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Effects of chlorpromazine on serotonin uptake in blood platelets
23
Psvchiozry Research, 9,23-28 (1983) Elsevier
Effects of Chlorpromazine Platelets Ramesh
C. Arora
Received November3,
and Herbert
on Serotonin
Uptake
in Blood
Y. Meltzer
1982: revised version received February 14.1983; accepted April 6, 1983.
Abstract. Platelet serotonin (5-HT) uptake was studied in schizophrenic patients before and after treatment with chlorpromazine (CPZ) for 2-3 weeks. No difference was noted in the affinity of 5-HT (Km) or maximum velocity of 5-HT uptake ( Vmax) of unmedicated schizophrenic patients and normal controls. Administration of CPZ was associated with a significant increase in Km and V,,,. Specific uptake of 5-HT, at 0.5 PM, was significantly decreased in most subjects. Chlorpromazine inhibited 5-HT uptake into platelets from normal controls in vitro (IC,,, 1.8 * 0. I ph4) in a competitive manner. Key Words. Chlorpromazine, V max.
A previous
report
from
this
platelet,
laboratory
serotonin
indicated
uptake, schizophrenia,
no significant
Km, and
difference
in the
(5-HT) uptake in blood platelets of acute or chronic schizophrenic patients and normal controls (Arora and Meltzer, 1982). However, Modai et al. (1979) reported that 5-HT uptake in blood platelets of acute schizophrenic patients was 40% less than that of normal controls. They found a decrease in V,,, (number of carrier molecules) but no difference in K, (a measure of the affinity of the carrier molecules for 5-HT) in the platelets of acute schizophrenic patients and normal controls (Rotman et al., 1979). Some of the patients in their study were receiving neuroleptic drugs. They were included because these investigators found no effect of neuroleptics on 5-HT uptake in blood platelets of normal controls in vitro (Modai et al., 1979; Rotman et al., 1979). However, other studies do indicate that neuroleptics can inhibit 5-HT uptake by platelets. Long and Lessin (1962) reported that chlorpromazine (CPZ) in vitro competitively inhibited 5-HT uptake into the blood platelets of oxen. Hussein et al. (1978) reported that haloperidol inhibited 5-HT uptake in a noncompetitive manner ex vivo in blood platelets from rabbits. Baldacci et al. (1980) reported an uncompetitive or mixed type of inhibition of 5-HT uptake by rabbit blood platelets treated with CPZ in ex vivo studies. Oxenkrug (1978) also reported an inhibition of 5-HT uptake by neuroleptics in vitro in normal human blood platelets. These findings led us to reinvestigate the effect of CPZ on 5-HT uptake by platelets from normal controls and schizophrenic patients in vitro and ex vivo, respectively. kinetic
parameters
(K,
and
V,,,,,) of serotonin
Ramesh C. Arora, Ph.D.. is Research
Associate (Associate Professor), Department of Psychiatry, University of Chicago, Pritzker School of Medicine, and Research Scientist at the Illinois State Psychiatric Institute(lSPI),Chicago, IL. Herbert Y. Meltzer, M.D., is Professorof Psychiatry. UniversityofChicago, Pritzker School of Medicine, and Director, Laboratory of Biological Psychiatry, ISPI. (Reprint requests to Dr. R.C. Arora. Illinois Slate Psychiatric Institute. 1601 W. Taylor Street. Chicago, IL 60612. USA.) 0165-1781/83/$3.00
Q Elsevier Science Publishers
B.V.
