Transcription rate of the follicle stimulating hormone (FSH) beta subunit gene is reduced by inhibin in sheep but this does not fully explain the decrease in mRNA.

Studies were conducted in vitro and in vivo to determine whether or not inhibin affects the transcription rate of the gene for the beta subunit of follicle stimulating hormone (FSH beta). Pituitary cells in primary culture were incubated with 0-3000 milli-units/ml inhibin; a dose-related decrement in mRNA was obtained but a parallel effect was not observed for the transcription rate of the FSH beta gene in a nuclear run-on experiment. To determine effects in vivo, ovariectomized ewes were treated with saline (group 1), 75 micrograms inhibin 6 h before slaughter (group 2), inhibin 6 h and 12 h before slaughter (group 3) or inhibin 12 h before slaughter (group 4). In samples taken each 2 h, plasma FSH levels were seen to be maximally reduced 6 h after a single injection of inhibin; at this time mRNA levels were reduced up to 100% whereas FSH beta gene transcription rate was reduced by 50%. A second injection at 6 h (group 3) caused a further reduction in plasma FSH levels with no additional effect on transcription rate. In those sheep killed 12 h after a single inhibin injection, transcription rate for the FSH beta gene, cytoplasmic mRNA levels and plasma FSH concentrations had recovered. These studies show that the rapid effect of inhibin on FSH beta mRNA levels may be due, in part, to an effect on transcription rate of the FSH beta gene. An additional mechanism is required, however, to fully explain the inhibin effect on FSH beta mRNA levels.(ABSTRACT TRUNCATED AT 250 WORDS)