A Phytoestrogen Diet Induces the Premature Anovulatory Syndrome in Lactationally Exposed Female Rats.” Biology of Reproduction 49:1117–21

The effects of a phytoestrogen diet on sexual differentiation were examined in lactationally exposed rat pups. Rat dams were provided a semipurified diet containing the isoflavonoid coumestrol at a concentration (0.01%) previously found to be utero-trophic. Coumestrol treatment did not significantly alter the time of vaginal opening, although vaginal opening did occur at a lighter body weight. By 132 days of age, 83 % of coumestrol-treated females exhibited the cornified smears of a persistent estrous state. By contrast, 91 % of control animals were cycling regularly at 132 days of age. Estradiol stimulation failed to elicit an LH elevation in the coumestrol-treated animals, suggesting the possibility of neuroendocrine impairments. These findings indicate that the female offspring of mothers fed a low-level phytoestrogen diet during lactation manifest early and nearly universal dis-ruption of cyclicity of the persistent-estrus type