Pharmacodynamics (Drug Receptors)

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  • Topic: Signal transduction, Cell membrane, G protein-coupled receptor
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  • Published : May 26, 2013
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Dose of drug administered


Drug in tissues

Drug in systemic circulation

Drug metabolized or excreted

Drug at site of action

Pharmacologic effect Pharmacodynamics Toxicity Efficacy

PHARMACOLOGY Pharmacodynamics
Actions of drug on the body  Specific to a drug/ class of drugs • Interaction with target sites (receptors/enzymes) • Effects at site of action • Dose-response relationship • Reduction in symptoms • Modification of disease process • Unwanted/side effects • Drug interactions • Inter- and intra-patient differences

Actions of body on the drug  Non-specific, general processes • Absorption from site of administration • Distribution to the site of action • Metabolism • Excretion • Onset of action • Duration of effect • Accumulation • Drug interactions • Inter- and intra-patient differences

Study of biochemical and physiological effects of drugs and their mechanism of action

 Describes the actions of a drug  Includes the measurement of response to drugs and how response relates to drug dose or concentration

Most drugs must bind to a receptor to bring about an effect



Drug binding is only the 1st step in a complex sequence of events

Lecture 1 Lecture 2

› Drug Receptors

› Drug-Receptor Interaction

Lecture 3

› Dose-Response Curve

What are Receptors?  Classification of receptors  Not all drugs have receptors 

Understand what receptors & their characteristics are’  Name and describe the classes of receptors.  Give an example of each class of receptors.  Understand that not all drugs require a receptor to work. Give examples of such drugs. 

Are usually proteins or part of a protein that have a distinct region to which drugs bind → 1.

produces a change that:
Directly induces a measurable response

2. Triggers a transduction chain that in turn produces a measurable response

Usually made up of at least 2 domains
 Ligand –binding domain  Effector/catalyic domain

Can be located at:

 Cell surface  Within the cytoplasm or  Inside the nucleus


 determine the quantitative relations between dose/concentration of drug and pharmacologic effects  are responsible for selectivity of drug action

Selectivity of Receptors

› If receptor serves a function that is

common to most cells

 Drugs binding to it  Widespread effect

› If receptor unique to only a few

types of differentiated cells

 Drugs binding to it  More specific effect

Subtypes of Receptors

Certain receptors have subtypes Example: Adrenergic receptors Noradrenalin

β1 Receptors in Heart

β2 Receptors in Bronchioles

4 main classes of receptors
transmembrane signalling

› Classification based on their mechanism of › Each uses a different strategy to overcome

the barrier posed by lipid bilayer of the plasma membrane

1. Intracellular receptors 2. Ligand-regulated transmembrane enzymes 3. Ligand-gated ion channels 4. G protein coupled receptor

(1) Intracellular Receptors

Receptors are located within the cell Location of these receptors: 1. In Cytoplasm 2. On Mitochondria 3. In nucleus

1 2


Ligands: usually lipid soluble,

→ Able to cross the plasma membrane → Act on these intracellular receptors

Examples: Steroids, Thyroid hormones, Glucocorticoids Binding of ligand with these receptors could lead to changes in intracellular activities

 Has 3 distinct


domains 1. Transcription activation domain 2. DNA binding domain and 3. Agonist-binding domain



At resting state (no hormone present) › Receptor is bound to hsp 90 › Hsp 90 - protein that prevents normal folding of several structural domains of receptor

Action state  Release of hsp 90  DNA-binding & Transcription-activating domain...
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