Effects of Gonadotropin-Releasing Hormone on Rat Gonadotropin Gene Transcriptionin Vitro: Requirement for Pulsatile Administration for Luteinizing Hormone-β Gene Stimulation

Abstract

The transcriptional regulation of the rat gonadotropin subunit genes was investigated under different regimens of GnRH administration in vitro. Anterior pituitary fragments (8-10/gland) from either intact or ovariectomized CD female rats were treated in static culture with 0.1 or 1 nM GnRH or on perifusion columns with pulsatile GnRH (25 ng pulse every 30 or 60 min) for 1-6 h. Gene transcription rates were measured in nuclear run-off assays, and hemipituitaries from the same animals were matched in control and treatment groups. In static culture, only rates of alpha-subunit mRNA synthesis were stimulated at 1, 3, and 6 h from 64 +/- 10 (control) to 170 +/- 29 (3 or 6 h of GnRH) parts/million (ppm). There was no change in FSH beta mRNA synthesis (28 +/- 6 ppm), and significant stimulation of LH beta was seen only at 1 h (98 +/- 10 vs. 34 +/- 1 ppm for control) with continuous GnRH. Similar results were obtained with both GnRH doses and with pituitaries from either intact or ovariectomized rats. In addition, continuous 1 nM GnRH administration to perifusion columns for 4 or 6 h resulted in no changes in the transcription rate for LH beta (44 +/- 10 vs. 40 +/- 12 ppm for control) or FSH beta (29 +/- 6 vs. 36 +/- 9 ppm for control), but consistent stimulation for alpha-subunit (240 +/- 29 vs. 71 +/- 16 ppm for control). Markedly different results were observed with pulsatile GnRH administration. In perifusion studies, LH beta mRNA synthesis was stimulated 2- to 2.5-fold after 1 h of pulses and 3- to 4-fold after 3 or 6 h. A slight (2-fold) stimulation was noted for FSH beta mRNA synthesis only after 1 h of pulsatile GnRH, while alpha-subunit gene transcription was elevated 2-fold after 1 h and 4- to 5-fold after 3 or 6 h of pulsatile GnRH. GnRH pulses in vivo may also be crucial to maintain gonadotropin mRNA synthesis, since administration of a GnRH antagonist ([Nal-Lys] GnRH; 20 micrograms/100 g BW) suppressed the transcription rate of all three genes to 10-25% of control values after 4 or 24 h. TSH beta mRNA synthesis was not changed by any GnRH treatment, and LH secretion was consistently stimulated by GnRH. No significant differences in transcription rate were noted between GnRH pulse intervals of 30 or 60 min in vitro.(ABSTRACT TRUNCATED AT 400 WORDS)