AJP - Regulatory, Integrative and Comparative Physiology, Vol 246, Issue 2 190-R196, Copyright © 1984 by American Physiological Society
Regulation of bone repletion in rats subjected to varying low-calcium stress
R. H. Drivdahl, C. C. Liu and D. J. Baylink
Weanling Sprague-Dawley rats subjected to varying degrees of low-Ca dietary
stress (depletion) showed graded increases in the rate of endosteal bone
formation when normal dietary Ca was restored (repletion). There was a
strong positive correlation between the rate of bone resorption in
depletion and the rate of bone formation attained after 1 wk of repletion.
However, bone formation declined rapidly within the first 4 wk of
repletion, despite the persistence of a substantial endosteal bone volume
deficit. Furthermore the medullary area (indicative of bone volume) did not
by itself determine the bone formation rate. Bone volume in test groups was
restored to control levels after 6 mo of repletion, and this result could
be predicted by a kinetic analysis. Thus, although very high rates of
formation in early repletion decline rapidly, smaller increments relative
to controls must be sustained for long periods. Our data indicate that
increased formation rats at all stages of repletion are a consequence of
elevations in both osteoblast number and osteoblast activity.
