Comparison of the pretranslational regulation of FSH synthesis by gonadal steroids in rats and mice.

There are significant differences between rats and mice in the gonadal regulation of several aspects of gonadotroph function. To investigate whether these extend to the pretranslational regulation of FSH synthesis by gonadal steroids, we have measured FSH-beta mRNA levels following gonadectomy and sex-steroid replacement and have related these to serum and pituitary FSH as a reflection of overall hormone synthesis. In ovariectomized rats, FSH-beta mRNA levels increased by 8 h, decreased, and then rose progressively over the next 28 days. A similar pattern of response was observed in orchidectomized rats. In mice, there were progressive increases in FSH-beta mRNA levels in both males and females following gonadectomy, without evidence of the early peaks observed in rats. In both species, the change in FSH-beta mRNA levels after gonadectomy was greater in females than in males. These changes in FSH-beta mRNA following gonadectomy were paralleled by changes in the serum FSH concentration. In ovariectomized female rats and mice, pituitary FSH stores increased by 8 h and 3 days respectively, whereas in male rats, pituitary FSH content did not rise until 10 days after orchidectomy. The most striking species difference was the marked and prolonged reduction of pituitary FSH after orchidectomy of mice. Treatment of rats and mice from the time of ovariectomy, with a dose of oestradiol that prevents increases in serum LH, only partially attenuated the rises in FSH-beta mRNA and serum FSH and did not prevent the increase in pituitary FSH content. Treatment of intact or orchidectomized rats with testosterone suppressed FSH-beta mRNA levels to 50% below intact control values without affecting pituitary FSH content.(ABSTRACT TRUNCATED AT 250 WORDS)