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Definition

noun, plural: agonists

(pharmacology) A molecule that combines with a receptor on a cell to trigger physiological reaction. An example is an acetylcholine being the agonist that combines with the cholinergic receptor.

(histology) A muscle that contracts while another muscle relaxes, e.g. when bending the elbow the biceps are the agonist.

Supplement

(pharmacology) There are different kinds of agonists:

• Full agonists have an affinity for and activate a receptor.
• Partial agonists bind and activate a receptor but have only partial efficacy at the receptor (compared with full agonists).
• Inverse agonists reverse constitutive activity of receptors.
• Co-agonists work with other co-agonists to produce the desired effect together.

Word origin: From the Greek αγωνιστής (agōnistēs), contestant; champion; rival < αγων (agōn), contest, combat; exertion, struggle < αγω (agō), I lead, lead towards, conduct; drive.
Related forms: agonistic (adjective).
Related phrases: physiological agonist.
Compare: antagonist.
See also: agonism.