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Exposure of Newborn Male and Female Rats to Environmental Estrogens: Delayed and Sustained Hyperprolactinemia and Alterations in Estrogen Receptor Expression¹

Department of Cell Biology, The Vontz Center for Molecular Studies, University of Cincinnati, Cincinnati, Ohio 45267

Address all correspondence and requests for reprints to: Dr. Nira Ben-Jonathan, Department of Cell Biology, University of Cincinnati Medical School, 3125 Eden Avenue, Cincinnati, Ohio 45267. E-mail: nira.ben-jonathan{at}uc.edu

Environmental estrogens (xenoestrogens) are synthetic compounds that are abundant in the environment and mimic natural estrogens. The estrogenicity of two such compounds, bisphenol A (BPA) and octylphenol (OP), during development of the neuroendocrine system was investigated. The objective was to compare the effects of neonatal exposure to BPA, OP, and diethylstilbestrol (DES), a potent synthetic estrogen, on prepubertal serum PRL levels and estrogen receptor (ER) expression in the anterior pituitary and medial basal hypothalamus. Receptor expression in the uterus and prostate, two peripheral estrogen-responsive tissues, was also examined. Newborn male and female Fischer 344 rats were sc injected on days 1–5 after birth with corn oil (control), BPA and OP (100 or 500 µg/day), or DES (5 µg/day). Rats were bled on days 15, 20, and 25 and on the day of death (day 30), and serum PRL was analyzed by RIA. Relative expressions of ER and ERß were determined by RT-PCR. BPA and OP induced delayed, but progressive, increases in serum PRL levels, up to 3-fold above control levels, in both males and females. The low dose of either compound was equally or more effective as the high dose in eliciting and sustaining elevated serum PRL levels, namely hyperprolactinemia. In contrast, the DES treatment resulted in a transient rise in serum PRL levels. BPA, OP, and, to a lesser extent, DES increased the expression of both ER and ERß in the anterior pituitary of males, but not females, whereas the hypothalamic ERs were less responsive to these compounds. DES treatment caused down-regulation of ER expression in the uterus and up-regulation of ERß in the prostate, whereas BPA or OP was without effect. In conclusion, exposure of newborn rats of either sex to environmental estrogens results in delayed and sustained hyperprolactinemia and differential alterations in ER expression in the hypothalamus and pituitary. DES appears to target the lower reproductive tract more effectively than the neuroendocrine system.

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