Effects of debrisoquin and haloperidol on plasma homovanillic acid concentration in schizophrenic patients

Peripheral biomarkers allow differential diagnosis between schizophrenia and bipolar disorder

Schizophrenia (SCZ) and bipolar disorder (BD) are severe mental disorders that pose important challenges for diagnosis by sharing common symptoms, such as delusions and hallucinations. The underlying pathophysiology of both disorders remains largely unknown, and the identification of biomarkers with potential to support diagnosis is highly desirable. In a previous study, we successfully discriminated SCZ and BD patients from healthy control (HC) individuals by employing proton magnetic resonance spectroscopy (¹H-NMR). In this study, ¹H-NMR data treated by chemometrics, principal component analysis (PCA) and supervised partial least-squares discriminant analysis (PLS-DA), provided the identification of metabolites present only in BD (as for instance the 2,3-diphospho-D-glyceric acid, N-acetyl aspartyl-glutamic acid, monoethyl malonate) or only in SCZ (as isovaleryl carnitine, pantothenate, mannitol, glycine, GABA). This may represent a set of potential biomarkers to support the diagnosis of these mental disorders, enabling the discrimination between SCZ and BD, and among these psychiatric patients and HC (as 6-hydroxydopamine was present in BD and SCZ but not in HC). The presence or absence of these metabolites in blood allowed the categorization of 182 independent subjects into one of these three groups. In addition, the presented data suggest disturbances in metabolic pathways in SCZ and BD, which may provide new and important information to support the elucidation and/or new insights into the neurobiology underlying these mental disorders.

Variability of plasma homovanillic acid over 13 months in patients with schizophrenia; relationship with the clinical response and the Wisconsin card sort test

In the present study we have measured, on a monthly basis, the concentration of plasma homovanillic acid (pHVA) in schizophrenic patients during 13 months of their pharmacological treatment. The average pHVA values of each patient were within the range of 7.30-17.70 ng/ml and the coefficients of variation for each patient (CV %) were within the range of 13-33%. Half of the patients that showed higher pHVA CV% values also showed higher scores on the Brief Psychiatric Rating Scale at the beginning of the study, and improved more after 6 months, when compared to the remaining 50% with lower CV% values. There was no significant relationship between the scores of the Wisconsin Card Sort Test and the concentration or the CV% of the pHVA of each patient. A greater variability in the pHVA may be associated with a greater plasticity of the dopaminergic system and a better clinical response.

In vivo temporal EPR study using a region-selected intensity determination method to estimate cerebral reducing ability in rats treated with olanzapine

Region-selected intensity determination (RSID) is a method for obtaining the temporal changes in electron paramagnetic resonance (EPR) signal intensity from a target region, without the use of complicated procedures employed in the conventional imaging methods. An in vivo 700-MHz radio frequency EPR spectrometer equipped with a bridged loop-gap resonator was used with the RSID method to estimate intracerebral reducing ability in the rat following acute administration of olanzapine (OZP) or haloperidol (HPD). To this end, temporal changes in EPR signal intensity of target regions (the striatum and the prefrontal cortex) of rats which had received a blood-brain-barrier-permeable nitroxide radical (3-hydroxymethyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl) via an intravenous route were observed. The half-lives of EPR signal intensity in both regions of OZP- or HPD-treated rats were significantly longer than in control animals. This indicated that reducing abilities of the striatum and cerebral cortex decreased in the rats to which either OZP or HPD had been acutely administered.

GABA and homovanillic acid in the plasma of Schizophrenic and bipolar I patients

We have determined the plasma (p) concentration of gamma-aminobutyric acid (GABA) and the dopamine metabolite homovanillic acid (HVA), and the pHVA/pGABA ratio in schizophrenic and bipolar patients. The research was undertaken in a geographic area with an ethnically homogeneous population. The HVA plasma concentrations were significantly elevated in the schizophrenic patients compared to the bipolar patients. The levels of pGABA was significantly lower in the two groups of patients compared to the control group, while the pHVA/pGABA ratio was significantly greater in the both groups of patients compared to the controls. As the levels of pHVA and pGABA are partially under genetic control it is better to compare their concentrations within an homogeneous population. The values of the ratio pHVA/pGABA are compatible with the idea of an abnormal dopamine-GABA interaction in schizophrenic and bipolar patients. The pHVA/pGABA ratio may be a good peripheral marker in psychiatric research.

