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Plasma prolactin response to domperidone in acute schizophrenia and schizophreniform illness
Psychiatry Research, 34:139-147 Elsevier
139
Plasma
Dina Nerozzi, Armando Magnani, Marco Cerilli, Costanzo Moretti, Herbert Y. Meltzer Received
Vincenzo Sforza, Elena Scaramucci, Gaetano Frajese, halo Antonozzi, and
October 27, 1989; revised version received July 24, 1990; accepted August 5, 1990.
Abstract. The prolactin (PRL) response to 20 mg of domperidone, a peripheral dopamine (DA) blocking agent, was evaluated in a group of 16 drug-free, acute, young schizophreniform and schizophrenic males and in a group of age-matched normal males. Although basal plasma PRL levels were normal, the PRL responses following domperidone were blunted in both patient groups. The PRL response was more blunted in the schizophreniform patients than in the schizophrenic patients. Possible explanations for these results include pharmacokinetic factors or abnormalities of the pituitary D, DA receptors. Key Words. Schizophrenia, receptors.
dopamine,
domperidone,
prolactin,
D, receptors,
D,
The hypothesis that at least some patients with the diagnosis of schizophrenia have a relative overactivity of the central dopaminergic system arose mainly from indirect lines of evidence linked to neuroleptic drug action (Randrup and Munkvard, 1972; Matthysse, 1973; Snyder et al., 1974; Meltzer and Stahl, 1976; Carlsson, 1978). For example, although neuroleptic drugs have many different actions on brain tissue, it is their ability to block D, dopamine (DA) receptors in the mesolimbic and mesostriatal system that has been shown to be highly correlated with their therapeutic action (Peroutka and Snyder, 1980), as well as their ability to stimulate prolactin (PRL) secretion (Langer et al., 1978). The ability of indirect DA agonists such as amphetamine to produce schizophrenia-like clinical syndromes after chronic administration also supports the DA hypothesis (Randrup and Munkvard, 1972; Meltzer and Stahl, 1976). It has been more difficult to obtain direct evidence for a dopaminergic abnormality in schizophrenia. Among the various methods that have been used is the assessment of
Dina Nero& M.D., is Assistant Professor, Department of Experimental Medicine, University of Rome “La Sapienza.” Armando Magnani, M.D., Vincenzo Sforza, M.D., Elena Scaramucci, M.D., and Marco Cerilli, M.D., are Research Fellows, Istituto di Clinica Medica V, University of Rome “La Sapienza.” Costanzo Moretti, M.D., is Researcher, Istituto di Clinica Medica V, University of Rome “La Sapienza.” Gaetano Frajese, M.D., is Professor of Endocrinology, University of Rome “La Sapienza.” Italo Antonozzi, M.D., is Director, Service for Genetic and Metabolic Diseases, Department of Experimental Medicine, University of Rome “La Sapienza.” Herbert Y. Meltzer, M.D., is Director, Laboratory of Biological Psychiatry, Case Western Reserve University, Cleveland, OH, USA. (Reprint requests to Dr. D. Nerozzi, Via di Porta Pinciana, 4 - 00187 Rome, Italy.) 0165-1781/90/$03.50
Q 1990 Elsevier Scientific
Publishers
Ireland
Ltd.
140
some aspects of the neuroendocrine system. It is well established that DA is involved in the regulation, synthesis, and release of a number of pituitary hormones; in particular, DA inhibits PRL release directly at the level of the pituitary both in vivo and in vitro (McLeod, 1976; Meltzer et al., 1978). According to the DA hypothesis, increased dopaminergic activity at the pituitary level might be expected to lower basal plasma PRL levels. This has generally not been observed (for review, see Meltzer et al., 1984~). Supersensitivity of pituitary DA receptors might lead to a shift to the left or enhanced suppression of PRL secretion by direct acting DA agonists, such as bromocriptine orapomorphine. This has also not been observed (for reviews, see Meltzer et al., 1984b; Rubin, 1987). There have also been some studies comparing the effect of single doses of DA antagonists on PRL secretion in unmedicated schizophrenic patients compared to that of normal controls. Increased DA activity might be expected to diminish the PRL response to a neuroleptic drug. Asnis et al. (1979) found no difference in the PRL response to haloperidol, 0.50 mg intramuscularly (i.m.), in six unmedicated schizophrenic patients and 13 normal control subjects. No difference in the PRL responses to chlorpromazine, i.m. 25 and 50 mg., was found between 6 male normal controls and 14 unmedicated schizophrenic patients (Meltzer et al., 1981). However, Keks et al. (1987) reported a smaller and slower PRL response to 0.50 mg haloperidol, given intravenously, in 14 drug-free male schizophrenic patients compared to 14 normal age- and sex-matched control subjects. Thus, there is still some ambiguity about dopaminergic activity at the pituitary level in schizophrenia. To gain more information about dopaminergic activity at the pituitary level in schizophrenia, we decided to administer domperidone, a peripheral DA blocking agent (Laduron and Leysen, 1979). It was thought that this could help to clarify whether any observed differences in PRL secretion between schizophrenic patients and controls could be due to peripheral or central mechanisms. Furthermore, to avoid all confounding variables due to age, gender, meals, physical activity, and time of the day (Thorner, 1977) we selected a very homogeneous population of young males (both patients and controls) living in the same community.
