Effects of alendronate and alfacalcidol on the femoral bone mass and bone strength in orchidectomized rats

The purpose of the present s'tudy was to compare the effects of alendronate (ALN) and alfacalcidol (ALF) on the femoral bone mass and bone strength in orchidectomized rats and to clarify the skeletal benefits of combined administration of ALN and ALF. Fifty male Sprague-Dawley rats, 3 months of age, were randomized by the stratified weight method into five groups: the age-matched control (CON), orchidectomy (ORX), ORX + ALN (2.5 μg/kg, s.c., 5 times a week), ORX + ALF (0.1 μg/kg, p.o., 5 times a week), and ORX + ALN + ALF groups. After 12 weeks of feeding, the femoral distal metaphysis and mid-diaphysis were processed for peripheral quantitative tomographic analysis and biomechanical testing. In the femoral distal metaphysis, ALN prevented the ORX-induced reduction in the trabecular volumetric bone mineral density (vBMD) and breaking energy, and ALF prevented the ORX-induced reduction in the trabecular vBMD and increased the breaking energy to values above those observed in the CON group. Both ALN and ALF increased the maximum load to values above those observed in the ORX group. The improvements in parameters described above were more pronounced when ALN and ALF were administered in combination. In the femoral mid-diaphysis, on the other hand, ALN did not significantly affect the cortical bone parameters, whereas ALF increased the cortical area and maximum load to values above those observed in the ORX group. Furthermore, no apparent benefit of combined administration of ALN and ALF was observed. These findings suggest differential effects of ALN and ALF on femoral bone mass and the beneficial effects of combined administration of ALN and ALF on the trabecular bone of the femur in ORX rats.