Alendronate influences bending force of femoral diaphysis after orchidectomy in rats.

BACKGROUND AND AIMS: We examined the effect of alendronate on bone following orchidectomy-induced osteoporosis. MATERIAL AND METHODS: Eighty male rats were used. Group I (C) served as the untreated control. In group II (ALN), alendronate was administered subcutaneously (18 microg/kg). In group III (ORC), rats were castrated only. In group IV (ORC+ALN), administration of alendronate (18 microg/kg) was started immediately after castration, and in group V (ORC + ALN-21) medication was started 21 days after castration. Alendronate was given twice a week for eight weeks in the treatment groups. Bone mineral density (BMD) of the proximal femur, ultimate bending forces of femoral diaphyses, ash weights of femurs (AWcc) and the calcium content (Ca) of femoral ash were determined. Histomorphometric analysis was performed on trabecular bone of proximal tibiae. RESULTS: BMD of the proximal femur was significantly decreased by orchidectomy compared with C and ALN. However, no statistical difference was observed between alendronate-treated groups (ORC + ALN and ORC + ALN-21) and the ORC group. Histologically, alendronate reduced the trabecular bone turnover. Ultimate bending force increased significantly in the ORC+ALN-21 group compared with group C, and had a good correlation with the cortical width of tibia (r = 0.53, p < 0.001). Ash weight per bone volume (AWcc) was lowest in the ORC group, whilst alendronate maintained AWcc after orchidectomy. CONCLUSION: Alendronate increased the ultimate bending force of the femoral diaphysis after orchidectomy. On the other hand, ALN treatment was not able to maintain the BMD of the proximal femur at the pre-orchidectomy level. Our results suggest that the remodelling and modelling of bone may influence the response to ALN treatment.