REGULATION OF FOLLISTATIN MESSENGER-RIBONUCLEIC-ACID LEVELS IN THE RAT PITUITARY

Follistatin is a glycoprotein, originally isolated from the gonads, that specifically inhibits follicle-stimulating hormone (FSH) biosynthesis and secretion. We have previously detected follistatin mRNA in rat pituitary gonadotropes. To assess the potential physiologic role of follistatin in the rat pituitary, we have investigated the effects of gonadectomy (GDX) and of sex steroid replacement on pituitary follistatin gene expression. Follistatin mRNA levels in individual rat pituitaries were measured by a quantitative reverse transcription-polymerase chain reaction assay. Female and male rats 21 d old underwent surgical GDX and were then killed 21 d after GDX. Follistatin mRNA levels in rat pituitary increased 3.2+/-1.5-fold (P < 0.01) in GDX female rats and 8.2+/-2.0-fold (P < 0.005) in GDX male rats, compared with intact female and male controls, respectively. Replacement therapy with 17beta-estradiol-3-benzoate (10 mug / 1 00 g body weight) subcutaneously daily for 7 d in GDX female rats resulted in a slight further increase in follistatin mRNA levels compared to GDX females. In contrast, therapy with testosterone propionate (500 gg/100 g body weight) subcutaneously daily for 7 d in GDX male rats resulted in a decrease in follistatin mRNA levels, towards but not completely back to baseline levels in intact males. Time-course studies in adult male and female rats showed that the increase in follistatin mRNA levels after GDX is rapid, with significant increases occurring within 24 h after GDX, and parallels or precedes increases in FSHbeta mRNA levels and FSH secretion. The regulation of follistatin mRNA levels in the rat pituitary by GDX and by sex steroids suggests that follistatin may be important as an autocrine or paracrine factor in the regulation of FSH.