Objective   Ovariectomized rat models were applied to study effects of soyisoflavones in serum estrogen, bone calcium content, and bone strength, to estimate the relationship between dosages and effects.

  Methods   Accordingto the quant ities of soy isoflavone g iven in the groups, the ov ar iectomized rats were divided into three groups LSI: (OVX+soy isoflavones 12.65 mg/kgbw), MSI(OVX+soy isoflavones 25.30 mg/kg bw), HSI(OVX+soy isoflavones 37.95 mg bw), The group of control(Ovx)and sham surgery(Sham)were established and the vehicle were given.The drugs were all oral administered using astomach tube.After 12 weeks, all rats were killed, their ser um were separated, at the same time, their right thighbone and right tibia were peeld off for measuringrelative index es.

  Results   Bone formation index serum alkakine phosphatis(AKP)activities were higher in Ovx group than those in Sham and HSI groups(P < 0.05), and hone absorptionindex tar trate-resistant acid phosphatase(StrACP)activities were significant lower in Sham, MSI and HSI groups(P < 0.05).There was a tendency of serum estradiolevels to be higher in the Sham group and all rats receiving soy isoflavones than that in Ovx group, serum estradio was significantly higher in MSI group(P < 0.01).In Sham, LSI, MSI groups, the femoral calcium content were sig nificanthigher than that in Ovx group, in addition, the indexes of bone strength, including max load, eladtic, energ y, were significanthigher than that inOvx group.

  Conclusion   Soy isoflavones mightexert estrogenlike effect in o varicetomized rats.In parallel with bone parameters, the effects of soy islflavones were increased in dose dependent manner between LSI and HSI groups, 25.30 mg/(kg·bw)soy isoflavones was effective in preventing osteoporosis induced by ovariectomy.But many indexes indicated that isflavone did not reverse established osteoporosis in adult ovariectomized rats.