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 oestrog en-like activity in the environment has focused attention on the need for d eveloping sensitive and specific methods for identifying these xenobiotics and to evaluate their degrees of toxic effects. We have conducted dose resp onse studies in immature (21 days old) CD-1 female mice treated with four c ompounds, diethylstilboestrol (DES) (0.1 mu g to 25 mg/kg body weight), alp ha-zearalanol (0.5 mg to 25 mg/kg body weight), methoxychlor (0.5 mg to 500 mg/kg body weight) and bisphenol A (10 mu g to 100 mg/kg body weight) admi nistered subcutaneously daily for 3 days, and measured a number of uterine markers in treated and control (vehicle treated) mice. These were, in addit ion to the commonly measured changes in relative uterus weight and histopat hological examination of uterine tissue, three other markers indicative of uterotrophic effects, namely, uterine luminal epithelium BrdU labelling ind ex over the last 24 hr, peroxidase activity and lactoferrin expression. All of these markers showed clear dose-related increases in DES- and methoxych lor-treated animals. In the case of alpha-zearalanol treatment, relative ut erine weight, peroxidase activity and lactoferrin expression showed dose-re lated 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 n o consistent changes in any of the four markers at the dose levels investig ated. 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 day s. 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 ex ploratory in vivo studies in CD-1 mice suggest that the measurement of a ra nge of uterine markers, in addition to organ weight and histopathology, wou ld provide useful information on me potential oestrogenicity of chemicals. (C) 2000 Elsevier Science Ltd. All rights reserved.