BIOL PSYCHIATRY 1992;32:1055-1061
1055
Effect of m-Chlorophenylpiperazine on Plasma Homovanillic Acid Concentrations in Healthy Subjects Ren6 S. Kahn, Peter Knott, Steven Gabriel, Kimberly DuMont, Lisa Mastroianni, and Michael Davidson
In view of the abundant anatomical and functional interactions between serotonin and dopamine systems, this study examined the effect of the serotonin agonist, m.chloro. phenylpiperazine (mCPP) on plasma concentrations of the dopamine metabolite, homovanillic acid. Plasma prolactin levels, body temperature, and mCPP blood level were also measured, mCPP (0.35 mg/kg) and placebo were administered orally to 10 healthy men in a randomized double-blind design. Variables were measured for 210 rain after administration of capsules, mCPP raised prolactin and temperature as compared to placebo, but did not affec~plasma homovaniilic acid concentrations. Results suggest that mCPP does not alter dopamine function.
Introduction m-Chlorophenylpiperazine (mCPP) is a serotonin (5-hydroxytryptamine, 5HT) agonist that binds to all 5HT receptor subtypes, most potently to 5HTIc receptors, with moderate affinity to the 5HTla and 5HT3 receptors. It may have antagonistic effects at the 5HT2 receptor (see Kahn and Wetzler 1991). Although mCPP is primarily used to test the state of the 5HT system, it can also be used to examine interactions between the 5HT and other monoaminergic systems if peripheral markers are available. For instance, a peripheral index of central dopamine (DA) activity in response to mCPP challenge could be used to examine the interrelationship between 5HT and DA systems. Measuring plasma concentrations of the DA metabolite, homovanillic acid, in plasma (pHVA) may be an appropriate marker of central DA activity. Although under normal circumstances only 12% of pHVA appears to be of central origin in healthy human subjects (Lambert et al 1991), pharmacological perturbation known to affect brain DA turnover is reflected by parallel changes in pHVA in animal and man. Specifically, administration of apomorphine induces a decrease (probably due to stimulation of presynaptic, inhibitory, DA receptors) in brain and plasma HVA within 30-60 min in rats (Kendler et ai 1982). Conversely, administration of DA antagonists produced an increase (probably due to autoreceptor
From the Department of Psychiatry, Mount Sinai School of Medicine, Bronx Veterans AdministrationHospital, Bronx, New York. Address correspondenceto Ren6 S. Kahn, MD, Department of Psychiatry,Bronx Veterans AdministrationHospital, 130 W. Kingsbridge Road, Bronx, NY 10468. Received May 4, 1992; revised August 22, 1992. © 1992 Society of Biological Psychiatry
0006-3223/92/$05.00
1056
BIOL PSYCHIATRY
R.S. Kahn et al
1992;32:1055-1061
blockade) in brain and plasma HVA in rodents (Bacopoulos et al 1979; Kendler and Davis 1984) with the magnitude of the peripheral HVA changes correlating strongly with the degree of change in central HVA (Bacopoulos et al 1979; Kendler et al 1981). Thus, tilese studies suggest that when central DA function is pharmacologically altered in rodents, these changes are mirrored by changes in pHVA concentrations. In addition, human studies have found that administration of DA antagonists increases pHVA concentrations in schizophrenic patients (Davila et al 1987; 1988; Pickar et al 1986; Davidson et al 1987; 1991), whereas apomorphine decreases it (Cutler et al 1981), suggesting that perturbations known to affect central DA function are accompanied by changes in pHVA in humans. The question of 5HT and DA interactions is relevant because both systems are highly interactive, both anatomically (see T6rk 1991) and functionally, with 5HT exerting an inhibitory effect on central DA systems (see Jenner et al 1983; Kelland et al 1990). To investigate the potential interactions between 5HT and DA neurotransmission in man, this study examined the effects of mCPP on pHVA concentrations in 10 healthy men. A dose of mCPP of 0.35 mg/kg was chosen for this study, on the basis of the prior doseresponse study, finding a large release of prolactin at 0.5 mg/kg, but also a significant increase in physical discomfort (Kahn et al 1990). To ensure that the dose of mCPP used induced a measurable physiological response, prolactin and temperature responses to mCPP were measured as well. Results on the latter variables were included in an earlier report (Kahn et al 1992). Methods Ten healthy men (age: 44.1 ± 12.1 years) participated in this study after having given written informed consent. Subjects were recruited using newspaper advertisements. All subjects had normal laboratory and physical' exams, including negative urine toxicology results. Subjects met Research Diagnostic Criteria for "never mentally ill." Subjects fasted (except for water) from 11 PM on the night before the day of the procedure. At 9 AM an intravenous catheter was inserted. They were not allowed to drink, eat, smoke, or sleep during the procedure. At 10 AM 0.35 mgtkg mCPP or placebo was administered orally in a randomized doub!e-blind design (six received placebo first, four received mCPP first). Time between procedures was minimally 72 hr. Prolactin, oral temperature anc~ pHVA were assessed at 30 rain intervals between 9 AM and 1:30 PM, All plasma samples were immediately frozen and stored at -80°C. Prolactin was analyzed as described in Kahn et al (1992). The prolactin radioimmu. noassay (RIA) has a sensitivity of 1.5 ng/mi. The intraassay and interassay coefficients of variation are 4% and 10%, respectively. HVA was assayed by high pressure liquid chromatography (HPLC) as described in Davidson et al (1991). The intraassay and interassay coefficients of variation were 2.4% and 6.0%, respectively. Time between collection of samples and assay of samples was approximately 18 months (the stability of the pHVA samples over 18 months stored at -80°C is excellent), mCPP was measured as described in Suckow et al (1990). To compare the effects of mCPP on pHVA, prolactin, and temperature a repeated measure ANOVA was used with two repeated measures, Test and Time (0-210 min). Baseline (time "0'3 was defined as the time (10 AM) when the capsules were administered. In addition to the general test for Time effects, a test for linear change was performed. Data are presented as mean and standard deviation (SD), unless stated differently.
