2. Receptor Mediated Hormonal
Regulation
By: Hina
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3. Contents
Hormones
Mechanism of action of hormones
Physiological roles of hormones
Site of synthesis of hormones
Target sites of horomes
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4. Hormone
 Hormones are chemical messengers secreted into blood or
extracellular fluid by one cell that affect the functioning of
other cells.
“ON”
“OFF”
Target
cell
Cell
origin
(Effects)
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5. Mechanism of action of hormones
The ability of a hormone to induce a response in a target cell is
usually mediated by a hormone receptor on, or in, the target
cell.
RECEPTOR
Receptors are the sensing elements in system of chemical
communication that cordinate cellular function in our body.
The binding sites on the target cells are called
hormone receptors.
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6. Types of Hormone Receptors
 Cell surface receptors
 G-Protein coupled receptor
 Kinase linked receptor
 Intracellular Receptors
 Nuclear receptor
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7. Cell surface receptors
G-Protein coupled receptor
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8. G-Protein coupled receptor
Adenylate cyclase mediated pathway
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9. G-Protein coupled receptor
Hormone Action using cAMP Second Messenger
Glycogen
synthase a
Glycogen
synthase b
Protein kinase
(Inactive)
Protein kinase
(Active)
Phosphoprotein
phosphatase
Insulin
(+)
(+)(+)
(+)
Glycogen
Phosphorylase b
Glycogen
Phosphorylase a
Glycogen
Glucose-1-PO4
(+)
GLYCOGENOLYSIS
Phosphorylase
kinase (inactive)
Phosphorylase
kinase (active)
Phospho-
protein
phosphatase
Adenylate
cyclase
(+)
(-)
(+)
Muscles
Liver
Adenylate cyclase mediated pathway
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10. G-Protein coupled receptor
Phospholipase mediated pathway
Receptor
DAG
IP3
Ca++
Protein kinase C
Phosphoproteins
Proteins
Physiologic responses
Ca++-Calmodulin
Calmodulin kinases
(+)
(+)
GDP GTP
Phospholipase C
GTP GDP
(+)
PIP2
Hormone Action using DAG, IP3 and Ca++
as Second Messengers 10

11. Mechanism of Tyrosine Kinase Receptors
When hormone binds to the extracellular domain the receptors aggregate
Kinase linked receptor
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12. When the receptors aggregate, the tyrosine kinase domains phosphorylate
the C terminal tyrosine residues
Mechanism of Tyrosine Kinase Receptors
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13. This phosphorylation produces binding sites for proteins with SH2 domains.
GRB2 is one of these proteins. GRB2, with SOS bound to it, then binds to the
receptor complex. This causes the activation of SOS.
Mechanism of Tyrosine Kinase Receptors
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14. SOS is a guanyl nucleotide-release protein (GNRP). When this is
activated, it causes certain G proteins to release GDP and exchange it for
GTP. Ras is one of these proteins. When ras has GTP bound to it, it
becomes active.
Mechanism of Tyrosine Kinase Receptors
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15. Activated ras then causes the activation of a cellular kinase called raf-1
Mechanism of Tyrosine Kinase Receptors
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16. Raf-1 kinase then phosphorylates another cellular kinase called
MEK. This cause the activation of MEK
Mechanism of Tyrosine Kinase Receptors
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17. Activated MEK then phosphorylates another protein kinase called MAPK
causing its activation. This series of phosphylating activations is called a
kinase cascade. It results in amplification of the signal
Mechanism of Tyrosine Kinase Receptors
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18. Among the final targets of the kinase cascade are transcriptions factors (fos
and jun showed here). Phosphorylation of these proteins causes them to
become active and bind to the DNA, causing changes in gene transcription
Mechanism of Tyrosine Kinase Receptors
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19. Hormone Metabolism
JACK/STAT Pathway
ES utilized by Growth hormone, Prolactin, EPO, cytokines…
Regulates transcription
Nucleus
Dimerization
X = SHC
GRB2
PLC
PI-3K
GAP
JAK PJAKP
P P
P P
STATs
X
SH2P
P)
(
JAK PJAKP
P P
P P
JAK JAK
Kinase linked receptor
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20. Intracellular (nuclear) receptor mediated pathway
Basic Structure of nuclear receptor
Hormone-bindind
domain
DNA-binding
domain
Transcription-
activating domain
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21. Hormones that can cross the membrane (e.g.
