Inhibitory effect of ritanserin on the 5-hydroxytryptophan-mediated cortisol, ACTH and prolactin secretion in humans

Pharmacology of rising oral doses of 5-hydroxytryptophan with carbidopa

5-hydroxytryptophan (5-HTP) is a direct 5-hydroxytryptamine (5-HT) precursor used to assess central serotonergic function. Its use has been limited by a narrow window between neuroendocrine changes and side effects, and variable kinetics related to inconsistent administration modes. By combining 5-HTP with carbidopa (CBD), increased bioavailability for brain penetration and decreased peripheral side effects would be expected, due to reduced peripheral decarboxylation of 5-HTP to 5-HT. A double-blind, placebo-controlled, single rising dose, four-way crossover trial with placebo randomisation was performed in 15 healthy male volunteers to investigate the neuroendocrine dose-response relationship at various 5-HTP levels; the tolerability and subjective effects of oral 5-HTP at 100, 200 and 300 mg combined with CBD and the pharmacokinetic properties of the 5-HTP/CBD-challenge. Dose-dependent increases in average cortisol concentrations were observed. Mean response (area-under-the-curve) over the first 4 hours (SD): 172.0 nmol/L (22.3) for placebo, 258.3 nmol/L (72.6) for 100 mg, 328.47 nmol/L (84.6) for 200 mg and 387.3 nmol/L (82.4) for 300 mg 5-HTP. Similar dose-dependent increases for prolactin were seen while adreno-corticotrophic hormone response was more variable. 5-HTP kinetics were adequately described using a one-compartment model with first-order absorption and a lag time (mean oral clearance 28 L/h interindividual coefficient of variation 31%). Nausea and vomiting occurred dose-dependently as most frequent side effects, resulting in dose-related dropout of 6.6% at 100 mg and 45.5% at 300 mg 5-HTP. Orally administered 5-HTP combined with CBD is an effective serotonergic challenge test, exhibiting dose-related plasma concentrations and neuroendocrine responsiveness. Frequent occurrence of nausea and vomiting limits the applicability of this challenge at 5-HTP doses above 100 mg.

L-5-Hydroxytryptophan augments the neuroendocrine response to a SSRI

The objective of the study was to assess l-5-hydroxytryptophan's (l-5HTP) augmentation effect on the neuroendocrine response to a SSRI (citalopram). A neuroendocrine challenge study was conducted in healthy Asian male subjects. The neuroendocrine response to oral citalopram and l-5HTP was measured primarily as the prolactin and cortisol area under the response curve (or AUC). The study comprised 2 studies: Study 1. A double blind, randomised dose ranging study was conducted with l-5HTP (50-200 mg) to explore the prolactin and/or cortisol dose response and select a dose that provided a threshold neuroendocrine response. Study 2. A randomized comparison of citalopram 20 vs 40 mg was used to assess the effect of these doses on prolactin and cortisol. Based on the results of the dose response assessments with l-5HTP and cortisol, 200 mg l-5HTP was subsequently used in Study 2 to explore the augmentation of the neuroendocrine response to 20 mg citalopram. Citalopram, but not l-5HTP, increased prolactin AUC(0-3h) while 5HTP and citalopram increased cortisol AUC(0-3h). A 200 mg dose of l-5HTP significantly augmented the prolactin and cortisol response AUC(0-3h) to 20mg oral citalopram. The results of the study suggest that an augmented neuroendocrine challenge may be a suitable marker to demonstrate increased 5-HT-mediated responses when exploring novel agents as improved SSRIs.

Ziprasidone decreases cortisol excretion in healthy subjects

AIMS

To determine the influence of the atypical antipsychotic ziprasidone on cortisol excretion.

METHODS

In a double-blind, placebo-controlled, randomized cross-over design 11 healthy male subjects were studied twice for 2 consecutive nights (N1, undisturbed sleep conditions; N2, exposure to acoustic stress) 5 days apart. Placebo or ziprasidone 40 mg was administered orally 2 h before bedtime on N1 and N2. Urine was collected during three fractionated collection periods (evening; night; morning) for the later determination of cortisol concentrations by standard radioimmunoassays.

RESULTS

Ziprasidone decreased the total amount of cortisol excreted by 4.9 (95% CI 3.3, 6.5) microg during N1 and by 10.8 (95% CI 5.7, 15.8) microg during N2 (P < 0.002). This effect was still detectable in the morning (P < 0.02), with decreases of 5.8 (95% CI -2.8, 14.4) microg after N1 and by 12.1 (95% CI 2.8, 21.4) microg after N2. The effect subsided in the evening. A significant intervention-condition interaction (P < 0.02), was found. The significant increase in cortisol excretion during acoustic stress observed with placebo was absent after treatment with ziprasidone.

CONCLUSIONS

The significant decrease in nocturnal cortisol excretion following ziprasidone reflects a decreased activity of the HPA-axis in healthy subjects. This effect may be an important contributor to the mode of action of ziprasidone in different patient populations, particularly in the treatment of depression and in cognitive impairment in schizophrenia.

Hormonal and temperature responses to flesinoxan in normal volunteers: an antagonist study

RATIONALE

Flesinoxan is a highly potent and selective 5-HT1A agonist. In a recent study, in normal volunteers, flesinoxan induced a significant and dose-dependent increase in adrenocorticotropic hormone (ACTH), cortisol, prolactin (PRL), growth hormone (GH) and a decrease in body temperature.

