Action of Dopamine at Different Doses
Dopamine Receptors and Sensitivity
Dopaminergic Receptors: D1 and D2
Most sensitive ⟶ Stimulated even at low concentration of dopamine ⟶ low dose is sufficient to activate them.
Renal blood vessels.
Proximal tubular cells.
Moderately sensitive ⟶ requires relatively high concentration ⟶ stimulated at moderate doses.
Present in heart.
Least sensitive ⟶ requires high concentration ⟶ stimulated only at large doses of dopamine.
Present in blood vessels
Actions of Dopamine at Different Doses
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.
Stimulates β1 receptor in heart
Stimulates α1 receptors in blood vessels
Increased blood pressure
Increased preload on heart.
Dopamine In Heart Failure
Actions produced at low to moderate doses are desired. i.e.
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.