Continuous C¹⁴O₂ and CO₂ Excretion Studies in Experimental Animals

Abstract

An apparatus has been devised which permits, after administration of labeled compounds to animals, the continuous measurement and recording of CO 2 excretion by means of infrared absorption, C 14 excretion by ion chambers, and specific activity by a ratio analyzer. Comparative excretion studies have been made using labeled amino acids, fats, fatty acids and sugars. The specific activity and total activity rate curves for breath carbon-14 are markedly different. The generally smooth nature of the specific activity curves gives an excellent indication of the continuous and steady processes by which radioactivity is distributed into the various body pools. Studies have been made with mice, rats, guinea pigs and rabbits. As small an amount as 0.1 µc C 14 has been used for an 8-hour study in mice. The instrument can be readily adapted for use in large animal or human studies following administration of small amounts of C 14 .