Accumulation of³⁵S-Thiouracil by the Rat Thyroid Gland

Discrimination between Synthetically Administered and Endogenous Thiouracil Based on Monitoring of Urine, Muscle, and Thyroid Tissue: An in Vivo Study in Young and Adult Bovines

“…High concentrations of thyreostats in thyroid tissue have been documented in several reports and are not attributed to a hampered elimination of these compounds but merely to the accumulation of this compound in its target tissue. ,− , Accumulation following low-level TU administration is further evidenced by the overall in vivo study results in which TU levels were demonstrated to be significantly higher in TU treated calves and cows, compared to both their control groups and the respective calves and cows supplemented with a rapeseed diet (Mann–Whitney U test; test versus control, TU versus RS, p < 0.05 for every comparison). Lees et al describe a faster accumulation in rats, if smaller doses of TU were administered, whereby increasing ratios between thyroid and plasma were noticed. This dose-dependent accumulation might explain why detectable but low TU levels are also monitored in rapeseed-administered cattle despite the large discrepancy in urinary levels of rapeseed treated cattle versus TU treated cattle.…”

“…22,[24][25][26]47 Accumulation following low-level TU administration is further evidenced by the overall in vivo study results in which TU levels were demonstrated to be significantly higher in TU treated calves and cows, compared to both their control groups and the respective calves and cows supplemented with a rapeseed diet (Mann−Whitney U test; test versus control, TU versus RS, p < 0.05 for every comparison). Lees et al 47 describe a faster accumulation in rats, if smaller doses of TU were administered, whereby increasing ratios between thyroid and plasma were noticed. This dose-dependent accumulation might explain why detectable but low TU levels are also monitored in rapeseedadministered cattle despite the large discrepancy in urinary levels of rapeseed treated cattle versus TU treated cattle.…”