Effects of rose bengal on serum levels of thyroid hormones and thyroid peroxidase activity in male mice.

The thyrotoxic effect of Rose bengal (RB) (4,5,6,7-tetrachloro-2',4',5',7'-tetraiodofluorescein disodium salt; Food Red No. 105) was examined in male (C57BL/6N X C3H/N) F1 mice. They were given drinking-water containing RB at levels of 0 (control), 0.125 and 0.250% for 2 weeks. The effect resulted in decreases in serum levels of 3,5,3'-triiodothyronine (T3) and thyroxine (T4), and slight increases in serum 3,3',5'-triiodothyronine (rT3) levels and thyroid weight, but no difference in the values for the body-weight gain, serum thyroid stimulating hormone (TSH) levels and thyroid peroxidase (TPO) activities. However, the in vitro inhibitory effect of RB on TPO activity was observed by addition of RB to the TPO-catalyzed guaiacol oxidation. These results suggest that RB might have weak goitrogenic properties, inhibiting the peripheral conversion of T4 to T3 and/or inhibiting TPO to lead a decrease of T4 and T3 formation.