MCPP Effects on Homovanillic Acid
BIOL PSYCHIATRY 1992,32:1055-1061
1057
12-
lO-
Figure 1. Group mean and SEM plasma concentration of prolactin after oral administration (at 0 min) of mCPP (0.35 mg/kg) [closed symbols] and placebo [open symbols].
i:l
,t
0
,
MINUTES
Results mCPP levels were 10.1 +_ 8.3 ng/ml at 11 AM, 14.7 +-- 9.4 ng/ml at 12 PM, and 13.2 +- 10.5 ng/ml at 1 PM. mCPP was well tolerated in all subjects, mCPP significantly elevated prolactin levels (Main effect Test: F - 6.07, df - 1,9, p < 0.05; Time: F 2.32, df ffi 7,63, p < 0.05; Test x Time: F -- 2.41, df - 7,63, p < 0.05). The Test x Time effect included a differential linear effect, with mCPP raising prolactin levels compared to placebo ( F - 13.4, df - 1,9, p < 0.005) [Figure 1]. mCPP also raised body temperature as compared to placebo (Main effect for Test: F - 0.07, df - 1,9, p - 0.79; Time; F - 3.83, df - 7,63, p < 0.002; Test x Time: F -- 3.06, df 7,63, p < 0.01). The Test x Time effect included a differential linear effect with mCPP raising temperature compared to placebo (F -- 8.94, df - 1,9, p < 0.05) [Figure 2]. mCPP's effect on pHVA concentrations was not consistently different from that of placebo, with pHVA decreasing over time in a linear fashion (Main effect for Test: F - 0.47, df -- 1,9, p - 0.51; Time: F - 3.72, df - 7,63, p < 0.002; Time linear effect: F -6.93, df -- 1,9, p < 0.05; Test x Time: F - 0.36, df - 7,63, p - 0.92) [Figure 3]. Baseline (placebo day; mCPP day) prolactin (6.3 -4-_ 1.7; 6.1 +_ 1.4 ng/ml), body temperature (97.9 _+ 0.8; 97.4 +_- 1.2°F) and pHVA concentrations (12.2 +_ 13.2; 10.2 -44.2 ng/ml) were not significantly different for the two test days. When baseline values were used as covariates these results did not change. No order effects were found.
Discussion This study reports that, although there were individual differences in pHVA response, the 5HT agonist, mCPP, did not consistently affect pHVA concentrations, mCPP in a dose of 0.35 mg/kg P.O. was found to elevate plasma prolactin concentrations and increase
1058
R.S. Kahn ct al
BIOL PSYCHIATRY 1992;32:1055-1061
98.6 -
T
98.2
Figure 2. Group mean and SEM oral temperature after oral administration (at 0 rain) of mCPP (0.35 mg/kg) [closed symbols] and placebo [open symbols].
97.8
97.4
97.0
,
o
~o
e'o
~
~o
~
~o
a;o
MINUTES
15
F Figure 3. Group mean and SEM plasma concentrations of homovanillic acid after oral administration (at 0 min) of mCPP (0.35 mg/kg) [closed symbols] and placebo [open symbols].
