Follicle stimulating hormone (FSH) is a hormone synthesised and secreted by gonadotropes in the anterior pituitary gland. In the ovary FSH stimulates the growth of immature follicles to maturation. As the follicle grows, it releases inhibin which shuts off the FSH production. In men, FSH enhances the production of androgen binding protein by the Sertoli cells of the testes and is critical for spermatogenesis.

Structure

FSH is a glycoprotein, that is, it is a dimeric protein subunit, each of which is connected to a sugar moiety. The structure is similar for LH, TSH, and hCG. The protein dimer contains 2 polypeptide units, labelled alpha and beta subunit. The alpha subunits of LH, FSH, TSH, and hCG are identical and contain 92 amino acids. The beta subunits vary, and FSH has a beta subunit of 118 amino acids that confers the specific biologic action and is responsible to interact with the FSH-receptor .The sugar part of the homone is composed of fructose, galactose, mannose, galactosamine , glucosamine, and sialic acid, the latter being critical for its biologic half-life . The half-life of FSH is 3-4 hours.

Genes

The gene for the alpha subunit is located on chromosome 6p21.1-23. It is expressed in different cells type. The gene for the FSH beta subunit is located on chromosome 11p13 and expressed in gonadotropes of the pituitary cells and controlled by GnRH, inhibited by inhibin, and enhanced by activin.

Activity

In both males and females, FSH stimulates the maturation of germ cells. In females, a FSH initiates follicular growth, and with the concomitant rise in inhibin B, FSH levels decline. This seems to be critical to select only the most advanced follicle to proceed to ovulation.

FSH levels are normally low during childhood and, in women, high after menopause.

Decifient FSH activity

1. Kallmann syndrome
2. Hypothalamic suppression
3. Hypopituitarism
4. Hyperprolactinemia
5. Gonadotropin deficiency
6. Gonadal suppression therapy
   1. GnRH antagonist
   2. GnRH agonist (downregulation)

Excess FSH activity

1. Pituitary tumor (gonadotropes)
2. Gonadal failure

Availability

FSH is available mixed with LH in the form of Pergonal and newer preparations of urinary gonadotropins, and pure in the form of recombinant FSH.