Comparative biokinetics of radiocarbon ingested as compounds or foods in rats

The biokinetics of radiocarbon (¹⁴C) in rats continuously ingested in the forms of amino acids (glycine and leucine) or as foods (wheat and rapeseed) were examined and compared with each other. The differences in the biokinetics between ¹⁴C-amino acids and ¹⁴C-foods were observed in the excretion of ¹⁴C in feces and in the incorporation and retention of ¹⁴C in the rat tissues. At the 10 week of continuous ingestion of ¹⁴C-amino acids, the integrated activities of ¹⁴C in all the tissues were within 5% of the ingested activity. The integrated activities in each tissue coming from ¹⁴C-food ingestion were higher by a factor of more than 2 compared to those coming from ¹⁴C-amino acid ingestion. Radiation dose rates estimated at the 10 week showed that the dose rates to the individual tissues coming from ¹⁴C-food ingestion were 2-5 times higher than those coming from ¹⁴C-amino acid ingestion. The difference in the dose rate between ¹⁴C-amino acid and ¹⁴C-food was more significant in adipose tissue by a factor of 7-30.