[Dynamic effects of glucocorticoid on bone mineral density and microarchitecture: experiment with rats].

Objective: To investigate the Dynamic effects of glucocorticoid (GC) on bone mineral density and microarchitecture time-related changes of trabecular bone in bone mineral density (BMD) and microarchitecture in glucocorticoid-treated rats.

Methods: Fifty-two 3.5-month-old female SD rats were randomly divided into 3 groups. Ten rats were killed at the beginning of experiment with their right tibiae taken out as the baseline group; 22 rats underwent subcutaneous injection of methylprednisolone once daily (GC-treated group), and the other 20 rats underwent subcutaneous injection of normal saline once daily as control group. One and 9 weeks after the beginning of experiment 11 and 10 rats from GCT Group and control group each were killed with their right tibiae taken out. High resolution micro-CT was used to identify the densitometric and microarchitectural properties of the trabecula in the proximal metaphysic of tibia.

Results: Compared with the control group the values of volumetric BMD (vBMD), tissue BMD (tBMD), bone volume fraction (BVF), trabecular number (Tb.N), degree of anisotropy (DA), and trabecular connectivity (Conn.D) in the trabecular bone at different time-points, of the GCT group all decreased; and the values in the ninth week were the lowest (all P < 0.05). The values of trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), and structure model index (SMI) at different time-points of the GCT group were higher than those of the control group. A time-related analysis within the GCT group showed there was a declination in BVF, Conn.D, Tb.N, and DA with administration time, but Tb.Th and Tb.Sp were increased significantly (all P < 0.05). The mean values of Tb.Th in the first week and the ninth week of GCT Group were (0.076 +/- 0.020) mm and (0.086 +/- 0.026) mm respectively, both higher than the baseline value [(0.067 +/- 0.014) mm] and the values of the control group in the first and ninth weeks [(0.075 +/- 0.022) mm and (0.072 +/- 0.009) mm respectively].

Conclusion: Administration of GC time dependently decreases the BMD and causes deterioration in microarchitecture of trabecular bone; and the remaining trabeculae seem thicken to increase their strength as compensation.