Shirazi-Fard Yasaman, Metzger Corinne E, Kwaczala Andrea T, Judex Stefan, Bloomfield Susan A, Hogan Harry A
Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA.
Department of Health & Kinesiology, Texas A&M University, College Station, TX 77843, USA.
Bone. 2014 Sep;66:296-305. doi: 10.1016/j.bone.2014.06.005. Epub 2014 Jun 11.
Spaceflight provides a unique environment for skeletal tissue causing decrements in structural and densitometric properties of bone. Previously, we used the adult hindlimb unloaded (HU) rat model to show that previous exposure to HU had minimal effects on bone structure after a second HU exposure followed by recovery. Furthermore, we found that the decrements during second HU exposure were milder than the initial HU cycle. In this study, we used a moderate intensity resistance exercise protocol as an anabolic stimulus during recovery to test the hypothesis that resistance exercise following an exposure to HU will significantly enhance recovery of densitometric, structural, and, more importantly, mechanical properties of trabecular and cortical bone. We also hypothesized that resistance exercise during recovery, and prior to the second unloading period, will mitigate the losses during the second exposure. The hypothesis that exercise during recovery following hindlimb unloading will improve bone quality was supported by our data, as total BMC, total vBMD, and cancellous bone formation at the proximal tibia metaphysis increased significantly during exercise period, and total BMC/vBMD exceeded age-matched control and non-exercised values significantly by the end of recovery. However, our results did not support the hypothesis that resistance exercise prior to a subsequent unloading period will mitigate the detrimental effects of the second exposure, as the losses during the second exposure in total BMC, total vBMD, and cortical area at the proximal tibia metaphysis for the exercised animals were similar to those of the non-exercised group. Therefore, exercise did not mitigate effects of the second HU exposure in terms of pre-to-post HU changes in these variables, but it did produce beneficial effects in a broader sense.
太空飞行给骨骼组织提供了一个独特的环境，导致骨骼的结构和密度特性下降。此前，我们使用成年后肢卸载（HU）大鼠模型表明，先前暴露于HU后，再次进行HU暴露并恢复后，对骨骼结构的影响最小。此外，我们发现第二次HU暴露期间的下降程度比最初的HU周期更轻。在本研究中，我们使用中等强度抗阻运动方案作为恢复期间的合成代谢刺激，以检验以下假设：暴露于HU后进行抗阻运动将显著增强小梁骨和皮质骨的密度、结构，更重要的是力学性能的恢复。我们还假设，恢复期间且在第二次卸载期之前进行抗阻运动，将减轻第二次暴露期间的损失。我们的数据支持了后肢卸载后恢复期间运动将改善骨质量这一假设，因为在运动期间，胫骨近端干骺端的总骨矿含量（BMC）、总体积骨密度（vBMD）和松质骨形成显著增加，并且在恢复结束时，总BMC/vBMD显著超过年龄匹配的对照组和未运动组的值。然而，我们的结果并不支持在随后的卸载期之前进行抗阻运动将减轻第二次暴露的有害影响这一假设，因为运动组动物在第二次暴露期间胫骨近端干骺端的总BMC、总vBMD和皮质面积的损失与未运动组相似。因此，就这些变量在HU前后的变化而言，运动并没有减轻第二次HU暴露的影响，但从更广泛的意义上讲，它确实产生了有益的效果。