Inter- and intra-individual variability in the levels of plasma homovanillic acid in schizophrenic patients

BACKGROUND

Changes in the levels of homovanillic acid in blood plasma (pHVA) may reflect changes which occur in the brain. In healthy individuals, this concentration of pHVA is stable over time.

METHODS

Over the course of one month, we studied 98 acute schizophrenic patients who had not been taking any medication but were administered neuroleptics upon hospital admission, together with 23 chronic schizophrenic patients on long-term treatment from whom medication was withdrawn. Blood samples were taken at regular intervals from each individual and the concentration of plasma homovanillic acid was measured.

RESULTS

We found relative stable values of pHVA with an intraclass correlation coefficient of 0.363 in acute patients and 0.638 (p<0.0001) in chronic patients, although no differences were found in mean values (13.79 and 14.18 microg/L, respectively) or in the variation range (7.20 to 26.7 microg/L and 6.96 to 29.96 microg/L respectively). The index of individuality was calculated to be 1.36 in acute patients and 0.74 in chronic patients.

CONCLUSIONS

Despite the wide range of values in the concentration of pHVA and the presence of pharmacological stimuli, we found a certain reproducibility in the levels of this dopamine metabolite. These findings are consistent with the idea that the dopaminergic activity is characterized by a constitutive value which would be under genetic control. The higher stability observed in chronic patients may reflect a weaker, age-related dopaminergic plasticity; conversely, it may indicate that a lack of plasticity in response to a pharmacological stimulus may be an indicator of poorer prognosis.

Reducing ability of the striatum and cerebral cortex in rats following acute administration of risperidone or haloperidol: an estimation by in vivo electron paramagnetic resonance imaging

In vivo temporal electron paramagnetic resonance (EPR) imaging of the blood-brain barrier-permeable nitroxide radical, 3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidin-1-yloxy (PCAM), in the brain of rats was conducted following acute administration of risperidone (RSP) or haloperidol (HPD). The half-life of the signal intensity of PCAM was obtained from a selected area in the temporal EPR images. The half-lives in the striatum and cerebral cortex for the RSP- or HPD-treated rats were significantly longer than for the control rats (p < 0.01). This finding indicates that the reducing abilities of the striatum and cerebral cortex decreased in the rats to which either RSP or HPD had been acutely administrated because the half-life of PCAM in the selected region of the brain reflects its reducing ability.

In vivo analysis of hydrogen peroxide and lipid radicals in the striatum of rats under long-term administration of a neuroleptic

It has been hypothesized that free radicals play a causative role in tardive dyskinesia, which is an inveterate movement disorder caused by chronic administration of neuroleptics. To verify this hypothesis, rats were reared while being regularly treated with water containing a neuroleptic, haloperidol (HPD), for 1 year (HPD group). The changes in the striatal hydrogen peroxide content of the rats in the HPD and control groups were measured by using a Pt-disk microelectrode while the animals were in a freely moving state following intraperitoneal administration of HPD (HPD challenge). We also performed electron spin resonance (ESR) detection of lipid radicals in the striatum before the HPD challenge. HPD challenge led to significant elevation of the intrastriatal hydrogen peroxide in all animals, but the elevation in the HPD group was smaller than that in the control group. However, in the HPD group, marked ESR signals of intrastriatal lipid radicals were observed. We think that these results support the hypothesis on the role of free radicals in tardive dyskinesia.

