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Pharmacology
Agonist
Agonist - A substance that binds a receptor and activates it - triggering its signal. Many peptides act as agonists, e.g. GLP-1 agonists.
Also called receptor agonistagonists
An agonist works like a matching key: it is a substance that docks onto a kind of docking site (the receptor) on the cell surface and activates it. This triggers the same response in the body as the body's own messenger would - or even a stronger or longer one.
A picture
Think of the receptor as a lock and the agonist as a matching key that opens it and starts the signal. Its counterpart is the antagonist, which fits the lock but blocks it without opening.
Relevance to peptides
Many well-known peptides - short protein chains that the body produces on its own or that are used as medicines - are agonists. A well-known example is GLP-1 receptor agonists: drugs that mimic a natural gut hormone important for feeling full and controlling blood sugar. Such medicines are used, among other things, in diabetes and weight-loss treatments. Some of these substances bind several receptor types at once (so-called dual or triple agonists).