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, ER alpha and beta, in relation to oestrogenic enzymes, P450aromatase (P450arom) and 17 beta HSD typel (17 beta HSD1) 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 ER alpha and beta was down-regulated by the treatment with PMSG. Following the hCG injection, fur ther down-regulation of both ERs occurred. Conversely, expression of P450arom and 17 beta HSD1 was initially up-regulated by PMSG and then rapidly down-regulated following injection of hCG. In isolated granulosa cell, ERP was the predominant ER while ER alpha was mainly expressed in residual ovary and corpora lutea (CL). These results indicate that ER alpha and ER beta 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. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.