Pharmacology
Pramipexole acts as a partial/full agonist at the following receptors:
- D2S receptor (Ki = 3.9 nM; IA = 130%)
- D2L receptor (Ki = 2.2 nM; IA = 70%)
- D3 receptor (Ki = 0.5 nM; IA = 70%)
- D4 receptor (Ki = 5.1 nM; IA = 42%)
Pramipexole also possesses low/insignificant affinity (500-10,000 nM) for the 5-HT1A, 5-HT1B, 5-HT1D, and α2-adrenergic receptors. It has negligible affinity (>10,000 nM) for the D1, D5, 5-HT2, α1-adrenergic, β-adrenergic, H1, and mACh receptors. All sites assayed were done using human tissues.
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 dopaminergic neurons, which are nerve cells 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.
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