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New Roles of Parathyroid Hormone

The parathyroid gland is an important organ that maintains extracellular calcium ion concentration. Secretion and synthesis of parathyroid hormone (PTH), as well as its degradation, are mainly regulated by signals through calcium-sensing receptor. Since maintaining a systemic balance of mineral is achieved in collaboration with the kidney, secondary hyperparathyroidism often develops as kidney function declines, finally resulting in uncontrolled secretion of PTH from enlarged parathyroid glands in severe cases on long-term renal replacement therapy (1). Prevention of secondary hyperparathyroidism has been mainly achieved through controlling serum phosphorus and calcium concentration by diet therapy, phosphate binders and vitamin D receptor activators (2). Recently, calcimimetic agents (3,4) have become widely used to control severe hyperparathyroidism, even partially replacing surgical parathyroidectomy (5). Since then, several papers have suggested the association of such strong reductions of PTH with better prognosis (3,5). These observations inspired unexpected new roles of PTH. In this special issue of Therapeutic Apheresis and Dialysis, six authors summarize such new aspects of PTH action and its mechanisms. In addition to its classic target organs such as the kidney and bone, PTH may act on the cardiovascular system, intestine and bone marrow. As guest editor of this issue, I sincerely hope these papers spark great interest in our readers.