steroid hormones) bind
to the receptor inside the cell, at the cytoplasm, or
they will enter the nucleus and bind nucleus and
bind to the receptor at the nucleus and initiate
transcription
Intracellular (nuclear) receptor mediated pathway
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22. The signal pathway by steroid hormones
Nuclear receptor mediated pathway
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23. The signal pathway by steroid hormones
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24. 24

25. 25

26. Insulin Pancreas Controls blood-sugar level and storage of glycogen.
Glucagon Pancreas Stimulates conversion of glycogen to glucose; raises
blood sugar level.
Oxytocin Pituitary gland Stimulates contraction of the uterine muscles and
secretion of milk by the mammary glands.
Vasopressin Pituitary gland Controls water excretion by the kidneys; stimulates
contraction of the blood vessels.
Growth hormone Pituitary gland Stimulates growth.
Adrenocorticotrophic Pituitary gland Stimulates the adrenal cortex, which,in turn,releases
hormone (ACTH) several steroid hormones.
Prolactin Pituitary gland Stimulates milk production by the mammary glands
after birth of baby.
Epinephrine Adrenal glands Stimulates rise in blood pressure, acceleration of
heartbeat, decreased secretion of insulin, and
increased blood sugar.
Hormone Source Principal functions
Physiological role of Hormones
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27. Cortisone Adrenal glands Helps control carbohydrate metabolism, salt
and water balance, formation and storage of
glycogen.
Thyroxine & Thyroid gland Increases the metabolic rate of carbohydrates
Triiodothyronine and proteins.
Calcitonin Thyroid gland Prevents the rise of calcium and phosphate in the
body.
Parathyroid Parathyroid gland Regulates the metabolism of calcium and
phosphate in hormone in the body.
Gastrin Stomach Stimulates secretion of gastric juice.
Secretin Duodenum Stimulates secretion of pancreatic juice.
Estrogen Ovaries Stimulates development and maintenance of
female sexual characteristics.
Progesterone Ovaries Stimulates female sexual characteristics and
maintains pregnancy.
Testosterone Testes Stimulates development and maintenance of male
sexual characteristics.
Hormone Source Principal functions
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28. Types of Hormones
 Catecholamines and Thyroid Hormones
Small and derived from amino acids (epinephrine,
thryoxine.)
 Steroid Hormones and Vitamin D
Relatively small and derived from cholesterol
 Prostaglandin's
Relatively small and derived from fatty acids
 Proteins or Polypeptides
Relatively large and derived from translation of hormone
specific mRNA (growth hormone, insulin)
Site of synthesis of various hormones
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29. Thyroid Hormones
 Synthesized solely in the thyroid gland ( T4; 3’,5’,3,5-
L-tetra-iodothyronine).
 Majority of the active form, T3 (3’,3,5-L-tri-
iodothyronine), is produced in the peripheral tissues
through deiodination of T4.
 Thyroid gland cells concentrates iodine for thyroid
hormone synthesis.
 Iodine is attached to tyrosine residues on a protein,
termed thyroglobulin. Tyrosine residues are then
coupled together to yield thyronines.
 Proteolytic digestion of thyroglobulin then yields T4
and T3 in a 10:1 ratio.
 Helps in the metabolism of sugars.
 The half life of T4 is 7 days and that of T3 is 1 day.
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30. Steroid Hormones
 Produced in the adrenals, ovaries, testes, and placenta.
 Derived from cholesterol.
 Enzymes in the various glands control the final product.
