Endocrine Abstracts

The Hypothalamic Pituitary Thyroid (HPT) axis is well-known as a classic endocrine negative feedback loop: increased levels of thyroxine (T4) in the blood are associated with a reduction of thyroid stimulating hormone (TSH) production and vice versa. However, the thyroid hormone (TH) system is sensitive to alterations by a number of endocrine disrupting chemicals (EDCs). Intriguingly, exposure to specific EDCs can decrease the levels of T4 but this might be not followed by the expected increase of TSH. The reasons for such patterns are still unclear. The aim of the present evidence mapping was to obtain a comprehensive picture of T4/TSH patterns evoked by EDC exposures in rodent models. We conducted an extensive systematic literature search of peer-reviewed articles in which we collected studies that met the following criteria: experimental data (T4, TSH) for rodent models (pups and/or dams) exposed during perinatal periods through the diet to different chemical doses. Our results show that the idealized view of the HPT axis is not supported by the evidence when EDCs are involved. When administered during gestation, some EDCs induced reductions of T4 serum levels in pups followed by increased TSH levels. These chemicals often disrupted the synthesis of THs and the hepatic metabolism. However, with others, the expected TSH increase did not materialise, and these chemicals often interfered with the removal of T4 via up-regulated conjugating enzyme systems in the liver. Acknowledgement: The ATHENA project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 825161.