Metabolism of ingested 14C-triolein. Estimation of radiation dose in tests of lipid assimilation using 14C-and 3H-labelled fatty acids

To estimate the radiation dose of ingested 14C- (and 3H-) labelled fatty acids, we measured 14CO2 in samples of expired air in five subjects, and serum 14C activity in four subjects, over 4 weeks. These investigations showed that 25%-40% of ingested 14C-fatty acids were metabolized and expired as 14CO2 within 10 days after ingestion. The residue was expired with a calculated half-life of 493 days. Six days after ingestion of the radiolipids, radioactivity in serum was barely detectable. From these data of 14C-fatty acid metabolism, a total whole-body radiation of 20 mrem/microCi 14C, 8 mrem/microCi 14C the first year, was calculated. The corresponding radiation dose for 3H-fatty acid was 2 mrem/microCi 3H and 1 mrem/microCi 3H respectively. Maximal organ-specific radiation (gonads and lungs) from the blood-borne radioactivity was 1 mrem/microCi of 14C-fatty acid.