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eLCRS - 팜 > PHARM 8: SNS Agonists > Flashcards

PHARM 8: SNS Agonists Flashcards

(38 cards)

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1
Q

briefly go over the mechanism of action of adrenoceptor a1

A

a1 = PLC –> IP3 + DAG

a1 –> causes vasoconstriction

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2
Q

briefly go over the mechanism of action of adrenoceptor a2

A

a2 = decrease cAMP

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3
Q

briefly go over the mechanism of action of adrenoceptor b1 + b2

A

b1 + b2 = Increase cAMP

b1 –> increase HR + contractility

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4
Q

What is meant by directly acting?

A

Directly acting = mimics the actions of A + NA

- through stimulating adrenoceptors

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5
Q

Compare between selectivity for NA and A

A

NA
more alpha selective

A
more beta selective

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6
Q

Describe metabolism of NA

A
  • using tyrosine hydroxylase, tyrosine from diet = converted to DOPA
  • DOPA = then converted to dopamine
  • dopamine = converted to NA
  • then uptake of NA occurs –> into nerve terminal itself / extra neuronal tissue
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7
Q

What is the significance of Presynaptic Alpha 2 Receptors ?

A

–> has negative effect on synthesis / release of NA

  • if conc of NA = high, stimulates presynaptic alpha 2 receptors
  • -> which reduces NA synthesis + release

NOTE: NA binds to presynaptic a2 –> which interferes with NA exocytosis
- controls secretion of NA

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8
Q

List some directly acting SNS agonists

A
  • Adrenaline - non-selective
  • Phenylephrine - Alpha 1
  • Clonidine - Alpha 2
  • Dobutamine - Beta 1
  • Salbutamol - Beta 2
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9
Q

describe how selectivity depends on concentration for directly acting SNS agonists

A

at low conc, drugs will be relatively selective –> but when you increase conc chance of binding to other receptors increases

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10
Q

Describe the onset of hypersensitivity reactions

A

1st exposure –> antibodies to antigen = generated

  • these antibodies circulate around the body
  • and binds to mast cells

on next exposure:
- mast cells = already primed with antibody on their surface
SO
- antigen cross links antibodies on mast cells
–> then you get massive release of mediators

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11
Q

List some symptoms of hypersensitivity

A
  • endothelial cells in blood vessel memb moves apart –> more fluid moves into tissues –> circulating fluid volume falls –> BP falls
  • anaphylactic shock
  • bronchial smooth muscle contraction
  • vomiting + diarrhea –> as GI tract smooth muscle constricts
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12
Q

Why is adrenaline more effective than NA as treatment for anaphylaxis?

A

A acts more on beta receptors than NA
–> which stimulates bronchodilation + relaxation of throat muscles –> helps breathing (V IMPORTANT)

  • A also stimulates alpha receptors –> vasoconstriction
  • A also slows down histamine release from mast cells (via beta 2 receptors)
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13
Q

What are some unwanted actions of adrenaline?

A
  • REDUCED + THICKENED MUCOUS
  • CVS EFFECTS
  • -> tachycardia, palpitation, hypertension, pulmonary oedema etc.
  • TREMOR
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14
Q

Phenylephrine

selective for =
resistant to =

A
  • very alpha 1 selective
  • most similar to adrenaline
  • resistant to metabolism by COMT (lasts longer in the system)
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15
Q

Phenylephrine is chemically related to adrenaline.

but it is resistant to _______

A

Phenylephrine is chemically related to adrenaline.
but it is resistant to COMT

note: but not MAO

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16
Q

Why might phenylephrine be used as a decongestant?

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A
  • inflammation in nasal sinus
  • congestion –> fluid leakage from blood vessel
  • vasoconstriction through a1 agonist
  • less leakage of fluid through the blood vessels
17
Q

list some clinical uses of phenylephrine

Study These Flashcards
A

clinical uses:

  • vasoconstriction
  • mydriatic
  • nasal decongestant
18
Q

How does Clonidine cause a fall in TPR and BP ?

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A
  • clonidine stimulates presynaptic alpha 2 receptors
  • -> which has negative effect on NA synthesis + release
  • less NA release –> less stimulation at effector organ
  • so less vasoconstriction –> fall in TPR + BP

–> causes reduced sympathetic effect

19
Q

What is the action of clonidine on the brainstem?

