Volume of Parathyroid Glands in Relation to Dietary Calcium and Phosphorus

Abstract

Enlargement of the parathyroid glands has been observed in the spontaneous rickets of rats 1 and humans 2 , 3 and has been experimentally produced in a variety of species by diets low in calcium. 4 - 9 However, typical rickets is produced experimentally by diets low, not in calcium, but in phosphorus. Not low phosphorus diets, but on the contrary, both high phosphate diets 10 and parenteral phosphate injections 11 , 12 have been found to cause parathyroid enlargement. Recently Ham and co-workers 9 essayed to determine, by dietary experiments, what alteration in blood calcium or phosphate constituted the essential physiological stimulus to parathyroid enlargement. These authors confirmed the fact that a low calcium diet (Steenbock) with its attendant hypocalcemia caused enlargement of the glands in young rats. They found no enlargement on a Steenbock low phosphorus diet with hypophosphatemia and marked rickets. Finally by adding a mixture of calcium phosphate and phosphoric acid to a “normal” diet they succeeded in raising the average serum phosphate of 4 rats 2 mg % above that of 3 controls without changing the serum calcium and without increasing parathyroid size. They concluded that “hypocalcemia, instead of hyperphosphatemia, is the primary cause of physiological hypertrophy of the parathyroid glands.”

We have attempted to confirm and extend these rather meager data. Albino rats of the Sherman strain have been placed on variations of the Steenbock diet∗ at weaning (age 3 weeks). After 4 weeks they were killed by bleeding from the heart under ether anesthesia. Pooled specimens of serum were analyzed† for calcium (Clark-Collip) and inorganic phosphate (Fiske-Subbarow). The parathyroids were fixed in Bouin's fluid, embedded in parafiin, serially sectioned at 10 micra and their volumes determined by tracingsand planimeter measurements. 6 Bones were fixed and decalcified in Mueller's fluid and studied histologically. A comparison has been made between the glands of rats on the low phosphorus diet and of those on a stock diet.‡