PTH and osteoporosis: One of the key mechanism of PTH-induced bone resorption is inducing bone cells to produce RANK, thus increasing the number of osteoblasts and promoting bone formation.[54] IGF-1 can increase bone mass of patients with osteoporosis and promote bone synthesis.[55,56] IGF-1 is mainly synthesized by liver cells in a growth hormone-dependent way, and also produced by bones and muscles.