Elevation of PTH and PTHrp Induced by Excessive Fluoride in Rats on a Calcium-deficient Diet

Study on the role of parathyroid hormone (PTH) and parathyroid hormone-related peptide (PTHrp) in the process of skeletal fluorosis, involved especially in calcium deficiency, is rare. We evaluated the level of serum PTH and mRNA expression of PTHrp in femur when rats were exposed to excessive fluoride with low-calcium diet. Wistar rats (n = 60) was divided into four groups, a control group, fluoride group, low-calcium group, and low-calcium fluoride group. The fluoride groups were treated with fluoride by drinking tap water containing 100 mg F-/L. The low-calcium diet contained 0.05% calcium. Serum was collected in the first, fourth, eighth, and 12th of phase for the detemination of PTH and Ca²⁺. RNA extraction from femora was used to analyze the mRNA express of PTHrp, osteopontin (OPN), and osteocalcin (OCN) after 12 weeks of fluoride dosing. Results showed that serum PTH increased gradually with the extension of fluoride exposure, but Ca²⁺ decreased, both of which embodied a time-dependent relationship. Cotreatment of excessive fluoride with low-calcium diet largely stimulated the secretion of PTH. The low dietary calcium markedly increased mRNA expression of PTHrp in animals with fluoride treatment. Expression of OPN and OCN significantly increased in the rats treated with excessive fluoride and low-calcium diet. We demonstrated that fluoride by itself affected the body's calcium metabolism and stimulate the secretion of PTH. PTH may play an important role in anabolic effect of excessive fluoride on bone turnover of skeletal fluorosis and calcium deficiency exacerbated the action of PTH and PTHrp on the characteristic bone lesion of fluorosis.