Effect of m-chlorophenylpiperazine on plasma homovanillic acid concentrations in healthy subjects

Relationship of the serotonin transporter with prolactin response to meta-chlorophenylpiperazine in cocaine dependence

BACKGROUND

Preclinical evidence indicates that exposure to cocaine influences the activity of the serotonin transporter (5-HTT) as well as several 5-HT receptor subtypes. However, little is known about the relationship between the 5-HTT and 5-HT receptors following cocaine exposure in humans.

OBJECTIVE

We examined the relationship between platelet 5-HTT, a presynaptic 5-HT measure, and prolactin (PRL) response to meta-chlorophenylpiperazine (m-CPP), a postsynaptic 5-HT receptor agonist in cocaine dependent individuals.

METHODS

Platelet [3H] paroxetine binding sites were assayed and the m-CPP challenge test was performed in 35 African American cocaine dependent individuals and 33 controls. Clinical measures included assessments of drug use severity and depression.

RESULTS

Cocaine subjects showed reduced Bmax of [3H] paroxetine (t=4.67, p<0.01) and blunted PRL response to m-CPP (F=21.86, p<0.01) compared to controls. There was a positive correlation between Bmax and delta PRL [peak-baseline PRL] in cocaine subjects (r=0.50, p<0.01) but not in controls (r=0.19). ANCOVA analyses showed that the cocaine subgroup with moderate and severe reduction in Bmax showed a greater blunting in PRL response compared to the subgroup with mild Bmax reductions (F=9.44, p<.005). Multivariate regression models showed that the main effects as well as the interaction of Bmax and severity of cocaine use significantly contributed to impaired PRL response (F=17.90, p<.001).

CONCLUSIONS

Disturbances in serotonin transporter binding and post-synaptic 5-HT receptor function seem to be associated in cocaine-dependent subjects. Severity of cocaine use appears to mediate this relationship. Whether there is a causal association between the two measures, or cocaine has separate and independent pre- and post-synaptic effects needs to be clarified.

Relationship of prolactin response to meta-chlorophenylpiperazine with severity of drug use in cocaine dependence

RATIONALE

Serotonergic (5-HT) mechanisms appear to mediate central effects of cocaine. Therefore 5-HT disturbances could be associated with drug severity.

OBJECTIVES

We investigated whether prolactin (PRL) response to meta-chlorophenylpiperazine (m-CPP), a mixed 5-HT agonist/antagonist were associated with severity of cocaine use.

METHODS

Thirty-six cocaine-dependent subjects and 33 controls underwent a challenge with 0.5 mg/kg of oral m-CPP. Severity of drug use was assessed using the Addiction Severity Index (ASI).

RESULTS

The PRL response to m-CPP was significantly blunted in cocaine patients compared to controls (F = 21.86, p < 0.001). DeltaPRL (peak PRL-baseline PRL) was negatively correlated with ASI-drug (r = -0.45, p < 0.01), ASI-alcohol (r = -0.32, p < 0.05), and ASI-psychological (r = -0.41, p < 0.01) composite scores, and with the quantity, frequency and duration of drug use (r ranged from - 0.41 to - 0.32, p ranged from < 0.01 to 0.05). Hierarchical regressions showed that ASI-drug composite scores significantly predicted the variance in DeltaPRL after controlling for behavioral and demographic variables (F = 4.27, p < 0.05).

CONCLUSIONS

The results indicate that disturbances in 5-HT function as reflected by a blunted response to m-CPP seem to be primarily associated with severity of drug use and to a lesser, although significant extent with behavioral traits in cocaine-dependent patients.

Relationship of disinhibition and aggression to blunted prolactin response to meta-chlorophenylpiperazine in cocaine-dependent patients

RATIONALE

Considerable evidence indicates that serotonergic (5-HT) mechanisms may mediate central effects of cocaine, and disinhibition and aggression.

OBJECTIVE

We investigated whether prolactin (PRL) response to meta-chlorophenylpiperazine (m-CPP), a mixed 5-HT agonist/antagonist, differed between abstinent cocaine-dependent patients and controls and whether m-CPP challenge responses were related to measures of disinhibition and aggression.

METHODS

Thirty-five cocaine-dependent African-American subjects who were abstinent for at least 2 weeks and 33 African-American controls underwent assessments of disinhibition and aggression and a challenge with 0.5 mg/kg of oral m-CPP.

RESULTS

The PRL response to m-CPP was compared between cocaine patients and controls and between subgroups categorized high or low based on disinhibition and aggression measures. Hierarchical regressions were used to determine whether behavioral measures predicted deltaPRL (peak PRL-baseline PRL). The PRL response to m-CPP was significantly diminished in cocaine patients compared to controls. The blunting was more robust in cocaine patients with high disinhibition and aggression. Among cocaine patients, the high-disinhibition subgroup showed greater blunting than the low-disinhibition subgroup and there was a trend for the high-aggression subgroup to be more blunted than the low-aggression subgroup. The subgroups of controls did not differ from each other. A combination of disinhibition and aggression measures significantly predicted deltaPRL in cocaine patients.

CONCLUSION

The results indicate that cocaine-dependent patients show disturbances in postsynaptic 5-HT function during early abstinence. It appears that the 5-HT disturbances are more pronounced in the subgroup of cocaine patients with high disinhibition and aggression.

