The OECD program to validate the rat uterotrophic bioassay: an overview.

Area of Science:

• Endocrinology
• Toxicology
• Environmental Health

Background:

• The rodent uterotrophic bioassay is a key method for assessing estrogenic activity.
• Previous validation efforts focused on reference compounds and initial protocol assessments.

Purpose of the Study:

• To conduct an international validation program for the rodent uterotrophic bioassay.
• To assess the operating characteristics and predictivity of four different bioassay protocols.
• To evaluate the assay's ability to detect weak estrogen agonists and antagonists.

Main Methods:

• A comprehensive review of existing data on the bioassay's history, mechanistic relevance, and predictivity.
• A multiyear validation effort involving two phases to demonstrate protocol operating characteristics.
• Testing of five weak estrogen agonists (bisphenol A, genistein, methoxychlor, nonylphenol, o,p -DDT) and a negative control (dibutylphthalate) across four protocols.

Main Results:

• All tested protocols successfully detected increased uterine weights in response to weak estrogen agonists at sufficient doses.
• The assay demonstrated reproducibility over time and across various experimental conditions, including different animal strains, diets, and housing.
• Data confirmed the reliability of detecting both reference agonists (ethinyl estradiol) and weak agonists.

Conclusions:

• The rodent uterotrophic bioassay protocols evaluated are valid for detecting estrogenic substances.
• The validation program provides robust evidence supporting the assay's predictivity and reproducibility.
• The findings support the use of the uterotrophic bioassay in regulatory assessments of endocrine-disrupting chemicals.