Soy phytoestrogen effects on progesterone receptor and ovalbumin synthesis in the chick oviduct

Developmentally inappropriate exposures to estrogenic compounds are known to alter morphology and function of the reproductive tract in various species. Chickens are continually exposed to the relatively potent estrogenic soy isoflavones through the diet. Previous experiments in this laboratory have demonstrated that the primary soy isoflavone genistein induces proliferation of the chick oviduct. However, information is lacking as to specific reproductive tract developmental effects of genistein exposure in chicks. Experiments were done to compare specific oviduct morphological and functional responses to genistein exposure with responses elicited by a classical estrogen, diethylstilbestrol (DES). To avoid the effects of dietary soy isoflavones, the experimental diets were formulated with dried egg white, rather than the usual soybean meal, as a protein source. 100 one day-old female chicks were assigned evenly to 10 treatments: egg white based diet with daily oral gavage of corn oil vehicle (CV); 1mg diethylstilbestrol (DES); 2.0mg genistein (G2); 20mg genistein (G20); or 40mg genistein (G40). At 15 days of age, half the birds from each treatment received a single injection of 2mg progesterone in a corn oil vehicle to induce ovalbumin synthesis in the oviduct. The classical oviduct responses to estrogen, induction of progesterone receptor and initiation of ovalbumin synthesis, were examined by immunohistochemistry. At 16 days of age, DES treatment increased oviduct weight and percentage of final body weight as compared to all other treatments (P<0.05). Immunohistochemistry of formalin fixed oviduct samples revealed that the DES, G20, and G40 treatments significantly increased specific staining for progesterone receptor and ovalbumin in the chick oviduct as compared to CV and G2 treatments. It was concluded that genistein can function as a classical estrogen in the chick oviduct and that dietary exposures to genistein may alter oviduct development.