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eLCRS - 팜 > PHARM 8: SNS Agonists > Flashcards

PHARM 8: SNS Agonists Flashcards

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?

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

A

clinical uses:

  • vasoconstriction
  • mydriatic
  • nasal decongestant
18
Q

How does Clonidine cause a fall in TPR and BP ?

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?

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 ?

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 …..

A

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

22
Q

list some clinical uses of clonidine

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

What is glaucoma characterized by?

A
  • increase in intraocular pressure
24
Q

What causes glaucoma?

A
  • poor drainage of the aqueous humour
25
Q

What happens in the development of glaucoma?

A
  • 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
Q

Why is adrenaline good for glaucoma?

A
  • 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
Q

give other clinical uses of adrenaline

A
  • cardiogenic shock
  • spinal anaesthaesia
  • local anesthesia
28
Q

Isoprenaline is chemically related to adrenaline but is more resistant to ….

A

Isoprenaline is chemically related to adrenaline but is more resistant to MAO + Uptake 1

29
Q

Give some clinical uses of isoprenaline

A
  • cardiogenic shock
  • acute heart failure
  • myocardial infarction
30
Q

Give some clinical uses of dobutamine

A
  • cariogenic shock

- administration = IV infusion

31
Q

What is the plasma half life of dobutamine?

A

2 mins

32
Q

What is salbutamol?

A
  • synthetic catecholamine derivative with relative resistance to MAO + COMT
33
Q

What are some clinical uses of Salbutamol?

A
  • 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
Q

Why is adrenaline used in the treatment of anaphylaxis?

A
  • reverses effect of histamine
  • b1 effect on heart –> tachycardia
  • B2 on lungs –> bronchodilator
  • a1 –> vasoconstriction
  • beta receptos on mast cells –> surppresses mediator release
35
Q

In what other situations may adrenaline be used?

refer to effects on b1, b2, a1

A

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
Q

How effect does phenylephrine have on the pupil

A
  • bind to a1 receptor on iris and promote pupil dilation

–> mydriatic

37
Q

Why might B2 receptor stimulation by isoprenaline be a problem

A
  • 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
Q

dobutamine better for cardiogenic shock?

A
  • dobutamine = more B1 selective

- so it has less side effect of reflex tachycardia compared to isoprenaline

eLCRS - 팜 (36 decks)

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