Bone and soft tissue changes with oral phosphate supplements

Oral phosphate supplements in divided doses were given to adult dogs for a period of 10 months. Bone density, bone turnover, serum chemistry values, and the calcium content of soft tissues were determined initially and at the end of the experimental period. Serum calcium remained the same; serum phosphate decreased slightly but significantly. The decrease in phosphate was related to an increase, compared with pre-experimental values, in bone resorption which was seen in the terminal ulna and iliac crest bone samples from all dogs. Serum immunoreactive parathyroid hormone was increased (compared with pre-experimental values) after 5 and 10 months of phosphate supplementation; this increase was related to the bone loss and the decrease in serum phosphate. Soft-tissue calcification could be demonstrated histologically in the kidney and in the lens of the eye where it resulted in cataracts. Calcium content increased in the thoracic aorta, kidney, heart, and tendon but not in skeletal muscle. Phosphate supplements in adult dogs appear to produce secondary hyperparathyroidism, bone loss, and calcification of soft tissues.