In vivo screening evaluation of 12 chemicals as candidate endocrine disruptors using ovariectomized mouse uterotrophic bioassay.

The rodent uterotrophic bioassay is helpful to easily predict and evaluate the estrogenic properties of chemicals by measuring changes in uterine weight as a screening test. We used this assay in ovariectomized (OVX) mice to screen 12 chemicals suspected to be estrogenic or antiestrogenic properties by in vitro assays in the screening project of the Ministry of Health, Labour and Welfare, Japan. We administered each chemical to 8-week-old OVX mice either orally (po) or by subcutaneous (sc) injection at 24-hr intervals for 7 consecutive days. Ethinyl estradiol was used as reference control. Our study revealed for the first time that po or sc administration of 1,1,1-tris(4-hydroxyphenyl)ethane exerted estrogenic effects at nontoxic dose, with a LOEL of 300 mg/kg for both routes. In contrast, sc administration, but not po administration, of dibenzoylmethane, tricresyl phosphate, and triphenylsilanol exerted antiestrogenic effects, with a LOEL of 30 mg/kg for each chemical. Furthermore, po and sc administration of 4,4'-butylidenebis[6-tert-butyl-3-methylphenol] exerted antiestrogenic effects, with a LOEL of 100 mg/kg for both routes. Taken together, we revealed that only 5 of the 12 substances of concern in vitro were active in vivo, which could be helpful for the effective detection of estrogenic and antiestrogenic activities. The five positive substances were considered to require further consideration in the prioritization list of higher-order toxicity testing for their endocrine disrupting effects.