THE HEART RATE OF UNANESTHETIZED NORMAL, VAGOTOMIZED, AND SYMPATHECTOMIZED CATS AS AFFECTED BY ATROPINE AND ERGOTOXINE

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Abstract
Observations on the heart rate of 12 unanesthetized cats (either normal or recovered from vagotomy, or sympathectomy) are summarized. The average minimal heart rate of normal, resting, unanes-thetized cats is about 95 beats per min. and is associated with respiratory arrhythmia, which is more marked the slower the rate. The respiratory arrhythmia is abolished by atropine or by vagotomy, but not by sympathec-tomy. The average heart rate rises to about 240 beats per min. after struggle. In the normal cat atropine raises the average resting or basal rate to 208, and the rate after struggle to 272 beats per min. In the same animals ergotoxine lowers the basal rate to 80, and the rate after struggle to 169 beats per min. After vagotomy (in which some cardio-aceelerator fibers are cut) the basal heart rate is increased to about 125 beats per min. Atropin still further raises the average basal rate (to about 155), but it does not much change the average rate produced by struggle. In this preparation ergotoxine does not markedly influence the basal heart rate; the rise due to struggle is, as a rule, reduced. After sympathectomy, with vagal supply to the heart intact, the average basal rate is reduced to about 75 beats per min. Atropine raises this basal rate to about 155, and struggle raises it little further (to about 160). In this preparation ergotoxine greatly reduces the average basal rate (to about 50 beats per min.) and also limits the effects of struggle (to about 90 beats per min.). The inference is drawn that atropine and ergotoxine have not only peripheral effects, but that in the unanesthetized animal atropine stimulates centrally cardio-acceleration and ergotoxine stimulates centrally cardio-inhibition. After sympathectomy the vagal mechanism can slow the heart of the unanesthetized cat from a maximum rate of 150 beats per min. to a minimum of about 75 beats per min., whereas after vagotomy the sympathetic mechanism can speed up the heart from a minimum rate of about 125 beats per min. to a maximum of about 225 beats per min. The respective ranges of operation of the 2 systems emphasize the view that the vagal mechanism serves especially to assure opportunity for rest and recuperation of the heart, and that the sympathetic mechanism, on the contrary, acts in emergency states when physical effort and stress require the heart to work vigorously.

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