Methods Subjects. The subjects were 16 physically healthy, nonobese, nonsubstance-abusing men (mean age = 20.4, SD = 1.5, range 19-25). All had the onset of a psychotic episode during military service and were referred to the Psychiatry Unit of the Military Medical Center in Rome. The study was conducted within the first 2-3 days of admission to the Psychiatric Unit. Diagnosis was established at admission and confirmed at discharge by consensus of two experienced psychiatrists according to
141 Procedure.
Results Table 1 presents the plasma PRL levels for the schizophreniform and schizophrenic patients, while Table 2 presents the PRL data for the controls. Analysis for outliers showed that one of the schizophreniform patients was an outlier. The data from this subject were discarded. Fig. 1 gives mean plasma PRL levels with the outlier omitted; Fig. 2 gives individual areas under the curve (AUC). Table 1. Serum prolactin levels in schizophreniform oatients
and schizophrenic
Serum prolactin level 0’
+90’
+1os
+120’
Schizophreniform 1
1.7
21.7
18.5
18.5
2
0.7
28.6
21.5
17.9
3
3.7
19.7
14.7
17.0
4
1.2
18.7
27.5
33.4
5
2.5
18.2
17.6
16.2
Mean*SD
2.6 + 1.8
43.0 + 53.1
42.8 + 56.2
22.1 * 7.4
6
2.0
49.9
62.8
71.1
7
0.9
61.3
88.4
77.2
8
3.1
44.2
49.0
59.5
Schizophrenic
9
2.4
39.8
38.6
75.0
10
4.6
42.1
59.9
51.0 23.7
11
3.1
20.1
14.6
12
7.6
95.0
73.8
87.2
13
3.9
13.9
18.0
37.2
14
7.0
25.4
18.7
17.2
15
4.6
37.2
45.0
56.1
Mean+SD
3.9 * 2.1
42.9 f 23.1
46.9 + 25.0
55.5 zt23.4
142
Table 2. Serum prolactin levels in normal controls Serum Drolactin level 0’
+90’
+1o!Y
+120’ 135.6
1
3.1
99.8
128.2
2
0.8
90.2
112.6
89.7
3
2.4
80.0
112.2
69.7 128.0
4
2.7
84.2
150.3
5
3.0
66.8
67.4
58.1
6
1.6
75.6
110.7
77.0
7
3.0
81.0
98.9
92.3
8
2.8
89.7
130.0
63.8
9
2.6
74.9
125.8
118.0
10
2.8
92.3
137.4
98.2
2.5 zt 0.7
83.5 + 9.7
Mean
IL SD
117.3 f
23.0
93.0 + 27.0
Fig. 1. Time course of prolactin (PRL) data in schizophreniform patients, schizophrenic patients, and normal controls 120 PRL (ng/ml) _A100 ‘.-----4
80
_.___._,_-.--
-.---.
_._._.-
Jr ---------__
t
__________-t
+ 0
-.
+90.
+120
+105’ Time(min,)
Schizophreniform
patients, solid circles; schizophrenic
patients, solid squares; and normal controls, solid triangles.
Fig. 2. Scattergram of AUC of PRL values in schizophreniform schizophrenic patients, and normal controls AUC
PRL
70
ng/ml/l20min
60. 50-
B
A l-
C .
I-
l
40
.
30 20.
-i-.
@-AP
0
lo0. SF
C @Mean
S of AUC
AUC = area under the curve. PRL = prolactin. SF = schizophreniform.
S = schizophrenic.
C = normal control.
and
143 Table 3 presents the AUC analysis. There was a significant group difference. hoc tests revealed all three groups were different from each other.
Post
Table 3. Area under the curve analysis Least mean square
n
Group
5
62.5
Schizophrenic
10
150.6
Normal control
10
295.6
Source
df
F
P
Group
2
34.9
0.0001
Prolactin
1
0.04
0.8358
Schizophreniform
Table 4 presents a repeated measures ANOVA. There was a significant group effect, time effect, and group X time interaction. Post hoc tests indicated that the schizophreniform patients had lower PRL levels than the schizophrenic patients at all time points. The schizophreniform and schizophrenic patients had lower serum PRL levels than the normal controls at all time points except for time 0. Fourteen of the 15 patients had lower plasma PRL levels at 90 min, 13/ 15 at 105 min, and lo/ 15 at 120 min than any of the controls. All the schizophreniform patients had PRL values lower than controls at all the time points. In the schizophrenic group, 90% of the patients had lower PRL levels at 90 min, 80% at 105 min, and 50% at 120 min. The mean peak plasma PRL levels were 21.4 (SD = 14.3) ng/ml in the schizophreniform patients, 55.5 (SD = 23.4) ng/ml in the schizophrenic patients, and 118.09 (SD = 7.44) ng/mg in the controls. PRL responses tended to peak earlier in the schizophreniform patients, 80?J0 at 90 min, while in the schizophrenic patients 60% peaked later, at 120 min; 20% earlier, at 90 min; and 20% at the same time as the controls, 105 min. AUC was lower in 100% of the schizophreniform patients and in 80% of the schizophrenic patients when compared with the normal controls.
