THE EFFECTS OF CERTAIN FOODS UPON THE RATE OF THE DENERVATED HEART OF THE SURVIVING UNANESTHETIZED CAT

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Abstract
The cardio-accelerator effects of foods were determined in cats in which the heart was so completely denervated as to exhibit no significant change in rate when the animal passed from a state of bodily rest to one of very active muscular exertion combined with extreme emotional excitement. Carbohydrate foods and fats caused in some instances an acceleration of the denervated heart, but these changes do not approach either in magnitude or in duration the effects which have been found to follow the administration of protein. Protein foods invariably bring about an acceleration of surprising magnitude and duration. After a meal of meat the increase in heart rate regularly amounts to a 25 to 50% rise above the fasting level and persists for 15 to 20 hours to reach a total of 13,000 to 22,000 extra heart beats. In other words, a protein meal throws an extra burden of work upon the heart, which, providing other factors than rate remain constant, is comparable in extent to the heart''s total performance during 3 or 4 hrs. under fasting conditions. Obviously, a high protein diet is incompatible with cardiac rest. The cardiq-accelerations which follow the administration of protein or of carbohydrate are not conditioned by any rise of body temperature accompanying the oxidation of these foodstuffs. Although changes in body temperature do not account for the initial rise in heart rate following the administration of fat, a rise in temperature which may occur during the later hours of fat digestion often serves to exaggerate the apparent effect of the fat-feeding and to prolong its duration. In view of the close association which must exist between the rate of the pace-setting region and its metabolism it has seemed reasonable to interpret these accelerations in terms of specific dynamic action. Thus whereas fat and carbohydrate may increase the metabolism of the heart muscle to a measurable degree, protein here, as elsewhere, excels as a stimulus to oxidation. Glycine, when administered intravenously at very rapid rates, causes an acceleration of the denervated heart. Rapid injections of equimolecular solutions of glucose produce the same effect. When glycine is injected at a physiological rate, i.e., at a rate approximating that of amino-acid absorption into the blood stream during protein digestion, no change in heart rate occurs, and, as a corollary, no change in the metabolism of the sinus node. A review of the literature upon the increases in total metabolism following the intravenous administration of glycine reveals tha.t glycine has commonly been administered in rates greatly exceeding the physiological. It is suggested that the changes in body metabolism following such injections may be a function of disturbances in the acid-base and osmotic equilibria of the blood, and do not necessarily point to any specific stimulating power of the glycine.

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