Abstract:
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Immobilization of an extremity causes
skeletal muscle atrophy and a dramatic increase in bone
resorption. Growth hormone (GH) is known to play an
important role in bone remodeling mediated in part by
local insulin-like growth factor-I (IGF-I). In this study, we
investigated changes in the levels of GH and IGF-I peptide
in bone extracts from the femur after hind-limb immobilization
for 5 days, 2, 4, and 8 weeks. The levels of
somatostatin, which interacts with GH, were also
measured in the bone extracts. GH levels increased after 8
weeks of hind-limb immobilization whereas the IGF-I
concentrations increased after 2 weeks, but returned to
control levels at 4 weeks, and decreased after 8 weeks of
immobilization. The somatostatin levels in the bone
extracts increased only after 8 weeks of hind-limb immobilization.
Our findings suggest that, after hind-limb
immobilization, changes in the concentrations of GH,
IGF-I, and somatostatin in bone may mediate bone resorption
either directly or through interaction with other
factors. |