Objective To explore the time-sequential changes of marrow fat fraction and adipocytes in rabbits with of glucocorticoid-induced osteoporosis ( GIOP) .Methods Twenty 20-week female New Zealand rabbits were randomly divided into control group and GIOP group, and each group had 10 rabbits.Bone mineral density ( BMD) and the marrow fat fraction ( FF) of the left proximal femur and the L3-L4 vertebrae were detected using dual energy X-ray absorptiometry and magnetic resonance spectroscopy (MRS) at the baseline (0week), the 4th, the 8th, and the 12th week, respectively.At the 8th week and the 12th week, half rabbits were executed and the quantitative analysis of bone marrow adipocytes was performed.Results At the 4th week, the FF in 2 groups showed significant difference, while the significant difference of BMD between 2 groups appeared at the 8th week (P<0.05).At the 4th week and the 12th week, FF in GIOP group showed a significant increase (35.9%and 75.2%, respectively), comparing with that in baseline (P<0.05).At the 8thweek and the 12thweek, the marrow adipocyte density (Ad.D) in GIOP group increased by 57.1% and 35.4%, respectively, comparing with that in control group.On the contrary, a reduction ( -13.3%) at the 8thweek and an increase (+22.7%) at the 12thweek of the adipocyte mean diameter (Ad.MD) were observed in GIOP group comparing with that in control group (P<0.05).The percentage area of marrow adipocytes in the GIOP group was 62.8 ±8.7%at the 8thweek and 79.2 ±7.7%at the 12thweek, respectively, and both were significantly higher than that in control group (P<0.05) The value of FF was moderately negatively correlated with BMD of the lumbar vertebrae and the proximal femur ( r =-0.598 and -0.675, respectively, P <0.05 ) , while highly negatively correlated with the percentage area of marrow adipocytes (r=0.874, P<0.05).Conclusion Marrow adipogenesis is characterizes by the accumulation of small sized marrow adipocytes at the early stage of GIOP, while at the late stage of GIOP it is characterized by the accumulation of large sized adipocytes.MRS is a method to dynamically evaluate the sequential changes of marrow fat content.%目的：探索糖皮质激素性骨质疏松（ GIOP）模型兔骨髓脂肪分数及脂肪细胞时序性变化的规律。方法20只20周龄雌性新西兰大白兔随机分为对照组及GIOP组，每组兔10只。分别于基线时（0周）、4、8、12周行腰3-4及股骨近端骨密度扫描及磁共振波谱检查，以获得骨密度（ BMD）及骨髓脂肪分数（ FF）。在第8周及12周各处死实验兔一半行骨髓脂肪细胞定量分析。结果第4周时，两组兔FF值有显著性差异，而组间BMD至第8周时才有显著性差异（P均＜0.05）。于第4及12周时，GIOP组FF值较基线时分别增高35.9％、75.2％（P均＜0.001）。于第8周及12周时GIOP组骨髓脂肪细胞密度较对照组分别增高57.1％、35.4％，而骨髓脂肪细胞直径分别降低13.3％、增高22.7％，骨髓脂肪细胞面积分别增高30.8％、53.8％。FF值与腰椎BMD、股骨近端BMD呈中度负相关（r分别为-0.598、-0.675，P均＜0.05），而FF值与骨髓脂肪细胞面积呈高度正相关（r＝0.874，P＜0.001）。结论 GIOP初期骨髓脂肪形成以小尺寸脂肪细胞堆积为主，而后期则以大尺寸脂肪细胞堆积为主。磁共振波谱是动态评估骨髓脂肪含量变化规律的方法之一。
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