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chemo > histamine > Flashcards

histamine Flashcards

1
Q

Lewis triple reaction

A

flush flare wheal

few seconds:
flush
vasodilatory substance rsuch as histamine from cells distrubed by the stimulus

flare: 30 - 60 seconds
neurogenic inflammation
antidromial along collateral branches to release vasodilatory subtances
orthodromially to cause pain sensation.
(sectioning of the central branch will prevent perception of the stimulsus but the falre will continue to cocur until the nerve degenerates )

few minutes:
localised swelling
increased permeability of the endothekium due to histamine

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2
Q

dermatographic urticaria

A

exaggerated triple response
idiopathic
H1 receptor antagonists
omalizumab - monoclonal antibody against IgE

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3
Q

histamine

A

2(1H imidazol-4-yl) ethanamine

made from histidine by histidine decarboxylase

made in: mast cells, basophils, ECL in gut and histaminergic neurons in the brain

= in acidic granules with high molecular wright heparin macroheparin

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4
Q

release of histamine from mast cells

A

C3a, C5a - bind alpha i GPCR, by activates PLC beta

substance P act through Mrgx2 - GPCR alpha q
activate PLC beta

allergen induced igE crosslinking
Fc epsilon I induce phosphorylation fo LAT which activates PLC beta

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5
Q

effects oh histamine

A

H1 - PLC beta - IP3 + DAG - inflammation

H2 - Gs - adenylate cyclase - cAMP, PKA - acid secretion

H3 - Gi - important inhibitory autoreceptor for CNS

H4 - Gi - chemotaxs

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6
Q

H1

A

smooth muscle contraction in ileum bronchioles and uterus

blood vessel dilation - endothelial NO

triple response

itching - activation of distinct sensory nerves - pruritoceptors H1

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7
Q

H2 -

A

HR increase
gastric acid
brain NTS - predominantly H1-3 but also H4

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8
Q

metabolism of histamine

A

histaminase / diamine oxidase:
oxidative deamination to imidazole acetaldehyde

histamine N=methltransferase
methyl group to N of the imidazole ring - Nt - methylhistamine

Both = inactive

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9
Q

pathologies involving histamine

A

allergic reactions - ie rhinitis, urticaria, allergies such as nut allergy, penicillin allergy

responses: swelling, itchiness, nasal congestion. watery eyes, poor coat quality

severe anaphylaxis - throat swells, HR increases and BP drops - need emergency adrenaline treatment

mastocytosis

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10
Q

mastocytosis

A

too many mast cells
heat cold stress infection exercise drugs trigger allerg ylike reaction

gain of function in c-kit/CD117 - R tyr kinase D816V

can be due to tumours or non tumour causes in cas and dogs .

drugs: sodium cromoglycate
omalizumab
imatinib
B2 antag

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11
Q

sodium cromoglycate

A

mast cell stabiliser

treat: mastocytosis, eye drops for hay fever ie Opticrom

occasionally for asthma

but has to be give 4 times a day
does not produce additive effects with corticosteroids

use for asthma replaced by leukotriene receptor antag

mechanism:
inhibit inward Cl- current needed to have low enough MP to enable a substained influxes of EC Ca2+

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12
Q

raise cAMP ( to prevent degranulation of mast cells )

asthma

A

salbutamol and formoterol
9 via beta 2 agonists

theophylline - PDE inhibitors

( some effects only, as main effect is via bronchodilatation )

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13
Q

omalizumab

A

block IgE

decrease mast cell degranulation

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14
Q

H1 antag

A

clasical antihistamines
inflammatory and allergic conditions

mepyramine
terfenadine
fexofenadine

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15
Q

mepyramine

A

1st generation anti-histamine
caused drowsiness as could cross BBB

used in topical creams for treating insect bites.

cold/flu medication to aid sleeping

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16
Q

terfenadine

A

2o generation
cannot cross BBB

increasing evidence of dveelping torsade de points
long QT syndrome
sudden cardiac death

sudden death seem to terfenadine involve Kv11.1 hERG which is important for repolaristaion of the cell

prodrug
to texofenadine
by Cytochrome 450 3A4

conditions of decreased texofenadine = increased risk of death

the enzyme CYP3A4 is inhibited by many drugs ie Bergamottin from grapefruit juice

every new drug now undergoes screening against hERG before going to whole organism trials

17
Q

fexofenadine

loratadine

A

3rd generation
anti histamine
no cardiac side effects
non drowsy

use: hayfever, allergy and urticaria

antihistamines little use in cattles - not part of underlying pathology?

18
Q

adrenaline use

+ co hydrocortisone

A

use for anaphylaxis

relieves bronchospasm

systemic vasodilatation
reduction in tissue perfusion
NA is too compotent a vasoconstrictor would lead to bradycardia reflex

19
Q

Imatinib

A

mastocytosis
FDA approved
only when patient does not have common D816V c-kit mutation ( in kinase domain)

bind TK active site - so the substrate cannot bind

chronic myeloid leukaemia

20
Q

Oclacitinib

A

allergic reaction in dogs - 10%

where H1 antag inefficacious

atopic dermatitis

inhibits JAK ( JAK1 )

lowers pro-inflammatory signalling
( ie il-6–> JAK1,2–>STAT)
acute phase proteins release

alternative to corticosteroids and ciclosporins

21
Q

H2 antag

A

gastric acid secretion inhibitors

act on H2R on parietal cells block histamine from ECL cells

cimetidine - first used
but inhibits cytochrome p450
use taken over by ranitidine

22
Q

proglumide

A

CCK2R inhibitor

directly reduce histamine secretion

23
Q

ranitidine

A

zantac
primary use for gastric ulcers
H2R antag

24
Q

cimetidine

A

first used H2R inhibitor
but inhibits cytochrome p450
use taken over by ranitidine

drug interactions
affects metab of methadone higher BP and greater side effects

hydroxychoroquine - antimalarial

increase toxicity of tricyclic antidepressants

25
Q

omeprazole

A

proton pump inhibitor

can be used on horses

26
Q

antacids

A

gaviscon

neutralise stomach acid

27
Q

cholinergic blockade

vagotomy

A

obsolete use

28
Q

eradication of h.pylori

A

clarithromycin
inhibits 50s of ribosome
inhibits peptidyl transferase activity
interferes with amino acid translocation

H.heilmannii also present

29
Q

arthrotec

A

used for rheumatoid arthritis
NSAID diclofenac + misoprostol

misoprostol can also be given to dogs

30
Q

ways to treat peptic ulcers

A 
CCK2R antag 
H2R antag 
prostaglandin analogue 
vagotomy + anti-AChR ( obsolete) 
proton pump inhibitor 
antacids 
eradication of H.pylori

chemo (7 decks)

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