Table 4. Repeated measures analysis of variance Source
df
F
P
Group
2
35.07
0.0001
Time
3
61.59
0.0001
Time X group
6
9.58
0.0001
Post hoc tests Time 0
F 3.58
D
SF/S
SF/N
SIN
0.045
0.03
0.54
0.05
90’
29.12
0.0001
0.02
0.0001
0.0001
105
42.29
0.0001
0.03
0.0001
0.0001
120
17.41
0.0001
0.01
0.0001
0.0015
Note. SF = schizophreniform. S = schizophrenic. N = normal control.
144
Discussion The major finding of this study is that there is a blunted plasma PRL response following a domperidone challenge in unmedicated schizophrenic and schizophreniform patients compared to normal controls. The PRL response in the schizophreniform group was significantly blunted compared to the schizophrenic group. There are two major DA receptor subtypes: D, receptors linked to the stimulation of adenylate cyclase and D, receptors linked to the inhibition of this enzyme (Kebabian and Calne, 1979). Whereas most brain areas contain both D, and D, receptors, D, receptors are the sole subtype in the anterior pituitary (Creese, 1987). Domperidone is a potent antagonist of D, receptors and has only a weak affinity for D, receptors. Since it acts at the pituitary level, which lacks D, receptors (Creese, 1987), it can be argued that hyperprolactinemia secondary to domperidone is a D, receptor-mediated response. The increase in plasma PRL levels of the normal controls at 90 min was 33.4-fold. This compares with a IO-fold increase at 90 min in three normal male subjects reported by Brouwers et al. (1980) following 20 mg domperidone orally. Baseline plasma PRL levels were not significantly different in the two studies. The larger increase observed in this study reflects a greater sensitivity in the PRL assay used here. Although we did not carry out a dose-response study, the magnitude of the plasma PRL responses in the control group is such that it strongly suggests that this dose of domperidone produces maximal PRL increases in normal controls. Fourteen of 15 schizophrenic and schizophreniform patients studied here showed a blunted PRL response to domperidone when compared to that of controls. Thus, these results are in agreement with those of Keks et al. (1987) and not Asnis et al. (1979) or Meltzer et al. (1981). This study, like that of Keks et al., used acute psychotic patients who were studied immediately after admission. Asnis et al. (1979) and Meltzer et al. (1981) studied patients who were more chronic. The results reported here could relate to the stress of acute psychosis and need to be confirmed in more chronic schizophrenic patients before they can be generalized. This explanation seems plausible since PRL values were more blunted in the schizophreniform patients, whose length of illness was shorter, than in the schizophrenic patients, whose illnesses were also of relatively recent onset. Further study is indicated to determine if there is a relationship between duration of illness and the PRL response to domperidone. Meltzer et al. (1984) previously reported that the growth hormone response to apomorphine is negatively correlated with the duration of illness in schizophrenia. There are several factors that could account for the differences between patients and controls reported here. The study conditions were made as similar as possible for the two groups of subjects, who were studied at the same time of the day on the same days whenever possible. The controls slept in a different section of the same Military Hospital. The lack of difference in basal plasma PRL levels is, however, the major evidence available that the two groups were comparable. Differences in plasma domperidone levels between the two groups, reflecting differences in absorption and metabolism of domperidone, could account for the results reported here. Future
145 studies will need to consider this issue with measurement of plasma domperidone levels. There is only one report that domperidone can increase PRL release in vitro at low concentration by blocking the inhibitory effects of DA whereas, at high concentrations, it can paradoxically inhibit the release of PRL (Besser et al., 1980). Thus, it is possible that higher concentrations of domperidone in the patients led to a decrease in PRL secretion. There is also evidence that the ability of domperidone to stimulate PRL secretion in man can be partially blocked by a y-aminobutyric acid (GABA)ergic mechanism. Thus, progabide, a GABA receptor agonist, produced a moderate inhibition of the PRL rise due to domperidone but not haloperidol (Menon et al., 1984). Increased GABAergic activity at the hypothalamic level in the schizophreniform patients could account for the decreased PRL response following domperidone in the schizophreniform patients with a normal response to haloperidol. Another possible explanation for these results is that there is a difference in dopaminergic mechanisms that affect the PRL response to domperidone between the two groups. The lack of a difference in basal plasma PRL levels between the patients and controls, which is consistent with much other evidence that basal plasma PRL levels are normal in unmedicated schizophrenic patients (Meltzer et al., 1984b), suggests normal DA release and normal numbers and responsivity of pituitary DA receptors in the patients in this study. If this is the case, the blunted PRL response to domperidone in the patients