Increase of serum free thyroxine after propylthiouracil in vitro or its peroral administration to rats
Michajlovskij, N.; Stastná, M.
Endocrinologia Experimentalis 10(1): 13-21
1976
ISSN/ISBN: 0013-7200 PMID: 1083797 Document Number: 109410
After the addition of 6-propyl-2-thiouracil (PTU) (2.4 mg/ml) in vitro to normal human serum a 2-fold increase of dialyzable free thyroxine fraction (%FT4) was found. The addition of the same PTU dose to the serum of intact Wistar rats caused up to a 4-fold increase of this fraction. After the addition of increasing doses of PTU (40-400 ng/ml) a linear increase of FT4 was found in human serum, while in rat serum a nonlinear dose-response relationship was observed. After a single peroral administration of PTU to rats (42 mg PTU per animal) the serum PTU level reached the maximum (55 ng PTU/ml) after 1 h and then decreased very slowly. The free %FT4 also increased up to 150% of the control value, but this maximum increase was observed 1 h later than the maximum PTU level. Then the values of %FT4 rapidly decreased to the initial value. Such an effect of PTU in vivo was about 2-fold greater than that obtained in the rat serum in vitro with the same PTU level. The results were compared with the similar effect of thiocyanate reported previously. The effect of PTU both in vitro and in vivo is greater than that of equimolar levels of thiocyanate.