The parathyroid hormone receptor type 1 (PTHR1) is bound and activated by two peptide hormones: the parathyroid hormone (PTH) secreted by the parathyroid gland and by parathyroid hormone related peptide (PTHrP) which is produced locally in many tissues. Although these two peptides bind the same receptor, they exert different actions. PTH regulates the concentrations of Ca²⁺, phosphate ions and vitamin D in the blood, stimulates bone formation/resorption and is distributed to the kidneys where it regulates Ca²⁺ and phosphate transport, and is also detected in the liver^1-3. PTHrP, on the other hand, plays a critical role early in development of bone, heart, mammary glands and other tissues, and is detected in the circulation only during lactation and secreted by some tumors^1,2,4,5. PTHR1 is obviously localized to all areas and tissues where PTH and PTHrP are known to exert their effects (i.e. bone, kidney, blood, heart, etc.).

PTHR1 belongs to the superfamily of G-protein coupled receptors. Like all members, PTHR1 has seven transmembrane spanning domains, an extracellular N-terminus and an intracellular C-terminal tail. Upon activation, the receptor couples to either G_s and G_q thereby activating adenylate cyclase and phospholipase C (PLC) respectively. In osteosarcoma cells, PTHR1 can also couple G_α^2,6,7.

PTH is being used today to treat osteoporosis, as a factor promoting bone formation. Mutations in PTHR1 are associated with Jansen’s disease (hypercalcemia and dwarfism) and Eiken syndrome (cartilage tumors of bone)^2,8-10.