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Gonadotropin-releasing Hormone (GnRH)
Gonadotropin-releasing hormone (GnRH) plays a key
role in the regulation of the reproductive system. GnRH has a
similar structure in all animals. It is a decapeptide, meaning that
it consists of a chain of 10 amino acids.
GnRH acts primarily to stimulate the anterior pituitary gland to
synthesise and secrete the gonadotropins FSH and LH. It exerts
three principal actions on the anterior pituitary gland:- Synthesis and storage of gonadotropins
- Activation: the movement of gonadotropins
from the reserve pool to a pool ready for direct action
- Immediate release (direct secretion) of
gonadotropins
Actions of GnRH on the anterior pituitary
gland
Because GnRH plays such a vital role in the secretion of
gonadotropins, several substances have been developed that mimic or
inhibit its action:
- A GnRH agonsit: a drug that has an affinity
for and stimulates physiologic activity at cell receptors normally
stimulated by naturally occurring GnRH.
- A GnRH analogue: a chemical compound with a
structure similar to that of GnRH, but differing from it in respect
to a certain component. It may have a similar or opposite action
metabolically.
- A GnRH antagonist: a substance that tends to
nullify or cancel out the action of GnRH, such as a drug that binds
to a cell receptor without eliciting a biological
response.
The role of GnRH and related substances in assisted reproductive
technologies is discussed in more detail
in Third Step: ART.
The specific rate and amplitude of GnRH secretion is the key to the
control of the female reproductive cycle that leads to the
maturation of an egg each month. In the male, FSH and LH released
from the anterior pituitary gland in response to GnRH stimulation
play a major role in spermatogenesis.
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