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Studies on a plasma cardiac glycoside assay based upon displacement of 3-H-ouabain from Na+-K+-ATPase.

We tested an assay system introduced for plasma glycoside measurements, basing on the displacement of 3-H-ouabain from Na+-K+-ATPase by unlabeled glycoside. ATPase preparations from hog, cat and guinea pig were used. Displacements were performed using 20 cardiac glycosides, genins and derivatives with different cardiac activity. Most of the glycosides and derivatives do not induce a continuous 3-H-ouabain displacement from the ATPase, but a very steep increase of unbound 3-H-ouabain between 10-minus 7 and 2 times 10-minus 7 M. Therefore this assay system shows a satisfactory discrimination only in a short concentration range. This behavior and a relatively low sensitivity make the ATPase displacement assay problematic for clinical and pharmacokinetical plasma glycoside measurements.

Adenosine Triphosphatases↗

The influence of reduced serum potassium level on the toxicity of some cardenolides in guinea pigs.

Recent experiments on the pharmacological properties of the semisynthetic cardiotonic steroid strophanthidin-3-bromoacetate (SBA) have challenged the well-known potassium digitalis antagonism in isolated heart muscle preparations. In order to establish these results in vivo, the minimum lethal doses (LDmin) of ouabain (OUA), digoxin (DO), digotoxin (DT), k-strophanthidin (STR) and SBA were determined by the infusion toxicity method in guinea pigs at normokalemia and hypokalemia. The experimentally induced decrease of the serum potassium concentration (5.0 mmoles/l vs. 3.3 mmoles/l) significantly reduced the LDmin of DO (1.42 vs. 1.05 mumoles/kg), DT (1.78 vs. 1.24 mumoles/kg) and STR (20.16 vs. 15.98 mumoles/kg), whereas the LDmin of OUA (0.37 vs. 0.34 mumoles/kg) was not altered. Contrary, the LDmin of SBA was even slightly, but not significantly increased during hypokalemia (16.77 vs. 19.04 mumoles/kg). In addition, from the experimental data an optimum time of infusion (Topt), corresponding to the LDmin, can be derived, which is equivalent to the time for optimum "utilization" of the drug. The obtained sequence: STR less than OUA less than DO less than DT less than SBA represents the well-known differences in the onset of the pharmacological action in man resp. animal. Hypokalemia in general resulted in a shortening of the Topt, thus indicating a more rapid "utilization" of the drug tested. The above differences of the cardenolide action at reduced serum potassium concentration may be dependent on the recently reported divergent influence of potassium on the association- resp. dissociation rate constants for the interaction of these drugs with their binding site at the Na+-K+-ATPase.

Animals↗

Multifocal or chaotic atrial rhythm: report of nine infants, delineation of clinical course and management, and review of the literature.

Nine infants with episodic or continuous chaotic atrial rhythm (CAR) are presented. In addition to 3 or more different P-wave contours, atrial rates greater than 100 per minute, variable PP, RR, and PR intervals, and a discrete isoelectric baseline, findings included atrial rates that varied from a low of 50 to 120 to a high of 140 to 270 per minute, ventricular rates that varied from a low of 40 to 50 to a high of 180 to 270 per minute, and periodic sinus arrest with junctional escape rhythm. Except for the arrhythmia, all had a normal cardiac examination, ECG, chest x-ray film, and echocardiogram. Six infants were otherwise normal; one had an orbital rhabdomyosarcoma; one had neonatal asphyxia; and one had respiratory distress, bronchopulmonary dysplasia, and an intraventricular cerebral hemorrhage. The CAR persisted from 3 days to 20 months; it spontaneously reverted to normal sinus rhythm in 8 infants and persists in 1 infant at age 7 months. Digoxin (4 patients), propranolol hydrochloride (3 patients), quinidine sulfate (2 patients), and lidocaine (1 patient) did not alter the CAR. No patient had heart failure secondary to the CAR, although three also had episodes of sustained atrial tachycardia, which while present caused heart failure. All patients are functioning normally at home and have normal findings on cardiac examination and have normal ECGs at ages 3 to 38 months. Seven are in normal sinus rhythm, one has rare atrial premature contractions, and one has persistent CAR. We conclude that specific treatment was not necessary in these infants with CAR, except in those with associated sustained atrial tachycardia, which itself may cause heart failure.

Anti-Arrhythmia Agents↗

Interactions of cationic drugs and cardiac glycosides at the hepatic uptake level: studies in the rat in vivo, isolated perfused rat liver, isolated rat hepatocytes and oocytes expressing oatp2.

This paper deals with a crucial mechanism for interaction of basic drugs and cardiac glycosides at the hepatic uptake level. Available literature data is provided and new material is presented to picture the differential transport inhibition of bulky (type2) cationic drugs by a number of cardiac glycosides in rat liver. It is shown that the so called organic anion transporting peptide 2 (oatp2) is the likely interaction site: differential inhibition patterns as observed in oocytes expressing oatp2, could be clearly identified also in isolated rat hepatocytes, isolated perfused rat liver and the rat in vivo. The anticipation of transport interactions at the hepatic clearance level should be based on data on the relative affinities of interacting substrates for the transport systems involved along with knowledge on the pharmacokinetics of these agents as well as the chosen dose regimen in the studied species. This review highlights the importance of multispecific tranporter systems such as OATP, accommodating a broad spectrum of organic compounds of various charge, implying potential transport interactions that can affect body distribution and organ clearance.

Animals↗

[Heart failure as a cardiac symptom of sarcoidosis. Successful treatment of heart failure with steroids, digitalis and an angiotensin-1-receptor antagonist in sarcoidosis].

BACKGROUND: Sarcoidosis is a multisystemic disorder that may involve every organ. A symptomatic manifestation of the myocardium is possible, in these cases arrhythmias are the most common symptoms. CASE REPORT: This case report presents a 26-year-old female with the recurrence of Boeck's sarcoid. Fever, chill and a severe reduction in stress tolerance were the first symptoms. At the time of admission she complained of Grade III dyspnea according to the NYHA classification. The echocardiogram showed a severe impairment of the global and left ventricular function. The left ventricular ejection fraction was reduced to 30% and the Tei index was elevated to 1.0. A specimen taken from a mediastinal tumor confirmed the hypothesis of the recurrence of the sarcoidosis. Myocardial perfusion scintigraphy showed typical lesions for myocardial sarcoidosis. There were signs of an old anteroseptal infarction in the resting ECG without evidence of myocardial ischemia during a stress test. Repeated Holter-ECGs were without signs of severe arrhythmias whereas ventricular late potentials were positive. After the combined therapy with steroids, digitalis and an angiotensin-1 receptor antagonist, mediastinal mass and Tei index were reduced and the ejection fraction moved to 56%. Dyspnoea was classified with Grade II according to the NYHA classification. CONCLUSION: Treatment of asymptomatic sarcoidosis is still controversial, whereas the treatment of life-threatening sarcoidosis, eye involvement or severe hypercalcemia is accepted. This case report presents the successful treatment of severe heart failure with prednisone, glycosides and an angiotensin-1 receptor antagonist. With this combined therapy an improvement of subjective and objective parameters was possible.

Adult↗