青春期时，下丘脑的抑制作用因骨骼包膜而异。
Hypothalamic suppression during adolescence varies by bone envelope.
机构信息
Department of Anthropology, College of Liberal Arts, Temple University, Philadelphia, PA, USA.
出版信息
Med Sci Sports Exerc. 2011 Apr;43(4):608-16. doi: 10.1249/MSS.0b013e3181f56a2c.
PURPOSE
The purposes of this study were to suppress estradiol levels in adolescent (postpubertal rats) using gonadotropin-releasing hormone antagonist (GnRH-a) injections and to determine the changes in bone structure and mechanical strength.
METHODS
In an Institutional Animal Care and Use Committee-approved study, female rats at 23 d of age were assigned to a baseline group (BL65; n = 10) sacrificed on day 65, a control group (Control; n = 15) sacrificed on day 90, or an experimental group (AMEN; n = 9) sacrificed on day 90 that received daily injections of GnRH-a for a 25-d period from 65 to 90 d of age (2.5 mg·kg(-1) per dose).
RESULTS
Body weights were similar on day 65; however, the AMEN group was significantly heavier than the Control group (17%, P = 0.001) on day 90. In the AMEN rats relative to the Control group, plasma estradiol levels were reduced by 36% (P = 0.0001) and plasma insulin-like growth factor 1 levels were 24% higher (P = 0.003). In the femur, there was no change in periosteal bone apposition or total cross-sectional area. The marrow area increased by 13.7% (P = 0.05) resulting in a 7.8% decrease in relative cortical area (P = 0.012), and endocortical bone formation rate increased by 39.4% (P = 0.04). Trabecular volume and number decreased by 51.5% (P = 0.0003) and 49.5% (P = 0.0003), respectively. The absolute peak moments of the tibiae and femurs were unchanged in the AMEN group relative to the Control group, but these were reduced by 8.8% (P = 0.03) and 7.5% (P = 0.09), respectively, when normalized by body weight.
CONCLUSIONS
Suppression of estradiol by 25 d of GnRH-a administration to 65-d-old (postpubertal) rats reduced trabecular volume and number by about 50%, increased endocortical bone turnover, and reduced relative cortical thickness without changing tibial and femoral total area. These changes in bone structure were associated with no change in absolute mechanical strength possibly because of increases in body weight or in insulin-like growth factor 1 concentrations.
目的
本研究旨在通过促性腺激素释放激素拮抗剂（GnRH-a）注射抑制青春期（青春期后）大鼠的雌二醇水平，并确定骨结构和机械强度的变化。
方法
在机构动物护理和使用委员会批准的研究中，23 天大的雌性大鼠被分配到基线组（BL65；n=10），于第 65 天处死；对照组（Control；n=15），于第 90 天处死；实验组（AMEN；n=9），从 65 天到 90 天每天接受 GnRH-a 注射，共 25 天（剂量为 2.5mg·kg(-1)）。
结果
第 65 天体重相似；然而，AMEN 组在第 90 天比对照组重 17%（P=0.001）。与对照组相比，AMEN 大鼠的血浆雌二醇水平降低了 36%（P=0.0001），血浆胰岛素样生长因子 1 水平升高了 24%（P=0.003）。在股骨中，骨膜骨形成和总横截面积没有变化。骨髓区增加了 13.7%（P=0.05），导致相对皮质面积减少 7.8%（P=0.012），内皮层骨形成率增加 39.4%（P=0.04）。小梁体积和数量分别减少了 51.5%（P=0.0003）和 49.5%（P=0.0003）。与对照组相比，AMEN 组胫骨和股骨的绝对峰值力矩没有变化，但当按体重归一化时，分别降低了 8.8%（P=0.03）和 7.5%（P=0.09）。
结论
对 65 天大（青春期后）的大鼠进行 25 天 GnRH-a 给药抑制雌二醇可使小梁体积和数量减少约 50%，增加内皮层骨转换，减少相对皮质厚度，而不改变胫骨和股骨总面积。这些骨结构的变化与绝对机械强度没有变化有关，可能是因为体重或胰岛素样生长因子 1 浓度的增加。
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