Changes in tissue levels of growth hormone, insulinlike growth factor-I, and somatostatin in the femurs of hind-limb immobilized rats

Immobilization of an extremity causes skeletal muscle atrophy and a dramati c increase in bone resorption, Growth hormone (GH) is known to play an impo rtant 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 immobi lization for 5 days, 2, 4, and 8 weeks. The levels of somatostatin, which i nteracts with GH, were also measured in the bone extracts. GH levels increa sed after 8 weeks of hind-limb immobilization whereas the IGF-I concentrati ons 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 conc entrations of GH, IGF-I, and somatostatin in bone may mediate bone resorpti on either directly or through interaction with other factors.