SUMMARY Endocrine disrupting compounds (EDC) are hormonally active, synthetic or natural chemicals that interfere with normal functioning of the endocrine system, most notably the reproductive endocrine axis. Concern about EDC has mainly been fueled by studies that point to likely effects of EDC exposure on humans including dramatic increases in estrogen sensitive cancers, decline in human sperm quality and quantity, a notable rise in endometriosis, and early puberty in women. Because of the universal and crucial role estradiol plays in reproduction and other biologic processes, estrogenic pollutants in the environment are of particular concern. Given that sex steroids play a crucial role in organ differentiation during development, it is reasonable to expect in utero exposure to exogenous steroid mimics may alter the developmental trajectory of the fetus culminating in adult reproductive dysfunction. Our preliminary studies using sheep as a model revealed that prenatal exposure to the plasticizer bisphenol A (BPA), an environmentally relevant EDC, at levels approaching that found in human maternal blood and amniotic fluids, resulted in low birth weight female offspring, early postnatal hypergonadotropism, and cycle defects manifested as severe dampening of the LH surge. In this proposal, we will test the hypothesis that prenatal exposure to BPA, an environmental estrogen mimic, at levels similar to what human fetuses are exposed to, will disrupt adult reproductive function by disrupting the mechanisms controlling postnatal neuroendocrine feedback controls of GnRH/LH secretion and ovarian sensitivity to gonadotropins. Further, prenatal exposure to BPA will exacerbate postnatal reproductive susceptibility to steroid exposure and culminate in reproductive failure. Three Specific Aims will test these hypotheses. Specific Aim 1 will determine if unconjugated BPA in the maternal circulation reaches the fetus and at levels seen by the human fetus disrupt adult reproductive function. Specific Aim 2 will determine if prenatal BPA effect is mediated at the neuroendocrine or ovarian level and involves disruption of the mechanisms controlling postnatal neuroendocrine feedback controls of GnRH/LH secretion and/or ovarian sensitivity to gonadotropins. Specific Aim 3 will determine if prenatal exposure to BPA exacerbates reproductive susceptibility to postnatal estradiol exposure culminating in reproductive failure. The proposal targets key elements of strategic plans that emanated from workshops convened by the NICHD in 2000-01 by focusing on three targeted areas: fetal antecedents of disease, reproductive health for the 21st century, and developmental biology. The findings will be relevant to research on fetal origin of infertility and the threat estrogenic environmental disruptors at current exposure levels pose to human health.