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Gonadotropin-releasing hormone agonist
A gonadotropin-releasing hormone agonist (GnRH agonist) is a synthetic peptide modeled after the hypothalamic neurohormone GnRH that interacts with the gonadotropin-releasing hormone receptor to elicit its biologic response, the release of the pituitary hormones FSH and LH.
GnRH agonists are pregnancy category X drugs.
Flare effect and downregulation
Agonists do not quickly dissociate from the GnRH receptor. As a result initially there is an increase in FSH and LH secretion (so-called "flare effect").
However after about ten days a profound hypogonadal effect is achieved through receptor downregulation. Generally this induced and reversible hypogonadism is the therapeutic goal.
Agonists with double and single substitutions
GnRH agonists are synthetically modeled after the natural GnRH decapeptide with specific amino acid substitutions typically in position 6 and 10. These substitutions inhibit rapid degradation. Agonists with 2 substitutions include:
Triptorelin is an agonist with only a single substitution at position 6.
GnRH agonists are useful in:
Women of reproductive age who undergo cytotoxic chemotherapy have been pretreated with GnRH agonists to reduce the risk of oocyte loss during such therapy and preserve ovarian function. Further studies are necessary to prove that this approach is useful.
Side effects of the GnRH agonists are signs and symptoms of hypoestrogenism, including hot flashes, headaches, and osteoporosis. In patients under long-term therapy, small amounts of estrogens could be given back (“add-back regimen”) to combat such side effects.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Gonadotropin-releasing_hormone_agonist". A list of authors is available in Wikipedia.|