Several chemicals have been identified as thyroid hormone axis disrupting chemicals (THADCs) able to interfere with the thyroid hormone system during fetal life and early life stages, thereby impairing neurodevelopment in mammals and inducing development and growth disorders in fish and amphibians. However, identification of THADCs is particularly challenging, and thyroid modalities are currently only assessed in vivo by mammalian and amphibian tests. The aquatic African clawed frog (Xenopus laevis/tropicalis) is the model species of the amphibian test guidelines developed by the OECD and the United States Environmental Protection Agency, but as most European amphibians are semi-aquatic, concern has been raised whether the sensitivity of native European species is comparable to Xenopus. A shortened version of the OEDC test guideline 241 (Larval Amphibian Growth and Development Assay, LAGDA) was used to investigate the effects of two model THADCs on the metamorphosis and thyroid histopathology in the European common frog (Rana temporaria). R. temporaria eggs were collected on the field and exposed till metamorphic climax to sodium perchlorate (11.9–426.5 μg/L perchlorate concentrations) and 6-propylthiouracil (PTU: 1.23–47.7 mg/L). PTU severely delayed metamorphosis and affected several thyroid gland histopathological endpoints at slightly lower concentrations compared to Xenopus. As opposed to what was described in similar Xenopus studies, we observed no effect of perchlorate on the investigated endpoints. Interspecies differences may be linked to mechanisms of action.
Bibliografisk noteFunding Information:
We thank Kristian Almstrup, from the Department of Growth and Reproduction, Copenhagen University Hospital, for kindly accepting to scan the slides from the 2018 experiment on the NanoZoomer 2.0 HT. This work was funded by the Danish Environmental Protection Agency via Danish Centre on Endocrine Disrupters (Project No MST-611-00012). The datasets used and analyzed in the present article are available as supplementary material. The experiments were carried out under permission 2018-15-0201-01419 from the Danish Animal Experimentation Board under the Danish Ministry of Justice.
This work was funded by the Danish Environmental Protection Agency via Danish Centre on Endocrine Disrupters (Project No MST-611-00012).