Pharmacodynamics

Agonist

Also known as:Receptor agonist

A drug or endogenous substance that binds to a receptor and activates it, producing a biological response; it possesses both affinity and efficacy (intrinsic activity).

In depth

A full agonist can elicit the maximal response of which the system is capable (intrinsic activity = 1), whereas a partial agonist produces a lower maximum even at full receptor occupancy. Agonists are characterised by potency (EC50) and efficacy (Emax); in tissues with spare receptors, a full agonist can produce a maximal response while occupying only a small fraction of receptors.

Most agonists act at the orthosteric site used by the endogenous ligand. Biased agonists preferentially activate some signalling pathways (e.g. G protein rather than β-arrestin pathways) over others, a property being explored in drug design.

Clinical pearl

Continued exposure to agonists commonly causes desensitisation and tolerance, as with opioids, nitrates and β2-agonists; with nitrates, a daily nitrate-free or low-nitrate interval is used to preserve the effect.

Example drugs

Morphine Phenylephrine Sumatriptan Isoprenaline
TRIn Turkish

Agonist

Bir reseptöre bağlanarak onu aktive eden ve biyolojik bir yanıt oluşturan ilaç veya endojen maddedir; hem afiniteye hem de etkinliğe (intrinsik aktiviteye) sahiptir.

Tam agonist, sistemin oluşturabileceği maksimal yanıtı ortaya çıkarabilir (intrinsik aktivite = 1); kısmi agonist ise reseptörlerin tamamını işgal ettiğinde bile daha düşük bir maksimal yanıt oluşturur. Agonistler potens (EC50) ve etkinlik (Emax) ile tanımlanır; yedek reseptörlerin bulunduğu dokularda tam agonist, reseptörlerin yalnızca küçük bir bölümünü işgal ederek maksimal yanıt oluşturabilir.

Agonistlerin çoğu endojen ligandın kullandığı ortosterik bölgeye bağlanır. Yanlı (biased) agonistler bazı sinyal yolaklarını (örneğin β-arrestin yolakları yerine G proteini yolaklarını) diğerlerine göre tercihli olarak aktive eder; bu özellik ilaç tasarımında araştırılmaktadır.

Agonistlere sürekli maruziyet sıklıkla desensitizasyon ve toleransa yol açar; opioidler, nitratlar ve β2-agonistler buna örnektir. Nitratlarda etkinin korunması için gün içinde nitratsız ya da düşük nitratlı bir aralık bırakılır.

Diğer adları:Reseptör agonisti
Updated 24.09.2026 0 views Educational reference — verify against current sources before clinical use.

Read next

Partial AgonistKısmi Agonist

An agonist that, even when occupying all available receptors, produces a maximal response smaller than that of a full agonist; its intrinsic activity lies between 0 and 1.

 Inverse AgonistTers Agonist

A ligand that binds to a receptor with constitutive (ligand-independent) activity and reduces that basal activity, producing an effect opposite in direction to that of an agonist.

 AntagonistAntagonist

A drug that binds to a receptor or other target without activating it (affinity but no efficacy) and thereby prevents or reduces the response to an agonist.

 EfficacyEtkinlik

The capacity of a drug to produce a response once bound to its receptor; in clinical terms, the maximal effect (Emax) a drug can produce, however much the dose is increased.

 Intrinsic Activityİntrinsik Aktivite

The ability of a drug, once bound, to activate its receptor and produce a response, expressed relative to a full agonist on a scale from 0 (antagonist) to 1 (full agonist); inverse agonists have negative values.

 Spare ReceptorsYedek Reseptörler

Receptors in excess of those needed to produce a maximal response, so that a full agonist can elicit its maximal effect while occupying only a fraction of the available receptors.