Dopamine is a neurohormone that belongs to the group of
catecholamines and has the formula (OH)2C6H3–CH2–CH2NH2.
Dopamine can be synthesized in the human organism from the
amino acids [[phenylalanine and
tyrosine respectively. The reaction stages necessary for the synthesis take place in the cells of
adrenal medulla,
hypothalamus, and
substantia nigra and in other parts of the nervous system.
Dopamine is a precursor of the synthesis of
adrenaline and
noradrenaline, but also functions by itself as a neurotransmitter.
In the first step of the dopamine
biosynthesis, the tyrosine molecule on the C3 atom is equipped with a second hydroxyl group by the
enzyme tyrosine
hydroxylase and thus is present as 3.4-Dihydroxyphenylalanine (dopa). After that, the enzyme dopa
decarboxylase decarboxylizes the developed molecule to biogenic amine, dopamine.
After secretion in the synaptic cleft, dopamine can be reabsorbed in the presynapsis; there is also the potential of an enzymatic activation. This is mediated by two enzymes:
- Catechol-O-methyltransferase (COMT): transmission of a methyl group from S-adenosyl methionine into catecholamines
- Monoaminooxidase (MAO): Deamination into vanillylmandelic acid, which can be detected in urine.
Dopamine takes effect in the human organism through
adrenoceptors or through the specific
dopamine receptors D1 to Dx (exact number remains unknown). It acts as a sympathomimetic, but in low concentration increases the circulation of the abdominal and kidney vessels, thus increasing
renal perfusion.
Besides, dopamine inhibits the secretion of
prolactin in the
hypothalamus and disinhibits it in the area of
striatum and
basal ganglia.
An
overproduction of dopamine can occur in the so-called
pheochromocytoma. This leads, among others, to
hypertension, sweating, headaches and
tachycardia. An increasing lack of dopaminergic
neurons of the substantia nigra is the cause of the
Parkinson’s disease.
Dopamines are used in
emergency therapy and
shock therapy. It is mainly used for the acute increase of blood pressure, for the stimulation of
heart and
kidney functions in cardiac arrest and acute cardiac insufficiency.
In Parkinson’s disease, dopamine is typically substituted in the form of its precursor molecule dopa, which can pass through the blood-brain barrier.
