21 Questions
What is the result of non-competitive antagonism on the receptor?
Change in the receptor so that the agonist can no longer bind
In non-competitive antagonism, a maximum effect is still produced.
False
What is the significance of spare receptors in non-competitive antagonism?
Spare receptors allow a maximum response to be reached despite non-competitive antagonism.
In physiological antagonism, two agonists act on different receptors to produce _______________ effects.
opposite
What is the effect of spare receptors on the dose-response curve?
Shifts the curve to the left
What is the primary requirement for an antagonist to produce its effect?
The presence of an agonist already producing a certain effect
Partial agonists can achieve maximum effect.
False
What is the mechanism of action of inverse agonists?
destabilisation of G-protein receptor coupling
The presence of an _______________ will increase the proportion of active receptors.
agonist
What is the result of potentiation of agonists?
Increased effect of the agonist
Competitive antagonism is a type of non-competitive antagonism.
False
Match the following agonists with their respective effect:
Acetylcholine = Increased effect in the presence of anticholinesterase Noradrenaline = Increased effect in the presence of an uptake blocker agonist = Decreased effect in the presence of an antagonist partial agonist = Never achieves maximum effect
What is the characteristic of a partial agonist that also acts as an antagonist?
blocking full agonist from binding
What is potency determined by?
The strength of binding of a drug to a receptor
An antagonist has high efficacy.
False
What is the term for the measure of the drug dosage needed to produce a particular therapeutic effect?
Potency
A lower Kd value indicates _______________ affinity and potency.
more
Match the following types of antagonism with their descriptions:
Competitive Antagonism = Occurs when agonists and antagonists compete for the same receptor sites Non-Competitive Antagonism = Maximal effect is reduced
What happens to the dose-response curve when there are spare receptors present?
It shifts to the left
Physiological antagonism occurs when agonists and antagonists bind to the same receptor site.
False
What is the term for the point at which all receptors are occupied, which is used to measure potency?
ED50
Study Notes
Types of Antagonism
- Non-competitive antagonism: produces irreversible changes, acts on the receptor itself, and makes binding impossible.
- Competitive antagonism: occurs when agonists and antagonists compete for the same receptor sites, and the maximal effect is unchanged (surmountable).
- Physiological antagonism: occurs when 2 agonists act on different receptors to produce opposite effects.
Spare Receptors
- Important in non-competitive antagonism as a receptor reserve can allow a maximum response to be reached.
- Spare receptors occur due to several amplification steps downstream from the initial drug-receptor interaction.
- ED50 for a drug effect with spare receptors may not be equal to KD, and this shifts the dose-response curve to the left of KD.
Potency and Efficacy
- Potency: the measure of the drug dosage needed to produce a particular therapeutic effect, determined by the strength of binding of a drug to a receptor or the receptor affinity for the drug.
- Efficacy: the measure of the effectiveness of a drug in producing a maximum response.
- Lower Kd = More affinity & potency.
Dose-Response Measurement
- Determines accurate dosing needed when new drugs are formulated.
- Cannot use these measurements to calculate affinity only dosing.
Agonists and Antagonists
- Agonists bind to receptors causing contractions, which are plotted, and increasing doses lead to an increasing response until 2 doses have an equal response.
- Partial agonists are less efficacious, never achieve maximum effect, and also act as an antagonist (locking full agonist from binding).
- Inverse agonists restore the receptor to its inactive state, and their mechanism of action involves the destabilization of G-protein receptor coupling.
Potentiation of Agonists
- Occurs due to the decreased inactivation of an agonist (i.e., the breakdown of the drug is reduced).
- The drug will be able to accumulate to higher concentrations and have a more potent effect.
- Examples: Acetylcholine in the presence of anticholinesterase (neostigmine; physostigmine), and Noradrenaline in the presence of an uptake blocker (cocaine, tricyclic antidepressants).
This quiz focuses on the concept of non-competitive antagonism in pharmacology, where the antagonist binds to the receptor and alters it, making it impossible for the agonist to bind.
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