The Effect of Vitamin D Deficiency on Bone Repletion

Abstract

Abstract

The present study was undertaken to determine the effects of vitamin D deficiency, serum calcium, and PTH on the two major bone changes associated with bone repletion: the increase in endosteal matrix formation and the decrease in endosteal bone resorption. Following a period of bone depletion induced by calcium deficiency, vitamin D-deficient repleting rats demonstrated a marked increase in endosteal bone matrix formation over that seen in pair-weighted nonrepleting control rats. Further, in repleting rats deficient in vitamin D, bone matrix deposition was equivalent to that seen in pair-weighted vitamin D-treated repleting rats, indicating that vitamin D is not essential for matrix repletion. Analysis of serum parameters showed that the repleting vitamin D-deficient rats were severely hypocalcemic and exhibited an eightfold elevation in serum iPTH. Thus, neither the normalizing of the hypocalcemia nor of the high PTH levels incurred during bone depletion is necessary for matrix repletion. On the other hand, in the absence of vitamin D, there was a severe impairment of mineralization of the repleting bone matrix. Bone resorption was depressed during repletion in both vitamin D-deficient and vitamin D-treated rats. The depression of resorption in the vitamin D-deficient rats occurred despite a sustained increase in serum PTH, suggesting that some aspect of the repletion state is capable of suppressing PTH-mediated bone resorption.