While pramipexole is used clinically (see below), its D3-preferring receptor binding profile has made it a popular tool compound for preclinical research. For example, pramipexole has been used (in combination with D2- and or D3-preferring antagonists) to interrogate the role of D3 receptor function in rodent models and tasks for neuropsychiatric disorders. Of note, it appears that pramipexole, in addition to having effects on dopamine D3 receptors, may also affect mitochondrial function via a mechanism that remains less understood. A pharmacological approach to separate dopaminergic from non-dopaminergic (e.g. mitochondrial) effects of pramipexole has been to study the effects of the R-stereoisomer of pramipexole (which has much lower affinity to the dopamine receptors when compared to the S-isomer) side-by-side with the effects of the S-isomer.
Parkinson's disease is a neurodegenerative disease affecting the substantia nigra, a component of the basal ganglia. The substantia nigra has a high quantity of dopaminergicneurons, which are nervecells that release the neurotransmitter known as dopamine. When dopamine is released, it may activate dopamine receptors in the striatum, which is another component of the basal ganglia. When neurons of the substantia nigra deteriorate in Parkinson's disease, the striatum no longer properly receives dopamine signals. As a result, the basal ganglia can no longer regulate body movement effectively and motor function becomes impaired. By acting as an agonist for the D2, D3, and D4 dopamine receptors, pramipexole may directly stimulate the underfunctioning dopamine receptors in the striatum, thereby restoring the dopamine signals needed for proper functioning of the basal ganglia.
In a single controlled study of twenty one patients, pramipexole was found to be highly effective in the treatment of bipolar depression. Treatment was initiated at 0.125 mg three times a day and increased at a rate of 0.125 mg three times a day to a limit of 4.5 mg daily until the patients' condition satisfactorily responded to the medication or they could not abide the side effects. The final average dosage was 1.7 ± 0.9 mg daily. The incidence of hypomania in the treatment group was no greater than in the control group.
Several unusual adverse effects of pramipexole (and related D3-preferring dopamine agonist medications such as ropinirole) may include compulsive gambling, punding, hypersexuality, and overeating, even in patients without any prior history of these behaviours. These behaviors have been reported to manifest in almost 14% of patients on dopamine agonist therapies. Other compulsive behaviors such as excessive shopping have been reported.L-DOPA is an indirect acting dopamine agonist with no specificity for any receptor subtypes. As it is the precursor for dopamine it is rarely associated with these disorders. These side effects are thought to be linked to the D3 activity of pramipexole, as D3 receptors are heavily expressed in brain regions involved in mood, behavior, and reward.
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