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Abstract
The aim of this study was to determine the dose-dependent effects of pentabrominated diphenyl ether (PBED-99), a flame retardant, on thyroid histological structure and function in rats. Four-week-old Sprague-Dawley rats were divided into four groups randomly, with five animals of each gender per group. Rats in treatment groups were orally gavaged with (PBED-99) at the dose of 30, 60 or 120 mg kg−1, while controls received an equal volume of corn oil. The levels of serum hormone were measured as well as change in histopathology, histochemistry and follicular cells ultramicroscopic structure 15 days following exposure to PBED-99. Serum levels of thyroxine (FT4) and triiodothyronine (FT3) decreased gradually dose-dependently at 15 days of exposure to PBED-99. However, thyroid-stimulating hormone levels increased. The thyroid follicular epithelium hyperplasia was aggravated gradually as dose increased. Proliferating cell nuclear antigen positive cells rose as dose increased. The activities of thyroperoxidase and succinate dehydrogenase in all treatment groups was significantly elevated compared to controls. The rough endoplasmic reticulum of the thyroid follicular cells appeared expanded with saccate using electron microscopy, whereas nucleolus, cell membrane and mitochondria were not damaged. BDE-99 may disturb thyroxine histological structure and function in a dose-dependent manner.