Abstract

1. The threshold dose of epinephrine necessary to provoke idioventricular rhythms in dogs under eyelopropane anesthesia was found to be increased slightly by tetraethylammonium chloride or by thoracic sympathectomy.

2. When such "protection" occurred, a reduction in the peak pressor response to epinephrine was always observed.

3. Infusion of blood or constriction of the aorta to a degree which restored the original arterial pressure in all cases restored the original cardiac sensitivity to epinephrine. It was concluded that the cardiac sympathetic innervation participates to no more than a minor extent in the induction of ectopic rhythms by epinephiine and cyclopropane.