• Subdiscipline of physiology
• Study of Hormones:
• `````Physiological roles
• `````Cellular sources
• `````Biosynthesis
• `````Chemistry and storage
• `````Factors and mechanisms controlling secretion
• `````Cellular Mechanisms of hormone action
• `````Pathophysiology of endocrine sys. disfunction

One's physical and mental health depended on the balance of the four humors.

This theory lasted until at least the 18th century.

1. Blood
2. Phlegm
3. Black Bile
4. Yellow Bile

• External structure
• Easy accessability
• Interest in human sexuality

• Eunuchs as guards for harems or brothels
• Castrados in church choirs
• Form of punishment and humiliation (Still even today, in some societies)
• Animal castration to improve the palatability of meat

He first wrote "On the Motion of the Heart and Blood in Animals"

 a.k.a. De Motu Cordis

It named the blood as the circulation medium throughout the body, pumped by the heart, in a circuit.

• Successfully transplanted gonads among birds:
• Demonstrating the testes droves maleness and the ovaries drove femaleness.
• Still no awareness of mechanism of secretion into blood at the time.

• The first to report and describe what is now called "internal secretion and humoral integration"
• His Hypothesis: Each gland and organ of the body is a workshop producing secrections, which pass into the blood and influence total body functions

• Conducted the first formal study in endocrinology
• Roosters - Capons : First recorded ablation / replacement experiment on testes.

• Left usually bigger than right
• Age-related, larger left testicle found in younger birds
• More primordial germ cells in left, aquired from right
• Age-related, larger right found in older roosters
• (Similar asymmetry found in ovaries in females)

• Developmental cost of having two large testicles
• `````Metabolic cost of two equally large testicles is too great because of the potent immunosuppressive effect of testosterone.
• `````Greater mass could affect flight
• Right Testis may be primarily compensatory (back-up)
• `````Low degrees of asymmetry suggests right testis has become fully developed to compensate for inadequate left testis
• `````Males in poor health might have larger right testis than left

• Firmly established, through chemical analysis, the idea that blood is altered when it passes through an organ.
• In his research, the liver was the primary organ studied.
• FIRST TO USE THE TERM "INTERNAL SECRETION"!!!!

• first use of tissue extracts in a clinical setting
• injected dog-testes-extracts into himself, claimed rejuvenation
• public interest drove further research

• 1891 - treated hypothyroidism with thyroid extract
• FIRST CLINICAL TREATMENT FOR AN ENDOCRINE DISORDER, EVEN THOUGH THYROID HORMONES HADN'T YET BEEN ELUCIDATED

• 1889 - DIABETES MELLITUS term coined.
• Ablation replacement experiments on dogs/pancreas
• Did not know about insulin yet

• 1902-1905
• Conducted experiments leading to discovery of SECRETIN - THE FIRST DISCOVERED HORMONE!!
• It's considered the "Start of endocrinology"
• S- Coined the term "HORMONE" !!

• Electron Microscopy
• Radioactive Isotopes
• Tissue Culture
• Analytical Methods

• Separation techniques
• Purification techniques
• Synthesis of protein hormones
• Studies on mechanism of hormone actions - PATHWAYS!!

• 1953 
• Determined structure of, and synthesized the first peptide hormones oxytocin and vasopressin/ADH/AVP
• (which are found in the posterior pituitary)

• 1954
• Determined the chemical structure of insulin
• First to determine the structure/sequence of any protein hormone

• 51 Amino Acid residues per molecule
• 2 chains (A&B)
• 1 intrachain disulfide bridge
• 2 interchain disulfide bridges

• 1960
• Discovered ecdysone, insect molting hormone that induces cell nucleus RNA increase (chromosome puffing)
• Showed that hormones could affect DNA / RNA

