Effects of ovariectomy and hypothalamic-pituitary disconnection on amounts of steroidogenic factor-1 mRNA in the ovine anterior pituitary gland

Steroidogenic factor-1 (SF-1) is a transcription factor involved in regulation of steroidogenic enzymes. Recent evidence indicates that SF-1 is also important in the anterior pituitary gland, where it may influence gene expression in gonadotropes. We isolated a cDNA encoding ovine SF-1 and demonstrated that the SF- 1 gene is expressed in the anterior pituitary gland of sheep. SF-1 transcripts and luteinizing hormone (LH) were colocalized in gonadotropes by in situ hybridization and immunohistochemistry, respectively. To test the hypothesis that GnRH stimulates pituitary expression of ovine SF-1 mRNA, ewes were ovariectomized to increase endogenous secretion of GnRH. Compared to ovary-intact ewes, ovariectomy resulted in three-and fourfold increases in steady-state amounts of mRNA encoding SF-1 and LHβ subunit respectively. In ovariectomized ewes in which delivery of GnRH to the anterior pituitary gland was prevented by hypothalamic-pituitary disconnection (HPD), steady-state amounts of mRNA encoding SF-1 and LHβ-subunit were decreased. These results provide evidence that pituitary SF-1 gene expression in sheep is regulated by GnRH. Coordinate regulation of mRNAs encoding SF-1 and LHβ-subunit raises the possibility that SF-1 may be an important transcriptional regulator of LHβ-subunit gene expression in ovine gonadotropes.