Action of Dopamine at Different Doses
Dopamine Receptors and Sensitivity
Dopaminergic Receptors: D1 and D2
D1
Most sensitive ⟶ Stimulated even at low concentration of dopamine ⟶ low dose is sufficient to activate them.
Present in:
Renal blood vessels.
Proximal tubular cells.
Heart.
Adrenergic receptors
β1
Moderately sensitive ⟶ requires relatively high concentration ⟶ stimulated at moderate doses.
Present in heart.
α1
Least sensitive ⟶ requires high concentration ⟶ stimulated only at large doses of dopamine.
Present in blood vessels
Actions of Dopamine at Different Doses
Low dose
↓
Stimulates D1 receptors
↓
1. In renal blood vessels ⟶ vasodilatation ⟶ maintains/increases renal perfusion ⟶ increases GFR.
2. In proximal tubular cells ⟶ decreases sodium reabsorption ⟶ natriuresis ⟶ decrease in blood volume ⟶ decrease preload on heart.
3. In heart ⟶ Positive ionotropic effect.
Moderated doses
↓
Stimulates β1 receptor in heart
↓
Positive ionotropic.
Large doses
↓
Stimulates α1 receptors in blood vessels
↓
Vasoconstriction
↓
Increased blood pressure
↓
Increased preload on heart.
Dopamine In Heart Failure
Actions produced at low to moderate doses are desired. i.e.
Maintaining GFR.
Natriuretic effect.
Positive ionotric effect.
Action produced at a large dose is not desired i.e. vasoconstriction.
So in heart failure, dopamine should be given in low to moderate doses but not in a large doses.