Follicle-stimulating hormone
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 Graafian
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. FSH and
LH act synergistically in
reproduction.
FSH is a
glycoprotein. Each monomeric unit is a protein molecule with a sugar attached to it; two of these make the full, functional protein. Its structure is similar to
LH,
TSH, and
hCG. The protein dimer contains 2
polypeptide units, labelled alpha and beta subunits. The
alpha subunits of LH, FSH, TSH, and hCG are identical, and contain 92
amino acids. The beta subunits vary. FSH has a beta subunit of 118 amino acids (FSHB) that confers its specific biologic action and is responsible for interaction with the
FSH-receptor.The sugar part of the hormone 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.
The gene for the
alpha subunit is located on chromosome 6p21.1-23. It is expressed in different cell types. The gene for the FSH beta subunit is located on chromosome 11p13 and is expressed in gonadotropes of the pituitary cells, controlled by
GnRH, inhibited by
inhibin, and enhanced by
activin.
In both males and females, FSH stimulates the maturation of
germ cells. In females, FSH initiates follicular growth, specifically affecting granulosa cells. With the concomitant rise in inhibin B FSH levels then decline in the late follicular phase. This seems to be critical in selecting only the most advanced follicle to proceed to ovulation. At the end of the luteal phase, there is a slight rise in FSH that seems to be of importance to start the next ovulatory cycle.
Like its partner,
LH, FSH release at the pituitary gland is controlled by pulses of
gonadotropin-releasing hormone (GnRH). Those pulses, in turn, are subject to the estrogen feed-back from the gonads.
FSH levels are normally low during
childhood and, in women, high after
menopause.
High FSH levels
High FSH levels are indicative of situations where the normal restricting feedback from the gonad is absent, leading to an unrestriced pituitary FSH production. While this is typical in the menopause, it is abnormal in the reproductive years. There it may be a sign of:#
Premature menopause#
Gonadal dysgenesis,
Turner syndrome#
Castration#
Swyer syndrome# Certain forms of
CAH# Testicular failure
Deficient FSH activity
Diminished secretion of FSH can result in failure of gonadal function (hypogonadism). This condition is typically manifest in males as failure in production of normal numbers of sperm. In females, cessation of reproductive cycles is commonly observed.Conditions with very low FSH secretions are:#
Kallmann syndrome#
Hypothalamic suppression#
Hypopituitarism#
Hyperprolactinemia#
Gonadotropin deficiency# Gonadal suppression therapy ##
GnRH antagonist##
GnRH agonist (
downregulation)
FSH is available mixed with LH in the form of
Pergonal, and other more purified forms of urinary
gonadotropins as well as in a pure forms as recombinant FSH (Gonal F, Follistim). It is used commonly in infertility therapy to stimulate follicular development, notably in
IVF therapy.
*
Day 3 FSH levels From the Infertility Blog by Dr. Fred Licciardi
*
High FSH: an excuse to send patients away From the Infertility Blog by Dr. Fred Licciardi
*
FSH and Estradiol*
Causes & Symptoms of High FSH*
Technostorks: Award-winning documentary on Infertility and IVF