OBJECTIVES

In order to better define the role of 5-HT receptor subtypes in response to flesinoxan, we assessed the influence of 5-HT1A and 5-HT2 antagonists on hormonal and temperature responses to flesinoxan.

METHODS

Hormonal and temperature responses were studied in 6 volunteers with or without pretreatment with pindolol (30 mg p.o.), a 5-HT1A antagonist, or ritanserin (10 mg p.o.), a selective 5-HT2 antagonist, using a double-blind crossover design.

RESULTS

Pindolol significantly antagonized ACTH, PRL, GH and temperature responses to flesinoxan and ritanserin exhibited similar activity on PRL and ACTH responses.

CONCLUSIONS

These results show the role of 5-HT1A mechanisms in the PRL, ACTH, GH, and temperature responses to flesinoxan, and the role of 5-HT2 mechanisms in PRL and ACTH responses. Therefore, they confirm the interest of flesinoxan as a 5-HT neuroendocrine probe.

Neuroendocrine evaluation of 5-HT1A function in male alcoholic patients

BACKGROUND

Preclinical evidences support the hypothesis of a serotonergic dysfunction in alcohol preference. In human, studies have demonstrated a serotonergic hypoactivity in alcoholism. However, little is known about the role of 5-HT1A receptors.

METHODS

We assessed the hormonal (prolactin and cortisol) responses to flesinoxan (a highly potent and selective 5-HT1A agonist) in 12 male inpatients meeting DSM-IV criteria for alcohol dependence, 3 weeks after the last reported use of alcohol and antidepressants. These patients were compared to 10 male controls.

RESULTS

There was a highly significant difference between alcoholic patients and controls for the area under the curve relative (AUCr) values of prolactin responses. AUCr values of cortisol responses to flesinoxan showed a trend towards lower values in alcoholics compared to controls.

CONCLUSION

These results support the implication of the serotonergic system, and particularly a decreased sensitivity of post-synaptic 5-HT1A receptors, in alcoholism.

Placebo-controlled comparison of three dose-regimens of 5-hydroxytryptophan challenge test in healthy volunteers

Single-dose administration of 5-hydroxytryptophan (5-HTP) is regularly used as a challenge test of the serotonergic system. The use of 5-HTP has been limited by an apparent small window between the occurrence of neuroendocrine endpoints and the occurrence of side effects. Therefore, many dosing strategies have been tried with and without concurrent administration of carbidopa, a peripheral inhibitor of the decarboxylation from 5-HTP to serotonin. The aim of the current study was to assess the relation between pharmacokinetics and pharmacodynamics of 5-HTP. Twelve healthy male volunteers were included in a placebo-controlled, randomized, four-way crossover, double-blind, single-dose investigation of oral 5-HTP with or without coadministration of carbidopa. The four dose regimens were placebo, 5-HTP 100 mg, 5-HTP 200 mg, and 5-HTP 100 mg with coadministration of carbidopa 100 mg and 50 mg at 3 hours before and 3 hours after the administration of 5-HTP, respectively. The last regimen resulted in a doubling of the elimination half-life, an apparent clearance at least 14 times smaller, and a 15.4 times greater area under the curve compared with 5-HTP 100 mg without carbidopa. Furthermore, it was the only regimen to induce a significant change in cortisol and prolactin. It did not induce any change in subjective psychologic symptoms or cardiovascular parameters, but it was the only regimen to induce some nausea in three participants. The authors conclude that this regimen of 5-HTP 100 mg plus carbidopa is a relatively simple, effective, and tolerable challenge of the presynaptic serotonergic system. Further increase of the dose of 5-HTP might improve the size of the effect on endpoints as long as the tolerability remains good.

Serotonin dysregulation in adolescents with major depression: hormone response to meta-chlorophenylpiperazine (mCPP) infusion

This study examined central serotonin disturbance, as reflected by neuroendocrine hormones, among adolescents with major depression. Prolactin, cortisol, and growth hormone were measured following the infusion of a serotonin agonist, meta-chlorophenylpiperazine (mCPP). Twelve (M=6, F=6) medication-free adolescents with major depression (MDD) were compared with 12 (M=6, F=6) matched normal control subjects, ranging in age from 13 to 17 years. Baseline evaluations and a battery of laboratory tests were completed. mCPP, 0.1 mg/kg i. v., was administered in a placebo-controlled design. Analyses of the neuroendocrine hormones revealed that the depressed group had a higher baseline prolactin level and an augmented prolactin response to mCPP challenge than did the control group. The depressed group experienced a sharper baseline-cortisol decline between 08.00 and 11.00 h, and compared to control subjects they displayed an augmented response to the challenge. The depressed group reported more side effects than the control group during saline infusion, but not during mCPP infusion. Findings suggest that depressed adolescents have an elevated baseline prolactin level, and also experience enhanced prolactin and cortisol responses to the serotonergic challenge. These preliminary findings will be confirmed during our ongoing study.

