Evaluation of the CCK-4 model as a challenge paradigm in a population of healthy volunteers within a proof-of-concept study

Rationale Experimental panic induction with cholecystokinin-tetrapeptide (CCK-4) has been established as a model to study the pathophysiology of panic disorder and might serve as a tool to asses the antipanic potential of novel anxiolytic compounds. However, assessment of CCK-4-induced panic does not follow consistent rules. Objectives To provide a basis for the use of the CCK-4 model in proof-of-concept studies, we investigated CCK-4-induced panic according to different criteria in 85 healthy volunteers who underwent a CCK-4 bolus injection. Methods We assessed panicker/non-panicker ratios according to different panic criteria and explored whether differences in cardiovascular and neuroendocrine responses to CCK-4 paralleled subjective panic responses. Subjective panic responses were measured with the Acute Panic Inventory (API) and the Panic Symptom Scale (PSS). Heart rate, blood pressure, adrenocorticotropic hormone (ACTH) and cortisol were assessed concomitantly. Results The API-derived panic rate was 10.6% higher than that derived from the PSS. CCK-4 induced an increase in heart rate, systolic blood pressure and ACTH/cortisol plasma levels, which did not differ between panickers and non-panickers. Conclusions The panic criterion applied appears to be of major importance for the panic rate achieved, whereas CCK-4-induced cardiovascular and hormonal alterations are not valuable as an objective “read out”. The CCK-4 challenge might serve as a useful model to study putative anxiolytic effects of novel compounds during the early phase of drug development if the challenge procedure is carried out according to strictly comparable conditions.     

Lithium and 5-HT1A receptor sensitivity: a neuroendocrine study in healthy volunteers

The effect of lithium administration (800 mg daily for 7 days) on the neuroendocrine and temperature responses to the 5-HT_1A receptor agonist, gepirone, was studied in eight healthy male volunteers. Gepirone (20 mg orally) significantly increased plasma levels of prolactin, growth hormone, corticotropin and cortisol, and lowered oral temperature. None of these responses was significantly altered by lithium treatment. The results suggest that the ability of short-term lithium treatment to increase 5-HT-mediated neuroendocrine responses in humans is unlikely to be related to changes in the sensitivity of pre- or post-synaptic 5-HT_1A receptors.     

Dissociable hormonal, cognitive and mood responses to neuroendocrine challenge: evidence for receptor-specific serotonergic dysregulation in depressed mood.

Fifteen patients with major depression, dysthymia, or anxiety disorder with depressed mood (DSM-IV diagnoses) and 16 controls received single oral doses of 0.5mg/kg metachlorophenylpiperazine (m-CPP), a 5-HT(2C) agonist, and 10 mg ipsapirone, a 5-HT(1A) agonist, according to double-blind, placebo-controlled, cross-over design. The groups' levels of cortisol, adrenocorticotrophic hormone (ACTH) and prolactin did not differ at baseline. Both 5-HT agonists significantly elevated cortisol, ACTH, and prolactin. The cortisol response to ipsapirone was significantly blunted in major depression and dysthymia patients. Neuroendocrine responses to m-CPP did not differ between groups, but m-CPP selectively increased profile of mood states (POMS) depression and tenseness scores in patients. No effects of ipsapirone on mood were found. However, ipsapirone impaired memory performance in controls, but tended to improve memory performance in patients. The results support the evidence for both hypothalamic and possibly hippocampal 5-HT(1A) receptor desensitisation and non-hypothalamic, 5-HT(2C) receptor sensitisation, probably fronto-cortical, in patients with major depression and dysthymia.     

Monoamine function in anxiety and depression: Information from neuroendocrine challenge tests

Neuroendocrine challenge tests are being increasingly employed to assess brain monoamine function in man. This review describes some recent studies which have used neuroendocrine tests to investigate brain noradrenaline (NA) and 5-hydroxytrytptamine function (5-HT) in patients suffering from anxiety and depression. A number of abnormalities, particularly in the noradrenergic system, have been identified, and some interesting similarities and contrasts have emerged between panic disorder and depression. Challenge tests can also be used to identify adaptive changes in monoamine pathways following administration of psychotropic drugs. Tolerance has been demonstrated to the ability of benzodiazepines to reduce brain 5-HT function, a finding which could underlie some of the symptoms of the withdrawal syndrome. In addition, it seems likely that long-term administration of tricyclic antidepressants stabilizes NA synaptic function.     

