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X Pharmacological Treatment Of Disease > Histamine and Antihistamine > Flashcards

Histamine and Antihistamine Flashcards

1
Q

what chemical mediators are involved in inflammation?

A 
complement
Eicosanoids
Cytokines
histamine
other agents
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2
Q

what role do eicosanoids have in inflammation?

A

eicosanoids -> prostaglandins -> main pathway

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3
Q

what other agents are involved in inflammation?

A

brankinin, platelet activating factors

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4
Q

what is 5-HT involved in?

A

haemostasis

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5
Q

what are leukotrienes involved in?

A

asthma

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6
Q

what are peptide mediators?

A

e.g. bradykinin

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7
Q

what are the 4 cardinal signs of inflammation?

A

dolor - heat
calor - redness
rubor - swelling
tumor - pain

(+ restriction of movement)

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8
Q

what are the most important cardinal signs of inflammation?

A

dalor, calor, rubor - drug targets. blood vessels

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9
Q

what is histamine?

A

a basic amine

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10
Q

where does synthesis of histamine occur?

A

mast cells and circulating basophils

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11
Q

where is histamine stored?

A

in granules in mast cells and circulating basophils

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12
Q

where is histamine found?

A

skin, lungs, face, GI tract and CNS

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13
Q

what complex does histamine occur in?

A

in a complex with heparin

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14
Q

how is histamine synthesised?

A

histidine —deoxycarbolates—> histamine

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15
Q

how is histamine released?

A
  • > degranulation by mass

- > individual mediators

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16
Q

where is histamine metabolised?

A

locally

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17
Q

what is the half life of histamine?

A

~4 mins

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18
Q

what is the mechanism of the metabolism/excretion of histamine?

A

histamine -> Imidazoleacetic acid by Diaminase
oxidase

histamie -> N-methyl histamine by N-methyl transferase
-> N-methyl imidazoleacetic acid by Monoamine oxidase (MAO)

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19
Q

what is Monoamine oxidase (MAO)?

A

breaks down monoamine

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20
Q

what is Monoamine oxidase (MAO) associated with?

A

presynaptic neurone

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21
Q

what kinds of histamine receptors are there?

A

H1
H2
H3
H4

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22
Q

what is the location of H1?

A

Smooth muscle
Endothelium
Brain

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23
Q

what is the location of H2?

A

Gastric mucosa
Cardiac muscle
Mast cells
Brain

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24
Q

what is the location of H3?

A

Presynaptic: Brain
Myenteric plexus
Other neurones

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25
Q

what is the location of H4?

A

Hematopoetic cells

Gastric mucosa

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26
Q

what is the post receptor mechanism of H1?

A

Gq -> ↑IP3 DAG

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27
Q

what is the post receptor mechanism of H2?

A

Gs -> ↑ cAMP

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28
Q

what is the post receptor mechanism of H3?

A

Gi -> ↓ cAMP

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29
Q

what is the post receptor mechanism of H4?

A

Gi -> ↓ cAMP

30
Q

what are the selective antagonists of H1?

A

Mepyramine
Triprolidine
Certirizine

31
Q

what are the selective antagonists of H2?

A

Cimetidine
Ranitidine
Tiotidine

32
Q

what are the selective antagonists of H3?

A

Thioperamide
Iodophenpropit
Impromidine

33
Q

what are the selective antagonists of H4?

A

Tioperamide

34
Q

what is the Triphasic skin response?

A 
• Flush
Red line at site of injury
• Flare
Redness extending around the site
• Wheal
Swelling due to local oedema
35
Q

what is Flush-

Red line at site of injury?

A

liberation of mast cells in the skin

36
Q

what is Flare-

Redness extending around the site?

A

due to vasodilation around site

vasodilators and dilation of sensory nerve -> release vasodilator -> dilation in blood vessel

37
Q

what is Wheal-

Swelling due to local oedema?

A

increased vascular permeability

38
Q

what is the difference in vasculature in normal/acute inflammation?

A

normal - closed precapillary sphincter, most capillaries empty

acute inflammation - open precapillary sphincter, most capillaries full

39
Q

what is the mechanism of increased vascular permeability?

A
  1. endothelial cells contract
  2. separate at their boundaries
  3. basement membrane exposed
  4. gap formed
  5. leakage of fluid and plasma proteins
  6. oedema
40
Q

5 effects of histamine

A
  • vasodilation
  • increased vascular permeability
  • bronchoconstriction
  • mucus secretion
  • itching
41
Q

how does histamine cause a fall in blood pressure?

