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IGF‐I enhances bone recovery after 2 weeks of unloading
Author(s) -
Boudig Benjamin,
Kurimoto Pam,
Nishida Shigeki,
Wang Yongmei,
Cao Jay,
Elalieh Hashem,
Bikle Daniel,
Halloran Bernard
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.5.a834-d
Subject(s) - anabolism , cortical bone , hindlimb , tibia , context (archaeology) , metaphysis , endocrinology , medicine , osteoblast , bone growth , chemistry , anatomy , biology , paleontology , biochemistry , in vitro
One of the most abundant growth factors in the bone, IGF‐I is produced by bone cells, and stimulates osteoblast proliferation and bone formation. Studies show that IGF‐I increases bone volume in normally loaded animals. However, during skeletal unloading induced by hindlimb elevation bone is resistant to the anabolic effects of IGF‐I. In this context we wanted to know whether IGF‐I could promote bone recovery during 2 weeks of reloading after a 2 week period hindlimb unloading. Thirty six, 12 week old rats were divided into six groups; loaded (4 weeks), unloaded (4 weeks) and unloaded/reloaded (2/2 weeks), and treated with IGF‐1 infusion (2.5 mg/kg/d) or vehicle during the final two weeks. Cortical bone volume (tibia) was assessed at the time of reloading and before sacrifice. Tibial fat free weight, cortical BFR, and bone histomorphometry of the tibial metaphysis were assessed at the end of the experiment. Cortical bone volume did not change significantly during the four week experiment, a finding not surprising in such a short amount of time. However, tibial fat free weight was less in unloaded vehicle treated animals than in the loaded animals. Periosteal BFR decreased during unloading. During the 2 week recovery period in which skeletal loading was restored to normal, BFR in both the vehicle and IGF‐I treated animals increased but the effect was greatly exaggerated in the animals treated with IGF‐I. In IGF‐I treated animals bone mass was restored more rapidly than in vehicle treated animals. These data show that unloading induces resistance to IGF‐I, but that reloading after a period of skeletal unloading increases bone sensitivity to IGF‐I.