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PubMed2000

Effects of cardiac glycosides on atrial contractile dysfunction after short-term atrial fibrillation.

BACKGROUND: Despite a long history of use in the treatment of paroxysmal atrial fibrillation (AF), the efficacy of cardiac glycosides has not been established. If such drugs are beneficial in this condition, the general view is that the benefit must be related to their inotropic actions. METHODS AND RESULTS: To assess the effects of the rapid-acting cardiac glycoside, acetylstrophanthidin (AS), on AF and AF-induced right atrial (RA) "stunning," RA wall motion (with ultrasonic crystals), RA pressure, and peak first derivative of pressure (dp/dt) (with microtip transducers) were measured before and after 5 min of high-intensity rapid atrial stimulation (10 Hz; 10 mA; 1 ms) and after the cessation of poststimulation AF. Measurements were made in neurally intact and autonomically blockaded dogs both before and after the administration of AS (0.01 mg/kg IV bolus and 0.015 mg/kg/h IV infusion). AS prevented the post-AF reduction in RA peak dp/dt under neurally intact and autonomically blockaded conditions, and it prevented the post-AF increase in the RA end-systolic dimension and the decrease in the percentage of RA systolic shortening with autonomic blockade. AS was beneficial whether or not baseline inotropy was enhanced by AS. The duration of AF following atrial stimulation was the same before and after AS, but when compared to controls, AS treatment appeared to prolong AF. CONCLUSIONS: Cardiac glycosides exert a favorable effect on AF-induced RA stunning, but this action is unrelated to its effects on the duration of AF.

Animals↗
PubMed1984

Cardiac glycoside receptors in cultured heart cells--I. Characterization of one single class of high affinity receptors in heart muscle cells from chick embryos.

Binding of (3H)-ouabain and ouabain-induced inhibition of the sodium pump and of the (Na+ + K+)-ATPase have been characterized in cultured cardiac muscle and non muscle cells, as well as in cardiac cell membranes--all obtained from chick embryos. In both cell types, ouabain binds to a single type of binding sites in a temperature-dependent manner. The association rate but not the dissociation rate, is lowered by K+; specific binding is lost after heat-denaturation of the cells. Binding parameters (association and dissociation rate constants, activation energies for association and dissociation) are similar in muscle and non muscle cells. The dissociation constant of specific ouabain binding is 1.5 X 10(-7)M in cardiac muscle cells, and 1.9 X 10(-7)M in cardiac non muscle cells, the binding capacity being 2.6 and 2.1 pmoles/mg protein respectively. Specific binding of ouabain to the cells is coupled to inhibition of the sodium pump, as can be seen from ouabain-induced inhibition of active (86Rb+ + K+)-uptake, decrease in cellular K+, and increase in cellular Na+ (EC50 = 10(-7)-10(-6)M). The data obtained with cardiac cells are in good agreement with results found for ouabain binding (dissociation constant 4.3 X 10(-7)M) and (Na+ + K+)-ATPase inhibition (EC50 = 1.4 X 10(-6)M) in cardiac cell membranes prepared from the same tissue. Due to the experimental evidence it is concluded that the binding site for ouabain is identical with the cardiac glycoside receptor of these cells. In cardiac non muscle cells, binding of ouabain to its receptor is strictly coupled to inhibition of active K+-transport in a stoichiometric manner. In cardiac muscle cells, however, active K+-transport is inhibited by less than 10% when up to 40% of cardiac glycoside receptors have bound ouabain. It is assumed that this non-stoichiometric coupling of receptor occupancy and sodium pump inhibition in cardiac muscle cells may prevent substantial changes of Na+- and K+-contents in the heart in the presence of therapeutic levels of cardiac glycosides.

Animals↗
PubMed1993

[Comparative study on use of angiotensin-converting enzyme inhibitors and cardiac glycosides in the treatment of cardiac insufficiency].