24
Methods Subjects. The patient population consisted of 19 schizophrenic patients (10 male, 9 female) diagnosed according to Research Diagnostic Criteria (Spitzer et al., 1978). Sixty normal controls (35 males, 25 females), who were drug free and had no history of medical or psychiatric illness, were also studied. The patients had not been taking psychotropic drugs for at least 2 to 4 weeks before admission. They were kept drug free (placebo) for at least 1 more week after admission, and then two fasting 8 a.m. blood samples were obtained on different days for uptake studies. The patients were treated with CPZ (200-600 mg) for 14-23 days (mean 16, SD 7). Uptake was studied again on 2 adjacent days during CPZ treatment. The values for the two determinations during placebo and CPZ treatment were averaged. The mean (* SD) ages of the patients and controls were 29. I f 7.3 and 32.4 f 7.2 years, respectively. Determination of 5-HT Uptake. Blood was drawn in plastic syringes from normal controls and patients and transferred into plastic tubes containing citrate-phosphate-dextrose (15% v: v) as anticoagulant. Platelet-rich plasma (PRP) was obtained by centrifugation at 600g for 2% minutes in a Sorvall RC-5 centrifuge at 0°C. Platelets were counted electronically by means of a Coulter thrombocounterJBr in triplicate and the average was taken. 5-HT uptake was studied as described earlier (Arora and Meltzer, 1981). In brief, PRP (0.3 ml) was preincubated with Kreb’s phosphate buffer (0.6 ml, pH 7.4) minus CaCl, for IO minutes at 37°C. Next, 0.1 ml of ‘4C-5-HT (0.3-I x IO-5A4) was added. The final concentrations of 5-HT in the incubation mixture were 0.3 uM,O.5 PM. 0.75 PM, and I pM. One set of tubes was immediately immersed in an ice bath after addition of 5-HT while the other set of tubes was incubated for an additional 4 minutes. The platelet pellet obtained by centrifuging the tubes at 10,OOOgfor 15 minutes was dissolved in Soluene-350 and counted as described earlier (Arora and Meitzer, 1981). Active uptake was determined from the differences in disintegrations per minute (dpm) in the tubes incubated for 4 minutes and the tubes that had been immediately immersed in the ice water. Inhibition Studies and Nature of Inhibition. The ability of CPZ to inhibit 5-HT uptake was studied in buffer for 10 minutes before the addition of 5-HT (5 x IO m7M). After the addition of
5-HT. the mixture was incubated for an additional 4 minutes and processed as described above. The ICse (concentration which produces 50% inhibition of 5-HT uptake) was estimated graphically. To determine the nature of inhibition, inhibition studies werecarried out at a single concentration of the drug and various concentrations of 5-HT (3 x 107M - 1 x 10-hM). The uptake of 5-HT in the presence and absence ofdrug was plotted by the method of Eadie-Hofstee (Eadie, 1942; Hofstee, 1952).
Results Chlorpromazine inhibited 5-HT uptake in vitro in a competitive manner in blood platelets from normal controls (Fig, 1). The IC,, was 1.8 f SD 0. I PM compared to 4 * 0.9 nM for imipramine. The kinetic parameters (Km and V,,, ) o f 5-HT uptake in blood platelets before and after CPZ treatment are reported in Table 1 and Fig. 2. The net initial velocity of 5-HT uptake at 0.5 pM of 5-HT, the concentration closest to the K,, is also reported in Table 1. As reported earlier (Arora and Meltzer, 1982), there was no significant difference in K, and V,,, of 5-HT uptake in schizophrenic patients and normal controls. However, after 14-23 days of CPZ treatment, an increase in K, and V,,, was found, an indication of mixed inhibition. A significant decrease in 5-HT uptake in the blood platelets of CPZ-treated patients at 5-HT, 0.5 pM, was found; the average decrease was 28 f. 14.3% (range lo-50%), but uptake increased in two patients (25 and 73%).
25
Fig. 1. Eadie-Hofstee
plot of 5-HT
uptake
in normal
human
blood
platelets
14 -
a
4
I6
I2
24
20
28
v/s
Table 1. Platelet 5-HT promazine treatment
uptake
kinetics
in patients
before
and after
chlor-
Active uptake 0.5 pM IO’ platelets/minute)
!I,,, Km (VW Condition
( pmoles/
5-HT (pmoles/107 platelets/minute)
Mean
SD
Mean
SD
Mean
SD
0.48
0.14
12.3
2.4
6.7
1 .5
0.47
0.15
1 1 .o
3.9
5.8
1 .7
0.32
13.12
5.6
4.73
1 .8
Normal controls (n = 60) Patients Placebo
(n = 19)
Chlorpromazine treatment (n = 19) 1
r =
2. I = 2.63, 3.
0.91’
6 54,~ < 0.0005, paired
r = 2.64.
i
test
p < 0.01,
paired
I test.
p <0
paired
f test.
