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 ho rmonal 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 reproduc tive organs as test endpoints for estrogenic activity of xenobiotics in Jap anese quail embryos. Two synthetic estrogens, diethylstilbestrol (DES) and ethynylestradiol (EE2), were injected into the yolks of embryonated eggs. A t a dose as low as 2 ng EE2/g egg, all male embryos became feminized, conta ining ovary-like tissue in the left testis. The extent of feminization of t he testes was determined by measuring the relative area of the ovary-like c omponent. Persistent Mullerian ducts (oviducts) in male embryos, and malfor mations of the Mullerian ducts in females occurred at 2 ng EE2/g egg and hi gher 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 t he quail egg as a simple in vivo test system for estrogenic compounds. (C) 1999 Elsevier Science B.V. All rights reserved.