Changes in calcium homeostasis present a potential problem during prolonged
space flight. Since mechanical forces imposed by muscle utilization and gravity
influence bone turnover, prolonged recumbency and/or prolonged weightlessness
with continuous hypercalciuria and bone loss could ultimately result in osteo-
porosis. To better understand the effect of space flight and gravity on bone,
the following parameters: formation and mineralization, resorption, length,
density and pore size distribution, and mechanical properties, were studied
in stationary and centrifuged space-flown rats both immediately following recovery
and 25 days postflight.
Density and pore size distribution were measured in the left femur by mercury
porosimetry; mechanical parameters were evaluated with a standard torsion test
machine. The rate of bone formation and resorption was determined in the left
tibia by quantitative histological techniques; in addition, osteoblast and osteoclast
cell number was determined.
The data obtained demonstrate that: no gross change in endosteal bone resorption
occurs during flight or postflight; mean periosteal bone formation rate decreases
about 45% and is not corrected by centrifugation; the decrease in formation
rate may be due, in part, to a cessation of bone formation which occurs sometime
after the eleventh day of flight and continues until the second postflight day;
although centrifugation did not correct the defect in periosteal bone formation
rate during flight, it appears to hasten the recovery following flight; femur
stiffness decreases about 30%; and centrifugation did correct the defect in
bone mechanical proper- ties. All perturbations normalized by 25 days postflight.
The reduction of mech- anical stress is probably not sufficient to account for
the decreased rate of bone formation since a comparable decrease occurred in
the flight centrifuged rats. However, the mechanical strength of the femur was
not reduced in these ani- mals, and bone formation was apparently reinitiated
immediately upon recovery in centrifuged rats, whereas it was delayed two to
three days in flight rats.
Holton, E.M.: Effects of Weightlessness on Bone and Muscle of Rats. Space
Gerontology, NASA CP-2248, 1978, pp. 59-66.
Morey-Holton, E.R. et al.: Quantitative Analysis of Selected Bone Parameters.
Final Reports of U.S. Experiments Flown on the Soviet Satellite Cosmos 936.
S.N. Rosenzweig and K.A. Souza, eds., NASA TM-78526, 1978, pp. 135-178.
Spengler, D.M. et al.: Effects of Spaceflight on Bone Strength. Physiologist,
supl., vol. 22, 1979, pp. S75-S76.
Spengler, D.M. et al.: Effects of Spaceflight on Structural and Material Strength
of Growing Bone. Proceedings of the Society for Experimental Biology and Medicine,
vol. 174, 1983, pp. 224-228.
Turner, R.T. et al.: Altered Bone Turnover During Spaceflight. Physiologist,
supl., vol. 22, 1979, pp. S73-S74.
Turner, R.T. et al.: Spaceflight Results in Formation of Defective Bone. Proceedings
of the Society for Experimental Biology and Medicine, vol. 180, 1985, pp. 544-549.
¥ = publication of related ground-based study