~10'
5
o
~
6'o
9~
i~o
MINUTES
a~o
i~o
alo
MCPP Effects on Homovanillic Acid
BIOL PSYCHIATRY 1992;32:1055-1061
1059
body temperature. Prior studies found mCPP in a dose of 0.5 mg,q~gPO to elevate prolactin (Mueller et al 1985; Murphy et al 1989; Kahn et al 1990) and body temperature (Mueller et al 1985; Murphy et al 1989) whereas 0.25 mg/kg PC} produced only a marginally significant prolactin release and no increase in body temperature (Kahn et al 1990). The finding that mCPP failed to increase pHVA while elevating prolactin and body temperature suggests that it did not affect DA turnover in a dose that was large enough to induce clear physiological effects. Although mCPP binding to DA receptors is minimal (Hamik and Peroutka 1989), mCPP could have affected DA systems indirectly because, as indicated, 5HT and DA systems are highly interactive. Interestingly, the finding that pHVA concentrations decreased during the tests is consistent with the reported diumal variation in pHVA (Doran et al 1985; Sack et al 1988). Indeed, the fact that pHVA decreases during the morning hours may have complicated detection of any additional (mCPP-induced) decrement in pHVA. It is also possible that mCPP could have affected certain subpopulations of DA neurons, without discernable changes in pHVA. Another explanation is that mCPP did alter central DA turnover but that this change was not reflected in pHVA, because central sources may only contribute 12% to pHVA (Lambert et al 1991). To improve the central contribution of DA to pHVA pretreatment with debrisoquin, a peripheral monoamineoxidase inhibitor, which inhibits the peripheral formation of HVA from its precursors has been propagated (Maas et al 1985). However, several studies suggest that, even without the use of debrisoquin, pharmacologically induced change in central DA function does appear to be reflected in change in pHVA concentrations in rodents (Bacopoulos et al 1979; Kendler et al 1981) and man (Cutler et al 1981; Davila et al 1987; Davidson et al 1987; Pickax et al 1986; Davidson et al 1991). Finally, it is possible that the large variability in pHVA concentrations in these subjects has obscured subtle changes of mCPP on pHVA concentrations. One may question whether the time-interval employed in this study (i.e., 3.5 hr) is sufficient to detect changes in pHVA on alteration of central DA function. Pharmacologically induced changes in DA function are reflected in changes in pHVA concentrations within I hr in rodents (Kendler et al 1981) and after 5 hr (the only time of measurement) in monkeys (Bacopoulos et al 1979). in human subjects two studies have addressed this issue. In a placebo-controlled study in five schizophrenic patients administration ~f apemorphine decreased pHVA in all patients within 20 min (Cutler et al 1981). Davila et al (1987) found that oral administration of haloperidol increased pHVA concentrations after 4 hr (only time of measurement) in seven schizophrenic patients. These studies therefore suggest that when DA function is pharmacologically altered, these changes are rapidly reflected in pHVA concentrations in rodent, monkey, and man. Thus, had mCPP affected central DA turnover, the time interval used in this study would probably have been sufficient to detect changes in pHVA concentrations. The finding from this study that mCPP raised temperature, although in a prior study 0.5 mg/kg it did not (Kahn et al 1990), appears surprising, as is the finding that mCPP blood level peaked at 14.7 ng/mi, whereas in the study using 0.25 mg/kg it peaked at 14.4 ng/ml (Kahn et al 1990). Comparing mCPP blood levels across studies in general is difficult, however. Moreover, mCPP levels were measured every hour instead of once every 30 min during the dose-response study (Kahn et al 1990). The finding that mCPP did not affect temperature responses in a dose of 0.5 mg/kg (Kahn et al 1990), while it did in the current study using 0.35 mg/kg may be caused by the fact that this study examined men only, whereas the other study examined both men and womea. This
1060
BIOL-PSYC-'dlATR"t ~ 1992;32:1055-1061
R.S. Kahn et al
difference may be particularly relevant as women may have lower mCPP blood levels than men (Kahn et al 1991). In conclusion, this study found that mCPP did not affect pHVA concentrations in healthy human subjects. However, the possibility that an interaction between central 5HT and DA transmission occurs but is not reflected in pHVA changes must still be entertained. This work was supported by NIMHgrants R01 MH46436(Dr. Davidson)and R01 MH46957(Dr. Kahn).
