No abstract

Environmental estrogens (xenoestrogens) are a diverse group of chemicals that mimic estrogenic actions. Bisphenol A (BPA), a monomer of plastics used in many consumer products, has estrogenic activity in vitro. The pituitary lactotroph is a well established estrogen-responsive cell. The overall objective was to examine the effects of BPA on PRL release and explore its mechanism of action. The specific aims were to: 1) compare the potency of estradiol and BPA in stimulating PRL gene expression and release in vitro; 2) determine whether BPA increases PRL release in vivo; 3) examine if the in vivo estrogenic effects are mediated by PRL regulating factor from the posterior pituitary; and 4) examine if BPA regulates transcription through the estrogen response element (ERE). BPA increased PRL gene expression, release, and cell proliferation in anterior pituitary cells albeit at a 1000- to 5000-fold lower potency than estradiol. On the other hand, BPA had similar efficacy to estradiol in inducing hyperprolactinemia in estrogen-sensitive Fischer 344 (F344) rats; Sprague Dawley (SD) rats did not respond to BPA. Posterior pituitary cells from estradiol- or BPA-treated F344 rats strongly increased PRL gene expression upon coculture with GH3 cells stably transfected with a reporter gene. Similar to estradiol, BPA induced ERE activation in transiently transfected anterior and posterior pituitary cells. We conclude that: a) BPA mimics estradiol in inducing hyperprolactinemia in genetically predisposed rats; b) the in vivo action of estradiol and BPA in F344 rats is mediated, at least in part, by increasing PRL regulating factor activity in the posterior pituitary; c) BPA appears to regulate transcription through an ERE, suggesting that it binds to estrogen receptors in both the anterior and posterior pituitaries. The possibility that BPA and other xenoestrogens have adverse effects on the neuroendocrine axis in susceptible human subpopulations is discussed.

The xenoestrogen bisphenol A (BPA) has been shown to mimic estrogen both in vivo and in vitro. BPA stimulates PRL secretion and the expression of a PRL regulating factor from the posterior pituitary in the estrogen-sensitive Fischer 344 rat (F344), but not in Sprague-Dawley (SD) rats. The goal of the present studies was to examine the in vivo actions of BPA on the reproductive tract. The specific objectives were 1) to characterize the short term effects of BPA on cell proliferation and c-fos expression in the uterus and vagina, and 2) to compare the effects of prolonged exposure to low doses of BPA on the reproductive tract of F344 and SD rats. Treatment with single high doses of BPA induced cell proliferation in the uterus and vagina of ovariectomized F344 rats, as determined by bromodeoxyuridine immunostaining. This proliferation was dose dependent (from 37.5-150 mg/kg) and followed a time course similar to that of estradiol (E2). Quantitative RT-PCR revealed that both BPA and E2 increased c-fos messenger RNA levels in the uterus 14- to 16-fold within 2 h, which returned to basal levels after 6 h. In the vagina, BPA-induced c-fos expression remained elevated for up to 6 h, compared with the transient increase caused by E2. Treatment of F344 rats for 3 days with continuous release capsules that supplied a much lower dose of BPA (approximately 0.3 mg/kg x day) resulted in hypertrophy, hyperplasia, and mucus secretion in the uterus and hyperplasia and cornification of the vaginal epithelium. The reproductive tract of SD rats did not respond to this treatment paradigm with BPA. These studies demonstrate that 1) the molecular and morphological alterations induced by BPA in the uterus and vagina are nearly identical to those induced by estradiol; 2) the vagina appears to be especially sensitive to the estrogenic actions of BPA; 3) the reproductive tract of the inbred F344 rat appears more sensitive to BPA than that of the outbred SD rat; and 4) continuous exposure to microgram levels of BPA is sufficient for exerting estrogenic actions.

The objective of this study was to purify PRL-releasing factor (PRF) from the bovine posterior pituitary (PP) and determine its structure. Five hundred bovine PPs were acid extracted and fractionated using gel filtration chromatography followed by semipreparative and analytical HPLC. PRF activity was determined by an in vitro bioassay. After six chromatographic steps, a single peak with PRF activity was resolved. As determined by mass spectrometry and microsequencing, this peak contained a major peptide composed of 30 amino acids with a mol wt of 3708K. A synthetic peptide was then produced by solid-phase synthesis. When tested both in vivo and in vitro, the synthetic peptide lacked PRF activity. Further HPLC fractionation under different conditions resolved the synthetic peptide from a highly purified PRF activity. This indicated that the isolated peptide was coincidentally eluted with PRF during the purification. The major isolated peptide has 94% identity with a sequence at the C-terminus of a rat protein named VGF. VGF is a nerve growth factor-inducible protein that has been identified in PC12 cells and is localized in selected sites throughout the central nervous system. The isolated peptide has an Arg-Arg cleavage site at its junction within the VGF protein. Based on this information, we named this substance Peptide V (VGF-derived peptide). We postulate that Peptide V is: 1) a natural cleavage product of the VGF protein; 2) produced and processed either in the hypothalamus or within the pituitary proper, and 3) a releasable peptide that fulfills one or more endocrine functions.