Selective neuroendocrine effects of low-dose haloperidol in normal adult men

Dopaminergic modulation of working memory for spatial but not object cues in normal humans

It appears that functionally segregated visual pathways exist in the primate brain for the processing of visuospatial versus nonspatial information. Functional segregation has been demonstrated for the early associative processing of sensory information but may also exist at higher levels of cognitive analysis. Namely, connections between the dorsal visual system and dorsolateral prefrontal cortex (PFC) appear to mediate spatial working memory, which is modulated by dopamine receptor fields in the principal sulcal region of the PFC. It is speculated that nonspatial working memory may be modulated within connections between ventral visual processing regions and the inferior convexity of the PFC. Whether dopamine facilitates nonspatial memory through connections between the ventral visual system and ventral PFC has not been examined. In this study, normal humans completed spatial and nonspatial working memory tasks under pharmacological challenges with a dopamine receptor agonist (bromocriptine) and antagonist (haloperidol) in a double-blind placebcxontrolled repeated measures design. Findings indicated facilitation of spatial delayed working memory functions by bromocriptine and impairment of spatial working memory functions by haloperidol. Neither drug was effective in manipulating nonspatial memory performance. Control tasks were included to measure drug effects on basic sensorimotor and attentional processes. Findings suggest that separate processing mechanisms for remembering "What" versus "Where" an object is may exist at structural, but also neurochemical, levels in the human brain.

The atypical antipsychotics olanzapine and quetiapine, but not haloperidol, reduce ACTH and cortisol secretion in healthy subjects

RATIONALE

Increased activity of the hypothalamic-pituitary-adrenal (HPA) axis is an important aspect of the pathophysiology of major depression and schizophrenia. Despite the usefulness of atypical antipsychotics in the treatment of depression and their positive influence on cognitive functioning possibly related to their impact on cortisol, little is known about their effect on HPA axis function.

OBJECTIVE

Therefore, this double-blind, placebo-controlled, randomized cross-over study investigated the influence of the atypical antipsychotics quetiapine and olanzapine in comparison with haloperidol and placebo on plasma adrenocorticotropic hormone (ACTH), cortisol, and prolactin levels. Eleven healthy male volunteers were studied during four sessions one week apart, orally receiving placebo, quetiapine (50 mg), olanzapine (5 mg), or haloperidol (3 mg). Blood samples were taken at hourly intervals from 0900 until 1700 hours. For ACTH, cortisol, and prolactin a significant effect of treatment condition (p < or = 0.005; p < or = 0.035; p < or = 0.0001, respectively) for area under the curve (AUC) was found. In comparison to placebo, quetiapine and olanzapine significantly reduced ACTH (p < or = 0.002; p < or = 0.05, respectively) and cortisol (p < or = 0.005; p < or = 0.03, respectively). No effect of haloperidol on AUC of ACTH or cortisol levels was observed. In comparison with placebo, haloperidol (p < or = 0.0001) and olanzapine (p < or = 0.0001) elevated AUC of prolactin plasma levels, whereas no significant effect was observed for quetiapine as a main effect of treatment condition. The atypical antipsychotics' strong influence on HPA-function with pronounced ACTH and cortisol lowering is possibly related to the atypicals' blockade of serotonergic receptors, but blockade of adrenergic or histaminergic receptors may play a role as well. The observed HPA-axis down-regulation may be clinically important for the atypicals' effects on depressive symptomatology and cognitive functioning.

