Studies on 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylglycol (DHPG) levels in human urine, plasma and cerebrospinal fluids, and their significance in studies of depression

Both concentrations of total 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylglycol (DHPG) in the human urine, plasma and CSF were determined with a high-pressure liquid chromatography with electrochemical detection in order to clarify the dynamic change in these noradrenaline metabolites. Three different biological fluids were collected simultaneously from 16 orthopedic patients who were regarded clinically as substitutes for normal subjects. In the urine, the MHPG concentrations were 1.67 +/- 0.65 micrograms/mg creatinine (mean +/- S.D.) and DHPG 0.39 microgram/mg creatinine +/- 0.21. The plasma levels were 21.16 ng/ml +/- 9.58 for MHPG, and 19.58 ng/ml +/- 8.13 for DHPG. The CSF levels of MHPG and DHPG were 24.08 ng/ml +/- 8.10 and 34.76 ng/ml +/- 11.46, respectively. The CSF levels of these metabolites were correlated significantly with those in the plasma (r = 0.852, p less than 0.001 for MHPG; r = 0.799, p less than 0.001 for DHPG), while no significant correlations were found between the urinary levels and either the plasma or CSF levels of these metabolites. In the urine, the MHPG levels were proportional to the DHPG levels, while the former were inversely proportional to the latter in the plasma or CSF. Neither the MHPG nor DHPG levels in the urine from depressed patients revealed to have any significant correlation with their clinical assessments using the Hamilton Rating Scale Score (HRS). The patients were treated with an antidepressant active selectively on the noradrenergic system, and no significant changes in urinary excretion of these metabolites were observed before and after the drug treatment. These findings suggest that in the case of psychiatric disorders such as depression, these compound levels in the plasma or CSF would provide more important information than those in the urine.     

Noradrenergic function and the dexamethasone suppression test in depression

We measured the plasma free 3-methoxy-4-hydroxyphenylglycol (MHPG) levels and the serum cortisol levels before and after the oral administration of dexamethasone. There was not a significant difference in the plasma free MHPG levels between the patients with major depression and normal subjects. There was a significant positive correlation between the plasma MHPG levels and postdexamethasone cortisol levels in patients with major depression. This indicates that there exists a certain relation between abnormalities of the central noradrenergic systems and hypothalamic-pituitary-adrenal axis in patients with major depression. The mean total scores of the Hamilton Rating Scale for Depression of the first (MHPG less than 5 ng/ml) and third (10 ng/ml less than or equal to MHPG) groups were significantly higher than those of the second (5 less than or equal to MHPG less than 10 ng/ml) group.     

Noradrenergic output and clinical response in depressed women during amitriptyline therapy

The measurement of the urinary excretion of 3-methoxy-4-hydroxyphenylglycol (MHPG) in 59 unipolar depressed women before and during administration of 100 mg amitriptyline (AMT) i.m. daily for four weeks showed that the patients could be divided into high or low MHPG excretors. An analysis of the excretion course of MHPG and 3-methoxy-4-hydroxy mandelic acid during therapy showed, in most patients, a lower urinary excretion of both these noradrenaline (NA) metabolites in comparison with basal values. Therapy also decreased plasma noradrenaline concentrations and blood pressure values both at rest and on orthostatic challenge. Available evidence seems to suggest that AMT administration caused a lower overall noradrenergic output that might be partially responsible for a diminished sympathetic nervous activity. The authors were unable to confirm that the baseline MHPG level can predict the clinical response to antidepressant treatment and they found no significant correlations between changes in bio-chemical or physiological variables and drug plasma concentrations or clinical response. The possibility that depressed patients might be grouped according to their different NA metabolism needs to be validated in a larger patient sample.     

