Dopamine receptor affinity follows which order?

Dopamine receptor affinity follows which order?

• A. Dopamine affinity is highest for D receptors, followed by beta, then alpha
• B. Beta receptors have the highest affinity, followed by D, then alpha
• C. Alpha receptors have the highest affinity, followed by D, then beta
• D. Dopamine affinity is equal for D, beta, and alpha receptors

Answer: (A)

Dopamine binds most strongly to its own receptor subtypes, the dopamine receptors (D1/D2), with progressively lower affinity for adrenergic receptors. This means dopamine has the highest affinity for D receptors, followed by β-adrenergic receptors, and the lowest affinity for α-adrenergic receptors. This ranking explains the dose‑dependent clinical effects: at low doses, dopamine mainly activates D receptors (e.g., renal vasodilation and increased perfusion); at intermediate doses, β receptors are engaged (increasing heart rate and contractility); at very high doses, α receptors may be activated (leading to vasoconstriction). The other suggested orders imply a stronger or equal affinity for β or α receptors, which does not align with the receptor-binding data.

Dopamine binds most strongly to its own receptor subtypes, the dopamine receptors (D1/D2), with progressively lower affinity for adrenergic receptors. This means dopamine has the highest affinity for D receptors, followed by β-adrenergic receptors, and the lowest affinity for α-adrenergic receptors. This ranking explains the dose‑dependent clinical effects: at low doses, dopamine mainly activates D receptors (e.g., renal vasodilation and increased perfusion); at intermediate doses, β receptors are engaged (increasing heart rate and contractility); at very high doses, α receptors may be activated (leading to vasoconstriction). The other suggested orders imply a stronger or equal affinity for β or α receptors, which does not align with the receptor-binding data.