Pituitary follistatin gene expression in female rats: evidence that inhibin regulates transcription.

Follistatin (FS), along with the members of the transforming growth factor beta family activin and inhibin, are important regulators of FSH secretion and messenger RNA production. While activin and inhibin appear to function as tonic modulators of FSH (stimulatory and inhibitory, respectively), dynamic changes in FS are noted through the estrous cycle and under varying physiological experimental paradigms. This suggests that FS is a major contributor to the precisely coordinated secretion of FSH that maintains reproductive function. The aim of this study was to investigate changes in FS, in particular the early (<12 h) rise observed after ovariectomy (OVX), and to determine whether these changes were as a consequence of variations in gene transcription rates. FS primary transcript (PT) and mRNA were found to increase 3-fold 12 h post-OVX, indicating increased gene transcription during this time period. Replacement with estradiol and/or blockade of GnRH had only modest effects on FS PT concentration. Inhibin immunoneutralization of intact rats resulted in a 3-fold increase in FS PT 12 h after administration of inhibin alpha antisera. Significant increases in FS mRNA at both 2 and 12 h also suggested that inhibin also may have effects on message stability. After administration of recombinant human inhibin A, there was a prompt decline in both FS PT and mRNA. These results indicate that inhibin is a major regulator of FS, both by transcriptional and nontranscriptional mechanisms.