2. Classification of ligands:
• Ligands are classified by effect upon binding to the receptor.
Agonist
LIGANDS
Antagonist
•Ligands:
• The molecules that bind to receptors.
• It is any molecule which attaches selectively to particular receptors
4. Agonist
Derived from Latin word – contender.
Aids in the enhancement of an action.
Drugs that bind to physiological receptors and mimic
the regulatory effects of the endogenous signaling
compounds are termed agonists.
Ligands that activate a receptor to produce a biological
response are called agonists.
5. There are several types of agonists
Receptors can be activated either by endogenous or exogenous , leads
to change in the biological response.
Types of agonist-
a) Endogenous agonist
b) Super agonist
c) Full agonist
d) Partial agonist
e) Inverse agonist
f) Irreversible agonist
6. •Endogenous agonist: Naturally present in the body and bind to and
activate the receptor
• Super agonist: Capable of binding to the receptor and producing a
greater maximal response than the endogenous
Agonist
•Full agonist – The ligands that increase the activity of the receptors
& produce the maximal response .
Ex.- Morphine ,mimics the action of endorphins at
opioid receptors.
7. Partial agonist – These ligands partially increase the activity of the receptors
but do not produce the maximal response like full agonist
even when present in excess amount.
Ex.- Buspirone , is an anxiolytic drugs , used to treat an anxiety disorder.
Inverse agonist – The ligands which decrease the activity of an active
receptors to their inactive state.
Ex.- Flumazenil drugs acts as a inverse agonist for the GABA receptor &
produce anxiogenic effect.
8. Irreversible agonist: binds and activates the receptor but the
binding is permanent; so, this happens only once and
the receptor is essentiallydestroyed
9. Antagonist
•Derived from Latin & Greek words –
competitor or opponent.
•Opposes the action of agonist and block
the reception.
•Ligands that block agonist mediated
responses (rather than eliciting a biological
response from binding itself) are called
antagonists
.
10.
11. Properties of Antagonist :
Site selectivity.
Structural conformation – mimics with the natural ligand.
Reduces the response.
Effect may be temporary or permanent.
14. Non-competitive antagonists : The antagonist binds at a different site
other than orthosteric site on the receptor.
- The effect of the antagonist cannot be overcome by increasing the
concentration of agonist.
Ex.- Binding of cyclothiazide with mGLUR1 receptor.
15. Irreversible antagonists:
May or may not competes with the agonist for orthosteric sites for
binding to the receptor.Forms covalent bond to the site..
Ex.- Aspirin.
16.
17. •Spare receptors: Some tissues have more receptors than are necessary
to produce a maximal response called spare receptor.
•Addiction : A brain disorder characterized by compulsive engagement
in rewarding stimuli despite adverse consequences.
•Drug tolerance : A pharmacological concept describing subjects'
reduced reaction to a drug following its repeated use. Increasing its
dosage may re-amplify the drug's effects; however, this may
accelerate tolerance, further reducing the drug's effects.
18. •Dependence: also known as drug dependence, is an adaptive state that
develops from repeated drug administration, and which results in withdrawal
upon cessation of drug use. ... Compulsive and repetitive use may result in
tolerance to the effect of the drug and withdrawal symptoms when use is reduced
or stopped.
•Tachyphylaxis :A medical term describing an acute, sudden decrease in
response to a drug after its administration; i.e. a rapid and short-term onset of
drug tolerance. It can occur after an initial dose or after a series of small doses.
•Idiosyncrasy :Refers to an idiosyncratic reaction, which is an adverse effect to
an agent, such as a drug, which does not occur in most patients who've used the
same agent. That shouldn't be too surprising.
• Allergy: the abnormal reaction of your immune system to a medication.