Antagonist
Say it: an-TAG-uh-nist
An antagonist is a drug that binds to a receptor without activating it, blocking the natural signal or an agonist from producing an effect.
Also: antagonists
Definition
What is an antagonist?
In pharmacology, an antagonist is a substance that occupies a receptor but has no efficacy of its own: it fits the binding site without switching the receptor on, and so stops agonists, whether natural messengers or drugs, from acting there. Beta-blockers, for example, block receptors for epinephrine and norepinephrine and slow the heart, while caffeine increases alertness partly by blocking adenosine receptors in the brain.
Antagonists are grouped by how they block. A competitive antagonist binds reversibly at the same site as the agonist, so enough extra agonist can overcome it; the agonist's dose-response curve shifts to the right but can still reach its full height. Naloxone, which reverses the effects of opioids such as morphine, works this way. A noncompetitive antagonist binds elsewhere on the receptor, or binds irreversibly, and lowers the maximum response that any amount of agonist can achieve.
The word is also used in anatomy for a muscle that opposes another, such as the triceps working against the biceps, and more generally for any substance that counteracts the action of another.
Word parts
Where does the word “antagonist” come from?
- ant(i)-
- againstGreek anti
- agonist
- combatantGreek agonistes
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Terms that go with it
- AgonistAn agonist is a drug or natural substance that binds to a receptor and activates it, producing a biological response.
- ReceptorA receptor is a protein, on a cell's surface or inside it, that binds a specific signaling molecule and triggers a response in the cell.
- PharmacodynamicsPharmacodynamics is the study of what a drug does to the body: how it acts on its molecular target and how its effects vary with dose.
- Dose–response curveA dose–response curve is a graph showing how the size of a drug's effect changes as its dose or concentration increases.
- Competitive inhibitionCompetitive inhibition is enzyme inhibition in which a molecule resembling the substrate occupies the active site and keeps the substrate out.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- MSD Manual Professional: Drug-Receptor Interactions
- OpenStax Introduction to Behavioral Neuroscience, 14.1 Basic Principles of Pharmacology
- OpenStax Pharmacology for Nurses, 2.2 Pharmacokinetics and Pharmacodynamics
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