• 1963
• Synthesized insulin 
• The first protein hormone to be synthesized

• 1957-1960
• Discovered cAMP as a hormone mediator
• Elucidated the mechanism of action of some hormones
• Discovered epinephrine affects liver to induce increase in blood glucose
• 1971 - NOBEL PRIZE!
• "Showed that hormones do not have a direct, but rather an indirect action via intermediates, which regulate, but do not mediate reactions"

• 1950s-1960s
• Elucidated hypothalmic control of the pituitary endocrines
• Discovered releasing factors
• 1st of all was Corticotropin Releasing Factor (CRF)
• Considered the "Fathers of neuroendocrinology"

1977 - Shared NOBEL PRIZE with Berson and Yalow

• 1960
• Developed radioimmunoassay (RIA) techniques
• Allowed for accurate measurements of hormone concentration (picogram/mL);
• Again, insulin was the first measured

1977 - Shared NOBEL PRIZE with Guilleman and Schally

• 1849
• Originated the concept of internal vs external environment
• "milieu interior which is the condition of free and independent life"

• 1932
• Built upon Claude Bernard's concept of milieu interior
• coined the term homeostasis and expanded idea
• steady state condition
• homeostasis is the result of a organized self-regulation
• early idea of fight or flight response

• Process by which organisms maintain the "constancy" of their internal environment in response to changes in their external environment
• Self adjusting mechanism involving feedback regulation (negative more commonly, and positive)
• Works to maintain the internal environment within a narrow range of conditions conducive to life

• Glucose (30-300mg/dL)
• Calcium
• Sodium
• Body Temp
• Blood Volume/Body Fluid levels

• The "Hypothalamus-pituitary-endocrine organ axis"

• The Hypothalamus -> Pituitary -> Endocrine Gland     -> Target Organ -> DESIRED EFFECT

1. The response of the target organs/glands diminishes the original stimulus
2. Output of a pathway inhibits inputs to the pathway
3. Can continue forever
4. Maintains homeostasis

1. Destabilizing stimulus is sensed
2. Hormone secretion is triggered
3. Hormone activity lowers a parameter to bring process back to pre-stimulus state

• Secretion
• Blood clotting
• Muscle contraction
• Thermoregulation
• Nerve signal conduction

Its concentration is maintained within very narrow limits both inside and outside the cell

Its level in the blood is what is regulated by the body

1. Elevation of blood glucose concentration
2. Beta cells in pancreas release insulin
3. Insulin facilitates entry of glucose into cells
4. Blood glucose level falls sufficiently
5. The stimulation for insulin release falls
6. Insulin secretion stops

1. Unstable system
2. It is used to trigger a sudden even / phenomenon
3. Cannot continue forever / always has a limit
4. Does not result in homeostasis
5. Beneficial in only special circumstances
6. Usually terminated by a dramatic event (i.e. Childbirth, Death)

Neuroendocrine Integration

definition and examples

Def: an intertwining of the nervous system and the endocrine system

Ex: Adrenal medulla - releases epinephrine, norepinephrine, and dopamine into the blood.

(It's innervated by the sympathetic autonomic nervous system)

The hypothalamic median eminence,

and the bloodstream. 

1. Endocrine/Neuroendocrine
2. Paracrine 
3. Autocrine
4. Neurocrine
5. Intracrine

Delivery via hormone feedback on the cell of origin in a form of self regulation

(e.g. the ultrashort loop)

Delivery via hormones released into the synaptic cleft by neurons that are in contact with the target cells

(e.g. peptide hormones)

Delivery via hormonal action within a cell

(e.g. steroid hormones acting through intracellular (mostly nuclear) receptors).

