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Cellular electrophysiologic effects of vertebrate digitalis-like substances.

Substances structurally and functionally similar to digitalis glycosides are produced by several vertebrate species. There also is evidence for a digitalis-like substance of human origin. Standard microelectrode techniques were used to study the direct effects on the cellular electrophysiology of canine Purkinje fibers of 1) bufalin, an unconjugated cardiotonic steroid molecule that is produced by the toad Bufo marinus, and 2) an extract of human bile that showed digitalis-like immunoreactivity on radioimmunoassay. The goal of this study was to determine whether these substances have arrhythmogenic effects comparable with those seen with toxic doses of digitalis glycosides. Bufalin, 2 x 10(-8) M, significantly (p less than 0.05) reduced maximal diastolic potential, action potential amplitude and duration and maximal rate of rise of phase 0 (Vmax) within 40 min of onset of exposure. All six fibers developed delayed afterdepolarizations and two developed triggered rhythms. Ouabain was less potent, in that a 2 x 10(-7) M concentration was required to comparably reduce maximal diastolic potential, action potential amplitude and duration and Vmax within 30 min. These Purkinje fibers also developed delayed afterdepolarizations and triggered rhythms. A sample of an extract of human bile that showed digitalis-like immunoreactivity with an antibufalin serum also reduced maximal diastolic potential, action potential amplitude and duration and Vmax, and produced delayed afterdepolarizations and triggered activity. In contrast, immunologically unreactive bile extracts had no appreciable effect on the action potential. In summary, the cardiac toxicity of digitalis substances produced by lower vertebrates is comparable with that induced by the glycosides. Moreover, it appears that humans may produce digitalis-like substances that may be cardiotoxic.

Action Potentials↗

Digitalis for treatment of congestive heart failure in patients in sinus rhythm.

BACKGROUND: Digitalis glycosides have been in clinical use in the treatment of congestive heart failure (CHF) for more than 200 years. In recent years several trials have been conducted to address concerns about efficacy and toxicity. Although a systematic review of the literature was published in 1990, an update is required to include more current trials. OBJECTIVES: To examine the effectiveness of digitalis glycosides in treating CHF in patients with normal sinus rhythm. To examine the effect of digitalis in patients taking diuretics, angiotensin converting enzyme inhibitors, and beta-blockers; patients with varying severity and duration of disease; patients with prior exposure to digitalis vs. no prior exposure; and patients with "CHF due to systolic dysfunction" vs. "CHF with preserved systolic function." SEARCH STRATEGY: The Cochrane Central Register of Controlled Trials (CENTRAL) 2003 Issue 4, MEDLINE (1966 to December 2003) and EMBASE (1990 to December 2003) were searched. Dissertation Abstracts and annual meeting abstracts of the American Heart Association, American College of Cardiology, and European Society of Cardiology were also searched from 1996-2003. In addition, reference lists provided by the pharmaceutical industry (Glaxo Wellcome Inc.) were searched. SELECTION CRITERIA: Included were randomized placebo-controlled trials of 20 or more adult patients of either sex with symptomatic CHF who were studied for seven weeks or more. Excluded were trials in which the prevalence of atrial fibrillation was 2% or greater, or in which any arrhythmia that might compromise cardiac function or any potentially reversible cause of CHF such as acute ischemic heart disease or myocarditis was present. DATA COLLECTION AND ANALYSIS: Articles selected from the searches described above were evaluated as a joint effort of the coauthors. The staff of the Cochrane Heart Group ran searches on the Cochrane Central Register of Controlled Trials. MAIN RESULTS: Thirteen articles meeting the defined criteria were identified, and major endpoints of mortality, hospitalization, and clinical status, based respectively upon 8, 4, and 12 of these selected studies, were recorded and analyzed. The data show that there is no evidence of a difference in mortality between treatment and control groups, whereas digitalis therapy is associated with a lower rate of hospitalization and of clinical deterioration. REVIEWERS' CONCLUSIONS: The literature indicates that digitalis has a useful role in the treatment of patients with CHF who are in normal sinus rhythm.

Cardiotonic Agents↗

[Ventricular arrhythmias in reduced glycoside tolerance and digitalis poisoning together with myocardial infarct].

Electrophysiological fundamental principles of the heart muscle cell and the conduction system are discussed in detail. Basic differences are described. Pathophysiology of ventricular arrhythmias is emphasized, especially the ectopic conduction development and conduction defect of the reentry mechanism. Decreased digitalis tolerance of different causes and overdosage of digitalis may lead to ventricular premature heart beats and tachycardias. Myocardial infarction is discussed in detail because lethality within the first hours of infarction is mostly caused by ventricular fibrillation.

Arrhythmias, Cardiac↗

[Alternatives to glycoside therapy?].

The narrow therapeutic range of digitalis glycosides and the danger of intoxication has prompted a search for alternative medication in recent years. Substances reducing the pre- and afterload of the heart are suitable therapeutic agents and vasodilators are, therefore, used as adjuvant or alternative therapy. Of all positive inotropic substances only the catecholamines play an established part in the treatment of acute myocardial failure. Pilot studies testing orally administrable positive inotropic substances are being conducted, but for the moment no such drugs are available for routine use. Digitalis still remains the drug of choice for all forms of primary impairment of contractility and/or supraventricular tachyarrhythmias. The appropriate dosage has to be adapted to the estimated lean body mass and, if necessary, reduced in a thin person, Digitoxin is preferentially used in cases with suspected renal insufficiency (especially in elderly patients).

Arrhythmias, Cardiac↗

Phenylethanoid glycosides from Digitalis purpurea and Penstemon linarioides with PKCalpha-inhibitory activity.

In a continuation of our search for potential tumor inhibitors from plants, it was found that the CH2Cl2-MeOH (1:1) extracts from Digitalis purpurea and Penstemon linarioides both showed PKCalpha-inhibitory bioactivity. Bioassay-directed fractionation of the extract from D. purpurea yielded the new, weakly active phenylethanoid glycoside 2-(3-hydroxy-4-methoxy-phenyl)-ethyl-O-(alpha-L-rhamnosyl)-(1-->3) -O- (alpha-L-rhamnosyl)-(1-->6)-4-O-E-feruloyl-beta-D-glucopy ran oside (1) together with the four known compounds calceolarioside A (2), calceolarioside B (3), forsythiaside (4), and plantainoside D (5). The extract from P. linarioides yielded the three known glycosides leucosceptoside A (6), acteoside (7), and poliumoside (8), together with the iridoid plantarenaloside (9). All of the isolated compounds, except compound 9, showed inhibitory activity against PKCalpha with IC50 values (in microM) of 125 (1), 0.6 (2), 4.6 (3), 1.9 (4), 14.8 (5), 19.0 (6), 9.3 (7), and 24.4 (8).

Caffeic Acids↗