is unlikely to be due to antagonism of its effects by greater release of DA from tuberoinfundibular DA neurons. It is possible that domperidone is less effective in blocking the effect of DA at pituitary D, receptors because it has a lower affinity for some of the pituitary D, receptors in the schizophrenic patients. This may constitute very preliminary evidence for an abnormal D, receptor subtype in the pituitary of schizophreniform and schizophrenic patients. Such an abnormality might be present in other DA regions as well. Whalley et al. (1989) reported increased basal PRL levels in acutely psychotic schizophrenic patients. However, in their study, this increase was present in other types of psychotic patients as well, suggesting it could have been a stress effect. Further study is indicated to account for the discrepancy between their results and those reported here. There is also evidence that cortisol can inhibit PRL secretion (Copinschi et al., 1975; Meltzer et al., 1982). Acutely psychotic patients have large increases in cortisol output (Sachar et al., 1963; Whalley et al., 1989). It is possible that this contributed to the decreased PRL response to domperidone. Unfortunately, serum cortisol levels were not available in these patients. In summary, we have found a significant decrease in the plasma PRL response to domperidone, a peripheral D, receptor blocker, in male acute schizophrenic patients. These results are consistent with an abnormality of the dopaminergic system in the early stages of schizophrenia. This could appear to be due to changes in the pituitary D, receptors. Acknowledgments. The authors thank the military authorities and military personnel for providing the possibility of performing our study. They also are grateful to all patients and controls for their patience and collaboration; to Professor Renato Lazzari, Professor and
146 Chairman of Psychology of the University of Rome “La Sapienza,” for performing statistical analysis; and Patrizia Severin for manuscript preparation. This research was supported in part by USPHS grants MH-41684 and MH-41594.
References American Psychiatric Association. DSM-III: Diagnostic and Statistical Manual of Mental Disorders. Washington, DC: APA, 1980. Asnis, G.M.; Sachar, E.J.; Langer, G.; Halpern, F.S.; and Fink, M. Normal prolactin responses in tardive dyskinesia. Psychopharmacology, 66:247-250, 1979. Besser, G.M.; Delitala, G.; Grossman, A.; Stubbs, W.A.; and Yes, T. Chlorpromazine, haloperidol, metoclopramide and domperidone release prolactin through dopamine antagonism at low concentrations but paradoxically inhibit prolactin release at high concentrations. British Journal of Pharmacology, 71:569-573, 1980. Brouwers, J.R.B.J.; Assies, J.; Wiersinga, W.M.; Huizing, G.; and Tytgat, J.N. Plasma prolactin levels after acute and subchronic oral administration of domperidone and of metoclopramide: A cross-over study in healthy volunteers. Clinical Endocrinology, 12:435-440, 1980. Carlsson, A. Antipsychotic drugs, neurotransmitters and schizophrenia. American Journal of Psychiatry, 135:164-73, 1978. Copinschi, G.; L’Hermite, M.; Leclercq, R.; Golstein, J.; Vanhaelst, L.; Virasoro E.; and Robyn, C. Effect of glucocorticoids on pituitary hormone response to hypoglycemia: Inhibition of prolactin release. Journal of Clinical Endocrinology and Metabolism, 40442-449, 1975. Creese, J. Biochemical properties of CNS. Dopamine receptors. In: Meltzer, H.Y., ed. Psychopharmacology: The 7’hird Generation of Progress. New York: Raven Press, 1987. pp. 257-264. Fraioli, F., and Isidori, A. Sistemi a Radioligandi in Endocrinologia. Rome: Societa Editrice Universale SEU, 1977. Kebabian, J.W., and Calne, D.B. Multiple receptors for dopamine. Nature, 277:93-96, 1979. Keks, N.A.; Copolov, O.L.; and Singh, B.S. Abnormal prolactin response to haloperidol challenge in men with schizophrenia. American Journal of Psychiatry, 144:1335-1337, 1987. Laduron, P.M., and Leysen, J.E. Domperidone, a specific in vitro dopamine antagonist, devoid of in vitro central dopaminergic activity. Biochemical Pharmacology, 28:2627-2665, 1979. Langer, G.; Sachar, E.J.; Gruen, P.H.; and Halpern, F.S. The prolactin responses to neuroleptic drugs as a test of dopaminergic blockade: Studies in normal men. Journal of Clinical Endocrinology and Metababolism, 45:996-1002, 1978. Matthysse, S. Antipsychotic drug actions: A clue to the neuropathology of schizophrenia? Federation Proceedings, 32:200-205, 1973. McLeod, R.M. Regulation of prolactin secretion. In: Martini, L., and Ganong, W.F., eds. Frontiers in Neuroendocrinology. Vol. 4. New York: Raven Press, 1976. pp. 169-174. Meltzer, H.Y.; Busch, D.A.; Creese, J.R.; Snyder, S.H.; and Fang, VS. Effect of intramuscular chlorpromazine on serum prolactin levels in schizophrenic patients and normal controls. Psychiatry Research, 5:95-105, 1981. Meltzer, H.Y.; Busch, D.A.; and Fang, V.S. Neuroendocrine abnormalities in schizophrenia: Prolactin, growth hormone and gonadotrophins. In: Brown, G.M.; Koslow, S.H.; and Reichlin, S., eds. Neuroendocrinology and Psychiatric Disorder. New York: Raven Press, 1984a. pp. l-28. B.J.; Robertson, A.; and Song, P. Effect of Meltzer, H.Y.; Fang, V.S.; Tricou, dexamethasone on plasma prolactin and cortisol levels in psychiatric patients. American Journal of Psychiatry, 139:263-268, 1982.
