Estradiol or methoxychlor stimulates estrogen receptor (ER) expression in uteri.

The estrogenic pesticide methoxychlor (MXC) abnormally alters reproduction in rodents. The influence of MXC on expression of the estrogen receptor (ER) gene was investigated in the uterus of BALB/c mice and compared to the effect of estradiol. Uterine epithelium in control mice is devoid of ER until 5 d of life. Sesame oil, 10.0 micrograms estradiol 17 beta or 1.0 mg of base-washed 95% MXC were injected into neonates (days 1 to 4) and immature mice (days 10 to 14), after which they were sacrificed. By day 5, E or MXC induced production of nuclear ER mRNA and its translation in uterine epithelium. The mRNA was detected by in situ hybridization and ER protein by immunocytolocalization. In controls, ER was present only in stroma and myometrium. By day 15, the nuclei of uterine epithelium, stroma, and myometrium expressed the ER gene, with no apparent influence of E or MXC. Both E and MXC induce premature nuclear expression of the ER gene in neonatal uterine epithelium, without apparent change in ER gene expression between days 10 and 14 of life.