Association of plasma homovanillic acid with behavioral symptoms in patients diagnosed with dementia: a preliminary report

Neuroleptic treatment of psychotic symptoms or agitated behavior in elderly patients diagnosed with dementia is associated with reduced efficacy and increased rates of neuroleptic-induced parkinsonism in comparison to younger patients with schizophrenia. We report the first study to examine the relationship between an in vivo measure of dopaminergic function, plasma homovanillic acid (pHVA), and ratings of psychosis, agitation, and parkinsonism before and after neuroleptic treatment in dementia patients. Pretreatment pHVA was significantly correlated with parkinsonian rigidity, with a trend observed with agitation and hostility. Though mean pHVA did not change during perphenazine treatment, intraindividual change in pHVA at day 15 was correlated with improvement in hostility, with a similar trend for improvement in agitation. These preliminary findings are consistent with reports associating dopaminergic function with agitated, but not psychotic, symptoms in patients diagnosed with dementia, and with a reduced responsivity of dopaminergic systems to neuroleptic treatment in these patients.

Relationship between 3-methoxy-4-hydroxyphenylglycol and homovanillic acid in saliva and plasma of healthy volunteers

Plasma 3-methoxy-4-hydroxyphenylglycol (MHPG) and homovanillic acid (HVA) levels may reflect changes in central noradrenergic and dopaminergic activity, respectively. The relationship between MHPG and HVA in saliva and plasma was investigated to evaluate the utility of salivary metabolite measurement as a relatively noninvasive and useful alternative to plasma analysis. MHPG and HVA in saliva and plasma, collected concurrently, from 12 healthy volunteers, were measured by high-performance liquid chromatography. Concentration of free MHPG in saliva correlated significantly with plasma free MHPG. Salivary free MHPG was significantly higher than in plasma. Enzymatic hydrolysis of conjugated MHPG corroborated other work that plasma free MHPG, MHPG-glucuronide, and MHPG-sulfate were in roughly equal proportions. Unpredictably, in saliva, free MHPG was greater than 80% of the total. Salivary and plasma free HVA concentrations also correlated significantly, but salivary HVA levels were significantly lower than in plasma. Conjugated HVA was consistently less than 10% of total both in saliva and plasma. These findings suggest that salivary MHPG and HVA can reflect plasma metabolite levels. Although local factors may influence their formation and concentration in saliva, large changes in plasma free MHPG or HVA could be reflected by parallel changes in saliva.

New dopaminergic and non-dopaminergic theories in schizophrenia and their therapeutic impact

The dopamine (DA) hypothesis of schizophrenia, postulating that schizophrenia is characterized by increased dopamine function, has been the most influential theory on the pathogenesis of schizophrenia. It has recently been revised based on the appreciation that the core symptoms of schizophrenia may not be the positive (psychotic) symptoms, but rather the negative symptoms and the cognitive deficits found in schizophrenic patients. This revision has prompted the hypothesis that schizophrenia is characterized by both decreased prefrontal dopamine activity (causing deficit symptoms) and increased dopamine activity in mesolimbic dopamine neurons (causing positive symptoms). Notwithstanding this revision of a role for dopamine in schizophrenia, it has become increasingly evident that dysfunction of other monoaminergic systems may be as important in contributing to the pathophysiology of schizophrenia. Specifically, the putative role of serotonin (5-hydroxytryptamine, 5-HT) in schizophrenia is gaining considerable attention. Several observations, such as the ability of the 5-HT antagonist, ritanserin, to alleviate schizophrenic symptoms and, when added to haloperidol (Haldol®), to decrease its extrapyramidal side-effects (EPS), have stimulated studies into a role of 5-HT in schizophrenia. The finding that clozapine (Leponex®), clinically superior to conventional neuroleptics, is a weak DA2 antagonist but a potent 5-HT1c and 5-HT2 antagonist has further stimulated 5-HT-related research in schizophrenia.

A study of the potential confounding effects of diet, caffeine, nicotine and lorazepam on the stability of plasma and urinary homovanillic acid levels in patients with schizophrenia

Ten men inpatients who met DSM-III-R criteria for schizophrenia participated. On five occasions at least one week apart, each subject had an intravenous line placed at 0730 after an overnight fast. On each occasion blood samples were drawn at 0800 and hourly thereafter through 1200 noon for measurement of plasma homovanillic acid (HVA). Total four-hour urine collections were obtained for measurement of urinary HVA. Subjects received five experimental conditions, in randomized sequence: no intervention, smoking one cigarette per hour, drinking one caffeinated cola per hour, lorazepam 2 mg IV push, or a high monoamine meal. Baseline (0800) plasma HVA measures showed only minor intrinsic variability. The average standard deviation in baseline plasma HVA over five occasions of measurement was low relative to the changes in HVA produced during treatment with antipsychotic medications. The high monoamine meal significantly elevated plasma HVA, with a similar trend for urinary HVA. Neither caffeine, nicotine, nor lorazepam significantly affected plasma or urinary HVA.

