Pulsatile GnRH regulation of gonadotropin subunit gene transcription

We investigated the requirement for gonadotropin-releasing hormone (GnRH) release in vivo and the pattern of GnRH administration in vitro on the expression of the gonadotropin subunit genes in female rats. Injection of the GnRH antagonist ([Nal-Lys] GnRH; 30 micrograms/100g bw) to ovariectomized rats rapidly suppressed transcription of the alpha-subunit and LH beta genes to 10-25% of control after 24 h, as measured by nuclear run-off assays. The rate of FSH beta gene transcription was also suppressed, but to a lesser extent (to 60-75% of control). Administration of 17 beta-estradiol (20 micrograms/100 g bw) in addition to antagonist did not suppress transcription of the genes beyond that seen with the antagonist alone. Administration of constant levels of GnRH (0.1, 1, or 10 nM) to pituitary fragments in static culture stimulated alpha-subunit mRNA synthesis 2- to 3-fold, but had no significant sustained effects on LH beta or FSH beta transcription. In contrast, pulsatile GnRH administered once per hour (25 ng over 10 min) to pituitary fragments mounted on perifusion columns stimulated both alpha-subunit and LH beta gene transcription 3-fold after 3 h, with inconsistent stimulation of FSH beta. Pulsatile GnRH appears to be crucial for LH beta gene stimulation, as continuous GnRH on the columns stimulated only alpha-subunit mRNA synthesis. Thus, pulsatile GnRH in vivo is required to maintain transcription of the alpha-subunit and LH beta genes, with lesser effects on FSH beta. While continuous GnRH can stimulate alpha-subunit mRNA synthesis, a pulsatile GnRH is required to stimulate the LH beta gene.