RISEDRONATE PLUS PROSTAGLANDIN E(2) IS SUPERIOR TO PROSTAGLANDIN E(2)ALONE IN MAINTAINING THE ADDED BONE AFTER WITHDRAWAL IN A NONGROWING BONE SITE IN OVARIECTOMIZED RATS

Effects of risedronate and prostaglandin E(2) (PGE(2)) alone or in com bination on the distal tibia, a nongrowing bone site with closed epiph ysis at 3 months of age, were studied in ovariectomized (ovx) rats. Si x-month-old Sprague-Dawley female rats were either ovx or sham-ovx. Ra ts were treated immediately after operation either with risedronate (5 mu g/kg/2x/wk), PGE(2) (6 mg/kg/d), or risedronate+ PGE(2) for 60 day s (on-groups) and followed by 60 days without treatment (off-groups). Trabecular area, width and numbers were determined in metaphyseal canc ellous bone of the distal tibia. No significant bone loss or structura l changes were observed in the distal tibial metaphysis after 120 days of ovx. Risedronate alone did not produce any affect on bone mass dur ing the treatment and the withdrawal periods. PGE(2) alone increased t he trabecular bone mass associated with thickened trabeculae and incre ased trabecular numbers. However, some of the newly formed bone was lo st at the end of 60 days withdrawal. Combination of risedronate and PG E(2) treatment added the same amount of bone mass as PGE(2) alone, and the added new bone was maintained during the 60 days withdrawal. Thes e results indicate that treatment with risedronate and PGE(2) can pres erve the anabolic effect of PGE(2) on bone mass for at least 60 days a fter treatment.