RESUMO
We investigated the effects of estrogen therapy (ET) associated with low-intensity and high-frequency mechanical vibration (MV) on bone tissue in osteopenic female mice. Fifty 3-month-old female Swiss mice were ovariectomized (OVX) or sham-operated, and distributed after 4â months into the following groups, with 10 animals per group: Sham; Control, OVXâ +â vehicle solution; MV, OVXâ +â MV; ET, OVXâ +â 17ß-estradiol; and MVâ +â ET, OVXâ +â MV and 17ß-estradiol. Both vehicle solution and 17ß-estradiol (10â µgâ kg-1â day-1 ) were injected subcutaneously 7â days per week, and vibration (0.6â g, 60â Hz) was delivered 30â min per day, 5â days per week. Bone mineral density (BMD) and body composition were evaluated by densitometry at baseline and after 60â days of treatment when the animals were euthanized, and their femurs underwent histomorphometric and histochemical analyses. The Control group showed increased weight and fat percentage, while the ET and MVâ +â ET groups showed increased lean mass but decreased fat percentage. At the end of the treatment period, the BMD decreased in Control, remained constant in Sham and MV, and increased in ET and MVâ +â ET. The MVâ +â ET group showed the greatest bone volume compared with Sham (129%), Control (350%), MV (304%) and ET (14%). No differences occurred in cortical thickness. The Control group showed the highest content of mature collagen fibers, while the MVâ +â ET group showed the highest content of immature collagen fibers. In conclusion, ET plus MV was effective in improving bone quality in osteopenic female mice, and this improvement is associated with specific changes in trabecular but not cortical bone.