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Pharmacology Yr2 > Drugs and histamine receptors > Flashcards

Drugs and histamine receptors Flashcards

1
Q

By what two methods can histamine act on nearby cells?

A

Paracrine (adjacent cells)

Autocrine (cell that produced the histamine itself)

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2
Q

Name 3 functions of histamine?

A

Principle mediator of allergy and inflammation
- released from cells upon stimulation (mast cells)

Involved in immune responses
- tissue repair, inflammation, control of local blood flow.

Regulating physiological function in the gut (gastric acid secretion). Acts as a neurotransmitter when binding to H2 receptors on parietal cells.

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3
Q

How is histamine metabolised?

A

Formed by decarboxylation of histidine by L-histidine decarboxylase.

Histamine is broken down by histamine-M-methyltransferase or diamine oxidase.

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4
Q

Where is histamine found?

A

All around the body with high concentration in skin, lungs, brain and GI tract.

It is mainly secreted by mast cells and basophils.

It is mainly bound in large cytoplasmic granules with protein and heparin.

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5
Q

What are mast cells?

A

Cells that are normally found in tissues, they are found throughout connective tissue.

They are produced by bone marrow as immature mast cells and mature in tissues.

They have receptors on surface which have high affinity for IgE antibody Fc region.

When IgE antibody is bound to an antigen, mast cells undergo degranulation which leads to massive amount of histamine being released from cytoplasmic granules to outside of the cell to mediate inflammation.

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6
Q

What receptor does IgE Fc region bind to on a mast cell?

A

FceR1

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7
Q

What is the process of mast cell degranulation?

A

Exposure to an allergen causing the production of IgE.

IgE antibodies Fc region binds to FCeR1 receptor on the surface of mast cells.

Then upon second exposure of the antigen it binds to IgE on the surface of mast cells which subsequently causes the movement of cytoplasmic granules towards the cell surface membrane due to an increase in intracellular Ca2+ and then finally degranulation occurs and histamine is released into the extracellular space to mediate acute inflammation.

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8
Q

What other substances can cause a release in histamine?

A

Substance P

Morphine, tubocurarine.

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9
Q

What intracellular signal molecule can cause a decrease in histamine release?

A

cAMP - this is released upon activation of B2 adrenergic receptors.

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10
Q

What is anaphylaxis?

A

A severe allergic reaction of a previously sensitised animal to the same antigen.

Causes large scale degranulation which causes bronchoconstriction, vasodilation, oedema, (due to increase in vascular permeability).

Can cause nausea, abdominal pain, palpitation, hypotension, and can lead to shock (insufficient organ perfusion) if not treated via epipen injection.

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11
Q

How can we treat anaphylaxis just using drugs?

A

Subcutaneous adrenaline

H1 receptor antagonists (chlorphenamine, promethazine)

Glucocorticoids - as they increase the cardiovascular output and decrease the inflammatory response.

  • stop bronchospasm, laryngeal oedema and hypotension
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12
Q

Name two H1 receptor antagonists.

A

Promethazine, Chlorphenamine, Diphenhydramine.

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13
Q

What is the outcome of activation of H1 receptor?

A

Bronchial smooth muscle contraction - bronchoconstriction.

Smooth muscle relaxation - vasodilation

Increased vascular permeability

pain and itching

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14
Q

What are some uses of H1 receptor antagonists?

A

allergy, nausea, vomiting

Sedative

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15
Q

What are some uses of promethazine?

A

Allergic disorders, nausea, vomiting, insomnia, sedation.

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16
Q

What are some uses of diphenhydramine?

A

First generation antihistamine with anticholinergic, antitussive and sedative properties.

17
Q

What is the difference btw 1st and 2nd generation antihistamines?

A

2nd generation has longer duration 12-24 hrs, compared to 4-6hrs.

Less CNS depression (less sedation).

18
Q

Name the 3 second generation antihistamines?

A

Cetirizine
- hay fever, allergies, angioedema, and urticaria.

Loratadine
- allergies

Cinnarizine
- motion sickness and vertigo.

19
Q

What may be a side effect of prolonged use of antihistamine syrups?

A

Erode primary enamel - reversed by using fluoride toothpaste.

20
Q

What is the functions of histamine as a neurotransmitter?

A

Histamine and histidine decarboxylase found in high concentrations in the hypothalamus neurones.

This indicates involvement in the sleep wake cycles

  • arousal
  • sleep
  • circadian rhythm

Histamine is also used as a neurotransmitter in the release of hydrochloric acid from parietal cells when it binds to H2 receptors.

21
Q

How can histamine cause motion sickness?

A

Disagreement btw the visual perceived movement and movement detected by vestibular system.

Activated histaminergic system in the hypothalamus.

Histamine activated H1 receptors in the vestibular nuclei.

Induced vomiting.

22
Q

What is the response due to activation of H2 histamine receptors?

A 
Vasodilation
Smooth muscle relaxation
Gastric acid secretion
Inhibition of antibody and cytokine production
Increase in heart rate.
23
Q

What is the use of H2 antagonists?

A

To reduce acid production to treat excess acid

treatment of gastric ulcers

24
Q

What are 2 H2 antagonists?

A

Cimetidine - used to treat heartburn and peptic ulcers

Ranitidine - used to treat peptic ulcers and gastroesophageal reflux disorder.

25
Q

What intracellular signalling molecules is H2 receptors linked to?

A

Gq - increases cAMP production and PKA activation.

26
Q

Where are H3 histamine receptors located?

A

CNS

27
Q

What is the function of H3 receptors?

A

Regulate production of histamine in the body, inhibiting the synthesis of more histamine.

28
Q

What occurs after the activation of H3 receptors?

A

inhibit synthesis and release of histamine.

it can act as an autoreceptor in presynaptic histaminergic neurones.

or an heteroreceptor in other neurones (a hetero receptor is a receptor which control the release of another neurotransmitter which isnt the same as its ligand.

29
Q

What g protein are H3 receptors linked to?

A

Gi, inhibit cAMP production.

30
Q

What is the result of activation of H4 receptor?

A

Regulated neutrophil release from bone marrow
Mast cell chemotaxis
Mediate eosinophil shape change

31
Q

What G protein is H4 receptors linked to?

A

Gi- cause decrease in cAMP.

32
Q

Where is H4 found?

A

Basophils in bone marrow, thymus, smooth muscle, spleen and colon.

33
Q

Where are H2 receptors found?

A

Parietal cells in gastric mucosa and vascular smooth muscle.

34
Q

Where are H1 receptors found?

A

Smooth muscle, endothelium, CNS

35
Q

What are some uses of H1 receptor antagonists?

A

Allergy, nausea, vomiting

Sedative

36
Q

What are some uses of promethazine?

A

Allergy, nausea, vomiting

Sedative

37
Q

What receptor does IgE Fc region bind to on mast cells?

A

FCeR1

Pharmacology Yr2 (11 decks)

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