Modulation of stress-induced and stimulated hyperprolactinemia with the group II metabotropic glutamate receptor selective agonist, LY379268

It is well recognized that glutamate is an integral excitatory neurotransmitter in the neuroendocrine control of several hormonal factors. While the ability of pharmacological agents acting at ionotropic glutamate receptors to modulate the levels of serum prolactin levels has been investigated, there have been few reports of the effects mediated by the G-protein coupled, metabotropic glutamate (mGlu) receptors. The present work was undertaken to investigate the role of the Group II mGlu receptors, mGlu2 and mGlu3 in the regulation of serum polactin levels. LY379268, a Group II selective agonist, did not alter basal levels of circulating prolactin in young (36-40 day old) male rats. However, when an immobilization stress-induced hyperprolactinemia was examined, 10 mg/kg s.c. of LY379268 significantly lowered serum prolactin levels. Similarly, pretreatment with LY379268 was able to reverse the hyperprolactinemia induced with the catecholamine synthesis inhibitor, alpha-methyl-p-tyrosine (aMPT). This inhibition of hyperprolactinemia could be prevented by pretreatment with LY341495, a Group II mGlu receptor antagonist. The Group II antagonist alone had no effect on either basal nor stimulated prolactin levels. The agonist LY379268 was able to prevent the transient hyperprolactinemia associated with stimulation of serotonin 5-HT2A receptors by 2,5-dimethoxy-4-iodoamphetamine (DOI), but did not alter the high levels of circulating prolactin induced with the D2 antagonist, haloperidol. When treatment with LY379268 was delayed until 1 h after aMPT, a time demonstrated to show a full effect of aMPT on serum prolactin levels, the Group II agonist was similarly able to reverse hyperprolactinemia, suggesting LY379268 did not act by preventing the partial catecholamine depletion by aMPT. Similarly, high doses of amphetamine, a dopamine (DA) releaser, were able to reverse the aMPT-induced hyperprolactinemia, consistent with sufficient levels of dopamine remaining after aMPT treatment to modulate prolactin levels. LY379268 did not alter the hyperprolactinemia seen in estrogen-primed, ovariectomized female rats. Taken together the results indicate that stimulation of mGlu2/3 has an indirect inhibitory action on pituitary prolactin release. It is speculated that disinhibition of tubero-infundibular DA release by presynaptic Group II mGlu receptors located on inhibitory inputs to the arcuate hypothalamic nucleus is a possible explanation for the findings.

Haloperidol increases prolactin release and cyclic AMP formation in vitro: inverse agonism at dopamine D2 receptors?

Haloperidol (30 nM, 3 microM) was found to increase prolactin release from GH4C 1 cells transfected with the D2 receptor cDNA (GH4ZR 7) and from wild-type (untransfected) GH 3 cells, but not from wild-type GH4C 1 cells. In addition, haloperidol (3 microM) stimulated cAMP formation in GH 3 cells. It is suggested that haloperidol may act as an inverse agonist rather than as a neutral antagonist at dopaminergic D2 receptors.

Does metergoline selectively attenuate 5-HT mediated prolactin release?

Administration of the non-selective 5-HT receptor antagonist metergoline (0.5 mg/kg) to male rats attenuated the prolactin response to the 5-HT releasing agent d-fenfluramine (7.5 mg/kg) but not to the dopamine receptor antagonist haloperidol (1.5 mg/kg). In contrast, in healthy male volunteers, pretreatment with metergoline (4 mg orally) abolished the prolactin response to intravenous haloperidol (5 micrograms/kg). The findings suggest that in humans blockade of a prolactin response by a conventional oral dose of metergoline cannot be taken as evidence of involvement of 5-HT-mediated mechanisms.

Prolactin response to low-dose haloperidol challenge in schizophrenic, non-schizophrenic psychotic, and control subjects

Haloperidol was administered IV to 46 male psychotic inpatients and 28 male control subjects. A two-way analysis of covariance, with age as the covariate, revealed that DSM-III schizophrenics (n = 27) had a lower prolactin response to haloperidol than did the controls (n = 28). There were no significant differences between the prolactin responses in schizophrenics, patients with affective disorders (n = 7), and those with other psychoses (n = 12), which included patients with paranoia, schizophreniform, schizoaffective disorder, and atypical psychoses. These findings support the proposition that tuberoinfundibular dopaminergic dysfunction may occur in certain patients with DSM-III schizophrenia.