01,
26 Fig. 2. K, and V,,, of platelet 5-HT uptake before and after treatment chlorpromazine for 14-23 days EFFECT
OF CHLORPROMAZINE PLATELETS
ON
Km AND
OF SCHIZOPHRENIC
vmox
with
IN BLOOD
PATIENTS 1
I
PRE
1
POST
I
I
PRE
POST
Discussion Chlorpromazine competitively inhibited 5-H-F uptake in vitro in blood platelets obtained from normal controls. Similar findings have been reported with most tricyclic antidepressants (Tuomisto, 1974). CPZ was much less potent than imipramine in inhibiting 5-HT uptake in blood platelets. The inhibitory effects of CPZ on 5-HT uptake in platelets reported here are similar to those reported by Oxenkrug (1978) and Long and Lessin (1962) but contrary to those reported by Rotman et al. (1979) who observed no effect of CPZ on K, and V,,, of 5-HT uptake by blood platelets of normal human controls. The possible explanation for this discrepancy may be that Rotman et al. (1979) studied the total uptake of SHT, whereas we studied active uptake of 5-HT by blood platelets from normal human controls. It is possible that CPZ may enhance passive diffusion. This effect might have contributed to the conclusion that no change in active uptake occurred since total uptake might have remained constant or even increased in their study. Chlorpromazine administration was found to increase both K, and V,,, of 5-HT uptake in blood platelets of schizophrenic patients. The increase in K, indicates that the affinity of S-HT for the carrier molecules decreases after CPZ treatment. The increase in V,,, indicates that CPZ treatment increases the number of 5-HT carrier molecules. These two effects produce opposite effects on 5-HT uptake so it is of interest to consider what the overall net effect is. This was examined by considering the
27 uptake of 5-HT at 0.5 PM, the concentration closest to the K, in this study. Net uptake decreased or showed no change in 17 of 19 CPZ-treated subjects. It is not yet known when this inhibition begins and whether it persists beyond the period of study reported here. Baldacci et al. (1980) reported a similar increase in V,,,, of 5-HT uptake in rabbits during CPZ treatment. As this effect takes 6-7 days to develop, which is close to the mean survival time of rabbit as well as human blood platelets, it would seem likely that such an increase in 5-HT uptake sites occurred in the megakaryocytes from which the platelets are derived. This effect would be consistent with increased synthesis of platelet membrane proteins. Whether the increase is related to the CPZinduced decrease in affinity of the 5-HT sites for 5-HT remains to be determined. It is also unclear whether all neuroleptics have similar effects on 5-HT uptake in platelets. The other possible reason for the increased K, and V,,, may be decreased efflux of 5-HT during the processing of CPZ-treated platelets. However, this explanation is unlikely, since we and others did not find any relationship between 5-HT content and 5-HT uptake in the platelets (unpublished observations; Stahl et al., 1983). Platelet 5-HT uptake has features in common with 5-HT uptake into 5-HT nerve terminals (Sneddon, 1973; Stahl, 1977). It is possible that the decreased platelet 5-HT uptake associated with CPZ treatment indicates a similar process occurs in some 5-HT neurons. There are as yet no data concerning the effect of chronic neuroleptic treatment on 5-HT uptake in rat brain synaptosomes. It is possible that the effects of neuroleptics on 5-HT uptake contribute to their therapeutic efficacy, their side effects, or both. The effects of neuroleptics on 5-HT uptake could differ among neuroleptics and need not correlate with their ability to block dopamine receptors. These effects may be relevant to the ability of neuroleptic drugs to produce antidepressant effects. In conclusion, we have shown that CPZ affects 5-HT uptake in blood platelets of normal human controls in vitro and of schizophrenic patients ex vim. These results indicate that the study of platelet 5-HT uptake in schizophrenic patients should be done in drug-free patients if an assessment of basal activity is sought. Our results also suggest that not only CPZ but possibly other neuroleptics may directly affect 5-HT uptake in man. The research reported was supported, in part, by USPHS MH-30059 and MH-30938, and the Department of Mental Health, State of Illinois. HYM is recipient of USPHS RCSA MH-47808.
Acknowledgments.
References Arora, R.C., and Meltzer, H.Y. A modified assay method for determining serotonin human platelets. Clinica Chimica Acta, 112, 225 (198 I). Arora. R.C., and Mehzer, H.Y. Serotonin uptake by blood platelets of schizophrenic Psychiarr~~ Research,
uptake in patients.
6, 327 (1982).
Baldacci, M., Baldacci, M., Bergel, T.D., Born, G.V.R., and Hickman, M. Increases in aggregation by and uptake of 5hydroxytryptamine with platelets from rabbits treated with chlorpromazine. British Journal of Pharmacology, 69, I I3 ( 1980). Eadie, G.S. The inhibition of cholinesterase by physostigmine and prostigmine. Journal of Biological Chemistr_v, 146,85 ( 1942). Hofstee, B.H.J. On the evaluation of the constants Pm and K, in enzyme reactions. Science, 116, 329 (1952).
