(−)-Quinpirole hydrochloride

(-)-Quinpirole hydrochloride has been used as a selective D2 dopamine (DA) receptor agonist in various experiments.

Quinpirole is a dopamine agonist with high affinity for the D₂ and D₃ dopamine receptor subtypes. Specific [³H]quinpirole binding in rat brain was saturable, and dependent on temperature, membrane concentration, sodium concentration and guanine nucleotides. The putative D₂ dopamine receptor agonist quinpirole (LY 171,555) is the most widely used D₂ agonist in in vivo and in vitro studies. Quinpirole hydrochloride is an active enantiomer of (±)-quinpirole.Saturation analysis revealed high affinity binding characteristics (K_D = 2.3 +/- 0.3 nM) which were confirmed by association-dissociation kinetics. The regional distribution of [³H]quinpirole binding sites roughly paralleled the distribution of [³H]spiperone binding sites, with greatest densities present in the striatum, nucleus accumbens and olfactory tubercles. A variety of drugs, most notably monoamine oxidase inhibitors (MAOls), inhibit the binding of [³H]quinpirole, but not [³H]spiperone or [³H](-)N-n-Propylnorapomorphine, in rat striatal membranes by a mechanism that does not appear to involve the enzymatic activity of MAO. Clinically antidepressant MAOIs exhibited selectivity between sites labeled by [³H]quinpirole and [³H]spiperone as did a number of structurally related propargylamines and N-acylethylenediamine derivatives and other drugs such as debrisoquin and phenylbiguanide. The MAOIs clorgyline and Ro 41-1049 were the most potent. MAOIs interact with a novel binding site that is labeled by [³H]quinpirole or that modulates [³H]quinpirole binding. This site may be associated with D₂-like dopamine receptors.

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