Estrogen receptor-beta expression in relation to the expression of luteinizing hormone receptor and cytochrome P450 enzymes in rat ovarian follicles

Changes in mRNA expression for estrogen receptor (ERP) in relation to mRNAs for LH receptor (LHr) and cytochrome P450 enzymes were examined in granulo sa and theca cells from proestrous rat ovarian follicles. Of the 30 ovaries harvested from 15 adult rats, 24 were processed for in situ hybridization, and the remaining were used for reverse transcription-polymerase chain rea ction. Messenger RNAs for ERP, LHr, cytochrome P450 side-chain cleavage enz yme (P450(scc)), 17 alpha -hydroxylase (P450(c17)), aromatase (P450(arom)), and steroidogenic acute regulatory protein (StAR) were localized in cross sections of ovaries by in situ hybridization and quantified in granulosa an d theca cell layers by a computer-image analyzing system. Ovarian follicles were classified as healthy or atretic. Healthy follicles were divided into four size groups: very small (40-100 mum), small (101-275 mum), medium (27 6-450 mum), and large (451-850 pm). Atretic follicles were divided into med ium (276-450 pm) or large follicles (451-850 mum). A low level of ERP mRNA expression was first detected in granulosa cells of very small healthy foll icles, and the expression increased progressively up to medium-sized follic les. The expression of ERP mRNA was highest (P < 0.01) in medium-sized foll icles that was followed by a decrease (P < 0.01) in large follicles. Messen ger RNAs for LHr, P450(scc), and P450(arom) were first detected in granulos a cells of medium-sized healthy follicles, while mRNAs for LHr, P450,,,, P4 50,,,, and StAR were first detected in theca cells associated with very sma ll follicles. The highest expression of LHr, P450(scc), P450(c17), P450(aro m), and StAR was seen in granulosa and/or theca cells of large healthy foll icles. In atretic follicles, level of gene expression was relatively low in both granulosa and theca cells. In conclusion, stage-specific expression o f ERP mRNA was observed in granulosa cells during follicular development. T he increased expression of ERP and a concomitant initiation of LHr, P450(sc c), and P450(arom) expression in granulosa cells of medium follicles may si gnify a role for estrogen in follicular development. Also, a strong correla tion between ERP mRNA expression in granulosa cells, and the expression of mRNAs for LHr, P450(scc), P450(c17), and StAR in theca cells associated wit h growing follicles suggests a possible role for estrogen in steroidogenesi s.