28 Hussein L., Goedde, H.W., Rosenfeld, M., and Freerksen, E. Subcellular distribution of 14C-5-hydroxytryptamine in the blood platelets of rabbits: Effects of imipramine and haloperidol. Hoppe-Seyier’s Zeitschrifr fiir Physioiogische Chemie, 359,803 (1978). Long, R.F., and Lessin, A.W. Inhibition of 5hydroxytryptamine uptake by platelets in vitro and in vivo. Biochemical Journal, 82,4P (1962). Modai, I., Rotman, A., Munitz, H., Tjano, S., and Wijsenbeek, H. Serotonin uptake by blood platelets of acute schizophrenic patients. Psychopharmacology, 54, 193 (1979). Oxenkrug, G.F. The effect of neuroleptic derivatives of butyrophenone on the uptake of 5-HT by human blood platelets. Journal of Pharmacy and Pharmacology, 30, 740 (1978). Rotman, A., Modai, I., Munitz, H., and Wijsenbeek, H. Active uptake of serotonin by blood platelets of schizophrenic patients. FEBS Letters, 101, 134 (1979). Sneddon, J.M. Blood platelets as a model for monoamine containing neurons. Progress in NeurobiologJj,
1, 15 I
( 1973).
Spitzer, R.L., Endicott, J., and Robins, E. Research Diagnostic Criteria: Rationale and reliability. Archives of General Psychiatry, 35, 773 (1978). Stahl, S.M. The human platelet: A diagnostic and research tool for the study of biogenic amines in psychiatric and neurological disorders. Archives of General Psychiatry, 34, 509 (1977). Stahl, SM., Wood, D.J., Mefford, I.N., Berger, P. A., and Ciaranello, R.D. Hyperserotonemia and platelet serotonin uptake and release in schizophrenia and affective disorders, American Journal
of Ps_vchiatry, 140, 26
(I 983).
Tuomisto, J. A new modification for studying 5-HT uptake by blood platelets: A re-evaluation of tricyclic antidepressants as uptake inhibitors. Journal of Pharmacy and Pharmacology, 26,92 ( 1974).
Psvchiozry Research, 9,23-28 (1983) Elsevier
Effects of Chlorpromazine Platelets Ramesh
C. Arora
Received November3,
and Herbert
on Serotonin
Uptake
in Blood
Y. Meltzer
1982: revised version received February 14.1983; accepted April 6, 1983.
Abstract. Platelet serotonin (5-HT) uptake was studied in schizophrenic patients before and after treatment with chlorpromazine (CPZ) for 2-3 weeks. No difference was noted in the affinity of 5-HT (Km) or maximum velocity of 5-HT uptake ( Vmax) of unmedicated schizophrenic patients and normal controls. Administration of CPZ was associated with a significant increase in Km and V,,,. Specific uptake of 5-HT, at 0.5 PM, was significantly decreased in most subjects. Chlorpromazine inhibited 5-HT uptake into platelets from normal controls in vitro (IC,,, 1.8 * 0. I ph4) in a competitive manner. Key Words. Chlorpromazine, V max.