References Bacopoulos NG, Hattox SE, Roth RH (1979): 3,4 Dihydmxyphenylacetic acid and homovanillic acid in rat plasma: Possible indicators of dopaminergic activity. Fur J Pharmaco156:225-236. Cutler NR, Jestc DV, Karoum F, Wyatt RJ (1981): Low-dose apomorphine reduces serum homovanillic acid concentrations in schizophrenic patients. Life $ci 30:753-756. Davidson M, Losonczy MF, Mohs RC, et al (1987): Effects of debrisoquin and haloperidol on plasma homovanillic acid concentration in schizophrenic patients. Neuropsychopharmacology 1:17-23. Davidson M, Kahn RS, Knott P, et al (1991): The effect of neumleptic treatment on plasma homovanillic acid concentrations and schizophrenic symptoms. Arch Gen Psychiatry 48.73--76. Davila R, Zumarraga M, Perea K, Andia I (1987): Elevation of plasma homovanillic acid level can be detected within four hours after initiation of haloperidol treatment. Arch Gen Psychiatry 44:837-838. Davila R, Manero E, Zumarraga-Andia !, Schweitzer JW, FriedhoffAJ (1988): Plasma homovanillic acid as a predictor of response to neumleptics.Arch Oen Psychiatry 45:564-567. Doran AR, Pickar D, Labarca R, et al (1985): Evidence for a daily rhythm of plasma HVA in normal controls but not in schizophrenic patients. Psychopharmacol Bull 21:694-697. Hamik A, Peroutka SJ (1989): l-(m-Chlorophenyl)piperazine (mCPP) interactions with neumtransmitter receptors in the human brain, Biol Psychiatry 25:569-575. Jenner P, Sheehy M, Marsden CD (1983): Noradrenaline and 5-hydroxytryptamine modulation of brain dopamine function: implications for the treatment of parkinsons disease. Br J Clin Pharmacol 15:2775-2895, Kahn RS, Wetzler S ( 199 I); m-Chlorophenylpiperazineas a probe of serotonin receptors: A review. Biol Psychiatry 30:1139-1166. Kahn RS, Wetzler S, Asnis GM, van Praag HM (1990): Effects of m-chlorophenylpiperazine in normal subjects: A dose-response study. Psychopharmacology, 100:339-344. Kahn RS, Wetzler S, Asnis GM, van Praag, HM (1991): Pituitary hormone responses to metachlorophenylpiperazine in panic disorder and healthy control subjects, Psychiatry Res 37:2534, Kahn RS, Siever L, Gabriel S, et al (1992): Serotonin function in schizophrenia: Effects of mchlorophenylpiperazine in schizophrenic patients and healthy subjects. Psychiatry Res 43:1-12. Kelland MD, Freeman AS, Chiodo LA (1990): Serotonergic afferent regulation of the basic physiology and pharmacological responsiveness of nigrostriatai dopamine neurons. J Pharm Exp Ther 255:803-81 I. Kendler KS, Davis KL (1984). Acute and chronic effects of neuroleptic drugs on plasma and brain homovanillic acid in the rat. Psychiatry Res 13:51-56. Kendler KS, Heninger GR, Roth RH (198 l): Brain contribution to the haloperidol-induced increase in plasma homovanillic acid. Fur J Pharmacology 71:321-326. Kendler KS, Heninger GR, Roth RH (1982): Influence of dopamine agonists on plasma and brain levels of homovanillic acid. Life Sci 30:2063-2069.
MCPP Effects on Homovanillic Acid
BIOLPSYCHIATRY 1992;32:1055-1061
1061
Lambert GW, Eisenhofer G, Cox HS, et al (1991): Direct determination of homovanillic acid release from the human brain, an indicator of central dopaminergic activity. Life Sci 49:10611072. Maas JW, Contreras SA, Bowden CL, Weintraub SE (1985): Effects of debrisoquin on CSF and plasma HVA concentrations in man. Life Sci 36:2163-2170. Mueller EA, Sunderland T, Murphy DL (1985): Neuroendocrine effects of m-CPP, a serotonin agonist, in humans. J Clin Endocrinol Metab 61:1179-1184. Murphy DL, Mueller EA, Hill JL, Tolliver TJ, Jacobsen FM (1989): Comparative anxiogenic, neuroendocrine, and other physiologic effects of m-Chlomphenylpiperazine given intravenously or orally to healthy volunteers. Psychopharmacology 98:275-282. Pickar D, Labarca R, Doran A, et al (1986): Longitudinal measurement of plasma homovanillic acid levels in schizophrenic patients. Arch Gen Psychiatry 43:669-6/6. Sack DA, James SP, Doran AR, Sherer MA, Linnoila M, Wehr TA (1988): The diurnal variation in plasma homovanillic acid levels persists but the variation in 3omethoxy-4-hydroxyphenylglycol level is abolished under constant conditions. Arch Gen Psychiatry 45:162-166. Suckow RF, Cooper ThB, Kahn RS (1990): High-performance liquid chromatographic method for analysis of plasma m-chlorophenylpiperazine. J Chromotogr 528:228-234. T6rk ! (1991): Anatomy of the serotonergic system. Ann NY Acad Sci 600:9-34.
