Pharmacodynamics 2: Receptor Theory

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Questions and Answers

What is the term used to describe anything a drug interacts with to cause an effect?

Ligand

Drug Receptor

Binding Site

Drug Target (correct)

Which of these scientists is credited with the development of the "side chain" chemical binding theory from immunology?

Clark

Ehrlich (correct)

Langley

Gaddum

What is the term for the binding site that an endogenous agonist binds to?

Allosteric binding site

Orthosteric binding site (correct)

Active binding site

Secondary binding site

What is the term for the ability of a ligand to generate an effect?

Efficacy Signup and view all the answers

Which of these is NOT a factor that contributes to the potency of a drug?

Concentration Signup and view all the answers

What is the term for the binding site that other ligands bind to, besides the primary agonist?

Allosteric binding site Signup and view all the answers

Which of the following scientists established the theory of receptor action through their work with propranolol?

Black Signup and view all the answers

What type of conformational change occurs in a receptor upon ligand binding?

Activation Signup and view all the answers

What is the x-axis in a concentration-effect curve?

Log10[Ligand] Signup and view all the answers

What is the difference between a concentration-effect curve and a dose-response curve?

A concentration-effect curve measures the effect of a drug at its target site, while a dose-response curve measures the physiological response to a systemically administered drug. Signup and view all the answers

What does the EC50 represent?

The concentration of a drug required to produce a half-maximal effect. Signup and view all the answers

What is the relationship between potency and EC50?

Potency is inversely proportional to EC50. Signup and view all the answers

How does a ligand with a higher affinity compare to a ligand with a lower affinity?

A ligand with a higher affinity will bind to its target with a lower concentration. Signup and view all the answers

What does efficacy refer to?

The maximum effect that a ligand can produce. Signup and view all the answers

What is the difference in efficacy and affinity between ligands A and C in the graph provided?

Ligand A has higher affinity and lower efficacy than ligand C. Signup and view all the answers

What does it mean if two ligands have the same efficacy but different affinities?

The two ligands will produce the same maximum effect but will require different concentrations to achieve it. Signup and view all the answers

Study Notes

Receptor Theory

Receptor theory is the main scientific theory of pharmacology, dating back to Ehrlich's "side chain" chemical binding theory from immunology.

Development of Receptor Theory

Langley (1878, 1905) proposed a chemical binding theory for all drugs, which was later developed by others, such as Clark and Gaddum (1920s-1930s).
The concept of receptors was firmly established by Sir James Black (1965) with the discovery of propranolol.

Definition of Receptors and Targets

A "drug receptor" refers to anything a drug interacts with to cause an effect, but the term "drug target" is preferable.
"Receptor" specifically refers to proteins that recognize and respond to endogenous signaling mediators.

Binding Sites

Receptors have an active ("orthosteric") binding site for endogenous, activating ligands (agonists) with high specificity.
Ligand binding induces conformational changes to activate the receptor.
Receptors may also contain secondary ("allosteric") binding sites for other ligands.

Affinity and Efficacy

Affinity refers to the ability of a ligand to bind to a target.
Efficacy refers to the ability of a ligand to generate an effect.
Together, affinity and efficacy determine potency, or the ability of a ligand to generate a response.

Concentration-Effect and Dose-Response Curves

Concentration-effect curves measure the effect of a drug at the target site.
Dose-response curves measure the physiological response to a systemically administered drug.
The x-axis is typically plotted on a logarithmic scale.

Affinity and Efficacy on D-R Curves

Ligands with different affinities or efficacies will have distinct D-R curves.
Ligands with the same efficacy but different affinities will have different EC50 values.
Ligands with the same affinity but different efficacies will have different Emax values.

EC50 and Potency

EC50 is the concentration at which the effect is half maximal.
Potency is the concentration of drug required to cause an effect, measured by EC50.

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Description

This quiz covers receptor theory, including concentration-effect curves, agonists, antagonists, and therapeutic range. It's a crucial concept in pharmacology, building on the work of Ehrlich and immunology. Test your knowledge of pharmacodynamics!