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LCRS Pharmacology and Therapeutics > SNS agonists > Flashcards

SNS agonists Flashcards

1
Q

Where do sympathetic nerves originate?

A

Thoracolumbar region

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2
Q

What is the neurotransmitter at sympathetic preganglionic nerve fibres?

A

Acetylcholine

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3
Q

What do most sympathetic postganglionic neurones release?

A

Noradrenaline

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4
Q

What are the two exceptions for sympathetic postganglionic neurones?

A

A preganglionic sympathetic neurone drives release of adrenaline (80%) and noradrenaline (20%) from the adrenal medulla
Sympathetic postganglionic neurone that innervates sweat glands releases acetylcholine

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5
Q

What are directly acting sympathomimetics?

A

They mimic the actions of NA/A by binding to and stimulating adrenoceptors (GPCRs)

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6
Q

Due to the actions on where are sympathomimetics mainly used for?

A

CVS, eyes and lungs

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7
Q

What sort of receptor are all adrenoceptors?

A

G protein coupled

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8
Q

What are the 4 types of adrenoceptor?

A

Alpha 1
Alpha 2
Beta 1
Beta 2

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9
Q

What is the mechanism of action of alpha 1?

A

PLC -> IP3 + DAG

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10
Q

What is the mechanism of action of alpha 2?

A

Decrease cAMP

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11
Q

What is the mechanism of action of beta 1 + 2?

A

Increase cAMP

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12
Q

Where are alpha 1 adrenoceptors found?

A 
Iris radial muscle
Lacrimal glands (tears)
Salivary glands
Liver (glycogenolysis/gluconeogenesis)
Adipose- lipolysis
Ureter (motility and tone)
Genitalia- male (stimulates ejaculation)
Skin- generalised sweating
Blood vessels- skin, mucus membranes, splanchnic area, abdominal viscera, salivary glands constriction
GIT- decreased stomach motility and tone
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13
Q

Where are beta 1 receptors found?

A 
Eye- aqueous humour production
Adipose- lipolysis
Kidney- increased renin secretion
Salivary glands
GIT- decreased stomach motility and tone
Heart- increased rate and contractility
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14
Q

Where are beta 2 receptors found?

A

Trachea and bronchioles- dilate
Urinary bladder- relaxes detrusor
Genitalia-female relaxation of uterus
Blood vessels- skeletal muscle blood vessels dilation

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15
Q

What are the principal actions of beta blockers when controlling blood pressure?

A

It is through the kidneys - beta 1 stimulation in kidneys increases renin release which leads to peripheral vasoconstriction and increase in blood pressure
The heart is mainly controlled by beta 1- increases contractility and increases heart rate
Beta blockers inhibit both of these functions

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16
Q

What can all adrenoceptors be activated by?

A

Noradrenaline and adrenaline

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17
Q

What type of receptor is noradrenaline more selective for?

A

Alpha

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18
Q

What type of receptor is adrenaline more selective for?

A

Beta

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19
Q

How is noradrenaline formed?

A

Tyrosine from the diet is converted to DOPA by tyrosine hydroxylase (rate limiting enzyme) which is then converted to dopamine which is taken up by vesicles and converted to noradrenaline

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20
Q

How is noradrenaline deactivated?

A

It is via reuptake into the nerve terminal itself or extra neuronal tissue

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21
Q

Which receptors have an influence on synthesis and release of noradrenaline and what influence do they have?

A

Presynaptic alpha 2 receptors- they have a negative effect (environmental monitoring system within the synapse- high conc of NA will stimulate presynaptic alpha 2 receptors which will decrease synthesis and release

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22
Q

Name an SNS agonist that is selective for Alpha 1?

A

Phenyleprine

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23
Q

Name an SNS agonist that is selective for Alpha 2?

A

Clonidine

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24
Q

Name an SNS agonist that is selective for Beta 1?

