DEXAMETHASONE EFFECTS ON MECHANICAL, GEOMETRIC AND DENSITOMETRIC PROPERTIES OF RAT FEMUR DIAPHYSES AS DESCRIBED BY PERIPHERAL QUANTITATIVE COMPUTERIZED-TOMOGRAPHY AND BENDING TESTS

In previous studies with cortisol, betamethasone and oxazacort we attr ibuted glucocorticoid effects on bone biomechanics to changes in bone mass and geometry rather than to an action on bone material properties . In this experiment, groups of 7 rats each received subcutaneous dose s of 15.6, 31.2, 62.5, 125, 250, 500 or 1000 mu g/kg per day of dexame thasone (DMS) and an additional 14 animals were controlled untreated f or 4 weeks. Their fresh femurs were then scanned by peripheral quantit ative computerized tomography (pQCT; XCT-960, Stratec, Germany) at the midshaft and submitted to three-point bending tests. In consonance wi th our earlier investigations, a significant, log-dose-related reducti on in bone load-bearing capacity was observed, associated with an impa irment in bone geometric properties (cross-sectional area and moment o f inertia) and in body weight gain. However, the pQCT-assessed volumet ric mineral density of cortical bone (vCtBMD; regarded as a material q uality indicator in terms of mineralization) was significantly reduced by DMS following a dose-response relationship; Furthermore, a direct association was detected between vCtBMD and diaphyseal load-bearing ca pacity and stiffness. In contrast with our previous approach, data sug gests that, apart from changes in bone geometric properties, glu cocor ticoid effects on bone material quality-as assessed by vCtBMD changes in this study-seem also to play a significant role in the determinatio n of their biomechanical consequences.