Skeletal site-specific response to ovariectomy in a rat model: change in bone density and microarchitecture

Objectives: Ovariectomized (OVX) rat model has been widely used in osteoporosis-related studies. However, the discrepancies in age and skeletal sites being investigated make it difficult to compare the results from different studies. The purpose of this study was to provide information of systemic skeletal site-specific changes in a stable OVX rat model.

Material and methods: Thirty-three 6-month Spraque-Dawley female rats were used. Fifteen rats underwent ovariectomy, and fifteen received sham surgery. Three animals without any surgery were sacrificed at week 0 to serve as baseline. Three animals in the OVX and sham group, respectively, were euthanized at week 2, 4, 12, 24 and 36 post-surgery. Ten bone sites, including parietal bone, interparietal bone, maxilla, mandible, humerus, ulna, femur, tibia, lumber vertebra, and ilium, were subjected to micro-CT.

Results: Overall, long bones, lumber vertebra, and ilium showed similar trend of bone loss post-OVX, with tibia and femur suffered the most bone loss and spine the least (decreased by 75.0%, 70.4% and 36.6% in bone mineral density BMD at week 36 from base line, respectively). Upon OVX, jaw bones and cranial bones only showed a minor reduction in BMD (decreased by 1~3% from baseline) at week 36. Significant deterioration of trabecular structure was detected in long bones, lumber vertebra, and ilium post-OVX, while jaw bones remained relatively stable.

Conclusions: This study for the first time assessed the systemic site-specific bone loss and microarchitecture changes in OVX rat model. It provided valuable information for selecting bone site and observation time in osteoporosis-related study.