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The pituitary gonadotropins FSH and LH are key hormones for regulating gametogenesis and steroidogenesis in the ovary and testis. The cell surface receptors that mediate the biological activities of these hormones are thought to be expressed in a cell-specific fashion in the ovary and are regulated as animals progress through the reproductive cycle. Using cloned receptor cDNAs, we have examined the expression and hormonal regulation of the ovarian FSH and LH receptor mRNAs in the rat. A quantitative reverse transcription-polymerase chain reaction amplification scheme was used to measure relative levels of the FSH and LH receptor mRNAs, while in situ hybridization was used to localize FSH and LH receptor transcripts. In immature animals, low levels of FSH receptor mRNA are observed in the granulosa cells of small follicles, while low levels of LH receptor mRNA are found in the thecal cells of these same follicles. After stimulation with PMSG, levels of both mRNAs increase, and the LH receptor mRNA is localized in both the granulosa and thecal cells of large follicles. Further treatment of PMSG-primed animals with hCG results in down-regulation, particularly of the LH receptor mRNA in granulosa cells. In adult animals, LH receptor mRNA levels change dramatically during the estrous cycle, particularly after the preovulatory LH surge. FSH receptor mRNA levels show a similar pattern of change, but the FSH receptor mRNA is of lower abundance and is not as highly regulated as the LH receptor mRNA. FSH receptor mRNA is confined to the granulosa cells of healthy developing follicles, whereas LH receptor mRNA is localized predominantly to thecal cells of small follicles on estrous morning, then appears in the granulosa cells of growing follicles by diestrous morning. LH receptor mRNA is also found in interstitial tissues and corpora lutea throughout much of the estrous cycle. Our results indicate that the gonadotropin receptor genes are regulated in a complex fashion during the recruitment, maturation, and ovulation of the ovarian follicle.

Cortisol treatment for 6 or 12 days had no effect on serum FSH in intact males and animals castrated for 1 or 7 days, but pituitary FSH was increased by the steroid in both intact and castrate groups. In contrast, cortisol inhibited serum LH in both intact and castrated animals while only increasing pituitary levels of LH in 7 day castrates. Cortisol also increased the mRNA for FSH beta without affecting alpha or LH beta mRNAs. These data suggest that the selective increase in pituitary content of FSH may be due to a selective increase in FSH beta mRNA following exposure to cortisol.

To pursue questions concerning the regulation of somatic growth in a species amenable to both genetics and germ-line manipulation, we have isolated and characterized a full-length cDNA clone encoding mouse GH-releasing hormone (mGHRH). A GHRH cDNA clone isolated from a mouse placental library contains an open-reading frame of 309 basepairs that predicts a 103 amino acid mouse GHRH precursor protein. The mature mouse GHRH is predicted to be 42 amino acids with a free carboxyl-terminus. Although the mGHRH precursor sequence is clearly related to those determined for rat and human, the mature mGHRH peptide differs at seven of its 42 positions from all previously characterized GHRH peptides. RNA blot analysis of mouse tissues indicates that the mature 750 nucleotide mGHRH mRNA is found in hypothalamus and placenta, while testis contains a larger GHRH-related transcript. In situ hybridization analysis of GHRH gene expression in the mouse brain indicates that GHRH mRNA is localized predominantly to the arcuate nucleus of the hypothalamus. In the placenta, GHRH mRNA levels are developmentally regulated and peak on days 16-17 of gestation. GHRH mRNA is localized predominantly to trophoblast giant cells and to cytotrophoblasts of the placental labyrinth.