147 Meltzer, H.Y.; Goode, D.J.; and Fang, V.S. The effect of psychotropic drugs on endocrine function: I. Neuroleptics, precursors and agonists. In: Lipton, M.A.; DiMascio, A.; and Killam, K.F., eds. Psychopharmacology: A Generation of Progress. New York: Raven Press, 1978. pp. 509-529. Meltzer, H.Y.; Kolakowska, T.; Fang, V.S.; Fogg, L.; Robertson, A.; Lewine, R.; Strahilevitz, M.; and Busch, D. Growth hormone and prolactin response to apomorphine in schizophrenia and affective disorders: Relation of duration of illness and depressive symptoms. Archives of General Psychiatry, 41572-579, 19846. Meltzer, H.Y., and Stahl, S.M. The dopamine hypothesis of schizophrenia. Schizophrenia Bulletin, 2:l l-18, 1976. Menon, V.J.; Butt, W.R.; Thiercelini, J.F.; Gomeni, R.; Marselli, P.L.; and London, D.R. Effects in man of progabide on prolactin release induced by haloperidol or domperidone. Psychoneuroendocrinology, 9: 101-l 14, 1984. Peroutka, S., and Snyder, S. Relationship of neuroleptic drug effects at brain dopamine, serotonin, alpha-adrenergic, and histamine receptors to clinical potency. American Journal of Psychiatry, 137:1518-1522, 1980. Randrup, A., and Munkvad, I. Evidence indicating an association between schizophrenia and dopaminergic hyperactivity in the brain. Orthomolecular Psychiatry, 1~2-7, 1972. Rubin, R. Prolactin and schizophrenia. In: Meltzer, H.Y., ed. Psychopharmacology: 7’he Third Generation of Progress. New York: Raven Press, 1987. pp. 803-807. Sachar, E.J.; Mason, J.W.; Kolmer, H.S., Jr.; and Artiss, K.L. Psychoendocrine aspects of acute schizophrenia reactions. Psychosomatic Medicine, 25510-537, 1963. Snyder, S.; Banerjee, S.; Yamamura, H.; and Greenberg, D. Drugs, neurotransmitters and schizophrenia. Science, 184: 1243- 1253, 1974. Thorner, M.O. Prolactin. In: Besser, G.M., ed. “The Hypothalamus and Pituitary.” Journal of Clinical Endocrinology and Metabolism, 61201-222, 1977. Whalley, L.J.; Christie, J.E.; Blackwood, D.H.R.; Bennie, J.; Dick, H.; Blackburn, I.M.; and Fink, G. Disturbed endocrine function in the psychoses: I. Disordered homeostasis or disease process? British Journnl of Psychiatry, 155:455-46 1, 1989.
139
Plasma
Dina Nerozzi, Armando Magnani, Marco Cerilli, Costanzo Moretti, Herbert Y. Meltzer Received
Vincenzo Sforza, Elena Scaramucci, Gaetano Frajese, halo Antonozzi, and
October 27, 1989; revised version received July 24, 1990; accepted August 5, 1990.
Abstract. The prolactin (PRL) response to 20 mg of domperidone, a peripheral dopamine (DA) blocking agent, was evaluated in a group of 16 drug-free, acute, young schizophreniform and schizophrenic males and in a group of age-matched normal males. Although basal plasma PRL levels were normal, the PRL responses following domperidone were blunted in both patient groups. The PRL response was more blunted in the schizophreniform patients than in the schizophrenic patients. Possible explanations for these results include pharmacokinetic factors or abnormalities of the pituitary D, DA receptors. Key Words. Schizophrenia, receptors.