The efficacy of captopril (capoten) and digoxin was comparatively studied in long-term randomized, double blind trials of 22 male patients with postinfarction cardiosclerosis, functional classes I-III and preserved sinus rhythm. The optimal doses of the drugs proved to be small (0.31 and 35 mg/day of digoxin and capoten, respectively). No adverse effects were noted. The mortality rate was 10 and 16.7% with digoxin and captopril, respectively. The drugs equally improved the functional class by 0.51 and 0.45 and VO2 max by 1.5 and 1.7 ml/min. Digoxin had a mild effect on heart rate (-8.4%) and ejection fraction (+5.7%) and deteriorated diastolic relaxation, by slowing down the early peak of transmitral Doppler spectrum by 16.2%. Captopril significantly improved diastolic function by increasing the early peak by 17.2%. No significant changes in left ventricular sizes were recorded. The clinical efficacy of captopril was explained by a significant decrease in angiotension II (70%) and norepinephrine (40%) levels and by associated normalization of baroreflex regulation. Digoxin insignificantly affected the levels of angiotensin II and norepinephrine, but improved the baroreceptor regulation of sympathetic control impaired in chronic heart failure. It is concluded that extracardiac mechanisms play a major role in the action of not only captopril, but digoxin in the treatment of patients with postinfarct cardiosclerosis and chronic heart failure with sinus rhythm.

Adult↗
PubMed1988

Subchronic treatment with vanadate does not potentiate the toxicity of cardiac glycosides.

Since it has been claimed that vanadate is an endogenous regulator of Na/K-ATPase activity and that it potentiates the toxicity of cardiac glycosides, we were alarmed to discover that certain Finnish physicians were prescribing vanadate in combination with other trace minerals to elderly patients for many different chronic diseases (e.g., cancer, rheumatism). To study the interaction of vanadate and cardiac glycosides, we fed vanadate in the drinking water (25 micrograms/mL) to guinea pigs for 20 d, and studied either their sensitivity to the acute toxicity of the cardiac glycoside ouabain or whether the vanadate would influence the subacute toxicity of ouabain. Vanadate had no influence on the toxicity of ouabain either acute or subchronically administered, nor was there any sign of inhibition of Na/K-ATPase activity as measured by 86Rb-uptake into intact erythrocytes (RBCs), RBC content of sodium or potassium or Na/K-ATPase activity in RBC membranes prepared from the vanadate-treated guinea pigs. Vanadate had been absorbed in substantial quantities from the gastrointestinal tract, since serum, heart, liver, and especially kidney contained measurable amounts of vanadium in contrast to controls, but it is concluded that this vanadate is not in a biologically active form.

Animals↗
PubMed1989

Mass spectrometric analysis of cardiac glycosides by the desorption/ionization technique potassium ion ionization of desorbed species.

The analysis of cardiac glycosides by the desorption/ionization (D/I) mass spectrometric technique potassium ion ionization of desorbed species (K+IDS) is presented. K+IDS mass spectra of digitonin, digoxin, digoxigenin, digitoxin and ouabain are discussed to demonstrate the capabilities of this D/I method. The K+IDS analysis consists of two steps: thermal desorption of neutral molecules representative of the analyte, followed by gas-phase addition of K+ ions to these species. Structural and molecular weight information of the cardiac glycosides is obtained with the K+IDS technique. The most intense peak in the K+IDS mass spectrum of an analyte, M, is frequently the [M]K+ ion. Interpretation of the K+IDS mass spectra is simple, since one thermal degradation mechanism dominates. This mechanism is a 1,2-elimination process. A variation of the original K+IDS technique, performed by changing the ionizing metal from K+ to Na+ (i.e. Na+IDS), is presented for the analysis of digoxin. The Na+IDS mass spectrum of digoxin contains more structural information than the K+IDS mass spectrum of that compound. This may lead to a means of controlling the types of information obtainable with this D/I technique by varying the cation that is thermionically generated. K+IDS analyses can be performed rapidly, no sample derivatization is necessary, no matrix is required and little instrument modification is necessary.

Cardiac Glycosides↗
PubMed1984

Cardiac glycosides with different effects in the heart.

Remarkable differences exist between the effects of different cardiac glycosides (native and semi-synthetic) with respect to the affinity and to the magnitude of inotropic responses and their time courses. At glycoside concentrations which lead to identical Na-K-ATPase inhibitions, the inotropic responses vary widely. This finding contradicts the hypothesis that the increase of contractile force is the consequence of an ATPase inhibition and causally related to it. We propose the hypothesis that the inhibition of ATPase and the inotropic stimulation provoked by cardiac glycosides are two parallel events, not causally related but both mediated by the same receptor. The inhibition of the Na-K-ATPase is the consequence of the occupation and thus proportional to the concentration of the glycoside-ATPase complexes. In contrast, the inotropic response is determined by the frequency of glycoside-ATPase-interactions. Glycosides which possess high association and dissociation rate constants will interact with the ATPase with high frequencies and thus will evoke larger inotropic responses at a given ATPase inhibition than glycosides with low turnover rates.

