Aripiprazole is the first
dopamine D(2)/D(3) receptor partial agonist approved for use in the treatment of
psychiatric disorders including
schizophrenia,
bipolar disorder, and
unipolar depression in the US.
Aripiprazole has demonstrated a relatively favorable side effect profile compared to other commonly prescribed
antipsychotics, including a low propensity for treatment-limiting extrapyramidal symptoms,
hyperprolactinemia, and
body weight gain. In an effort to elucidate
aripiprazole's pharmacological activity in relation to clinically relevant fluctuation of
dopamine D(2) receptor reserves, we compared the properties of
aripiprazole to other
antipsychotics,
quetiapine,
clozapine,
olanzapine,
ziprasidone,
risperidone and
haloperidol, a
dopamine D(2) receptor partial agonist,
bifeprunox,
dopamine D(3) receptor modulators, BP897 (N-[4-[4-(2-Methoxyphenyl)-1-piperazinyl]butyl]
naphthalene-2-carboxamide) and
GR103691 (4'-Acetyl-N-[4-[4-(2-methoxyphenyl)piperazin-1-yl]butyl]
biphenyl-4-carboxamide), and a 5-HT(1A) partial agonist,
buspirone using
forskolin-stimulated cAMP accumulation in clonal Chinese hamster ovary cell lines expressing low and high densities of human
dopamine D(2S) receptors (hD(2S)-Low and hD(2S)-High, respectively). In hD(2S)-Low cells lacking receptor reserves for
dopamine, all drugs antagonized
dopamine responses, and their potencies correlated well with respective affinities. In hD(2S)-High cells possessing receptor reserves, all
antipsychotics except
aripiprazole antagonized
dopamine responses, and their antagonist potencies were less than those in hD(2S)-Low cells treated with the equal
dopamine concentration. In contrast,
aripiprazole and
bifeprunox acted as full agonists. BP897,
GR103691 and
buspirone acted as partial agonists. These data suggest that the level of receptor reserves influences antagonist potencies and side effects associated with
antipsychotics.
Aripiprazole's unique receptor reserve dependent properties may account for its favorable tolerability in the clinical setting.