Histomorphological confirmation of bone loss in the femoral-metaphyseal tissues of rats with skeletal unloading.

The alteration of mineral content in the femoral metaphysis of rats with skeletal unloading was investigated using a model of hindlimb suspension. Animals were fed for 4 days during the unloading. The femoral length, femoral dry weight and femoral mineral density were significantly decreased by the unloading. The calcium, phosphorus and zinc contents in the femoral metaphysis were appreciably reduced by the unloading, although, except for zinc, similar decreases were not seen in the femoral diaphysis. Moreover, the trabecular bone at the femoral metaphysis was clearly reduced by the unloading. Skeletal unloading caused a decrease in osteoid tissue in the primary and secondary spongiosa, indicating that osteoblastic bone formation may be inhibited. The present results clearly demonstrate that skeletal unloading can induce bone loss in the femoral metaphysis.