1055
Effect of m-Chlorophenylpiperazine on Plasma Homovanillic Acid Concentrations in Healthy Subjects Ren6 S. Kahn, Peter Knott, Steven Gabriel, Kimberly DuMont, Lisa Mastroianni, and Michael Davidson
In view of the abundant anatomical and functional interactions between serotonin and dopamine systems, this study examined the effect of the serotonin agonist, m.chloro. phenylpiperazine (mCPP) on plasma concentrations of the dopamine metabolite, homovanillic acid. Plasma prolactin levels, body temperature, and mCPP blood level were also measured, mCPP (0.35 mg/kg) and placebo were administered orally to 10 healthy men in a randomized double-blind design. Variables were measured for 210 rain after administration of capsules, mCPP raised prolactin and temperature as compared to placebo, but did not affec~plasma homovaniilic acid concentrations. Results suggest that mCPP does not alter dopamine function.
Introduction m-Chlorophenylpiperazine (mCPP) is a serotonin (5-hydroxytryptamine, 5HT) agonist that binds to all 5HT receptor subtypes, most potently to 5HTIc receptors, with moderate affinity to the 5HTla and 5HT3 receptors. It may have antagonistic effects at the 5HT2 receptor (see Kahn and Wetzler 1991). Although mCPP is primarily used to test the state of the 5HT system, it can also be used to examine interactions between the 5HT and other monoaminergic systems if peripheral markers are available. For instance, a peripheral index of central dopamine (DA) activity in response to mCPP challenge could be used to examine the interrelationship between 5HT and DA systems. Measuring plasma concentrations of the DA metabolite, homovanillic acid, in plasma (pHVA) may be an appropriate marker of central DA activity. Although under normal circumstances only 12% of pHVA appears to be of central origin in healthy human subjects (Lambert et al 1991), pharmacological perturbation known to affect brain DA turnover is reflected by parallel changes in pHVA in animal and man. Specifically, administration of apomorphine induces a decrease (probably due to stimulation of presynaptic, inhibitory, DA receptors) in brain and plasma HVA within 30-60 min in rats (Kendler et ai 1982). Conversely, administration of DA antagonists produced an increase (probably due to autoreceptor
From the Department of Psychiatry, Mount Sinai School of Medicine, Bronx Veterans AdministrationHospital, Bronx, New York. Address correspondenceto Ren6 S. Kahn, MD, Department of Psychiatry,Bronx Veterans AdministrationHospital, 130 W. Kingsbridge Road, Bronx, NY 10468. Received May 4, 1992; revised August 22, 1992. © 1992 Society of Biological Psychiatry
0006-3223/92/$05.00
1056
BIOL PSYCHIATRY
R.S. Kahn et al
1992;32:1055-1061
blockade) in brain and plasma HVA in rodents (Bacopoulos et al 1979; Kendler and Davis 1984) with the magnitude of the peripheral HVA changes correlating strongly with the degree of change in central HVA (Bacopoulos et al 1979; Kendler et al 1981). Thus, tilese studies suggest that when central DA function is pharmacologically altered in rodents, these changes are mirrored by changes in pHVA concentrations. In addition, human studies have found that administration of DA antagonists increases pHVA concentrations in schizophrenic patients (Davila et al 1987; 1988; Pickar et al 1986; Davidson et al 1987; 1991), whereas apomorphine decreases it (Cutler et al 1981), suggesting that perturbations known to affect central DA function are accompanied by changes in pHVA in humans. The question of 5HT and DA interactions is relevant because both systems are highly interactive, both anatomically (see T6rk 1991) and functionally, with 5HT exerting an inhibitory effect on central DA systems (see Jenner et al 1983; Kelland et al 1990). To investigate the potential interactions between 5HT and DA neurotransmission in man, this study examined the effects of mCPP on pHVA concentrations in 10 healthy men. A dose of mCPP of 0.35 mg/kg was chosen for this study, on the basis of the prior doseresponse study, finding a large release of prolactin at 0.5 mg/kg, but also a significant increase in physical discomfort (Kahn et al 1990). To ensure that the dose of mCPP used induced a measurable physiological response, prolactin and temperature responses to mCPP were measured as well. Results on the latter variables were included in an earlier report (Kahn et al 1992). Methods Ten healthy men (age: 44.1 ± 12.1 years) participated in this study after having given written informed consent. Subjects were recruited using newspaper advertisements. All subjects had normal laboratory and physical' exams, including negative urine toxicology results. Subjects met Research Diagnostic Criteria for "never mentally ill." Subjects fasted (except for water) from 11 PM on the night before the day of the procedure. At 9 AM an intravenous catheter was inserted. They were not allowed to drink, eat, smoke, or sleep during the procedure. At 10 AM 0.35 mgtkg mCPP or placebo was administered orally in a randomized doub!e-blind design (six received placebo first, four received mCPP first). Time between procedures was minimally 72 hr. Prolactin, oral temperature anc~ pHVA were assessed at 30 rain intervals between 9 AM and 1:30 PM, All plasma samples were immediately frozen and stored at -80°C. Prolactin was analyzed as described in Kahn et al (1992). The prolactin radioimmu. noassay (RIA) has a sensitivity of 1.5 ng/mi. The intraassay and interassay coefficients of variation are 4% and 10%, respectively. HVA was assayed by high pressure liquid chromatography (HPLC) as described in Davidson et al (1991). The intraassay and interassay coefficients of variation were 2.4% and 6.0%, respectively. Time between collection of samples and assay of samples was approximately 18 months (the stability of the pHVA samples over 18 months stored at -80°C is excellent), mCPP was measured as described in Suckow et al (1990). To compare the effects of mCPP on pHVA, prolactin, and temperature a repeated measure ANOVA was used with two repeated measures, Test and Time (0-210 min). Baseline (time "0'3 was defined as the time (10 AM) when the capsules were administered. In addition to the general test for Time effects, a test for linear change was performed. Data are presented as mean and standard deviation (SD), unless stated differently.
