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BIOL2016 - Pharmacology > Histamine and 5-HT > Flashcards

Histamine and 5-HT Flashcards

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?

A

Prostaglandins and Histamine have opposing effects on HCl secretion

22
Q

H2 antagonists?

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?

A

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

24
Q

H3 receptor effects?

A

Release in the brain follows a distinct circadian pattern

25
Q

H4 receptor effects?

A

Regulate cytokine networks

26
Q

Mast cells & tumours?

A

Often found with tumours.

Not sure if they facilitate tumour development or if part of the host defence.

27
Q

Mast cells & fetus?

A

Growing fetus produces lots of histamine

28
Q

Another name for 5-Hydroxytrptamine?

A

Serotonin

29
Q

Where is 5-HT found?

A

CNS, GI tract and in platelets

30
Q

Which diseases are linked to 5-HT?

A

Depression and migraines

31
Q

Where is 5-HT synthesised?

A

CNS

32
Q

Where is 5-HT stored?

A

Enterochromaffin cells in gut, 90% of it is stored here

33
Q

5-HT & platelets?

A

Taken up by platelets as they pass through intestinal circulation and stored in granules - not synthesised

34
Q

How much 5-HT in an avg adult?

A

10mg

35
Q

Which drugs alter 5-HT levels?

A

Fenfluramine - appetite supressant depletes CNS levels

Ecstasy - release of 5-HT in CNS followed by tissue levels dropping

36
Q

Carbohydrate diet affects 5-HT?

A

Boosts levels. Promotes wellbeing and sleepiness.

37
Q

How many 5-HT 1 receptor types?

A 
5, affect cAMP
Mainly in CNS
Neural inhibition
Vasoconstriction
Mood & behaviour, thermoregulation, feeding, sleep
38
Q

How many 5-HT 2 receptor types?

A

3, up IP3 and DAG

CNS and periphery

39
Q

How many 5-HT 3 receptor types?

A

1, internal cationic channel
Peripheral NS - evoke pain
Brain - vomit reflex

40
Q

5-HT 4-7 types?

A

up cAMP

41
Q

Most effective migraine drug?

A

sumatriptan - 5-HT 1D agonist.

42
Q

Methiothepin?

A

5-HT 1 antagonist on all subtypes

43
Q

LSD?

A

Agonist at central 5-HT2 receptors
Hallucinations.

Antagonist at peripheral 5-HT2 receptors

44
Q

5-HT 2 antagonists?

A

Methysergide

Ketotifen

45
Q

5-HT 3 antagonist?

A

Ondansetron

Anti-emetic - control severe vomiting and nausea with cancer chemotherapy

46
Q

5-HT 4 receptor?

A

Found in CNS, main role is regulating GI motility

47
Q

5-HT 4 agonist?

A

Tegaserod

Relieve IBS

48
Q

5-HT in migraines?

A

Cause vasoconstriction in cerebral arteries. 5-HIAA found in urine of patients with migraines.

49
Q

5-HT in gut?

A

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
Q

5-HT in circulation?

A

Can act indirectly via NO release from endothelial cells - inhibits noradrenaline release
Injection of 5-HT causes a rise in blood pressure - flushing

51
Q

5-HT in platelets?

A

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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