Receptor Antagonism Flashcards
What is receptor antagonism?
Receptor antagonism refers to a mechanism of drug action where one drug, known as an antagonist, blocks or inhibits the action of another drug, known as an agonist, by binding to the same receptor. This interaction prevents the agonist from exerting its desired effect.
Why is receptor antagonism important in drug action?
Receptor antagonism is crucial in drug action because many physiological signal molecules act through specific receptors. By blocking these receptors, antagonists can produce specific and significant pharmacological effects
How do receptor antagonists work?
Receptor antagonists are selective in their action, meaning they specifically block the receptors targeted by the agonist. For example, an anticholinergic drug will oppose the contraction of intestinal smooth muscle induced by cholinergic agonists. However, it will not interfere with contractions induced by histamine or 5-HT, as these substances act through different sets of receptors.
What are the two types of receptor antagonism?
The two types of receptor antagonism are competitive antagonism and noncompetitive antagonism
What is competitive antagonism?
In competitive antagonism, the antagonist is chemically similar to the agonist and competes with it for binding to the same receptor site. The antagonist binds to the receptor, excluding the agonist molecules. As the antagonist has affinity but no intrinsic activity, it does not produce a response. This results in a rightward shift of the agonist’s dose-response curve (DRC). However, the block by the antagonist is reversible, and higher concentrations of the agonist can progressively overcome the antagonism, leading to a parallel shift of the agonist’s DRC without suppressing the maximal response.
What is noncompetitive antagonism?
In noncompetitive antagonism, the antagonist is chemically unrelated to the agonist and binds to a different allosteric site on the receptor. This binding alters the receptor in such a way that it is unable to bind with the agonist or transduce the response downstream. Noncompetitive antagonism is also known as allosteric antagonism. Since the agonist and antagonist bind to different sites, there is no competition between them. Even high concentrations of the agonist cannot completely reverse the block. Increasing concentrations of the antagonist progressively flatten the agonist’s DRC.
What is nonequilibrium antagonism?
Nonequilibrium antagonism occurs when certain antagonists bind to the receptor with strong (covalent) bonds or dissociate slowly from the receptor due to very high affinity. This results in the agonist molecules being unable to reduce the receptor occupancy of the antagonist molecules. Nonequilibrium antagonism is considered irreversible or nonequilibrium because the law of mass action does not apply. The agonist’s DRC is shifted to the right, and the maximal response is lowered. Phenoxybenzamine is an example of a non-equilibrium antagonist of adrenaline at α-adrenergic receptors
