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Pharmacology > Receptor theory and Classification of drug action > Flashcards

Receptor theory and Classification of drug action Flashcards

1
Q

What kinds of regularly proteins are involved as primary drug targets? (4)

A
  • receptors
  • enzymes
  • carrier molecules
  • ion channels
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2
Q

What is a receptor?

A

A target molecule through which soluble physiological mediators produce their effects.

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3
Q

What happens when a ligand binds to a receptor?

A

Leads to a ligand-receptor complex which leads to a response.

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4
Q

What are the fastest receptor effects?

A

G protein-coupled receptors

seconds

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5
Q

A minimum —– point attachment of a drug to a receptor site is required.

A

3 point attachment

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6
Q

What type of bonds are irreversible?

A

Covalent bonds - this type of bond formation is rare except in a rather toxic situation.

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7
Q

2 principles of binding studies:

A
  • understand affinity of selected ligands for the receptor of interest
  • analyse the mechanism. of interaction of ligands with the receptor alone, and in combination
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8
Q

3 types of binding studies:

A

kinetic experiments

saturation experiments

competition/modulation experiments

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9
Q

What is radio receptor assay?

A

Measures the binding of drugs to receptor using a tissue preparation

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10
Q

What would be the curve produced from the radio receptor assay?

A
  • total binding
  • non specific binding

allows us to calculate specific binding.

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11
Q

Define Agonist

A

A substance that interacts with a receptor leading to an observer biological response.

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12
Q

Agonist can be endogenous or exogenous, what does this mean?

A

Endogenous - found naturally in the body

Exogenous - administered into the body

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13
Q

Dose-response curve would show…

A

Threshold response - minimum concentration required to produce a response

Ed50 = concentration of the drug that would produce 50%maximum response.

Ceiling - maximum response.

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14
Q

What is a partial agonist?

A

Binds like an agonist but cannot produce the same maximal biological effect, regardless of the dose.

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15
Q

What is an inverse agonist?

A

Binds like an agonist but has a negative effect - like an antagonist.

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16
Q

What is a biased agonist?

A

Not natural substances used in drug development to produce ligands which will produce a favourable cellular response over e.g. side effects.

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17
Q

Define spare receptors

A

receptors which exist in excess to those required to produce a full effect.

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18
Q

Define Intrinsic activity

A

Ability of the agonist to activate the receptor as compared to the maximally active compound - like efficacy.

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19
Q

Define antagonist

A

An antagonist inhibits the effect of an agonist by binding to the same receptor and not producing any effect. Simply blocks.

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20
Q

What types of antagonists are there? (4)

A

Competitive
Non competitive
Allosteric
Physiologic

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21
Q

What is the difference between the competitive vs the non competitive antagonists?

A

Competitive binds to the same site as agonist but is reversible

Noncompetitive is not reversible

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22
Q

Define allosteric antagonists:

A

Antagonists and agonists bind to different sites on the same receptors.

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23
Q

Define physiological antagonists:

A

Two drugs have opposite effects through differing mechanisms. Contradicting.

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24
Q

How to overcome competitive antagonists?

A

Increase the dose of agonist

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25
Q

Can we overcome non-competitive antagonists?

A

No, hence the name.

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26
Q

What happens to the dose response curve of an agonist in the presence of a competitive antagonist?

A

The curve shifts to the right meaning a higher concentration of agonist is needed to produce the response.

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27
Q

What happens to the dose response curve of an agonist in the presence of a non competitive antagonist?

A

The curve shifts to the right but cannot be overcome by increasing the concentration of agonist.

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28
Q

What are the types of allosteric antagonists? How would they look on a curve?

A

Competitive and Non-competitive.

Same as the other antagonists.

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29
Q

Define Heteroreceptors

A

A receptor that regulates the synthesis and/or the release of chemical mediators other than its own ligand.

30
Q

Define Auto-receptor

A

A macromolecule typically found in the nerve ending that regulates the synthesis and/or the release of its own ligand.

31
Q

Receptor down-regulation is..

A

a phenomenon whereby an agonist actually induces a decrease in the number of those receptors available for binding.

32
Q

Receptor up- regulation is…

A

a phenomenon whereby an agonist actually induces an increase in the number of those receptors available for binding.

33
Q

Define affinity

A

the ability of a drug to combine with its receptor.

34
Q

A ligind of low affinity requires..

A

a higher concentration to produce the same effect.

35
Q

A ligand of high affinity requires..

A

a lower concentration to produce the same effect.

36
Q

Efficacy is a measure of the…

A

biochemical or physiological effect which results, following the binding of a drug to its target.

Efficacy is a measure of the maximum effect the drug can produce.

37
Q

Potency refers to..

A

The dose of a drug required to produce a specific effect of given magnitude.

38
Q

Potency is dependent upon…

A

Affinity and Efficacy.

