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BIOL2016 - Pharmacology > Histamine and 5-HT > Flashcards

Histamine and 5-HT Flashcards

(51 cards)

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1
Q

Similarities between histamine and 5-HT

A

biogenic amines
small molecules
local hormones in vasculature and smooth muscle
neurotransmitters

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2
Q

Diseases caused by histamine?

A 
Allergies (H1)
Peptic Ulcers (H2)
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3
Q

pKa of Imidazole ring?

A

5.74

Uncharged at physiological pH

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4
Q

pKa of amino group?

A

9.8

Charged at physiological pH

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5
Q

Where is histidine decarboxylase found?

A

In mast cells, rapidly growing tissues and gastric mucosa cells.

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6
Q

Where is histamine stored?

A

In mast cells.

Lung - 15ug/g tissue
Skin - 5ug/g tissue
Gut - 60ug/g tissue
Stomach - 10ug/g tissue

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7
Q

What does histamine bind to?

A

Heparin (proteoglycan core)

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8
Q

What is in the mast cell granules?

A

Proteolytic enzymes - tryptase and chymase

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9
Q

How do the mast cell granules get released in allergic disease?

A

IgE dependent release
Mast cells bind IgE and when re-exposed, gets crosslinked and the mast cell granules are released.

Allergic disease

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10
Q

How do other stimuli trigger granule release?

A

Bacterial products (LPS) can activate.
Complement peptides can activate.
Specific receptors cause histamine release during bacterial infections

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11
Q

Non specific release of granules?

A

Morphine and tubocurarine.

Released following trauma to tissues.

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12
Q

H1 receptor location?

A

Cardiovascular system
Smooth muscle
Peripheral system

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13
Q

H2 receptor location?

A

Regulates gastric acid secretion in stomach

Increases rate/output of heart

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14
Q

H3 receptor location?

A

CNS

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15
Q

H4 receptor location?

A

Inflammatory cells

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16
Q

Effect of H1 receptors?

A
  1. Increase in vascular permeability at sites of inflammation (proteins escape - swelling)
  2. Vasodilation (redness/heat)
  3. Peripheral nerve stimulation (pain/itch)
  4. Smooth muscle contraction (asthmatics are more susceptible)

Gq -> phospholipase C

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17
Q

Effect of H2 receptors?

A
  1. Increase in release of gastric acid
  2. Regulates cardiac output and rate
  3. Modulates actions of immune cells

Gs

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18
Q

Wheal and flaring?

A

Wheal - swelling

Flaring - red patch

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19
Q

Effect of histamine on bp?

A

Constricts large vessels and dilates small vessels.
Drop in peripheral resistance and bp.
Loss of fluid from capillaries –> circulatory collapse –> anaphylactic shock

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20
Q

H1 antagonists?

A

Mepyramine - drowsiness
Cetrizine - no drowsiness as can’t pass BBB

Treat allergies, sedative action, local anaesthetic actions.

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21
Q

Gastric acid secretion?

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A

Prostaglandins and Histamine have opposing effects on HCl secretion

22
Q

H2 antagonists?

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A

Cimetidine.
Inhibits cytochrome p450 and can retard the metabolism of a range of different drugs.
Widely used to treat the symptoms of gastric ulcers and in reflux oesophagitis.

23
Q

H3 antagonists?

Study These Flashcards
A

Thioperamide
Include control of sleep/wake cycles
Control of food/water intake

24
Q

H3 receptor effects?

Study These Flashcards
A

Release in the brain follows a distinct circadian pattern

25
H4 receptor effects?
Regulate cytokine networks
26
Mast cells & tumours?
Often found with tumours. | Not sure if they facilitate tumour development or if part of the host defence.
27
Mast cells & fetus?
Growing fetus produces lots of histamine
28
Another name for 5-Hydroxytrptamine?
Serotonin
29
Where is 5-HT found?
CNS, GI tract and in platelets
30
Which diseases are linked to 5-HT?
Depression and migraines
31
Where is 5-HT synthesised?
CNS
32
Where is 5-HT stored?
Enterochromaffin cells in gut, 90% of it is stored here
33
5-HT & platelets?
Taken up by platelets as they pass through intestinal circulation and stored in granules - not synthesised
34
How much 5-HT in an avg adult?
10mg
35
Which drugs alter 5-HT levels?
Fenfluramine - appetite supressant depletes CNS levels | Ecstasy - release of 5-HT in CNS followed by tissue levels dropping
36
Carbohydrate diet affects 5-HT?
Boosts levels. Promotes wellbeing and sleepiness.
37
How many 5-HT 1 receptor types?
``` 5, affect cAMP Mainly in CNS Neural inhibition Vasoconstriction Mood & behaviour, thermoregulation, feeding, sleep ```
38
How many 5-HT 2 receptor types?
3, up IP3 and DAG | CNS and periphery
39
How many 5-HT 3 receptor types?
1, internal cationic channel Peripheral NS - evoke pain Brain - vomit reflex
40
5-HT 4-7 types?
up cAMP
41
Most effective migraine drug?
sumatriptan - 5-HT 1D agonist.
42
Methiothepin?
5-HT 1 antagonist on all subtypes
43
LSD?
Agonist at central 5-HT2 receptors Hallucinations. Antagonist at peripheral 5-HT2 receptors
44
5-HT 2 antagonists?
Methysergide | Ketotifen
45
5-HT 3 antagonist?
Ondansetron | Anti-emetic - control severe vomiting and nausea with cancer chemotherapy
46
5-HT 4 receptor?
Found in CNS, main role is regulating GI motility
47
5-HT 4 agonist?
Tegaserod | Relieve IBS
48
5-HT in migraines?
Cause vasoconstriction in cerebral arteries. 5-HIAA found in urine of patients with migraines.
49
5-HT in gut?
Stimulates GI motility directly (2) via smooth muscle receptors and indirectly via (3 and 4) on enteric neurons Stimulates fluid secretion and elicits nausea and vomiting Peristalsis
50
5-HT in circulation?
Can act indirectly via NO release from endothelial cells - inhibits noradrenaline release Injection of 5-HT causes a rise in blood pressure - flushing
51
5-HT in platelets?
2 receptors on platelets, trigger the release of more 5-HT and causing them to become sticky. Platelet plug.

BIOL2016 - Pharmacology (6 decks)

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