Heterogeneous decrease of bone mineral density in the vertebral column of ovariectomized rats

The long-term effect of ovariectomy on the loss of bone mineral density (BMD) was evaluated in rats with and without estrogen treatment; BMD was studied in the lumbar and caudal vertebrae, measured by DXA, to find how the losses of BMD occur in the axial skeleton. Seventy female Wistar rats of 3 months of age were divided into four groups as follows: group 1: control animals; group 2: ovariectomized animals; group 3: ovariectomized animals undergoing treatment with estrogen (0.25 mg/kg per week of 17-β estradiol); group 4: ovariectomized rats undergoing estrogen treatment only during the last 3 months of the experimental period. No significant differences were found among the groups in regard to the BMD values of the caudal vertebrae at either 3 or 6 months. Likewise, in the lumbar vertebrae there were no significant differences among the groups after 3 months. However, at 6 months, a decrease in the BMDs of the ovariectomized animals with respect to the remaining groups was found: 226 ± 11 mg/cm2 in the ovariectomized group; 262 ± 14 mg/cm2 in the controls; 255 ± 4 mg/cm2 in the rats receiving estrogen treatment for 6 months; and 259 ± 5 mg/ cm2 in the animals receiving estrogen for 3 months. The study also reveals the absence of differences in the bone mineral density between the ovariectomized and control rats when the former received estrogen treatment. According to the changes in bone remodeling, the ovariectomized rats showed an increase in the hydroxyproline/creatinine and Ca++/creatinine ratios; this increase is accompanied by an increase in serum alkaline phosphatase and osteocalcin levels. In summary, measurement of the BMD in rats by the DXA method permits detection of loss of bone mineral density occurring in certain zones of the axial skeleton at 6 months after ovariectomy.