IB 140 LECTURE 6A GNIH MT II

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jeannette_ruiz
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IB 140 LECTURE 6A GNIH MT II
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2010-03-31 14:25:33
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IB 140 LECTURE 6A GNIH MT II
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IB 140 LECTURE 6A GNIH MT II
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  1. What is GNIH?
    Peptide that is produced in the Hypothalamus and in gonads.
  2. Hypothalamic-Adenohypophysial Connection:
    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
    • hormone
  3. 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
  4. Release-Inhibiting Hormones from Hypothalamus:
    - GnIH (gonadotropin inhibiting hormone)

    - PRIH (prolactin release-inhibiting hormone) inhibits release of prolactin from adenohypophysis
  5. GnIH
    • 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.
  6. 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).
  7. GnIH in hypothalamus
    • • Fibers from GnIH neurons have been demonstrated to contact GnRH neurons
    • directly in hypothalamus.

    • Injection of GnIH decreases firing rate of GnRH neurons (Ducret 2009).

    • • Evidence indicating that GnIH can also inhibit the GnRH surge center (Anderson
    • 2009).
    • • Stress increases hypothalamic GnIH in rats (Kirby 2009)

    • • Melatonin increases hypothalamic GnIH in rats (Revel 2008) and birds
    • (Chowdhury 2010)
  8. Hormones produced by gonads
    • Steroid hormones: estrogen, progesterone, and testosterone

    • Glycoprotein hormones: inhibin, activin, follistatin

    • Peptide hormone: GnIH (gonadotropin inhibiting hormone)
  9. 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
  10. Human life stages
    • • Embryonic & fetal
    • • Infancy & childhood
    • • Puberty & adolescence
    • • Early & middle adulthood
    • • Late adulthood & old age
  11. 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).
  12. 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.
  13. 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.
  14. GnIH
    • • 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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