The development of methods for assessing the in vivo oestrogen-like effects of xenobiotics in CD-1 mice.

The increasing awareness and concern about the potential health risks posed to the ecosystem and to man by endocrine disrupting chemicals with oestrogen-like activity in the environment has focused attention on the need for developing sensitive and specific methods for identifying these xenobiotics and to evaluate their degrees of toxic effects. We have conducted dose response studies in immature (21 days old) CD-1 female mice treated with four compounds, diethylstilboestrol (DES) (0.1 microg to 25 mg/kg body weight), alpha-zearalanol (0.5 mg to 25 mg/kg body weight), methoxychlor (0.5 mg to 500 mg/kg body weight) and bisphenol A (10 microg to 100 mg/kg body weight) administered subcutaneously daily for 3 days, and measured a number of uterine markers in treated and control (vehicle treated) mice. These were, in addition to the commonly measured changes in relative uterus weight and histopathological examination of uterine tissue, three other markers indicative of uterotrophic effects, namely, uterine luminal epithelium BrdU labelling index over the last 24 hr, peroxidase activity and lactoferrin expression. All of these markers showed clear dose-related increases in DES- and methoxychlor-treated animals. In the case of alpha-zearalanol treatment, relative uterine weight, peroxidase activity and lactoferrin expression showed dose-related increases at all the doses investigated. BrdU incorporation (an index of cell proliferation) also progressively increased at dose levels ranging from 0.1 mg to 5.0 mg/kg body weight, but apparently decreased at 25 mg/kg body weight. In contrast to these findings, bisphenol-A treatment showed no consistent changes in any of the four markers at the dose levels investigated. Additionally, studies were also conducted on a number of chemicals in CD-1 mice at one dose level. The chemicals investigated were: bisphenol A (1 g/kg body weight/day), naringenin (1 g/kg body weight/day) o,p'-DDT (500 mg/kg body weight/day), genistein (1 g/kg/day), coumestrol (0.5 mg/kg/day) and chlordecone (20 mg/kg/day) administered subcutaneously daily for 3 days. There was some variability in response of the markers perhaps indicating that the chemicals did not all act in the same way. The findings of our exploratory in vivo studies in CD-1 mice suggest that the measurement of a range of uterine markers, in addition to organ weight and histopathology, would provide useful information on the potential oestrogenicity of chemicals.