Dopamine (Intropin)

• Dopamine is the immediate precursor of norepinephrine.

• Dopamine is a CNS neurotransmitter associated with the basal ganglia and motor control.

• Cardiovascular Effects (Dopamine)

  • Vasodilator:

    • At low doses, dopamine (Intropin) interactions with D₁ receptor subtype result in renal, mesenteric and coronary vasodilation.

      • This effect is mediated by an increase in intracellular cyclic AMP

    • Low doses result in enhancing glomerular filtration rates (GFR), renal blood flow, and sodium excretion.

  • Positive inotropism:

    • At higher doses, dopamine increase myocardial contractility through activation of ß₁ adrenergic receptors

    • Dopamine (Intropin) also promotes release of myocardial norepinephrine.

    • Dopamine (Intropin) at these higher dosages causes an increase in systolic blood and pulse pressure with little effect on diastolic pressures.

  • Vasopressor:

    • At high doses dopamine (Intropin) causes vasoconstriction by activating a₁ adrenergic receptors

• Therapeutic use (Dopamine)

  •  Dopamine may be helpful in managing both cardiogenic and hypovolemic shock

    • Dopamine also may improve kidney function by enhancing renal blood perfusion despite low cardiac output.

      • Oligouria (low urine output) may be an indication of inadequate renal perfusion.

    • Example: dopamine may be used, in postoperative cardiopulmonary bypass patients who exhibit:

      • Low systemic blood-pressure

      • Increased atrial filling pressures

      • Low urinary output

    • Unique among catecholamines in that dopamine can simultaneously increase:

      • Myocardial contractility

      • Glomerular filtration rate

      • Sodium excretion

      • Urine output

      • Renal blood flow

• Increased sodium excretion following dopamine may be due to inhibition of aldosterone secretion.

  • Dopamine may inhibit renal tubular solute reabsorption (suggesting that natriuresis & diuresis may occur by different mechanisms.)

• Fenoldopam and dopexamine are examples of drugs that may be useful in treating heart failure by improving myocardial contractility.

• Dopamine (Intropin) at higher doses increases myocardial contractility by ß₁ - adrenergic receptor activation.

  • Ventilation effects:

    •  Dopamine IV infusion interferes with ventilatory responses to arterial hypoxemia

• Dopamine (Intropin) acts as inhibitory neurotransmitter at carotid bodies and as a result one may observe an unexpected ventilation depression in patients treated with IV dopamine (Intropin), for example, to enhance myocardial contractility.

• Dopexamine (Dopacard)

  • Dopexamine is a synthetic catecholamine that activates both dopaminergic and β₂-adrenergic receptors.

  • Administration of dopexamine may result in a slight positive inotropic effect due to β₂-adrenergic agonist activity; furthermore, this drug may potentiate effects of endogenous norepinephrine, secondary to reuptake blockade.

  • Dopexamine enhances creatinine clearance.