Pharmacokinetic and pharmacodynamic profile of oral and intravenous meta-chlorophenylpiperazine in healthy volunteers

meta-Chlorophenylpiperazine (mCPP) is a compound that is frequently used in challenge tests of the serotonergic system. Its human pharmacology is largely unexplored. The objective of this study was to investigate the pharmacokinetic and pharmacodynamic profile of mCPP. Eight female and six male healthy volunteers were included in a randomized, double-blind, double-dummy, three-way crossover design of single-dose intravenous (0.1 mg/kg), oral (0.5 mg/kg), and placebo treatment, with 24-hour follow-up. mCPP showed a large variability in clearance (11-92 mL/hr) and bioavailability (14-108%). Two female subjects dropped out because of headache and dysphoria. During the 27 occasions in which mCPP was administered, autonomic physical symptoms were observed in 23 subjects and disturbances of mood in 6 subjects. Oral and intravenous mCPP caused sudden increases in cortisol levels, prolactin levels, and total scores of the Body Sensation Questionnaire. Administration of mCPP also led to concentration-dependent increases of saccadic peak velocity and adaptive tracking performance and to a decrease of electroencephalographic occipital theta activity. No clinically relevant effects on electrocardiogram, temperature, and blood pressure were found. In conclusion, it is doubtful whether mCPP is a useful compound for challenge tests in view of the large pharmacokinetic variability after intravenous and oral administration. The effects of mCPP are consistent with disinhibition of the central nervous system.

The m-chlorophenylpiperazine test in cluster headache: a study on central serotoninergic activity

The central serotoninergic agonist m-chlorophenylpiperazine (m-CPP) stimulates several 5HT receptor subtypes. It induces the release of both cortisol and prolactin (PRL). In this study we investigated central serotoninergic responsiveness in cluster headache by monitoring cortisol and PRL responses to m-CPP administration. Twenty-three patients with episodic cluster headache and 17 sex-matched and age-matched healthy subjects were studied. The cluster headache patients were tested during a cluster period, and none were receiving prophylaxis. A single oral dose of m-CPP, 0.5 mg/kg, was given at time 0. Blood samples were drawn at -30, 0, 30, 60, 90, 120, 150 and 180 min. PRL and cortisol levels were assayed in the samples. PRL and cortisol delta maxima (delta maximum = maximum response - baseline level at time 0/baseline level at time 0) were evaluated in each patient and mean values compared. Serum levels of m-CPP were detected by HPLC and correlated to hormonal responses. Reduced cortisol (p < 0.02) and increased PRL (p < 0.05) delta maxima were observed in cluster headache patients. Increased basal cortisol plasma levels (p < 0.05) and reduced basal PRL plasma levels (p = 0.06) also characterized cluster headache patients. This is the first study evaluating central serotoninergic responsiveness to m-CPP in cluster headache and these data suggest impaired central serotoninergic function in this pathology.

The meta-chlorophenylpiperazine challenge test in cocaine addicts: hormonal and psychological responses

We report on the neuroendocrine and psychological responsivity of 31 cocaine addicts and 14 controls to the serotonergic agonist, meta-chlorophenylpiperazine (m-CPP) (0.5 mg/kg p.o.). Cocaine addicts were subdivided into subjects with aggressive tendencies and other features similar to those found in type 2 alcoholics and subjects without these features. Following m-CPP, aggressive and nonaggressive patients had a significantly blunted prolactin response compared to controls, but there was no difference between the two patient subgroups. There was no difference between the cortisol responses of nonaggressive patients and controls, but aggressive patients had a significantly blunted cortisol response compared to controls and nonaggressive patients. Both patient subgroups reported more intense "activation-euphoria" and "high" responses following m-CPP than controls. These results could indicate the existence of alterations along serotonergic pathways in cocaine addicts taken as a group. In addition, a subgroup of patients who could be described as type 2 cocaine addicts appear to be biologically different from healthy subjects and from other cocaine addicts as indicated by a greater cortisol blunting following m-CPP.

Pindolol pretreatment blocks stimulation by meta-chlorophenylpiperazine of prolactin but not cortisol secretion in normal men

Previous reports from this laboratory have shown that pindolol, a partial serotonin1A receptor agonist, inhibited prolactin, but not cortisol secretion induced by administration of the serotonin (5-HT) precursor L-5-hydroxytryptophan or the direct-acting 5-HT2A/5HT2C receptor agonist MK-212. The findings suggest additive or interactive effects of 5-HT1A and 5-HT2A/5-HT2C receptors in modulating 5-HT-related prolactin, but not cortisol, responsivity. To examine further the role of 5-HT1A and 5-HT2A/5-HT2C receptors in prolactin and cortisol secretion in healthy men, the effects of meta-chlorophenylpiperazine (mCPP), a potent 5-HT receptor agonist, on the above hormones were studied in eight healthy men with and without pindolol pretreatment. It has previously been demonstrated that ketanserin, a 5-HT2A antagonist, and ritanserin, a 5-HT2A/5-HT2C antagonist, block the prolactin and attenuate the hypothalamic-pituitary-adrenal axis responses to mCPP in man or rodents. Administration of mCPP induced a significant increase in plasma concentrations of prolactin and cortisol. The mCPP-induced prolactin concentrations were significantly blocked by pretreatment with pindolol, whereas mCPP-stimulated cortisol levels were not diminished by pindolol pretreatment. Thus, mCPP-induced prolactin secretion appears to require the availability of both 5-HT2C and 5-HT1A receptor activation, since blockade of either of these receptors may diminish the mCPP-induced prolactin response. Cortisol secretion stimulated by mCPP may occur following 5-HT2C receptor stimulation in the presence of 5-HT1A receptor blockade.