1. They must be metabolized rapidly and removed, so FEEDBACK MECHANISMS can operate and cellular functions can be regulated
2. Removal/inactivation of these follows a pattern of exponential decay (kinetics).
3. Its "half-life" is how its longevity is measured
4. Synthetic versions/analogues are designed to have a longer half-life in order to be more effective for longer periods of time than those naturally occuring

1. Peptidases - e.g. cathepsins (proteases): in lysosomes split all the peptide bonds in the molecules
2. Exopeptidases - degrade peptides from the carboxy-terminal OR the amino terminal end.
3. Endopeptidases - e.g. trypsin and chymotrypsin: degrade proteins at specific sites like lysine or arginine, and phenylalanine or tryptophan or tyrosine
4. Deamination or reduction of disulfide bonds (like the ones in insulin) - This occurs in the kidney, liver, and in target cell lysosomes

How can a hormone increase its half-life?

1. Be a steroid hormone (which can hang out in adipose tissue due to the steroids' lipophilicity)

2. Bind to a protein carrier

3. Stay away from the liver and kidney to avoid the 2-phase degradation process

1. Concerted/Additive - Thyroid,  T_3, Growth Hormone works on RNA expression and thus, growth
2. Non-Additive - Epinephrine works on insulin and glucagon, so does cortisol to release more glucose into the bloodstream
3. Synergistic - T₃ and Cortisol, genes affected, somatotropin
4. Permissive - estradiol permits expression of progesterone receptors in oviduct

1. Concentration of hormone in blood and exracellular fluid
    
2. Hormone-receptor interaction (Binding)
    
3. Intracellular signaling mechanisms (Phosphorylation, signal transduction pathway, etc.)
    

• Melatonin
• Cortisol
• Thyrotropin
• Growth hormone

• Core Body Temperature
• Urine Volume
• Cerebral Blood Flow
• Systolic Blood Pressure

It's a consequence of 

1. Feeback Controls

2. Regulated Secretion

3. Limited lifespan of a hormone

1. Circhoral - an hour (testosterone)
2. Ultradian - recurrent periods/cycles repeated during a 24-hour circadian day (sleep, feeding)
3. Circadian - endogenously driven cycle of roughtly 24-hours (Melatonin, corticosteroids)
4. Quotidian (diurnal) - occurs every day (body temperature)
5. Infradian - periods longer than a day (human menstrual cycle)
6. Circatrigintan - a month, approximately (ovulation)
7. Circannual (seasonal) - a year (thyroxine, dog reproduction)

Diet

Disease

Light

Temperature

Noise

Ca⁺⁺

Lipid

Temperature

Na⁺

P

Mg

1. Changes in cellular metabolism 
2. Activate genes to influence gene expression and ultimately protein synthesis
3. Alter catalytic rates of enzymes by phosphorylation or dephosphorylation
4. Alter membrane permeability (affects transport processes and ion movements, muscle contraction, exocrine secretion, and water permeability)

1. Morphological changes (sex steroids alter appearance)
2. Act as mitogens (accelerate cell division or alter gene expression to trigger differentiation of cells)
3. Simulate overall rate of protein synthesis or synthesis of specific proteins
4. Stimulating smooth muscle contractions (oxytocin stimulates contraction of myoepithelium in the mammary gland for milk ejection)

1. Affects exocrine secretions; (secretin peptide hormone from intestine stimulates pancreatic secretions)
2. Controls endocrine secretions (trophic hormones from ant.pit. stimulate/inibit hormone secretion from target organs)
3. Regulate ion movements across membranes and permeability to water (ADH, vasopressin)
4. Affects behavior (sex-related behavioral characteristics, maternal behavior)

1. Target cells have specific receptors 
• (hypophyseal - portal system)
• hypothalamus to the pituitary gland
• smaller quantities of hormones are needed due to less dilution across space.
2. Many Hormones linked to CARRIER PROTEINS
• stabilize the hormone / increase half-life
• (Sex hormone-binding globulin)

Hormone Selectivity

(Receptor specificity)

1. Specific (protein) receptors bind a specific hormone
2. Receptors present in small numbers (10,000 molecules per cell)
3. Two types (cell-surface and intracellular)
4. Peptide / protein hormones usually do not enter the cell, but interact with cell-surface receptors

