This is a program project grant involving individual and collaborative studies by members of the Endocrine, Renal, Gastro-Intestinal, Arthritis and Thyroid Units. These projects involve the acute physiological effects of human parathyroid hormone in man; therapeutic studies of idiopathic osteoporosis, glucocorticoid-induced osteoporosis, primary hyperparathyroidism and renal osteodystrophy; the effects of glucocorticoids on bone matrix and bone mineral metabolism; the production and turnover rates of 1,25-(OH)2 vitamin D3 in normals and in patients with renal, thyroid, parathyroid and drug-induced diseases; the use of the isolated perfused kidney to study the relationship between H ion and Pi transport, the inter-relationships of vitamin D, PTH, and P, the structural requirements for PTH actions, and the metabolism of PTH; the biochemical basis of vitamin D's effects on intestinal calcium absorption in vitro, in experimental animals, and in man; the effects of hereditary diseases, glucocorticoids, Paget's disease, calcium and vitamin D metabolites on the structure and metabolism of collagen in skin and bone in vivo and in vitro: improved clinical methods of investigating bone collagen turnover; the effects of inflammatory joint disease and its treatment on collagen resorption and Pagetic bone cells in vitro and their response to hormonal and chemical manipulations; the role of prostaglandins in the genesis of inflammatory joint disease and certain metabolic bone diseases; the inter-relationships of parathyroid hormone and vitamin D metabolites in idiopathic hypophosphatemia and their alterations during therapy; and the role of urinary oxalate and urinary gamma-carboxy-glutamic acid in the genesis of kidney stones.