FSH (Follicle Stimulating Hormone)

FSH is a glycoprotein with molecular weight about 35kDa, and is a heterodimer composed of α-subunit (a common subunit to FSH, LH and TSH) and specific β-subunit. FSH is produced by basophilic cells (gonadotrophs) of the pituitary together with LH. FSH acts on ovarian follicle in females to cause follicular growth, estrogen production and secretion, and on testicular seminal tubules causing growth and sperm production with the help of androgen in males. FSH secretion is stimulated by a hypothalamic peptide, GnRH. Another stimulatory substance is activin produced in pituitary, ovary, placenta, hypothalamus, etc. FSH biosynthesis is inhibited by inhibin, and follistatin also inhibits FSH synthesis through inactivation of activin. Inhibiting action of PACAP (pitiutary adenylatecyclase activating peptide) on FSH production is made by promotion of follistatin production. Sex steroid hormones lower FSH synthesis and secretion via hypothalamus (negative feedback), and may directly act on FSH gene. Circulating FSH levels change with sexual cycle, and increase after menopause, aging, gonadectomy, and azospermia, while stay low in infancy, pregnancy and confinement.