EFFECTS OF OVARIECTOMY AND HYPOTHALAMIC-PITUITARY DISCONNECTION ON AMOUNTS OF STEROIDOGENIC FACTOR-I MESSENGER-RNA IN THE OVINE ANTERIOR-PITUITARY GLAND

Steroidogenic factor-1 (SF-1) is a transcription factor involved in re gulation of steroidogenic enzymes, Recent evidence indicates that SF-1 is also important in the anterior pituitary gland, where it may influ ence gene expression in gonadotropes. We isolated a cDNA encoding ovin e SF-1 and demonstrated that the SF-1 gene is expressed in the anterio r pituitary gland of sheep. SF-1 transcripts and luteinizing hormone ( LH) were colocalized in gonadotropes by in situ hybridization and immu nohistochemistry, respectively. To test the hypothesis that GnRH stimu lates pituitary expression of ovine SF-1 mRNA, ewes were ovariectomize d to increase endogenous secretion of GnRH. Compared to ovary-intact e wes, ovariectomy resulted in three- and fourfold increases in steady-s tate amounts of mRNA encoding SF-1 and LH beta subunit, respectively. In ovariectomized ewes in which delivery of GnRH to the anterior pitui tary gland was prevented by hypothalamic-pituitary disconnection (HPD) , steady-state amounts of mRNA encoding SF-1 and LH beta-subunit were decreased. These results provide evidence that pituitary SF-1 gene exp ression in sheep is regulated by GnRH, Coordinate regulation of mRNAs encoding SF-1 and LH beta-subunit raises the possibility that SF-1 may be an important transcriptional regulator of LH beta-subunit gene exp ression in ovine gonadotropes.