The effects of fasting and diabetes mellitus on myocardial metabolism in man

Abstract

1. 1. The normal human heart extracts glucose. lactate, pyruvate and oxygen in direct relation to the arterial blood level of each metabolite, independent of other factors. This phenomenon, which is shared with the dog, is best expressed by computing the myocardial extraction coefficient (A-V/A) for each metabolite. 2. 2. Fasting in normal human subjects is accompanied by a decline in arterial blood levels of glucose, pyruvate, and lactate, and by a decreased myocardial extraction of carbohydrate substrate. The myocardial respiratory quotient averages 0.74, suggesting a major dependence upon fat for energy production. 3. 3. In the postprandial state human subjects extract enough total carbohydrate to account for the entire oxygen consumption of the heart. The myocardial respiratory quotient is 0.90, which suggests, however, that some of the energy production of the heart is accounted for by fat under these conditions and that some of the extracted carbohydrate is used for non-oxidative purposes. 4. 4. In fasting subjects with mild diabetes the myocardial glucose extraction was nil and the extraction of lactate and pyruvate markedly reduced despite increased arterial blood levels of glucose and normal levels of lactate and pyruvate. The myocardial respiratory quotient averaged 0.70, consistent with exclusive fat oxidation. 5. 5. Administration of glucose or a meal to diabetic subjects resulted in markedly increased arterial blood glucose levels and some increase in myocardial extraction. Only simultaneous administration of insulin restored the myocardial extraction coefficients for glucose, pyruvate and lactate to normal.