Actions of parathyroid hormone in the vitamin D-deficient dog.

The effects of parathyroid hormone on bone and kidney have been well documented (1). It has not been settled, however, whether the hormone exerts similar actions in the rachitic animal. Ras-mussen and associates have found that parathy-roid hormone lowers the serum phosphorus in the vitamin D-depleted rat (2). Harrison and Har-rison, however, observed that vitamin D-depleted rats did not respond to parathyroid hormone with either an increase in urinary phosphorus or a decrease in serum phosphorus (3). In both of these studies, the serum calcium of vitamin D-depleted rats failed to increase after an injection of para-thyroid extract at a dosage that elevated the serum calcium of control animals (2, 3). In contrast , in recent studies by Toverud (4, 5), it was found that the serum calcium decreases after para-thyroidectomy in vitamin D-depleted rats; an increase in serum calcium was observed after the administration of parathyroid extract to the vitamin D-depleted, parathyroidectomized animals. Earlier investigations (6) had shown that para-thyroid extract could increase the serum calcium in the rachitic dog, although the effect was not as great as that in normal dogs and bore no consistent relationship to dosage. However, the rachitic dogs were not parathyroidectomized before the administration of parathyroid-extract. It was therefore possible that the animals were under the influence of large quantities of endoge-nous parathyroid hormone, which obscured the action of exogenous extract. In the present studies , serial observations have been made of calcium and phosphorus metabolism and of hydroxyproline excretion in the vitamin D-depleted dog. Animals were studied before and after parathyroidectomy and with the subsequent administration of para-thyroid extract. Methods Seventeen mongrel pups were placed on a rachitogenic diet at the time of weaning. The daily diet for each animal contained 400 g of oatmeal, 100 g of powdered skimmed milk, 7 g of brewer's yeast, 3.5 g of NaCl, 10 mg of vitamin C, 1,000 U of vitamin A, and 15 ml of peanut oil. The diet provided 200 mg of calcium and 800 mg of phosphorus daily. Five control pups of comparable age were studied while on an identical diet; these animals also received 500 U of vitamin D2 daily. Three additional control pups were maintained on a constant diet of standard dog food, providing 500 mg of calcium and 1,000 mg of phosphorus daily. All animals were kept in a room protected from sunlight, illuminated by an ultraviolet-free light source. …