Estrogenic Activity of Octylphenol, Nonylphenol, Bisphenol A and Methoxychlor in Rats

Abstract

Considerable attention has recently been focused on environmental chemicals that disrupt the reproductive system by altering steroid receptor function. Although numerous in vitro and in vivo methods have been shown to be useful approaches for identifying chemicals that can disrupt reproduction through a direct interaction with the estrogen receptor, it is imperative that the protocols selected be capable of detecting chemicals with a broad range of estrogenic activity. Here we evaluate the reliability of the 3-day uterotrophic assay for detecting chemicals with strong or weak estrogenic activity in both prepubertal and ovariectomized adult Long Evans rats. These data were compared to additional measures of estrogenic activity, which included the age of vaginal opening, the induction of cornified vaginal epithelial cells in ovariectomized adult rats, and estrous cyclicity in intact adult rats. Test chemicals selected for these studies included 17-beta-estradiol, ethynyl estradiol, methoxychlor, 4-tert-octylphenol, 4-nonylphenol and bisphenol A. Data from in vitro receptor binding assays compared the ability of the test chemicals to compete with [3H]-estradiol or [3H]-promegestone for binding to estrogen or progesterone receptors. As expected, the binding affinities for the estrogen receptor ranged from high to low, as reflected by Ki concentrations of 0.4 nM for 17-beta-estradiol and ethynyl estradiol, and 0.05-65 microM for 4-tert-octyphenol, 4-nonylphenol, and methoxychlor. Although none of the test chemicals demonstrated a high affinity for binding to the progesterone receptor, 4-tert-octylphenol and 4-nonylphenol exhibited a weak affinity, with Ki concentrations ranging from 1.2 to 3.8 microM. In vivo studies indicated that the 3-day uterotrophic assay in prepubertal rats was the best method for detecting estrogenic activity when compared with all other end points, based upon the dose-response data for ethynyl estradiol (0.01-0.1 mg/kg), 4-tert-octylphenol (50-200 mg/kg, oral), and 4-nonylphenol (25-100 mg/kg, oral). Although oral doses of ethynyl estradiol (0.01 mg/kg) and 4-nonylphenol (50 mg/kg) induced a significant increase in uterine weight in the prepubertal rats, these doses were ineffective for stimulating a similar response in ovariectomized adult rats. The age of vaginal opening was advanced following oral exposure from postnatal days 21-35 to ethynyl estradiol (0.01 mg/kg), methoxychlor (50 mg/kg), 4-tert-octylphenol (200 mg/kg), and 4-nonylphenol (50 mg/kg). Although bisphenol A (200 mg/kg, oral) induced a significant uterotrophic response within 3 days in prepubertal rats, doses up to 400 mg/kg failed to advance the age of vaginal opening. Monitoring changes in the vaginal epithelium of ovariectomized adult rats was the least effective method for detecting estrogenic activity for 4-tert-octylphenol and bisphenol A. The number of 4-5 day estrous cycles was reduced during a 25-day exposure to ethynyl estradiol (0.01 mg/kg), methoxychlor (50 mg/ kg), 4-tert-octylphenol (200 mg/kg), 4-nonylphenol (10...

Measurement of bisphenol A levels in human urine

“…In rats, BPA produces a variety of hormone-like effects (Laws et al, 2000;Long et al, 2000 ). The health effects of BPA exposure on humans have not been studied.…”

Tools to evaluate estrogenic potency of dietary phytoestrogens:A consensus paper from the EU Thematic Network “Phytohealth” (QLKI-2002-2453)

“…The most common short-term in vivo assay for (anti)estrogenicity is the uterine growth test, suitable for screening ERα agonists and antagonists. Either immature intact or adult ovariectomized female rats or mice are used (Odum et al, 1997;Kang et al, 2000;Laws et al, 2000;Cotroneo et al, 2001;Newbold et al, 2001;Kanno et al, 2003). The test compounds are administered either subcutaneously or orally for a period of 3-7 days.…”

Glucuronidation and Excretion of Nonylphenol in Perfused Rat Liver

“…The delay of nonylphenol excretion is possible because of the adverse effects of nonylphenol on rat reproductive systems (Laws et al, 2000).…”

“…Early neonatal exposure to nonylphenol has been reported to cause dysfunction of postpubertal reproductive function in female rats as well as disrupted development of gonads in male and female rats (Nagao et al, 2000). It has also been reported that nonylphenol administered orally at a dose of 50 mg/kg of body weight induced a significant increase in uterine weight of prepubertal rats and advanced the age of vaginal opening (Laws et al, 2000). Elucidation of the metabolism and fate of nonylphenol is important for estimating the risks of the chemical for animals.…”