Post on 16-Jan-2016
Pheromones
Other Cellular Regulators-Act like hormones
Neurotransmitters
Other Cellular Regulators
Besides well recognized kinds of hormone, other substances play important roles as chemical messengers
Ca++
Glucose-specific stimuli for insulin secretion from the b cells of the pancreas.
Amino acids
None of these effectors are not TRADITIONAL hormones, but act like hormones.
Besides classics
NTsPheromones
GlucoseCalcium
Control of Endocrine Activity
The physiologic effects of hormones depend largely on their concentration in blood and extracellular fluid. Almost inevitably, disease results when hormone concentrations are either too high or too low, and precise control over circulating concentrations of hormones is therefore crucial. The concentration of hormone as seen by target cells is determined by three factors:
1.Rate of production:
2.Rate of delivery
3.Rate of degradation and elimination:
Control of Endocrine Activity
[Hormone] as seen by target cells is determined by 3 factors:
Rate of production: Synthesis and secretion of hormones are the most highly regulated aspect of endocrine control. Such control is mediated by positive and negative feedback circuits.
Rate of delivery: An example of this effect is blood flow to a target organ or group of target cells - high blood flow delivers more hormone than low blood flow.
Rate of degradation and elimination: Hormones have characteristic rates of decay, and are metabolized and excreted from the body via several routes. Shutting off secretion of a hormone that has a very short halflife causes circulating hormone concentration to plummet, but if a hormone's biological halflife is long, effective concentrations persist for some time after secretion ceases.
Hormone Synthesis
Diversity of hormones structuresLots of interesting pathways of biosynthesis
Simplest of hormones-amino acidsGlycine and glutamate -act as NTs in brain
F and Y-are precursors of dopamine, NE and EpiWhich also function as NTs
Hormone Synthesis
Y also substrate for generation of thyroid hormones
W is precursor for serotonin, a CNS NTand melatonin, a pineal hormone
Hormone Synthesis
Peptide Hormones -translated on secretory pathway (ER..golgi. Sec ves)
Made in RER
Can have continuous or regulated secretion
Hormone Synthesis
Steroid Hormones
Made within the SERSteroid secreting cells easily recognized by large
amounts of SER
Complex multiple enzyme system for synthesis secretion
Hormone Synthesis
Thyroid Hormones
Made on protienaceous substrates outside the cellThyroglobulin
Then taken up via endocytosis into the thyroid gland-released from carrier protein prior to
secretion from thyroid.
UNIQUE PROCESS
Hormone Synthesis
ProhormonesResult from cleavage events after translation
Even have preprohormones
ExamplesRenin (enzyme from Kidney)
Acts on angiotensinogen (substrate from liver)Results in ANGIOTENSIN I which is converted
by another enzyme to Antgiotensin II
Hormone Synthesis
Prohormones
Angiotensin II and bradykins are examples of hormones that are released from liver cells as larger prohormones and converted to active hormone in the
blood.
Hormone Synthesis
NTs
Made in axon end of neurons
Neuropeptides like oxytocin and vasopressin also made in neurons
Hormone Synthesis
Summary
Variety of processes and intracellular locations involved
SER, RER, Cholesterol from inside and outside the cell,
Secretory pathway involved in hormone modifications, particulary
glycosylation
Control of Hormone Secretion
Most hormones are made within cellsare packaged in secretory vesicles until
released
Except thyroid and steroid hormonesWhich are not in secretory vesicles
Control of Hormone Secretion
Internal and external effectors
Extrinsic-light, sounds, smell, temp, Etc.
