Ultrastructural Observations of the Influence of Fluoride Ingestion on the Parathyroid Gland of the Rat

In addition to the documented action of fluoride on bone, there is evidence for hyperfunction of the parathyroid glands in skeletal fluorosis. To investigate this, rats were given 150 ppm fluoride in the drinking water for 10 weeks. The ultrastructure of the parathyroid glands from these animals were then studied and compared to the parathyroid glands of untreated control rats. In control rats, the majority of the parenchymal cells were light chief cells with low cytoplasmic density and relatively straight cell membranes. The Golgi complex and rough endoplasmic reticulum were inconspicuous. Secretory granules were sparsely represented. In contrast, the majority of the parenchymal cells of the fluoride-treated rats were dark chief cells which exhibited well-developed cytoplasmic organelles and numerous interdigitations among neighboring cells. Multiple, large Golgi complexes associated with numerous vesicles and granules were observed. The rough endoplasmic reticulum consisted of large lamellar arrays; polyribosomes were aggregated into spiral clusters. Increased numbers of secretory granules were observed within the cytoplasm of the dark chief cells, within cytoplasmic projections of the chief cells in perivascular spaces, and within the capillary endothelial cells. Based on these ultrastructural observations it is suggested that, as a result of fluoride ingestion and its effect on bone, a type of secondary hyperparathyroidism developed with increased production of parathyroid hormone in order to maintain the normal serum calcium concentration.