Animals↗
PubMed1983

Comparison of the inotropic potencies of some synthetic and naturally occurring cardiac glycosides using isolated left atrium of guinea pig.

The inotropic activity of 19 cardioactive steroids was determined using the electrically driven left atrium of the guinea pig. The compounds tested included five alpha-L-rhamnosides and four alpha-L-thevetosides. These were compared with their related genins and with representative examples of beta-D-glycosides. The study showed that rhamnosides and thevetosides were amongst the most active of all cardiac glycosides. The high activity of these compounds was probably related to the alpha-L-glycoside linkage and the configuration of the 4'-hydroxyl group and the 5'-methyl group. There was a stepwise loss of activity when the hydroxyl groups of the sugars were acetylated. The extent to which rhamnose enhanced the potency of different genins varied with the nature of the genin and ranged from 6- to 35-fold. The great variation in the published values for some of the glycosides tested demonstrates the need to standardize methods for testing cardiac glycosides.

Animals↗
PubMed1998

A specific binding protein for cardiac glycosides exists in bovine serum.

Searching for a binding protein in blood, which may be involved in the specific transport of cardiac glycosides to their receptor sites on the sodium pump, we isolated a cardiac glycoside-binding protein (CGBG) of 26 kDa from the globulin fraction of bovine serum by affinity chromatography and on a ouabain-Sepharose 4B column by a purification factor of 5000. The cardiac glycoside-binding globulin was labeled specifically and covalently by the protein-reactive digoxigenin derivative HDMA (N-hydroxysuccimidyldigoxigenin-3-O-methylcarbonyl-epsilon-+ ++aminocapro ate). Even very high concentrations of other steroids, such as estrogen, testosterone, progesterone, and cortisone, did not prevent HDMA-labeling (at 5 and 100 nM) of CGBG, but the cardenolides ouabain and digoxin or the bufadienolide proscillaridin A did so. CGBG is a homodimer of two 26-kDa subunits forming disulfide bonds, since HDMA labeling of a protein of 53 kDa was observed in SDS-polyacrylamide gel electrophoresis when beta-mercaptoethanol was absent during SDS denaturation. The N-terminal amino acid sequence K-D-V-Y-R-A-P-D-G-T-Q-S-A showed no sequence similarity with proteins recorded in gene and protein sequence data banks. A 90-kDa cytosolic CGBG exists in bovine kidneys and reacts with antibodies against CGBG. Binding of ouabain to the cardiac glycoside-binding globulin was monitored by quenching of intrinsic tryptophan fluorescence. Such studies reveal two negatively cooperative ouabain binding sites with Kd' of 1.52 nM and Kd' = 75 nM and with an interaction factor of 50 using a Koshland-Némethy-Filmer model. The demonstration of a cardiac glycoside-binding globulin in plasma is consistent with the recent finding of endogenous cardiac glycosides in mammals.

Affinity Labels↗
PubMed1987

Cardiac glycosides stimulate phospholipase C activity in rat pinealocytes.

Ouabain and related cardiac glycosides stimulate phospholipase C activity 5-fold in rat pinealocytes. The combined treatment of ouabain and norepinephrine, which also stimulates phospholipase C, produces an additive effect. The effects of either ouabain or norepinephrine are blocked by EGTA. However, there are notable differences. The stimulatory effect of ouabain is lost when extracellular Na+ is reduced to 20 mM and is not blocked by prazosin. In contrast, the stimulatory effect of norepinephrine is not blocked when extracellular Na+ is reduced to 20 mM but is blocked by prazosin. Ouabain appears to increase phospholipase C activity through a mechanism involving inhibition of Na+,K+-ATPase, and an accumulation of intracellular Na+ and Ca2+, not involving alpha 1-adrenoceptors. These findings raise the possibility that activation of phospholipase C might be a more general effect of cardiac glycosides.

Animals↗
PubMed1977

[Use of glucagon in cardiac glycoside poisoning in patients with congestive circulatory insufficiency].

The use of glucagon in 25 patients with congestive circulatory insufficiency of stage IIB-III (according to the classification suggested by N. D. Strazhesko and V. Kh. Vasilenko) on the background of intoxication due to cardiac glycosides showed the drug to be effective as a cardiotonic and antiarrthythmic agent in 12 patients with stage IIB circulatory insufficiency. The data obtained also bear evidence that glucagon may be used in combination with cardiac glycosides, this treatment in some cases having a more marked positive effect on the hemodynamics in patients with decompensation than that encountered in treatment with glucagon alone. When used together with glucagon, cardiac glycosides did not induce intoxication.

