Mepiprazole, a new psychotropic drug: Effects on uptake and retention of monoamines in rat brain synaptosomes

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Abstract
The influence of mepiprazole (EMD 16,923), a new pyrazol-ylalkyl-piperazine derivative, on the uptake of 3H-norepinephrine (NE), 3H-dopamine (DA), and 3H-serotonin (5-HT) into rat brain synaptosomes from cerebral cortex, corpus striatum, and hypothalamus was investigated in comparison with several psychotropic drugs, including oxypertine, d-amphetamine, imipramine, desipramine, chlorimipramine, amitriptyline, and chlorpromazine in vitro. Mepiprazole was a relatively weak inhibitor of monoamine uptake and exhibited its strongest action on the hypothalamic 5-HT uptake, being almost equipotent with desipramine (IC50=0.9 μM). Furthermore, the influence of the drugs on the retention of 3H-amines previously taken up by whole rat brain synaptosomes was studied. Unlike the tricyclic antidepressants, mepiprazole as well as oxypertine and d-amphetamine markedly increased the efflux of radioactivity during a 20-min incubation at 37°C at low concentrations (10−6 to 10−5 M), whereas at 10−4M all drugs greatly enhanced the efflux. The ability of mepiprazole to increase 5-HT concentration at the receptor level by a combination of neuronal uptake inhibition and release is discussed in relationship to the central actions of the drug.