The avian egg as a test system for endocrine disrupters: effects of diethylstilbestrol and ethynylestradiol on sex organ development

Many environmental contaminants are known or suspected to interfere with hormonal function in animals. In vivo test methods to detect and characterize chemicals that disrupt the endocrine system are therefore urgently needed. In this study, we assessed the usefulness of abnormalities of the reproductive organs as test endpoints for estrogenic activity of xenobiotics in Japanese quail embryos. Two synthetic estrogens, diethylstilbestrol DES. and ethynylestra- diol EE2., were injected into the yolks of embryonated eggs. At a dose as low as 2 ng EE2rg egg, all male embryos became feminized, containing ovary-like tissue in the left testis. The extent of feminization of the testes was determined by measuring the relative area of the ovary-like component. Persistent M¨ullerian ducts oviducts. in male embryos, and malformations of the M¨ullerian ducts in females occurred at 2 ng EE2rg egg and higher doses. DES was approximately one-third to one-tenth as potent as EE2. The morphological changes studied were dose-dependent, indicating that they are useful as test endpoints for estrogenic activity. Feminization of the left testis in males proved to be the most sensitive endpoint. We propose the quail egg as a simple in vivo test system for estrogenic compounds.