The goal of this proposal is to define the intra-gonadotrope signal transduction pathways in primary pituitary gonadtrope cells that mediate differential transcriptional responses to gonadotropin releasing hormone (GnRH) pulse frequency. Mammalian reproduction is controlled by luteinizing hormone (LH) and follicle stimulating hormone (FSH), which consist of a common alpha (a) subunit and unique beta (b) subunits that provide biological specificity. Gonadotropin subunit and other gonadotrope genes are regulated by GnRH pulse pattern, particularly pulse frequency. Gonadotrope genes are also regulated by gonadal steroids and peptides, which act in part on the pituitary to modify gene expression and responses to GnRH. Additionally, an intra-gonadotrope system, activinbB and follistatin (FS), regulates FSHB expression. We propose to use dissociated female rat pituitary cells to delineate the roles of GnRH receptor number and specific intracellular (3rd) messenger pathways (ERK, JNK, p38, PKC, Ca/CaMK II and IV, PKA) in effecting differential gonadotrope gene (a, LHb, FSHb, GnRH receptor, activinbB, FS) responses to GnRH pulse frequency. As recent data show that gonadal steroids can modulate several of these pathways, we will also assess the actions of steroids in modulating specific 3rd messenger responses to GnRH. This scientific approach will be somewhat unique, in that normal rat pituitary cells will receive physiological experimental paradigms (i.e. pulsatile GnRH) with effects on transcriptional activity assessed by quantitation of endogenous gene products (i.e. gonadotrope primary transcripts, PTs; measured by RT-PCR). Since PT half-life is relatively short (< 20 min for LHb and FSHb PTs), this method allows assessment of near 'real-time' transcriptional activity. In women, the sequential stimulation of FSH and LH is essential for cyclic ovulatory function and abnormalities in GnRH pulse pattern and gonadal steroid feedback occur in anovulatory disorders. Slow frequency pulses are present in hypothalamic amenorrhea and hyperprolactinemia. In contrast, persistently rapid GnRH pulse frequency is a feature of polycystic ovarian syndrome (PCOS). Recent data show that elevated testosterone disrupts normal hypothalamic-pituitary regulation of gonadotrope function and appears to play a role in the genesis of PCOS. Thus, understanding the mechanisms of GnRH and steroid actions at the gonadotrope are essential to evolving effective methods to restore normal LH and FSH expression/secretion and treating human infertility.
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