[Effects of different doses of dexamethasone on bone qualities in rats]

This study was aimed to investigate the effects of different doses of dexamethasone (Dex) on bone quality in rats. Thirty-one SD rats were randomly divided into 4 groups, Control (7 with saline), Dex-L (8 with 1 mg Dex. / kg), Dex-M (8 with Dex. 2.5 mg/kg), Dex-H (8 with Dex. 5 mg/kg), with tail injection, twice per week for 8 weeks. All the rats were killed then. Their proximal tibia were processed into undecalcified sections and measured for bone histomorphometry. The content of Ca2+ and hydroxyproline in their left ulnars were tested. Bone mineral density (BMD) and biomechanical property of the thigh bone were tested to observe the qualities of bone. Compared to the control group, the bodyweights of the rats in different Dex treatment Groups decreased remarkably. Percent labeled perimeter (%L. Pm), Mineral apposition rate(MAR), Bone formation rate (BFR/BV) and so on reduced significantly. Percent trabecular area (%Tb. Ar) and Trabecular number (Tb. N) were obviously higher while Trabecular separation (Tb. sp) was remarkablely lower than those of the control group. BMD in Dex-L and the content of hydroxyproline in Dex-M reduced notablely. Biomechanical property of Dex groups decreased significantly. Dex suppressed bone formation and reduced bone turnover significantly. As the increase doses of Dex, %Tb. Ar increased, and, on the contrary, BMD and biomechanical property decreased with the reduced matrix in bone at the same time. It suggested that non-mineralized bone formation increased and biomechanical property deceased. The doses of 1 mg/kg Dex had the most obvious effect on bone quality. This dose slightly increased %Tb. Ar, however, bone formation, bone biomechanical property and matrix in bone decreased obviously. Diffferent doses of Dex have different effects on bone qualities. However the dose has no direct influcing ratio to the bone qualities.