A previous
report
from
this
platelet,
laboratory
serotonin
indicated
uptake, schizophrenia,
no significant
Km, and
difference
in the
(5-HT) uptake in blood platelets of acute or chronic schizophrenic patients and normal controls (Arora and Meltzer, 1982). However, Modai et al. (1979) reported that 5-HT uptake in blood platelets of acute schizophrenic patients was 40% less than that of normal controls. They found a decrease in V,,, (number of carrier molecules) but no difference in K, (a measure of the affinity of the carrier molecules for 5-HT) in the platelets of acute schizophrenic patients and normal controls (Rotman et al., 1979). Some of the patients in their study were receiving neuroleptic drugs. They were included because these investigators found no effect of neuroleptics on 5-HT uptake in blood platelets of normal controls in vitro (Modai et al., 1979; Rotman et al., 1979). However, other studies do indicate that neuroleptics can inhibit 5-HT uptake by platelets. Long and Lessin (1962) reported that chlorpromazine (CPZ) in vitro competitively inhibited 5-HT uptake into the blood platelets of oxen. Hussein et al. (1978) reported that haloperidol inhibited 5-HT uptake in a noncompetitive manner ex vivo in blood platelets from rabbits. Baldacci et al. (1980) reported an uncompetitive or mixed type of inhibition of 5-HT uptake by rabbit blood platelets treated with CPZ in ex vivo studies. Oxenkrug (1978) also reported an inhibition of 5-HT uptake by neuroleptics in vitro in normal human blood platelets. These findings led us to reinvestigate the effect of CPZ on 5-HT uptake by platelets from normal controls and schizophrenic patients in vitro and ex vivo, respectively. kinetic
parameters
(K,
and
V,,,,,) of serotonin
Ramesh C. Arora, Ph.D.. is Research
Associate (Associate Professor), Department of Psychiatry, University of Chicago, Pritzker School of Medicine, and Research Scientist at the Illinois State Psychiatric Institute(lSPI),Chicago, IL. Herbert Y. Meltzer, M.D., is Professorof Psychiatry. UniversityofChicago, Pritzker School of Medicine, and Director, Laboratory of Biological Psychiatry, ISPI. (Reprint requests to Dr. R.C. Arora. Illinois Slate Psychiatric Institute. 1601 W. Taylor Street. Chicago, IL 60612. USA.) 0165-1781/83/$3.00
Q Elsevier Science Publishers
B.V.
24
Methods Subjects. The patient population consisted of 19 schizophrenic patients (10 male, 9 female) diagnosed according to Research Diagnostic Criteria (Spitzer et al., 1978). Sixty normal controls (35 males, 25 females), who were drug free and had no history of medical or psychiatric illness, were also studied. The patients had not been taking psychotropic drugs for at least 2 to 4 weeks before admission. They were kept drug free (placebo) for at least 1 more week after admission, and then two fasting 8 a.m. blood samples were obtained on different days for uptake studies. The patients were treated with CPZ (200-600 mg) for 14-23 days (mean 16, SD 7). Uptake was studied again on 2 adjacent days during CPZ treatment. The values for the two determinations during placebo and CPZ treatment were averaged. The mean (* SD) ages of the patients and controls were 29. I f 7.3 and 32.4 f 7.2 years, respectively. Determination of 5-HT Uptake. Blood was drawn in plastic syringes from normal controls and patients and transferred into plastic tubes containing citrate-phosphate-dextrose (15% v: v) as anticoagulant. Platelet-rich plasma (PRP) was obtained by centrifugation at 600g for 2% minutes in a Sorvall RC-5 centrifuge at 0°C. Platelets were counted electronically by means of a Coulter thrombocounterJBr in triplicate and the average was taken. 5-HT uptake was studied as described earlier (Arora and Meltzer, 1981). In brief, PRP (0.3 ml) was preincubated with Kreb’s phosphate buffer (0.6 ml, pH 7.4) minus CaCl, for IO minutes at 37°C. Next, 0.1 ml of ‘4C-5-HT (0.3-I x IO-5A4) was added. The final concentrations of 5-HT in the incubation mixture were 0.3 uM,O.5 PM. 0.75 PM, and I pM. One set of tubes was immediately immersed in an ice bath after addition of 5-HT while the other set of tubes was incubated for an additional 4 minutes. The platelet pellet obtained by centrifuging the tubes at 10,OOOgfor 15 minutes was dissolved in Soluene-350 and counted as described earlier (Arora and Meitzer, 1981). Active uptake was determined from the differences in disintegrations per minute (dpm) in the tubes incubated for 4 minutes and the tubes that had been immediately immersed in the ice water. Inhibition Studies and Nature of Inhibition. The ability of CPZ to inhibit 5-HT uptake was studied in buffer for 10 minutes before the addition of 5-HT (5 x IO m7M). After the addition of
5-HT. the mixture was incubated for an additional 4 minutes and processed as described above. The ICse (concentration which produces 50% inhibition of 5-HT uptake) was estimated graphically. To determine the nature of inhibition, inhibition studies werecarried out at a single concentration of the drug and various concentrations of 5-HT (3 x 107M - 1 x 10-hM). The uptake of 5-HT in the presence and absence ofdrug was plotted by the method of Eadie-Hofstee (Eadie, 1942; Hofstee, 1952).