Neuroendocrine correlates of temperamental traits in humans

Studies investigating temperament traits in humans and their biological correlates have found high levels of novelty seeking (NS) linked with dopaminergic system changes, and particularly a deficit of dopamine transporter. Harm avoidance and reward dependence, on the other hand, appeared to be associated, respectively with serotonin and noradrenaline changes. In the present study, we have investigated the dopaminergic (DA), serotonergic (5-HT), and noradrenergic (NE) functions in healthy volunteers by challenging the monoamine systems with the DA agonist bromocriptine, the 5-HT agonist D-fenfluramine, and the NE agonist clonidine, respectively. Parallel to this investigation, we examined the temperament traits of our subjects by measuring NS, harm avoidance (HA) and reward dependence (RD) using the 'Three-dimensional Personality Questionnaire' (TPQ). The aims of the study were to see whether or not the monoamine functions were correlated with temperament traits. Bromocriptine challenge induced a significant GH increase and a significant suppression of PRL. D-fenfluramine test significantly increased PRL and cortisol plasma levels and Clonidine test induced a significant rise in GH values. NS scores showed a significant direct correlation with brom-stimulated GH values (r=0.426, P<0.05) and a significant inverse correlation with brom-inhibited PRL values (r=-0.498, P<0.01). HA scores correlated significantly with D-fen-stimulated PRL and CORT AUCs, (PRL: r=0.424, P<0.05; CORT: r=0. 595, P<0.005). RD scores correlated positively with clon-stimulated GH values (r=0.55; F=8.6; P<0.01) and negatively with brom-inhibited-PRL AUCs (r=-0.439, P<0.05). Our data support Cloninger theory concerning the biological correlates of temperamental traits, and evidence the link between the neuroendocrine responses to dynamic challenges and stable temperament features.

Serotonergic dysfunction in women with pure premenstrual dysphoric disorder: is the fenfluramine challenge test still relevant?

The fenfluramine (FEN) neuroendocrine challenge paradigm, which involves measuring the response of prolactin (PRL) release to an oral challenge dose of FEN, provides a means of assessing serotonin (5-HT) function. The purpose of this study was to ascertain the role of 5-HT in premenstrual dysphoric disorder (PMDD) by measuring: (1) PRL and cortisol (CORT) responses to FEN; and (2) platelet 3H-imipramine binding levels, in females with pure PMDD (without a past or present comorbid mood disorder) in comparison to healthy controls. FEN challenge tests were administered to nine female patients with pure PMDD and nine healthy female controls during the follicular and late luteal phases of a menstrual cycle. There were no differences in the PRL response to FEN for women with PMDD compared to healthy controls. However, the trend toward a delayed response to FEN and a significant negative correlation between delta(max) PRL and basal CORT in patients but not in controls during both phases of the menstrual cycle suggest an underlying 5-HT dysfunction in patients as compared to controls. This is further supported by the finding of significantly lower Bmax 3H-imipramine binding levels in the patients during the late luteal phase.

Selective serotonin reuptake inhibitors and neuroendocrine function

Selective serotonin (5-HT) reuptake inhibitors (SSRIs) are effective drugs for the treatment of several neuropsychiatric disorders associated with reduced serotonergic function. Serotonergic neurons play an important role in the regulation of neuroendocrine function. This review will discuss the acute and chronic effects of SSRIs on neuroendocrine function. Acute administration of SSRIs increases the secretion of several hormones, but chronic treatment with SSRIs does not alter basal blood levels of hormones. However, adaptive changes are induced by long-term treatment with SSRIs in serotonergic, noradrenergic and peptidergic neural function. These adaptive changes, particularly in the function of specific post-synaptic receptor systems, can be examined from altered adrenocorticotrophic hormone (ACTH), cortisol, oxytocin, vasopressin, prolactin, growth hormone (GH) and renin responses to challenges with specific agonists. Neuroendocrine challenge tests both in experimental animals and in humans indicate that chronic SSRIs produce an increase in serotonergic terminal function, accompanied by desensitization of post-synaptic 5-HT1A receptor-mediated ACTH, cortisol, GH and oxytocin responses, and by supersensitivity of post-synaptic 5-HT2A (and/or 5-HT2C) receptor-mediated secretion of hormones. Chronic exposure to SSRIs does not alter the neuroendocrine stress-response and produces inconsistent changes in alpha2 adrenoceptor-mediated GH secretion. Overall, the effects of SSRIs on neuroendocrine function are dependent on adaptive changes in specific neurotransmitter systems that regulate the secretion of specific hormones.

Psychoneuroendocrinology of depression. Prolactin

Prolactin provides us with a window to the brain in our quest for understanding the psychobiology of depression, since the regulation of its release involves some of the monamine neurotransmitter systems that have been implicated in the pathophysiology of depression. Investigation examining basal prolactin plasma concentrations in depressed patients, including assessments of the rhythm of prolactin release, have not provided clear, consistent findings. Further exploration of the precise mechanisms involved in serotonin-stimulated prolactin release should shed light on the pathophysiology of abnormal prolactin responsivity in depression, and by extension, the psychobiologic basis of depression.

Changes in plasma prolactin during SSRI treatment: evidence for a delayed increase in 5-HT neurotransmission

We studied the effect of the selective serotonin reuptake inhibitor (SSRI), paroxetine, on basal plasma prolactin concentrations in 11 healthy subjects. Subjects were tested before paroxetine, and after 1 and 3 weeks of treatment (20 mg daily). On each test occasion prolactin levels were sampled before and following administration of a placebo capsule, for a total of 4 h. After 3 weeks paroxetine treatment plasma prolactin levels were significantly higher than those seen either pre-treatment or after 1 week of treatment. In contrast, 1 week of paroxetine treatment did not significantly increase prolactin concentrations over pre-treatment values. Plasma concentrations of paroxetine did not differ between 1 and 3 weeks of treatment. The secretion of plasma prolactin is, in part, under the tonic regulation of serotonergic pathways and the present results therefore support animal experimental data suggesting that SSRIs produce a delayed increase in some aspects of brain serotonin neurotransmission.

