Differential distribution of oestrogen receptor-α and -β mRNAs in the female reproductive organ of rats as revealed by in situ hybridization

The cellular distribution of two oestrogen receptor (ER) subtypes, ER alpha and ER beta mRNAs, was studied in the entire female reproductive organ of the rat using in situ hybridization. Expression of ER alpha and ER beta mRNAs was predominant in the reproductive tract and ovary respectively. ER alpha mRNA had the most pronounced expression in epithelial cells and subepithelial stromal cells from the oviduct to the vagina, while in the ovary it was moderately detected in only the theca folliculi and interstitial glands. The oviduct showed a region-dependent expression of ER alpha: mRNA: the isthmus had the most intense signals while the infundibulum revealed a low intensity of expression. Signals for ER beta mRNA in the ovary were most intense in the granulosa cells of healthy follicles, whereas degenerating follicles lacked any significant expression. Less intense signals for ER beta mRNA were localized in the theca folliculi and corpus luteum. Detectable levels of ER beta mRNA were observed in the subepithelial stromal cells from the oviduct to the vagina. This study shows that the two ER subtypes are differentially expressed in cells and compartments of the reproductive organ, suggesting that the mediation of oestrogen action in these tissues may be accomplished through the respective predominant receptor.