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 CO2 excretion by means of infrared absorption, C14 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 C14 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 C14.

An Organism-Level Quantitative Flux Model of Energy Metabolism in Mice

“…The carcass was digested into a solution, and the radioactivity was measured using a scintillation counter. We detected 26% of the administered dose in the carcass ( Figure 1C ), consistent with our 13 CO 2 measurement and a previous result (Tolbert et al, 1956).…”

“…Palmitate (C16:O), oleate (C18:1), and linoleate (C18:2), the most abundant NEFAs in circulation, have f ox values of around 45%, suggesting prominent fluxes from circulating NEFAs back to tissue triglycerides (Reshef et al, 2003). The branched-chain amino acid (BCAA) valine has a f ox of only 32%, similar to that of BCAA leucine (Tolbert et al, 1956). Together with f ox of 24∼26% for the essential amino acids methionine and tryptophan, this result reveals that the majority of proteolysis-released circulating amino acids are recycled back into proteins.…”

Effect of 2,4-dichlorophenoxyacetic acid on the in vivo metabolism of acetone in adult rats

“…The maximum incorporation in the expired C1402 appears in the first hour, indicating that the acetate molecule is absorbed quickly and metabolized to C02. This is in agreement with the report of others (6,12,22,23). The rates of elimination for the methyl and carboxyl carbons are not exactly the same, suggesting that the two acetate carbons are not metabolized in quite the same manner.…”

Catabolism of heme in vivo: comparison of the simultaneous production of bilirubin and carbon monoxide

“…Air exiting from the metabolic chamber was dried by anhydrous CaSO4, passed through an ionization chamber, and the signal generated, representing "C activity in the expired air, was continuously recorded (25). Carbon dioxide (CO2) was then measured separately by an infrared detector.…”