Mood,prolactin and cortisol responses following intravenous L-tryptophan challenge: evidence for serotonergic vulnerability in first-degree relatives of bipolar patients

Central serotonergic vulnerability indicated by altered mood and neuroendocrine responses to an intravenous (i.v.) tryptophan (Trp) challenge was assessed in healthy adult unaffected first-degree relatives of bipolar disorder (BD) patients (n = 30) (family history; FH). The effects of a single dose of 7.0 g Trp on mood, cortisol and prolactin (Prl) in FH subjects were compared with healthy matched controls (n = 15) in a placebo-controlled, double blind cross-over design. Prl and cortisol responses increased following Trp. Overall, Trp lowered mood. Hormonal and mood effects did not differ between FH and controls. Results show some evidence for differences in serotonergic vulnerability between relatives of type I BD patients and relatives of type II BD patients.     

An integrated model for the effect of budesonide on ACTH and cortisol in healthy volunteers

AIMS: Budesonide, a glucocorticosteroid, is used as a first-line treatment for asthma. The aim of the study was to develop a PK/PD model for the effect of budesonide on ACTH and cortisol. METHODS: The modelling data were generated by conducting a single-blind, randomized, placebo-controlled cross-over study. Ten healthy volunteers inhaled placebo (Placebo Turbohaler) and 1600 microg budesonide (Pulmicort Turbohaler), with a wash-out period of 7 days between treatments. Baseline concentrations of cortisol and ACTH were measured after placebo treatment and concentrations of cortisol, ACTH and budesonide were assessed after budesonide treatment. A one-compartment disposition model was used for budesonide disposition. Based on indirect response models, two types of models, distinguishing between production driven by a sum of cosine functions and production driven by surges, were used in parallel to describe the data. RESULTS: The surge-based approach was the most appropriate, based on goodness-of-fit, objective function values and number of parameters. The surge-based model that integrated both ACTH and cortisol data was chosen as the final model. The estimated half-lives of endogenous ACTH and cortisol were 9 and 113 min, respectively. The budesonide and ACTH concentrations producing 50% of the maximal response (IC(50) and A(50)) were 0.325 microg l(-1) and 4.96 pmol l(-1). CONCLUSIONS: The present PK/PD model of the effect of budesonide on ACTH and cortisol can serve as a tool for further understanding of the hypothalamic-pituitary-adrenal (HPA) axis and be useful in the development of drugs interacting with the axis.     

Repeated cortisol administration attenuates the EEG response to buspirone in healthy volunteers: evidence for desensitization of the 5-HT1A autoreceptor

It has previously been postulated that the therapeutic effect of antidepressants, particularly selective serotonin re-uptake inhibitors (SSRIs), is mediated by a down-regulation of somatodendritic (presynaptic) 5-HT(1A) autoreceptors with chronic treatment. Animal studies have revealed that repeated administration of corticosteroids similarly down-regulate this receptor. However, it has previously been difficult to explore if this receptor is similarly modulated in man in vivo. The objective of this study was to explore the effect of repeated administration of cortisol to healthy volunteers utilising a novel putative index of somatodendritic 5-HT(1A) autoreceptor function. This method involves the administration of the 5-HT(1A) agonist buspirone and observing the subsequent negative shift in the frequency spectrum of the electroencephalogram (EEG). Healthy male volunteers were treated with cortisol 20 mg, or placebo, orally twice daily for 7 days in a double-blind random-order crossover study. After each treatment period volunteers were administered buspirone 30 mg orally prior to EEG recordings. Following a week's treatment with placebo, buspirone led to a negative shift in the EEG frequency spectrum as previously reported. However, following treatment with cortisol, the effect of buspirone was significantly attenuated. This is consistent with corticosteroids having a similar effect on somatodendritic 5-HT(1A) autoreceptors in man as seen in rodents.     

