Hormonal regulation of luteinizing hormone/chorionic gonadotropin receptor mRNA in rat ovarian cells during follicular development and luteinization.

To determine whether hormone-dependent changes in the levels of LH/CG receptor in the rat ovary are associated with changes in expression of LH/CG receptor mRNAs, total RNA from rat follicles and corpora lutea at various stages of development was prepared and analyzed by Northern blots and/or solution hybridization. Whereas small antral follicles contained lo amounts of LH/CG receptor mRNAs, the growth of preovulatory (PO) follicles was associated with an increase in all LH/CG receptor mRNA transcripts. Induction of LH/CG receptor mRNAs in granulosa cells of hypophysectomized rats was dependent on the synergistic effects of estradiol and FSH. An LH/CG surge in vivo or LH treatment of PO follicles in vitro caused a rapid decline of all LH/CG receptor mRNAs in PO follicles, which was prevented by cycloheximide. Newly formed corpora lutea (days 1-4 postovulation) contained low amounts of LH/CG receptor mRNAs unless the rats were pregnant or treated exogenously with PRL. During pregnancy, corpora lutea isolated on days 4-19 of gestation contained high levels of LH/CG receptor mRNAs, which decreased markedly on days 21 and 24, the time of functional luteolysis and decreasing LH/CG receptor levels. These studies demonstrate that hormonal regulation of LH/CG receptor mRNA in rat ovarian cells parallels changes in LH/CG receptor levels and involves diverse molecular mechanisms, including 1) low concentrations of cAMP (elicited by FSH) in developing follicles, 2) inhibition by high concentrations of cAMP (elicited by LH/CG) in PO follicles, and 3) induction and maintenance by PRL in corpora lutea of gestation.