Mechanism of action / Targets / Receptors

Question 1

What are the 4 types of signalling molecules?

Answer 1

Neurotransmitters (released at nerve endings) noradrenaline, dopamine
Local hormones (released from cells, local effects) histmine, prostaglandins
Cytokines (chemical messengers in immune system) interferons, interleukins
Hormones (released from glands into the bloodstream) thyroxine, insulin

Question 2

What is the second messenger system?

Answer 2

Ligand-receptor binding causes futher signalling within the cell - causing alteration to cell structure or function
Once a receptor is activated, it can set off a train of events or ‘signals’ that change the function of the cell in some way (e.g., smooth muscle cells contract)

Question 3

What drug types do not have receptor targets?

Answer 3

Osmotic diuretics and antacids

Question 4

Where are molecular drugs targets mainly found?

Answer 4

Cell membrane receptors (major site)
Cell nucleus receptors (prednisone, corticosteroids)
Ion channels (local anesthetics, calcium channel blockers)
Enzymes (ACE inhibitors, COX inhibitors (NSAIDs))
Carrier molecules (transporters) (diuretics, SSRI’s)

Question 5

What are the 2 main mechanisms of cessation of drug effects?

Answer 5

Enzymatic degradation - breaking down of the drug by enzymes (acetylcholine)
Reuptake - of the drug back into the cells from which it was released (serotonin)

Question 6

What are the main receptor subtypes of 
Histamine
Adrenergic (noradrenaline/adrenaline) 
Dopamine
Serotonin

Answer 6

Histamine: 2 main subtypes (H1, H2)
Adrenergic (Noradrenaline/Adrenaline): 2 main subtypes α-, β-, with subfamilies e.g., α1-, β1-, α2-, β2-,
Dopamine: 5 subtypes (D1, D2, D3, D4, D5)
Serotonin (5-hydroxytryptamine): 7 sub-types: 5-HT1 to 5-HT7 with sub-families

Question 7

H1 receptors

Answer 7

located in skin, blood vessels, CNS and bronchi and produce itching, vasodilation, nausea and bronchoconstriction on stimulation
e.g. H1 antagonist = promethazine, cetirizine - reverse or prevent itching, vasodilation, nausea, and bronchoconstriction

Question 8

H2 receptors

Answer 8

located in parietal cells of stomach and produce gastric acid on stimulation
H2 antagonist = e.g., ranitidine would be used to reduce gastric acid secretion in treatment of peptic ulcer etc.

Question 9

5-HT1B and 1D receptors

Answer 9

found in cerebral blood vessels and produce constriction of these vessels on stimulation
5-HT1B and 1D receptor stimulants (agonists) e.g., sumatriptan would be used to prevent dilation of cerebral blood vessels in treatment or prevention of migraine

Question 10

5-HT3 receptors

Answer 10

found in the stomach and chemoreceptor trigger zone (CTZ) and produce emesis when stimulated
e.g., ondansetron would be used to treat or prevent nausea/emesis during chemotherapy

Question 11

Specificity vs selectivity

Answer 11

Selectivity – broadly selective – such as effecting beta agonists – still can spill over into other receptors

Specificity – targeting on particular receptor subtype – less side effects

Question 12

Receptor diversity

Answer 12

The aim to create a drug that targets a specific receptor – minimising unwanted effects and maximising wanted effects