Preventive effects of the plant isoflavones, daidzin and genistin, on bone loss in ovariectomized rats fed a calcium-deficient diet.

The effects of the plant isoflavones, daidzin and genistin, on bone loss in ovariectomized (ovx) rats fed a calcium-deficient diet were investigated. Daidzin and genistin were orally administered to ovx rats for 4 weeks. The femurs of these rats showed significantly lower density, strength (breaking forces), ash weight and calcium and phosphorus content (p<0.01) in comparison with those of sham-operated rats. These changes were largely prevented in animals receiving oral daidzin or genistin for 4 weeks at a dose of 50 mg/kg/d and in animals receiving subcutaneous estrone (7.5 microg/kg/d) as a positive control. Ovariectomy caused atrophy of the uterus and increased the ratio of the urinary excretion of pyridinoline and deoxypyridinoline to endogenous creatinine excretion. This was prevented by administration of daidzin or estrone, but, interestingly, not genistin. The preventive effect of daidzin treatment on bone loss in ovariectomized rats appears to be due to suppression of bone turnover. Genistin has a different mechanism of action from daidzin.