Prevention of osteopenia induced with a gonadotropin-releasing hormone agonist in rats

We investigated the effects of conjugated estrogens as an add-back replacem ent drug, incadronate sodium as a bisphosphonate, and alfacalcidol as a vit amin D-3 analog on femoral bone mineral density (BMD) and bone mineral cont ent (BMC) in female rats chronically treated with the gonadotropin-releasin g hormone (GnRH) agonist leuprorelin acetate. The chemical castration of th e rats by the administration of GnRH agonist for 16 weeks reduced the BMD v alues to 92.3%, 91.3%, and 93.3%;of those of the normal control animals in the whole femur, metaphysis, and diaphysis of the femur, respectively. The BMC value was decreased to 91.0% of that of the normal central animals by t he chronic GnRH agonist treatment. However, a simultaneous 8-week administr ation of conjugated estrogens, bisphosphonate, and vitamin D-3 analog marke dly augmented the BMC values to 110.3%, 110.1%, and 114.4%, respectively, o f those in the rats treated with the GnRH agonist alone. These findings ind icate that antiosteoporotic agents could be useful for preventing induced o steopenia under the careful monitoring of biochemical markers of osteoblast ic activity or bone resorption and BMD or BMC in patients undergoing GnRH t reatment.