Reproductive effects of dietary soy in female Wistar rats

This study was designed to assess the effects of administration of dietary soy on reproductive function and fertility of female Wistar rats. Four grou ps, each of 20 females, were used. Control animals were fed a standard cere al-based diet for rats. Treated animals were fed a standard diet supplement ed with 0.7%, 1.2% or 2.4% of a soy extract. Treatment started at weaning a nd continued until day 7 post-partum (day of sacrifice). Growth depression was seen in the 2.4% soy group. Vaginal opening occurred earlier in fe xmal es receiving soy supplemented feed when compared with controls. Analysis of vaginal smears revealed that all animals were cycling, although an increas e in the mean duration of each cycle was seen in the 2.4% soy group. Uterin e effects were observed in high-dose females and included increases in weig ht, oedema, endothelial hyperplasia and leucocytic infiltration. Vaginal mo difications (i.e. inflammation, hyperkeratosis and dyskeratosis) and altera tions in the distribution of follicular size in the ovaries were also obser ved among treated animals. These data suggest that longterm exposure to hig h doses of phytoestrogens can produce significant agonistic actions in seve ral oestrogen-dependent tissues and parameters, even though in this model n o clear influence on reproductive processes was observed. (C) 1999 Elsevier Science Ltd. All rights reserved.