Exposure to the endocrine disruptor nonylphenol alters structure and function of thyroid gland in rats

Objective: Nonylphenol (NP) is an estrogenic-like compound which can induce vitellogenin synthesis in males and immature teleostean species. Known as an endocrine disruptor, it has been reported to affect endocrine glands; however, little is known about its effects on thyroid function. The present study aimed to evaluate whether exposure to NP alters the structure and function of the thyroid gland of rats and/or the underlying mechanisms. Methods: Rats were gavaged with NP (40,80 and 200 mg/kg/d) for 15 days. Serum levels of thyroid-stimulating hormone were determined by radioimmunoassay. Ultramicroscopic structure of follicular cells was examined by a transmission electron microscope. Histopathology was conducted with hematoxylin-eosin (HE) staining. Results: We found that NP exposure induced a decrease in serum levels of free tetraiodothyronine (FT) 3 and FT4 while it induced an increase in serum levels of thyroid-stimulating hormone (TSH) in a dose-dependent manner. There was a negative correlation between different doses of NP with serum levels of FT3 and FT4 (FT4 r = -0.932; FT3 r = -0.926) and a positive correlation with serum levels of TSH (r = 0.967). Histological and morphometric study in the NP-exposed group revealed dilation of endoplasmic reticulum into cystic in thyroid follicular cells. Mitochondrion was damaged in the 80 and 200 mg/kg/d groups. Conclusions: Exposure to NP may lead to thyroid dysfunction. It may be a potential contributor to thyroid disruption. (C) 2013 Elsevier B.V. All rights reserved.