Results Chlorpromazine inhibited 5-HT uptake in vitro in a competitive manner in blood platelets from normal controls (Fig, 1). The IC,, was 1.8 f SD 0. I PM compared to 4 * 0.9 nM for imipramine. The kinetic parameters (Km and V,,, ) o f 5-HT uptake in blood platelets before and after CPZ treatment are reported in Table 1 and Fig. 2. The net initial velocity of 5-HT uptake at 0.5 pM of 5-HT, the concentration closest to the K,, is also reported in Table 1. As reported earlier (Arora and Meltzer, 1982), there was no significant difference in K, and V,,, of 5-HT uptake in schizophrenic patients and normal controls. However, after 14-23 days of CPZ treatment, an increase in K, and V,,, was found, an indication of mixed inhibition. A significant decrease in 5-HT uptake in the blood platelets of CPZ-treated patients at 5-HT, 0.5 pM, was found; the average decrease was 28 f. 14.3% (range lo-50%), but uptake increased in two patients (25 and 73%).
25
Fig. 1. Eadie-Hofstee
plot of 5-HT
uptake
in normal
human
blood
platelets
14 -
a
4
I6
I2
24
20
28
v/s
Table 1. Platelet 5-HT promazine treatment
uptake
kinetics
in patients
before
and after
chlor-
Active uptake 0.5 pM IO’ platelets/minute)
!I,,, Km (VW Condition
( pmoles/
5-HT (pmoles/107 platelets/minute)
Mean
SD
Mean
SD
Mean
SD
0.48
0.14
12.3
2.4
6.7
1 .5
0.47
0.15
1 1 .o
3.9
5.8
1 .7
0.32
13.12
5.6
4.73
1 .8
Normal controls (n = 60) Patients Placebo
(n = 19)
Chlorpromazine treatment (n = 19) 1
r =
2. I = 2.63, 3.
0.91’
6 54,~ < 0.0005, paired
r = 2.64.
i
test
p < 0.01,
paired
I test.
p <0
paired
f test.
01,
26 Fig. 2. K, and V,,, of platelet 5-HT uptake before and after treatment chlorpromazine for 14-23 days EFFECT
OF CHLORPROMAZINE PLATELETS
ON
Km AND
OF SCHIZOPHRENIC
vmox
with
IN BLOOD
PATIENTS 1
I
PRE
1
POST
I
I
PRE
POST
Discussion Chlorpromazine competitively inhibited 5-H-F uptake in vitro in blood platelets obtained from normal controls. Similar findings have been reported with most tricyclic antidepressants (Tuomisto, 1974). CPZ was much less potent than imipramine in inhibiting 5-HT uptake in blood platelets. The inhibitory effects of CPZ on 5-HT uptake in platelets reported here are similar to those reported by Oxenkrug (1978) and Long and Lessin (1962) but contrary to those reported by Rotman et al. (1979) who observed no effect of CPZ on K, and V,,, of 5-HT uptake by blood platelets of normal human controls. The possible explanation for this discrepancy may be that Rotman et al. (1979) studied the total uptake of SHT, whereas we studied active uptake of 5-HT by blood platelets from normal human controls. It is possible that CPZ may enhance passive diffusion. This effect might have contributed to the conclusion that no change in active uptake occurred since total uptake might have remained constant or even increased in their study. Chlorpromazine administration was found to increase both K, and V,,, of 5-HT uptake in blood platelets of schizophrenic patients. The increase in K, indicates that the affinity of S-HT for the carrier molecules decreases after CPZ treatment. The increase in V,,, indicates that CPZ treatment increases the number of 5-HT carrier molecules. These two effects produce opposite effects on 5-HT uptake so it is of interest to consider what the overall net effect is. This was examined by considering the
27 uptake of 5-HT at 0.5 PM, the concentration closest to the K, in this study. Net uptake decreased or showed no change in 17 of 19 CPZ-treated subjects. It is not yet known when this inhibition begins and whether it persists beyond the period of study reported here. Baldacci et al. (1980) reported a similar increase in V,,,, of 5-HT uptake in rabbits during CPZ treatment. As this effect takes 6-7 days to develop, which is close to the mean survival time of rabbit as well as human blood platelets, it would seem likely that such an increase in 5-HT uptake sites occurred in the megakaryocytes from which the platelets are derived. This effect would be consistent with increased synthesis of platelet membrane proteins. Whether the increase is related to the CPZinduced decrease in affinity of the 5-HT sites for 5-HT remains to be determined. It is also unclear whether all neuroleptics have similar effects on 5-HT uptake in