Studies on 3-Methoxy-4-Hydroxyphenylglycol (MHPG) and 3,4-Dihydroxyphenylglycol (DHPG) Levels in Human Urine, Plasma and Cerebrospinal Fluids, and Their Significance in Studies of Depression

Abstract: Both concentrations of total 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylglycol (DHPG) in the human urine, plasma and CSF were determined with a high-pressure liquid chromatography with electrochemical detection in order to clarify the dynamic change in these noradrenaline metabolites. Three different biological fluids were collected simultaneously from 16 orthopedic patients who were regarded clinically as substitutes for normal subjects. In the urine, the MHPG concentrations were 1.67±0.65 μg/mg creatinine (mean±S. D.) and DHPG 0.39 μg/mg creatinine±0.21. The plasma levels were 21.16 ng/ml±9.58 for MHPG, and 19.58 ng/ ml±8.13 for DHPG. The CSF levels of MHPG and DHPG were 24.08 ng/ml±8.10 and 34.76 ng/ml±11.46, respectively. The CSF levels ofthese metabolites were correlated significantly with those in the plasma (r = 0.852, p <0.001 for MHPG; r = 0.799, p <0.001 for DHPG), while no significant correlations were found between the urinary levels and either the plasma or CSF levels of these metabolites. In the urine, the MHPG levels were proportional to the DHPG levels, while the former were inversely proportional to the latter in the plasma or CSF. Neither the MHPG nor DHPG levels in the urine from depressed patients revealed to have any significant correlation withtheir clinical assessments using the Hamilton Rating Scale Score (HRS). The patients weretreated with an antidepressant active selectively on the noradrenergic system, and no significant changes in urinary excretion of these metabolites were observed before and afterthe drug treatment. These findings suggest that in the case of psychiatric disorders suchas depression, these compound levels in the plasma or CSF would provide more important information than those in the urine.     

Beta-phenylethylamine and noradrenergic function in depression.

1. The relationship between plasma levels of beta-phenylethylamine (PEA) and 3-methoxy-4-hydroxyphenylglycol (MHPG) was investigated in depressive patients. 2. The mean PEA level in plasma in healthy subjects was 1.19 ng/ml (N = 32). No clearly age-related difference was found. The plasma levels of PEA were measured in major depression, but no significant difference was found between healthy and depressive subjects. 3. Plasma levels of MHPG correlated positively with age in healthy subjects (N = 22, R = 0.71, p less than 0.01). There was no significant difference in MHPG levels between healthy subjects and depressive patients. 4. There was no significant correlation between PEA and MHPG levels in healthy subjects; however, in depressive patients, there was a significant negative correlation between plasma PEA levels and plasma MHPG levels (N = 14, R = -0.73, p less than 0.05). These results suggested that PEA may regulate noradrenergic function in depression.     

Haloperidol plasma levels and clinical response: a therapeutic window relationship.

OBJECTIVE: The purpose of the study was to assess the relationship between plasma haloperidol and clinical response. METHOD: Sixty-nine newly admitted drug-free schizophrenic men were randomly assigned to receive haloperidol, 5, 10, or 20 mg daily for 4 weeks, and clinical response was measured at the end of the fixed-dose period. Haloperidol was assayed by a sensitive and specific radioimmunoassay. RESULTS: The authors found a curvilinear relationship between clinical response and plasma haloperidol during fixed-dose treatment, with an apparent optimum between 5 and 12 ng/ml. When plasma levels above 12 ng/ml were lowered to the 5-12 ng/ml range, all patients improved to varying degrees and no patient deteriorated. When plasma levels of nonresponders within this therapeutic window were raised above 12 ng/ml (as in routine practice), they, on balance, deteriorated in that they became more dysphoric. With the 20-mg dose, half the patients had plasma levels above 12 ng/ml. CONCLUSIONS: In this sample of newly admitted schizophrenic men, optimal clinical response occurred with a plasma haloperidol range of 5-12 ng/ml.     

Treatment with risperidone for 4 weeks increased plasma 3-methoxy-4-hydroxypnenylglycol (MHPG) levels, but did not alter plasma brain-derived neurotrophic factor (BDNF) levels in schizophrenic patients

In the present study, we investigated the effects of risperidone treatment for 4 weeks on plasma levels of 3-methoxy-4-hydroxyphenylglycol (MHPG) and brain-derived neurotrophic factor (BDNF) in 89 schizophrenic patients. We also compared the plasma levels of BDNF and MHPG between the schizophrenic group and 103 sex-and age-matched normal controls. In addition, we investigated the effects of two SNPs of the noradrenaline transporter (NAT) gene on plasma levels of MHPG, BDNF, and clinical improvement. The mean dose of risperidone was 3.8+/-1.4 mg/day. We demonstrated that treatment with risperidone increased plasma MHPG levels, and this increase was associated with an improvement of the negative symptoms of schizophrenia. In contrast, plasma BDNF did not change after 4 weeks of risperidone treatment, and the two SNPs in NAT did not influence the response to risperidone treatment or plasma MHPG and BDNF levels. These results suggest that the enhancement of noradrenergic neurons by risperidone, which occurs independently of the two SNPs of NAT, plays a role in the clinical efficacy of the drug.     

