Baek Kyunghwa, Barlow Alicia A, Allen Matt R, Bloomfield Susan A
Dept. of Health and Kinesiology. Texas A&M, Univ., College Station, TX 77843-4243, USA.
J Appl Physiol (1985). 2008 Apr;104(4):1086-93. doi: 10.1152/japplphysiol.01209.2007. Epub 2008 Feb 14.
Leptin is responsible for linking energy metabolism to bone mass. Because astronauts are commonly in negative energy balance during spaceflight, this study was designed to assess individual and combined effects of food restriction and simulated microgravity on bone mass and serum leptin. Six-month-old male Sprague-Dawley rats were randomly assigned to four groups (n = 12 each): two hindlimb-unloading (HU) groups fed 100% (HU100) and 70% (HU70) and two cage-activity control (CC) groups fed 100% (CC100) and 70% (CC70) of their baseline food requirement. After 28 days, CC100 rats gained body weight, whereas all other groups lost body weight; this loss was greater in HU70 than in CC70 and HU100 rats. Serum leptin decreased in CC70 and HU100 (-60% and -27%, respectively) and was not detectable in HU70 animals. Percent osteoid surface in CC70 and HU100 was lower than that of CC100 (7.80%, 8.60% vs. 10.70%, respectively), and this decrease was more pronounced in HU70 animals (4.38%). Mineral apposition rate of CC70, HU100, and HU70 rats was lower than that of CC100 (1.5, 1.6, and 1.5 vs. 2.1 mum/day, respectively). Bone formation rate of CC70, HU100, and HU70 rats was lower than that of CC100 (13.4, 13.1, and 12.2 vs. 40.8 mm(3).mm(-2).day(-1), respectively). The change in bone formation rate was correlated with the change in serum leptin value over 28 days (r(2) = 0.69, P = 0.0007). We conclude that moderate caloric restriction may cause bone loss at susceptible bone sites to a similar degree as does the unloading effect of microgravity; serum leptin may be an important endocrine regulator contributing to this change in skeletal integrity.
瘦素负责将能量代谢与骨量联系起来。由于宇航员在太空飞行期间通常处于能量负平衡状态，本研究旨在评估食物限制和模拟微重力对骨量和血清瘦素的单独及联合影响。将6个月大的雄性Sprague-Dawley大鼠随机分为四组（每组n = 12）：两个后肢卸载（HU）组，分别给予其基线食物需求量的100%（HU100）和70%（HU70）；两个笼内活动对照（CC）组，分别给予其基线食物需求量的100%（CC100）和70%（CC70）。28天后，CC100组大鼠体重增加，而其他所有组大鼠体重均减轻；HU70组大鼠的体重减轻幅度大于CC70组和HU100组大鼠。CC70组和HU100组大鼠的血清瘦素水平下降（分别下降60%和27%），而HU70组动物血清瘦素水平未检测到。CC70组和HU100组的类骨质表面百分比低于CC100组（分别为7.80%、8.60%和10.70%），且这种下降在HU70组动物中更为明显（4.38%）。CC70组、HU100组和HU70组大鼠的矿物质沉积率低于CC100组（分别为1.5、1.6和1.5 vs. 2.1μm/天）。CC70组、HU100组和HU70组大鼠的骨形成率低于CC100组（分别为13.4、13.1和12.2 vs. 40.8mm³·mm⁻²·天⁻¹）。28天内骨形成率的变化与血清瘦素值的变化相关（r² = 0.69，P = 0.0007）。我们得出结论，适度的热量限制可能会在易感骨部位导致与微重力卸载效应程度相似的骨质流失；血清瘦素可能是导致骨骼完整性发生这种变化的重要内分泌调节因子。
