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Changes in markers of bone formation and resorption in a bed rest model of weightlessnessTo study the mechanism of bone loss in physical unloading, we examined indices of bone formation and bone resorption in the serum and urine of eight healthy men during a 7 day -6 degrees head-down tilt bed rest. Prompt increases in markers of resorption--pyridinoline (PD), deoxypyridinoline (DPD), and hydroxyproline (Hyp)/g creatinine--during the first few days of inactivity were paralleled by tartrate-resistant acid phosphatase (TRAP) with significant increases in all these markers by day 4 of bed rest. An index of formation, skeletal alkaline phosphatase (SALP), did not change during bed rest and showed a moderate 15% increase 1 week after reambulation. In contrast to SALP, serum osteocalcin (OC) began increasing the day preceding the increase in Hyp, remained elevated for the duration of the bed rest, and returned to pre-bed rest values within 5 days of reambulation. Similarly, DPD increased significantly at the onset of bed rest, remained elevated for the duration of bed rest, and returned to pre-bed rest levels upon reambulation. On the other hand, the other three indices of resorption, Hyp, PD, and TRAP, remained elevated for 2 weeks after reambulation. The most sensitive indices of the levels of physical activity proved to be the noncollagenous protein, OC, and the collagen crosslinker, DPD. The bed rest values of both these markers were significantly elevated compared to both the pre-bed rest values and the post-bed rest values. The sequence of changes in the circulating markers of bone metabolism indicated that increases in serum OC are the earliest responses of bone to head-down tilt bed rest.
Document ID
Document Type
Reprint (Version printed in journal)
Lueken, S. A.
(Veterans Administration Medical Center Loma Linda, California)
Arnaud, S. B.
Taylor, A. K.
Baylink, D. J.
Date Acquired
August 22, 2013
Publication Date
December 1, 1993
Publication Information
Publication: Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research
Volume: 8
Issue: 12
ISSN: 0884-0431
Subject Category
Aerospace Medicine
Distribution Limits
NASA Discipline Number 26-10
NASA Program Flight
NASA Program Space Physiology and Countermeasures
NASA Discipline Number 00-00
NASA Discipline Musculoskeletal

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