The effects of tyrosine depletion in normal healthy volunteers: implications for unipolar depression

Rationale In recent years, there has been a growing interest in the role of dopamine (DA) both in the pathogenesis of unipolar depression and in motivated behaviour. The innovative technique of acute tyrosine depletion presents an opportunity to characterise further its function in these domains.Objective The present study examined the physiological, subjective and cognitive effects of acute tyrosine depletion in healthy volunteers.Methods A double-blind, placebo-controlled, parallel group design was employed. Half of the participants ingested a balanced amino-acid mixture (BAL) and the other half received an identical mixture except that tyrosine and phenylalanine were absent (TYR-free). Plasma amino acid concentrations and subjective ratings were monitored at both baseline (T₀) and 5 h following consumption (T₅) of the mixtures. A comprehensive neuropsychological test battery was also administered at T₅.Results Relative to the BAL group, the reduction in TYR availability to the brain was more marked in the TYR-free group. Employment of psychological rating scales revealed that, compared with the BAL group, the TYR-free group became less content and more apathetic. For the affective go/no-go task, whilst the BAL group exhibited a happy latency bias, the TYR-free group demonstrated a sad latency bias. Furthermore, in the decision-making task, the rate at which the TYR-free group increased their bets in response to more likely outcomes was lower than that of the BAL group. Taken together, these neuropsychological findings strikingly paralleled those reported in previous investigations of unipolar depression. The experimental groups could not be differentiated on any of the other neuropsychological measures, including more classical assessments of fronto-executive function.Conclusion These findings are consistent with the hypothesis that dopaminergic factors are particularly involved in disrupted affect/reward-based processing characteristic of clinical depression.     

Behavioral, physiological and neuroendocrine responses in healthy volunteers to m-chlorophenylpiperazine (m-CPP) with and without ondansetron pretreatment

Several serotonin3 (5-HT₃) antagonists have been shown to attenuate the anxiogenic effects of the serotonergic agent, m-chlorophenylpiperazine (m-CPP), in animal models, but little data regarding possible effects of 5-HT₃ antagonists on responses to m-CPP are available from studies in humans. Therefore, we studied the behavioral, physiological and neuroendocrine responses of 12 healthy volunteers to IV administered placebo and m-CPP (0.08 mg/kg), with and without IV pretreatment with the selective 5-HT₃ antagonist, ondansetron (0.15 mg/kg). Compared to placebo, m-CPP given alone significantly increased ratings of anxiety and several other behavioral measures. m-CPP also produced statistically significant increases in temperature, systolic and diastolic blood pressure, heart rate, and in plasma concentrations of adrenocorticotropic hormone, cortisol, prolactin and norepinephrine. Responses to ondansetron given alone were no different from those of placebo. Pretreatment with ondansetron did not affect peak behavioral responses to m-CPP, but was associated with a significantly earlier return to baseline levels of ratings of anxiety and functional deficit as well as a summary measure of overall behavioral effects. Following ondansetron pretreatment, the increases produced by m-CPP in systolic and diastolic blood pressure and heart rate were no longer significantly different from placebo. Ondansetron pretreatment significantly reduced their plasma cortisol response to m-CPP without affecting the other plasma hormone responses. Plasma concentrations of m-CPP were unaffected by ondansetron pretreatment. These findings suggest that in normal human subjects some behavioral, cardiovascular and neuroendocrine effects of m-CPP may be partially modulated by 5-HT₃ receptor-mediated mechanisms. Received: 11 March 1996/ Final version: 8 August 1996     

Erythropoietin production in healthy volunteers subjected to controlled haemorrhage: evidence against a major role for adenosine

1 This study was carried out to assess the role of adenosine in the regulation of human erythropoietin (EPO) production. To this end we investigated in healthy volunteers whether the nonspecific adenosine antagonist theophylline increases and the adenosine uptake inhibitor dipyridamole decreases EPO production in response to an haemorrhage of 750  ml.
2 Healthy male nonsmokers received i.v. in a parallel, randomized, single-blind trial theophylline (loading dose 5  mg  kg⁻¹ over 20  min, followed by 0.5  mg  kg⁻¹ min⁻¹), dipyridamole (0.21  mg  kg⁻¹ h⁻¹) or placebo (0.9% NaCl) for 6  h following the phlebotomy. EPO concentrations were followed up to 72  h after phlebotomy.
3 Following blood loss EPO concentrations increased during all treatments. The AUC_EPO (0,72  h) were not statistically significantly different (theophylline: 398±30, dipyridamole: 301±15, placebo: 332±57 [mu  ml⁻¹ h]). Creatinine clearance and urinary cAMP excretion were unaltered by any treatment. Urinary excretion of adenosine was significantly increased during infusion of dipyridamole. Plasma renin activitiy was significantly increased during theophylline infusion.
4 In our model of controlled, physiological stimulation of EPO production by haemorrhage, adenosine appears unlikely to play a major role as a mediator of renal EPO production.     

