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Dopamine

German: Dopamin

1 Definition

Dopamine is a neurohormone that belongs to the group of catecholamines and has the formula (OH)2C6H3–CH2–CH2NH2.

2 Metabolism

2.1 Synthesis

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.

2.2 Decomposition

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.

3 Function

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.

4 Pathophysiology

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.

5 Pharmacology

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.

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