Brain 5-HT neurotransmission during paroxetine treatment

BACKGROUND

Animal experimental studies suggest that repeated administration of selective serotonin reuptake inhibitors (SSRIs) produces complex adaptive changes in brain serotonin (5-HT) pathways. The effect of these adaptive changes on different aspects of brain 5-HT neurotransmission and their clinical consequences are not well understood.

METHOD

We studied the effect of repeated administration of the SSRI, paroxetine (20 mg daily), on the cortisol responses to the 5-HT precursor, 5-hydroxytryptophan (5-HTP), in healthy subjects and depressed patients.

RESULTS

In healthy subjects, following one week of paroxetine treatment there was a large increase in the cortisol response to 5-HTP. This increase had all but disappeared following 3 weeks treatment. In contrast, in depressed patients treated with paroxetine for 8 weeks, the cortisol response to 5-HTP was significantly increased.

CONCLUSIONS

SSRI treatment in depressed patients produces a persistent increase in the cortisol response to 5-HTP, a probable measure of neurotransmission at central 5-HT2 receptors. Potentiation of 5-HT2 neurotransmission is unlikely to account for the efficacy of SSRIs in major depression but might underlie their actions in obsessive-compulsive disorder and also perhaps certain of their adverse effects, notably sexual dysfunction.

Clomipramine challenge responses covary with Tridimensional Personality Questionnaire scores in healthy subjects

Cloninger's Unified Biosocial Theory of Personality postulates a relationship between the relative functional activity of central serotonergic, dopaminergic, and noradrenergic neurotransmitter systems, and the strength of three elemental dimensions of personality. These dimensions are Harm Avoidance, Novelty Seeking, and Reward Dependence, respectively. Accordingly, we predicted that neuroendocrine responses to serotonergic challenge would correlate with Harm Avoidance scores, but not with Novelty Seeking or Reward Dependence scores. We examined the relationship between the prolactin and cortisol responses to a 12.5-mg intravenous clomipramine challenge and these personality dimensions as measured by Cloninger's Tridimensional Personality Questionnaire in 32 healthy subjects. The cortisol response correlated only with Harm Avoidance scores, as predicted; however, prolactin response did not correlate with Harm Avoidance scores. Instead, it demonstrated an inverse relationship with Novelty Seeking scores. There was a positive relationship of baseline prolactin with Harm Avoidance in a post hoc analysis. Cortisol response to serotonergic challenge may be a better indicator for responsivity of serotonergic systems as they relate to the personality dimension of Harm Avoidance than is prolactin. Prolactin responses may be overly affected by dopaminergic influences; however, baseline prolactin may still be a valid indicator of serotonergic tone.

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.

Neuroendocrine challenge studies of suicidal behavior

This article reviews the research data regarding human neuroendocrine systems and suicidal behavior. Special emphasis is placed on pharmacochallenge studies. Such studies uniquely allow for functional assessment of neuroendocrine parameters in living subjects. Serotonergic mechanisms have been the most fruitful areas of research. While discussing the major areas of controversy, theoretical approaches to integration are offered.

Distribution of the 5-hydroxytryptamine2C receptor protein in adult rat brain and spinal cord determined using a receptor-directed antibody: effect of 5,7-dihydroxytryptamine

A synthetic peptide, corresponding to the N-terminal decapeptide (+Y11C12) of the rat 5-hydroxytryptamine2C (5-HT2C) receptor protein was used to produce a sheep polyclonal antiserum. Western blot analysis showed that the resultant antibody G241 recognised two membrane proteins, one (55 kDa) approximating the molecular mass of the 5-HT2C receptor (52 kDa) and a second (63 kDa), which may be a glycosylated form of the receptor protein. HEK 293 cells transfected with human 5-HT2C cDNA displayed intense cell surface immunoreactivity with the 5-HT2C antiserum, which was completely prevented by incubating the antibody with the synthetic 5-HT2C peptide (10 microM), whilst neither non-immune serum nor untransfected cells displayed any immunoreactivity. A radioimmunoassay was developed to quantify the regional distribution of 5-HT2C-like immunoreactivity (LI) in the adult rat brain. The choroid plexus contained five-fold higher levels of 5-HT2C-LI than any brain region but high levels were found in the frontal cortex, septum, hypothalamus, and striatum, intermediate levels in the thalamus and midbrain, and lower levels in brainstem, cerebellum, and spinal cord. In rat cortical membranes, the B(max) value from [3H]-mesulergine binding was ten-fold lower than 5-HT2C-LI levels determined by radioimmunoassay, which may reflect measurement of internalised receptor protein by radioimmunoassay which is not detected with conventional 5-HT2C ligands. Ten days after depletion of 5-HT with the serotonergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT), there was a significant increase in 5-HT2C-LI in the choroid plexus and the ventral cervical spinal cord, suggesting that receptors therein are located post-synaptic to destroyed serotonergic nerve terminals. In contrast, the significant reduction in 5-HT2C-LI observed in the midbrain, brainstem, and dorsal thoracic spinal cord following 5,7-DHT implies that 5-HT2C receptors may be located on 5-HT nerve terminals in these regions.