MCPP Effects on Homovanillic Acid
BIOL PSYCHIATRY 1992,32:1055-1061
1057
12-
lO-
Figure 1. Group mean and SEM plasma concentration of prolactin after oral administration (at 0 min) of mCPP (0.35 mg/kg) [closed symbols] and placebo [open symbols].
i:l
,t
0
,
MINUTES
Results mCPP levels were 10.1 +_ 8.3 ng/ml at 11 AM, 14.7 +-- 9.4 ng/ml at 12 PM, and 13.2 +- 10.5 ng/ml at 1 PM. mCPP was well tolerated in all subjects, mCPP significantly elevated prolactin levels (Main effect Test: F - 6.07, df - 1,9, p < 0.05; Time: F 2.32, df ffi 7,63, p < 0.05; Test x Time: F -- 2.41, df - 7,63, p < 0.05). The Test x Time effect included a differential linear effect, with mCPP raising prolactin levels compared to placebo ( F - 13.4, df - 1,9, p < 0.005) [Figure 1]. mCPP also raised body temperature as compared to placebo (Main effect for Test: F - 0.07, df - 1,9, p - 0.79; Time; F - 3.83, df - 7,63, p < 0.002; Test x Time: F -- 3.06, df 7,63, p < 0.01). The Test x Time effect included a differential linear effect with mCPP raising temperature compared to placebo (F -- 8.94, df - 1,9, p < 0.05) [Figure 2]. mCPP's effect on pHVA concentrations was not consistently different from that of placebo, with pHVA decreasing over time in a linear fashion (Main effect for Test: F - 0.47, df -- 1,9, p - 0.51; Time: F - 3.72, df - 7,63, p < 0.002; Time linear effect: F -6.93, df -- 1,9, p < 0.05; Test x Time: F - 0.36, df - 7,63, p - 0.92) [Figure 3]. Baseline (placebo day; mCPP day) prolactin (6.3 -4-_ 1.7; 6.1 +_ 1.4 ng/ml), body temperature (97.9 _+ 0.8; 97.4 +_- 1.2°F) and pHVA concentrations (12.2 +_ 13.2; 10.2 -44.2 ng/ml) were not significantly different for the two test days. When baseline values were used as covariates these results did not change. No order effects were found.
Discussion This study reports that, although there were individual differences in pHVA response, the 5HT agonist, mCPP, did not consistently affect pHVA concentrations, mCPP in a dose of 0.35 mg/kg P.O. was found to elevate plasma prolactin concentrations and increase
1058
R.S. Kahn ct al
BIOL PSYCHIATRY 1992;32:1055-1061
98.6 -
T
98.2
Figure 2. Group mean and SEM oral temperature after oral administration (at 0 rain) of mCPP (0.35 mg/kg) [closed symbols] and placebo [open symbols].
97.8
97.4
97.0
,
o
~o
e'o
~
~o
~
~o
a;o
MINUTES
15
F Figure 3. Group mean and SEM plasma concentrations of homovanillic acid after oral administration (at 0 min) of mCPP (0.35 mg/kg) [closed symbols] and placebo [open symbols].