dopamine,
domperidone,
prolactin,
D, receptors,
D,
The hypothesis that at least some patients with the diagnosis of schizophrenia have a relative overactivity of the central dopaminergic system arose mainly from indirect lines of evidence linked to neuroleptic drug action (Randrup and Munkvard, 1972; Matthysse, 1973; Snyder et al., 1974; Meltzer and Stahl, 1976; Carlsson, 1978). For example, although neuroleptic drugs have many different actions on brain tissue, it is their ability to block D, dopamine (DA) receptors in the mesolimbic and mesostriatal system that has been shown to be highly correlated with their therapeutic action (Peroutka and Snyder, 1980), as well as their ability to stimulate prolactin (PRL) secretion (Langer et al., 1978). The ability of indirect DA agonists such as amphetamine to produce schizophrenia-like clinical syndromes after chronic administration also supports the DA hypothesis (Randrup and Munkvard, 1972; Meltzer and Stahl, 1976). It has been more difficult to obtain direct evidence for a dopaminergic abnormality in schizophrenia. Among the various methods that have been used is the assessment of
Dina Nero& M.D., is Assistant Professor, Department of Experimental Medicine, University of Rome “La Sapienza.” Armando Magnani, M.D., Vincenzo Sforza, M.D., Elena Scaramucci, M.D., and Marco Cerilli, M.D., are Research Fellows, Istituto di Clinica Medica V, University of Rome “La Sapienza.” Costanzo Moretti, M.D., is Researcher, Istituto di Clinica Medica V, University of Rome “La Sapienza.” Gaetano Frajese, M.D., is Professor of Endocrinology, University of Rome “La Sapienza.” Italo Antonozzi, M.D., is Director, Service for Genetic and Metabolic Diseases, Department of Experimental Medicine, University of Rome “La Sapienza.” Herbert Y. Meltzer, M.D., is Director, Laboratory of Biological Psychiatry, Case Western Reserve University, Cleveland, OH, USA. (Reprint requests to Dr. D. Nerozzi, Via di Porta Pinciana, 4 - 00187 Rome, Italy.) 0165-1781/90/$03.50
Q 1990 Elsevier Scientific
Publishers
Ireland
Ltd.
140
some aspects of the neuroendocrine system. It is well established that DA is involved in the regulation, synthesis, and release of a number of pituitary hormones; in particular, DA inhibits PRL release directly at the level of the pituitary both in vivo and in vitro (McLeod, 1976; Meltzer et al., 1978). According to the DA hypothesis, increased dopaminergic activity at the pituitary level might be expected to lower basal plasma PRL levels. This has generally not been observed (for review, see Meltzer et al., 1984~). Supersensitivity of pituitary DA receptors might lead to a shift to the left or enhanced suppression of PRL secretion by direct acting DA agonists, such as bromocriptine orapomorphine. This has also not been observed (for reviews, see Meltzer et al., 1984b; Rubin, 1987). There have also been some studies comparing the effect of single doses of DA antagonists on PRL secretion in unmedicated schizophrenic patients compared to that of normal controls. Increased DA activity might be expected to diminish the PRL response to a neuroleptic drug. Asnis et al. (1979) found no difference in the PRL response to haloperidol, 0.50 mg intramuscularly (i.m.), in six unmedicated schizophrenic patients and 13 normal control subjects. No difference in the PRL responses to chlorpromazine, i.m. 25 and 50 mg., was found between 6 male normal controls and 14 unmedicated schizophrenic patients (Meltzer et al., 1981). However, Keks et al. (1987) reported a smaller and slower PRL response to 0.50 mg haloperidol, given intravenously, in 14 drug-free male schizophrenic patients compared to 14 normal age- and sex-matched control subjects. Thus, there is still some ambiguity about dopaminergic activity at the pituitary level in schizophrenia. To gain more information about dopaminergic activity at the pituitary level in schizophrenia, we decided to administer domperidone, a peripheral DA blocking agent (Laduron and Leysen, 1979). It was thought that this could help to clarify whether any observed differences in PRL secretion between schizophrenic patients and controls could be due to peripheral or central mechanisms. Furthermore, to avoid all confounding variables due to age, gender, meals, physical activity, and time of the day (Thorner, 1977) we selected a very homogeneous population of young males (both patients and controls) living in the same community.
Methods Subjects. The subjects were 16 physically healthy, nonobese, nonsubstance-abusing men (mean age = 20.4, SD = 1.5, range 19-25). All had the onset of a psychotic episode during military service and were referred to the Psychiatry Unit of the Military Medical Center in Rome. The study was conducted within the first 2-3 days of admission to the Psychiatric Unit. Diagnosis was established at admission and confirmed at discharge by consensus of two experienced psychiatrists according to
