IB 140 LECTURE 6A GNIH MT II
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What is GNIH?
Peptide that is produced in the Hypothalamus and in gonads.
Releasing and Release-Inhibiting Hormones
- Releasing Hormones from Hypothalamus:
- • GnRH (gonadotropin releasing hormone)
- • PRH (prolactin-releasing hormone)
- • CRH (corticotropin-releasing hormone)
- • TRH (thyrotropic releasing hormone)
- • GHRH (growth hormone releasing hormone)
- • MSHRH (melanophore-stimulating releasing hormone)
- Release-Inhibiting Hormones from Hypothalamus:
- - GnIH (gonadotropin inhibiting hormone)
- - PRIH (prolactin release-inhibiting hormone)
- - MSHRIH (melanophore-stimulating hormone releaseinhibiting
Releasing Hormones from Hypothalamus:
• GnRH (gonadotropin releasing hormone) increases release of FSH & LH from adenohypophysis
• PRH (prolactin-releasing hormone) increases release of prolactin from adenohypophysis
Release-Inhibiting Hormones from Hypothalamus:
- GnIH (gonadotropin inhibiting hormone)
- PRIH (prolactin release-inhibiting hormone) inhibits release of prolactin from adenohypophysis
- • GnIH is a peptide that is produced in
- neurons in the dorsomedial hypothalamus.
- • It is released from GnIH neuron fibers at the
- median eminence, where it travels to the
- pituitary through the portal system.
- • There are receptors for GnIH on LH- and
- FSH- producing cells in the pituitary.
- • It appears to act in opposition to GnRH in
- the pituitary.
GnIH affect on pituitary
• appears to act in opposition to GnRH in the pituitary.
• reduces GnRH-stimulated synthesis and secretion of LH and FSH.
- • When GnRH and GnIH are both released, the LH and FSH levels are reduced compared to
- when GnRH is released alone.
- • While much of this work was done in Starlings, quails, and sheep, a recent publication from the
- Bentley lab demonstrates these these findings in humans (Ubuka 2009).
GnIH in hypothalamus
• Injection of GnIH decreases firing rate of GnRH neurons (Ducret 2009).
- • Fibers from GnIH neurons have been demonstrated to contact GnRH neurons
- directly in hypothalamus.
- • Evidence indicating that GnIH can also inhibit the GnRH surge center (Anderson
- • Stress increases hypothalamic GnIH in rats (Kirby 2009)
- • Melatonin increases hypothalamic GnIH in rats (Revel 2008) and birds
- (Chowdhury 2010)
Hormones produced by gonads
• Steroid hormones: estrogen, progesterone, and testosterone
• Glycoprotein hormones: inhibin, activin, follistatin
• Peptide hormone: GnIH (gonadotropin inhibiting hormone)
Gonad Glycoprotein Hormones
- • Gonads (testes and ovaries) release glycoprotein hormones that influence gonadotropin secretion
- • Inhibin: acts directly on the pituitary to selectively suppress the secretion of FSH
- • Activin: opposes the action of inhibin and stimulates the release of FSH
- • Follistatin: binds to activin and blocks its action
Human life stages
- • Embryonic & fetal
- • Infancy & childhood
- • Puberty & adolescence
- • Early & middle adulthood
- • Late adulthood & old age
GnIH in gonads
- • GnIH is also produced in and has receptors in the male and female gonads of birds, hamsters, and primates (Bentley 2008, McGuire 2008, Zhao 2009, Bentley 2010).
- • It is not known where in ovary GnIH is produced.
- • In males, GnIH is produced in leydig cells and in germ cells at different stages of spermatogenesis (Zhao 2009, McGuire & Bentley 2010).
- • GnIH receptors are present in interstitium of testes and in germ cells at different stages of spermatogenesis (Zhao 2009, McGuire & Bentley 2010).
GnIH in bird gonads
- • Acts directly testes to reduce testosterone secretion
- • Acts directly on ovary to reduce estradiol production
- • This action on both the testes and ovary is thought to be a paracrine action from GnIH produced in gonads.
GnIH from infancy to puberty
- • GnIH produced in hypothalamus plays a role in suppressing the production and action of GnRH.
- • GnIH produced in the gonads plays a role in reducing the production of steroid hormones.
- • Melatonin increases hypothalamic GnIH in rats (Revel 2008) and birds (Chowdhury 2010).
- • All these affects collectively may contribute to the suppression of the hypothalamic-pituitary-gonad axis in humans from infancy up until puberty….research on this topic needs to be done.
- • Stress increases hypothalamic GnIH in rats (Kirby 2009).
- • This helps explain why stress can result in females not ovulating even if they have adequate body fat for ovulation.
- • Stress which increases GnIH could also potentially cause some females to have a delay in menarche/puberty even if they have adequate body fat.
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