~10'
5
o
~
6'o
9~
i~o
MINUTES
a~o
i~o
alo
MCPP Effects on Homovanillic Acid
BIOL PSYCHIATRY 1992;32:1055-1061
1059
body temperature. Prior studies found mCPP in a dose of 0.5 mg,q~gPO to elevate prolactin (Mueller et al 1985; Murphy et al 1989; Kahn et al 1990) and body temperature (Mueller et al 1985; Murphy et al 1989) whereas 0.25 mg/kg PC} produced only a marginally significant prolactin release and no increase in body temperature (Kahn et al 1990). The finding that mCPP failed to increase pHVA while elevating prolactin and body temperature suggests that it did not affect DA turnover in a dose that was large enough to induce clear physiological effects. Although mCPP binding to DA receptors is minimal (Hamik and Peroutka 1989), mCPP could have affected DA systems indirectly because, as indicated, 5HT and DA systems are highly interactive. Interestingly, the finding that pHVA concentrations decreased during the tests is consistent with the reported diumal variation in pHVA (Doran et al 1985; Sack et al 1988). Indeed, the fact that pHVA decreases during the morning hours may have complicated detection of any additional (mCPP-induced) decrement in pHVA. It is also possible that mCPP could have affected certain subpopulations of DA neurons, without discernable changes in pHVA. Another explanation is that mCPP did alter central DA turnover but that this change was not reflected in pHVA, because central sources may only contribute 12% to pHVA (Lambert et al 1991). To improve the central contribution of DA to pHVA pretreatment with debrisoquin, a peripheral monoamineoxidase inhibitor, which inhibits the peripheral formation of HVA from its precursors has been propagated (Maas et al 1985). However, several studies suggest that, even without the use of debrisoquin, pharmacologically induced change in central DA function does appear to be reflected in change in pHVA concentrations in rodents (Bacopoulos et al 1979; Kendler et al 1981) and man (Cutler et al 1981; Davila et al 1987; Davidson et al 1987; Pickax et al 1986; Davidson et al 1991). Finally, it is possible that the large variability in pHVA concentrations in these subjects has obscured subtle changes of mCPP on pHVA concentrations. One may question whether the time-interval employed in this study (i.e., 3.5 hr) is sufficient to detect changes in pHVA on alteration of central DA function. Pharmacologically induced changes in DA function are reflected in changes in pHVA concentrations within I hr in rodents (Kendler et al 1981) and after 5 hr (the only time of measurement) in monkeys (Bacopoulos et al 1979). in human subjects two studies have addressed this issue. In a placebo-controlled study in five schizophrenic patients administration ~f apemorphine decreased pHVA in all patients within 20 min (Cutler et al 1981). Davila et al (1987) found that oral administration of haloperidol increased pHVA concentrations after 4 hr (only time of measurement) in seven schizophrenic patients. These studies therefore suggest that when DA function is pharmacologically altered, these changes are rapidly reflected in pHVA concentrations in rodent, monkey, and man. Thus, had mCPP affected central DA turnover, the time interval used in this study would probably have been sufficient to detect changes in pHVA concentrations. The finding from this study that mCPP raised temperature, although in a prior study 0.5 mg/kg it did not (Kahn et al 1990), appears surprising, as is the finding that mCPP blood level peaked at 14.7 ng/mi, whereas in the study using 0.25 mg/kg it peaked at 14.4 ng/ml (Kahn et al 1990). Comparing mCPP blood levels across studies in general is difficult, however. Moreover, mCPP levels were measured every hour instead of once every 30 min during the dose-response study (Kahn et al 1990). The finding that mCPP did not affect temperature responses in a dose of 0.5 mg/kg (Kahn et al 1990), while it did in the current study using 0.35 mg/kg may be caused by the fact that this study examined men only, whereas the other study examined both men and womea. This
1060
BIOL-PSYC-'dlATR"t ~ 1992;32:1055-1061
R.S. Kahn et al
difference may be particularly relevant as women may have lower mCPP blood levels than men (Kahn et al 1991). In conclusion, this study found that mCPP did not affect pHVA concentrations in healthy human subjects. However, the possibility that an interaction between central 5HT and DA transmission occurs but is not reflected in pHVA changes must still be entertained. This work was supported by NIMHgrants R01 MH46436(Dr. Davidson)and R01 MH46957(Dr. Kahn).