A

Dobutamine

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25
Name an SNS agonist that is selective for Beta 2?
Salbutamol
26
What does the selectivity of the drugs depend on?
Concentration- low conc high selectivity but high conc lower selectivity
27
What happens in hypersensitivity reactions after first exposure?
You generate antibodies to the antigen and these circulate around the body and bind to mast cells
28
What happens in hypersensitivity reactions after subsequent exposure?
The mast cells are already primed with antibody on their surface so the antigen cross links these antibodies on the surface of the mast cells and you get a massive release of mediators
29
What are the symptoms of hypersensitivity?
Fall in blood pressure Anaphylactic shock- unconsciousness Respiratory distress D and V
30
Why is there a fall in blood pressure during hypersensitivity?
Endothelial cells within membranes of blood vessels move apart so you get a lot of fluid moving into tissues which leads to a fall in circulating fluid volume and hence a fall in blood pressure
31
Why is adrenaline more effective as a treatment than noradrenaline for hypersensitivity?
Noradrenaline, like adrenaline, binds to alpha receptors and will cause vasoconstriction and increase blood pressure But key thing is breathing- you need the patient to get breathing first and adrenaline acts more on the beta receptors the noradrenaline and this stimulates bronchodilation and relaxation of throat muscles Adrenaline will also stimulate heart to cause tachycardia and slow down release of histamine from mast cells
32
What common conditions is adrenaline used as a treatment for?
Pulmonary obstructive conditions- Asthma Acute bronchospasm- chronic bronchitis or emphysema
33
What treatments are preferable to adrenaline for these conditions?
Selective beta-2 agonists but adrenaline is useful in hypotensive crisis
34
Where are adrenoceptors are in the eye?
Alpha receptors on blood vessels in the ciliary body | Beta receptors that control the enzyme that makes the aqueous humour in the eye
35
Why is adrenaline used as a treatment for glaucoma?
It stimulates the alpha receptors in the vessels within the ciliary body causing vasoconstriction of these vessels- less blood will be delivered to the ciliary body and production of aqueous humour is reduced
36
What is cardiogenic shock?
Sudden inability of the heart to pump sufficient oxygen-rich blood (heart attack/MI or cardiac arrest)- mainly happens via beta 1 receptor
37
Why is adrenaline given during spinal anaesthesia?
As you are anaesthetising the spine you are taking away the sympathetic output to peripheral resistance vessels so they relax and patient won't be able to maintain blood pressure but with a little bit of adrenaline at same time this will constrict blood vessels and maintain blood pressure
38
Why is adrenaline also given during local anaesthesia?
Causes constriction of blood vessels so prevents clearance of anaesthetic from the area
39
What are the unwanted actions of adrenaline?
Secretions- reduced and thick CVS effects- tachycardia, palpitations, cold extremities, hypertension Overdose- cerebral haemorrhage and pulmonary embolism GIT- minimal Skeletal muscle- tremor
40
What adrenoceptors is phenylephrine more selective for?
Alpha 1 > Alpha 2 > Beta
41
Phenylephrine is chemically related to adrenaline but has a slight change in structure, why?
Makes it more resistant to COMT degradation
42
What is phenylephrine used for clinically?
Vasoconstriction (slight hypertension) Mydriatic Nasal decongestant
43
What adrenoceptors is clonidine more selective for?
Alpha 2 > Alpha 1 > Beta
44
What is the effect of clonidine on noradrenaline?
It will stimulate presynaptic alpha 2 receptors which has a negative effect on synthesis and release of noradrenaline
45
What will be the effect of reduced noradrenaline?
Less stimulation at effector organ so less vasoconstriction and fall in TPR and blood pressure
46
What is the effect of clonidine on the brainstem?
Works on baroreceptors in this pathway and reduces sympathetic drive from brain which reduces TPR and reduces amount of noradrenaline
47
