The Glucose and Lactate Consumption of the Dog's Heart

When the volume of blood in a heart‐lung circuit was increased the lactate in the blood tended to rise, and vice versa . This is as predicted from the facts that lactate arises by glycolysis in the blood and is removed by the heart. Estimation of the amounts of glucose utilized by the heart and based on the fall of blood sugar in heart‐lung preparations are certain to be too high if the rates of glycolysis in the blood and in the lungs are ignored or assessed at too low values. 2. To obviate the attempt at such calculations in which the lungs introduce an uncertain factor, recourse was had to an isolated heartoxygenator circuit. By the use of this the glucose and lactic acid utilization of the dog's heart were assessed at an average of 70 mg. and 200 mg. respectively, per 100 grm. heart/hr., the blood being oxygenated by a mixture of 5 per cent. CO 2 and 95 per cent. oxygen, and each ventricle, doing reasonable amounts of work under normal conditions of arterial pressures, at a temperature of about 37° C. 3. There was considerable fluctuation in the glucose usages in different hearts, but a general tendency for lactate and glucose utilizations to be reciprocally related. The sum of lactate and glucose utilizations was in the majority of experiments insufficient if combusted to account for the known oxygen usages of heart muscle. The rate of usage of either constituent was increased if its concentration in the blood was increased and, below certain critical levels, was reduced when its concentration was reduced. 4. Addition of insulin, the blood sugar being normal or low, increased the utilization of glucose but did not clearly affect that of lactic acid, whether this was at high or low concentration in the blood. The authors express their thanks to the Government Grants Committee of the Royal Society for a grant to one of us (C. L. E.), which covered part of the cost of animals. Also to Mr J. Trendall and Mr V. C. Tindley for skilled help in constructing and maintaining the necessary apparatus.