141 Procedure.
Results Table 1 presents the plasma PRL levels for the schizophreniform and schizophrenic patients, while Table 2 presents the PRL data for the controls. Analysis for outliers showed that one of the schizophreniform patients was an outlier. The data from this subject were discarded. Fig. 1 gives mean plasma PRL levels with the outlier omitted; Fig. 2 gives individual areas under the curve (AUC). Table 1. Serum prolactin levels in schizophreniform oatients
and schizophrenic
Serum prolactin level 0’
+90’
+1os
+120’
Schizophreniform 1
1.7
21.7
18.5
18.5
2
0.7
28.6
21.5
17.9
3
3.7
19.7
14.7
17.0
4
1.2
18.7
27.5
33.4
5
2.5
18.2
17.6
16.2
Mean*SD
2.6 + 1.8
43.0 + 53.1
42.8 + 56.2
22.1 * 7.4
6
2.0
49.9
62.8
71.1
7
0.9
61.3
88.4
77.2
8
3.1
44.2
49.0
59.5
Schizophrenic
9
2.4
39.8
38.6
75.0
10
4.6
42.1
59.9
51.0 23.7
11
3.1
20.1
14.6
12
7.6
95.0
73.8
87.2
13
3.9
13.9
18.0
37.2
14
7.0
25.4
18.7
17.2
15
4.6
37.2
45.0
56.1
Mean+SD
3.9 * 2.1
42.9 f 23.1
46.9 + 25.0
55.5 zt23.4
142
Table 2. Serum prolactin levels in normal controls Serum Drolactin level 0’
+90’
+1o!Y
+120’ 135.6
1
3.1
99.8
128.2
2
0.8
90.2
112.6
89.7
3
2.4
80.0
112.2
69.7 128.0
4
2.7
84.2
150.3
5
3.0
66.8
67.4
58.1
6
1.6
75.6
110.7
77.0
7
3.0
81.0
98.9
92.3
8
2.8
89.7
130.0
63.8
9
2.6
74.9
125.8
118.0
10
2.8
92.3
137.4
98.2
2.5 zt 0.7
83.5 + 9.7
Mean
IL SD
117.3 f
23.0
93.0 + 27.0
Fig. 1. Time course of prolactin (PRL) data in schizophreniform patients, schizophrenic patients, and normal controls 120 PRL (ng/ml) _A100 ‘.-----4
80
_.___._,_-.--
-.---.
_._._.-
Jr ---------__
t
__________-t
+ 0
-.
+90.
+120
+105’ Time(min,)
Schizophreniform
patients, solid circles; schizophrenic
patients, solid squares; and normal controls, solid triangles.
Fig. 2. Scattergram of AUC of PRL values in schizophreniform schizophrenic patients, and normal controls AUC
PRL
70
ng/ml/l20min
60. 50-
B
A l-
C .
I-
l
40
.
30 20.
-i-.
@-AP
0
lo0. SF
C @Mean
S of AUC
AUC = area under the curve. PRL = prolactin. SF = schizophreniform.
S = schizophrenic.
C = normal control.
and
143 Table 3 presents the AUC analysis. There was a significant group difference. hoc tests revealed all three groups were different from each other.
Post
Table 3. Area under the curve analysis Least mean square
n
Group
5
62.5
Schizophrenic
10
150.6
Normal control
10
295.6
Source
df
F
P
Group
2
34.9
0.0001
Prolactin
1
0.04
0.8358
Schizophreniform
Table 4 presents a repeated measures ANOVA. There was a significant group effect, time effect, and group X time interaction. Post hoc tests indicated that the schizophreniform patients had lower PRL levels than the schizophrenic patients at all time points. The schizophreniform and schizophrenic patients had lower serum PRL levels than the normal controls at all time points except for time 0. Fourteen of the 15 patients had lower plasma PRL levels at 90 min, 13/ 15 at 105 min, and lo/ 15 at 120 min than any of the controls. All the schizophreniform patients had PRL values lower than controls at all the time points. In the schizophrenic group, 90% of the patients had lower PRL levels at 90 min, 80% at 105 min, and 50% at 120 min. The mean peak plasma PRL levels were 21.4 (SD = 14.3) ng/ml in the schizophreniform patients, 55.5 (SD = 23.4) ng/ml in the schizophrenic patients, and 118.09 (SD = 7.44) ng/mg in the controls. PRL responses tended to peak earlier in the schizophreniform patients, 80?J0 at 90 min, while in the schizophrenic patients 60% peaked later, at 120 min; 20% earlier, at 90 min; and 20% at the same time as the controls, 105 min. AUC was lower in 100% of the schizophreniform patients and in 80% of the schizophrenic patients when compared with the normal controls.
Table 4. Repeated measures analysis of variance Source
df
F
P
Group
2
35.07
0.0001
Time
3
61.59
0.0001
Time X group
6
9.58
0.0001
Post hoc tests Time 0
F 3.58
D
SF/S
SF/N
SIN
0.045
0.03
0.54
0.05
90’
29.12
0.0001
0.02
0.0001
0.0001
105
42.29
0.0001
0.03
0.0001
0.0001
120
17.41
0.0001
0.01
0.0001
0.0015
Note. SF = schizophreniform. S = schizophrenic. N = normal control.
