Plasma drug and homovanillic acid levels in psychotic patients receiving neuroleptics.

Plasma neuroleptic and homovanillic acid (HVA) levels are reported for a group of psychotic subjects exhibiting clinical improvement in response to neuroleptic medication. Clinically effective plasma neuroleptic levels, measured by a radioreceptor assay and expressed as either nanomolar concentration of parent drug or as haloperidol equivalents, were different for the seven neuroleptics tested. Plasma HVA, measured by high-pressure liquid chromatography with electrochemical detection (LCEC), increased in response to initiation of neuroleptic treatment and decreased when neuroleptic medication was withdrawn. No correlations were found between plasma neuroleptic level and HVA level or between HVA level and clinical response. Mean therapeutic plasma levels of neuroleptics, expressed as nanomolar concentration of parent drug, correlated with the potencies of the same drug in displacing 3H-dopamine from D-1 and D-2 receptors in rat striatal membranes. This represents the first report that clinically measured plasma concentrations are high enough to displace dopamine from its specific receptors in the CNS.

Dopaminergic 3H-agonist receptors in rat brain. New evidence on localization and pharmacology.

Recent methodological advances have allowed the reliable assay of specific dopaminergic 3H-agonist binding sites in rat striatum. Successful assay depends on preincubation of tissue homogenates at 37 degrees C; this results in a guanyl nucleotide-sensitive and dopamine (DA)-dependent increase in the density (Bmax) of 3H-agonist binding. Lesions of DA terminals or drugs which deplete DA levels prevent the preincubation-induced increase in binding, and this effect is completely reversible by preincubation with added DA. In contrast, kainic acid lesions irreversibly reduce 3H-agonist binding. It is concluded that the evidence supporting the existence of presynaptic "D-3" sites is artefactual and that 3H-DA binding sites are more likely related to post-synaptic receptors. 3H-DA binding involves two sites, one of which has pharmacologic properties similar to D-1 receptors, whereas the other resembles D-2 receptors. The affinity of 15 antipsychotic drugs for 3H-haloperidol binding sites was highly correlated (R = 0.94) with their inhibitory potency at a subset of 3H-DA binding sites. However, the inhibition of 3H-DA binding by antipsychotic drugs was noncompetitive. These findings can be explained by an allosteric model, whereby antagonists bind to a site different from but allosterically linked to a high-affinity 3H-DA binding site.

Differential effects of the enantiomers of 3-(3-hydroxyphenyl)-N-n-propylpiperidine (3-PPP) at dopamine receptor sites.

The agonist actions of 3-PPP at central dopamine (DA) autoreceptors were found to reside mostly in its (+) enantiomer, (+)-3-PPP also reduced striatal content of DOPAC and HVA, whereas (-)-3-PPP elevated HVA levels. Only (-)-3-PPP antagonized DA stimulation of DA-receptor linked adenylate cyclase. It was more effective than (+)-3-PPP at inhibiting [3H]DA binding to striatal membranes. The results suggest that (+)-3-PPP may act predominantly at DA autoreceptors, while (-)-3-PPP exhibits weak affinity for presynaptic and postsynaptic DA receptors.

[3H]dopamine binds to D-1 and D-2 receptors in rat striatum.

Although saturation studies suggest that [3H]dopamine binds to a homogeneous class of stereospecific sites in rat striatal membranes, pharmacologic analysis reveals two distinct sites, one with high and another with low antagonist affinities. The affinity of antagonists for the first site is correlated with their affinity for [3H]butyrophenone binding sites; affinity for the second site is correlated with inhibitory potency against the dopamine-stimulated adenylate cyclase. These results suggest that [3H]dopamine binds to D-1 and D-2 receptors.

Reversible decrease in dopaminergic 3H-agonist binding after 6-hydroxydopamine and irreversible decrease after kainic acid.

Six days after the unilateral intrastriatal injection of 30 ug 6-hydroxydopamine (6-OHDA) the number of stereospecific 3H-dopamine and 3H-apomorphine binding sites (Bmax) was reduced by 50-60% in the caudate nucleus ipsilateral to the lesion. The dopamine content of the lesioned caudate nucleus was also reduced to 2% of the contralateral side or of sham-operated controls. The preincubation of depleted homogenates with added dopamine reversed the effects of 6-OHDA on the Bmax of 3H-agonists. A similar pattern of depletion, decrease in binding and in vitro reversal by dopamine was observed after a single injection of reserpine (4.0 mg/kg, im.). The intrastriatal injection of kainic acid also lowered the Bmax of 3H-agonists by 65% without altering dopamine content. Preincubation of homogenates of kainic acid-lesioned caudate nuclei with 355 nM (endogenous) dopamine did not reverse the decrease in binding. We conclude that treatments which deplete endogenous dopamine, including the lesion of nigrostriatal terminals, induce a reversible change in the parameters of 3H-agonist binding whereas the destruction of intrinsic caudate neurons with kainic acid results in an irreversible loss of receptors.

Dopamine receptors in rat brain regions. Optimal conditions for 3H-agonist binding, pH dependency and lack of inhibition by ascorbic acid.

