Agonist
Say it: AG-uh-nist
An agonist is a drug or natural substance that binds to a receptor and activates it, producing a biological response.
Also: agonists
Definition
What is an agonist?
An agonist is a molecule that binds to a receptor and switches it on, triggering a response in the cell. Natural agonists include hormones and neurotransmitters, such as epinephrine acting on adrenergic receptors. Many medicines are agonists too: morphine activates opioid receptors, and injected insulin acts on the insulin receptor just as the body's own hormone does.
Two properties describe an agonist. Affinity is how readily it binds the receptor, and efficacy, or intrinsic activity, is how strongly it activates the receptor once bound. A full agonist can drive the largest response the system allows. A partial agonist, such as buprenorphine at opioid receptors, produces a smaller response even at high doses and can blunt the effect of a full agonist competing for the same site. An inverse agonist binds a receptor that is active on its own and lowers that baseline activity.
Agonists are compared on dose-response curves, which show their potency and the largest effect they can reach. A drug that binds a receptor without activating it is the opposite, an antagonist.
Word parts
Where does the word “agonist” come from?
- agonist
- contestant, combatantGreek agonistes
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Terms that go with it
- AntagonistAn antagonist is a drug that binds to a receptor without activating it, blocking the natural signal or an agonist from producing an effect.
- 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.
- NeurotransmitterA neurotransmitter is a chemical messenger that a neuron releases at a synapse to excite or inhibit a target neuron, muscle cell or gland cell.
- HormoneA hormone is a chemical messenger released into the blood by a gland or cell that changes the activity of distant target cells with matching receptors.
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Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Introduction to Behavioral Neuroscience, 14.1 Basic Principles of Pharmacology
- MSD Manual Professional: Drug-Receptor Interactions
- OpenStax Pharmacology for Nurses, 2.2 Pharmacokinetics and Pharmacodynamics
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