Effect of moderate weight loss on prolactin secretion in normal female volunteers

Sleep-related prolactin secretion and prolactin responses to the infusion of low doses of the dopamine antagonist, metoclopramide, and thyrotropin-releasing hormone were measured in 11 female volunteers before and after undertaking a diet in which they lost a mean of 3.1 kg in weight in 3 weeks. No effect of weight loss on these measures was found, but there was a significant, although modest, reduction in fasting plasma tryptophan concentration without any change in the concentration of competing amino acids.

Lithium increases 5-HT-mediated prolactin release

The effects of short-term (3-4 days) lithium treatment on the prolactin responses to intravenous clomipramine (0.1 mg/kg), metoclopramide (5 micrograms/kg) and haloperidol (2.5-5 micrograms/kg) were assessed in male volunteers. Prolactin responses to clomipramine were significantly enhanced by lithium while those following administration of haloperidol and metoclopramide were not significantly altered. Lithium did not change the cortisol response to clomipramine. The results suggest that lithium may selectively enhance 5-HT mediated prolactin release. These data are consistent with the hypothesis that synergistic effects of lithium and clomipramine on brain 5-HT function may be involved in their therapeutic effect in resistant depression.

Prolactin responses to haloperidol in normal young women

The prolactin (PRL) responses to intramuscular haloperidol (HPD) (0.5, 1.0, and 1.5 mg) were evaluated in six normal premenopausal women during the follicular and luteal phases of their menstrual cycles. These were compared to the PRL responses to these doses of HPD in normal young men. PRL responses to HPD did not differ between the follicular and luteal phases. The mean log-transformed PRL response to the lowest HPD dose (0.5 mg) in women was less than that in the men, but the women had greater PRL responses than the men to the higher haloperidol doses (1.0 mg and 1.5 mg).

Characterization of the hepatic prolactin receptors induced by chronic iron deficiency and neuroleptics

Nutritional iron deficiency (ID), like neuroleptic treatment, results in a reduction in dopaminergic activity and a rise in serum prolactin (PRL). Since PRL has been shown to regulate its own receptors, we studied PRL binding sites during the above treatments. ID induced in 21 day old male rats for 28 days, or treatment with either chlorpromazine (10 mg/kg per day i.p.) or fluphenazine (5 mg/kg per day i.p.) for 21 days or haloperidol (5 mg/kg per day i.p.) for 9 days, caused significant increases (3- to 8-fold) in [125I]oPRL specific binding to the liver membranes. The combined treatment with haloperidol and ID, as above, resulted in an additive effect on hepatic PRL receptors, suggesting that the actions of neuroleptics and ID may be either submaximal or mediated by two different mechanisms. After 7 days or recovery from ID, the induced PRL receptors were completely reduced to the control values. In vitro desaturation of the induced PRL binding sites with MgCl2 caused a further increase (1.57-fold) in PRL binding. Characterization of the hepatic PRL binding sites induced by ID showed properties similar to those reported for the classical PRL receptors, including specificity for the lactogenic hormones, a high affinity constant (2.38 X 10(10) M-1) and inhibition of PRL binding to the induced receptors by an anti-PRL receptor antibody. The results of this study further support the suggested role of endogenous PRL in inducing its own receptors.

The TRH test during dopamine receptor blockade in depressed patients

In an evaluation of the possible role of dopamine on TRH test results, 21 depressed patients were given TRH before and after one week of treatment with a low dose of haloperidol. Haloperidol significantly increased serum prolactin (both basal and after TRH) and cortisol levels, decreased body temperature, and had no effect on serum TSH, growth hormone, or thyroid hormone levels. Five of six patients with initial TSH blunting were retested with TRH; in four patients the TSH response remained blunted. These data render it unlikely that dopamine exerts a major inhibitory input on TSH secretion in depression.

Effect of benztropine on the diurnal prolactin responses to haloperidol

Prolactin (PRL) responses to haloperidol were investigated at 0900 and 1800 h in six young healthy men under basal conditions and after benztropine mesylate administration. Haloperidol administration induced significantly higher PRL release during the evening compared to the morning. The anticholinergic drug, benztropine, potentiated the PRL responses to haloperidol both in the morning and in the evening. The possible mechanisms of these findings are discussed.