Effect of sleep deprivation on neuroendocrine response to a serotonergic probe in healthy male subjects

Neuroendocrine responses to stimulation with a selective serotonin reuptake inhibitor (citalopram) were measured to investigate the effects of all-night sleep deprivation on serotonergic function in healthy male subjects (n = 7). We studied citalopram-stimulated prolactin and cortisol plasma concentrations in a placebo-controlled cross-over protocol following sleep and sleep deprivation. Citalopram infusion (20 mg i.v. at 14:20-14:50 h) after a night of undisturbed sleep prompted robust increases in both plasma prolactin and cortisol concentrations. Following a night of sleep deprivation, by contrast, the citalopram-induced prolactin response was blunted, but the cortisol response was not significantly altered. This differential response pattern relates to the distinct pathways through which serotonin may activate the corticotrophic and the lactotrophic systems. While an unchanged cortisol response does not indicate (but also does not refute the possibility of) an altered serotonergic responsivity following sleep deprivation, the suppressed prolactin response could reflect a downregulation of 5-HT1A or 2 receptors. An alternative, not mutually exclusive, explanation points to the possibility that sleep deprivation activates the tubuloinfundibular dopaminergic system, the final inhibitory pathway of prolactin regulation.

Serotonin-induced cortisol release in CPAP-treated obstructive sleep apnea patients

Previously, we demonstrated elevated cortisol production/release in response to the administration of the serotonin precursor, L-5-hydroxytryptophan (L-5-HTP) in untreated patients with obstructive sleep apnea (OSA). We hypothesized that if this elevated cortisol response to L-5-HTP was related to OSA, this finding would not be present in OSA patients treated with nasal continuous positive airway pressure (nCPAP). Eleven OSA patients treated for at least 1 month with nCPAP were studied. On two different days, we measured blood cortisol level every 15 min for 4 h following the ingestion of L-5-HTP, 0.4 mg/kg, or placebo, both given with carbidopa, a peripheral tryptophan decarboxylase inhibitor, used to prevent peripheral L-5-HTP metabolism before brain absorption. For a given subject, the cortisol response was calculated as the difference between the area under the curve of the L-5-HTP and placebo responses. In the nCPAP-treated OSA patients, this net cortisol response, 577 +/- 240 min.micrograms/dL, was less than the value found in the previously studied untreated OSA group, 1,198 +/- 227 min.micrograms/dL (p < 0.05) and not different from the previously studied nonapneic control group, 469 +/- 154 min.micrograms/dL. From these results, we speculate that nCPAP treatment reverses the elevated cortisol response to serotonergic stimulation seen in untreated OSA patients.

5-HT2a/2c receptor blockade by amesergide fully attenuates prolactin response to d-fenfluramine challenge in physically healthy human subjects

Prolactin responses to d-fenfluramine (d-FEN) challenge (0.5 mg/kg PO) were examined after pre-treatment with and without the 5-HT2a/2c receptor antagonist amesergide in eight physically healthy male volunteers. Compared to pretreatment with placebo, pre-treatment with amesergide completely blocked the prolactin (PRL) response to d-FEN challenge in all subjects. These data are consistent with data demonstrating a complete blockade of the PRL response to d-FEN with the 5-HT2a/2c receptor antagonist ritanserin, and suggest that the PRL response to d-FEN challenge in humans may largely be due to activation of the 5-HT2a/2c receptor.

Effect of fenfluramine on episodic ACTH and cortisol secretion

OBJECTIVE

The central serotoninergic system is known to modulate the activity of the hypothalamic-pituitary-adrenal axis, but the effect of fenfluramine, a serotonin reuptake inhibitor, on ACTH and cortisol secretion is not well understood. We have therefore evaluated its effects on the hypothalamic-pituitary-adrenal axis in healthy controls.

DESIGN

Episodic secretion of ACTH and cortisol was investigated in 6 healthy volunteers under basal conditions and again during treatment with 20 and 60 mg fenfluramine given orally every 8 hours. On all occasions blood samples were obtained at 10-minute intervals for 24 hours and the mode of hormone secretion was analysed by three different methods (PULSAR, CLUSTER, DESADE). In addition ACTH and cortisol responses to CRH were tested at the end of the sampling period.

RESULTS

At the lower dose fenfluramine had no effect on ACTH and cortisol secretion. At the higher dose a significant increase of mean plasma ACTH (+85%) and cortisol (+129%) levels as well as of urinary free cortisol secretion (+44%) was observed. Fenfluramine did not modulate the frequency, but increased the amplitudes of ACTH and cortisol secretory episodes. ACTH and cortisol responses to CRH injection remained unchanged. Maximum plasma levels of d-fenfluramine and d-norfenfluramine were documented 2-4 hours after the ingestion of the drug.

CONCLUSION

Fenfluramine stimulates the activity of the hypothalamic-pituitary-adrenal axis at a suprapituitary level by modulating the amplitude of ACTH and cortisol secretory bursts.

Behavioral, neuroendocrine and biochemical effects of different doses of 5-HTP in panic disorder

To investigate the role of serotonin (5-HT) in the pathophysiology of panic disorder (PD) a challenge test with L-5-hydroxytryptophan (5-HTP) was conducted. Seven patients suffering from PD and seven healthy controls received an i.v. challenge with 10 mg, 20 mg and 40 mg 5-HTP and placebo in random order on four different occasions. Before, during and until 2 h after 5-HTP administration anxious and depressive symptomatology was assessed. In addition, plasma levels of 5-HTP, cortisol, and 5-HIAA were measured at several timepoints. During and after infusion of placebo or any of the different dosages of 5-HTP, none of the patients or controls experienced a panic attack or showed an increase in anxiety or depressive symptoms. There was a dose-related increase in side effects, like nausea, dizziness and fatigue. Only infusion with 40 mg 5-HTP led to an increase in plasma cortisol in both patients and controls. The observed increase in plasma cortisol level was higher for patients compared to controls only at 30 min after infusion. In conclusion, stimulation of the serotonergic neuronal system by three different dosages of 5-HTP did not induce panic or anxiety in PD patients and healthy controls. The 5-HT hypersensitivity hypothesis of PD could not be confirmed in the present study.