Pharmacoclinical correlations in schizophrenic patients treated with haloperidol decanoate: clinical evaluations, concentrations of plasma and red blood cell haloperidol and its reduced metabolite, and plasma homovanillic acid

1. The aim of this open study was to determine whether a more rational therapeutic approach could be devised for psychotic patients (n = 11) treated for long periods with long-acting (LA) haloperidol. The mean multiplication factor for the transition from the oral formulation to the long-acting one was 12.8 (10.4, standard deviation), lower than the theoretically recommended factor of 20. 2. The best dose (mg/kg)-concentration correlations were found for haloperidol (HAL) and reduced HAL (RHAL) in the red blood cells (RBC) (representative of the free drug fraction) rather than in the plasma of patients that had attained the steady state (at the third cycle and afterwards) 3. Pharmacokinetic analyses were conducted at the same time as clinical evaluations, grading using the BPRS and determinations of plasma levels of total, free and conjugated homovanillic acid (HVA), a marker of central dopaminergic activity. 4. A between groups comparison at the steady state (patients (n = 20) with oral administration and the above patients (n = 11) with long-acting form of HAL), showed that the plasma and RBC RHAL/HAL ratios of long-acting HAL decreased significantly (p < 0,005) in comparison with oral administration, at least by half. 5. Plasma HVA values complete the information provided by plasma and more especially RBC HAL and RHAL levels. All these results taken together, as substantiated by the clinical assessment scales (BPRS), assure a better pharmacoclinical surveillance and can be predictive of a patient's response.

Effects of raclopride treatment on plasma and CSF HVA: relationships with clinical improvement in male schizophrenics

Thirty-two acutely psychotic, male schizophrenic patients received raclopride, at 2, 6, or 12 mg/day, or haloperidol, 15 mg/day for 4 weeks after randomized, double-blind assignment. Twenty-six patients, including 19 who had been assigned one of the three doses of raclopride, completed the study. Raclopride, particularly at 12 mg/day, increased CSF homovanillic acid (HVA) at 4 weeks, and plasma HVA at 2 days, of treatment. The clinical response to raclopride was significantly correlated with plasma raclopride concentrations and baseline plasma HVA concentrations. Although raclopride is a substituted benzamide with atypical properties in animals, these results suggest that the doses of raclopride required for clinical efficacy and elevation of clinical indices of brain dopamine turnover are similar.

A comparison of plasma homovanillic acid in the deficit and nondeficit subtypes of schizophrenia

Plasma homovanillic acid (pHVA) was measured over a 13 hr-period in 16 DMS-III-R schizophrenic patients, all treated with neuroleptic drugs and in a stable clinical and therapeutic status for the preceeding 12 months. Patients were categorized into deficit (n = 9) and nondeficit (n = 7) forms of schizophrenia according to the Schedule for the Deficit Syndrome (SDS) criteria. As compared to the nondeficit group, deficit patients display significantly lower mean pHVA concentrations from 9 AM to 12 AM and a lack of diurnal variations. None of the demographic, clinical, and therapeutic variables can explain these biological differences. These data suggest a specific biochemical basis for the deficit syndrome of schizophrenia as defined by the SDS criteria, that is, primary, enduring, negative symptoms.

Persistent psychosis after reduction in pre- and post-synaptic dopaminergic function

The purpose of this study was to evaluate the hypothesis that neuroleptic non-response in the face of "adequate" DA post-synaptic receptor blockade reflects failure of regulatory mechanisms to decrease DA pre-synaptic activity. Eight chronic schizophrenics, meeting rigorous criteria for neuroleptic non-response, were treated for four weeks with alpha-methylparatyrosine as an adjunct to their previously stable neuroleptic dose. Treatment with AMPT produced a prompt decrease in plasma HVA that was, on average, 72% lower at the end of the study. While there was also strong clinical evidence of reduction in central dopaminergic activity (both a significant reduction in dyskinetic movements and increase in extrapyramidal symptoms), there was virtually no change in severity of psychotic symptoms. Thus, in this group of non-responders, psychotic symptoms persisted despite both extensive dopamine post-synaptic receptor blockade and marked reduction of presynaptic activity. These symptoms may not be directly DA dependent.

