Clozapine effects on neuroendocrine response to apomorphine challenge testing in chronic neuroleptic nonresponsive schizophrenia: Preliminary findings

N BRIEFREPORTS Clozapine Effects on Neuroendocrine Response to Apomorphine Challenge Testing in Chronic Neuroleptic Nonresponsive Schizophrenia: Preliminary Findings Sally Szymanski, Jeffrey Lieberman, Simcha Pollack, Allan Safferman, Rafael Munne, Daniel Umbricht, John Kane, Michael Kronig, Miranda Chakos, and Thomas Cooper Key Words: Apomorphine, clozapine, chronic, schizophrenia, treatment, neuroendocrine

Introduction Apomorphine, a dopamine D 1 and D2 receptor agonist, has been used as a pharmacologic probe of dopaminergic function (Meltzer et al 1984, 1989). By examining apomorphine's effect on plasma prolactin (PRL) and growth hormone (GH) levels, the functional state of dopaminergic receptors in the hypothalamus-pituitary axis has been studied (Ettigi et al 1976; Jeste et al 1983; Levy et al 1984; Miiller-Spahn et al 1984; Garver 1988). To investigate the in vivo antidopaminergic action of an atypical antipsychotic medication, apomorphine challenge testing has been used to stimulate growth hormone production and inhibit prolactin secretion in clozapinetreated chronic schizophrenics. Nair et al (1979) reported that clozapine inhibited apomorphine-induced growth hormone secretion and blunted prolactin suppression in seven acute and chronic schizophrenic subjects. In a later study, Meltzer (1989) found that in a group of 10 chronic schizophrenics, clozapine suppressed growth hormone response to apomorphine to approximately the same degree as did typical neuroleptics. Neither study correlated apomorphine's effects with treatment response. Clozapine has been proposed to have multiple mechanisms of action includingboth antidopaminergicand antiserotonergic properties. Since the relationship of ctozapine's antidopaminergic acFrom the University of Pennsylvania, Department of Psychiatry, Neuropsychiatry Program, Philadelphia, PA (SS, who is now at the University of Pennsylvania), Hillside Hospital, a division of Long Island Jewish Medical Center, Glen Oaks, NY (JL, SP, AS, RM, DU, JK, MK, MC); the Department of Quantitative Analysis St. John's University Jamaica, NY (SP); and the Nathan Kline Institute, Orangeburg, NY (TC). Address reprint requests to S. Szymanski, D.O., University of Pennsylvania, Neuropsychiatry Program, 10th Floor Gates Building, 35th and Spruce Streets, Philadelphia, PA 19104, Fax: (215) 662-7903. Received September 27, 1993; revised June 29, 1994.

© 1995 Society of Biological Psychiatry

tion to medication responsivity is uncertain, this study examined the results of dopaminergic challenge testing using apomorphine on growth hormone and prolactin secretion in clozapine-treated chronic schizophrenics.

Methods Chronic multiepisode neuroleptic refractory schizophrenic patients were recruited from the Psychiatric Services of Hillside Hospital. All patients met the following criteria upon study entry: a) had a DSM-III-R diagnosis of schizophrenia (APA 1987) and were neuroleptic refractory, i.e., had a minimum of three periods of treatment in the preceding 5 years with neuroleptic agents from at least two different chemical classes at dosages --> 1000 mg/d chlorpromazine for a period of 6 weeks, each without significant symptomatic relief; b) were aged 18-40 years; c) had no known prior or current history of serious neurologic or medical disorder; d) had no current or recent use within the past several years of decanoate antipsychotic medications; and e) were able to give informed consent. Antipsychotic medication was discontinued, followed by a 2week drug washout period. Following an overnight fast, patients underwent an apomorphine challenge procedure (challenge I) between 8:00 AM-I 1:30 AM. A 6 mg tablet of apomorphine (Lilly Pharmaceuticals, Inc.) was crushed and dissolved in l0 ml of saline to make an aqueous preparation. After the adaptation period of 45 minutes, apomorphine (0.0075 mg/kg) was administered subcutaneously over 60 seconds. Plasma prolactin and growth hormone levels were assessed at -30, -15, 0, +15, +30, +60, +90 minute time points prior to and following apomorphine administration. The prolactin levels were analyzed by the method of Fri et 0(X)6-3223/95/$09.50 SSDI 0006-3223(94)00191-5

