Browsing by Subject "Hindlimb Unloading"
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Item Osteogenic effect of electric muscle stimulation as a countermeasure during hindlimb unloading(Texas A&M University, 2007-09-17) Alcorn, Justin DowRats that undergo hindlimb unloading (HU) as a simulation for space flight experience bone changes similar to astronauts in microgravity. The purpose of this research was to assess whether an exercise countermeasure would be effective in preventing or mitigating bone degradation during HU. Controlled electrical muscle stimulation was applied to the lower left hindlimb to simulate resistive exercise. Adult 6-mo. old male rats were assigned to 3 groups of 12 each: hindlimb unloaded (HU), aging cage control (CC), and baseline (BL). The CC group was pair-fed to match the nutritional intake of HU animals during the 28 days of the study. The left leg was exercised 3 days a week for the duration of the study, with the unexercised right leg serving as a contra-lateral control. Mechanical tests were conducted to assess the strength of cancellous bone in the proximal tibia metaphysis. Although isolated specimens of cancellous bone are not feasible, reduced platen compression (RPC) was employed to directly load only the cancellous core region of each specimen. There was no significant difference in ultimate stress or elastic modulus between BL, CC, and HU-Ex (exercised). However, HU-Ex results were dramatically and significantly higher than HU-No Ex (contra-lateral unexercised control) for both ultimate stress (68%) and elastic modulus (81%). It is also notable that ultimate stress was 32% higher (but not statistically significant) for HU-Ex compared to CC. The total bone mineral density in the tibial metaphysis was significantly larger, 11%, in the HUEx compared to the HU-No Ex group's values. The results clearly demonstrate the efficacy of the exercise protocol in preventing the substantial mechanical deterioration induced by HU.Item Sequential High-Impact, Free-Fall Loading and Zoledronic Acid as a Novel Pre-Treatment for Disuse-Induced Bone Loss(2014-03-31) Boudreaux, RamonThe purpose of our investigation was to evaluate the efficacy of prophylactic interventions consisting of simulated exercise (high-impact, free-fall loading) and/or a bisphosphonate (zoledronic acid), to counter disuse-induced bone loss of adult male rats (6 months old) subjected to 28 days of hindlimb unloading. Furthermore, we aimed to define the effects of these treatments on mechanical strength properties and bone turnover. We hypothesized that monotherapy would mitigate adverse alterations in bone mass, microarchitecture, and strength, while the combined sequential treatment would completely prevent them. Animals were assigned to one of six groups (n=12 each): baseline control (BC, euthanized on study day 0), cage control (CC), hindlimb unloading (HU), zoledronic acid treatment plus hindlimb unloading (ZA+HU), simulated exercise treatment plus hindlimb unloading (Ex+HU), and simulated exercise and zoledronic acid treatments plus hindlimb unloading (Ex+ZA+HU). Ex animals were dropped 25 times (five drops from 30 cm followed by 20 drops from 60 cm) three times per week for the first five weeks of the study. ZA (60 ?g/kg body weight) was administered on day 36, immediately following Ex and just prior to HU. HU began on day 37 and persisted for four weeks. At the distal femur metaphysis (DFM), proximal tibia metaphysis (PTM), and femoral neck (FN), HU caused declines in cancellous bone volume fraction (BV/TV, -25%) and total volumetric bone mineral density (vBMD, -4.7% and -14%), respectively, compared to CC. Mechanical strength and bone turnover were also impaired due to unloading. Individually, Ex and ZA attenuated HU-induced changes in mass, microarchitecture, and strength, but when given sequentially, Ex+ZA fully rescued them. While HU caused an uncoupling of bone remodeling, ZA treatment successfully reduced bone degradation without affecting bone formation. Treatment with Ex followed by ZA resulted in enhanced DFM BV/TV (+20%) and trabecular thickness (Tb.Th, +5%), and PTM total vBMD (+13%). Also, FN ultimate force was highest with combination treatment. While Ex and ZA alone attenuated the deleterious effects of disuse on bone quality, when the two were administered in sequence adult male rats were fully protected against HU-induced alterations in bone mass, microarchitecture, strength, and turnover.