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[Effect of cardiac desympathization, stimulation of the central adrenergic structures and blockade of beta-adrenergic receptors on cardiotonic and cardiotoxic effect of cardiac glycosides].

The object of study were rabbits who had been subjected to ligation of 3 or 4 large branches of the left descending coronary artery 14-20 days before the experiment. In experiments with surgical desympathization of the heart it was established that the inotropic effect of cardiac glycosides did not depend on the concentration of catecholamines in the myocardium. In stimulation of adrenergic structures of the posterior hypothalamus attended with an increase in sympathetic innervation of the cardiovascular system the cardiotoxic threshold of cardiac glycosides was considerably reduced. Propranolol (Inderal) administered in a dose which blocks the beta-adrenergic apparatus of the heart prevents the development of the positive inotropic effect of therapeutic doses of strophanthin K on a hypodynamic left ventricular myocardium.

Animals↗

[Therapeutic equivalence and inequivalence of chemically identical substances using cardiac glycosides for an example (author's transpl)].

The problem of therapeutic equivalence or inequivalence cannot be solved by "ignoring facts and proclaiming opinions". The entire problem is multifarious and is not even clearly arranged although heart glycosides have been used for 200 years in the therapy of cardiac insufficiency. It comprises the physico-chemical properties of the drugs, its preparation and its pharmacolinetic behaviour in the organism. Therapeutic equivalence or inequivalence can primarily only be evaluated in connection with the disease and the symptoms of disease, respectively. Thus, manufacturers, pharmacists and physicians likewise are confronted with the problem. The differences in bioavailability of the individual cardiac glycosides show the necessity for: 1. The number of fixed combinations of heart glycosides should be limited in the interest of drug safety. 2. Only such drugs should be approved whose quantitative and qualitative equivalence has been demonstrated with regard to the monoglycoside. 3. When prescribing digoxin derivatives one should not only observe the bioavailability but take also into account the chemical stability and the pharmacolinetic behaviour.

Animals↗

Behaviour of cardiac glycosides and cardenolides related to digitoxigenin on sephadex LH-20.

The behaviour of six cardenolides and eight cardiac glycosides related to digitoxigenin during column chromatography on Sephadex LH-20 gel has been investigated. Complete resolution was obtained for mixtures of digitoxigenin, gitoxigenin and digoxigenin, but not for those of the 3-epimeric cardenolides. It was possible to achieve a group separation of cardenolides and their glycosides of the digitoxigenin series from those of the digoxigenin or gitoxigenin series.

Cardanolides↗

[Utilization of cardiac glycosides in Czechoslovakia--does it correspond to need?].

The data are given on the consumption of cardiac glycosides (CD) in the CSSR over the past 18 years (1970-1987). Consumption expressed in terms of defined daily doses (DDD) permitted to construct time series of the consumption of this group of pharmacotherapeutic agents as a whole as well as individual CG and to compare the data thus obtained with similar data from abroad. The results indicate that the consumption of CG as a whole culminated in Czechoslovakia in 1983 (27.6 DDD per a population of 1000 per day = 27.6 DDD/1000/d) and that there has been a slow decline ever since. Compared with foreign data, Czechoslovakia's quantitative consumption of CG is roughly between countries noted for traditionally high consumption (GDR 84.8 DDD/1000/d) and those with low consumption (Scandinavian countries with the exception of Sweden, about 10 DDD/1000/d). Unlike Czechoslovakia, however, all other countries with well established CG consumption have been exhibiting a relatively steep and lasting decline in CG consumption since the late 1970s. This reduction reflects modern trends of CG pharmacotherapy, especially stricted consideration of the uses as distinct from the risks of CG administration, as well as some of the recent efforts to terminate long-term CG treatment particularly in vaguely indicated cases. As for individual CG consumption, Czechoslovakia, similarly as other countries, has been favouring more rational prescription of oral digoxin at the expense of the oral form of lanatoside C, while parenteral digoxin has for all practical purposes become a substitute for strophantin.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Glycosides↗

Effects of cardiac glycosides on excitation-contraction coupling in frog skeletal muscle fibres.