Plasma levels, psychophysiological variables, and clinical response to amitriptyline

Hamilton depression scale ratings and physiological measurements were made for 37 patients with primary depression before treatment with amitriptyline (150 mg/day) and again after 2 and 4 weeks of treatment; plasma drug levels were determined weekly. Improvement was maximal at mean amitriptyline + nortriptyline concentrations of 125-200 ng/ml (14 patients), while at lower levels the outcome was significantly poorer (12 patients). Highly variable results were seen in 11 patients with levels between 200 and 301 ng/ml, with lesser improvement occurring in those patients who exhibited poor habituation of the skin resistance response before treatment. Other psychophysiological variables showed significant changes during treatment, but no correlation with clinical results or drug levels.     

Relationship of free nortriptyline levels to therapeutic response

The relationship between the free plasma concentration of nortriptyline and therapeutic response was examined. Eighteen depressed inpatients were treated for 21 days with steady state total nortriptyline plasma concentrations between 50-150 ng/ml. Steady state free nortriptyline concentrations were measured. The therapeutic nortriptyline response was measured by administering the Hamilton and the Carroll Rating scales at day zero and day 21. Statistical relationships between free levels of drug and clinical response were found to be insignificant. Qualitative assessment of the data suggest that free serum levels of nortriptyline in excess of 10 ng/ml may have an inhibitory effect on clinical response.     

Loss of the cortisol response to naltrexone in Alzheimer's disease

The administration of a single dose of the opiate antagonist naltrexone (NT) was accompanied by significant elevations in plasma cortisol in normal elderly subjects; in contrast, the cortisol response to NT was absent in individuals of comparable age with Alzheimer's disease (AD). The differential effect of AD on the cortisol response was not accompanied by a significant group difference in plasma prolactin in response to NT administration. Furthermore, this differential cortisol response to NT was not associated with any evident differences in age, sex ratio, plasma levels of naltrexone or its major metabolite beta-naltrexol, or with differences in measures of nonspecific stress, such as plasma free MHPG, pulse, or blood pressure, between the two groups. The absence of the well-characterized cortisol response to NT in AD, together with other reports of abnormal responses to other pharmacological challenges, suggests that neuroendocrine abnormalities might be an important concomitant and possibly a central contributor to the pathophysiology of Alzheimer's disease.     

Amisulpride – dose,plasma concentration,occupancy and response: implications for therapeutic drug monitoring

Objective: To evaluate the relationships between dose, plasma concentration, pharmacological activity and clinical outcome to evaluate the appropriateness of therapeutic drug monitoring (TDM) in patients receiving amisulpride. Method: Literature search of Embase, Medline and PubMed databases. Results: Amisulpride plasma concentration is closely correlated with dose (r² = 0.96, P < 0.0001), dopamine occupancy, response and with extra‐pyramidal symptoms (EPS). Dose is correlated with response, dopamine occupancy and EPS. Optimal clinical response was found at doses of 400–800 mg/day, corresponding to plasma levels of approximately 200–500 ng/ml. EPS appears to be more reliably predicted by a plasma level above 320 ng/ml than by a particular dose. Conclusion: The effects and safety of amisulpride in the treatment of schizophrenia and schizoaffective disorder are predicted by daily dose. The plasma concentration threshold for response appears to be approximately 200 ng/ml. EPS are more reliably predicted by plasma level than by dose. TDM for patients prescribed amisulpride is thus of some clinical value.     

Reproducibility of monoamine metabolite measurements in human cerebrospinal fluid

The levels of homovanillic acid (HVA), 5-hydroxy indoleacetic acid (5HIAA), and 3-methoxy-4-hydroxy phenylglycol (MHPG) were determined in the cerebrospinal fluid (CSF) of 28 patients with cognitive disorders on Day 1 and Days 8 or 15. During that period all patients were kept hospitalized under strict standard conditions, did not develop any acute CNS lesion, had no changes in their treatment and no acute systemic disease. The mean levels found in the first and second determinations were almost identical for the 3 metabolites; respectively 37.8 ng/ml and 36.3 ng/ml for HVA, 27.8 ng/ml and 27.9 ng/ml for 5HIAA, and 12.9 ng/ml and 12.3 ng/ml for MHPG. Thus, the mean values of these metabolites in CSF are reproducible at least during a 15-day hospitalization. However statistically significant individual changes in metabolite levels were found between the two samples in 82% of patients for HVA, 32% for HIAA and 48% for MHPG. The number of patients required to detect a significant change in the mean levels of each monoamine metabolite has been calculated taking into account the extent of intraindividual variations.     

