Ketone bodies (acetoacetic acid, beta-hydroxybutyric acid, and acetone) are insignificant in the blood and urine of normal individuals in the postprandial or overnight-fasted state. However, these ketoacids become important sources of metabolic energy in circumstances in which the availability of glucose is restricted, as during prolonged fasting, or when the ability to use glucose is greatly diminished, as in decompensated diabetes mellitus. During prolonged starvation the arterial concentrations of these metabolically active strong organic acids increase approximately 70-fold to 10 to 12 mM and to significantly higher levels of 30 to 40 mM in diabetic ketoacidosis. The mechanisms responsible for the development of ketonemia are: (1) increased production by the liver; (2) decreased peripheral utilization in muscle; and (3) reduced volume of distribution. Since ketone bodies are not bound to plasma proteins, they are freely filterable solutes in the renal glomerulus and appear quantifiably in the tubular urine. At the very low plasma concentrations of ketone bodies that are encountered normally after an overnight fast, urinary excretion rates are negligible. When plasma levels increase beyond 0.1 to 0.2 mM, however, excretion increases and measurable amounts of ketone bodies appear in the urine.
Copyright © 1990, Butterworth Publishers, a division of Reed Publishing.