Stimulation of hormone secreting cells results in vesicle fusion with the PM and exocytosis of secretory granules
Control of Hormone Secretion
Glycos.In Cis
Sorting in
Trans Golgi
Control of Hormone Secretion
Hormones often stimulate secretion of hormones from other endocrine glands
Pit hormones TSH, FSH, LH and ACTH simulate target tissue cells of thyroid, adrenal, gonads to secrete their own
hormones
Hormones control other hormonesCascade effect
Control of Hormone Secretion
Neuroendocrine transduction
stimulation of hormone secretion by nerves
Control of Hormone Secretion
Hormone interaction with some membrane receptors results in
membrane depolarization -stimulates movement of Ca++into cells which
results in sec. vesicle exocytosis
Some chemical messenger inhibit secretion by resulting hyper polarization
Hormone Delivery-several routes
Endocrine, Para, auto
neurocrine- neuron contact target cell and releases hormone
neuroendocrine-neuron to blood
lumonal-released into lumen of the gut
Some delivered by all multiple routes
Hormone Circulation and metabolism
Peptide hormones have short half lives
Exopeptidases and endopeptidases
Most steroid hormones bound to plasma proteins. Steroid hormones
much more stable
Feedback Control of Hormone Production
Feedback circuits are at the root of most control
mechanisms in physiology, and are particularly prominent
in the endocrine system.
Instances of positive feedback certainly occur, but negative
feedback is much more common.
Feedback Control of Hormone Production
Negative feedback is seen when the output of a pathway
inhibits inputs to the pathway.
Feedback loops are used extensively to regulate secretion of hormones
An important negative feedback loop is seen in control of thyroid hormone secretion.
The thyroid hormones thyroxine and triiodothyronine ("T4 and T3") are synthesized
and secreted by thyroid glands and affect metabolism throughout the body.
The basic mechanisms for control in this system (illustrated on next slide) are:
1.Neurons in the hypothalamus secrete thyroid releasing hormone (TRH), which stimulates cells in the anterior pituitary to secrete thyroid-stimulating hormone (TSH).
2. TSH binds to receptors on epithelial cells in the thyroid gland, stimulating synthesis and secretion of thyroid hormones, which affect probably all cells in the body.
3.When blood concentrations of thyroid hormones increase above a certain threshold, TRH-secreting neurons in the hypothalamus are inhibited and stop secreting TRH. This is an example of "negative feedback".
Inhibition of TRH secretion leads to shut-off of TSH secretion, which leads to shut-off of thyroid hormone secretion. As thyroid hormone levels decay below the threshold, negative feedback is relieved, TRH secretion starts again, leading to TSH secretion ...
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+
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Target cell response
TRH receptors only found in anterior pituitary
TSH receptors only found in thyroid gland
TH receptors found on every cell
Cascade effect
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Another type of feedback is seen in endocrine systems that regulate concentrations of blood components such as glucose.
Drink a glass of milk or eat a candy bar and the following (simplified) series of events will occur:
Glucose from the ingested lactose or sucrose is absorbed in the intestine and the level of glucose in blood rises.
Elevation of blood glucose concentration stimulates endocrine cells in the pancreas to release insulin.
Insulin has the major effect of facilitating entry of glucose into many cells of the body - as a result, blood glucose levels fall.
When the level of blood glucose falls sufficiently, the stimulus for insulin release disappears and insulin is no longer secreted.
Numerous other examples of specific endocrine feedback circuits will be presented in the sections on specific hormones or
endocrine organs.
Hormone Profiles: Concentrations Over Time
One important consequence of the feedback controls that govern hormone concentrations and the fact that hormones have a limited lifespan or half-life is that most hormones are secreted in "pulses". The following graph depicts concentrations of luteinizing hormone in the blood of a female dog over a period of 8
hours, with samples collected every 15 minutes:
The pulsatile nature of LH secretion in this animal is evident.
LH is secreted from the anterior pituitary and critically involved in reproductive function; the
frequency and amplitude of pulses are quite different at different stages of the reproductive
cycle.
With reference to clinical endocrinology, examination of the graph should also
demonstrate the caution necessary in interpreting endocrine data based on isolated samples.
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A pulsatile pattern of secretion is seen for virtually all hormones, with
variations in pulse characteristics that reflect specific physiologic states.
In addition to the short-term pulses, longer-term temporal oscillations or endocrine
rhythms are also commonly observed and undoubtedly important in both normal
and pathologic states.
Mechanisms of Hormone Action
Immediately after discovery of a new hormone, a majority of effort is devoted to delineating its sites of synthesis and target cells, and in
characterizing the myriad of physiologic responses it invokes.
An equally important area of study is to determine precisely how the hormone acts to change the physiologic state of its target
cells - its mechanism of action.
