Abstract
Electrocardiographic studies of pigeons were made with the idea of comparing the emetic and cardiac actions of digitalis, since emesis is a prominent action of the drug in pigeons, and the emetic assay method appears to predict the therapeutic dosage for slowing of the heart in man. Using tinctures of the drug injected intravenously, one-fourth the minimum emetic dose of digitalis caused a 10% slowing of the rate, and one-half the dose a 20% decrease in auricular rate and an A-V block in some pigeons. A single minimum emetic dose, causing emesis in 10 minutes, produced heart block or marked slowing in 1 to 5 minutes and 3 times the emetic dose produced all the effects in 10 to 15 seconds. The cardiac slowing was always preceded by a short period of acceleration which was due only partly to the injection fluid. On the other hand, veratrum and aconite, which also affect the heart through the vagus mechanism but do not cause emesis in pigeons, caused an immediate but brief slowing followed by tachycardia, either auricular or ventricular in origin, and in the case of veratrum there was, in addition, a curious waxing and waning of electrical complexes in cycles, 20 to 30 beats long. That the cardiac changes after digitalis and the slowing of veratrum were of vagal origin was shown by the fact that the effects were prevented and abolished by atropine and vagotomy. The effects were not altered by previous injection of ergotoxine, which by itself slowed the pulse through paralysis of the accelerator nerves, although epinephrine, in large doses, still caused a marked and prolonged acceleration presumably due to muscular stimulation.
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