Estrogen is Required for Mechanical Loading Induced Restoration of Bone Following Disuse

To determine whether E sub(2) influences the REAMB-induced and/or EX-induced restoration of BMD following HLU of OVX rats. Eighty-one 5 month old female Sprague-Dawley rats were randomized into the following groups: 1) Baseline controls, 2) OVX controls, 3) OVX+E sub(2) controls, 4) OVX+ 4 weeks HLU, 5) OVX+E sub(2)+HLU, 6) OVX+HLU+ 2 weeks REAMB, 7) OVX+E sub(2)+HLU+REAMB, 8) OVX+HLU+REAMB+ 2 weeks climbing, jumping, and balancing EX, or 9) OVX+E sub(2)+HLU+REAMB+EX. Serial DXA scans were performed to track total body bone characteristics throughout the study and peripheral quantitative computerized tomography (pQCT) was utilized to determine differences in distal femoral metaphyseal bone mineral characteristics between groups. Total body BMD increased 4-8% in all animals receiving supplemental E sub(2), while BMD did not change in animals without E sub(2). OVX reduced trabecular (t)BMD at the distal femoral metaphysis by 35% (p [< or =] 0.001) and OVX+HLU exacerbated this loss by an additional 52% (p [< or =] 0.001), while also reducing cortical (c)BMD by 11% compared with Baseline controls (p [< or =] 0.001).