Octylphenol does not mimic diethylstilbestrol-induced oestrogen receptor-alpha expression in the newborn mouse uterine epithelium after prenatal exposure

This study examined whether the endocrine disrupter octylphenol (OP) mimics the synthetic oestrogen diethylstilbestrol (DES) in ability to induce oest rogen receptor-alpha (ER-alpha) expression in the newborn mouse uterine epi thelium after prenatal exposure. Pregnant mice were given daily s.c. inject ions with DES (10 or 100 mug DES/kg maternal wt) or OP (100 or 250 mg/kg ma ternal wt) or with vehicle alone from day 11.5 to 16.5 of pregnancy. ER-alp ha expression was evaluated on histological sections by detecting ER-alpha mRNA with the in situ hybridization technique and ER-alpha protein using im munohistochemistry. The immunostaining was quantitated using a microspectro photometer. Oestrogen-like activity of the DES and OP batches used for in v ivo exposure was confirmed in an in vitro assay based on transient gene exp ression of an oestrogen-dependent reporter plasmid. In mice exposed prenata lly to vehicle alone, the uterine epithelium did not express either ER-alph a mRNA or protein, while both were highly expressed in the stroma. Exposure to either DES dose induced the expression of both ER-alpha mRNA and protei n in the epithelium, whereas it was unchanged in the stroma. In contrast, n either OP dose induced the expression of ER-alpha mRNA or protein in the ep ithelium and expression was unchanged in the stroma. Our data stress the im portance of in vivo studies when investigating endocrine disrupters.