Fluphenazine plasma levels and clinical response

Plasma levels of fluphenazine and clinical response were examined in 19 inpatient schizophrenics (DSM-III diagnoses) using a constant dose, steady-state methodology. A significant curvilinear correlation was demonstrated between clinical response and steady-state plasma levels of fluphenazine (p less than .05). A therapeutic range of plasma fluphenazine is suggested in the range of .13-.70 ng/ml. The lowest plasma level detected (.13 ng/ml) appeared to be well within the therapeutic range. The 9 patients with plasma fluphenazine levels in this range demonstrated a mean clinical improvement of 59% compared to 34% for patients with plasma levels above .70 ng/ml (p less than .01).     

CSF neurochemical study of tardive dyskinesia

Twenty-three inpatients who met DSM-III criteria for schizophrenia were selected for cerebrospinal fluid (CSF) neurochemical study of tardive dyskinesia (TD). Ten inpatients had tardive dyskinesia, and the remaining 13 patients without TD served as controls. There were no intergroup differences in sex, age, duration of neuroleptic treatment, or in total amount of neuroleptics received between the TD and the control groups. Cerebrospinal fluid was collected by lumbar puncture, and concentrations of homovanillic acid (HVA), MHPG, 5-hydroxyindoleacetic acid (5-HIAA), and acetylcholinesterase (AChE) activity were measured. The concentrations of MHPG (TD 11.56 +/- 3.48 ng/ml versus control 14.20 +/- 3.86 ng/ml), 5-HIAA (45.27 +/- 9.77 ng/ml versus 40.34 +/- 13.77 ng/ml), and HVA (38.26 +/- 18.31 ng/ml versus 31.40 +/- 7.83 ng/ml), and the activity of AChE (TD 7.95 +/- 5.21 mmol/g.hr versus control 12.89 +/- 8.04 mmol/g.hr) showed no significant differences between the two groups, but the ratios of HVA/AChE (t = 2.21, p = 0.05), 5-HIAA/AChE (t = 2.62, p = 0.02), MHPG/HVA (t = -2.16, p = 0.04), and MHPG/5-HIAA (t = -2.48, p = 0.02) were statistically different. The results indicated that TD might involve an imbalance of dopamine-acetylcholine, noradrenalin-dopamine, noradrenalin-serotonin, and serotonin-acetylcholine.     

Therapeutic drug monitoring for optimizing amisulpride therapy in patients with schizophrenia

Amisulpride is a clinically effective antipsychotic drug in a broad dose range with low propensity for extrapyramidal symptoms (EPS). Daily doses and plasma levels of amisulpride were analyzed within a large-scale therapeutic drug monitoring (TDM) survey to find plasma level ranges for optimized treatment under naturalistic conditions. Data of 378 schizophrenic patients treated with amisulpride (100-1550 mg) were included (40% female). Amisulpride plasma levels were analyzed at steady state; assessment comprised improvement (CGI-I) and side-effects, particularly EPS. For detection of cut-off values regarding non-response or EPS, receiver operating characteristics (ROC) curves were applied and the area under the ROC curve (AUC) was calculated. Amisulpride daily doses (594+/-262 mg) and plasma levels (315+/-277 ng/ml) were significantly correlated (r=0.53; P<0.0001). Patients with non-response to amisulpride (8.9%) had significantly (P<0.05) lower plasma levels (248+/-291 ng/ml) than patients with at least moderate improvement (316+/-253 ng/ml) despite comparable amisulpride doses (628+/-253 vs. 590+/-263 mg). Patients with EPS (14.6%) had significantly (P<0.05) higher amisulpride plasma levels (377+/-290 ng/ml) than patients without EPS (305+/-274 ng/ml) despite similar doses in both groups (595+/-266 vs. 594+/-246 mg). ROC analyses revealed significant predictive properties of amisulpride plasma levels (P<0.05) for non-response (AUC=0.65+/-0.05) and EPS (AUC=0.62+/-0.05), respectively. Daily amisulpride doses did not significantly predict non-response or EPS. Optimal amisulpride plasma level values to avoid non-response and EPS were 100 or 320 ng/ml, respectively. Analysis of clinical utility revealed that blood levels must be analyzed in 7 patients until one patient benefits from the TDM procedure by avoiding non-response or EPS. Although our results were mainly explorative, TDM of amisulpride seems very useful for clinical decision making.     