144
Discussion The major finding of this study is that there is a blunted plasma PRL response following a domperidone challenge in unmedicated schizophrenic and schizophreniform patients compared to normal controls. The PRL response in the schizophreniform group was significantly blunted compared to the schizophrenic group. There are two major DA receptor subtypes: D, receptors linked to the stimulation of adenylate cyclase and D, receptors linked to the inhibition of this enzyme (Kebabian and Calne, 1979). Whereas most brain areas contain both D, and D, receptors, D, receptors are the sole subtype in the anterior pituitary (Creese, 1987). Domperidone is a potent antagonist of D, receptors and has only a weak affinity for D, receptors. Since it acts at the pituitary level, which lacks D, receptors (Creese, 1987), it can be argued that hyperprolactinemia secondary to domperidone is a D, receptor-mediated response. The increase in plasma PRL levels of the normal controls at 90 min was 33.4-fold. This compares with a IO-fold increase at 90 min in three normal male subjects reported by Brouwers et al. (1980) following 20 mg domperidone orally. Baseline plasma PRL levels were not significantly different in the two studies. The larger increase observed in this study reflects a greater sensitivity in the PRL assay used here. Although we did not carry out a dose-response study, the magnitude of the plasma PRL responses in the control group is such that it strongly suggests that this dose of domperidone produces maximal PRL increases in normal controls. Fourteen of 15 schizophrenic and schizophreniform patients studied here showed a blunted PRL response to domperidone when compared to that of controls. Thus, these results are in agreement with those of Keks et al. (1987) and not Asnis et al. (1979) or Meltzer et al. (1981). This study, like that of Keks et al., used acute psychotic patients who were studied immediately after admission. Asnis et al. (1979) and Meltzer et al. (1981) studied patients who were more chronic. The results reported here could relate to the stress of acute psychosis and need to be confirmed in more chronic schizophrenic patients before they can be generalized. This explanation seems plausible since PRL values were more blunted in the schizophreniform patients, whose length of illness was shorter, than in the schizophrenic patients, whose illnesses were also of relatively recent onset. Further study is indicated to determine if there is a relationship between duration of illness and the PRL response to domperidone. Meltzer et al. (1984) previously reported that the growth hormone response to apomorphine is negatively correlated with the duration of illness in schizophrenia. There are several factors that could account for the differences between patients and controls reported here. The study conditions were made as similar as possible for the two groups of subjects, who were studied at the same time of the day on the same days whenever possible. The controls slept in a different section of the same Military Hospital. The lack of difference in basal plasma PRL levels is, however, the major evidence available that the two groups were comparable. Differences in plasma domperidone levels between the two groups, reflecting differences in absorption and metabolism of domperidone, could account for the results reported here. Future
145 studies will need to consider this issue with measurement of plasma domperidone levels. There is only one report that domperidone can increase PRL release in vitro at low concentration by blocking the inhibitory effects of DA whereas, at high concentrations, it can paradoxically inhibit the release of PRL (Besser et al., 1980). Thus, it is possible that higher concentrations of domperidone in the patients led to a decrease in PRL secretion. There is also evidence that the ability of domperidone to stimulate PRL secretion in man can be partially blocked by a y-aminobutyric acid (GABA)ergic mechanism. Thus, progabide, a GABA receptor agonist, produced a moderate inhibition of the PRL rise due to domperidone but not haloperidol (Menon et al., 1984). Increased GABAergic activity at the hypothalamic level in the schizophreniform patients could account for the decreased PRL response following domperidone in the schizophreniform patients with a normal response to haloperidol. Another possible explanation for these results is that there is a difference in dopaminergic mechanisms that affect the PRL response to domperidone between the two groups. The lack of a difference in basal plasma PRL levels between the patients and controls, which is consistent with much other evidence that basal plasma PRL levels are normal in unmedicated schizophrenic patients (Meltzer et al., 1984b), suggests normal DA release and normal numbers and responsivity of pituitary DA receptors in the patients in this study. If this is the case, the blunted PRL response to domperidone in the patients is unlikely to be due to antagonism of its effects by greater release of DA from tuberoinfundibular DA neurons. It is possible that domperidone is less effective in blocking the effect of DA at pituitary D, receptors because it has a lower affinity for some of the pituitary D, receptors in the schizophrenic patients. This may constitute very preliminary evidence for an abnormal D, receptor subtype in the pituitary of schizophreniform and schizophrenic patients. Such an abnormality might be present in other DA regions as well. Whalley et al. (1989) reported increased basal PRL levels in acutely psychotic schizophrenic patients. However, in their study, this increase was present in other types of psychotic patients as well, suggesting it could have been a stress effect. Further study is indicated to account for the discrepancy between their results and those reported here. There is also evidence that cortisol can inhibit PRL secretion (Copinschi et al., 1975; Meltzer et al., 1982). Acutely psychotic patients have large increases in cortisol output (Sachar et al., 1963; Whalley et al., 1989). It is possible that this contributed to the decreased PRL response to domperidone. Unfortunately, serum cortisol levels were not available in these patients. In summary, we have found a significant decrease in the plasma PRL response to domperidone, a peripheral D, receptor blocker, in male acute schizophrenic patients. These results are consistent with an abnormality of the dopaminergic system in the early stages of schizophrenia. This could appear to be due to changes in the pituitary D, receptors. Acknowledgments. The authors thank the military authorities and military personnel for providing the possibility of performing our study. They also are grateful to all patients and controls for their patience and collaboration; to Professor Renato Lazzari, Professor and
146 Chairman of Psychology of the University of Rome “La Sapienza,” for performing statistical analysis; and Patrizia Severin for manuscript preparation. This research was supported in part by USPHS grants MH-41684 and MH-41594.
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