1. Activity mediated by how many receptors are bound to hormones
2. Cell-surface receptors (usually) require a second-messenger system to transmit the hormone response signal from the outside to inside
• Protein kinase A phosphorylation
3. Steroid hormones / Thyroid hormones enter the cell to interact with intracellular receptors to regulate gene expression (penetrate plasma membrane)

1. -Hormone 
2. > membrane spanning receptor 
3. > Active protein Kinase 
4. > Protein Substrate phosphorylation 
5. > Cellular response

1. Cell surface
2. Inside the cell

1. Extracellular
1. Second messenger system
• cAMP 
• cGMP
2. Intracellular Receptors
• Protein Kinase A (PKA)
• Protein Kinase C (PKC)

1. Large macromolecules
• Insulin receptor= 200-400kDa (2alpha 130kDA/2beta subunits 90kDa)
• Must span the membrane, bind a hormone, and undergo conformational change- requires many moving subunits.

1. Adenylate cyclase
• cAMP or cGMP
• PKA or PKC
2. Inositol Phosphate
• Phospholipase C
• Calcium dependent

cAMP messenger system example:

Epinephrine

1. Epinephrine binds to RECEPTOR, causes conformational change
2. Activates G-PROTEIN (alpha, beta&gamma subunits dissociate)
3. The active G-protein (now with GTP bound rather than GDP) binds to ADENYLATE CYCLASE
4. Alter activitiy of a.c. converts ATP to cAMP!
5. cAMP activates PROTEIN KINASE A!
6. PKA phosphorylates various targets, activating or deactivating them, to initiate a cellular response 

• (In epinephrine's case, elevates blood glucose levels by:
• phosphorylating "phosphorylase kinase" which then 
• phosphoylates "Glycogen phosphorylase A" which then 
• Degrades Glycogen to 
• Release glucose into the bloodstream)

1. Hormone binds to the receptor (transcription factor)
2. Activates PHOSPHOLIPASE C which splits into
• Inositol phosphate (in the cell membrane) and 

•  Diacylglycerol
1. Inositol Phosphate increases levels of intracellular calcium
2. DAG activates Protein Kinase C (along with the C++)

1.What enzyme degrades cAMP?

2. What's the end product of the degradation?

1. Phosphodiesterase

2. AMP

1. Chemical stability - derived from ATP
2. ATP is ubiquitous - is formed from ATP in a single reaction (doesn't take a lot of energy to make)
3. It's an allosteric regulator ( not a metabolic precursor) - controlled separately independently of metabolism
4. It's a small and easily diffusable molecule, has functional groups that allow specific binding to regulatory subunits of protein kinases (PKA)

• Increased heart rate
• Cortisol secretion
• Glycogen breakdown
• Fat breakdown 

1. Cholera toxin - increases levels of cAMP
2. Forskolin- a diterpine natural product that activates adenylate cyclase
3. Caffeine and theophylline- inhibits cAMP phosphodiesterase
4. Bucladesine (dibutyryl cAMP, db cAMP) - Also an inhibitor of phosphodiesterase

1. cAMP phosphodiesterase- and dephosphorylates cAMP into AMP,
2. Gi Proteins- inhibitory G proteins inhibit adenylate cyclase,
3. Pertussis toxin- decreases cAMP levels (whooping cough)

PHOSPHODIESTERASES!!!

(PDE)

1. PDE1A and PDE1B preferentially hydrolyse cGMP
2. PDE1EC degrades both cAMP and cGMP, high affinity
• (Generic PDE1 does more than 50 percent of hydrolysis of cyclic nucleotides in airway smooth muscle)

What does Phosphodiesterase do?

