Resorcinol as “endocrine disrupting chemical": Are thyroid-related adverse effects adequately documented in reptiles? In vivo experimentation in lizard Podarcis siculus

The endocrine system and particularly thyroid hormones regulate almost all physiological processes in a timely manner in all vertebrates, from fish to reptiles to mammals, so risk assessment of endocrine disrupting chemicals (EDCs) is extremely important given their persistent presence in all environmental matrices. Resorcinol, as well as nonylphenol, octylphenol, and bisphenol A, F, S, are non-Halogenated Phenolic (non-HPCs) Chemicals known as EDCs. Resorcinol is a particular example in that most studies are based exclusively on humans while animal studies are few and often inadequate. The aim of this study was to assess the effects of exposure to different doses of resorcinol on the thyroid gland of the lizard Podarcis siculus during different periods of the thyroid gland activity cycle. Our results showed histopathologic changes in thyroid (follicular cell height increase and colloid area decrease), a thyroid weight increase in combination with serum T4 and T3 decrease, serum TSH, TRH increase in male lizards treated with 0.8,3.9,13.1, and 36.9 mg/kg/d of resorcinol. Besides, we also investigated the impacts of resorcinol treatments on hepatic 5′ORD (type II) deiodinase and hepatic content of T3 and T4. Our findings showed that they are in agreement with in vivo in humans and in rodents data and therefore, resorcinol in reptiles may meet the WHO definition of ECDs.