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Year 2 - LCRS - Pharmacology > SNS agonists > Flashcards

SNS agonists Flashcards

14.10.2019

1
Q

What intracellular actions happen at alpha1, alpha 2, beta1 and beta2?

A

Alpha-1: PLC, IP3, DAG
Alpha-2: decrease in cAMP
Beta-1: increase in cAMP
Beta-2: increase in cAMP

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2
Q

Where are adrenoreceptors found?

A
  • at effector organs in the SNS
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3
Q

Relative selectivity SNS agonists

A

All Adrenoreceptors can be activated by A and NA.

  • Selectivity for A: b1 = b2 > a1 = a2
  • Selectivity for NA: a1 = a2 > b1 = b2
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4
Q

Heart

A

Beta-1 tissue

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5
Q

Lungs

A

Beta-2 tissue

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6
Q

Blood Vessles

A

Alpha-1 tissue

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7
Q

Noradrenaline Metabolism

A

1) Tyrosine -> DOPA (via tyrosine hydroxylase)
2) DOPA -> Dopamine (via DOPA decarboxylase)
3) Dopamine enters vesicle
4) Dopamine -> NA (via dopamine beta hydroxylase)
5) exocytosis

  • NA binding to Alpha 2 receptor (prejunctional receptor)
    • > controls its own secretion
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8
Q

Directly Acting SNS agonists

A
  • Adrenaline (non-selective)
  • Phenylephrine (a1)
  • Clonidine (a2)
  • Dobutamine (b1)
  • Salbutamol (b2)
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9
Q

How does NA control its own secretion?

A
  • alpha-2 receptor on presynaptic cell

- NA binding negatively feeds back on NA release

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10
Q

Name a non-specific SNS agonist

A

Adrenaline (e.g. epi-pen)

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11
Q

Why is adrenaline used in the treatment of anaphylaxis?

A

b2 – broncho dilation
b1 – tachycardia
a1 – vasoconstriction

  • suppression of mediator release
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12
Q

What are the effects on alpha 2 receptors?

A
  • suppresses the release of NA (neg. feedback)
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13
Q

What are other clinical uses of Adrenaline?

A
  • Asthma (i.m. or s.c. in emergencies) beta-2
  • Acute bronchospasm (ass. with chronic bronchitis or emphysema) beta-2 mediator release
  • cariogenic shock - sudden inability of the heart to pump sufficient O2 rich blood (beta-1 inotropic effect)
  • spinal anaesthesia (alpha 1 maintains BP)
  • local anaesthesia (alpha 1 vasoconstrictor - prolongs action)
  • anaphylactic shock
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14
Q

What are some unwanted effects of adrenaline?

A

Secretions – reduced and thickened mucous

  • CNS – minimal
  • CVS effects
    • tachycardia, palpitations, arrhythmias
    • cold extremities, hypertension
    • overdose – cerebral haemorrhage,pulmonaryoedema
  • GIT – minimal
  • Skeletal muscle - tremor
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15
Q

Name an alpha-1 specific agonist?

A

Phenylephrine

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16
Q

Selectivity of phenylephrine

A

a1&raquo_space; a2&raquo_space;> b1/b2

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17
Q

Why might phenylephrine be used as an anticongestant?

A
  • e.g. sudafed or lemsip

- vasoconstriction: less white cell infiltration, less fluid exudation

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18
Q

Properties of phenylephrine

A
  • chemically related to adrenaline
  • more resistant to COMT but not MAO
  • clinical use as a decongestant
  • Mydriatic (induces pupil dilation)
  • vasoconstriction
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19
Q

Name an a2 selective SNS agonist

A

Clonidine

20
Q

Selectivity of Clonidine

A

a2&raquo_space; a1&raquo_space;> b1/b2

21
Q

What are the clinical uses of clonidine?

A
  • Treatment of hypertension and migraine
  • Reduces sympathetic tone
    • a2 adrenoceptor mediated
    • presynaptic inhibition of NA release
      -Central action in brainstem within baroreceptor
      pathway to reduce sympathetic outflow.
  • Glaucoma
22
Q

Properties of clonidine

A
  • agonist, however acts like an antagonist because a2 receptor suppresses release of NA
  • a2 selective
23
Q

What is glaucoma?

