General Principles of Drug Action: Receptor Pharmacology – Agonists

What is a receptor

A receptor is a molecule to which a drug binds to bring about change in function of the biological system

What are ligands

A ligand is a chemical which specifically binds to a receptor. An agonist is a ligand

Outline some characteristics of a receptor

Receptor possess structural and steric specificity

Receptors are saturable and finite

Receptors are expressed in select tissues

What does the dose-response curve show

dose response curve refers to the relationship between the effect of a drug and the amount of drug given

What does the size of the response depend on

The size of response varies with the proportion of receptors occupied by the agonist which varies with the concentration of the agonist

What parameters can you obtain from Dose response curves

Emax and EC50

What is Emax and EC50

Emax is the maximum effect an agonist can produce regardless of dose

EC50 is an effective concentration of drug required to produce 50% of maximal effect

In dose binding curve what can be found

Bmax and Kd

What is Bmax and Kd

Bmax: Maximum number of receptors bound

 

Kd: Concentration at which 50% of receptors are bound

What is the Langmuir equation

What does the Langmuir equation show

The Langmuir equation shows that the amount of frug bound to the receptor is dependent on the drug concentration and Kd

When are spare receptors present

When EC50 is less than Kd

What is an agonist , partial agonist and antagonist

An agonist is a drug that activates its receptor upon binding eliciting

a full response (effect)

A partial agonist binds to its receptor but produces a smaller

effect (E_max) at full dosage then a full agonist

An antagonist is a substance that binds to a receptor but does

    not activate and can block the activity of other agonists