Objective: To study the effect of soy isoflavones (SI) at various doses on the incidence of breast tumors induced by 7, 12-dimethyl-benz(a) anthracene (DMBA) in ovariectomized and normal rats.
Methods: 96 SD female rats were randomly divided into ovariectomized group and normal group. Rats in the former group were ovariectomized, then those in each group were randomly placed into six subgroups: blank control, positive control, estrogen control, SI of high dose (100 mg/kg SI), moderate dose (50 mg/kg SI) and low dose(10 mg/kg SI) group according to the body weight. All rats received a single oral dose of 5 mg DMBA, except for the blank control and were palpated weekly to monitor the tumor development. Body weight and diet intake were also recorded weekly. Rats were executed 24 weeks after DMBA administration, the incidence of breast tumors in each group was computed and the activities of superoxide dismutase (SOD) and contents of malondialdehyde (MDA) in rats' plasma were examined.
Results: Compared with the positive group, incidence of breast tumors in ovariectomized rats at high, moderate and low dose SI group was not statistically different (P>0.05), and the activities of SOD in those groups were statistically lower(P<0.01); however, incidence of breast tumors in normal rats at high and moderate dose SI group was statistically different from the positive group (P<0.01), and the activities of SOD in those groups were statistically higher(P<0.01).
Conclusion: SI of 50 mg/kg and 100 mg/kg could decrease the incidence of breast tumors in normal rats, which may be related to the higher activities of SOD induced by SI; however, SI could not decrease the incidence of breast tumors and inhibit the activities of SOD in ovariectomized rats. The effects of SI on the incidence of breast tumors and antioxidant activities may be influenced by different basal levels of estrogen in ovariectomized and normal rats.