Gonadotropin-Releasing Hormone Regulation of Gonadotropin Subunit Gene Expression in Female Rats: Actions on Follicle-Stimulating Hormoneβ Messenger Ribonucleic Acid (mRNA) Involve Differential Expression of Pituitary Activin (β-B) and Follistatin mRNAs1

GnRH is the primary stimulus in the regulation of gonadotropin subunit mRNA expression. Additionally, local (pituitary) production of activin and follistatin appear to modulate the expression of FSH β mRNA. The current studies aimed to determine whether GnRH regulation of pituitary activin (β-B) and follistatin mRNAs could play a role in the differential actions of GnRH pulse pattern on gonadotropin mRNA expression in female rats. In response to altered GnRH pulse amplitude, the expression of FSH β and follistatin mRNAs followed an inverse pattern. Only high dose GnRH increased expression of follistatin whereas, in contrast, β-B and FSH β expression were increased following lower doses of GnRH. To determine whether increased follistatin mRNA expression was correlated with FSH β mRNA responses, we examined their temporal relationship following high dose GnRH. Both FSH β and follistatin mRNAs were increased within 2 h and remained increased through 6 h. However, by 12 h FSH β mRNA levels returned to values ...