Objective
The purpose of this study is to evaluate the loss of bone mineral density on ovariectomized (ovx) rat in young and old rats.

Method
Total 110 Sprague-Dawley female rats which composed of 3 months aged 88 rats and 12 months aged 22 rats were used. They were divided randomly into 5 ovx groups (15 rats for each group) and 5 sham operation group (7 rats for each group). The bone mineral density was measured by Hologic 4,500 Fan Beam bone densitometry at the time of second postoperation week, 4th week, 8th week, and 16th week in young aged group and 4th, 8th week in old aged group.

Results
The bone mineral density in young ovx rats was decreased measured at 2 week, 4 week and 8 week, but not 16 week compared with that of sham operation rats (p＜0.05). In old rats, there was no significant change in bone mineral density between ovx and sham group (p＞0.05).

Conclusion
For the purpose of osteoporosis inducing experiment, young aged rat is more reliable for the detection of bone density change than old aged rat and the bone mineral density change will be continued at least 16 week postovariectomy period.