Serotonin and the regulation of hypothalamic-pituitary-adrenal axis function

That serotonin (5HT) is involved in regulating hypothalamic-pituitary- adrenal axis (HPA) function has long been recognized. A variety of drugs including precursors of 5HT such as 5HTP, drugs which release 5HT such as fenfluramine and drugs which act directly on 5HT receptors such as ipsapirone increase cortisol and ACTH concentrations. There is a general assumption that such stimulation occurs at a hypothalamic level. However, our increasing understanding of the complex interplay between 5HT and the HPA raises questions as to the validity of this simple model. An increasing volume of experimental research indicates that 5HT can act directly on the adrenal gland and possibly on the anterior pituitary as well. These findings have major implications for the interpretation of neuroendocrine studies of 5HT conducted in psychiatric conditions, such as depression.

Circadian rhythms and the pharmacology of affective illness

The chronic effects of antidepressant drugs (ADs) on circadian rhythms of behavior, physiology and endocrinology are reviewed. The timekeeping properties of several classes of ADs, including tricyclic antidepressants, selective serotonin reuptake inhibitors, monoamine oxidase inhibitors, serotonin agonists and antagonists, benzodiazepines, and melatonin are reviewed. Pharmacological effects on the circadian amplitude and phase, as well as effects on day-night measurements of motor activity, sleep-wake, body temperature (Tb), 3-methoxy-4-hydroxyphenylglycol, cortisol, thyroid hormone, prolactin, growth hormone and melatonin are examined. ADs often lower nocturnal Tb and affect the homeostatic regulation of sleep. ADs often advance the timing and decrease the amount of slow wave sleep, reduce rapid eye movement sleep and increase or decrease arousal. Together, AD effects on nocturnal Tb and sleep may be related to their therapeutic properties. ADs sometimes delay nocturnal cortisol timing and increase nocturnal melatonin, thyroid hormone and prolactin levels; these effects often vary with diagnosis, and clinical state. The effects of ADs on the coupling of the central circadian pacemaker to photic and nonphotic zeitgebers are discussed.

Effect of pindolol on hormone secretion and body temperature: partial agonist effects

Pindolol has been shown to be a partial agonist at 5-HT1A receptors in preclinical studies. It has also been reported to inhibit the effects of other 5-HT1A partial agonists such as ipsapirone and buspirone on hormone secretion and body temperature in man, indicating its antagonist action at 5-HT1A receptors in man. To determine if pindolol has 5-HT1A agonist as well as antagonist effects in man, pindolol, 30 mg, p.o. and placebo, were given single blind in random order to 23 normal men with indwelling venous catheters and its effects on hormone secretion and body temperature noted. Pindolol significantly increased basal plasma cortisol concentrations, whereas it decreased plasma prolactin (PRL) concentrations and body temperature. The increase in plasma cortisol due to pindolol suggests a 5-HT1A agonist action and is consistent with a 5-HT1A partial agonist mechanism in man whereas the PRL effects are consistent with an antagonist action at 5-HT1A receptors. The effects of pindolol on plasma cortisol concentration and body temperature were significantly negatively correlated. Furthermore, these results indicate significant differences in the 5-HT1A-dependent regulation of PRL and the hypothalamo-pituitary-adrenal (HPA) axis and body temperature, and suggest that human basal PRL secretion is tonically stimulated by 5-HT1A mechanism whereas the HPA axis and body temperature are not. Since rodent studies suggest differences in 5-HT1A receptor sensitivity between males and females, the results reported here need to be replicated in females. These differences in the effect of pindolol are discussed in terms of receptor reserve theory.

Effects of ipsapirone on plasma cortisol and body temperature in major depression

Major depressed patients have been reported to exhibit significantly attenuated hypothermic responses to ipsapirone, a serotonin (5-HT)-1A partial agonist, compared to normal controls. This study further investigated the cortisol and temperature responses to ipsapirone (0.5 mg/kg orally) and placebo in 20 normal volunteers and 12 major depressed patients. Both plasma cortisol and temperature were measured every 30 min before ipsapirone or placebo administration until 180 min post administration. Ipsapirone administration produced a significant increase in plasma cortisol levels as well as hypothermia. Major depressed patients showed significantly blunted ipsapirone-induced cortisol responses compared to normal controls. No significant differences in ipsapirone-induced hypothermic responses were found between major depressed patients and normal controls.

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.

Effect of pindolol pretreatment on MK-212-induced plasma cortisol and prolactin responses in normal men

Previous reports based on studies with serotonin (5-HT) precursors or direct acting agonists have suggested that postsynaptic 5-HT1A and 5-HT2A/5-HT2C receptors may stimulate cortisol and prolactin (PRL) secretion in man. To further clarify the role of these receptors in the regulation of cortisol and PRL secretion in man, the effects of 6-chloro-2-(1-piperazinyl) pirazine (MK-212), a centrally acting direct 5-HT2A/5-HT2C agonist, on the above hormones were studied in 11 normal men with and without pretreatment with pindolol, a 5-HT1A partial agonist. MK-212 induced a significant increase in plasma concentrations of cortisol and PRL. The MK-212-induced response in plasma cortisol was not diminished by pindolol pretreatment, whereas the MK-212-induced PRL response was significantly inhibited by pindolol pretreatment. These data suggest that the MK-212-induced cortisol response may be mediated by 5-HT2A or 5-HT2C receptor activation, or both, despite 5-HT1A inhibition; however, PRL secretion by MK-212 requires 5-HT1A receptor availability as well as 5-HT2A/5-HT2C receptor activation, since blockade of the former appears to blunt the PRL responses to MK-212. These findings may be explained by postulating a cooperativity between 5-HT1A and 5-HT2A/5-HT2C receptors with regard to the 5-HT-dependent stimulation of PRL secretion.

