Citrus flavanones mildly interfere with pituitary-thyroid axis in old-aged male rats

Abstract Citrus flavanones naringenin (NAR) and hesperetin (HES) are potent antioxidants that may contribute to maintenance of health at old age by improving cardiovascular and metabolic status. However, they may also affect thyroid hormone economy. Keeping in mind impaired thyroid function at older age, in this study we tested wheather NAR or HES administration potentiate this decline. 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. Qualitative and quantitative immunohistochemical and immunofluorescent expression of specific proteins and stereological analyses of thyroid tissue were performed. Thyroid stimulating hormone (TSH) and total thyroxine (T 4 ) concentrations were measured in serum. Thyroid parenchyma of both flavanone-treated groups was characterized by lower (p  4 bound to Tg (T 4 -Tg) increased (p  4 remained unchanged after both treatments. In conclusion, NAR elevated serum TSH in old-aged males, thus being more potent than HES in altering pituitary-thyroid axis. However, changes in thyroid structure, namely moderate colloid depletion and higher Tg and T 4 -Tg protein expressions after both treatments, indicate preserved capacity of the gland to compensate flavanone interfering, and maintain T 4 production in old-aged males.