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.
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