Mechanisms of Hormone Action
Understanding mechanism of action is itself a broad task, encompassing
structure and function of the receptor, how the bound receptor transduces a
signal inside the cell and the end effectors of that signal. This information is not only
of great interest to basic science, but critical to understanding and treating
diseases of the endocrine system, and in using hormones as drugs.
Physiological roles of Hormones
What do hormones do???
Physiological roles of Hormones
Hormones control activity of all cells in the body
Affect cellular synthesis and secretion of other hormones
After metabolic processes (catabolic and anabolic). Turnover of sugar, proteins
and fats
Affect Contraction, relaxation and metabolism of Muscle
Physiological roles of Hormones
Reproduction
Cell growth and proliferation
Excretion and reabsoroption of ions
Affect action of other hormones
Role in animal behavior
Physiological roles of Hormones
Some hormones only exist a few times in the life of an individual hCG
Sometimes still have hormone but not sensitive to it any longer
Sometimes no longer produce hormone-thyroid hormone, estrogen
General mechanisms of Hormone
action
Receptors
Second messengers
Phosphorylation involves STY
Kinases and phosphatases
Reminder about
General mechanisms of Hormone action
Steroid hormones have intracellular receptors. So do Thyroid hormones
Endocrine pathophysiology
Failure of a gland to secrete enough hormone can lead to fatal consequences
No insulin-hyperglycemia-coma and death if untreated
General mechanisms of hormone action
Hormones regulate specific target tissuesNOT ALL CELLS IN the body
Determined by??Receptors-proteins bind hormones
Contribute to specificity of action
Can be PM or cytosolic or nuclear
Hormone response effected by Receptor Levels and hormone levels
Oxy and vasopressin AVP have similar structure and both hormones stimulate uterine smooth muscle contraction and
activate renal cAMPUterine receptors more sensitive to OXY
Renal receptor more sensitive to AVPNormal hormone conc. Each hormone only
activate appropriate cell type
Hormone response effected by Receptor Levels and hormone levels
When one hormone binds to the receptor of another hormone, this is called
CROSS TALK
Happens with lots of hormones.If hormone levels are high, will not only act
on its own receptor, but similar hormone receptors
Some hormones stimulate a number of tissues.
Insulin stimulates glucose uptake into skeletal muscle and Fat cells
But also talks to liver to shut down output of glucose from liver
High Insulin receptor levels on fat, muscle and liver, but low levels in
other tissues.
Insulin receptors at high levels in skeletal muscle
Fat cellsLIVER
Cells where INSULIN MODULATES glucose metabolism
Insulin receptors at low levels in all other tissues where this hormone
only has a modest effect on GROWTH
DOES NOT MODULATE GLUCOSE METABOLISM IN
THESE OTHER TISSUES
RECEPTORS FOR A PARTICULAR HORMONE ARE ONLY EXPRESSED IN CELLS
WHERE THE HORMONE ACTS.MORE ACTION-MORE
RECEPTORS
UNDERSTAND INSULIN EXAMPLE (IT IS AN
EASY ONE)
Hormone response effected by Receptor Levels and hormone levels
Have high levels of receptor in tissue that are primary responders
Hormones act via own receptors at normal concentrations
At high hormone concentrations, hormones can act on similar receptors
NE and EpiOxy and vaso
IGF-1 and insulin
In most cases, a maximum biological response to a
hormone is achieved when only a small % of the
receptors are occupied.
WHY?
Agonists and Antagonists Exocrine
Endocrine, Paracrine, AutocrineSecretinHumoral
Development origin of hormoneHomeostasis pH= ___ Temp=___CIf you secrete one, then you secrete
many…..
Endocrine Activity-rate of
production, delivery, and degradation
Steroid hormones, made in SERThyroid hormones-outside of cell
Not Secreted in vesicles like peptide hormones
Feedback circuits
Contribute to complexity of Hormone Action
Pulsatile secretion
General mechanisms of Hormone
action
Receptors
Second messengers
Kinases and phosphatases
CROSS talk
Hormones are complexLots of things to be studied regarding
hormones
Methods are used to performENDOCRINOLOGY EXPERIMENTS?
