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 liver1-3. 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 tumors1,2,4,5. 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.).