Alfacalcidol increases cancellous bone in low turnover, fatty marrow sites in aged, orchidectomized rats.

The objectives of this study were to determine the responses of cancellous bone in the distal tibial metaphysis (DTM), a low turnover, fatty (yellow) marrow site, to sham-aged, orchidectomy (ORX) and alfacalcidol treatment in sham-aged and ORX rats. Eighteen-month-old male sham and ORX rats were treated with 0.1 and 0.2 microg/kg alfacalcidol 5 days/wk p.o. for 12 weeks, double fluorescent labeled, and the DTM were processed for bone histomorphometry analyses. The current study found the DTM in sham-aged male rats were resistant to age-related and ORX-induced cancellous bone loss and alfacalcidol-induced bone gain, findings that differ from that in the proximal tibial metaphysis (PTM) and lumbar vertebral body (LVB), two high turnover, red marrow bone sites. However, alfacalcidol treatment increased DTM bone mass in ORX rats where bone turnover was elevated by androgen deficiency. These results in concert with the previously positive findings in red marrow bone sites following alfacalcidol treatment suggest that alfacalcidol is more effective in increasing cancellous bone mass in the skeletal sites with higher bone turnover.