The OECD program to validate the rat uterotrophic bioassay. Phase 2: dose-response studies.

Abstract

The Organisation for Economic Co-operation and Development has completed phase 2 of an international validation program for the rodent uterotrophic bioassay. The purpose of the validation program was to demonstrate the performance of two versions of the uterotrophic bioassay, the immature female rat and the adult ovariectomized rat, in four standardized protocols. This article reports the dose-response studies of the validation program; the coded single-dose studies are reported in an accompanying paper. The dose-response study design used five selected weak estrogen agonists, bisphenol A, genistein, methoxychlor, nonylphenol, and o,p -DDT. These weak agonists were administered in a prescribed series of doses to measure the performance and reproducibility of the protocols among the participating laboratories. All protocols successfully detected increases in uterine weights when the weak agonists were administered. Within each protocol, there was good agreement and reproducibility of the dose response among laboratories with each substance. Substance-specific variations were observed in the influence of the route of administration on the uterine response, the potency as related to the dose producing the first statistically significant increase in uterine weights, and the maximum increase in uterine weight. Substantive performance differences were not observed between the uterotrophic bioassay versions or among the standardized protocols, and these were judged to be qualitatively equivalent. It is noteworthy that these results were reproducible under a variety of different experimental conditions (e.g., animal strain, diet, housing, bedding, vehicle, animal age), indicating that the bioassay's performance as a screen is robust. In conclusion, both the intact, immature, and adult OVX versions, and all protocols appear to be reproducible and transferable across laboratories and are able to detect weak estrogen agonists.

Usefulness of immature golden hamster (Mesocricetus auratus) as a model for uterotrophic assay

“…The mean uterine relative weight was approximately 60% of EE2 control value and histopathological examination confirmed attenuated proliferative effect. Our results are largely consistent with the literature data obtained using immature rats, in which case significant uterotrophic effects of EE2 were observed at doses from 0.3 to 3 µg/kg b.w./d (9,12,13,14,16,24,28) and antagonistic effects of tamoxifen at the dose of 1 mg/kg b.w/d (7).…”

“…Although much attention has been focused on identifying protocol variables and reproducibility among laboratories (12,13,14,16,23,24), direct comparison of uterine responses among rodent species has been rarely addressed (26). However, it is expected that the risk to humans takes into account the results obtained in the most sensitive species (26,30).…”

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.…”

The OECD program to validate the rat uterotrophic bioassay. Phase 2: coded single-dose studies.

“…The management of the validation program and the results of other portions of the validation program have been described in other reports (Kanno et al 2001(Kanno et al , 2003. A central objective of the OECD validation program is to establish the reliability of standardized protocols for the uterotrophic bioassay.…”

“…A previous article demonstrated the reproducibility of the dose response of the reference agonist, 17α-ethinyl estradiol (EE), with both versions and all protocols (Kanno et al 2001). An accompanying article demonstrates the reproducibility of both versions and all protocols using dose responses of the five weak agonist test substances (Kanno et al 2003). Because all laboratories performed the EE dose response separate from these data, and almost all laboratories performed the weak agonist dose-response and coded single-dose studies at separate times, a comparison of the data provides for an assessment of bioassay reproducibility over time.…”