DIETARY SOYBEAN MAY BE ANTIESTROGENIC IN MALE-MICE

We tested-whether dietary soybeans alter prostatic growth and developm ent of prostatic dysplasia in mice that were treated with a synthetic nonsteroidal estrogen, diethylstilbestrol during the first 3 d after b irth. Soybeans were chosen because they contain substantial amounts of isoflavonic estrogens. The presence of estrogenic isoflavonoids in so ybean-containing feed was confirmed by measuring the excretion of seve n different plant estrogens in the urine of normal adult male mice. Es trogenicity of dietary soybean was confirmed by the growth response in uteruses of immature mice. In addition to their estrogenic effect, an tiestrogenic properties of soybeans on uterine growth were observed in the presence of a more potent estrogenic growth stimulator, diethylst ilbestrol in feed. In neonatally estrogenized male mice, soybean feedi ng reduced the prostatic growth inhibition due to diethylstilbestrol a nd, in preliminary experiments, delayed the development of dysplastic changes in the prostate. The number of animals showing severe dysplasi a in prostatic epithelium was significantly lower in 9-mo-old animals given soybean-containing feed from fertilization onwards, but in 12 mo -old animals the difference was less obvious and was not significant. Our findings suggest an antiestrogenic action for dietary soybean in m ale mice, which may be important for the hormonal regulation of normal as well as neoplastic prostatic growth.