1. The effects of digoxin and ouabain on the calcium release flux from the sarcoplasmic reticulum (SR), isometric tension and intramembrane charge movement were studied in voltage clamped skeletal muscle fibres of the frog. 2. Both cardiac glycosides increased both calcium transients and simultaneously recorded tension at all membrane potentials, showing different effects on the peak and on the steady components of the calcium release flux. These effects were attained at an extracellular digoxin concentration of 5 nM and an estimated intracellular ouabain concentration of 1-2 nM. Digoxin and ouabain thus exerted their effects at the same concentration on calcium release in skeletal muscle as previously observed in isolated cardiac-type ryanodine receptor (RyR) calcium release channels. 3. The peak of SR calcium release increased at all voltages, with the largest potentiation at intermediate membrane potentials. This increase in calcium release flux was attained despite an unchanged SR calcium content. The attenuated release rate therefore reflected an increased number of open RyR channels rather than increased SR loading. 4. These effects could be attributed to an increase in calcium release activation and not a decrease in the rate of inactivation. Rather, the rate of inactivation was enhanced at all voltages as expected from the increased calcium concentration in the triadic junction. 5. In contrast, CMA (17 alpha-acetoxy-6-chloro-4, 6-pregnadiene-3,20-dione; 5 microM), a Na(+)-K(+)-ATPase inhibitor with no positive inotropic effects on the heart, neither influenced SR calcium release nor antagonized the effects of ouabain. 6. Both digoxin and ouabain preserved total intramembrane charge apart from a small negative shift in the mid-point voltage and increase in slope factor. 7. Both digoxin and ouabain induced calcium release from heavy SR vesicles at rates comparable to that induced by ryanodine or caffeine. 8. It is concluded that at least part of the inactivating component of SR calcium release involves distinct RyR calcium release channels that resemble the cardiac RyR isoform in its specific sensitivity to cardiac glycosides.

Animals↗

[Influence of high intravenous doses of D-penicillamine on toxic actions of cardiac glycosides in the guinea pig. Short communication (author's transl)].

Intravenous infusions of arrhythmogenic and lethal doses of ouabain and digoxin in anesthetized guinea pigs were not influenced by pretreatment with 1 g/kg D-penicillamine. The respective doses of proscillaridin and digitoxin, however, were significantly decreased by D-penicillamine. As could be demonstrated with proscillaridin this effect of D-penicillamine was dose-dependent between 0.25 and 1.0 g/kg. Obviously the strong plasma-protein binding of D-penicillamine leads to a displacement from binding sites of such cardiac glycosides which are also strongly bound to plasma proteins and thus reduces toxic doses of cardiac glycosides. Because of the extremely different doses of D-penicillamine in the animal experiments compared to those used therapeutically in man the present findings are irrelevant for clinical practice.

Animals↗

Systems approach to study of solute transport across membranes using suspension cultures of mammalian cells V: Uptake and release kinetics of cardiac glycosides by Burkitt lymphoma cells.

Mass transport studies with three cardiac glycosides in the Burkitt lymphoma cell system have provided significant examples of the factorization and quantification of the influences of serum-drug binding, membrane-drug binding, cell interior binding, and intrinsic membrane permeability upon the uptake and release kinetics of drugs in living cell systems. All of the data from the glycosides are in agreement with the general physical model involving the rapid equilibration of the solute within the cell after permeation through the rate-determining plasma membrane barrier. The transport of digitoxin was influenced by membrane and serum binding and that of digoxin was influenced by membrane binding. There was no binding of ouabain to the plasma membrane and serum. The variables in the uptake and release kinetic studies at pH 7.3 included the use of viable and heat-inactivated cells, fetal bovine serum levels, and temperature.

Burkitt Lymphoma↗