Studies on digitalis. 13. A comparison of the effects of potassium on the inotropic and arrhythmia-producing actions of ouabain.

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Abstract
The present investigation was directed toward determining the relative effects of potassium on the arrhythmia-producing and inotropic action exerted by digitalis glyco-sides on the intact heart. Ten anesthetized dogs were given ouabain (30 ug per kg, followed by 30 ug per kg per hour) while right ventricular contractile force was measured with a Walton-Brodie strain gauge arch. Arterial pressure and body temperature were kept constant. When toxic arrhythmias occurred, sinus rhythm was restored with an infusion of KC1, and the administration of both KC1 and ouabain was continued until toxicity recurred. Plasma K increased from an average control value of 3.2 mEq per L to 4.1 mEq per L at initial toxicity and was 5.7 mEq per L. when toxicity recurred. Contractile force increased by an average of 65% of control before initial toxicity developed. After restoration of sinus rhythm, there was a further increase in force averaging 19% of control before toxicity recurred. These results were not modified by adrenalectomy or by maintaining heart rate constant with right atrial stimulation, and KC1 infusion without ouabain did not affect contractile force. It is concluded that the suppression of ouabain-induced arrhythmias by KC1 does not depress the positive inotropic effect of the glycoside and permits the administration of additional amounts of the glycoside, which actually produce a further increase in contractile force.