Ovarian estrogen receptor alpha and beta mRNA expression: impact of development and estrogen

We tested the hypothesis that ER alpha and ERP mRNAs in the rat ovary are r egulated during the post-natal period and in immature rats in response to e strogen treatment. Total ovarian ERP mRNA was more abundant than ER alpha m RNA and expression of ERP increased between post-natal days 4 and 12, coinc iding with advancing folliculogenesis and an increase in granulosa cell num bers. In contrast, ER alpha mRNA levels remained relatively constant during this period. In situ hybridisation studies localised both ER alpha and ERP to granulosa cells of growing follicles, in 25 day old ovaries, although n ot ail granulosa cells in a follicle or all follicles expressed the ERs. Di ethylstilboestrol (DES) administered in vivo to 21 day old rats, for up to 4 days, did not significantly alter the expression of either ER as determin ed by RT-PCR, despite a 5.5-fold increase in granulosa cell number in these ovaries. In situ hybridisation studies established that DES-treatment down -regulated granulosa cell ER mRNAs. RT-PCR analyses on isolated granulosa c ells confirmed that ERa was significantly down-regulated by DES. The predom inance of ERP over ERa in the ovary and the regulation of ERP mRNA expressi on during ovarian development, is consistent with an important biological r ole for ERP in granulosa cell proliferation and differentiation. (C) 1999 E lsevier Science Ireland Ltd. All rights reserved.