Active Ingredients

Dopamine agonist – effect, application & risks

Dopamine agonist

dopamine agonist or dopamine antagonist is a drug that can stimulate dopamine receptors. Dopamine agonists are used, among other things, to treat Parkinson’s disease , restless legs syndrome or as emetics.

What is a dopamine agonist?

Dopamine agonists can bind to dopamine receptors (D-receptors) just like the neurotransmitter dopamine . Depending on the receptor selectivity, the agonists are divided into D1/5 and D2/3/4 agonists.

By binding to the receptor, dopamine agonists produce a dopamine-like effect. The selective D1/5 agonists such as SKF 81297 or dihydrexin play no role in the treatment of diseases. Agonists that bind to the D2 receptors play a role in the therapy of various diseases.

Known D2 receptors are the drugs ropinirole , rotigotine , piribedil or pramipexole . Side effects such as nausea , vomiting , low blood pressure , hallucinations , or confusion may occur with the use of dopamine agonists .

Pharmacological action

Dopamine agonists work by stimulating dopamine receptors like dopamine. Dopamine is a neurotransmitter that belongs to the group of catecholamines . It is made in the human body from the amino acids tyrosine and phenylalanine . The neurotransmitter belongs to the sympathomimetics. These substances increase the effect of the sympathetic nervous system . In low concentrations, dopamine increases blood flow to the abdominal and kidney vessels.

One dopaminergic processing pathway is the mesostriatal system, which originates in the substantia nigra in the midbrain . Here, dopamine takes on important tasks in controlling movements. Disturbances in this system are one of the causes of the hypokinetic movement disorders in Parkinson’s disease.

In the mesolimbic system, a lack of dopamine leads to listlessness . Dopamine antagonists can compensate for a lack of dopamine and help the patient to be more active and enjoy life . If the mesocortical system is underactive, psychoses of the schizophrenic type can develop. Dopamine agonists also become effective in this system by binding to the corresponding receptors .

Dopamine agonists are also effective in the tuberoinfundibular system. They inhibit the release of the hormone prolactin on the neurons that go from the arcuate nucleus to the anterior lobe of the pituitary gland . Prolactin is a hormone responsible for milk secretion (lactation) during breastfeeding .

Medical Application & Use

One of the main indications for the use of dopamine agonists is Parkinson’s disease. Degenerative changes in the extrapyramidal motor system (EPMS) result in a lack of dopamine. This messes up the neurotransmitter balance. This manifests itself in neurological disorders and in particular in motor system disorders .

Typical symptoms of Parkinson’s disease are immobility, slowed voluntary motor activity , increased basic tension in the skeletal muscles and tremors . In order to slow down the course of the disease and alleviate the clinical symptoms, patients are usually administered dopamine in the form of the precursor L-dopa . However, the effectiveness of this precursor alone is usually not sufficient, so that the D2 receptors are additionally simulated with the help of the agonists.

Another indication for dopamine agonists is restless legs syndrome (RLS). The disorder of the extrapyramidal motor system is one of the hyperkinesias. The disease manifests itself in twitching , abnormal sensations and pain in the legs. Similar to Parkinson’s disease, restless legs syndrome is treated with a combination of L-dopa and dopamine agonists.

But dopamine agonists not only play a role in motor function, they also have an inhibiting effect on prolactin secretion. That is why they are also used for weaning . They are also used in the treatment of hormonal complaints that are associated with increased production of prolactin. Prolactinomas are treated with dopamine agonists such as cabergoline or bromocriptine .

Prolactinomas are hormone-producing tumors of the anterior pituitary gland . The resulting prolactinemia leads to hypoestrogenemia in women with no ovulation and no menstrual bleeding . In half of the patients, breast milk leaks spontaneously from the mammary glands ( galactorrhea ). Some dopamine agonists are used to treat erectile dysfunction . The term erectile dysfunction refers to the lack of erection of the penis when aroused .

Risks & side effects

Typical side effects of dopamine agonists include nausea, vomiting, and headaches. It can lead to a drop in blood pressure and tiredness . Some patients experience somnolence or sleep disturbances . Restlessness is also frequently observed.

Other side effects of dopamine agonists are incontinence , edema , hair loss or dizziness . In rare cases, patients develop hallucinations or even psychosis after taking dopamine agonists .

In some patients, inhibition of prolactin production is desirable. However, during lactation , the effect of dopamine agonists on milk flow needs to be considered. Otherwise, the flow of milk may inadvertently stop.

Dopamine agonists must not be administered in organ fibrosis . There is then a risk of connective tissue transformation (fibrosis) of the heart valves . A pleural effusion and high blood pressure are also contraindications . The use of dopamine agonists in hepatic insufficiency is also counterproductive. As a rule, the drugs must not be combined with neuroleptics .

Website | + posts

Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.