Bone
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Droloxifene (DRO) is a selective estrogen receptor modulator that prevents bone loss by inhibition of bone turnover associated with estrogen deficiency in both growing and aged female rats. The purposes of this study were to test: (a) whether DRO can maintain prostaglandin E2 (PGE2)-restored bone after discontinuation of PGE2 in aged, ovariectomized (ovx) rats; (b) if an inhibition of bone turnover by DRO reduces bone anabolic effects of PGE2; and (c) whether bone mass restored by PGE2 plus DRO can be maintained after discontinuation of both agents. Female rats at 12 months of age were sham-operated (sham) or ovx. ⋯ Treatment with DRO in the maintenance phase inhibited bone turnover and prevented bone loss induced by withdrawal of PGE2. Trabecular bone mass was maintained in the PGE2 plus DRO followed by vehicle group and further increased in the PGE2 plus DRO followed by DRO groups. We found that: (a) DRO is efficacious in maintaining PGE2-restored bone after discontinuation of PGE2; (b) DRO did not blunt the anabolic effects of PGE2; (c) bone loss occurred after cessation of treatment in the PGE2-alone group, whereas it was maintained after cessation of treatment in PGE2 plus DRO group; and (d) an additional anabolic effect was found in ovx rats treated with PGE2 plus DRO followed by DRO.