The effect of aging and ovariectomy on the vertebral bone mass and biomechanical properties of mature rats.

Ovariectomy has a proven pronounced effect on bone mass, as has been shown in several animal models and in clinical studies. The aim of this study was to investigate the effect of ovariectomy on both vertebral bone mass and biomechanical competence. The study was performed on a long-term mature rat model. One hundred and five, three-month-old female Wistar rats were randomized into seven groups. One group was killed at the start of the study and was used as a baseline group. Three groups were ovariectomized and followed for one, three, or six months after the operation. Three groups were sham-operated and followed for the same periods. At death, three lumbar vertebrae were obtained from each rat, and changes in bone mass (ash content, trabecular bone volume (TBV)), bone structure, and biomechanical competence were assessed from these vertebrae. The results revealed an age-related (three-nine months) increase in bone mass and biomechanical competence in the sham-operated control groups. In the ovariectomized groups, an age-related decrease in TBV was disclosed. The ash content remained constant, whereas the biomechanical parameters--after an initial increase--showed decreasing values with age in the ovariectomized groups. When age-matched control and ovariectomized rats were compared, an increasing difference in both bone mass and bone biomechanical competence was disclosed. The study has shown that ovariectomy has a pronounced effect not only on vertebral bone mass, but also on bone quality, and that this mature rat model forms an excellent basis for evaluating potential therapeutic regimens for the treatment of osteoporosis.