INTERMITTENT CYCLICAL ETIDRONATE TREATMENT MAINTAINS THE MASS, STRUCTURE AND THE MECHANICAL PROPERTY OF BONE IN OVARIECTOMIZED RATS

We examined the mechanical properties of rat bones treated with etidro nate intermittent cyclic treatment (etidronate-ICT). Fifty Fisher rats , 7 months of age, underwent ovariectomy (OVX; n = 40) or sham operati on (n = 10). The OVX rats were assigned to 4 groups injected with etid ronate at the respective dose of 0, 2, 4, or 8 mg/kg of body weight (b w) 5 days each week for 2 weeks, followed by a 10-week period of no tr eatment. This regimen was repeated for 48 weeks. At the end of the tre atment period, the ultimate bending strength and structural stiffness of the femoral midshaft in the OVX-alone group were not reduced compar ed with the values of the sham group, while those in the etidronate-tr eated groups were significantly larger than the values of the OVX grou p. The compressive stiffness and strength of the vertebral bodies spec imens prepared from L3 and L5 vertebrae were markedly decreased in the OVX group compared with those in the sham group, but the values in th e etidronate-treated groups were maintained at the same levels as thos e in the sham group. Mechanical properties at the tissue level, such a s elastic modulus and material strength of the femoral cortex, were in creased in etidronate-treated groups compared with the OVX group. The flexural modulus was also increased. The compressive elastic modulus o f vertebral body in treated groups was preserved at the same level as that in the sham group. These results clearly demonstrate that in ovar iectomized rats long-term etidronate intermittent cyclic treatment pre serves the mechanical properties both at the whole bone and the tissue level.