Plasma homovanillic acid in neuroleptic responsive and nonresponsive schizophrenics

Changes in plasma homovanillic acid (HVA) were investigated in neuroleptic responsive and nonresponsive schizophrenics in order to delineate parameters of dopamine regulation, which may underlie differences in neuroleptic responsivity. Nineteen schizophrenics were treated with haloperidol for 6 weeks. HVA was sampled at baseline, 24 hr after initial neuroleptic dose, and after 6 weeks of treatment. Subjects were pretreated with debrisoquin in order to reduce the peripheral production of HVA. The responders had an initial rise in HVA at 24 hr after first neuroleptic dose, followed by a decline back to baseline over the 6 weeks of treatment. The nonresponders' HVA failed to rise at 24 hr after first neuroleptic dose. At 6 weeks of treatment their HVA had fallen to significantly below baseline. Thus, a rise in HVA 24 hr after the first dose of neuroleptic predicted treatment response; a fall in HVA at 6 weeks to below pretreatment values was associated with neuroleptic nonresponse.

Acute effects of neuroleptics on unmedicated schizophrenic patients and controls

Acute administration of haloperidol (0.2 mg/kg) produced many more side effects in normal controls than in unmedicated schizophrenic patients. Prior to the neuroleptic challenge, both groups were on the peripheral monoamine oxidase inhibitor, debrisoquin, for at least 1 week, in order to enhance the relative contribution of CNS catecholamine metabolites to those measured in both plasma and urine. The patient group had higher plasma levels of methoxyhydroxyphenylglycol (MHPG) and homovanillic acid (HVA) and higher urinary MHPG output than controls, but there were no effects of haloperidol challenge, compared to placebo challenge. In both groups there were significant declines in plasma HVA levels from 8:30 AM to 12 NOON. These declines were unaffected by the haloperidol challenge. Explanations for the marked differences in behavioral effects of haloperidol on patients and controls include the possibility that dopamine receptor numbers were increased in the brains of the schizophrenic patients.

Effects of single dose haloperidol administration on plasma homovanillic acid levels in normal subjects

Homovanillic acid (HVA), an oxidative metabolite of dopamine, has been shown in a number of studies to reflect severity of symptoms and to predict response to neuroleptic treatment in schizophrenic patients. In several clinical studies, HVA levels have been shown to have a positive relationship with symptom severity and to decline over time upon treatment with antipsychotic agents. The magnitude of this decline appears to be related to the degree of symptom reduction in patients so treated. However, administration of dopamine postsynaptic antagonists should be expected to increase synaptic dopamine availability, thereby increasing HVA concentrations, according to traditional models of drug action. While in some studies, this appears to be the case, we saw no evidence of an early phase of HVA elevation after administration of 4- and 10-milligram doses of haloperidol to human volunteers. Rather, HVA levels declined during the period of absorption and attainment of peak haloperidol levels. Baseline HVA levels of 51.6 +/- 3.83 pmoles/ml and 56.8 +/- 5.70 pmoles/ml (after 4 mg and 10 mg., respectively) declined to minima of 35.6 +/- 1.67 pmoles/ml and 26.3 +/- 5.34 pmoles/ml respectively, at 3-4 hours after haloperidol administration. A trend was noted for the 10-mg dose to produce a greater decline than the 4-mg dose, which was most apparent at 4 hours after drug administration. The shape of both curves did not appear to be substantially different than expected on the basis of diurnal variation. These preliminary findings support the concept that dopamine turnover in humans is not increased and may be decreased by short-term administration of conventional neuroleptics.

