Pharmacodynamics

Spare Receptors

TRYedek Reseptörler
Also known as:Receptor reserve

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.

In depth

Receptor reserve arises when signal amplification downstream of the receptor (e.g. G protein and second-messenger cascades) saturates before all receptors are occupied. It is demonstrated when partial irreversible receptor blockade (e.g. with phenoxybenzamine) first shifts the agonist curve to the right and only later depresses its maximum, and it makes the agonist EC50 lower than its Kd.

Reserve is tissue- and agonist-specific: the same partial agonist may act as a full agonist in a tissue with a large reserve and as a weak partial agonist or antagonist where reserve is small. Examples include insulin receptors on adipocytes and nicotinic receptors at the neuromuscular junction.

Clinical pearl

The large receptor reserve at the neuromuscular junction means that most nicotinic receptors must be blocked before muscle strength falls, so bedside tests can appear normal despite substantial residual neuromuscular block.

TRIn Turkish

Yedek Reseptörler

Maksimal yanıtın oluşması için gerekenden fazla olan reseptörlerdir; bu sayede tam agonist, mevcut reseptörlerin yalnızca bir kısmını işgal ederek maksimal etkiye ulaşabilir.

Reseptör rezervi, reseptörün sonrasındaki sinyal amplifikasyonunun (örneğin G proteini ve ikinci haberci kaskadlarının) tüm reseptörler işgal edilmeden doyuma ulaşması sonucu ortaya çıkar. Varlığı, reseptörlerin kısmen ve geri dönüşümsüz olarak bloke edilmesinin (örneğin fenoksibenzaminle) agonist eğrisini önce sağa kaydırması, maksimumu ise ancak daha sonra düşürmesiyle gösterilir; reseptör rezervi ayrıca agonistin EC50 değerinin Kd'den düşük olmasına yol açar.

Rezerv dokuya ve agoniste özgüdür: aynı kısmi agonist, rezervin büyük olduğu bir dokuda tam agonist gibi, rezervin küçük olduğu bir dokuda ise zayıf kısmi agonist veya antagonist gibi davranabilir. Adipositlerdeki insülin reseptörleri ve nöromüsküler kavşaktaki nikotinik reseptörler buna örnektir.

Nöromüsküler kavşaktaki büyük reseptör rezervi nedeniyle kas gücünün azalması için nikotinik reseptörlerin çoğunun bloke edilmesi gerekir; bu nedenle yatak başı testler belirgin rezidüel nöromüsküler bloka karşın normal görünebilir.

Diğer adları:Reseptör rezervi · Rezerv reseptörler
Updated 24.09.2026 0 views Educational reference — verify against current sources before clinical use.

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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.

 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.

 Half-Maximal Effective ConcentrationYarı Maksimal Etkili Konsantrasyon

The concentration of a drug that produces 50% of its own maximal effect (Emax); the standard measure of agonist potency in concentration–response studies.

 Dissociation ConstantDisosiyasyon Sabiti

The equilibrium constant for dissociation of a drug–receptor complex, equal to the free drug concentration at which half of the receptors are occupied at equilibrium; a lower Kd means higher affinity.

 Non-Competitive AntagonismYarışmasız Antagonizma

Antagonism that cannot be overcome by increasing the agonist concentration, because the antagonist binds irreversibly or acts at a site or step distinct from agonist binding; the maximal agonist response is reduced.

 AgonistAgonist

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).