Once bound with the receptor, the mimicker can produce a normal hormone response, cause an abnormal response or elicit no response as it blocks the receptor site and prevents natural hormones from binding. Not all endocrine disruptors alter hormonal action by binding to hormone receptors. Some relay molecular messages through a complex array of cellular proteins that indirectly turn genes on and alter cell growth and division. These results suggest that the same chemical can influence the endocrine system in more than one way. If understood, these complex modes of action may be able to answer the questions of how different molecules impact the endocrine system and how pollutants may form and feed some types of tumors.
Several factors confound how environmental estrogens affect the endocrine system.
Natural estrogen production varies with gender, age and reproductive cycles. For instance, women produce more estrogen than men, estrogen is abundant during fetal development and post-menopausal women have very little estrogen. Phytoestrogens , the natural plant compounds capable of acting like estrogen hormones, may produce opposing effects. At very high amounts, some cause infertility in farm animals and wildlife. Others seem to protect against breast and reproductive cancers in humans.