Dopamine
| Overview |
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- Dopamine is a central neurotransmitter important for regulation of movement and control of certain pituitary hormones (See: Basic Hypothalamic-Pituitary Coordination). It is also the immediate synthetic precursor of norepinephrine in adrenergic neurons. When administered pharmacologically, dopamine does not cross the blood brain barrier, and thus primarily acts as a direct adrenergic agonist as discussed here.
| Pharmacological Targets |
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- Overview
- The pharmacological targets of dopamine are concentration dependent. At low concentrations, dopamine only activates its cognate dopamine receptors; however, at moderate concentrations dopamine can activates beta1 receptors and at high concentrations dopamine displays activity on alpha1 receptors
- Dopamine Receptors
- These are the endogenous receptor for dopamine and are prominently found on the renal and mesenteric vasculature. Activation of these receptors leads to vasodilation.
| Pharmacological Effects |
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- Vascular Effects
- As described above activation of dopamine receptors in renal and mesenteric vessels leads to their vasodilation and thus modest drops in systemic vascular resistance (SVR). This reduction in SVR may be reversed at extremely high pharmacological doses of dopamine due to activation of alpha1 receptors as these levels.
- Cardiac Effects
- Stimulation of beta1 receptors yields increased increased heart rate and contractility, yielding higher cardiac outputs.
- Blood Pressure
- The effects of dopamine on blood pressure are the result of its modulation of SVR and cardiac activity. In general, at low to moderate doses the reductions in SVR are modest and occur in the context of significant increases in cardiac output. Consequently, dopamine infusions typically lead to increased systolic arterial pressures, unchanged diastolic pressures, and thus a widened pulse pressure and mean arterial pressure (MAP).
| Therapeutic Uses |
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- The theoretical advantage of using dopamine in contexts of shock are its capacity to raise arterial pressures without sacrificing renal blood flow due to the actions of dopamine receptors. Thus, dopamine was seen as the drug of choice for shock in the context of acute renal failure. However, subsequent studies have shown little evidence that usage of dopamine increases survival above that of other vasopressors.
- The major use of dopamine in critical care contexts now is the fact that dopamine can be administered via peripheral IV lines, whereas as epinephrine and norepinephrine require larger, central lines. Therefore, in critically ill patients with poor vascular access, dopamine is the vasopressor of choice until a larger line can be placed.