Regulation of follicle-stimulating hormone beta and common alpha-subunit messenger ribonucleic acid by gonadotropin-releasing hormone and estrogen in the sheep pituitary.

The effect of gonadotropin-releasing hormone (GnRH) and/or estradiol (E2) on pituitary messenger ribonucleic acid (mRNA) levels of luteinizing hormone beta (LH beta), follicle-stimulating hormone beta (FSH beta) and the common alpha-subunit were determined in anterior pituitary glands from ovariectomized (OVX) ewes. Hypothalamo-pituitary disconnected (HPD) ewes receiving appropriate hormonal treatment were used to assess the relative roles of GnRH and E2 in directly regulating FSH beta and alpha-subunit mRNA levels. Levels of LH beta mRNA were increased in OVX animals compared with intact controls, and E2 treatment of OVX animals significantly reduced mRNA levels of LH beta and FSH beta. HPD substantially reduced FSH beta and alpha-subunit mRNA levels. Treatment of OVX/HPD animals with pulses of GnRH (250 ng/2 h) for 1 week restored FSH beta and alpha-subunit mRNA to OVX levels. Combined GnRH and E2 treatment significantly lowered FSH beta mRNA levels, but resulted in a rise in alpha-subunit mRNA levels. Treatment of OVX/HPD ewes with E2 alone had no effect on FSH beta and alpha-subunit mRNA levels. These findings indicate that E2 acts directly on the pituitary to negatively regulate FSH beta mRNA levels, and to positively regulate alpha-subunit mRNA levels in the presence of GnRH.