Thyroid Research Thyroid Research Archive Thyroid Hormone Action

Thyroid hormone stimulates bone growth by increasing the action of insulin-like growth factor-I

(March 2002)

The background of the study. Thyroid hormone is essential for normal bone growth in children, and it stimulates the turnover of bone in adults. In children and adults with hypothyroidism, the production of growth hormone and insulin-like growth factor (IGF)-I, which are needed for normal growth, are decreased, but the decreases may not be sufficient to account for the growth retardation in the children. Bone cells contain receptors for thyroid hormone; therefore thyroid hormone probably has direct effects on bone. This study evaluated the effects of triiodothyronine (T3) on the production of IGF-I, the receptors for IGF-I, and the growth-promoting actions of IGF-I in bone cells in vitro.

How the study was done. Bone-forming cells (osteoblasts) were grown from pieces of bone obtained at the time of knee or hip joint replacement in six women and five men with osteoarthritis. The cultured cells were characterized as osteoblasts by several biochemical tests.

The results of the study. Incubation of osteoblasts with T3 for 24 hours did not increase the cellular levels of IGF-I, but did increase the cellular levels of IGF-I receptors. T3 and IGF-I alone stimulated osteoblast proliferation, and the effect of IGF-I was amplified by exposing the cells to T3 before they were exposed to IGF-I.

The conclusions of the study. In osteoblasts T3 increases IGF-I receptors and increases the ability of IGF-I to stimulate proliferation of the cells. These results help to explain why children with hypothyroidism grow poorly

The original article. Pepene CE, Kasperk CH, Pfeilschifter J, Borcsok I, Gozariu L, Ziegler R, Seck T. Effects of triiodothyronine on the insulin-like growth factor system in primary human osteoblastic cells in vitro. Bone 2001;29:540-6.