References Bacopoulos NG, Hattox SE, Roth RH (1979): 3,4 Dihydmxyphenylacetic acid and homovanillic acid in rat plasma: Possible indicators of dopaminergic activity. Fur J Pharmaco156:225-236. Cutler NR, Jestc DV, Karoum F, Wyatt RJ (1981): Low-dose apomorphine reduces serum homovanillic acid concentrations in schizophrenic patients. Life $ci 30:753-756. Davidson M, Losonczy MF, Mohs RC, et al (1987): Effects of debrisoquin and haloperidol on plasma homovanillic acid concentration in schizophrenic patients. Neuropsychopharmacology 1:17-23. Davidson M, Kahn RS, Knott P, et al (1991): The effect of neumleptic treatment on plasma homovanillic acid concentrations and schizophrenic symptoms. Arch Gen Psychiatry 48.73--76. Davila R, Zumarraga M, Perea K, Andia I (1987): Elevation of plasma homovanillic acid level can be detected within four hours after initiation of haloperidol treatment. Arch Gen Psychiatry 44:837-838. Davila R, Manero E, Zumarraga-Andia !, Schweitzer JW, FriedhoffAJ (1988): Plasma homovanillic acid as a predictor of response to neumleptics.Arch Oen Psychiatry 45:564-567. Doran AR, Pickar D, Labarca R, et al (1985): Evidence for a daily rhythm of plasma HVA in normal controls but not in schizophrenic patients. Psychopharmacol Bull 21:694-697. Hamik A, Peroutka SJ (1989): l-(m-Chlorophenyl)piperazine (mCPP) interactions with neumtransmitter receptors in the human brain, Biol Psychiatry 25:569-575. Jenner P, Sheehy M, Marsden CD (1983): Noradrenaline and 5-hydroxytryptamine modulation of brain dopamine function: implications for the treatment of parkinsons disease. Br J Clin Pharmacol 15:2775-2895, Kahn RS, Wetzler S ( 199 I); m-Chlorophenylpiperazineas a probe of serotonin receptors: A review. Biol Psychiatry 30:1139-1166. Kahn RS, Wetzler S, Asnis GM, van Praag HM (1990): Effects of m-chlorophenylpiperazine in normal subjects: A dose-response study. Psychopharmacology, 100:339-344. Kahn RS, Wetzler S, Asnis GM, van Praag, HM (1991): Pituitary hormone responses to metachlorophenylpiperazine in panic disorder and healthy control subjects, Psychiatry Res 37:2534, Kahn RS, Siever L, Gabriel S, et al (1992): Serotonin function in schizophrenia: Effects of mchlorophenylpiperazine in schizophrenic patients and healthy subjects. Psychiatry Res 43:1-12. Kelland MD, Freeman AS, Chiodo LA (1990): Serotonergic afferent regulation of the basic physiology and pharmacological responsiveness of nigrostriatai dopamine neurons. J Pharm Exp Ther 255:803-81 I. Kendler KS, Davis KL (1984). Acute and chronic effects of neuroleptic drugs on plasma and brain homovanillic acid in the rat. Psychiatry Res 13:51-56. Kendler KS, Heninger GR, Roth RH (198 l): Brain contribution to the haloperidol-induced increase in plasma homovanillic acid. Fur J Pharmacology 71:321-326. Kendler KS, Heninger GR, Roth RH (1982): Influence of dopamine agonists on plasma and brain levels of homovanillic acid. Life Sci 30:2063-2069.
MCPP Effects on Homovanillic Acid
BIOLPSYCHIATRY 1992;32:1055-1061
1061
Lambert GW, Eisenhofer G, Cox HS, et al (1991): Direct determination of homovanillic acid release from the human brain, an indicator of central dopaminergic activity. Life Sci 49:10611072. Maas JW, Contreras SA, Bowden CL, Weintraub SE (1985): Effects of debrisoquin on CSF and plasma HVA concentrations in man. Life Sci 36:2163-2170. Mueller EA, Sunderland T, Murphy DL (1985): Neuroendocrine effects of m-CPP, a serotonin agonist, in humans. J Clin Endocrinol Metab 61:1179-1184. Murphy DL, Mueller EA, Hill JL, Tolliver TJ, Jacobsen FM (1989): Comparative anxiogenic, neuroendocrine, and other physiologic effects of m-Chlomphenylpiperazine given intravenously or orally to healthy volunteers. Psychopharmacology 98:275-282. Pickar D, Labarca R, Doran A, et al (1986): Longitudinal measurement of plasma homovanillic acid levels in schizophrenic patients. Arch Gen Psychiatry 43:669-6/6. Sack DA, James SP, Doran AR, Sherer MA, Linnoila M, Wehr TA (1988): The diurnal variation in plasma homovanillic acid levels persists but the variation in 3omethoxy-4-hydroxyphenylglycol level is abolished under constant conditions. Arch Gen Psychiatry 45:162-166. Suckow RF, Cooper ThB, Kahn RS (1990): High-performance liquid chromatographic method for analysis of plasma m-chlorophenylpiperazine. J Chromotogr 528:228-234. T6rk ! (1991): Anatomy of the serotonergic system. Ann NY Acad Sci 600:9-34.
