Effect of fluoride on parathyroid activity of normal and calcium-deficient rats

Forty 5-week-old rats were randomly divided into 1 control group given a normal diet and water low in fluoride (0.026 mM/1) and experimental group receiving the same basic diet and a fluoride supplement of 2.6 mMol/l in the drinking water. After 30 weeks, half of the fluoride-supplemented and half of the nonsupplemented animals were given a calcium-deficient diet for another 16 weeks. Parathyroid activity was estimated by determinations of serum levels of parathyroid hormone and by light microscopic, morphometric evaluation of randomized sections of the parathyroid glands. Serum iPTH and parathyroid nuclear size were significantly increased in the calcium-deficient animals without any fluoride supplement. Fluoride administration to animals on a normal diet did not cause any increase in the serum iPTH levels or in the morphometric parameters for nuclear size. Calcium-deficient animals given a fluoride supplement also showed normal serum iPTH levels and normal parathyroid nuclear size. It is therefore concluded that fluoride does not induce hyperparathyroidism and, further, that fluoride seems to inhibit increased parathyroid activity caused by calcium deficiency.