What is clonidine used to treat?
Hypertension and migraine
48
Why did clonidine fall out of favour?
It was very effective at reducing hypertension but patients got persistent colds and felt generally under the weather
49
What adrenoceptors is isoprenaline more selective for?
Beta 1 + 2 > Alpha 1 + 2
50
Isoprenaline is chemically similar to adrenaline but has a slight change in structure, what does this cause?
Less susceptible to uptake 1 and MAO breakdown
51
What does this decrease in susceptibility of isoprenaline mean?
It has a much longer plasma half-life (2 hours) than adrenaline so can provide long-term beta stimulation
52
What are the clinical uses of isoprenaline?
Cardiogenic shock Acute heart failure Myocardial infarction
53
What is a problem with isoprenaline?
It drives beta-1 receptors in heart to support heart but will also stimulate beta-2 receptors in VSM which will cause dilation of the blood vessels in the muscles so you get a lot of pooling of blood within the muscles hence you get decreased venous return so via baroreceptors you will get reflex tachycardia
54
What adrenoceptors is dobutamine selective for?
Beta 1 > Beta 2 > Alpha
55
Why is dobutamine better as a treatment for cardiogenic shock than isoprenaline?
It doesn't cause reflex tachycardia because it's selective for beta-1 - it is administered by IV and has a plasma half life of 2 minutes
56
What adrenoceptors is salbutamol selective for?
Beta 2 > Beta 1 > Alpha
57
What is salbutamol (ventolin) most commonly used to treat?
Asthma
58
How does salbutamol treat asthma?
It causes beta-2 mediated relaxation of bronchial smooth muscle and inhibits release of bronchoconstrictor substances from mast cells
59
What effect does using an inhaler have?
Provides a localised effect in the lungs
60
What else is salbutamol used to treat?
Threatened premature labour
61
How does salbutamol prevent threatened premature labour?
Beta 2 mediated relaxation of uterine smooth muscle- prevents abortion of foetus
62
What are the side effects of using salbutamol?
Reflex tachycardia Tremor Blood sugar dysregulation
63
What are the two main indirectly acting SNS agonists?
Cocaine | Tyramine
64
How does cocaine act as an SNS agonist?
Inhibits the uptake 1 mechanism for dopamine and noradrenaline
65
Why does cocaine give you a high?
In the nucleus accumbent (centrally in brain), dopamine is neurotransmitter and cocaine inhibits reuptake of dopamine at uptake 1 site so you get an accumulation of dopamine at the synapse
66
What are the effects of cocaine on the CNS in low doses?
Euphoria, excitement and increased motor activity
67
What are the effects of cocaine on the CNS in high doses?
Activation of chemotactic trigger zones (vomiting), CNS depression, respiratory failure, convulsions and death
68
What are the effects of cocaine on the CVS in low doses?
Tachycardia, vasoconstriction and raised blood pressure
69
What are the effects of cocaine on the CVS in high doses?
Ventricular fibrillation and cardiac arrest
70
What is tyramine and where is it found?
Dietary amino acid that is commonly found in cheese, red wine and soy sauce
71
What does tyramine work as?
A false neurotransmitter
72
What effect does this have on normal people?
None except from stimulating dreams
73
When does a problem occur with tyramine?
If a patient is on MAO inhibitors to control depression
74
How does tyramine act as a false neurotransmitter?
It acts as a weak agonist at effector organ at which noradrenaline will stimulate receptors It also piggy backs on the uptake systems and competes with NA for the uptake 1 site so more NA in synapse Tyramine then gets taken up into vesicles and displaces NA Normally displaced NA will be broken down by MAO but tyramine competes with NA for MAO binding site- less breakdown of NA which leaks out into cleft and there is build up of NA in synaptic cleft
75
What happens with tyramine in patients on MAO inhibitors?
MAO capabilities are completely blocked so NA can't be broken down and this leads to mass build up of NA and will lead to a hypertensive crisis

LCRS Pharmacology and Therapeutics (33 decks)

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