Effects of serotonin precursors on the negative feedback effects of glucocorticoids on hypothalamic-pituitary-adrenal axis function in depression

In order to investigate the relationships between brain serotonergic turnover and hypothalamic-pituitary-adrenal (HPA) axis function in unipolar depression, the authors measured intact adrenocorticotropic hormone (ACTH) and cortisol levels in baseline conditions and after combined dexamethasone (1 mg PO) and L-5-hydroxytryptophan (L-5-HTP, 200 mg PO) administration in 13 minor, 17 simple major, and 17 melancholic subjects. L-5-HTP significantly enhanced post-DST ACTH and cortisol secretion in major--but not in minor--depressed subjects. Major depressed subjects with or without melancholia exhibited significantly higher post-DST ACTH and cortisol responses to L-5-HTP than minor depressed subjects. L-5-HTP administration converted some major depressed ACTH or cortisol suppressors into nonsuppressors. L-5-HTP stimulated ACTH or cortisol secretion to the same extent in major depressed HPA-axis suppressors and nonsuppressors. It is concluded that L-5-HTP loading may augment ACTH and, consequently, cortisol escape from suppression by dexamethasone in major but not in minor depressed subjects. The findings show that serotonergic mechanisms modulate the negative feedback of glucocorticoids on central HPA-axis regulation. It is hypothesized that the higher L-5-HTP-induced post-DST HPA-axis hormone responses in major depression reflect upregulated 5-HT2 receptor-driven breakthrough secretion of pituitary ACTH from suppression by dexamethasone.

Hormonal responses to dl-fenfluramine challenge are not blunted in seasonal affective disorder

Prolactin and cortisol responses to acute challenge with dl-fenfluramine (60 mg PO) were examined in 10 (6 women and 4 men) patients with seasonal affective disorder (SAD) and the same number of age, gender, menstrual status, and season matched healthy controls. Neither prolactin nor cortisol response was different in SAD patients in comparison to controls. The reasons for discrepancy in findings between studies are discussed.

Effect of pindolol on the L-5-HTP-induced increase in plasma prolactin and cortisol concentrations in man

Previous studies with direct-acting serotonin (5-HT) agonists and antagonists have demonstrated that stimulation of 5-HT1A, 5-HT1C and 5-HT2 receptors may promote cortisol and prolactin (PRL) secretion in man. There is also evidence that 5-HT1C/2 receptor stimulation contributes to the cortisol and PRL responses following administration of the 5-HT precursor, L-5-hydroxytryptophan (L-5-HTP), in man. To clarify the possible contribution of 5-HT1A receptor stimulation to the ability of L-5-HTP to stimulate cortisol and PRL secretion in man, the effect of pindolol, a beta adrenoceptor antagonist that is also a 5-HT1A partial agonist, on the L-5-HTP-induced increases in cortisol and PRL secretion, was examined in 12 normal male volunteers. Pretreatment with pindolol, 30 mg orally, significantly inhibited the PRL but not the cortisol response to L-5-HTP, 200 mg PO. Pindolol alone decreased basal plasma PRL levels and increased basal plasma cortisol levels, possibly due to 5-HT1A antagonist and agonists effects, respectively. These data, coupled with observations from other studies, suggest that the L-5-HTP-induced increase in PRL but not cortisol secretion requires 5-HT1A receptor activation. PRL secretion due to 5-HT formed from exogenous L-5-HTP may require the availability of both intact 5-HT1A and 5-HT2/5-HT1C receptors, since blockade of either receptor type inhibited the PRL response to L-5-HTP. The implication of this synergistic effect for interpretation of neuroendocrine studies involving the serotonergic system in man is discussed.

Buspirone induced prolactin release in mania

Prolactin responses to buspirone challenge were examined in 11 manic patients and 11 healthy controls. Of the 11 manic patients, six were treated with lithium alone for 3 weeks, and the buspirone challenge test was repeated. The results showed (1) that there was no difference in prolactin response to buspirone challenge between manic patients and healthy controls, and (2) that there was no correlation between delta (delta) prolactin levels and severity of manic symptoms. Lithium treatment led to a large reduction in delta (delta) prolactin levels, which did not correlate with changes in symptom severity. These results support the possibility that 5HT1A receptors are probably not involved in the pathophysiology of mania.

Is 5HT1A receptor subsensitivity a trait marker for late luteal phase dysphoric disorder? A pilot study

Prolactin responses to buspirone challenges were examined in seven women with late luteal phase dysphoric disorder and the same number of healthy controls. The responses were found to be blunted during the follicular phase in the women with LLPDD suggesting that 5-HT1A receptor subsensitivity is perhaps a trait rather than a state marker for LLPDD.

