Erect bipedal stance exercise partially prevents orchidectomy-induced bone loss in the lumbar vertebrae of rats

This study investigates the responses of the fourth and fifth lumbar vertebral bodies of 6-month-old male Sprague-Dawley (SD) rats to orchidectomy (orx) and to erect bipedal stance for feeding for 12 weeks in specially designed raised cages (RC) for which the heights were raised from 20 cm to 35.5 cm. A total of 30 rats were divided into groups of: baseline; sham + housed in normal height cage (NC); orx + NC; sham + RC; and orx + RC. Bone histomorphometry was performed on the triple-labeled undecalcified fourth sagittal (LVL-4) and fifth transverse (LVX-5) sections. We found that orchidectomy induced high-turnover trabecular and cortical bone loss in the lumbar vertebrae. Forcing the rats to rise to erect stance for feeding reduced trabecular and cortical bone loss caused by orx. Apparently, depressing the elevated bone resorption next to the marrow induced by orx, and stimulating bone formation at the ventral periosteal surfaces, caused these effects. Orchidectomy and raised cage had similar effects on the two vertebrae except that the percentage of trabecular bone loss was greater in the LVL-4 than in LVX-5, and that bipedal stance exercise increased the total tissue area and mineral apposition rates (0-80 day interval) of ventral periosteal and dorsal endocortical surfaces of LVX-5 to a greater extent than it did in LVL-4. Such findings suggest that forcing rats to rise to an erect bipedal stance for feeding helps prevent loss of trabecular and cortical bone "mass," and presumably bone strength, in orchidectomized rats. This method also provides an inexpensive, noninvasive, reliable model to increase in vivo vertebral loading in rats that is similar in humans.