PTH and osteoporosis: Intermittent administration of PTH, a treatment for severe osteoporosis approved by the United States Food and Drug Administration, increases the bone mass and bone mineral density (BMD) and improves bone microstructure in a number of animal models and in humans.13 PTH exerts its anabolic activity in bone through the action of PTH1R that is primarily expressed in cells of the osteoblastic lineage.