Dietary soy-phytoestrogens decrease testosterone levels and prostate weight without altering LH, prostate 5 alpha-reductase or testicular steroidogenic acute regulatory peptide levels in adult male Sprague-Dawley rats

Nutritional factors, especially phytoestrogens, have been extensively studi ed for their potential beneficial effects against hormone-dependent and age -related diseases. The present study describes the short-term effects of di etary phytoestrogens on regulatory behaviors (food/water intake, locomotor activity and body weight), prostate weight, prostate 5 alpha -reductase enz yme activity, reproductive hormone levels, and testicular steroidogenic acu te regulatory peptide (StAR) levels in adult Sprague-Dawley rats. Animals were fed either a phytoestrogen-rich diet containing approximate to 600 mug/g isoflavones (as determined by HPLC) or a phytoestrogen-free diet . After 5 weeks of consuming these diets, plasma phytoestrogen levels were 35 times higher in animals fed the phytoestrogen-rich vs Phytoestrogen-free diets. Body and prostate weights were significantly decreased in animals f ed the phytoestrogenrich diet vs the phytoestrogen-free fed animals; howeve r, no significant change in prostate 5 alpha -reductase enzyme activity was observed between the treatment groups. Locomotor activity levels were high er in the phytoestrogen-rich vs the phytoestrogen-free animals during the c ourse of the treatment interval. Plasma testosterone and androstenedione le vels were significantly lower in the animals fed the phytoestrogen-rich die t compared with animals fed the phytoestrogen-free diet. However, there wer e no significant differences in plasma LH or estradiol levels between the d iet groups. Testicular StAR levels were not significantly different between the phytoestrogen-rich vs the phytoestrogen-free fed animals. These results indicated that consumption of dietary phytoestrogens resultin g in very high plasma isoflavone levels over a relatively short period can significantly alter body and prostate weight and plasma androgen hormone le vels without affecting gonadotropin or testicular StAR levels. The findings of this study identify the biological actions of phytoestrogen s on male reproductive endocrinology and provide insights into the protecti ve effects these estrogen mimics exert in male reproductive disorders such as benign prostatic hyperplasia and prostate cancer.