Temporal response of bone to unloading

Journal Article · Sat Feb 01 04:00:00 EST 1986 · Endocrinology; (United States)

DOI:https://doi.org/10.1210/endo-118-2-733· OSTI ID:5634367

Globus, R K; Bikle, D D; Morey-Holton, E

A model of weightlessness in which the hindlimbs of rats are elevated by their tails at a 40 degrees angle to unload the hindlimbs while maintaining normal weight bearing on the forelimbs has been used to simulate certain conditions of space flight. When we used this model in growing rats, we found that growth in bone weight ceased by 1 week in the hindlimbs and lumbar vertebrae, whereas growth in bone weight in the forelimbs and cervical vertebrae remained unaffected. Within 2 weeks, however, the accretion of bone weight in the hindlimbs and lumbar vertebrae returned to normal despite continued skeletal unloading. Since bone weight in the growing rat is primarily determined by bone formation (bone resorption is modest), we investigated the effects of selective skeletal unloading on bone formation during 2 weeks of hindlimb elevation using radioisotope incorporation (with /sup 45/Ca and (/sup 3/H)proline) and histomorphometry (with tetracycline labeling). The studies using radioisotope incorporation showed that bone formation was inhibited by the fifth day of skeletal unloading. By the 10th to 12th day, bone formation had returned toward normal. In comparison with cortical bone, cancellous bone (lumbar vertebrae and proximal tibiae) incorporated more /sup 45/Ca and (/sup 3/H)proline (indicating greater metabolic activity) and had a greater absolute response to skeletal unloading. The results of these studies were confirmed by histomorphometric measurements of bone formation using triple tetracycline labeling. We conclude that this model of simulated weightlessness results in an initial inhibition of bone formation in the unloaded bones. This temporary cessation of bone formation is followed by a cessation in the accretion of bone weight, which then resumes at a normal rate by 14 days despite continued skeletal unloading.

• Research Organization: N.A.S.A.-Ames Research Center, Moffett Field, CA
• OSTI ID: 5634367
• Journal Information: Endocrinology; (United States), Journal Name: Endocrinology; (United States) Vol. 2; ISSN ENDOA
• Country of Publication: United States
• Language: English

Related Subjects

550801* -- Morphology-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ALKALINE EARTH ISOTOPES
AMINES
AMINO ACIDS
ANIMAL GROWTH
ANIMALS
AZOLES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOLOGICAL EFFECTS
BIOLOGICAL MODELS
BODY
CALCIUM 45
CALCIUM ISOTOPES
CARBOXYLIC ACIDS
DAYS LIVING RADIOISOTOPES
EVEN-ODD NUCLEI
GROWTH
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INTERMEDIATE MASS NUCLEI
ISOTOPE APPLICATIONS
ISOTOPES
LABELLED COMPOUNDS
MAMMALS
NUCLEI
ONTOGENESIS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANS
PROLINE
PYRROLES
PYRROLIDINES
RADIOISOTOPES
RATS
RODENTS
SKELETON
SPACE FLIGHT
TIBIA
TRACER TECHNIQUES
TRITIUM COMPOUNDS
VERTEBRATES
WEIGHTLESSNESS