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A
  • clonidine works on baroreceptors on brainstem –> reduces sympathetic drive coming out of brain

–> less NA released –> TPR reduced

20
Q

What are the 2 routes of action for clonidine ?

Study These Flashcards
A
  1. stimulates presynaptic alpha 2 receptors –> so less NA released
  2. acts on baroreceptors on brainstem –> reduces sympathetic drive –> less NA release
21
Q

NA usually binds to Beta 1 receptors in the kidneys and …..

Study These Flashcards
A

NA usually binds to Beta 1 receptors in the kidneys and stimulates renin release

22
Q

list some clinical uses of clonidine

Study These Flashcards
A
  • hypertension treatment
  • migraine treatment
  • -> vasodilation of blood vessels to the brain
23
Q

What is glaucoma characterized by?

Study These Flashcards
A
  • increase in intraocular pressure
24
Q

What causes glaucoma?

Study These Flashcards
A
  • poor drainage of the aqueous humour
25
What happens in the development of glaucoma?
- ciliary body produces aqueous humour - which flows out into anterior chamber of eye - gets drained through canals of schlemm - if poor drainage of the aqueous humour - increase in intraocular pressure -b1 facilitates the production of aqueous humor b2 inhibits production of aqueous humour a1 - causes vasoconstriction of blood vessels that deliver the humour a2 - causes decrease in humour formation
26
Why is adrenaline good for glaucoma?
- alpha receptors on blood vessels in ciliary body - beta receptors controls enzyme that makes aq humour ADRENALINE: - stimulates alpha receptors in vessels within ciliary body - -> causes vasoconstriction so less blood = delivered to ciliary body - production of aq humour = reduced
27
give other clinical uses of adrenaline
- cardiogenic shock - spinal anaesthaesia - local anesthesia
28
Isoprenaline is chemically related to adrenaline but is more resistant to ....
Isoprenaline is chemically related to adrenaline but is more resistant to MAO + Uptake 1
29
Give some clinical uses of isoprenaline
- cardiogenic shock - acute heart failure - myocardial infarction
30
Give some clinical uses of dobutamine
- cariogenic shock | - administration = IV infusion
31
What is the plasma half life of dobutamine?
2 mins
32
What is salbutamol?
- synthetic catecholamine derivative with relative resistance to MAO + COMT
33
What are some clinical uses of Salbutamol?
- treatment of asthma - -> causes B2-relaxation of bronchial smooth muscle - -> inhibits release of bronchoconstrictor substances from mast cells - treatment of threatened premature labour - -> causes B2-relaxation of uterine smooth muscle
34
Why is adrenaline used in the treatment of anaphylaxis?
- reverses effect of histamine - b1 effect on heart --> tachycardia - B2 on lungs --> bronchodilator - a1 --> vasoconstriction - beta receptos on mast cells --> surppresses mediator release
35
In what other situations may adrenaline be used? refer to effects on b1, b2, a1
b2 - airway mediator release - for asthma - acute bronchospasm b1 - for inotropic effects - e.g cariogenic shock a1 - for spinal anesthesia --> to maintain BP - for local anesthesia --> to keep drug in area for longer - reduce blood flow to the particular region --> so less likely for drug to be washed away from an area
36
How effect does phenylephrine have on the pupil
- bind to a1 receptor on iris and promote pupil dilation --> mydriatic
37
Why might B2 receptor stimulation by isoprenaline be a problem
- b2 receptors are in vascular smooth muscle in the skeletal muscle - vasodilation occurs - -> causing fall in BP - baroreceptors respond to this - and sends signal back to heart - to increase HR - you want normal cardiac output - but you interfere with rate generation --> less rhythmical contractions - which can leads to cariogenic shock SUMMARY = to treat cardiogenic shock - you want a normal CO --> but if you give isoprenaline --> then you get reflex tachycardia which interferes with the stable rate generation
38
dobutamine better for cardiogenic shock?
- dobutamine = more B1 selective | - so it has less side effect of reflex tachycardia compared to isoprenaline

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