A
  • raised intraocular pressure in the anterior chamber of the eye
24
Q

What causes glaucoma?

A
  • poor drainage of aqueous humour

- If untreated, it permanently damages the optic nerve, blindness.

25
Q

What produces the aqueous humour in the eye?

A
  • the cilary body
26
Q

Why are sympathomimetics used in Glaucoma?

A

Think about the receptors on the ciliary body:

  • a1: vasoconstricton -> effective for glaucoma because restricted blood flow -> restricted humour production
  • a2: negative feedback, interferes with beta function
27
Q

What is the difference between blood vessel control in the brain and in other parts of the body?

A
  • body: predominantly alpha-1 controlled, vasoconstriction

- brain: predominantly beta-2 controlled, vasodilation (associated with increased blood flow)

28
Q

Isoprenaline

A
  • beta selective but not for b1 or 2
  • chemically related to adrenaline
  • more resistant to MAO and uptake 1
29
Q

Selectivity of Isoprenaline

A

b1 = b2&raquo_space;» a1/a2

30
Q

Clinical use of isoprenaline

A
  • cariogenic shock
  • MI
  • acute HF
31
Q

What do you have to be careful about earn giving beta2 receptor agonists?

A

Caution - b2-stimulation in vascular smooth muscle in skeletal muscle results in fall in venous blood pressure which triggers a reflex tachycardia via the stimulation of baroreceptors.

massive vasodilation + reflex tachycardia

32
Q

Dobutamine selectivity

A

b1&raquo_space; b2&raquo_space;> a1/a2

33
Q

Name a b1 selective agonist

A

Dobutamine

34
Q

What are the properties of dobutamine?

A
  • short acting
  • lacks isoprenaline’s reflex tachycardia
  • plasma half life is 2 minutes (rapid metabolism by COMT)
35
Q

What are the clinical uses of Dobutamine?

A
  • Cardiogenic shock
  • Lacks isoprenaline’s reflex tachycardia
  • Plasma half life 2 minutes (rapidly metabolised by COMT)
36
Q

Name a beta-2 selective agonist

A

Salbutamol (ventolin)

37
Q

Selectivity of Salbutamol (Ventolin)

A

b2&raquo_space; b1&raquo_space;> a1/a2

38
Q

What are the properties of salbutamol?

A
  • Synthetic catecholamine derivative with relative resistance to MAO and COMT
  • more resistant to breakdown!!
39
Q

What are the clinical uses of salbutamol?

A
  • Treatment of Asthma
    • b2-relaxation of bronchial smooth muscle
    • inhibition of release of brochoconstrictor substances
      from mast cells.
  • Treatment of threatened premature labour
    • b2-relaxation of uterine smooth muscle
      Side effects- Reflex tachycardia, Tremor, blood sugar dysregulation
40
Q

Which ventilators are salbutamol?

A

the blue ones

41
Q

How does salbutamol cause dilation of airways?

A
  • inhalation
  • binds to b2R
  • increase in ic cAMP
  • almost hyperpolarisation
  • K+ efflux
  • relaxation of the muscle
  • dilation of airways -> breathing is easier
42
Q

How does adrenaline help in anaphylactic shock?

A
  • it produces the opposite effect of that of histamine
    = physiological antagonism
  • effects like bronchodilation, tachycardia, vasoconstriction
43
Q

Which enzyme converts dopamine to NA?

A

dopamine beta hydroxylase

44
Q

Directly acting SNS agonists

A

APCDS

Adrenaline (non-selective)
Phenylephrine (a1)
Clonidine (a2)
Dobutamine (b1)
Salbutamol (b2)
45
Q

What happens during anaphylaxis?

A
  • IgE coated mast cells
  • degranulation and release of inflammatory mediators

a) heart and vasculature: increased capillary permeability, entry of fluid into tissues, swelling of tissues incl. tongue, fall in BP, reduced O2 to tissues, irregular heart beat, anaphylactic shock, loss of conciusness
b) resp: contraction of SM and constriction of throat and airways; difficulty swallowing; difficulty breathing wheezing;
c) GIT: contraction of SM, cramps, vomiting, fluid outflow into gut, diarrhoea.

46
Q

Clinical use of phenylephrine

A
  • nasal decongestant
  • mydriatic
  • vasoconstriction

Year 2 - LCRS - Pharmacology (34 decks)

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