Plasminogen activators t-PA, u-PA and its inhibitor (PAI) in normal males and females.

We determined the plasma levels of tissue plasminogen activator (t-PA), plasminogen activator inhibitor (PAI) activity and their antigen levels including urokinase plasminogen activator (u-PA) in 33 male and 27 female normal subjects. Males had mean t-PA activity of 0.50 iu/ml which was significantly lower (p less than 0.01) than the females 0.64 iu/ml. Males had higher (p less than 0.001) mean PAI activity (15.5 AU/ml) as compared to females 10.3 AU/ml. The respective mean levels of t-PA and PAI antigen were significantly higher (p less than 0.01) in males (8.1 ng/ml and 17.6 ng/ml) than in females (6.2 ng/ml and 12.1 ng/ml). The mean u-PA level in males was 1.54 ng/ml which was significantly higher (p less than 0.01) than in females with 1.02 ng/ml. In post-venous occlusion studies, females had a greater mean response of 8.6 fold in t-PA activity as compared to males with a mean of 4.5 fold increase. The mean t-PA antigen response in males was 2.0 fold increase as compared to 2.6 fold increase in the females. No significant responses were seen in both sexes in either PAI activity or antigen levels when compared with the resting state. In zymography studies, free t-PA, its inhibitor complexes and u-PA were demonstrated in the euglobulin fractions of stored plasma. This study demonstrates that significant differences in t-PA, u-PA and PAI exist between male and female subjects which should be taken into account when determining their levels in clinical conditions.     

Urinary MHPG excretion in minimal brain dysfunction and its modification by d-amphetamine.

The authors studied the excretion of 3-methoxy-4-hydroxyphenlyglycol (MHPG) in 15 hyperactive boys and 13 controls. They further examined soft neurologic signs and clinical drug response to d-amphetamine administration for two weeks in the hyperactive boys. MHPG excretion was significantly lower in the hyperactive boys than in the controls. d-Amphetamine decreased MHPG excretion significantly in the drug responders only. Pretreatment MHPG excretion did not predict clinical drug response. The responders had more soft neurologic signs than the nonresponders. Furthermore, soft neurologic signs were not related to pretreatment MHPG levels.     

Plasma levels of MHPG, HVA and total 5-HIAA in depression. Preliminary study]

This study was aimed at assessing monoamine catabolites plasma levels in depressed patients and healthy volunteers. Plasma levels of 3-methoxy-4-hydroxyphenylglycol (MHPG), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) of 21 control subjects and 26 depressed patients (according to DSM III-R criteria) were measured at baseline (day 0) and day 4, day 7, day 30 of prescribed antidepressant treatment. The clinical assessment, at baseline as well as during treatment, used the Hamilton depression rating scale and the BPRS. Our data show the interest of these results in predicting response. The respondent patients showed a significant decrease in plasma MHPG level at J7, contrary to non-respondent patients. Moreover, a positive correlation between plasma levels of MHPG and HVA before any prescribed antidepressants was found only with respondent patients. The lack of correlation for non-respondent patients can suggest that the relationships between this monoamine systems should be disrupted in these patients. Significant relationships appear between clinical symptoms and plasma catabolites, allowing us to consider new physiopathological aspects of the depressive picture. The 3 monoamines seemed involved in sleep disorders. Perturbations of norepinephrine and serotonin metabolism could intervene in suicidal ideation and behaviour. Motor activity was associated with a modification in dopamine and serotonin metabolism. Moreover significant correlations were observed between items referring to thought content and monoamine plasma catabolites such as MHPG and blunted affect, 5-HIAA and obsessions, HVA and guilt feelings, devalorization and without hope items.(ABSTRACT TRUNCATED AT 250 WORDS)     

Stress at work alters serum brain-derived neurotrophic factor (BDNF) levels and plasma 3-methoxy-4-hydroxyphenylglycol (MHPG) levels in healthy volunteers: BDNF and MHPG as possible biological markers of mental stress?

