COMPARATIVE DISTRIBUTION OF ESTROGEN RECEPTOR-ALPHA (ER-ALPHA) AND RECEPTOR-BETA (ER-BETA) MESSENGER-RNA IN THE RAT PITUITARY, GONAD, AND REPRODUCTIVE-TRACT

The present study used in situ hybridization histochemistry to compare the distribution of estrogen receptor (ER)-alpha and ER-beta mRNA-con taining cells in rat pituitary, gonads, uterus, and prostate of intact animals or after hormonal manipulations. Cryostat tissue sections wer e hybridized with S-35-labeled antisense riboprobes complimentary to E R-alpha or ER-beta mRNA, stringently washed and apposed to emulsion. T he results of these studies indicate that the expression of the two re ceptors is tissue and region specific, with estrogen target tissues sp ecifically expressing ER-alpha, ER-beta, or both forms of ER. In the i ntact rat, ER-alpha and ER-beta mRNA were both seen in the pituitary, although more cells expressed ER-alpha than ER-beta mRNA. The distribu tion of the two transcripts in the ovary was qualitatively different, with ER-alpha being primarily localized in the stromal cells, while ER -beta mRNA was concentrated in the granulosa cells of developing folli cles. In the uterus, ER-alpha mRNA was abundant in the stromal and epi thelial cells of the endometrium, while only very weak ER-beta hybridi zation signal was detected in these cells. ER-beta mRNA- expressing ce lls, but not ER-alpha, were also detected in the prostate and in the S ertoli cells, and the large, round spermatocytes of the testis. Gonade ctomy markedly attenuated the expression of ER-beta mRNA in the periph eral tissues, with the level of ER-beta mRNA in the uterus and prostat e reduced to non-detectable levels. The results of these in situ hybri dization studies demonstrate that the distribution and regulation of E R-beta mRNA expression is tissue specific and different from ER-alpha mRNA. The differential expression of ERs in these tissues may explain in part the tissue selective activity of estrogenic compounds. (Steroi ds 63:498-504, 1998) (C) 1998 by Elsevier Science Inc.