Prolactin response to single and multiple doses of haloperidol in schizophrenic patients

Serum prolactin and blood levels of haloperidol were assessed in schizophrenic patients after single acute oral doses of haloperidol and during fixed dose treatment with this medication. Although significant intrapatient correlations between prolactin responses to different doses of haloperidol were found, no statistically significant interpatient relationship between haloperidol dose and prolactin response emerged. There were statistically significant relationships between steady-state plasma and red cell haloperidol levels (measured by radioreceptor or gas liquid chromatographic techniques) and serum prolactin response, but not between blood levels after the acute haloperidol dose and prolactin response.

Serum sulfhydryl levels in rheumatoid patients treated with haloperidol

Six months of haloperidol treatment significantly increased the serum sulfhydryl (SH) levels in all 12 rheumatoid arthritis (RA) patients studied and significantly decreased the PIP joints technetium index (Tc-index), erythrocyte sedimentation rate (ESR) and joint count. These findings suggest a specific antirheumatic activity of haloperidol in the RA patients.

Serum prolactin levels following intramuscular chlorpromazine: two- and three-hour response as predictors of six-hour response

Neuroendocrine studies that examine the changes in serum prolactin levels following intramuscular (im) neuroleptics have usually monitored prolactin levels before and for 90 minutes to 3 hours after neuroleptic injection. Recent studies have suggested that this may be an inadequate period of time. In the present study, six male and four female psychiatric inpatients, who had not received neuroleptic medication for at least 1 week before the study began, received an injection of chlorpromazine (CPZ) 25 mg im; serum prolactin levels were monitored for 6 hours after injection. Peak serum prolactin levels occurred at 60 minutes in one subject, 90 minutes in three subjects, 120 minutes in two subjects, 180 minutes in three subjects, and 240 minutes in one subject. Area under the serum prolactin curve at 2 hours and area under the curve at 3 hours after CPZ injection were found to be good predictors (r = 0.86; r = 0.95, respectively) of 6-hour area under the curve. Two-hour studies should therefore not be considered inadequate; however, a 3-hour study length results in more precise characterization of prolactin response to im CPZ.

Variability of prolactin response to intravenous and intramuscular haloperidol in normal adult men

Serum prolactin (PRL) concentrations were monitored in seven normal adult men for 1 h before and 7 h after i.v. and i.m. injection of 0.25 mg and 0.50 mg haloperidol. The magnitude of the PRL response was dose-related but quite variable across subjects. The patterns of PRL secretion over the 7 h post-injection period also varied greatly among the subjects. Differences in serum heloperidol concentrations accounted for 88% of the variability in the magnitude of the PRL response to the 0.5 mg IM haloperidol dose, but only accounted for 60% of the PRL variability following the 0.5 mg IV dose. The pattern of haloperidol disappearance from serum was similar across the seven subjects and thus unrelated to the variable patterns of PRL response.

Methylphenidate and serum prolactin in man

Methylphenidate induces psychostimulation and increases cardiovascular parameters, and its psychostimulant effects have been proposed to occur via a dopaminergic mechanism. The effect of methylphenidate on serum prolactin was utilized as a method of evaluating methylphenidate's central dopamimergic effects. Methylphenidate was not found to exhibit a consistent effect on serum prolactin. Thus, its effect on serum prolactin does not parallel its behavioral activating properties, suggesting that such activation may not involve dopamine. Possibly, norepinephrine or other noncatecholaminergic neurotransmitters are involved in methylphenidate-induced behavioral activation.

Effect of lithium on hypothalamic-pituitary dopaminergic function

The effect of lithium on apomorphine-induced growth hormone secretion and haloperidol-induced prolactin secretion was examined in eight male subjects without history of manic-depressive illness. Lithium had no effect on baseline or drug-induced changes in serum growth hormone or prolactin concentrations. These data suggest that lithium does not alter hypothalamic-pituitary dopamine receptor function.