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

This study investigates the responses of the fourth and fifth lumbar verteb ral bodies of 6-month-old male Sprague-Dawley (SD) rats to orchidectomy (or x) and to erect bipedal stance for feeding for 12 weeks in specially design ed raised rages (RC) for which the heights were raised from 20 cm to 35.5 c m. 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 histomo rphometry 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 verte brae, Forcing the rats to rise to erect stance for feeding reduced trabecul ar and cortical bone loss caused by err. Apparently, depressing the elevate d bone resorption next to the marrow induced by err, and stimulating bone f ormation at the ventral periosteal surfaces, caused these effects. Orchidec tomy and raised cage had similar effects on the two vertebrae except that t he percentage of trabecular hone loss was greater in the LVL-4 than in LVX- 5, and that bipedal stance exercise increased the total tissue area and min eral 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. Su ch findings suggest that forcing rats to rise to an erect bipedal stance fo r feeding helps prevent loss of trabecular and cortical bone "mass," and pr esumably bone strength, in orchidectomized rats, This method also provides an inexpensive, noninvasive, reliable model to increase in vivo vertebral l oading in rats that is similar in humans. (C) 2000 by Elsevier Science Inc. All rights reserved.