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al (1974) and the growth hormone samples as per Glick et al (1963). The coefficients of variation within and between assays for growth hormone concentrations were: at 1.5 ng/ml, 9.6% and 12.4%; at 7.5 ng/ml, 3.2% and 3.8%; and at 33 ng/ml, 2.6% and 3.9%. The coefficients of variation within and between assays for the prolactin levels were: at 3.7 ng/ml, 6.4% and 6.9%; at 27.0 ng/ml, 3.8% and 5.7%; and at 46.3 ng/ml, 2.0% and 3.5%. A baseline behavioral rating was obtained using the Brief Psychiatric Rating Scale-Anchored Version (BPRS-A; Woemer et al 1988). Clozapine was then begun and titrated over a 2-week period to 500 mg per day and held constant at this dose for 1 week with the apomorphine challenge testing repeated (challenge II). Subsequently, the dose was adjusted from 500 to 900 mg/day to achieve optimal treatmem response in alleviating psychopathology over a 12-week period of time with BPRS-A ratings performed at 3-week intervals. All of the behavioral ratings were obtained by a research psychiatrist (SS) trained in the assessment of psychopathology. Statistical analyses included the area under the curve (AUC) as a measure of hormonal response over time and an examination of peak (GH) and minimal hormonal values (PRL). A repeated measures analysis of variance (ANOVA) with preinfusion values as a covariate was used to compare outcome for challenges I and II. As these analyses were exploratory in nature, they include multiple comparisons and numerous Pearson correlations. To highlight the "clustering" of significant results all calculated correlations are presented in the tables. Again, due to the exploratory nature of this research, alpha was not adjusted to account for the number of significance tests, as our primary purpose was to uncover any potential findings in the data. Any downward modification of alpha would increase the probability of committing a type II error or decrease the power of our tests.

Results Data from 10 male DSM-III-R chronic undifferentiated schizophrenic patients were analyzed. The subjects were 67% Caucasian and 33% black. The sample had a mean age (±SD) of 29.2 ± 5.9 years with a mean duration of illness prior to study entry of 11.3 ± 4.3 years. The mean global Brief Psychiatric Rating Scale (BPRS) rating (± SD) for baseline and treatment weeks 3, 6, 9, 12 were as follows: 55.7 ± 17.7; 51.3 - 15.2;48.4 _+ 11.3;43.7 ± 12.3;44.2 + 11.6. The mean daily clozapine dosages (± SD) for treatment weeks 3, 6, 9, and 12 were: 300 ± 200 mg; 441.7 -+ 280.0 mg; 490 - 374.8 mg; 591.7 ± 284.9 mg. Examinationof the response of the mean plasma prolactin levels (PRL) to apomorphine challenges I (preclozapine) and II (on clozapine) revealed the following results: Basal (preinfusion) PRLs were: challenge I, 6.1 ± 1.7 ng/ml; challenge II, 8.0 + 5.0 ng/ml. Postinfusion minimal values were for challenges I and II, 4.2 -+ 0.7 ng/ml and 5.7 - 3.9 ng/ml, respectively. The basal (preinfusion) AUC measures were: challenge I, 6.2 ± 1.7 ng/ml x sec; challenge II, 8.0 ± 5.0 ng/ml x sec. The postinfusion AUC measures were: challenge I, 5.1 ± 0.9 ng/ml × sec; challenge II, 6.4 ± 4.5 ng/ml x sec. No statistically significantdifferences were found between the PRLs of challenges I and II possibly due to the broad distribution of these values.