Treatment with clozapine and its effect on plasma homovanillic acid and norepinephrine concentrations in schizophrenia

Measurement of plasma concentrations of the dopamine metabolite, homovanillic acid (pHVA), is an indirect tool to assess changes in dopamine turnover. Levels of pHVA have been reported to decrease during treatment with conventional antidopaminergic, neuroleptics, with the decrement correlating with symptomatic improvement in schizophrenic symptoms. Clozapine, an atypical neuroleptic, is the only drug proved to be effective in treatment-refractory patients. However, the mechanism mediating this unique efficacy has not been fully elucidated. This study examined the effect of clozapine on pHVA concentrations in schizophrenic patients. Since clozapine potently binds to alpha 2-adrenergic receptors, plasma norepinephrine (pNE) concentrations were also measured. Twenty-eight treatment-refractory schizophrenic patients (24 men, 4 women) were treated with clozapine (up to 600 mg/day) for 5 weeks, after a minimum 1-week drug-free period. Symptomatology and pHVA and pNE concentrations were measured at the last drug-free day and weekly for 5 weeks. Fourteen patients responded to clozapine treatment, while an equal number did not. Mean pHVA concentrations did not significantly change during treatment with clozapine. Although clozapine tended to lower pHVA concentrations in treatment responders, the effect was small and not significant. Clozapine treatment significantly raised pNE concentrations, but this did not differentiate responders from nonresponders to clozapine. These findings suggest that clozapine's effect on DA turnover is small and that clozapine may be effective in treatment-refractory schizophrenia by mechanisms other than, or in addition to, dopamine receptor blockade. However, since about one-third of NE is metabolized into HVA, the clozapine-induced increase in pNE may have overshadowed a possible lowering effect of clozapine on pHVA.

Effect of m-chlorophenylpiperazine on plasma homovanillic acid concentrations in healthy subjects

In view of the abundant anatomical and functional interactions between serotonin and dopamine systems, this study examined the effect of the serotonin agonist, m-chlorophenylpiperazine (mCPP) on plasma concentrations of the dopamine metabolite, homovanillic acid. Plasma prolactin levels, body temperature, and mCPP blood level were also measured. mCPP (0.35 mg/kg) and placebo were administered orally to 10 healthy men in a randomized double-blind design. Variables were measured for 210 min after administration of capsules. mCPP raised prolactin and temperature as compared to placebo, but did not affect plasma homovanillic acid concentrations. Results suggest that mCPP does not alter dopamine function.

Plasma prolactin and homovanillic acid as markers for psychopathology and abnormal movements during maintenance haloperidol treatment in male patients with schizophrenia

Measurement of plasma prolactin (PRL) concentration and plasma homovanillic acid (HVA) concentration was performed in 24 patients with schizophrenia during maintenance haloperidol treatment. A significant inverse correlation was found between plasma PRL and ratings of both dyskinesia and thought disorder. Plasma PRL was also correlated with negative symptoms. No relationship was found between plasma HVA and any symptom grouping. Twelve patients received an apomorphine challenge; a trend toward a significant inverse relationship was found between baseline dyskinesia and apomorphine-induced decreases in plasma PRL. Plasma PRL and plasma HVA may reflect different elements of dopamine function in the central nervous system during maintenance treatment; plasma PRL may be the useful marker under these conditions.

The acute effects of central- and peripheral-acting dopamine antagonists on plasma HVA in schizophrenic patients

The short-term effects of fluphenazine on plasma HVA concentrations were compared with the effects of fluphenazine and concurrent administration of debrisoquin, a monoamine oxidase inhibitor which does not cross the blood brain barrier and is used to enhance the CNS contribution to circulating plasma HVA concentrations. Fluphenazine significantly increased plasma HVA with or without debrisoquin 24 hours following the initiation of treatment. Domperidone, a butyrophenone dopamine antagonist which acts only in the peripheral nervous system, failed to alter plasma HVA concentrations. These data suggest that the acute effects of neuroleptic drugs on plasma HVA concentrations are dependent upon interaction with CNS dopaminergic systems and provide additional support for the use of plasma HVA as a reflection of CNS dopamine system activity in clinical studies.

