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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.

  • Îą1

    • 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 Îą1 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.

 

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