Abstract
Different environmental contaminants disturb the thyroid system at many levels. AlkylPhenols (APs), by-products of microbial degradation of AlkylPhenol Polyethoxylates (APEOs), constitute an important class of Endocrine Disrupting Chemicals (EDCs), the two most often used environmental APs being 4-nonylphenol (4-NP) and 4-tert-octylphenol (4-t-OP). The purpose of the present study was to investigate the effects on the thyroid gland of the bioindicator Podarcis siculus of OP alone and in combination with NP. We used radioimmunoassay to determine their effects on plasma 3,3′,5-triiodo-L-thyronine (T3), 3,3′,5,5′-L-thyroxine (T4), thyroid-stimulating hormone (TSH), and thyrotropin-releasing hormone (TRH) levels in adult male lizards. We also investigated the impacts of AP treatments on hepatic 5′ORD (type II) deiodinase and hepatic content of T3 and T4. After OP and OP + NP administration, TRH levels increased, whereas TSH, T3, and T4 levels decreased. Lizards treated with OP and OP + NP had a higher concentration of T3 in the liver and 5′ORD (type II) activity, whereas T4 concentrations were lower than that observed in the control group. Moreover, histological examination showed that the volume of the thyroid follicles became smaller in treated lizards suggesting that that thyroid follicular epithelial cells were not functionally active following treatment. This data collectively suggest a severe interference with hypothalamus–pituitary–thyroid axis and a systemic imbalance of thyroid hormones.Graphic
Highlights
Thyroid is a gland with an endocrine activity and a follicular organization
This gland secretes thyroid hormones (THs), and its secretory activity is regulated by the thyroid-stimulating hormone (TSH) secreted by the anterior pituitary gland, which in turn is regulated by the thyrotropin-releasing hormone (TRH) produced by the hypothalamus
The incidence of thyroid diseases has continuously increased in recent years (Tingi et al 2016), and it seems to correlate to exposure to several environmental pollutants, such as endocrine-disruptor chemicals (EDCs) (Benedetti et al 2017; Djordjevic et al 2020)
Summary
Thyroid is a gland with an endocrine activity and a follicular organization. This gland secretes thyroid hormones (THs), and its secretory activity is regulated by the thyroid-stimulating hormone (TSH) secreted by the anterior pituitary gland, which in turn is regulated by the thyrotropin-releasing hormone (TRH) produced by the hypothalamus. EDCs are a broad group of persistent and lipophilic compounds detected in different environmental matrices, able to bioaccumulate in animals and humans, and interfering temporarily or permanently with the hormonal signaling pathways in the endocrine system As a consequence, they adversely affect different organs by binding to hormone receptors or interfering with the production, metabolism, and transfer of hormones and/or modifying gene expression (Ghassabian and Trasande 2018). Several reports suggested a xenoestrogenic activity of alkylphenols (APs), such as Bisphenol A (BPA), NonylPhenol (NP), an OctylPhenol (OP) (Acconcia et al 2017; Forte et al 2016, 2019; In et al 2015; Liu et al 2017) These substances are largely used in industry to optimize the production of different products, such as herbicides, pesticides, lubricants, plastics, and personal care products (Asimakopoulos et al 2012; Raecker et al 2011). Few studies investigated the effects of NP and OP on HPT, suggesting that both chemicals are capable of interfering with its function and, influence basic growth as well as development (Göktekin and Barlas 2008; He et al 2019; Naderi et al 2014; Wang et al 2019; Xi et al 2013)
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