Evaluating the effects of endocrine disrupters on endocrine function during development

The major concerns with endocrine disrupters in the environment are based m ostly on effects that have been observed on the developing embryo and fetus . The focus of the present manuscript is on disruption of three hormonal sy stems: estrogens, androgens, and thyroid hormones. These three hormonal sys tems have been well characterized with regard to their roles in normal deve lopment, and their actions during development are known to be perturbed by endocrine-disrupting chemicals. During development, organs are especially s ensitive to low concentrations of the sex steroids and thyroid hormones. Ch anges induced by exposure to these hormones during development are often ir reversible, in contrast with the reversible changes induced by transient ho rmone exposure in the adult. Although it is known that there are difference s in embryonic/fetal/neonatal versus adult endocrine responses, minimal exp erimental information is available to aid in characterizing the risk of end ocrine disrupters with regard to a number of issues. Issues discussed here include the hypothesis of greater sensitivity of embryos/fetuses to endocri ne disrupters, irreversible consequences of exposure before maturation of h omeostatic systems and during periods of genetic imprinting, and quantitati ve information related to the shape of the dose-response curve for specific developmental phenomena.