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*Y2 LCRS Pharmacology* > SNS Agonists > Flashcards

SNS Agonists Flashcards

1
Q

Where do sympathetic nerves originate?

A

Thoracolumbar region of spinal cord

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2
Q

What do sympathetic post-ganglionic neurones release?

What are the two exceptions?

A

Noradrenaline

A preganglionic sympathetic neurone drives the release of Adrenaline (80%) and Noradrenaline (20%) from the ADRENAL MEDULLA

ACh is released from the post-ganglionic neurone that innovates the sweat glands

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3
Q

What type of receptors are adrenoceptors?

A

G-protein coupled

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4
Q

What are the mechanisms of action of the 4 types of adrenoceptors?

A

Alpha 1 = PLC –> IP3 + DAG

Alpha 2 = DECREASE cAMP

Beta 1 + 2 = INCREASE cAMP

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5
Q

What are directly acting sympathomimetics?

A

They mimic the actions of Adrenaline and NA by stimulating adrenoceptors

Mainly used for their actions in the CVS, eyes, heart and lungs

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6
Q

Which Adrenoceptors are more selective for Adrenaline and NA?

A

ALL adrenoceptors can be activated by NA and A

NORADRENALINE is more selective for ALPHA receptors

ADRENALINE is more selective for BETA receptors

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7
Q

How is synthesis and release of Noradrenaline controlled?

A

by Presynaptic Alpha 2 Receptors

When stimulated, they have a negative effect on synthesis and release

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8
Q

Name five Directly acting SNS agonists and which adrenoceptor they are selective to:

A

Adrenaline - non-selective

Phenylephrine - Alpha 1

Clonidine - Alpha 2

Dobutamine - Beta 1

Salbutamol - Beta 2

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9
Q

Which factor affects selectivity of a drug the most?

A

Concentration - at low concentrations the drug will be relatively selective but at high concentrations, the chance of binding to other receptors increases

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10
Q

Why does a Hypersensitivity reaction cause a fall in blood pressure?

A

Endothelial cells within the membranes of the blood vessels move apart so you get a lot of fluid moving into the tissues
This leads to a fall in circulating fluid volume and hence a fall in blood pressure

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11
Q

What are the symptoms of an Anaphylactic hypersensitivity reaction?

A

Constriction of Bronchial smooth muscle

Constriction of muscles around the throat

Fall in blood pressure

Vomiting and diarrhoea

Collapse of circulatory system leading to unconsciousness

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12
Q

Why is Adrenaline and not NA given in anaphylactic shock?

A

ABC - Airway and breathing need to be considered first before circulation

NA would cause vasoconstriction and increase BP, but Adrenaline acts more on beta receptors than NA which will stimulate bronchodilation and relaxation of throat muscles.

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13
Q

What are the effects of Adrenaline when given during anaphylaxis?

A

Bronchodilation

Relaxation of throat muscles

Tachcardia

Vasoconstriction (via alpha)

Slows release of histamine from mast cells

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14
Q

What processes are mainly controlled by α1 adrenoceptors?

A

α1+++:

Vasoconstriction

Piloerection

Ejaculation

α1++:

Pupil dilation

Constriction of Trigone and sphinctor

α1+:

Gluconeogenesis, lipolysis

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15
Q

What processes are mainly controlled by β1 adrenoceptors?

A

β1 ++:

Increased HR and contractility

Increased renin secretion

Lipolysis

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16
Q

What processes are mainly controlled by β2 adrenoceptors?

A

β2 +++:

Glycogenolysis and Gluconeogenesis

β2 ++:

Vasodilation

β2 +:

Bronchodilation

Relaxes Detrusor

Relaxes Uterus

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17
Q

Name 5 other uses of adrenaline:

A

Asthma emergencies

Acute bronchospasm

Cardiogenic shock

Spinal Anaesthesia

Local Anaesthesia

18
Q

Why is adrenaline used to treat an acute bronchospasm?

A

It causes beta-2 mediated bronchodilation and suppresses mediator release

19
Q

What is Cardiogenic shock and why is adrenaline used to treat it?