Correlates of rapid neuroleptic response in male patients with schizophrenia

Correlates of neuroleptic response latency were assessed in 16 male schizophrenic inpatients during 4 weeks of fixed dose (20 mg/day) haloperidol treatment. Rapid responders showed a mean 40% reduction in Brief Psychiatric Rating Scale (BPRS) positive symptom scores by day 10 of treatment. Rapid responders had significantly lower plasma homovanillic acid (pHVA) concentrations compared to non-rapid responders during week 4 of haloperidol treatment. However, rapid versus non-rapid responders did not differ with respect to demographics, baseline positive or negative BPRS symptom scores, performance on tests of neuropsychological function, or mean plasma haloperidol concentrations.

A pharmacodynamic model to predict the time dependent adaptation of dopaminergic activity during constant concentrations of haloperidol

The concentration-response relationship of the accumulation of brain homovanillic acid (HVA) has been studied by giving rats a shorter (12 h) and a longer (76 h) constant intravenous infusion of haloperidol, respectively, at rates aiming at different steady state blood concentrations of haloperidol of 5 to 30 ng mL-1. The observed response on brain HVA concentration vs increasing steady state blood concentration of the drug produced a bell-shaped type of curve during the 12 h infusion. When the infusion proceeded for 76 h a similar type of curve was obtained but it was shifted downwards compared with the 12 h infusion. The dopaminergic activity of the rat brain, as reflected by the HVA levels, therefore adapted to a lower activity during the prolonged exposure to haloperidol. To follow the time course of this adaptation, one steady state level of about 12 ng mL-1 was established and kept for 12, 28, 52 and 76 h. The result showed that the accumulation of brain HVA decreased over time compared with control animals given placebo. A pharmacodynamic model was set up to quantitatively describe the time-dependent adaptation of HVA accumulation in the whole rat brain during constant haloperidol administration. By fitting this model to all three sets of experimental data simultaneously, an adaptation half-time of about 38 h +/- 14 (s.d.) and a tolerance potency of about 7 ng mL-1 were obtained which could be used to calculate that, for example, at a constant blood level of 10 ng mL-1 haloperidol over 5 days the accumulation of brain HVA decreased by approximately 91% of the maximal decrease.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma catecholamine metabolites in schizophrenics: evidence for the two-subtype concept

Plasma homovanillic acid (pHVA) and plasma methoxyhydroxyphenyl glycol (pMHPG), as well as plasma haloperidol, were measured in 33 schizophrenic patients before and during 6 weeks of haloperidol treatment. Good responders had higher baseline pHVA values compared with poor responders (17.4 +/- 8.8 ng/ml, n = 22 versus 11.4 +/- 5.0 ng/ml, n = 11, p less than 0.05). A higher than 15 ng/ml pretreatment pHVA level was associated with a more consistent clinical response to the subsequent treatment. Differential pHVA changes during treatment were also found between good and poor responders. Within the good responder group, a significant decline in pHVA over time was found. By contrast, pHVA showed a transient increase in the poor responder group. Plasma MHPG changes showed a similar pattern during treatment in good responders, although no significant differences in baseline values were found between the good (n = 13) and poor (n = 9) responders, and pMHPG showed no change during treatment in poor responders. Significant correlations between baseline pHVA and pMHPG values were found in 22 patients. Good responders and poor responders did not differ significantly in terms of age, duration of illness, severity of presenting symptoms, haloperidol dose, or plasma drug concentration. Two hypothetical subtypes of schizophrenia and both dopamine and norepinephrine systems involved in schizophrenic psychopathology are proposed.

Measurement of plasma homovanillic acid concentrations in schizophrenic patients

1. Several lines of evidence suggest that abnormalities of central dopaminergic transmission may be involved in the expression of some schizophrenic symptoms. However, elucidation of the role of dopamine (DA) in schizophrenia has eluded investigative efforts partially because no accurate and easily repeatable measure of brain DA activity exists. 2. The development of a technique to measure homovanillic acid in plasma has offered the possibility of performing serial measurements of this major DA metabolite. 3. Assuming that plasma homovanillic acid (PHVA) concentrations is an index of brain DA activity, measurement of PHVA can play a role in elucidating the DA abnormality in schizophrenia. 4. Results to date suggest that plasma homovanillic acid concentrations are lower in chronic schizophrenic patients compared to normal controls, and that PHVA values correlate with schizophrenic symptom severity. 5. In addition, PHVA levels were shown to initially rise and subsequently decline during chronic neuroleptic administration in treatment responsive but not in treatment refractory schizophrenic patients.

