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Dopamine is a vital neurotransmitter in the brain. It plays a role in several functions in the brain including movement, memory, pleasurable reward, behavior and cognition, attention, inhibition of prolactin production, sleep, mood and learning.
Excess and deficiency of this vital chemical is the cause of several disease conditions. Parkinson's disease and drug addiction are some of the examples of problems associated with abnormal dopamine levels.
Uses of dopamine are both in cardiovascular diseases as well as central nervous system diseases.
Dopamine in blood is unable to cross the blood-brain barrier to reach the brain. In Parkinson’s disease and dopa-responsive dystonia there is a deficiency of dopamine in specific areas of the brain like the basal ganglia.
Levodopa is a dopamine precursor. It enters the brain by crossing the blood-brain barrier. It is typically co-administered with an inhibitor of peripheral decarboxylation (DDC, dopa decarboxylase), such as carbidopa or benserazide. This additional drug prevents breakdown of the levodopa to dopamine in the peripheral blood and ensures that maximum amount reaches the brain.
There are several other dopamine agonists and inhibitors of alternative metabolic route for dopamine by catechol-O-methyl transferase that may be used for these diseases. These include entacapone and tolcapone.
When administered through an IV line, dopamine does not cross the blood brain. It acts on the heart by raising its contractility and blood pressure. This is useful in heart failure
The effects of intravenous dopamine are dose dependent. The dosages include:
2-5 μg/kg/min (low dose) - This dose leads to renal and mesentric vasodilation (via D1 receptors). This dilatation of blood vessels of kidney leads to raised glomerular filtration rate and sodium excretion and raises urine output, leads to better tissue perfusion, BP stabilization. This dose is used in Cardiogenic shock as IV infusion.
5-10 μg/kg/min (moderate dose) - This dose also causes renal and mesentric vasodilation (via D1). This raises the GFR and sodium excretion and raises urine output, better tissue perfusion and BP stabilization. This dose also acts on Beta 1 receptors on heart and makes its contractions and pumping more forceful. This is used in Acute exacerbation of congestive heart failure as IV infusion.
More than 20 μg/kg/min (high dose) - This leads to constriction of blood vessels via Alpha 1 receptors. This leads to decreased renal blood flow and decreased urine output.