Effect of physostigmine on ventricular fibrillation and myocardial glycogen in hypothermic dogs.

1. Physostigmine (0.1 mg/kg i.v.) given at 37 degrees C and 25 degrees C rectal temperatures, completely protected the hypothermic dog heart against ventricular fibrillation.2. Pentolinium, atropine, vagotomy and reserpine did not significantly alter the incidence of ventricular fibrillation.3. The incidence of ventricular fibrillation under hypothermia could be significantly increased by ligating the anterior descending branch of the left coronary artery. The incidence of ventricular fibrillation in coronary ligated hypothermic dogs was reduced to half by physostigmine pretreatment.4. Hypothermia produced ventricular glycogen depletion and physostigmine prevented ventricular glycogenolysis under hypothermia. However, in the normothermic state physostigmine itself produced a significant decrease in cardiac glycogen.5. The relation between the antifibrillatory and antiglycogenolytic effects of physostigmine under hypothermia are discussed.