The OECD program to validate the rat uterotrophic bioassay to screen compounds for in vivo estrogenic responses: phase 1.

Abstract

The Organisation for Economic Co-operation and Development has completed the first phase of an international validation program for the rodent uterotrophic bioassay. This uterotrophic bioassay is intended to identify the in vivo activity of compounds that are suspected agonists or antagonists of estrogen. This information could, for example, be used to help prioritize positive compounds for further testing. Using draft protocols, we tested and compared two model systems, the immature female rat and the adult ovariectomized rat. Data from 19 participating laboratories using a high-potency reference agonist, ethinyl estradiol (EE), and an antagonist, ZM 189,154, indicate no substantive performance differences between models. All laboratories and all protocols successfully detected increases in uterine weights using EE in phase 1. These significant uterine weight increases were achieved under a variety of experimental conditions (e.g., strain, diet, housing protocol, bedding, vehicle). For each protocol, there was generally good agreement among laboratories with regard to the actual EE doses both in producing the first significant increase in uterine weights and achieving the maximum uterine response. Furthermore, the Hill equation appears to model the dose response satisfactorily and indicates general agreement based on calculated effective dose (ED)(10) and ED(50) within and among laboratories. The feasibility of an antagonist assay was also successfully demonstrated. Therefore, both models appear robust, reproducible, and transferable across laboratories for high-potency estrogen agonists such as EE. For the next phase of the OECD validation program, both models will be tested against a battery of weak, partial estrogen agonists.

Comparative responses of three rat strains (DA/Han, Sprague-Dawley and Wistar) to treatment with environmental estrogens

“…Wistar, Sprague-Dawley, Fischer 344, and Noble) and various endpoints were used, some strain differences in the response to treatment with environmental estrogens have been reported (Long et al 2000;Steinmetz et al 1998;McKim et al 2001). Yet, these and other published data (Odum et al 1999a(Odum et al , 1999bKanno et al 2001) do not indicate significant differences in uterine response among rat strains. Nonetheless, further data are needed to prove or disprove the existence of consistent differences in sensitivity among strains (Owens and Ashby 2002).…”

“…Protocol variables such as the rodent diet and the route of application can apparently result in more profound differences than the strain of rat (Kanno et al 2001(Kanno et al , 2003a(Kanno et al , 2003b. This is further exemplified by recent studies of experimental responses in the uterotrophic bioassay with rodent diets of high/low phytoestrogen contents (Degen et al 2002b;Kanno et al 2002;Yamasaki et al 2002), and an influence of application routes (oral, intraperitoneal or subcutaneous) on uterotrophic weight changes in rats (Kang et al 2000;Laws et al 2000;Yamasaki et al 2000).…”

“…Much effort has been placed in identifying protocol variables to improve reproducibility between laboratories (Odum et al 1997;Christian et al 1998;OÕConnor et al 1998aOÕConnor et al , 1998b. Attention has been paid to variables such as animal model (immature or ovariectomized), application route (Kanno et al 2001), and also to rodent diet (Odum et al 1997;Thigpen et al 2002;Degen et al 2002b). On the other hand, the question whether toxicodynamic and toxicokinetic variations of different laboratory rodent strains may affect their sensitivity to estrogenic stimuli has been rarely addressed.…”

Low-dose effects of bisphenol A on early sexual development in male and female rats

“…Health concerns regarding human exposures to BPA have in the past arisen from its well-known oestrogenic properties (Salian et al 2011). BPA has affinity for nuclear oestrogen receptors (ERa and ERb) and oestrogenic activity in vivo giving rise to increased uterine wet weights in the uterotrophic assay (Kanno et al 2001). Furthermore, BPA exposure during development has been shown to affect semen quality (Sakaue et al 2001, Salian et al 2009), alter prostate weights (Vom et al 1998, Timms et al 2005, Prins & Korach 2008 and increase the incidence of prostate intraepithelial neoplasia (PIN) lesions in the prostate of adult rodents (Prins et al 2011).…”

Evaluation of the Estrogenic Activity of Pueraria (Kudzu) Flower Extract and Its Major Isoflavones Using ER-Binding and Uterotrophic Bioassays

“…Phytoestrogens have recently received great attention because of their beneficial effects, including the prevention of atherosclerosis [9], and bone density loss [10]. However, the consumption of relatively high levels of some phytoestrogens has been shown to increase the risks of breast cancer [11], endometrial hyperplasia [12], and reproductive toxicity [13]. A previous study demonstrated that the high binding affinities of select isoflavones is associated with the structural properties of these molecules.…”