A Comparison of Effects of Stimulation of Right and Left Peripheral Vagus with Action of Acetylcholine on Electrocardiogram of the Cat

Electrocardiograms were taken in a series of experiments on 40 cats, in which nembutal was the anesthetic employed. The procedures were as follows:

1 Stimulation of the right and left peripheral vagus only; (20 cats.)

2 Jugular injection of acetylcholine (2 to 6 mg./kg.). (20 cats.)

Typical electrocardiograms illustrate the following results:

1 Stimulation of the right vagus brings about a decrease in the rate of both P and QRS complexes, i. e., a sinus bradycardia.

2 Stimulation of the left vagus brings about the dropping out of some QRS complexes, i. e., a partial block.

3 Acetylcholine brings about (a) a decrease or temporary cessation. of QRS Complexes; (b) a heavier dosage (sublethal, about 6 mg./kg.) may result in temporary elimination of P-waves also.

Dale 1 has stated that “vagus impulses produce their effect by liberating acetylcholine among the fibers of the muscular wall of the heart.” From these results it would seem that the action of acetylcholine on the heart more closely approximates that of the left, than of the right, vagus. The question is, therefore, raised as to whether some vagus fibers to the heart may not be more “cholinergic” than others, and a further differentiation of their activity on such a basis ultimately attempted.