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The response of the mean plasma growth hormone (GH) levels to apomorphine challenges I and II found the following results: Basal (preinfusion) plasma growth hormone levels were: challenge I, 1.6 + 3.0 ng/ml; challenge II, 2.0 ± 3.9 ng/ml. The preinfusion AUC values were: challenge I, 1.8 ± 3.4 ng/ml x sec; challenge II, 1.9 + 3.6 ng/ml x sec. The postinfusion AUC values were: challenge I, 13.1 ± 11.7 ng/ml x sec; challenge II, 5.7 -+ 9.8 ng/ml x sec. The maximal GH levels for challenges I and II were 22.5 ng/ml and 9.3 ng/ml, respectively. No statistically significant differences were noted between the GH values of challenges I and II, possibly due to the broad distributionof these values. To determine if there was an association between drug response and apomorphine-induced alterations in plasma prolactin and growth hormone concentrations in challenges I or II, or the differences in the levels (challenge H-I), the change in both the global BPRS ratings from baseline to treatment weeks 3, 6, 9, and 12 and in the neuroendocrine measures were correlated. Although basal neuroendocrine levels were not associated with treatmem response, certain apomorphine-induced alterations between prolactin and growth hormone concentrations did show such a relationship (Tables 1 and 2). Statistically significant correlations between prolactin levels and the change in BPRS ratings at certain treatment weeks from baseline were as follows: challenge I AUC with week 12; challenge II AUC with weeks 9 and 12; the change in PRL AUC for challenge II as compared to I with weeks 9 and 12. Alterations in minimum PRL levels did not correlate with any change from baseline BPRS ratings at any treatment week. Statistically significant correlations of GH levels with treatment response as measured by the change in BPRS ratings at certain treatment weeks from baseline were as follows: challenge I AUC with weeks 9 and 12; the difference in GH AUC between challenges II and I with weeks 9 and 12; the difference in maximal GH levels between challenges II and I with week 12. A correlation analysis of the BPRS thought disorder factor composed of four items (conceptual disorganization, grandiosity, hallucinatory behavior, and unusual thought control) with the change between challenge II and 1 AUC GH and PRL levels found a statistically significant relationship with GH at treatment week 9 (r = .7; p < .05) and PRL at weeks 9 and 12 (r = -.7; p < .04). There were no significant associations of the other BPRS factors (anergia, activation, and hostile-suspiciousness) with the neuroendocrine measures,

Discussion Clozapine has a moderate antidopaminergic action against D2 receptors in in vitro binding assays ( p ~ D2 = 7.01, Meltzer 1993) with Farde et al (1989) reporting a 40%-60% in vivo occupancy rate of striatal receptors at clinical doses in a positron emission tomography (PET) study. Although these results are limited by the small sample size and the absence of a placebo challenge, the relationship of clozapine's modest antidopaminergic mechanism of action to treatment responsivity may still be important. In this study, clozapine's ability to partially suppress apomorphine's dopaminergic agonist effect on neuroendocrine measures correlated with treatment response at certain time points. Furthermore, the

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Table 1. Correlation of Challenge I and II AUC Prolactin Hormone Levels with Change in BPRS Ratings from Baseline Change in BPRS ratings from baseline Apomorphine-induced changes in plasma PRL levels (Challenges I and 11)o

Treatment Week 3

Treatment Week 6

Treatment Week 9

Treatment Week 12

.48

.36

.53

.59*

-. 18

-.02

-.61"

-.62**

-.47

-.31

-+65 *

-.70" *

Challenge I AUC PRL Levels Challenge II AUC PRL Levels Change in AUC PRL Levels Challenge 11-I *.05 < p < .08.

**.001

Table 2. Correlation of Challenge I and II AUC and Maximal Growth Hormone (GH) Levels with Change in BPRS Ratings from Baseline Change in BPRS ratings from baseline Apomorphine-induced change in plasma GH levels (Challenges I and II)

Treatment Week 3

Treatment Week 6

Treatment Week 9

Treatment Week 12

-.02

-.27

-.77**

-.77**

.19

.30

.11

.12

.10

.37

.71 **

.71 * *

.04

.15

.54

.57 *

Challenge I AUC GH Levels Challenge II AUC GH Levels Change in AUC GH Levels Challenge II-I Change in Maximal GH Levels Challenge II-I *.05 < p < ,08.

** .001 < p < .05. "ChallengeI is at baselineor preclozapine;ChallengeII is at treatmentweek3. BPRS = BriefPsychiatricRatingScale;AUC = area underthe curve.

fact that the decrease in PRL and increase in GH in response to pretreatment apomorphine stimulation correlates with a decrease in psychopathology suggests that the magnitude of endocrine responses of patients reflects their capacity for antipsychotic response to clozapine. Kahn et al (1993) reported similar findings in measuring ACTH response to the serotonin agonist MCPP. Consequently, these results suggest that the I:)2antagonism of clozapine, in addition to its D1, D4, and antiserotonergic activity and the responsivity of dopamine neuroreceptors to pharmacologic

stimulation, remains an important consideration in the continued research effort directed towards establishing the full mechanism of action of clozapine in schizophrenia.

This work was supported by the Mental Health Clinical Research Center of Hillside Hospital (MH-41960), RSDA to Dr. J. Lieberman (MH-00537), and the Sandoz Research Institute.

References

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