agoniste

An agonist is a molecule that binds to a receptor and activates it, producing a biological response. In French, the term is agoniste, and the concept is the same in pharmacology: a ligand that can trigger receptor signaling.

Agonists can be endogenous or exogenous. Endogenous agonists include neurotransmitters and hormones that regulate normal physiological processes. Exogenous agonists are drugs or toxins introduced from outside the body that mimic natural signaling to produce a response. Key properties of agonists are affinity (how tightly the molecule binds the receptor) and efficacy (the ability to activate the receptor and elicit a response).

There are different classes of agonists. Full agonists generate near-maximal receptor responses when they occupy receptors, while partial agonists produce only a submaximal response even at full occupancy. Inverse agonists reduce the baseline, or constitutive, activity of receptors that have intrinsic activity. Antagonists block agonist effects by occupying the receptor without activating it, thereby preventing endogenous or exogenous agonists from binding.

Mechanistically, agonists interact with various receptor types, including G protein–coupled receptors, ion channels, and enzyme-linked receptors, to initiate signaling cascades that alter cellular function. Clinical relevance arises from the use of agonists as medicines (for example, morphine as a mu-opioid receptor full agonist; salbutamol as a beta-2 adrenergic receptor agonist) and from studying endogenous signaling systems to understand physiology and disease.