Making Rats Rise to Erect Bipedal Stance for Feeding Partially Prevented Orchidectomy-Induced Bone Loss and Added Bone to Intact Rats

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Abstract
The objectives of this study were to investigate the different effects on muscle mass and cancellous (proximal tibial metaphysis [PTM]) and cortical (tibial shaft [TX]) bone mass of sham-operated and orchidectomized (ORX) male rats by making rats rise to erect bipedal stance for feeding. Specially designed raised cages (RC) were used so that the rats had to rise to erect bipedal stance to eat and drink for 12 weeks. Dual-energy X-ray absorptiometry (DEXA) and peripheral quantitative computerized tomography (pQCT) were used to estimate the lean leg mass and bone mineral. Static and dynamic histomorphometry were performed on the triple-labeled undecalcified sections. We found that making the intact rats rise to erect bipedal stance for feeding increased muscle mass, cortical bone volume, and periosteal bone formation. Orchidectomy increased net losses of bone next to the marrow by increasing bone turnover. Making the ORX rats rise to erect bipedal stance increased muscle mass, partially prevented cancellous bone loss in the PTM, and prevented net cortical bone loss in TX induced by ORX by depressing cancellous and endocortical high bone turnover and stimulating periosteal bone formation. The bone-anabolic effects were achieved mainly in the first 4 weeks in the PTM and by 8 weeks in the TX. These findings suggested that making the rats rise to erect bipedal stance for feeding helped to increase muscle mass and cortical bone mass in the tibias of intact rats, increase muscle mass, and partially prevented cancellous and net cortical bone loss in ORX rats.