Increments in plasma homovanillic acid concentrations after neuroleptic discontinuation are associated with worsening of schizophrenic symptoms

1. Thirty-two male schizophrenic patients participated in this study. 2. Plasma concentrations of the dopamine metabolite, homovanillic acid (pHVA) were assessed once on neuroleptic medication and twice a week for a maximum of six weeks after its discontinuation. 3. Psychiatric symptomatology was assessed once on neuroleptic medication and once a week for a maximum of six weeks after its discontinuation, using the brief psychiatric rating scale (BPRS). 4. pHVA and total BPRS score increased significantly after discontinuation of neuroleptic as compared to baseline. 5. The magnitude of pHVA and BPRS increments after discontinuation of neuroleptic correlated significantly. 6. Results of this study suggest that worsening of schizophrenic symptoms after discontinuation of neuroleptic treatment is associated with increased pHVA concentrations.

The effect of neuroleptic discontinuation on psychopathology, involuntary movements, and biochemical measures in patients with persistent tardive dyskinesia

As some of the pharmacological activities of neuroleptic medication may involve pathophysiological mechanisms underlying schizophrenia and tardive dyskinesia (TD), it is useful to study patients undergoing medication discontinuation. In this study, 19 stable, neuroleptic-maintained patients with persistent TD underwent taper and discontinuation of their neuroleptic medication over a 3-week period, and multiple behavioral and biochemical (plasma HVA, MHPG, and prolactin) measures were obtained. The major finding was that early relapsing patients had lower baseline and a significantly greater increase in plasma HVA levels after discontinuation than nonrelapsing patients. In addition, patients exhibiting withdrawal-exacerbated TD had significantly lower plasma MHPG levels than patients not exhibiting this phenomenon. The clinical and pharmacological implications of these findings are discussed.

Pharmacodynamics and pharmacokinetics of haloperidol and reduced haloperidol in schizophrenic patients

Twelve male chronic schizophrenic inpatients, neuroleptic-free for at least 4 weeks, were given an oral test dose of 10 mg haloperidol (HAL) and reduced HAL (RHAL) in a random order, with a 2-week interval. Two weeks after the last test dose, the patients were given HAL, 5 mg orally twice daily for 7 days. Blood samples were drawn at baseline and between 0.5 and 24 hr after the test doses, and during HAL treatment as well. Plasma drug concentrations and homovanillic acid (HVA) levels were measured with high-performance liquid chromatography using electrochemical detection. HAL, but not RHAL, produced increments in plasma HVA (pHVA) levels at 24 hr after a test dose. pHVA levels remained higher than baseline during HAL treatment. Detectable interconversion between HAL and RHAL was observed in eight patients. The capacity of the reductive drug-metabolizing enzyme system, however, was greater than that of the oxidative processes. The plasma RHAL:HAL ratios on days 6 and 7 were higher than and positively correlated with those at Tmax after a single dose of HAL and were negatively correlated with the HAL:RHAL ratios at Tmax after a single dose of RHAL. Thus, both reductive and oxidative drug-metabolizing systems probably contribute to individual differences in plasma RHAL:HAL ratios in HAL-treated schizophrenic patients.

Biogenic amines and their metabolites in body fluids of normal, psychiatric and neurological subjects

The biogenic monoamines and their metabolites have been isolated, identified and quantified in human body fluids over the past forty years using a wide variety of chromatographic separation and detection techniques. This review summarizes the results of those studies on normal, psychiatric and neurological subjects. Tables of normal values and the methods used to obtain them should prove to be useful as a reference source for benchmark amine and metabolite concentrations and for successful analytical procedures for their chromatographic separation, detection and quantification. Summaries of the often contradictory results of the application of these methods to psychiatric and neurological problems are presented and may assist in the assessment of the validity of the results of experiments in this field. Finally, the individual, environmental and the methodological factors affecting the concentrations of the amines and their metabolites are discussed.