Abstract: AIM: To observe the changes of bone in female Sprague-Dawley rats aged 4.5 and 7.5 months. METHODS: Forty 4-month-old virgin female Sprague-Dawley rats were randomly divided into 4.5 month group and 7.5 month group.Bone histomorphometric analysis of the proximal tibial metaphysis (PTM), tibial shaft (Tx) and the fifth lumbar vertebral body (LV5) was performed in undecalcified sections.RESULTS: There was no significant change in bone volume of PTM, LV5 and Tx between 4.5 and 7.5 months of age.However, the bone formation parameters (%L.Pm, MAR, BFR/TV, BFR/BV, BFR/BS) of LV5 and Tx fall rapidly between 4.5 and 7.5 months of age.CONCLUSION: There is no significant change in cancellous and cortical bone mass, but the bone formation of LV5 and Tx decreases in female Sprague-Dawley rats aged from 4.5 to 7.5 months.

Key words: osteoporosis, bone histomorphometry, rats, cancellous bone, cortical bone