Citrus flavanones naringenin and hesperetin induced mild functional alteration in thyroids of old-aged Wistar rats
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Aging is a complex process characterized by a progressive decline in cellular function, alterations of the endocrine system and the increased incidence of thyroid diseases. Citrus flavanones naringenin (NAR) and hesperetin (HES) may contribute to maintenance of health at old age however they may also affect thyroid hormone economy. The aim of this study was to test weather NAR or HES administration alter thyroid functioning. NAR or HES were administrated orally (15 mg/kg) to male 24-month-old Wistar rats during 4 weeks. Control groups received vehicle, sunflower oil. Immunohistochemical staining of thyroglobulin (Tg), thyroxine (T4) bound to Tg (T4-Tg) and sodium iodide sysmporter (NIS) were performed. Immunopositivity of Tg or T4-Tg in thyroid follicles were measured as intensity of optical density (OD) or relative intensity of fluorescence (RIF). Thyroid stimulating hormone (TSH) and total T4 concentrations were measured in serum. After citrus flavanones treatments, thyroids showed Tg and T4-Tg immunopositivity mainly in the colloid of the follicles. The obtained results showed increased (P ! 0.05) intensity of OD for Tg and T4-Tg RIF after both flavanones treatments, while NIS expression did not change. Serum TSH increased (P ! 0.05) only after NAR, although T4 remained unchanged after both treatments. In conclusion, citrus flavanones induced stronger expression of thyroid-specific proteins in gland of old-aged males. However, only NAR elevated serum TSH, being more potent than HES. This alteration is in line with preserved capacity of the thyroid to compensate the mild interference of flavanones treatments with thyroid hormone production in old-aged males.