THE POSITIVE EFFECT OF PARATHYROID-HORMONE ON FEMORAL-NECK BONE STRENGTH IN OVARIECTOMIZED RATS IS MORE PRONOUNCED THAN THAT OF ESTROGEN ORBISPHOSPHONATES

This study elucidates the effect of PTH, estrogen, and the bisphosphon ate Risedronate (NE-58095) on femoral neck bone strength in ovariectom ized (OVX) rats aged 90 days at the beginning of the investigation. Fu rthermore, the effects of these monotherapies were compared with those of concurrent treatment with PTH plus estrogen or PTH plus bisphospho nate. Four weeks after surgery the rats were randomized into a sham-op erated vehicle-treated group, an OVX vehicle-treated group, and the va rious treatment groups and followed for 5 and 15 weeks. The proximal o ne-third of the left femur was then subjected to geometrical measureme nts and biomechanical testing. Neither ovariectomy nor the different t reatment regimens influenced femoral neck geometry. OVX rats exhibited a decrease in femoral neck bone strength compared with control rats. This was most evident after 5 weeks. Treatment of OVX rats with Risedr onate or estrogen alone tended to increase bone strength to control le vel, though these findings were nonsignificant. In contrast, treatment with PTH showed a highly significant increase in femoral neck biomech anical competence. Concurrent treatment with PTH plus estrogen or PTH plus Risedronate also significantly increased the femoral neck bone st rength, but neither showed any advantage over treatment with PTH alone . It is concluded that treatment with PTH increases the strength of th e femoral neck in estrogen-depleted rats in a highly significant manne r, and that this effect is much more pronounced than the effect of the two antiresorptive agents estrogen or Risedronate. Thus, these findin gs provide further support for the anabolic effect of PTH and add weig ht to the argument for the promising potential of PTH in the treatment of postmenopausal osteoporosis.