(picture)

1. aka cAMP-dependent protein kinase
2. activity depends on cAMP levels w/in the cell
3. regulates (indirectly) metabolism of glycogen, sugar, and lipids
4. activity is affected by epinephrine and glucagon (upregulated via adenylate cyclase)
5. phosphorylates many important metabolic enzymes
• acetyl-CoA carboxylase
• pyruvate dehydrogenase
• allosteric regulation inhibits lipogenesis
• promotes net gluconeogenesis
• (insulin works in opposition and promotes lipogenesis)

Calcium-Dependent phospholipase C-protein kinase

(PKC)

• Primary intracellular effector in this pathway is Ca²⁺
• Activates calcium-dependent protein kinase C

Phospholipase C-PKC System

(steps)

1. Hormone binds to receptor, 
2. G-Protein activated
3. Phospholipase C activation
4. Phosphatidylinositol-4,5-bisphosphate hydrolyzed to produce:
• Diacylglycerol (DAG) -> ER Ca²⁺ Channels open
• Inositol-1,4,5-phosphate (IP3) -> activates PKC (w/Ca²⁺)
5. PKC then phosphorylates cellular proteins to regulate their activity

1. Using 
• a non-hydrolysable form of GTP
• Cholera toxin
• (both inhibit GTPase activity)

Codes for a permanently active G-Protein

(might explain its role in the development of cancer)

The cGMP system works in opposition to cAMP

(activation of cAMP-dependent kinases results in smooth muscle relaxation, while activation of cGMP-dependent kinases results in smooth muscle contraction)

What hormones act via

the adenylate cyclase-cAMP-protein kinase A

pathway?

1. Glucagon
2. Vasopressin
3. Thyrotropin (TSH)
4. Adrenocorticotropic hormone (ACTH)
5. Luteinizing hormone (LH)
6. Follicle stimulating hormone (FSH)
7. Chorionic gonadotropin
8. Parathyroid hormone
9. Thyrotopin
10. Thyrotropin Releasing Hormone (TRH)
11. Secretin
12. LH Releasing Hormone (LHRH)
13. Calcitonin

1. Thyroid hormone receptors (TR)
2. Estrogen receptors (ER)
3. Progesterone receptors (PR)
4. Retinoic Acid receptors (RAR)
5. 1,25-dihydroxy vitamin D3 receptors (VDR)

1. Glucocorticoid receptors (GR)
2. Mineralocorticoid receptors (MR)
3. Androgen receptors (AR)

1. the receptor undergoes a conformational change
2. the hsp90 comes off
3. the receptor and hormone (bound together) enter the nucleus to act upon transcription

1. Group A: Estrogen Receptors (sex-hormones)
2. Group B: Estrogen-Related Receptor
3. Group C: 3-Ketosteroid Receptors

What are the 4 common steroid hormone receptor domains?

What do they do?

1. Variable Domain - 
• N-terminal and is the most variable domains
2. DNA Binding domain - 
• Centrally located highly conserved DNA binding domain;
• This region controls which gene will be actived.
• On DNA it interacts with the hormone response element (HRE)
3. Hinge Region - 
• Controls the movement of the receptor to the nucleus
4. Hormone binding domain - 
• Moderately conserved ligand binding domain

1. Type I
• Bind Steroids
• Have a heat shock protein (hsp) associated with the inactive receptor that will be released when the receptor interacts with the ligand
2. Type II
• HAVE NO HEAT SHOCK PROTEIN (NO HSP)
• Located only in the cell nucleus

1. Hormone penetrates plasma membrane
2. Receptor/hsp90 complex binds hormone in cytosol
3. Hormone/receptor/hsp90 complex alltogether enters nucleus, 
4. Hsp90 chaperone dissociates
5. Receptor hormone complex binds to DNA Associated receptor
6. Phosphorylation of sites on chromatin

NO HSP

Hormone binds to receptor (Transcription factor) in the nucleus

Transcription factor affects transcription of RNA

1. once the hormones interact with their receptors, the cluster together and trigger vesicularization of the membrane and endocytosis
2. receptors are then degraded by lysosomal enzymes or the receptor can be recycled
3. The hormone at the cell surface can be degraded by plasma enzymes
4. The cyclic nucleotides are degraded by phosphodiesterases and the phosphorylated proteins are dephosphorylated by phosphoprotein phosphorylase

