Human Reproductive Endocrinology


Gonadotropin-releasing hormone (Wiki)   

http://en.wikipedia.org/wiki/Gonadotropin-releasing_hormone 
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Gonadotropin-releasing hormone (GnRH) ... is a tropic peptide hormone responsible for the release of FSH and LH from the anterior pituitary. GnRH is synthesized and released from neurons within the hypothalamus.
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GnRH is secreted in the hypophysial portal bloodstream at the median eminence. The portal blood carries the GnRH to the pituitary gland, which contains the gonadotrope cells..." 
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At the pituitary, GnRH stimulates the synthesis and secretion of the gonadotropins, follicle-stimulating hormone (FSH), and luteinizing hormone (LH). These processes are controlled by the size and frequency of GnRH pulses, as well as by feedback from androgens and estrogens. Low-frequency GnRH pulses lead to FSH release, whereas high-frequency GnRH pulses stimulate LH release." 


Luteinizing hormone (Wiki)  
http://en.wikipedia.org/wiki/Luteinizing_hormone 
"Luteinizing hormone (LH, also known as lutropin[1]) is a hormone produced by the anterior pituitary gland.
In females, an acute rise of LH called the LH surge triggers ovulation [2] and development of the corpus luteum. In males, where LH had also been called interstitial cell-stimulating hormone (ICSH),[3] it stimulates Leydig cell production of testosterone. [4]
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In the male, LH acts upon the Leydig cells of the testis and is responsible for the production of testosterone,
an androgen that exerts both endocrine activity and intratesticular activity on spermatogenesis. The release of LH at the pituitary gland is controlled by pulses of gonadotropin-releasing hormone (GnRH) from the hypothalamus.



Melatonin and the Human GnRH Pulse Generator (PubMed) 
http://www.ncbi.nlm.nih.gov/pubmed/1999677?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_SingleItemSupl.Pubmed_Discovery_RA&linkpos=1&log$=relatedreviews&logdbfrom=pubmed 
Abstract only.  "Melatonin, identified as N-acetyl-5-methoxy tryptamine, is secreted by the pineal gland at night in a diurnal rhythm at a steady rate after maturation of the gland at the age of about 3 months. Meanwhile the GnRH pulse generator was functioning since birth, but is inhibited when melatonin levels increase beyond about 500 pmol/1 for several hours nightly, at age 3 months. Throughout childhood the GnRH axis remains inhibited. At puberty, body mass increases to the point where melatonin falls below the threshold concentrations so the GnRH pulse generator is re-activated..." 


The Pineal Gland and Reproduction (PubMed) 
http://www.ncbi.nlm.nih.gov/pubmed/9079415?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_SingleItemSupl.Pubmed_Discovery_RA&linkpos=4&log$=relatedreviews&logdbfrom=pubmed 
Abstract only.  "The pineal apparently influences human reproductive function not only at the hypothalamic-pituitary level, by inhibition of the hypothalamic pulsatile secretion of gonadotrophin-releasing hormone, but also at the gonadal level, where melatonin receptors have also been found."


Melatonin: a Contraceptive for the Nineties (PubMed) 
http://www.ncbi.nlm.nih.gov/pubmed/8365512?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_SingleItemSupl.Pubmed_Discovery_RA&linkpos=2&log$=relatedarticles&logdbfrom=pubmed 
Abstract only.  "Darkness affects the retino-pineal nervous pathway to cause the synthesis and release of melatonin from the pineal gland at night. The duration of the night time release of melatonin is longer in winter than in summer; and it is the prolongation in the duration of the night time release of melatonin, with the change of season from summer to winter, which acts as the endocrine signal for inactivating the hypothalamic GnRH pulse generator.










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