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Year 2 - Pharmacology and Therapeutics > SNS Agonists > Flashcards

SNS Agonists Flashcards

1
Q

Difference between adrenoceptors, nicotinic and muscarinic drugs?

A

Do NOT really have specific GBDs or MRAs

BUT

DO HAVE selective adrenoceptor drugs

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2
Q

How do Alpha-1 and 2 work?

A

Alpha-1:
x PLC, IP3 & DAG

Alpha-2:
x DOWNREGULATES cAMP

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3
Q

How do Beta-1 and 2 work?

A

BOTH:

UPREGULATE cAMP

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4
Q

How do SNS agonists work?

A

Mimic actions of NA/A by binding to and stimulating adrenoceptors (GPCRs)

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5
Q

Where do SNS agonists primarily work?

A

CVS
Eyes
Lungs

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6
Q

What are all adrenoceptors activated by?

A

Either by NA or A

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7
Q

What are the adrenoceptor selectivity for NA?

A

Alpha1/2 > Beta1/2

can act on ALL just slightly more selective for ALPHA

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8
Q

What are the adrenoceptor selectivity for A?

A

Beta1/2 > Alpha1/2

can act on ALL just slightly more selective for BETA

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9
Q

Where are NA and A synthesised?

A

NA - made in NERVE TERMINALS

A - made in ADRENAL MEDULLA

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10
Q

NA biosynthesis?

A

Tyr –> DOPA –> DA –> NA

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11
Q

What controls NA biosynthesis?

A

x Transport proteins (either into tissue or back into axon)

x Alpha 2!!

NA bind to these prejunctional receptors, negatively feedbacking on NA exocytosis

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12
Q

5 DIRECTLY acting SNS Agonists?

A
  1. Adrenaline (non-selective)
  2. Phenylephrine (alpha 1)
  3. Clonidine (alpha 2)
  4. Dobutamine (beta 1)
  5. Salbutamol (beta 2)
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13
Q

3 main areas that A acts on as a SNS agonist?

A
  1. Anaphylaxis
  2. COPD
  3. Glaucoma
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14
Q

Why is A used in the treatment of anaphylaxis (hint: adrenoceptors)?

A

Beta 2 = bronchoDILATION (airways, breathing)

o Histamine causes the blocking of airways so beta 2 just antagonises this = PHYSIOLOGICAL ANTAGONISM

Beta 1 = TACHYcardia (reduced chonotropic & ionotropic effect)

o Has massive HYPOTENSION so speeds it up

Alpha 1 = vasoCONSTRICTION (peripheral vasodilation)

o Combats HYPOTENSION caused by histamine

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15
Q

What other effects does A have on anaphylaxis?

A

o Suppresses mediator release - as also have beta-receptors on mast-cells

o Reduces stomach cramps - relaxing effect on the guy

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16
Q

Why is A more important than NA in anaphylaxis?

A

A has a GREATER SELECTIVITY for beta-receptors which are more important in being triggered for this

So in epi-pens have A!

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17
Q

A as a SNS agonist for COPD?

A

Used in asthma (emergency so I.M or S.C)

o Beta 2 - causes bronchoDILATION
o Suppresses mediator release

18
Q

Is A the best choice as a SNS agonist for COPD?

A

NO - a selective beta-2 agonist is preferable

19
Q

A as a SNS agonist for glaucoma?

A

Increases IOP - alpha 1 receptors (vasoconstriction)

Vasoconstriction of ocular blood vessels = restricts blood flow = limits production of aq. humour

20
Q

Other uses of A as a SNS agonist?

A

o Cardiogenic shock - use beta-1

o Spinal anaesthesia - maintain BP keeps TPR & BP UP (maintaining it)

o Local anaesthesia - vasoconstricts = prolong action (as constrict b.v in region so anaesthesia cannot diffuse into blood and systemic and remains in desired region)

21
Q

Unwanted effects of A as a SNS agonist?

A

o Secretions - reduced & thickened

o CNS - minimal

o CVS - tachycardia/palpitations/arrhythmias
cold extremities/hypertension
overdose - cerebral haemorrhage, pulmonary oedema

o GIT - minimal

o Skeletal muscle - tremor

22
Q

Phenylephrine?