A

1) histamine -> Vasodilation in microvasculature
-Direct effect via H1 receptors (rapid)
- Indirect effect via H2 receptors (slow)
- Fall in:
• peripheral resistance,
• venous return
• cardiac output
= fall in blood pressure

2) histamine -> Increased permeability in microcirculation
- oedema
-loss of blood volume
=fall in blood pressure

42
Q

how does histamine cause itching?

A

stimulation of nerve endings - H1 receptor mediated

43
Q

what do H1-histamine antagonists cause

A

oedema
itching
fall in blood pressure (so stop the fall in blood pressure)

44
Q

what does the immunological release of histamine involve?

A

Mast cells & basophils
IgE molecules attached
Antigen exposure
=> degranulation.

45
Q

how does an allergen cause inflammation?

A

allergen -> B cell -> release of IgE antibodies -> antibodies bind to mast cell surface -> rexposure to allergen -> Antigen-antibody complex causes degranulation -> histamine and other mediators -> inflammation

46
Q

how can you DISPLACE histamine?

A

basic amines- displace histamine from the
histamine-heparin complex.
e.g. Tubocurarine and Morphine

(Receptors are not involved)
(release is not associated with mast cell damage or degranulation)

47
Q

what is tubocarine?

A

muscle relaxant

48
Q

how can you DEGRANULATE histamine?

A

Compound 48/80, a diamine polymer

specifically releases histamine from mast cells
by exocytotic degranulation

49
Q

what is a physiological antagonist of histamine?

A

adrenaline

50
Q

what are release inhibitors of histamine?

A

Cromolyn

Nedrocromil

51
Q

what are receptor antagonists of histamine?

A

H1:- Mepyramine
H2:- Ranitidine

52
Q

what is the difference between physiological and pharmacological antagonist of histamine?

A

physiological - creating opposing affect

pharmacological - blod H1 receptor

53
Q

what do H1 Antihistamines do?

A

(in vitro):

  • reduce contraction of bronchial smooth muscle by histamine
  • reduce histamine-induced contraction of intestinal and uterine smooth muscle
  • reduce vascular permeability caused by histamine
54
Q

what other receptors do H1 Antihistamines work as antagonists at?

A

muscarinic, 5-HT and alpha-1 adrenoceptors

55
Q

what would be an adverse effect of blocking H1 receptor?

A

sedating -useful to reduce awareness of itching

travel sickness

56
Q

what would be an adverse effect of blocking muscarinic receptor?

A

(muscarinic - parasympathetic)

loss of GI motility - constipation
dry mouth
urinary retention

57
Q

what would be an adverse effect of blocking alpha-1 adrenoreceptor?

A

(vasoconstriction)

so would cause vasodilation

leads to reflex tachycardia, fainting

58
Q

what are the uses of H1 antihistamines in allergic reactions?

  • hay fever
  • Urticaria
  • Insect bites
  • Drug hypersensitivites
A

Histamine = main mediator: H1 antihistamines effective

59
Q

what is the use of H1 antihistamines in asthma?

A

H1 antihistamines not v. effective

60
Q

what is the use of H1 antihistamines in

  • Motion sickness
  • Morning sickness
  • Vertigo
A

Cyclizine, cinnarizine
• Promethazine

Act via CNS H1 receptors.
Antimuscarinic effects may also play a part

61
Q

how do you combat sedation?

A

-blood brain barrier

lipid solubility
molecular size
efflux pumps

62
Q

what are antimuscarinic effects?

A

dry mouth
blurred vision (loss of accommodation)
anti-nausea
antiparkinson

63
Q

2 older antihistamines that produce antimuscarinic effects and sedation?

A

Promethazine, mepyramine

64
Q

what are newer antihistamines?

A

Loratadine, certirizine

65
Q

what is the difference in newer antihistamines than older?

A

Fewer CNS effects - cross BBB only slowly

Negligible antimuscarinic effects

66
Q

what are H2 Receptor Antagonists used for?

A

treatment/prevention of gastric and duodenal ulcers

67
Q

what is an example of an H2 Receptor Antagonist?

A

cimetidine and ranitidine

68
Q

how do H2 Receptor Antagonists affect gastric ulcers?

A

Reduce secretion of gastric acid stimulated by histamine, gastrin, ACh

69
Q

how do H2 Receptor Antagonists affect duodenal ulcers?

A

Promote healing of duodenal ulcers

70
Q

what is the dosage of H2 Receptor Antagonists?

A

Once (ranitidine) or twice (cimetidine) daily

71
Q

how do H2 receptor antagonists work?

A

histamine ->
vagal stimulation ->
cholinomimetics ->
gastrin ->

H2 receptor antagonists block -»»> acid secretion

X Pharmacological Treatment Of Disease (9 decks)

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