Montufar-Solis D, Duke P J
University of Texas Health Science Center, Department of Orthodontics and Dentofacial Orthopedics, Houston 77225, USA.
Aviat Space Environ Med. 1999 Mar;70(3 Pt 1):245-9.
Microgravity significantly affects chondrocyte differentiation within the tibial epiphyseal growth plate of space flown rats. The changes produced in height and number of cells in different zones of the plate are associated with ultrastructural changes in the extracellular matrix. Given the importance of the growth plate in endochondral ossification, we began to assess the response of the plate to hypergravity, and the countermeasure value of excess G.
Rats of the strain used in Cosmos biosatellite missions were housed under conditions similar to Cosmos flights and subjected to continuous hypergravity (2 G) for 14 d, in a 12-ft radius centrifuge.
Histomorphometrical analyses of tibial growth plates from these rats found the hypertrophic/calcification zone to be significantly reduced in both height and cell number, and the proliferation zone in cell number.
These results, along with those of spaceflight and of studies using suspension-centrifugation, indicate that rat growth plate responds to gravitational changes according to Hert's curve: i.e., a) an increased baseline (minimal) loading reduces cartilage differentiation; and b) a reduced baseline loading may lead to increased cartilage differentiation but only within a range, beyond which lack of differentiation results. The plasticity of the plate, i.e., its ability to increase or decrease its activity in response to changes in gravity suggests the possibility of a range of G that will produce the load necessary to maintain normal growth of the plate, i.e., possible countermeasures to the effects of either hypo- or hyper-gravity.
微重力显著影响太空飞行大鼠胫骨骨骺生长板内的软骨细胞分化。生长板不同区域细胞高度和数量的变化与细胞外基质的超微结构变化相关。鉴于生长板在软骨内骨化中的重要性，我们开始评估生长板对超重力的反应以及超重的对抗措施价值。
使用与宇宙生物卫星任务中相同品系的大鼠，将其饲养在与宇宙飞行相似的条件下，并在半径为12英尺的离心机中持续承受14天的超重力（2G）。
对这些大鼠胫骨生长板的组织形态计量学分析发现，肥大/钙化区的高度和细胞数量均显著减少，增殖区的细胞数量也减少。
这些结果，连同太空飞行和使用悬吊-离心法研究的结果，表明大鼠生长板根据赫特曲线对重力变化做出反应：即，a）增加的基线（最小）负荷会减少软骨分化；b）降低的基线负荷可能导致软骨分化增加，但仅在一定范围内，超过该范围则会导致分化缺失。生长板的可塑性，即其响应重力变化增加或降低其活性的能力，提示存在一系列重力值，能够产生维持生长板正常生长所需的负荷，即可能存在针对低重力或高重力影响的对抗措施。