There is growing evidence that blood levels of brain-derived neurotrophic factor (BDNF) and catecholamine, and cytokines are related to not only to depressive, suicidal, and anxious states but also to depression-associated personality traits. Psychological job stress is well known to lead to symptoms of depression and anxiety. In the present study, we examined effects of psychological job stress on serum levels of BDNF and plasma levels of catecholamine metabolites, and cytokines in healthy volunteers (n=106, male/female=42/64, age=36+/-12 yr) working in a hospital setting. The values (mean+/-SD) of scores for stress items in the Stress and Arousal Check List (s-SACL), plasma MHPG levels, and, serum BDNF levels in all participants were 7.2+/-3.3, 5.2+/-3.4 ng/mL, and 23.3+/-14.7 ng/mL, respectively. A negative correlation was found between scores for s-SACL and serum BDNF levels (rho=-0.211, p=0.022). A positive correlation was also found between scores on the s-SACL and plasma levels of 3-methoxy-4-hydroxyphenylglycol (MHPG) (rho=0.416, p=0.01), but not homovanillic acid (HVA). No relationship was found between s-SACL scores and plasma levels of interleukin-6 (IL-6) or tumor necrosis factor alpha (TNFalpha). These results suggest that serum BDNF levels and plasma MHPG levels might be biological markers reflective of psychological job stress in hospital employees.     

Blood biogenic amines during clozapine treatment of early-onset schizophrenia

Summary The aims of this investigation were to evaluate long-term and short-term effects of clozapine-treatment on plasma biogenic amines and psychopathology measures in adolescents with schizophrenia (DSM-III-R criteria). The long-term study was conducted in a study sample of 40 young patients (age 14–22 years) following a mean of 3.4 years of neuroleptic treatment. During the study, 20 patients received clozapine, and the other 20 patients were treated with standard neuroleptic medications. At the beginning of the open clinical trials, the patients had already been receiving clozapine treatment for 24 ± 15 months. Assessment of the biochemical and psychopathological measures was performed on six occasions at consecutive 6-week intervals during maintenance treatment with clozapine or conventional neuroleptics. Blood levels of serotonin, 3-methoxy-4-hydroxy-phenylglycol (MHPG), norepinephrine, and epinephrine were significantly higher in clozapine-treated patients than in conventionally treated patients. During long-term treatment, higher serotonin levels were associated with significantly fewer negative symptoms of schizophrenia, whereas higher MHPG levels were correlated with less depression. The short-term effects of clozapine were assessed in a second and independent study sample. After failing on conventional neuroleptics in clinical trials lasting a mean of 1.6 years, 15 inpatients (aged 11–20 years) received clozapine. Weekly ratings of psychopathological symptoms using standard rating scales were performed in parallel to blood samplings for measurements of biogenic amines and serum levels of clozapine. These measures were obtained for 6 weeks during conventional neuroleptic treatment and for 6 weeks during the open-label clozapine trial. Serum levels of serotonin and plasma norepinephrine levels were significantly higher during treatment with clozapine than during pretreatment with typical neuroleptics. A comparison of plasma epinephrine levels in responders (n=7) and nonresponders (n=8) to clozapine revealed that response to clozapine can be predicted by epinephrine levels prior to initiation of treatment with clozapine (responders ranging from 32.2 to 90.3 pg/ml; nonresponders ranging from 92.5 to 473.5 pg/ml). Additionally, subjects who responded to clozapine showed increased mean plasma concentrations of MHPG and epinephrine during treatment with this drug in comparison to the levels measured during pretreatment with typical neuroleptic medication. Nonresponders to clozapine failed to show this increase. Finally, in responders to clozapine a negative linear relationship between negative symptoms of schizophrenia and the concentrations of plasma norepinephrine and serum serotonin were observed. In conclusion, our results demonstrate that plasma epinephrine levels prior to initiation of clozapine therapy predict response to this atypical neuroleptic. Our findings derived from short-term and maintenance treatment with clozapine suggest involvement of norepinephrine, epinephrine and serotonin in the therapeutic actions of the atypical neuroleptic clozapine.