39
Q

More potent means…

A

An effect is achieved at a lower concentration.

40
Q

2 fathers of receptor theory:

A

John Langley

Paul Ehrlich

41
Q

What did John Langley do?

Theory

A

Suggested that there must be a receptive substance causing a response - lead to the drug action.

42
Q

What did Paul Ehrlich do?

Theory

A

Side chain theory of cellular interaction

Immune cells have receptors which allow toxins to bind - the cell would be activated and more receptors produced - released into the bloodstream as antibodies to neutralise the toxin.

43
Q

Occupation Theory

Drug effect is directly proportional to…

A

Drugs act on independent binding sits and activate them - resulting in a biological response.

The response increases when there are more complexes.

Drug effect is directly proportional to the number of receptors occupied (not necessarily true)

44
Q

What did Emil Fischer say?

Theory

A

Lock and Key analogy
lock - enzyme
key - substrate
has to fit like a lock and key.

45
Q

Explain Rate Theory

A

Pharmacological activity is directly proportional to the rate of dissociation and association, not the number of receptors occupied.

46
Q 
Describe 
Agonist
Partial Agonist
Antagonist
in terms of rate theory:
A

Agonist - fast association and dissociation

Partial Agonist - drug with intermediate association and dissociation.

Antagonist- fast association and slow dissociation.

47
Q

Explain Induced-Fit theory

A

Contradicts lock and key.

The receptor alters the conformation of its binding site to produce drug-receptor complex.

48
Q

Explain Macromolecular perturbation theory:

A

When a drug-receptor interaction occurs one of two types is possible:

  • a specific conformational perturbation leads to a response (agonist)
  • a non specific leads to no response (antagonist)
49
Q

Explain Activation-Aggregation theory:

A

A drug receptor (in absence of drug) still exists in an equilibrium between an activated state (bioactive) and an inactivated (bio-inactive)

agonist binds to activated sate

antagonist binds to inactivated state

50
Q

What is the current theory?

A

The two state receptor model

A receptor always exists between the R state (resting) and R* (activated state) which are in equilibrium with each other.

51
Q

Normally when there is no ligand, where is the equilibrium?

A

in the R - resting state.

52
Q

What is a drug?

A

All chemicals other than food that affect living processes.

Can either be a medicine or a poison.

53
Q

How are drugs classified? (3)

A
  • chemotherapeutic agents - used to cure infectious diseases and cancer
  • pharmacodynamic agents - used in non-infectious diseases.

Miscellaneous agents - e.g. anesthetics.

54
Q

Where can drugs interact?

A

Molecular, cellular level

on tissues

on whole systems e.g. CNS

55
Q

Describe Physical mechanisms

A

No chemical reaction or change in cells - just physical effect

56
Q

Describe Chemical mechanisms

A

Drugs act by producing chemical reactions in the body.

57
Q

Describe Drug-Receptor Interaction

A

Drugs act on the cell membrane by physical/chemical interactions - this is through drug receptor sites on membrane.

58
Q

Define Ligands

A

Substances, molecules or compounds which bind with receptors present in the body.

59
Q

Common points between Ligands and Agonists:

A

Coupling of the receptor - the receptor is occupied and causes an effect.

60
Q

Drug binding may be of 2 types…

A

Reversible binding

Irreversible binding

61
Q

What is Desensitization of a receptor?

A

When the maximum response is achieved - the response starts to decrease although agonist still binds.

No one knows the mechanism for this.

62
Q

Explain Drug-enzyme interaction

A

Similar to drug-receptor interactions, but with enzymes.

Activation/inhibition of enzymes.

Combination of drugs with enzyme can be competitive or non-competitive.

63
Q

Explain Drug-channel interactions

A

Drug acts on channels which interferes with the flow of ions e.g. Na+, Cl- channels.

64
Q

Explain Miscellaneous mechanisms

A

Drugs do not act through any of the mechanisms already mentioned.

65
Q

Explain Non-specific interactions

A

Drugs that act physically outside of cells - e.g. neutralisation of stomach acid by antacids.

66
Q

Actions of drugs are..

A

the biochemical physiological mechanism by which the chemical produces a response in living organisms.

67
Q

The effect is…

A

the observable consequence of drug action.

68
Q

Interactions of drugs can lead to.. (4)

A

Additive effect - total effect is sum of effect by both drugs

Antagonist effect

Synergistic - net effect is bigger than the sum of the effects produced.

Cumulative - long term use, and additive effect.

69
Q

Types of effects by drugs: (4)

A

primary effect - desired

secondary - side effects that could be harmful

local effect - only on application

systemic - away from the site of administration e.g. oral.

70
Q

Examples of mode of drug action (2)

A
  • killing or weakening foreign organisms - selective toxicity.
  • stimulation and depression - drugs act by stimulating or depressing normal physiological functions.

Pharmacology (11 decks)

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