Adult↗
PubMed1985

Conformational factors in cardiac glycoside activity.

Gomphoside, a 5 alpha-H cardiac glycoside isolated from Asclepias fructicosa, has an unique double glycosidic linkage to the aglycon through oxygen atoms at 2 alpha and 3 beta of the steroid. The 3'-axial hydroxyl of its conformationally rigid sugar residue appears to be the functional group responsible for its potent inotropic activity. With use of gomphoside as the model compound, the conformation of the flexible glycosidic linkage of the 5 beta-H cardenolides, digitoxigenin alpha-L-rhamnoside and digitoxigenin beta-D-digitoxoside, and the 5 alpha-H cardenolides, uzarigenin alpha-L-rhamnoside and uzarigenin beta-D-6-deoxyalloside, were investigated with the aid of computer graphics and conformational potential energy calculations. The relative inotropic potencies of these cardenolides can be accounted for by considering their active binding conformations with their potential energy distributions. The conformational distribution of the glycosidic moiety was postulated to be the major determinant of the biological activity of these cardenolides.

Animals↗
PubMed1992

The MDR1 gene product, P-glycoprotein, mediates the transport of the cardiac glycoside, digoxin.

Digoxin, a widely used cardiac glycoside with a low therapeutic index, is known to interact with a large and diverse group of co-administered drugs, frequently leading to toxic accumulation of the glycoside. Establishing the mechanism(s) of these interactions, therefore, has potential clinical significance. The present studies implicate P-glycoprotein, the MDR1 gene product overexpressed in multidrug resistant cells, as the apical membrane protein responsible for the renal secretion of digoxin and provide an explanation for the occurrence of digoxin toxicity in the presence of certain co-administered medications. Since digoxin is considered a prototype for endogenous digitalis-like glycosides, the results also allow for speculation that endogenous digitalis-like glycosides may be the natural substrates for P-gp.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

Cardiac glycosides from erysimum cheiranthoides.

Two new cardiac glycosides were isolated from the seeds of Erysimum cheiranthoides. Their structures were characterized as strophanthidin glycosides of 3-O-alpha-L-rhamnopyranosyl-(1-->4)-3-O-acetyl-beta-D-digitoxopyranosyl and 3-O-beta-D-glucpyranosyl-(1-->4)-alpha-L-rhamnopyranosyl-(1-->4)-3-O-acetyl-beta-D-digitoxopyranosyl.

Journal Article↗
PubMedDate not supplied

Maquiroside A, a new cytotoxic cardiac glycoside from Maquira calophylla.

Maquiroside A, a new cardiac glycoside, was isolated from the Peruvian plant Maquira calophylla. The structure was established using spectroscopic methods, and the aglycone was found to be cannogenol. The sugar portion was identified as D-cymarose. Maquiroside A demonstrated activity against the KB cell culture.

Animals↗
PubMed1990

[Synergism in the action of gamma radiation and cardiac glycosides].

Synergism of gamma radiation with 137Cs and cardiac glycosides was investigated in experiments on mice and transplantable Raji tumor cells. A single ip administration of these drugs at nontoxic concentrations 30-60 min. after irradiation at the LD30/30 resulted in the survival of 13-20% of animals and the reduction of the mean survival time up to 8.4-12.5 days versus 22.3 days in the control group. Synergism was slightly decreased at administration of glycosides 24 h after irradiation. Glycosides introduced in the irradiated (at a dose of 1-2.5 Gy) human lymphoblastic line caused sharp suppression of lymphoma growth and cellular lysis in experiments in vitro. One hundred per cent death of cells was noted after the use of the drugs at mean toxic concentrations.

Animals↗
PubMedDate not supplied

PST 2238 as an antihypertensive compound that antagonizes the effect of endogenous cardiac glycosides.

This review examines the role of endogenous cardiac glycosides (OLF--ouabain like factors) in the pathogenesis of hypertension. The discovery of ouabain as a new adrenal hormone affecting salt and water homeostasis has initiated research on a new group of compounds. OLF may provide new insights into the mechanisms and therapy of common cardiovascular diseases. PST 2238 (17beta-(3-furyl)-5beta-androstane-3beta-14beta-17alpha-triol), an antagonist of endogenous ouabain, might open new possibilities for the therapy of hypertension and congestive heart failure.

Androstanols↗