Expression of oestrogen receptor isoforms in relation to enzymes of oestrogen synthesis in rat ovary.

Oestrogen acts as a local regulator of follicular development, mediated by specific nuclear oestrogen receptors (ER). The aim of this study was to examine the gene expression of two ER isoforms, ERalpha and beta, in relation to oestrogenic enzymes, P450aromatase (P450arom) and 17betaHSD type1 (17betaHSD1) during follicular maturation and luteinization. Ovaries were obtained from immature rats treated with PMSG (10 iu for 48 h) followed by hCG (10 iu). Expression of ERalpha and beta was down-regulated by the treatment with PMSG. Following the hCG injection, further down-regulation of both ERs occurred. Conversely, expression of P450arom and 17betaHSD1 was initially up-regulated by PMSG and then rapidly down-regulated following injection of hCG. In isolated granulosa cell, ERbeta was the predominant ER while ERalpha was mainly expressed in residual ovary and corpora lutea (CL). These results indicate that ERalpha and ERbeta mRNAs are expressed in different cell types and are both down-regulated during gonadotrophin stimulated follicular maturation and luteinization in the rat ovary. Down-regulation of ER is accompanied by down-regulation of oestrogenic enzymes during luteinization. Thus both oestrogen production and reception are shut down as ovulation approaches.