EFFECTS OF GONADOTROPIN-RELEASING-HORMONE ON RAT GONADOTROPIN GENE-TRANSCRIPTION INVITRO - REQUIREMENT FOR PULSATILE ADMINISTRATION FOR LUTEINIZING HORMONE-BETA GENE STIMULATION

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 hemipitui-taries from the same animals were matched in control and treatment groups. In static culture, only rates of α-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 FSHβ mRNA synthesis (28 ± 6 ppm), and significant stimulation of LHβ 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 LHβ (44 ±10 vs. 40 ± 12 ppm for control) or FSHβ (29 ± 6 vs. 36 ± 9 ppm for control), but consistent stimulation for α-subunit (240 ± 29 vs. 71 ± 16 ppm for control). Markedly different results were observed with pulsatile GnRH administration. In perifusion studies, LHβ 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 FSH0 mRNA synthesis only after 1 h of pulsatile GnRH, while α-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 µg/100 g BW) suppressed the transcription rate of all three genes to 10-25% of control values after 4 or 24 h. TSHβ 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. Thus, there are striking effects of GnRH in vitro on gonadotropin subunit gene transcription, which are subunit and administration specific. While α-subunit transcription is stimulated up to 5-fold in either static or perifusion systems, stimulation of LHβ (2- to 4-fold) gene transcription requires pulsatile GnRH administration. © 1990 by The Endocrine Society.