Abbreviation for L-3,4-dihydroxyphenylalanine, the direct biochemical precursor for DOPAMINE (see NEUROTRANSMITTERS). In the biosynthetic pathway for CATECHOLAMINE synthesis (dopamine, NORADRENALINE and ADRENALINE), the amino acids TYROSINE and phenylalanine are converted to L-DOPA by the enzyme TYROSINE HYDROXYLASE. L-DOPA is then converted to dopamine by the enzyme DOPA DECARBOXYLASE. In the dopamine-containing neurons of the brain, the dopamine is packaged into VESICLES and serves as the neurotransmitter for that neuron. In noradrenaline-containing neurons, the dopamine is further transformed into noradrenaline.
Thus, L-DOPA serves as a precursor for both dopamine and noradrenaline. L-DOPA is best known for its role as the principle pharmacotherapeutic treatment for PARKINSON’S DISEASE, offering relief from symptoms by temporarily increasing levels of dopamine, thus improving motor function. Such treatment is known as a REPLACEMENT THERAPY because it seeks to replace chemicals absent from the diseased brain. L-DOPA is taken orally by patients in combination with a peripheral decarboxylase inhibitor to prevent the L-DOPA being degraded in the gut. (When it was first introduced into clinical practice, very large doses were given because it was not realized how much L-DOPA was being broken down before it reached the brain—see Sacks, 1976.)
Reference
Sacks O. (1976) Awakenings, revised edition, Pelican Books: Harmondsworth.
ANN E.KELLEY
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