EGYPT: Effect of fluoride on thyroid in rats

All adverse health effects of fluoride are related to thyroid hormone metabolism.
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EGYPT: Effect of fluoride on thyroid in rats

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Selim, Assmaa O.; Abd El-Haleem, Manal R.; Ibrahim, Iman H. - "Effect of sodium fluoride on the thyroid gland of growing male albino rats: histological and biochemical study" The Egyptian Journal of Histology:
35(3): 470–482 (2012)

Introduction: Sodium fluoride (Na–F) is commonly added to drinking water and decay-preventive ingredients. Long-term exposure to Na–F leads to some adverse effects on various organs. Its structural shape is similar to iodine, with a considerable potential to cause thyroid gland dysfunction.

Aim of the work: The aim of the present work was to study the possible histological and biochemical changes induced by chronic Na–F exposure on the thyroid gland.

Materials and methods: Twenty male rats (30 days, 40–45 g) were equally divided into two groups. Group I served as a control and group II included rats that received 11 mg/kg/day Na–F orally by a gastric tube for 120 days. At the end of the experiment, rats were sacrificed after ether inhalation and blood samples were subjected to a hormonal assay of T3, T4, and thyroid-stimulating hormone (TSH) levels in addition to superoxide dismutase (SOD) and malondialdehyde (MDA). The thyroid gland tissue samples were processed for light and electron microscopic examination. Also, an immunohistochemical study was carried out for the detection of parafollicular or C cells. The results obtained were analyzed morphometrically and statistically.

Results: Histological examination of the thyroid follicles in the Na–F-treated rats showed different changes. Some follicles showed signs of degeneration in the form of a decrease in area % of colloid and fusion of the follicles; also, the follicular cells showed irregular dilation of rough endoplasmic reticulum, cytoplasmic vacuolation, and irregular nuclei. Other follicles showed signs of hyperactivity manifested by the presence of microfollicles, follicular epithelial cell stratification, and extensive vacuolated colloid, with an increase in the number of lysosomes. Also, hyperplasia was observed in parafollicular cells and confirmed statistically. Alterations in the thyroid structure were further confirmed by the results of the hormonal assay, which showed a significant and a highly significant decrease in serum T4 and T3, respectively, with a subsequent increase in TSH. The MDA activity increased significantly, whereas the SOD content decreased.

Conclusion: Our study showed that long-term low-dose exposure to Na–F affects the thyroid structure and function, leading to hypothyroidism. It can also be concluded that a mutual cooperation exists between the follicular and the C cells.

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