A

The sudden inability of the heart to pump sufficient oxygen-rich blood (can be from MI or cardiac arrest)

Adrenaline stimulates HR and contractility via Beta-1 positive ionotropic action

20
Q

How is Adrenaline used in Spinal anaesthesia and why?

A

During spinal anaesthesia, sympathetic output to the peripheral resistance vessels is removed, so they relax and the patient cannot maintain BP

A little bit of adrenaline at the same time will constrict the blood vessels and Bp can be maintained.

21
Q

Why is Adrenaline mixed in with Local anaesthetic?

A

It causes local alpha-1 mediated vasoconstriction which prevents the clearance of the anaesthetic from the area - without it, it would wear off faster

22
Q

What are the main unwanted actions of adrenaline?

A

Reduced and thickened secretions

CVS: Tachycardia, palpitations, arrhythmias, cold extremities, hypertension

Tremor (Skeletal muscle)

23
Q

What can an overdose of adrenaline lead to?

A

Cerebral haemorrhage

Pulmonary embolism

24
Q

What is the selectivity of Phenylephrine?

A

Alpha 1 >> Alpha 2 >>> Beta 1/Beta 2

25
Q

Phenylephrine is chemically similar to Adrenaline - why is this significant to its metabolism?

A

It is more resistant to COMT degradation

(But is not resistant to MAO degradation)

26
Q

What are the clinical uses of Phenylephrine?

A

Vasoconstriction

Mydriatic

Nasal Decongestant

27
Q

What is the selectivity of Clonidine?

A

Alpha 2 >> Alpha 1 >>> Beta 1/Beta 2

28
Q

What is the main route of action of Clonidine?

What is the second route of action of Clonidine?

A

It stimulates the presynaptic alpha 2 receptors - negative effect on synthesis and release of NA

Within the brainstem it works on the baroreceptors in this pathway and reduces the sympathetic drive coming out of the brain. The reduction in sympathetic activity reduces the TPR and it also reduces the amount of noradrenaline released at the nerve terminal thus reducing TPR further

29
Q

What are the clinical uses of Clonidine?

A

Treatment of Hypertension and Migrane

30
Q

What is the selectivity of Isoprenaline?

A

Beta 1 + Beta 2 >>>>>> Alpha 1/Alpha 2

31
Q

How is Isoprenaline different in terms of metabolism to Adrenaline?

A

Less susceptible to Uptake-1 and MAO

Has a much longer half-life than adrenaline so better if you need long term beta stimulation

32
Q

What are the clinical uses of Isoprenaline?

A

Cardiogenic shock

Acute Heart Failure

Myocardial Infarction

33
Q

Why is Isoprenaline not good for patients with Heart failure?

A

It drives Beta-1 receptors to increase HR and Contractility

BUT it will also stimulate Beta-2 in vascular smooth muscle to cause vasodilation in muscles

This gives pooling of blood in the muscles and hence a decreased venous return

Via baroreceptors, you get a reflex tachycardia

Beta-2 stimulation is therefore bad.

34
Q

What is the selectivity of Dobutamine?

A

Beta 1 >> Beta 2 >>> Alpha 1/Alpha 2

35
Q

What is the clinical use for Dobutamine?

A

Treatment of Cardiogenic shock

36
Q

How does the difference in selectivity between Dobutamine and Isoprenaline effect the actions of Dobutamine

A

Because it’s not very Beta-2 selective it doesn’t cause the reflex tachycardia that Isoprenaline does.

37
Q

What is the selectivity of Salbutamol?

A

Beta 2 >> Beta 1 >>> Alpha 1/Alpha 2

38
Q

What is Salbutamol?

(what is it resistant to?)

A

Synthetic catecholamine derivative with relative resistance to MAO and COMT

39
Q

What is Salbutamol used to treat and how?

A

Asthma

Beta-2 mediated relaxation of bronchial smooth muscle

Inhibition of release of bronchoconstrictor substances from mast cells

40
Q

What is the second clinical use of Salbutamol?

A

Threatened premature labour:

Beta-2 mediated relaxation of uterine smooth muscle

41
Q

What are the side effects of Salbutamol?

When is it therefore contraindicated?

A

Reflex tachycardia

Tremor

Blood sugar dysregulation - Unsuitable for diabetic patients

*Y2 LCRS Pharmacology* (20 decks)

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