General considerations
1. Source2. Structure determination
3. Biosynthesis4. Control of secretion
5. Cellular mechanism of secretion6. Circulation and metabolism7. Biological actions/functions
8. Mechanisms of action
Scientific Method – observation + experiments
formulate hypotheses
Must be testable via observation or experimentation
Lot of Data Theory
Theory accepted Law of Principle or DOGMA
Always need a control vehicle if using solution
Sham operation if doing surgery
Always limit variables
Show specificity
Effects Usually Time and Dose Dependent
Old principle of Logic
Occam’s razor of several reasonable
explanations….
The simplest is most probable.
Types of Experiments in Endocrinology
Chemical ID
10 -amino acid sequence
20 –secondary 30 – R group interactions
40 –association with other proteins
Modifications like glycosylation, phosphorylation and sulfation
Methods of Endocrine Analysis
Microscopy(light, EM to whole-body scanning
techniques – (CAT, PET, MRI)
Imaging studies are important component of endocrinology studies
Imaging also important component of diagnosis and treatment
The picture shows a tumor cell
disintegrating after an attack by a T cell.
Two additional, intact tumor cells are shown
in. The successful cytotoxic T
lymphocyte may now make these cells its
targets.
Bioassays
Different approaches to examine hormone activity
Based on activity (enzymatic)Or association with another molecule
Structure-Activity Studies
Mutate part of the gene or one base of the gene to determine if that part is important in hormone activity and
function
Site directed mutagenesis
Site directed mutagenesis
Histological and cytological studies
Hypertrophic-enlarged This means bigger cells
Contain more ER and GolgiOpposite of atrophic
Hyperplasia or HyperplasticAn increase in number
Enlarged spleen cells
Enlarged fat cells at top
Hypertrophic-enlarged This means bigger cells
Contain more ER and GolgiOpposite of atrophic
Hyperplasia or HyperplasticAn increase in number
Can have Hypertrophy or Hyperplasia
or both depending on condition
Immunocytochemistry
This is method to examine peptide or peptide hormone in a tissue.
Must have an antibody against that protein.
Antibody bind hormone (protein).Use Fluorescent dye to bind antibody to
visualize location of protein.
Immunocytochemistry to show marker of Hodgkins lymphoma
Immunocytochemistry to two proteins
Immunocytochemistry
This is method CAN ALSO BE used to determine what tissue produces a
hormone and/or where in the cell it is localized
Radioisotope Studies
I125 take up by thyroid
Radioactive Ca measured
P to perform phosphorylation studiesHalf life studiesKinase studies
Radioisotope Studies
I125 take up by thyroidthe amount of iodide the thyroid absorbs is a reliable indicator
of how much hormone the gland is producing
Surgical Methods
Endocrine organs can be transplanted to a new location
Ectopic-abnormal site
Hypophysectomy-removal of pituitaryPituitary target organs become atrophic
Ectopic-abnormal
site
Removal of both members of paired (bilateral roans) such as adrenals or gonads usually leads to COMPLETE
loss of dependent tissue/organFUNCTION.
Only unilateral (one) removalHave compensatory hypertrophy
To account for ablated organ
ParabiosisAnimals are sutured together and
share vascular systems
Remove endocrine gland of one mouse, the organs of other animal
will hypertrophy. Chemical communication between
animals
Obese gene-genetic defect in this gene causes obesity and type II diabetes
The obesity gene codes for a hormone called leptin that is made exclusively in FAT
diabetes gene-genetic defect in this gene causes obesity and type II diabetes
The diabetes gene codes for the leptin receptor which is primarily expressed in the
hypothalamus
Ob/ob mice-no leptin db/db-no leptin receptor
2 commonly used rodent models of type II diabetes
Parabiosis of ob/ob and db/db miceOb/ob mice-no leptin
db/db-no leptin receptor
Gray mouse is wild type
Ob mouse and wild type-get leaner ob mouse. Sharing Hormone
db mouse and wild type-db does not get leaner because of defective
receptor, not a problem with the hormone.
db mouse and ob mouse-ob mouse gets better as it gets circulating
hormone from db mouse. Db mouse does not improve because of defective
receptor
This pivotal parabiosis experiment showed that ob gene coded for
circulating factor and that db did not.
