Dopamine is one of the best known neurotransmitters and one of the most important in regulating our behavior. It influences aspects as relevant as the perception of gratification and pleasure, as well as movement, memory and motivation. It is a hormone that is synthesized in different areas of the organism, one of the best known being the substantia nigra and its connection with the basal ganglia, and the neurons of the mesocortical pathway.
However, there are numerous disorders and problems that cause it not to be synthesized as much as it should be, making it necessary to use external mechanisms such as drugs to increase its levels. One of these drugs, frequently used, is levodopa . In this article we will talk about it.
Levodopa: what is it?
Levodopa or L-dopa is a medication or psychopharmaceutical that has been isolated from dopa, the metabolic precursor of dopamine, which in turn is derived from tyrosine (like all other catecholamines including noradrenaline) thanks to the enzyme tyrosine hydroxylase.
It is a catecholamine that is part of the body, being synthesized by the body while also being added externally from the diet. It is usually obtained directly from the diet. Inside the body it is degraded by the enzyme monoamine oxidase or MAOI , which allows its synthesis and levels to be regulated.
Used externally as a medication, it enables the absence of dopamine to be dealt with at brain level, as it can cross the blood-brain barrier (unlike dopamine itself) and be degraded and transformed into dopamine thanks to the enzyme decarboxylase. This makes it possible to treat problems derived from the deficit of this last neurotransmitter , as occurs with many motor disorders.
Mechanism of action
Levodopa works as a treatment for problems such as Parkinson’s due to its action on the nervous system. The blood-brain barrier does not allow external dopamine to enter the brain. However, levodopa, its immediate precursor, does have this ability. This drug will later be transformed into dopamine in the striated body of the basal ganglia thanks to the decarboxylation produced by dopaminergic neurons, which will eventually increase dopamine levels in the brain.
Levodopa is applied in conjunction with peripheral action inhibitors such as carbidopa , which allows levodopa to remain undegraded as it passes through the gastrointestinal tract and to enter the central nervous system properly.
Disorders in which it is used
Levodopa as a drug is often used in various disorders and in different medical situations and complications arising from a lack of dopamine in some brain region. Its main medical uses include the following.
The main and best known disorder in which Levodopa is used as a drug is Parkinson’s disease. This disorder is characterized by a degeneration of the substantia nigra and in the basal ganglia produced by a deficit in dopamine synthesis. The well-known parkinsonian tremors appear, in situation of rest, motor slowing down and postural and movement problems, as well as facial inexpressivity.
Levodopa drug treatment is one of the most common, generating an increase in dopamine levels in the brain . It is the drug of choice and produces an important improvement in the symptoms (for example, it eliminates weakness and lack of movement and in some cases reduces tremors).
Parkinsonian syndromes due to encephalitis or cerebral arteriosclerosis
Inflammation of the brain or encephalitis can generate alterations in the cerebral nuclei that regulate dopaminergic transmission, movement and the nigrostriatal pathway. The use of levodopa is indicated in these cases.
Consumption of neuroleptics
One of the most common side effects of neuroleptics or antipsychotics, especially the typical or first-generation ones, is the presence of extrapyramidal symptoms such as akathisia or tremors . This is produced by the blockage of dopamine receptors in the nigrostriatal pathway (although the target of typical neuroleptics is the mesolimbic pathway, their action is non-specific and reaches other nerve pathways as well).
Therefore, the use of antiparkinsonian medication is frequent, using among other substances levodopa (sometimes mixed with other substances such as carbidopa) in order to reduce these symptoms.
Poisoning: carbon monoxide or manganese
Another indication for levodopa is in therapeutic use to treat damage to the nervous system caused by manganese or carbon monoxide poisoning .
Side effects of levodopa
As with all psychotropic drugs, levodopa use can have more or less serious side effects. However, these are usually mild and in many cases temporary. The most likely are typical of many other medications: nausea, vomiting, decreased appetite, tremors and nervous contractions , blurred vision, darkening of urine, insomnia or sedation, fatigue and agitation or restlessness.
Behavioral alterations such as hypersexuality may also appear, and paranoid-type ideas and depressive symptoms may appear. Oedemas, urinary problems (excess or deficit), weakness, headaches or numbness may also appear.
In addition, it should be noted that more serious problems may occur that require immediate attention such as seizures, persistent diarrhea, arrhythmias, suicidal ideation, or allergic reactions.
Contraindications and precautions
In addition to the secondary symptoms, it should be noted that it is not always advisable to use this drug. Among its multiple contraindications are mainly those cases of malignant melanoma (since it can activate the tumor and make it worse). Also should avoid the consumption of this medicine and MAO inhibitors , antihypertension medication, anesthetics (can generate arrhythmia) or anticonvulsants or tranquillizers (reduces the effect).
Finally, patients with glaucoma, minors, pregnant women, subjects with psychosis (unless it is applied as an antiparkinsonian to the consumption of neuroleptics) or heart problems should not consume it either or if necessary they should consult their doctor what precautions to use.