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Na(+)-channel activators increase cardiac glycoside sensitivity in failing human myocardium.

Na(+)-channel activators increase intracellular Na+ and thereby enhance the transport rate of sarcolemmal Na+,K(+)-ATPase. We investigated the interaction of the new Na(+)-channel activator BDF 9148 (BDF) with the cardiac glycoside ouabain (OUA) in human myocardium. The influence of OUA (0.01-0.1 microM) and of OUA after prestimulation with BDF (0.1 microM, 1 microM; BDF+OUA) on isometric force of contraction (FOC, force of contraction; +T/-T, peak rate of tension increase/decay) of electrically driven (1 Hz, 37 degrees C) papillary muscle strips from terminally failing [New York Heart Association classification IV (NYHA IV) heart transplants, n = 19] human myocardium was studied. We also examined the effects of BDF and OUA on nonfailing human myocardium (brain death resulting from traumatic injury, n = 5). 0.01 microM OUA enhanced FOC only after prestimulation with BDF (NYHA IV+2.9 +/- 0.4 mN; p less than 0.01). The time until maximal (Tmax: BDF+OUA 117 min, OUA 166 min), half-maximal (T1/2max: BDF+OUA 47 min, OUA 85 min) inotropic effects and time until toxic signs (contracture, extrasystoles) occurred were significantly shorter with BDF+OUA as compared with OUA alone. BDF influenced Tmax, T1/2max, and time until toxic side effects occurred (Ttox) of the OUA-mediated inotropism in a concentration-dependent manner. Both OUA and BDF enhanced +T and -T. The effectiveness of OUA and BDF in increasing FOC was similar to that of Ca2+ (1.8-15 mM) but significantly (p less than 0.01) higher as compared with the beta-adrenoceptor-agonist isoprenaline in NYHA IV. In myocardial membranes, [3H]ouabain binding (Bmax, Kd) was not affected by BDF.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Effects of cardiac depression and of anesthesia on the myocardial action of a cardiac glycoside.

The effects of ouabain (G-strophanthin) 20 mug/kg, on left ventricular (LV) pressure (P), diameter (D), velocity of contraction (dD/dt), and dP/dt were studied in conscious dogs instrumented with ultrasonic diameter gauges and miniature pressure gauges. The effects of ouabain were compared on separate occasions in the same dogs after cardiac depression with propranolol, 3.0 mg/kg, and also after general anesthesia with Na pentobarbital, 30 mg/kg. Maximal pressor effects were observed in the first 10 min, but maximal effects on the contractile state occurred at 30 min after ouabain. At this time, in conscious dogs, ouabain had increased LV isolength systolic pressure by 5%, LV isolength velocity by only 9%, and LV (dP/dt)/P by 21%, while end systolic diameter (ESD) decreased slightly and end diastolic diameter (EDD) and heart rate (HR) were unchanged. After anesthesia, ouabain increased LV systolic pressure by 8%, velocity 32%, (dP/dt)/P by 47%, and ESD decreased by 1.2 mm while EDD rose slightly and HR fell by 26 beats/min. Returning HR to control with atrial pacing decreased EDD 0.9 mm below control. After cardiac depression with propranolol, ouabain caused responses similar to those observed in the anesthetized dogs. Thus, the cardiac glycoside was found to exert only minor inotropic effects on the nonfailing heart of conscious dogs but far more striking inotropic responses in the anesthetized state.

Acetylcholine↗

The cardiac glycoside ouabain potentiates excitotoxic injury of adult neurons in rat hippocampus.

We demonstrate that the enzyme family responsible for the restoration of the transmembrane cation balance, namely the sodium pump (Na+, K(+)-ATPase), plays a critical role in whether glutamate injures adult neurons in vivo. Partial inhibition of the sodium pump by the cardiac glycoside ouabain in young adult rats is not itself damaging. This treatment, however, markedly potentiates ordinarily subtoxic dosages of the glutamate analog kainic acid to produce limbic seizures and widespread neurodegeneration within the hippocampus in a pattern closely resembling that observed for human temporal lobe epilepsy.

Animals↗

[Differential diagnosis of supraventricular rhythm disorders and the tactics in the treatment with cardiac glycosides].

The article discusses the possibilities of differential diagnosis of supraventricular arrhythmians by means of carotid zone stimulation, atrial VCG and ECG recorded from right-bronchial leads. Atrial VCG can reveal the character of the ectopic P-wave and thus helps in the diagnosis of arrhythmias with conspicuous atrial activity. ECG recorded from bronchial leade makes it possible to obtain a large atrial wave and determine elements of decisive importances in the diagnosis of many rhythm disorders: junctional and combined contractions, various types of ectopic P-waves, the character of antero- and retrograde conduction. The tactics of treatment with cardiac glycosides is determined by precise diagnosis of the arrhythmia and its connection with digitalis toxicosis.

Arrhythmias, Cardiac↗