The progestin norethisterone affects thyroid hormone-dependent metamorphosis of Xenopus laevis tadpoles at environmentally relevant concentrations

Composition and endocrine effects of water collected in the Kibale national park in Uganda

“…In particular, as tadpoles at the stages employed in the XETA are functionally athyroid, inhibitors of TH synthesis (i.e., NIS or TPO inhibitors) are not expected to be detected (OECD TG 248, 2019). In larger animals such as those used in the AMA or LAGDA, gene expression in thyroid and pituitary tissue may complement effects on metamorphosis-related endpoints (Lorenz et al, 2018). Using stage NF 54 tadpoles characterized by the onset of thyroid gland-function, the in vitro TPO inhibitor 2-Mercaptobenzothiazole was shown to upregulate NIS expression in the thyroid gland in a robust and sensitive manner after 7 days of exposure, consistent with others signs of classical HPT compensatory responses (i.e., decreased T4 and elevated TSH levels in serum, and increased follicular cell hypertrophy (size) and hyperplasia (number) of the thyroid gland) (Tietge et al, 2013).…”