Regulation of estrogen receptor mRNA in normal and neoplastic rat pituitary tissues

The effects of estradiol 17β (E₂) on the regulation of estrogen receptor (ER) mRNA amounts in normal and neoplastic rat pituitary tissues were analyzed by in situ hybridization with an oligonucleotide probe. E₂ treatment produced a significant increase in ER mRNA amounts in two transplantable pituitary tumors (MtT/Wl5 and MtT/F4) and in the GH₃ cell line. ER mRNA amounts were also increased In normal pituitaries after 6 weeks of E₂ treatment, but the differences were not significant. Biochemical assay of ER proteins confirmed the presence of ER protein in MtT/Wl 5 and MtT/F4 tumors. "Cytoplasmic" ER proteins were decreased by E₂ in the MtT/Wl5 tumor.These results indicate that ER mRNA is present in normal pituitaries and in pituitary tumors and can be regulated by estrogen treatment in vivo and in vitro. The inhibitory effects of high estrogen concentration on proliferation of transplantable pituitary tumors in vivo and GH₃ cells in vitro is not explained by the absence of ER mRNAs in these tumors.