For example, cytochrome P450c11 which is located in
the adrencortical cells, is involved in coritsol
production. This enzyme is lacking in the gonads, that
do not produce cortisol or aldosterone.
 Gonads, however, can produce dihydroxytestosterone,
estradiol, or progesterone depending upon the enzymes
present in the gonadal tissue.
 Over 50 different steroid metabolites have been
described.
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31. Catecholamines
 Are synthesized in nervous tissues from which the adrenal
medulla is derived.
 Adrenal medulla is the major source for circulating
epinephrine.
 Synthesized from tyrosine which is converted to
dihydroxyphenylalanine (DOPA) by tyrosine hydroxylases.
 Subsequent conversions to dopamine and then to nor
epinephrine which is released by most catecholamine-
producing cells of the body.
 In the adrenal medulla and a few other tissue, nor epinephrine
is converted to epinephrine.
 The half life is 1-2 minutes.
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32. Prostaglandins and Leukotrienes
 They can be produced by most cells depending upon lipid
and enzyme content of the cells.
 Arachidonic acid, which is derived from lipid metabolism,
is the precursor compound.
 Depending upon the lipoxygenase present in the cell,
either, HETE, prostaglandin (G2) or leukotrienes
 Cyclooxygenase (involved in PGG2 synthesis) is widely
distributed throughout the body and is inhibited by aspirin,
indomethacin, and other nonsteroidal and anti-
inflammatory agents.
 The half-life is a few seconds.
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33. Target Sites of hormones
Target cells:
 Cells that respond to a specific hormone
 Can be found anywhere in the body
 All target cells have receptors that detect
specific hormones
 Ex:
Thyroid hurmone act on almost all cells of
the body to increase rate of metabolism
 Hormones specifically affect or alter the
activities of the responsive tissue (target
tissue).
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34. 1. Endocrine
Chemicals act on distant cells via the bloodstream
Ex: thyroxine, sex hormones
2. Paracrine
Chemicals act on the surrounding cells or neighboring tissues
without entering the blood
Ex: GIT hormones
3. Autocrine
Chemicals act on the cell that produce it
Ex : nitric oxide
4. Neuroendocrine
Synthesize & release into blood stream by nerves
signals between neurons
Ex: neurotransmitters ( Ach, dopamine)
Actions of hormones
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35. Endocrine Blood vessel
Distant target cellsHormone secretion
into blood by
endocrine gland Paracrine
Secretory cell Adjacent target cell
Autocrine
Target sites on same cell
Receptor
Hormone or
other extra
cellular
signal
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36. Second target mechanism
 By receptors and target cells
 The receptor and target cell action depends on
two terms broadly
 Agonist
 Antagonist
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37. Agonists
Agonists are molecules that bind the receptor and induce
all the post-receptor events that lead to a biologic effect
Natural hormones are themselves agonists.
For a given receptor, different agonists can have
different potencies
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38. Antagonist
Antagonists are molecules that bind the receptor and
block binding of the agonist, but fail to trigger intracellular
signalling events.
They don't themselves perform useful work, but block
the activities of those that do have the capacity to
contribute.
Hormone antagonists are widely used as drugs.
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39. Antagonist to Use
1. Growth Hormone Acromegaly, Diabetes
2. Progesterone Contraceptive, abortion
3. Glucocorticoid Spontaneous Cushing’s Syndrome
4. Mineralo-corticoid Primary and secondary
mineralocorticoid excess
5. Androgen Prostate cancer
6. Estrogen Breast cancer
7. GnRH Prostate cancer
8. Adrenrgic Hypertension, hyperthyroidism
9. Prostaglandin Acute and chronic inflammatory
disease
Examples of hormone antagonist used in therapy
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40. When you do not succeed in taking giant
steps on the road to your goal,
be satisfied with little steps,
and wait patiently till the time that you are
able to run, or better still, to fly.
Be satisfied to be a little bee in the hive who
will soon become a big bee capable of making
honey…
Thank you …
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