Abstract
The reported effectiveness of clonidine in depressing sympathetic cardiac nerves led us to test whether this agent would counteract cardiac arrhythmias induced by digitalis. This was done by administering clonidine to Dial-urethane-anesthetized cats in which arrhythmias had been induced by deslanoside and in which we monitored the: 1) electrocardiogram, 2) femoral arterial blood pressure, 3) right ventricular contractile force and 4) spontaneous electrical activity in preganglionic sympathetic nerve fibers. Clonidine in a dose range of 18.1 to 60.2 mg/kg was found to convert an established ventricular tachycardia to a regular sinus rhythm while simultaneously depressing the increased sympathetic nerve firing induced by deslanoside. Clonidine was relatively ineffective against similar arrhythmias produced in spinal-sectioned cats. Pretreatment with 6.25 mg/kg of clonidine significantly increased the doses of deslanoside necessary to produce ventricular tachycardia and ventricular fibrillation. Although depression of cardiac force, blood pressure and heart rate occurred with clonidine administration, these effects were not detrimental to the animals in the doses required for prophylaxis and treatment of the arrhythmias. These results support our hypotheses that agents which depress sympathetic nerve firing have the capacity to antagonize digitalis-induced cardiac arrhythmias and that effective antidigitalis materials may be found by screening agents which are neurodepressant to the sympathetic nervous system.
Footnotes
- Received November 16, 1971.
- Accepted March 30, 1972.
- © 1972 by The Williams & Wilkins Co.
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