonstrated parallelism to the calibration curves of ouabain and marinobufagenin. These findings suggest that an endogenous bufodienolide Na,K-ATPase inhibitor, rather than an endogenous ouabain-like compound, is increased after 8 days of treatment of rats with ACTH.

Topics: Adrenocorticotropic Hormone; Animals; Blood Pressure; Body Weight; Bufanolides; Erythrocytes; Heart Rate; Hypertension; Immunoassay; Male; Ouabain; Rats; Rats, Inbred F344; Sarcolemma; Sodium; Sodium-Potassium-Exchanging ATPase; Systole