Pharmacology: Agonists and Antagonists Quiz

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Questions and Answers

What defines an agonist in terms of its interaction with receptors?

It prevents binding of any ligands.

It blocks the receptor activity.

It has no effect on the receptor.

It enhances the receptor's activity. (correct)

Which of the following is considered an exogenous ligand?

Hormones

Local Hormones

Toxins (correct)

Neurotransmitters

What is the primary role of antagonists in pharmacology?

To facilitate the binding of agonists.

To block or inhibit receptor activity. (correct)

To enhance the natural hormone production.

To mimic the action of natural ligands.

Which type of receptor is characterized by fast ion channels with a central pore?

Ionotropic receptors Signup and view all the answers

What does pA2 measure in pharmacology?

The potency of an antagonist. Signup and view all the answers

What characterizes metabotropic receptors?

They are 7 trans-membrane receptors coupled to a G protein. Signup and view all the answers

What is EC50 in pharmacology?

The effective concentration of an agonist that results in 50% of maximum tissue response. Signup and view all the answers

What defines a partial agonist?

A drug that produces a response less than that of a full agonist despite occupying all receptors. Signup and view all the answers

What happens when an intracellular receptor is activated?

It enters the nucleus to act on gene expression. Signup and view all the answers

Which statement about the receptor occupancy theory is true?

It is a two-state model that describes how drugs interact with their receptors. Signup and view all the answers

What happens to the concentration-response curve of an agonist in the presence of an antagonist?

The curve shifts rightwards without a change in maximum response. Signup and view all the answers

What is represented by the term KB in pharmacology?

The concentration of an antagonist needed to occupy 50% of the receptors. Signup and view all the answers

If an agonist's EC50 is influenced by an antagonist blocking 50% of available receptors, how is the new EC50 related to the original?

It is doubled. Signup and view all the answers

What does the term pA2 refer to in the context of antagonists?

The negative logarithm of antagonist concentration causing a two-fold shift. Signup and view all the answers

What is the dose ratio when an antagonist causes a two-fold shift in the concentration-response curve?

2 Signup and view all the answers

What relationship describes the shift in antagonism when plotted on a graph of antagonist concentration versus dose ratio for competitive antagonism?

Linear relationship Signup and view all the answers

What does the slope of the Schild plot indicate for a competitive antagonist?

Slope equals 1 Signup and view all the answers

Which of the following is NOT a characteristic of the pA2 value?

Dependent on tissue type Signup and view all the answers

What is the significance of the dissociation constant (KB) in the Schild equation?

It indicates the affinity of antagonist Signup and view all the answers

How can the pA2 value be determined when plotting a graph of log dose ratio -1 versus antagonist concentration?

When the log of 2-1 equals 0 Signup and view all the answers

What is the main characteristic of reversible competitive antagonism?

It competes with both endogenous and exogenous ligands. Signup and view all the answers

Which of the following describes the effect of a competitive antagonist on the concentration-response curve?

It causes a rightward shift without affecting the slope. Signup and view all the answers

What does the term 'spare receptors' refer to in pharmacology?

Receptors that provide additional response without occupation. Signup and view all the answers

Which type of antagonism is characterized by its inability to be overcome by increasing agonist concentration?

Irreversible antagonism Signup and view all the answers

What factor influences the degree of ligand specificity for drugs?

Chemical changes like amino acid alterations Signup and view all the answers

In drug-receptor interactions, what does KA represent?

Agonist dissociation constant (affinity) Signup and view all the answers

What is a limitation when discussing drug specificity?

No drug is completely selective. Signup and view all the answers

How is the potency of a competitive antagonist determined?

By how effectively it competes with the agonist for the receptor site. Signup and view all the answers

What is the EC50 value for histamine at H1-receptors indicated in the data?

100 Signup and view all the answers

Which drug has the lowest potency at H2-receptors based on the provided EC50 values?

Thioperamide Signup and view all the answers

Which receptor's activity is demonstrated to be mediated by endothelial 5-HT2B receptors according to the research?

Relaxation of pig pulmonary artery Signup and view all the answers

What characteristic of receptors is associated with inverse agonists as mentioned?

They decrease constitutive activitiy. Signup and view all the answers

Which compound has an EC50 value closest to histamine for histamine release from the CNS?

Cimetidine Signup and view all the answers

Study Notes

Drug Receptor Theory

Pharmacology is the study of drugs and their effects on the body.
Drug targets include receptors.
Ligands are endogenous (within the body) or exogenous (outside the body) molecules that bind to receptors.
Endogenous ligands include neurotransmitters, hormones, and autocoids (local hormones).
Exogenous ligands include drugs, poisons, and toxins.
Ligands bind to receptors, and specificity/selectivity determines the binding reaction.
Agonists and antagonists are two types of ligands.

Receptor Types

Ionotropic receptors are fast ion channels with a central pore. Examples include nicotinic receptors for acetylcholine.
Metabotropic receptors are 7 transmembrane receptors coupled to G proteins. Indirectly acting via a cascade.
Kinase-linked receptors.
Intracellular receptors are within the cytoplasm and enter the nucleus upon activation.

Receptor Occupancy Theory

Receptor occupancy is the theory governing drug and receptor interactions.
Receptor states are resting and activated (by an agonist).
Agonist potency is determined by its affinity.
Agonist efficacy is determined by the ability to produce a stimulus.
Antagonists bind, but don't produce a stimulus. Their potency is determined by affinity.
EC₅₀ is the effective concentration of agonist required to produce 50% of maximal tissue response.

Isolated Tissue Experiments

A method to measure drug response and effect.
Drugs are added to isolated tissue, and response is monitored.

Types of Agonists

Full agonists produce 100% maximum response.
Partial agonists produce less than 100% maximum response.

Spare Receptors

The condition in which a full agonist requires less than 100% receptor occupancy to produce maximal response.
This occurs when the tissue has more receptors than are needed for full activation.

Antagonist Types

Competitive antagonists compete for the same receptor site as agonists.
Non-competitive antagonists do not compete with agonists for the receptor site.
Antagonist affinity (K_B) is expressed as a concentration needed to occupy half the available receptors.
pA₂ is the negative logarithm of K_B, measuring the potency of an antagonist. (a measure of antagonist affinity as a log scale [more or less]).

Schild Plot and pA₂

The Schild plot is an analytical tool for measuring the potency of a competitive antagonist.
This linear plot results in a straight line if the antagonistic relationship is competitive.
The x-intercept is the log K_B (log of the dissociation constant of the antagonist).

Importance of pA₂

Antagonist potency can be expressed and measured as pA₂.
This is independent of tissue used, agonist used, or receptor density.
Single receptor types have identical pA₂ values.

Inverse Agonists

Inverse agonists cause a reduction in receptor activation at rest.
They produce the opposite effect to agonists.

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Description

Test your knowledge on the roles of agonists and antagonists in pharmacology with this quiz. Explore the characteristics of different receptors, ligand interactions, and key pharmacological concepts such as EC50 and pA2. This quiz is designed for students studying pharmacology or related fields.