Positive Feedback Loop

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Positive Feedback Loop
E2 increases OT-R
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OT Signal Transduction Systems
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ADH Signal Transduction Systems
V2
H2O permeability
V1 or V2
V1
pressor effects
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Why is Master Gland the nickname of the
anterior pituitary?
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What controls the controler?
First suggestions of fine level of neural control
over hormone secretion first came from a toad
study. A barrier was surgically inserted between
hypothalamus and pituitary.
The toads stopped growing and were unable to
background-adapt. In some toads with incomplete
surgery, portal vessels grew around barrier. In
these toads, growth, thyroid activity, even
background adaptation was regained.
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Hypothalamic Neurons
GnRH
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Are parvicellular neurons neuroendocrine neurons?
Nerve terminals synapse on a vascular
bed. Secrete specific substance. The substance
travel through circulation to target. Target has
specific receptors.
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HYPOTHALAMIC RELEASING AND INHIBITING HORMONES
(HYPOPHYSIOTROPIC)
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Hypothalamic Nuclei
Endocrine methods to study hypothalamic input
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Major Hypophysiotropic Areas in Mammals
1. Paraventricular nucleus - AVP, TRH, SRIF,
CRH 2. Anterior hypothalamic area GnRH 3.
Preoptic area GnRH 4. Supraoptic nucleus -
Oxytocin 5. Arcuate nucleus - GHRH, DA
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What regulates corticotrophs?
?
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Corticotropin-Releasing Hormone (CRH)
Major role in mammals is to control ACTH
secretion.
The first releasing factor discovered in 1970s
by Wylie Vale (hypophysiotropin), but it was not
the first one whose structure determined.
CRH is one of the largest hypothalamic hormones
at 41amino acids. The smallest active peptide
derivable from CRH is 38 AA in length,
corresponding to residues 4-41AA.
When CRH binds to the CRH receptor on the surface
of basophilic cells, adenylate cyclase is
activated, and cyclic AMP levels increase.
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Corticotropin-Releasing Hormone (CRH)
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Gonadotropin-Releasing Hormone (GnRH)
First referred to as luteinizing RH (LHRH). Later
found to release both LH FSH. Thats why now
called GnRH. Released in pulsatile manner.
The vertebrate gonadotropin-releasing hormone
(GnRH) is a decapeptide involved in controling
gonadotropin secretion.
pyro-Glu1-His2-TRP3-Ser4-Tyr5-Gly6-Leu7-Arg8-Pro9-
Glu10-NH2
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Thyrotropin-Releasing Hormone (TRH)
First hypophysiotropin isolated. Structure is
identical in all vertebrates. Major role in
mammals is to control the release of TSH from the
adenohypophysis.
First isolated from porcine hypthalamus. Took
several thousand pigs. When first isolated,
injected into rats, and measured variety of other
hormones in blood to see effect.
Schally
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Thyrotropin-Releasing Hormone (TRH)
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Dopamine (DA)
Major role in mammals is to control Prl release.
Bromocriptine is the best established therapy.
Side-effects include nausea and vomiting,
dizziness and syncope, constipation and cold
peripheries.
New agents more specific for the D2 dopamine
receptor, which are longer-acting and better
tolerated, may become the treatments of choice in
due course.
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Dopamine (DA)
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Somatostatin (SRIF)
Major role in vertebrates is to inhibit pituitary
growth hormone (GH) secretion.
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Growth Hormone-Releasing Hormone (GHRH)
Major role in mammals is to control GH release.
40 to 44-amino acid peptide stimulates GH release
but only first 29-amino acids needed for
biological activity.
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Hypothalamo-Pituitary-Endocrine Gland Axis