Abstract
Intravenous picrotoxin injection has been established as a model of producing arrhythmias, mainly through enhanced central sympathetic outflow. The effects of calcium-channel blockers, and a beta-blocker on these arrhythmias were tested in chloralose-anesthetized cats. Picrotoxin (10mg/kg, i.v.) produced mostly ventricular, sometimes supraventricular tachycardias and ectopic beats, as well as a marked elevation of arterial blood pressure. Nifedipine at the doses of 2μg/kg (i.v. or i.c.) and 5μg/kg (i.v.) transiently suppressed the arrhythmias in some of the cats tested. With the dose of 10μg/kg (i.v.), it promptly and consistently abolished the arrhythmias without recurrence and significantly reduced the blood pressure (-62±8/-59±8mmHg, Δsystolic pressure/Δdiastolic pressure, p<0.001, n=9). A similar degree of blood pressure reduction (-69±8/-67±7mmHg, n=6) after sodium nitroprusside (4-5mg/kg, i.v.) injection abolished the arrhythmias in 4 of 6 cats; however, there was marked ECG evidence of myocardial ischemia in 3 cats. Verapamil (50μg/kg, i.v.) transiently abolished the arrhythmias and significantly decreased the blood pressure (7/7 cats), whereas a larger dose (150μg/kg) had a persistent effect (2/4 cats). Propranolol at a dose of 240μg/kg also consistently abolished the arrhythmias without recurrence in all 4 cats.
We conclude that nifedipine, verapamil and propranolol are effective in the treatment of picrotoxin-induced arrhythmias. This result indicates that calcium-channel blockers or beta-blockers may be clinically effective in the treatment or prevention of arrhythmias caused by intracranial lesions with enhanced sympathetic outflow.
