Parathyroid Hormones and Phosphate Metabolism

¹ National Heart Institute, National Institutes of Health, Bethesda, Maryland

Parathyroid hormone decreases tubular reabsorption of phosphate, lowering the serum phosphorus, and induces dissolution of bone, elevating the serum calcium. Whereas the effect on bone should elevate the serum phosphorus as well, the renal effect usually predominates in the intact organism. The hormone may also promote reabsorption of calcium by the renal tubule, and it may decrease the clearance of calcium by mammary glands. Hypoparathyroidism leads clinically to aplasia of the dentin and to aplasia and deformity of the enamel. Experimentally, hypoparathyroidism has been shown to produce acalcification of dentinoid and marked deformities of dentin and enamel; parathyroid extract or calciferol restores calcification of the dentinoid. Hyperparathyroidism may produce loss of teeth as osteitis fibrosa affects the alveoli, but it never induces osteitis in the teeth. Less caries is found in patients with hyperparathyroidism than in the average populace. If ingested phosphate must be absorbed to affect dental caries, a study to this effect should include the measurement of serum phosphorus, serum calcium, and salivary phosphate. A measure of urinary phosphate may serve as a useful index of the amount of phosphate actually absorbed.