1. Steroids - (cholesterol as a building block)
2. Proteins, polypeptides, and glycoproteins (added sugar moiety)
3. Amino-acid derivatives (especially derivatives of tyrosine; neurotransmitters)
4. Fatty acids and derivatives (prostaglandins)

1. Pineal gland
2. Thyroid gland
3. Heart
4. Bone
5. Pituitary gland
6. Parathyroid gland
7. Pancreas
8. Adrenal gland
9. Kidney
10. Ovaries
11. Testes

1. A short sequence of 15-30 hydrophobic amino acids located at the amino-terminal (beginning) of the proteins
2. a signal sequence (S) directs the newly synthesized protein into the ER and then to export from the cell
3. other proteins enter the cytosol and from there are directed to the mitochondria (M) or nucleus (N) or to other sites within the cell
4. proteins move between the various compartments by vesicular transport
5. uptake of proteins by particular vesicles is controlled by the sorting signal sequences in the proteins

• Newly synthesized protein hormones CONTAINING SIGNAL SEQUENCES

Structure of protein hormones: Prohormones

(e.g. proparathyroid hormone)

1. Peptide hormones synthesized as part of a larger precursor
• (Proparathyroid hormone) the precursor of Parathyroid hormone
• (Proinsulin) the precursor of insulin
• (Proopiomelanocortin) is the precursor of several tropic hormones produced in the anterior pituitary.
• Newly synthesized prohormone with a signal peptide is known as a preprohormone

1. No health risk, minimal hormonal effect itself
2. Enhances the strength (a ready supply, to be activated)
• Prohormone Example: Pro-opiomelanocortin
3. For peptide hormones, the conversion process from prohormone to hormone typically occurs after transport to the endoplasmic reticulum, requiring multiple processing enzymes. 
4. For small molecule hormones, the conversion is often one step, and is often used to regulate hormone levels

1. Thyroid stimulating hormone (TSH), follicle stimulating hormone (FSH), and Luteinizing Hormone (LH), have sugar units attached to the amino-acid side chains
2. After protein synthesis, the preprohormone moves from the ER moves to the Golgi apparatus, where sugar residues are attached to asparagine, serine and other amino-acid side-chains in a process called glycosylation

Cortisol - A major glucocorticoid, promotes gluconeogenesis and fat & protein degradation.

Aldosterone - a major mineralocorticoid, increases absorption of sodium, chloride and bicarbonate by the kidney to increase blood volume and blood pressure

1. Occurs in the thyroid gland
2. Stimulated by thyrotropin (TSH) released from the anterior pituitary
3. Thyrotropin is released in response to Thyrotropin Releasing Hormone produced from the hypothalamus in mammals (in birds, the MEDIAN EMINENCE is the primary source of TRH)

1. Thyroid hormones are synthesized by iodination of tyrosine residues in the thyroglobulin protein
2. PROTEASES IN LYSOSOMES DEGRADE THYROGLOBULIN TO RELEASE THYROXINE (T4)
3. T4 is converted to T3 (in the liver and thyroid) by selenium-dependent iodothyronine deiodinases
4. T3 is metabolically more active than T4 in most animals, (but T3 and T4 are equally potent in birds)

1. Prostaglandins
2. Prostacyclins
3. Thromboxanes
4. Leukotrienes

They:

1. stimulate inflammation, 
2. regulate blood flow 
3. blood pressure, 
4. affect ion transport, 
5. modulate synaptic transmission

(they stimulate other hormone release)

• TSH stimulates the release of thyroxine
• FSH and LH stimulate the synthesis and release of adrenal steroids
• ACTH stimulates the synthesis and release of adrenal steroids

Light

smell,

sound,

temperature

Glucagon

Insulin