Positional cloning is method to identify and clone the gene that
creates a phenotype. So-finding the genotype
Positional cloning is method to identify and clone the gene that
creates a phenotype. So-finding the genotype
Obese mice-defect in obese geneTook over 10 years to find gene
Same with diabetes gene
Obese mice-defect in obese geneFound was fat
specific
RIADetection of hormones at
minute concentrations.
Need an antibody
RIADetection of hormones at minute concentrations. Need an antibody
RIA
Nobel Prize in Medicine (1977) to Rosalyn Yalow
RIA
At first was only useful for petptides. Now possible to trick antibody
producing cells to make specific anitbodies against all type of
chemical substancesCan measure Steroid and Thyroid
hormones now with this assay
Electrophysiology membrane potential
Electrophysiology The cell-attached patch clamp uses a
micropipette attached to the cell membrane to
allow recording from a single ion channel.
"Current Clamp" is a common technique in electrophysiology. This is a whole-cell
current clamp recording of a neuron firing due to it being depolarized by current
injection
Chemicals
Alloxan or streptozoticn destroy islets which produce insulin-induce Type I
diabetes in an animal
Cobalt chloride destroy glucagon secreting cells
Induce diabetes chemically or surgically
Hormone Replacement Therapy (HRT)
Reverse the undesirable effects of hormone loss following surgery or
disease state or age.
Children lacking GH are given this hormone to avoid stunted growth
Immunological Neutralization of
Hormone activity Antibodies against a hormone injected.
Bind hormone and inhibit its actionMostly used as Experimental rather
than treatment approach to understand the actions of specific hormones
Inject anti-NGF antibodiesno growth and dev’t of SNS
Pharmacological experiments
Actinomycin D-inhibits transcriptionCycloheximide-inhibits translation
Colchicine-disrupt microtubulesCytochalasin B-disrupts microfilament
Pharmacological experiments
Actinomycin D and Cycloheximide
Can be used to determine if an action of a hormone is genomic
Specific Example
To determine if effect of a hormone is dependent on new proteins synthesis, treat target cells with CH then look at
hormone action.
If action is blocked, know the effect is genomic
Pharmacological experiments
Colchicine and Cytochalasin can be used to tell if signaling or secretion is
dependent on cytoskeleton
Tissue Extracts and purification
Type I diabetics need daily injections of insulin
Used to come from pigs, cattle, horse.Slaughterhouse blood
Contaminants from animalsSpecificity issues
Insulin now made recombinant
Sheep melatonin Bovine GH
Disadvantages of using hormones
purified from animals or Slaughterhouse blood
-Contaminants from animals-Specificity issues
-Cost, much cheaper to make recombinantly
Sheep melatonin Bovine GH
Recombinant DNA methods
Way in which we make insulin
Genetic engineering in various speciesFish, mice, rats.
Transgenic Animals
introduce gene in animal-Usually replace wild type with a mutant
-Or express gene from a different promoter.
Transgenic Mice over expressing TropomodulinHave enlarged right atrium and ventricle and are larger
Labeled for two different proteins which are normally present in myofibrils. The alternating bands of tropomodulin (green) and alpha-
actinin (red) show the dense packing of myofibril throughout the interior of the cell.
The normal alternating pattern of tropomodulin and alpha-actinin immunoreactivity has been disturbed. The yellow color indicates
colocalization of both red and green labels (an abnormal distribution). Transgenic mice with this level of tropomodulin overexpression suffer
from cardiomyopathy
transgenic mice that
overexpress TGFß1 in the CNS
animals developed severe hydrocephalus
transgenic colony serves as a model of congenital
hydrocephalus
overexpress neurotrophin-3 (NT-3) in skeletal muscle
When lifted by the tail, wildtype extend their hindlimbs and digits. In contrast, all transgenic NT-3 mice retract their hindlimbs to the body and clench their paws in a
"clasping phenotype"
Transgenic mice has different
coat color
Transgenic mice extremely useful in studying diseases