The gonadolibérine (or GnRH , of the English Gonadotropin Releasing Hormone ) is a peptide Hormone responsible for the synthesis and secretion of FSH and LH by the Ante-pituitary gland. GnRH is synthesized and secreted by the Hypothalamus. GnRH is a neurohormone, because they are Neuron S of the hypothalamus which synthesizes it.
Gene
The Gène of the precursor of GnRH is located on the Chromosome 8. This precursor contains 92 amino-acids and is transformed into GnRH, a décapeptide (in other words 10 amino-acids).
Structure
The discovery of GnRH was made in 1977 by Roger Guillemin and Andrew V. Schally, both prizes winner of the Nobel Prize:-
pyroGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly CONH2
GnRH as a neurohormone
GnRH is a Neurohormone produced by specialized neurons of the Noyau arched of the Hypothalamus. GnRH is released at the nervous end of the terminations in the system of Circulation carries hypophyseal. It then sets on the receivers specific to GnRH of the plasmic Membrane of the cells Gonadotrope S, to activate cascades of intracellular indication. GnRH is then degraded in a few minutes.
Control FSH and LH
GnRH stimulates the synthesis and the release of the Gonadotrophine S FSH and LH, processes which are controlled by the frequency and the amplitude of the oscillations of GnRH, they same controlled by the quantity of sex hormones in blood (Testostérone for the man; estrogen and Progesterone for the woman). Thus, only one hormone, GnRH, controls a complex process allowing the development of a Follicule, the Ovulation, and the maintenance of the Corps lutéal (yellow body) in the menstrual Cycle (sexual cycle) at the woman, but control also the Spermatogénèse (production of spermatozoa in the seminiferous tubes of the Testicule S) at the man.
Ces process uses positive and negative retro-controls (according to the rate of such hormone in blood) to control the activity of the peaks of GnRH.
Activity
The activity of GnRH is very weak in the child. It appears at the time of puberty to install the development of the reeproductives functions. At the time of a pregnancy, the synthesis and the secretion of GnRh stop, just as in period of breast feeding (by a negative retro-control of the Prolactine). The Dopamine also decreases the activity of GnRH.In physiopathology, the activity of GnRH can be disturbed in the case of disease of the hypothalamo-hypophyseal-gonade axis (traumatism, tumors…). There exists also a hereditary pathology which led to the absence of secretion of GnRH, the Syndrome of $kalman, characterized by a puberty absence of development.
GnRH in other bodies
It should be noted ectopic secretions of GnRH by other fabrics that the hypothalamus on the level of the placenta and gonades. Their roles are currently little known.
Agonists and antagonists
Synthetic GnRH is currently synthétisable and marketed, but its Demi-vie requires the use of pump with infusion for clinical uses. Analogues of GnRH are used for endocriniens treatments which aim to stimulate (agonists) or to repress (antagonistic) secretions of hypophyseal hormones in the event of disorder endocrinien.
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