Neuroendocrine probes of serotonergic function: a critical review

Neuroendocrine probes of serotonergic function are based on the premise that serotonin (5-HT) exhibits an excitory influence on the release of certain anterior pituitary hormones and that the extent of release of these hormones following a challenge with a 5-HT agonist would provide an index of central 5-HT activity. This paper critically reviews studies published to date on healthy volunteers to assess the validity of tests of serotonergic function. Using standardized criteria, it is concluded that although extensive data is available on 5-HT-neuroendocrine probes, there is no test that is currently available that would fulfil all the proposed requirements for a test to be acceptable, although ipsapirone, m-chlorophenylpiperazine (m-CPP), and possibly fenfluramine challenge tests come very close. The rapid development and availability of more specific and stereo-selective 5-HT agonists/antagonists seem to indicate that it will not be too long before a valid neuroendocrine test for the assessment of serotonergic function emerges.

Fluoxetine and suicidal behaviour. Some clinical and theoretical aspects of a controversy

“In the practical decisions of life it will scarcely ever be possible to go through all the arguments in favour of or against one possible decision, and one will therefore always have to act on insufficient evidence” Werner Heisenberg (1962).

The development of selective serotonin (5-hydroxytryptamine, 5-HT) reuptake inhibitors (SSRIs) has added a new dimension to the pharmacotherapy of depression. Their lack of sedative and anticholinergic effects together with relative safety in overdose, has led some authors to suggest that the older tricyclic antidepressants (TCAs) should not now be considered a first-line treatment (Montgomery, 1988). However, since a report by Teicher et al (1990) of suicidal preoccupation associated with fluoxetine treatment, there has been both intense media interest and animated correspondence in clinical and scientific journals (O'Donnell, 1991).

The metabolic fate of infused L-tryptophan in men: possible clinical implications of the accumulation of circulating tryptophan and tryptophan metabolites

L-Tryptophan (Trp) was widely used as a natural tool for the support of serotonin-mediated brain functions and as a challenge probe for the assessment of serotonin-mediated neuroendocrine responses. The metabolic fate of the administered Trp and the kinetics of the accumulation of Trp metabolites in the circulation, however, have never thoroughly been investigated. This study describes the time- and dose-dependent alterations in the plasma levels of various Trp metabolites and large neutral amino acids after the infusion of Trp to healthy young men (1, 3 and 5 g; placebo-controlled, double-blind, cross-over study during day- and night-time). The major Trp metabolites (kynurenine, indole acetic acid and indole lactic acid) in plasma increased dose-dependently but rather slowly after Trp administration to reach their maximal plasma levels (up to 10-fold after the 5 g dose) at about 3 h p.i., and remained at an elevated level (about 5-fold) for up to 8 h. N-acetyl-Trp and 5-hydroxy-Trp rose rapidly and massively after Trp infusions, at the 5 g dose more than 200- and 20-fold, respectively, and declined rapidly to about 5-fold baseline levels within 2 h. Whole blood serotonin levels were almost unaffected by the Trp infusions. A rather slow increase of 5-hydroxyindole acetic acid was seen, reaching maximum values (3-fold at the 5 g dose) at about 2 h after the infusion of Trp. Additionally, a dose-dependent rise of circulating melatonin was observed after L-Trp infusions. The administration of L-Trp caused a depletion of the concentrations of the other large neutral amino acids and a dose dependent decrease of the ratio between plasma tyrosine and the sum of the plasma concentrations of the other large neutral amino acids. Apparently, none of the existing pathways of peripheral Trp metabolism is saturated by its substrate, Trp in men. At least some of the central effects reported after L-Trp administration may be mediated by the Trp-stimulated formation of neuroactive metabolites or by the decreased availability of tyrosine for catecholamine synthesis.

Serotonergic function and late luteal phase dysphoric disorder

Thirty-eight subjects who met criteria for the DSM-III-R diagnosis late luteal phase dysphoric disorder (LLPDD) were compared with 18 controls in 5-HT uptake kinetics of the platelets in the premenstrual (day 26) as well as in the postmenstrual phase (day 4) of the cycle. Furthermore, 5-hydroxytryptophan (5-HTP) was administered to LLPDD patients and controls in both phases of the cycle, to investigate pituitary sensitivity for serotonin. Plasma samples for the measurement of cortisol and beta-endorphin were taken before and after oral administration of 200 mg 5-HTP, and considered as an index of pituitary-adrenal function. LLPDD was not associated with a lower platelet 5-HT uptake and content in the premenstrual phase of the cycle, compared with the postmenstrual phase. Patients appeared not to be different from controls in 5-HT uptake kinetics of platelets in the premenstrual phase of the cycle. No main differences were observed between LLPDD patients and controls in their ability to respond with secretion of cortisol and beta-endorphin to 5-HTP stimulation, either in the premenstrual, or in the postmenstrual phase. This observation could not be attributed to differences in 5-HTP metabolism. The findings of the present study do not support a specific role for 5-HT in the pathophysiology LLPDD.

Neuroendocrine responses to serotonergic agents in alcoholics

Previous studies have suggested a possible deficit in serotonergic function in alcoholism. In order to further assess the serotonergic system in alcoholism, the plasma cortisol and prolactin (PRL) responses following 6-chloro-2-[1-piperazinyl]pyrazine (MK-212), a direct-acting serotonin2 (5-HT2)/5-HT1c receptor agonist, L-5-hydroxytryptophan (L-5-HTP), a precursor of 5-HT, and placebo were compared in male alcoholics and normal controls. The increase in plasma cortisol following L-5-HTP was significantly lower in the alcoholic subjects compared with the normal controls. The plasma PRL, but not the plasma cortisol response, following MK-212 was also significantly lower in the alcoholics. L-5-HTP had no significant effect on plasma PRL levels in either group. The basal plasma cortisol and PRL concentrations of the alcoholics and normal controls were not significantly different. These data are consistent with previous reports of a serotonergic abnormality in alcoholism.