Subcutaneous treatment of p-tert-octylphenol exerts estrogenic activity on the female reproductive tract in normal cycling rats of two different strains.

Effects of p-tert-octylphenol (OP), an endocrine disrupting chemical (EDC), on the female reproductive tract of normal cycling Fischer 344 (F344) and Donryu rats were investigated. OP was subcutaneously injected at concentrations of 12.5, 25, 50 or 100 mg/kg for 28 days. The most notable changes were the disappearance of normal cyclicity in the 50 mg/kg or more OP-treated groups of both the strains, and the appearance of persistent estrus (PE) evident on examination of vaginal smears in the 100 mg/kg groups of both the strains, the effects being time- and dose-dependent. In PE rats of both the strains, the uterine morphology deviated from the normal for each estrous stage of the cycling rats, and proliferation in the endometrium was slightly increased. The data for uterine weights, luminal epithelial cell-heights and/or numbers of epithelial cells in the endometrium demonstrated equivocal alteration. In both the strains, the serum 17beta-estradiol (E2) levels were decreased with 50 mg/kg of OP or more. Serum concentrations of the administrated chemical were dose and duration-dependently increased in all the treated groups of both the strains. The results demonstrate that subcutaneous administration of OP at doses of 50 mg/kg or more exerts time- and dose-dependent estrogenic activity on the reproductive tract of normal cycling female Donryu and F344 rats, indicating similar qualitative sensitivity to the effects in both the strains. Vaginal cytology may be the most sensitive endpoint for the detection of estrogenic activity of potential EDCs using adult cycling rats.