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Sympathetic neural influence on bone metabolism in microgravity (Review)
Tadaaki Mano1, N Nishimura, S Iwase
1Gifu University of Medical Science Seki, Gifu 501-3892 Japan. tadaaki.mano@nifty.com
Acta Physiologica Hungarica
|December 9, 2010
Summary
Spaceflight and bed rest increase sympathetic nerve activity, leading to bone loss. This may involve noradrenaline and beta-adrenoreceptors, suggesting beta-blockers could prevent bone density reduction.
Area of Science:
- Bone Metabolism
- Neuroendocrinology
- Space Physiology
Background:
- Bone loss is a significant complication in microgravity (astronauts) and with aging (elderly).
- The sympathetic nervous system (SNS) is increasingly recognized for its role in regulating bone metabolism.
- Existing research suggests a link between SNS activity and bone density.
Purpose of the Study:
- To review current findings on sympathetic influences on bone metabolism.
- To hypothesize the mechanism linking sympathetic neural function to microgravity-induced bone loss.
- To explore potential therapeutic interventions for preventing bone loss.
Main Methods:
- Review of animal and human studies on sympathetic nervous system activity and bone.
- Analysis of microneurography data from microgravity simulations (space, dry immersion, bed rest).
- Correlation analysis between muscle sympathetic nerve activity and bone resorption markers (deoxypyridinoline).
Main Results:
- Animal studies indicate leptin stimulates sympathetic outflow to bone, enhancing resorption via noradrenaline and beta-adrenoreceptors.
- Human studies show mixed results for beta-blockers, but some suggest benefits for osteoporosis and fracture prevention.
- Sympathetic nerve activity is elevated in microgravity-simulated conditions and in elderly individuals with reduced bone mass.
- A significant correlation was found between muscle sympathetic nerve activity and bone resorption markers.
Conclusions:
- Prolonged microgravity exposure may increase sympathetic neural traffic to bone.
- This sympathetic enhancement elevates noradrenaline, inhibiting bone formation and promoting resorption via beta-adrenoreceptors.
- Beta-blocker administration is proposed as a potential strategy to mitigate bone loss in microgravity.
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