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Growth Hormone Is Permissive for Skeletal Adaptation to Mechanical Loading
Author(s) -
Forwood Mark R.,
Li Li,
Kelly Wendy L.,
Bennett Michael B.
Publication year - 2001
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1359/jbmr.2001.16.12.2284
Subject(s) - permissive , adaptation (eye) , growth hormone , hormone , endocrinology , medicine , biology , neuroscience , virology
The Lewis dwarf (DW) rat was used as a model to test the hypothesis that growth hormone (GH) is permissive for new bone formation induced by mechanical loading in vivo. Adult female Lewis DW rats aged 6.2 ± 0.1 months (187 ± 18 g) were allocated to four vehicle groups (DW), four GH treatment groups at 32.5 μg/100 g body mass (DW GH1 ), and four GH treatment groups at 65 μg/100 g (DW GH2 ). Saline vehicle or GH was injected intraperitoneally (ip) at 6:30 p.m. and 6:30 a.m. before mechanical loading of tibias at 7:30 a.m. A single period of 300 cycles of four‐point bending was applied to right tibias at 2.0 Hz, and magnitudes of 24, 29, 38, or 48N were applied. Separate strain gauge analyses in 5 DW rats validated the selection of loading magnitudes. After loading, double‐label histomorphometry was used to assess bone formation at the periosteal surface (Ps.S) and endocortical surface (Ec.S) of tibias. Comparing left (unloaded) tibias among groups, GH treatment had no effect on bone formation. Bone formation in tibias in DW rats was insensitive to mechanical loading. At the Ec.S, mechanically induced lamellar bone formation increased in the DW GH2 group loaded at 48N ( p < 0.05), and no significant increases in bone formation were observed among other groups. The percentage of tibias expressing woven bone formation (Wo.B) at the Ps.S was significantly greater in the DW GH groups compared with controls ( p < 0.05). We concluded that GH influences loading‐related bone formation in a permissive manner and modulates the responsiveness of bone tissue to mechanical stimuli by changing thresholds for bone formation.