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Suspension "hypokinesia/hypodynamia" may decrease bone mass by stimulating osteoclast production in ovariectomized
T Kawata1, T Fujita, C Tokimasa
1Department of Orthodontics, Hiroshima University School of Dentistry, Japan.
Journal of Nutritional Science and Vitaminology
|January 27, 1999
Summary
Mechanical stress significantly impacts bone remodeling. In ovariectomized mice, suspension-induced hypokinesia/hypodynamia led to substantial trabecular bone loss and increased osteoclasts in femurs.
Area of Science:
- Bone biology
- Skeletal physiology
- Osteoporosis research
Background:
- Ovariectomy (OVX) in mice is a common model for postmenopausal osteoporosis.
- Mechanical stress plays a crucial role in regulating bone remodeling processes.
- Understanding the interplay between hormonal changes and mechanical unloading is vital for bone health.
Purpose of the Study:
- To investigate the detailed histological changes in the femurs of suspended ovariectomized (OVX) mice.
- To assess the specific role of mechanical stress (hypokinesia/hypodynamia) on bone remodeling in the context of OVX.
- To quantify the impact of combined OVX and reduced mechanical loading on bone structure and cellular activity.
Main Methods:
- Four groups of mice were used: suspended-OVX, suspended-sham-operated, non-suspended-OVX, and non-suspended-sham-operated.
- Hypokinesia/hypodynamia was induced using a suspension harness for one week immediately post-operation.
- Femur histological analysis was performed 9 weeks after birth, focusing on trabecular bone and tartrate-resistant acid phosphatase (TRAP)-positive cells.
Main Results:
- Suspended-OVX mice exhibited extensive loss of trabecular bone in the femur, replaced by bone marrow.
- A significant increase in tartrate-resistant acid phosphatase (TRAP)-positive cells (osteoclasts) was observed in the femurs of suspended-OVX mice.
- No significant differences in TRAP-positive cell counts were found between suspended-sham-operated, non-suspended-OVX, and non-suspended-sham-operated groups.
Conclusions:
- Combined ovariectomy and suspension-induced hypokinesia/hypodynamia leads to significant trabecular bone loss in mouse femurs.
- Increased osteoclast activity, indicated by elevated TRAP-positive cells, is associated with this bone loss.
- Mechanical unloading exacerbates bone loss in an ovariectomized state, highlighting the importance of mechanical loading for bone maintenance.