Catecholamines

Question 1

Which nervous system uses catecholamines?

Answer 1

The sympathetic

Question 2

Describe the normal neurone structure of nerves in the sympathetic and then compare to the neurons of the adrenal medulla

Answer 2

Normal= short pre ganglionic and long post
Adrenal= long pre ganglionic and short post

Question 3

Describe the difference between the tumours of the adrenal cortex and adrenal medulla

Answer 3

• Diseases of the medulla are less common

- Can get tumours of the medulla= they are functional and produce excess catecholamines

Question 4

What is the rate limiting step in the synthesis of catecholamines?

Answer 4

-The enzyme tyrosine hydroxylase

Question 5

Where does circulating epinephrine and nor epinephrine come from?

Answer 5

• ALL epinephrine in the blood is from the adrenal medulla
• Norepinephrine comes from 2 sources
  1) adrenal medulla
  2) postganglionic sympathetic neurons

Question 6

How is vascular tone maintained?

Answer 6

• Basal sympathetic tone

- It is accomplished by the resting secretion from adrenal medulla

Question 7

Describe the kinetics of catecholamines

Answer 7

• Stored in secretory vesicles
• Released via exocytosis
• Circulate freely in the blood
• Metabolised by liver and kidneys
• Very short plasma half life (not very stable)
• Unmetabolised epinephrine/ norepinephrine is excreted in the urine

Question 8

What stimulates release of adrenaline and noradrenaline from the adrenal medulla?

Answer 8

• Action potential from the pre ganglionic fibre secretes dopamine which causes an influx of Ca
• Stimulates more catecholamines to be produced and the exocytosis of the secretory vesicles resulting in epinephrine and norepinephrine entering the blood.

Question 9

List adrenergic receptors

Answer 9

-A/B adrenergic receptors

Question 10

What are the effects of catecholamines binding to alpha receptors?

Answer 10

• Vasoconstriction
• Pupil dilation
• Intestinal relaxation
• Pilomotor contraction
• Bladder sphincter contraction

Question 11

What are the effects of catecholamines binding to B1 and B2 receptors?

Answer 11

B1= increases heart rate and contractility
B2= vasodilation, bronchodilation, glycogenolysis and lipolysis

Question 12

Which receptor is found on the cardiac myocytes?

Answer 12

B1

Question 13

List some of the consequence of SNS activation

Answer 13

• Dilated pupils
• Sweating
• Tachycardia
• General vasoconstriction
• Increased cardiac output
• Bronchodilation

Question 14

Describe the signal transduction of catecholamines

Answer 14

-Binds to receptors and activates second messengers- often G coupled

Question 15

Which adrenergic receptors use adenyl cyclase?

Answer 15

B receptors

remember adenyl cyclase-> cAMP-> activates pkA-> protein is phosphorylated and response occurs

Question 16

What are the effects of cAMP?

Answer 16

• Subunit of pkA enters nucleus
• Binds to CREB and phosphorylates
• CREB-P binds to CRE and changes gene expression

Question 17

Explain the impact of phospholipase C at alpha receptors

Answer 17

• Hormone binds to cell receptor
• Phospholipase C activated via a G protein
• PIP2 is broken down to IP3 and DAG
• DAG activated membrane bound protein kinase C
• Protein is phosphorylated
• Biological response resulting in increased intracellular Ca

Question 18

Which receptor does albuterol act on and what are its affects?

Answer 18

Beta 2

Stimulates adenyl cyclase -> increased cAMP results in dilation of bronchiole smooth muscle

Question 19

Which receptor does dobutamine work on and what are its effects?

Answer 19

B1

Question 20

What receptor does atenolol work on and what are its effects?

Answer 20

Blocks B1

Decreases blood pressure and slows heart rate

Question 21

Why are the different receptors important in the sympathetic nervous system?

Answer 21

• Allow catecholamines to produce different effects in different tissues to help with fight/ flight
  e. g. reduces blood flow to intestines whereas increases blood flow to muscle

Question 22

What are the metabolic effects of catecholamines?

Answer 22

• Increase glycogenolysis
• Stimulate gluconeogenesis
• Stimulates HSL (hormone sensitive lipase) -> increases circulating plasma fatty acid levels used to beta oxidation in mitochondria.

Question 23

Describe the differences between epinephrine and norepinephrine

Answer 23

• Norepinephrine has greater impact on blood vessels: increases total peripheral resistance and raises blood pressure
• Epinephrine has more profound effect on the heart: increases heart rate and contractility and raises cardiac output