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Drugs: Molecules To Man > Agonists To Antagonists > Flashcards

Agonists To Antagonists Flashcards

(43 cards)

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1
Q

What type of receptors are dopamine receptors?

A

GPCRs

GPCRs stands for G-Protein Coupled Receptors.

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2
Q

What condition is associated with lost dopamine receptor function?

A

Parkinson’s Disease

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3
Q

What effect would an agonist have in Parkinson’s Disease?

A

Improve function

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4
Q

In schizophrenia, dopamine receptors are __________.

A

Overactive

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5
Q

What effect would an antagonist have in schizophrenia?

A

Improve function

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6
Q

What happens at very high doses of an agonist in Parkinson’s Disease?

A

Schizophrenia-like symptoms

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7
Q

What happens at very high doses of an antagonist in schizophrenia?

A

PD-like symptoms

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8
Q

What do agonists do?

A

Activate receptors

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9
Q

What are the two conformations of a receptor?

A

Resting = usually predominates

Active = this state is less stable

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10
Q

What assay is used to measure cAMP levels in β1 adrenoceptor cell lines?

A

cAMP assay

Known as concentration-effect or concentration-response curve

Has a rectangular hyperbola shape

Drug concentration on the X axis and cAMP concentration on the Y axis

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11
Q

What does Emax represent?

A

Maximal effect

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12
Q

What does EC50 measure?

A

Potency —> concentration or dose of drug required to produce a specific effect

Effect is 50% of maximum effect

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13
Q

EC50 is defined as the concentration of agonist giving __________ of Emax.

A

50%

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14
Q

What is pEC50?

A

-log EC50

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15
Q

What is the relationship between Emax and Bmax?

A

Emax is directly related to Bmax

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16
Q

What factors influence the values of EC50 and Emax?

A
  • Ratio of receptors to G-protein
  • Number of G proteins receptor activates
  • Ratio of G protein to target enzyme
  • Stability of product (cAMP broken down by PDE)
  • Events downstream of cAMP
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17
Q

As EC50 goes down, what happens to potency?

A

Potency goes up

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18
Q

What is efficacy in pharmacology?

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A

How well a drug activates a receptor once bound

19
Q

What is the difference between a full agonist and a partial agonist?

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A
  • Full agonist: 100% efficacy
  • Partial agonist: <100% efficacy where lower percentage is weak
20
Q

What is the functional Gaddum equation used for?

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A

Predicting surmountable antagonism

21
Q

What characterizes a competitive antagonist?

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A
  • No change in maximum response
  • Increase in apparent EC50 for the agonist
  • Parallel shift of the curve to the right
22
Q

What is a non-competitive antagonist?

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A

Binds to a different site than the agonist

23
Q

What is an example of an irreversible competitive antagonist?

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A

Clopidogrel = covalent modification of the receptor

Cobra toxin = ultra slow dissociation

24
Q

What is the significance of dose in pharmacology?

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A

It is crucial for determining effects in whole organism assays

25
What does ED50 measure?
Potency in dose-effect relationships
26
Potency increases as ED50 __________.
Decreases
27
Effects of agonists on a receptor
Causes the equilibrium to favour the active state as the binding energy stabilises it
28
What are the different types of assays?
1. Cell based biochemical assay —> uses wells, often used for GPCRs and receptor activation is measured by measuring concentrations of intracellular messengers 2. Isolated organ assay —> measures how normal physiological functions of the organ changes in response to drugs 3. Cell based electrophysiological assay —> measures how membrane potential changes in response to drugs & requires electrodes on or in the cell = measures ion channel activity 4. Whole animal assay or human trials —> measures changes a drug produces on physiology, behaviour or disease, tends to be expensive
29
How to find Emax and EC50
Emax is where the curve plateaus and EC50 is half of Emax followed down to the X axis
30
Log concentration-effect curves
S-shaped (sigmoid) shape Log EC50 = half of Emax also is log [drug]
31
What is the relationship between EC50 and KD?
EC50 is directly related to KD
32
What happens in the case of ‘spare’ receptors?
When one receptor activates multiple signalling cascades or only a few are activated instead of all Emax is reached before Bmax and EC50 will be less than KD So they are not directly related
33
How does EC50 behave like KD?
As EC50 goes down, potency goes up
34
How does a partial agonist differ in efficacy compared to a full one?
Has the same logE50 value but will only have partial efficacy = same potency but different efficacy
35
What is the efficacy of antagonists?
Zero as they occupy the binding site but do nothing
36
Important features of competitive antagonism
- the maximal effect of the agonist is not changed - in the presence of an antagonist, need to use more agonist to bring about a particular effect - increase in the apparent EC50 for the agonist - parallel shift in the curve to the right
37
What is apparent EC50?
EC50 X [I]/Ki To get EC50, it is 1 + [I]/Ki
38
Types of antagonism
- Reversible competitive antagonism/reversible orthosteric antagonism —> same site as the agonist & surmountable (able to overcome by increasing concentration of agonist) - Non-competitive antagonism —> different site to the agonist, can get simultaneous binding & antagonist changes conformation of the receptor so agonist can’t activate it
39
Non-competitive antagonism
Also known as negative allosteric modulator Reduces maximum effect an agonist can produce Insurmountable (can’t overcome by increasing concentration of agonist)
40
Irreversible competitive antagonism
Insurmountable Antagonist is permanently eliminating receptors from the pool an agonist can bind to = reduces maximum response the agonist can achieve Behave like a non-competitive antagonist
41
Antagonists and tone
Vagal tone keeps the heart beating at a lower rate An antagonist such as Atropine blocks receptors so that ACh can’t bind and so heart rate increases Even though the antagonist is ‘doing nothing’ directly, it is still producing an effect by blocking the receptors and thus ACh access
42
What do whole organism assays measure?
Absorption (some drugs are metabolised in the GI tract) Distribution (how the drug moves to the site of action) Metabolism (drugs are metabolised in the liver) Excretion (excreted in the urine via the kidney)
43
Analysing dose-effect data
- Log X axis - Maximal effect can be continuous (e.g. blood pressure) or can be all or nothing (cured/not cured) - Potency is measured by ED50 not EC50 but behaves in the same way - Can use pED50 = -logED50

Drugs: Molecules To Man (14 decks)

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