A

ALPHA 1 selective!!

Alpha 1&raquo_space; alpha 2&raquo_space;> beta 1/2

23
Q

Property of Phenylephrine?

A

Chemically related to A

BUT

o MORE RESISTANT to COMT [peripheral enzyme] (more resistant to breakdown)

o BUT NOT to MAO [central enzyme]

So longer-lasting as a peripheral agent as not broken-down as easily

24
Q

Clinical uses of Phenylephrine?

A

Decongestant! (as most alpha 1 action is ability to vasoconstrict)

o Vasoconstriction
o Mydriatic (pupil dilation)
o Nasal decongestant (vasoconstrict = less WBC accumulate = less mucous)
25
Q

Clonidine?

A

ALPHA 2 selective!!

Alpha2&raquo_space; alpha1&raquo_space;> beta1/2

26
Q

Property of Clonidine?

A

Mainly acts on the prejunctional neuronal alpha-2 receptor to
INHIBIT NA release

i.e. get ANTI-SN response

27
Q

Clinical uses of Clonidine?

A

o Hypertension & migrane

o Reduces SN tone:

  • alpha-2 adrenoceptor mediated
  • central brainstem action within baroreceptor pathway to REDUCE SN outflow
28
Q

Why are the vessels in the brain predominantly beta-2 controlled but rest of body vessles in alpha-1?

A

In brain do NOT want the vessels to be vasoconstricted!

29
Q

Glaucoma - which adrenoceptors do the ciliary bodies (produce aqueous humour) have?

A

Alpha 1
Alpha 2
Beta 1

30
Q

Which adrenoceptors on the ciliary body would you want to agonise to combat glaucoma?

A

Alpha 1 (BEST!) & 2

o BETA 1
- would get MORE A.H production so do NOT want this as would only INCREASE IOP further

o ALPHA 2
- interferes w. beta-1 function as LESS NA released so would want this

o ALPHA 1
- caused vasoconstriction, reducing blood flow to region = ciliary body needs blood flow to produce A.H so inhibit this

31
Q

Isoprenaline?

A

BETA SELECTIVE!!

Beta 1 = beta 2&raquo_space;»> alpha 1/2

32
Q

Property of Isoprenaline?

A

Chemically related to A

BUT

o MORE RESISTANT to MAO & uptake 1

o Plasma half-life of 2 hours (very fast!)

33
Q

Clinical uses of Isoprenaline?

A

Primarily for its CVS actions - as tries to activate BETA-1

o Cardiogenic shock
o Acute heart failure
o MI

34
Q

Why might beta-2 stimulation be a problem when using Isoprenaline?

A

Beta 2 stimulation in the VASCULAR SM in skeletal muscles causes huge vasoDILATION:

o triggers FALL in VENOUS BP = triggers reflex tachycardia via. stimulation of baroceptors

35
Q

What drug is now used in place of Isoprenaline and why?

A

Dobutamine!

o Lacks Isoprenaline’s reflex tachycardia (as selective for beta 1)
o Plasma half-life of 2 minutes (rapidly metabolised by COMT)

36
Q

Dobutamine?

A

BETA 1 selective!!

Beta 1&raquo_space; Beta 2&raquo_space;» Alpha 1/2

37
Q

Salbutamol?

A

BETA 2 selective!!

Beta 2&raquo_space; Beta 1&raquo_space;» Alpha 1/2

38
Q

Property of Salbutamol?

A

o Synthetic catecholamine derivative

o Relative resistance to MAO & COMT

39
Q

Clinical uses of Salbutamol?

A

o Treating Asthma

  • Beta-2 = bronchodilation
  • Inhibits release of bronchoconstrictor substances from mast cells

o Treatment of threatened pre-mature labour
- Beta-2 = relaxes uterine SM

40
Q

Issues with Salbutamol?

A

o Reflex tachycardia

o Tremor
o Blood sugar dysregulation

Year 2 - Pharmacology and Therapeutics (9 decks)

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