Parathyroid hormone

First hormone isolated from the parathyroid gland to have hypercalcemic action. PTH is a drug target for hypoparathyroidism and osteoporosis. The presence of PTH in the parathyroid gland was reported in 1925. It was isolated in 1970 from bovine parathyroid glands. It was believed that PTH was absent in fish because the parathyroid gland is thought to appear when ancestral amphibians evolved. However, PTH was first identified from the fugu genome database in 2003, and thereafter the existence of PTH has been established in fish.

PTH is a single-chain polypeptide composed of 84 amino acid residues that is devoid of disulfide bonds and has a molecular weight of 9500. Biological activity of the human hormone resides primarily in the amino terminal end of the protein (i.e., amino acids 1–34).This portion of PTH has full biological activity both in vivo and in vitro. Synthetic fragments of the 1-34 portion of the PTH molecule have been synthesized. A paraneoplastic hormone, PTH related peptide (PTHrP) has been identified, isolated, and synthesized. PTHrP is structurally homologous to the amino terminal portion of PTH and interacts with the PTH receptor in bone and kidney. This hormone is responsible for hypercalcemia in certain forms of malignancy. It has been used as a therapeutic agent in osteoporosis in some clinical trials.

Treatment of osteoporosis, as an antiosteoporotic, in the treatment of bone and mineral disease and disorders, bone metabolism regulator, blood calcium regulator, and as a diagnostic aid (pseudohypoparathyroidism; hypocalcemia).