Sodium fluoride was the first fluoride compound used in the fluoridation of drinking water and it is still commonly used for that purpose to prevent dental caries. It exerts toxic effects on many soft tissues and organs. The thyroid gland has a strong capacity for absorbing and accumulating fluoride.
Objective: The present work aimed to study the histological and ultrastructural effect of sodium fluoride (NaF) on the thyroid follicular cells and the amelioration by calcium supplementation in albino rats.
Materials and methods: Four groups of adult albino rats were used for this study. The 1st and 2nd groups were used as control. The 3rd group was treated with NaF in a dose of 10 mg/kg bw/day orally by gavage once daily for 35 days. The 4th group was treated with NaF in the same dose for the same period followed by calcium chloride in a dose of 20mg/kg bw/day once daily for 35 days. The animals were anaesthetized and specimens from the thyroid gland were obtained and processed for light and electron microscopic examination.
Results: The NaF had adverse effects on the follicular cells of the thyroid gland in NaF-treated group in comparison with that of the control groups where the follicular epithelium appeared with reduced cell height and the follicles had low colloid content. The basal membrane was ill defined. Colloid droplets appeared in the apical and basal parts of the cytoplasm. Overall cytoplasmic disorganization was observed with scattered stacks of rough endoplasmic reticulum and loss of mitochondria. The apical border showed pseudopods directed into the colloidal lumen. The nucleus appeared irregular, heterochromatic with deformed nuclear membrane. Co-administration of calcium to NaF-treated rats ameliorated the adverse effect of NaF. The follicular epithelium increased in height and most of the follicles contained colloid. The follicular cell regained some of its normal characteristic features with intact basal lamina. The cytoplasm showed rough endoplasmic reticulum, mitochondria and small apical vesicles. The nucleus appeared regular in shape and euchromatic with well-formed nuclear membrane and prominent nucleoli.
Conclusion: Calcium supplementation can ameliorate the adverse effects of NaF on thyroid follicular cells in people at risk of high exposure.