Radioactivity of Blood Carbon Dioxide in Animals oxidizing Glucose labelled with Carbon-14 and Other Labelled Substances

Abstract

THE rate of appearance of radioactive carbon dioxide in the expired air following the administration to an animal of a carbon-labelled oxidizable material has been widely used in making calculations of the rate of degradation of the particular material^1,2. However, it is evident that, before isotopic carbon introduced into the body in this way can be excreted in the expired air, a number of physical processes must have intervened, quite apart from the chemical transformations which are involved. These physical processes include the passage of the original substance through the blood and tissue fluids, its mixing with unlabelled molecules of the same species and also the subsequent transport of the carbon dioxide produced at the sites of oxidative reactions to the alveoli of the lungs. The factors which determine the rate of elimination of radioactive carbon dioxide from the animal body have in particular received theoretical treatment³.