Figure 1.

Schematic diagram of the hypothalamic, pituitary (local), and ovarian regulation of FSH secretion in female mammals. At the hypothalamic level, GnRH pulses are transported to the anterior pituitary by the hypothalamic-hypophyseal portal vasculature to stimulate FSH synthesis and secretion by gonadotrope cells. There is also evidence suggesting the existence of a hypothalamic FSH-releasing factor (FSH-RF). At the anterior pituitary level, a local loop involving activin, inhibin, and follistatin regulates FSH secretion in an autocrine/paracrine fashion. At the ovarian level, estradiol and inhibin are two key negative feedback regulators of FSH secretion. While the ovary also produces activin and follistatin, these hormones are not believed to play an endocrine role in controlling FSH secretion.