The binding of dopaminergic agonist and antagonist radioligands was investigated in rat brain regions. A 30-min preincubation of homogenates of caudate nucleus or mesolimbic brain regions at 37 degrees induced a several-fold increase in the stereospecific binding of [3H]-dopamine or [3H]apomorphine to the subsequently washed particulate fraction, whereas it induced a slight decrease in [3H]spiroperidol binding. Stereospecific 3H-agonist binding was not observed in brain regions devoid of dopaminergic innervation. Guanosyl nucleotides, EDTA or ethyleneglycol-bis-(beta-amino-ethyl ether) N,N'-tetraacetate (EGTA), included in the preincubation buffer, antagonized the stimulation of 3H-agonist binding. The stereospecific binding sites of 3H-agonists were saturable with equilibrium dissociation constants (Kd) of 1-2 nM. High-affinity binding was pH dependent, with different pH optima for each radioligand. Several dopamine receptor agonists and antagonists were potent inhibitors of stereospecific [3H]dopamine binding, whereas l-ascorbic acid was inactive at concentrations as high as 1.0 mM. The stereospecific binding of [3H]apomorphine or [3H]spiroperidol was also unaffected by ascorbic acid. The nonspecific (d-butaclamol-insensitive) portion of 3H-agonist binding was weakly inhibited by concentrations of ascorbic acid higher than 0.01 mM. This effect was also observed in the cerebellum and spinal cord, where none of the 3H-agonist binding was stereospecific. It is concluded that the portion of 3H-agonist or 3H-antagonist radioligand binding which is related to dopamine receptors is unaffected by ascorbic acid.

Biogenic amine metabolites in human lung tumor cells: histochemical and mass-spectrographic demonstration.

Three continuous cell lines isolated from small cell carcinoma of the lung (SCCL) have been examined for their ability to take up and metabolize the biogenic amine precursors, L-DOPA and 5-hydroxytryptophane (5-HTP). In two of the three lines formaldehyde-induced fluorescence (FIF) and mass-spectrographic analysis indicated specific uptake and metabolism of L-DOPA and 5-HTP.

Antipsychotic drug effects on dopamine and serotonin receptors: in vitro binding and in vivo turnover studies.

The stereospecific binding sites of [3H]spiroperidol in frontal cortical regions of the rat brain have a higher affinity for serotonin than they do for dopamine, although the reverse relative affinity is observed in the caudate nucleus and in mesolimbic regions. The antipsychotic butyrophenones haloperidol and butaclamol compete with comparably high affinities for [3H]spiroperidol binding sites in all of the above brain regions. Both butyrophenones accelerated dopamine turnover in these three brain regions without altering serotonin turnover. A chronic treatment regimen with fluphenazine which induced tolerance to the metabolic effects of haloperidol in all three brain regions also induced tolerance to its behavioral effects. The number of binding sites of [3H]spiroperidol were increased in the caudate nucleus and mesolimbic regions but not in the frontal cortex of tolerant animals. These results are consistent with the hypothesis that [3H]spiroperidol interacts with a serotonergic site in the frontal cortex. However, the in vitro interaction of antipsychotic drugs with this receptor does not seem to be related to their acute or chronic effects on neurotransmitter function in the frontal cortex in vivo.

Apomorphine-haloperidol interactions: different types of antagonism in cortical and subcortical brain regions.

Apomorphine, a dopamine (DA) receptor stimulant induced a dose-dependent decrease in the content of the dopamine metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the olfactory tubercle and striatum of rats, but it was ineffective in the frontal cortex. Apomorphine also antagonized the haloperidol-induced accumulation of DOPAC and HAV in the olfactory tubercle and striatum, whereas in the frontal cortex it antagonized the effects of haloperidol on DOPAC but not on HVA. The total (free and conjugated) content of DA metabolites was measured in these experiments.

Chronic haloperidol or fluphenazine: effects on dopamine metabolism in brain, cerebrospinal fluid and plasma of Cercopithecus aethiops (vervet monkey).

Chronic treatment with haloperidol for 3 to 5 weeks (0.5 mg/kg, daily) resulted in significant increases of homovanillic acid (HVA) content in dorsal and orbital frontal cortex and in cingulate cortex. No change in HVA was seen in the olfactory cortex, basal ganglia, cisternal cerebrospinal fluid or plasma of animals chronically treated with haloperidol. Treatment with a single weekly dose of fluphenazine decanoate (5 mg/kg) for 3 weeks resulted in increased HVA levels in all the above brain regions, cisternal cerebrospinal fluid and plasma. Moreover, the fluphenazine-treated group had a significantly higher incidence of extrapyramidal side effects than the haloperidol-treated group. It is concluded that chronically increased dopamine metabolite production in the basal ganglia but not in cortex is reflected by increases in the HVA level of cerebrospinal fluid and plasma and is accompanied by severe extrapyramidal side effects.

3,4-Dihydroxyphenylacetic acid and homovanillic acid in rat plasma: possible indicators of central dopaminergic activity.

The concentrations of dopamine (DA) metabolites (free and conjugated) was measured in plasma and brain regions of rats by the mass spectrometric method of selected ion monitoring. Experimental treatments which altered the function of central dopamine neurons also induced concomitant changes in plasma 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). Stimulation of the nigrostriatal pathway increased plasma DOPAC and HVA whereas lesion of the pathway decreased plasma metabolites. Several drug treatments induced parallel changes in brain and plasma concentrations of DA metabolites. It is suggested that changes in the concentration of DOPAC and HVA in rat brain are reflected by parallel changes in plasma. No conjugated forms of DOPAC and HVA were found in plasma and brain tissue of vervet monkeys (Cercopithecus aethiops).