platelets. The other possible reason for the increased K, and V,,, may be decreased efflux of 5-HT during the processing of CPZ-treated platelets. However, this explanation is unlikely, since we and others did not find any relationship between 5-HT content and 5-HT uptake in the platelets (unpublished observations; Stahl et al., 1983). Platelet 5-HT uptake has features in common with 5-HT uptake into 5-HT nerve terminals (Sneddon, 1973; Stahl, 1977). It is possible that the decreased platelet 5-HT uptake associated with CPZ treatment indicates a similar process occurs in some 5-HT neurons. There are as yet no data concerning the effect of chronic neuroleptic treatment on 5-HT uptake in rat brain synaptosomes. It is possible that the effects of neuroleptics on 5-HT uptake contribute to their therapeutic efficacy, their side effects, or both. The effects of neuroleptics on 5-HT uptake could differ among neuroleptics and need not correlate with their ability to block dopamine receptors. These effects may be relevant to the ability of neuroleptic drugs to produce antidepressant effects. In conclusion, we have shown that CPZ affects 5-HT uptake in blood platelets of normal human controls in vitro and of schizophrenic patients ex vim. These results indicate that the study of platelet 5-HT uptake in schizophrenic patients should be done in drug-free patients if an assessment of basal activity is sought. Our results also suggest that not only CPZ but possibly other neuroleptics may directly affect 5-HT uptake in man. The research reported was supported, in part, by USPHS MH-30059 and MH-30938, and the Department of Mental Health, State of Illinois. HYM is recipient of USPHS RCSA MH-47808.
Acknowledgments.
References Arora, R.C., and Meltzer, H.Y. A modified assay method for determining serotonin human platelets. Clinica Chimica Acta, 112, 225 (198 I). Arora. R.C., and Mehzer, H.Y. Serotonin uptake by blood platelets of schizophrenic Psychiarr~~ Research,
uptake in patients.
6, 327 (1982).
Baldacci, M., Baldacci, M., Bergel, T.D., Born, G.V.R., and Hickman, M. Increases in aggregation by and uptake of 5hydroxytryptamine with platelets from rabbits treated with chlorpromazine. British Journal of Pharmacology, 69, I I3 ( 1980). Eadie, G.S. The inhibition of cholinesterase by physostigmine and prostigmine. Journal of Biological Chemistr_v, 146,85 ( 1942). Hofstee, B.H.J. On the evaluation of the constants Pm and K, in enzyme reactions. Science, 116, 329 (1952).
28 Hussein L., Goedde, H.W., Rosenfeld, M., and Freerksen, E. Subcellular distribution of 14C-5-hydroxytryptamine in the blood platelets of rabbits: Effects of imipramine and haloperidol. Hoppe-Seyier’s Zeitschrifr fiir Physioiogische Chemie, 359,803 (1978). Long, R.F., and Lessin, A.W. Inhibition of 5hydroxytryptamine uptake by platelets in vitro and in vivo. Biochemical Journal, 82,4P (1962). Modai, I., Rotman, A., Munitz, H., Tjano, S., and Wijsenbeek, H. Serotonin uptake by blood platelets of acute schizophrenic patients. Psychopharmacology, 54, 193 (1979). Oxenkrug, G.F. The effect of neuroleptic derivatives of butyrophenone on the uptake of 5-HT by human blood platelets. Journal of Pharmacy and Pharmacology, 30, 740 (1978). Rotman, A., Modai, I., Munitz, H., and Wijsenbeek, H. Active uptake of serotonin by blood platelets of schizophrenic patients. FEBS Letters, 101, 134 (1979). Sneddon, J.M. Blood platelets as a model for monoamine containing neurons. Progress in NeurobiologJj,
1, 15 I
( 1973).
Spitzer, R.L., Endicott, J., and Robins, E. Research Diagnostic Criteria: Rationale and reliability. Archives of General Psychiatry, 35, 773 (1978). Stahl, S.M. The human platelet: A diagnostic and research tool for the study of biogenic amines in psychiatric and neurological disorders. Archives of General Psychiatry, 34, 509 (1977). Stahl, SM., Wood, D.J., Mefford, I.N., Berger, P. A., and Ciaranello, R.D. Hyperserotonemia and platelet serotonin uptake and release in schizophrenia and affective disorders, American Journal
of Ps_vchiatry, 140, 26
(I 983).
Tuomisto, J. A new modification for studying 5-HT uptake by blood platelets: A re-evaluation of tricyclic antidepressants as uptake inhibitors. Journal of Pharmacy and Pharmacology, 26,92 ( 1974).