Effects of fasting on responses to intravenous fentanyl in healthy volunteers

The effects of food deprivation on the subjective, psychomotor, and physiological responses to intravenous fentanyl (50 μg/70 kg) were studied in 6 healthy male volunteers. A randomized, placebo-controlled, crossover design was used in which subjects were injected with fentanyl or saline after either 2, 12, or 24 hours of fasting. Subjects completed several subjective effects questionnaires as well as psychomotor tasks prior to, and at regular intervals, following the intravenous injection for a 3-hour period. An observer-rated behavioral checklist was completed at regular intervals during the session and several physiological measures (including measurement of pupil size) were recorded. Fentanyl induced opiate-like mood changes, miosis (pupil constriction), and impairment of extraocular muscle control, and 4 of the 6 subjects reported liking the effects; however, fasting had no impact on any of fentanyl's effects. We conclude that food deprivation up to 24 hours does not alter the subjective, psychomotor, or physiological response to the opiate, fentanyl.     

Erythropoietin production in healthy volunteers subjected to controlled hypobaric hypoxia: further evidence against a role for adenosine

Aims Objective of this study was to investigate whether adenosine modulates renal erythropoietin production.
Methods In the present study erythropoietin production was stimulated by hypobaric hypoxia by subjecting healthy volunteers to a simulated altitude of 4000  m in a low pressure chamber for 5.5  h. During exposure to hypoxia the subjects received i.v. in a randomized, single-blind, cross-over fashion the non-specific adenosine antagonist theophylline, the adenosine reuptake inhibitor dipyridamole and placebo.
Results Contrary to the working hypothesis, theophylline did not decrease and dipyridamole did not further boost erythropoietin concentrations.
Conclusions The results are in agreement with our earlier study using haemorrhage as a controlled physiological stimulus of erythropoietin production, and would question a major role for adenosine as a mediator of renal erythropoietin production.     

The effect of lithium on cholinergically mediated GH responses in healthy volunteers

The phosphoinositide (PI) cycle second messenger system mediates the effect of muscarinic receptor binding. Inositol, which is an essential substrate for phosphoinositide synthesis penetrates the blood-brain barrier poorly, and is vulnerable to depletion. Lithium uncompetitively inhibits inositol-1-monophosphatase, a key enzyme in the recycling of inositol for the PI messanger system. There is evidence for cholinergic overactivity in depression from clinical and experimental observations. Among these, pyridostigmine (PYD) stimulated growth hormone (GH) release is found to be elevated relative to healthy controls. PYD/GH responses were examined in six healthy male volunteers before and after 10 days of lithium administration. GH responses did not differ significantly after lithium from those observed at baseline. These results suggest that lithium does not significantly inhibit cholinergically mediated GH secretion in healthy volunteers and provide further support for the selective action of lithium on upregulated cholinergic tracts, consistent with uncompetitive inhibition of the phosphoinositide cycle.     

Neuroendocrine effects of ipsapirone on the hypothalamic-pituitary adrenal axis: CRF,ACTH and cortisol in healthy volunteers

Summary The neuroendocrine effects (changes in plasma CRF, ACTH and cortisol) of single and multiple (t.d.s. for 2 days) doses of ipsapirone (BAY Q 7821) 5 and 10 mg have been investigated in 6 healthy male volunteers. The study followed a balanced complete block, placebo-controlled and double blind design with two baseline phases (pre and post-treatment). Volunteers were investigated on identical days during 5 successive weeks.The results do not show a specific effect of ipsapirone on the hypothalamic-pituitary-adrenal axis when doses in the range of 5–30 mg per day were given.     

Withdrawal phenomena after atenolol and bopindolol: haemodynamic responses in healthy volunteers.

1. The effect of withdrawal of atenolol and bopindolol administration was studied in 12 normal volunteers; six on each drug. 2. Following sub-maximal cycle-ergometer exercise training six sets of base-line observations were made of heart-rate (HR) and blood pressure (BP) responses; supine, 60 degrees head-up tilt, during graduated isoprenaline infusion and sub-maximal cycle exercise. 3. The results show that withdrawal phenomena occur following both drug treatments. Atenolol produced a hypersensitivity to isoprenaline and a small overshoot of HR in response to physiological manoeuvres. In contrast bopindolol produced a prolonged state of reduced sensitivity to isoprenaline and some evidence of overshoot of HR with physiological manoeuvres. The differences between the responses may be explained by the different properties of the two beta-adrenoceptor blocking drugs. 4. Some subjects showed clear evidence of overshoot of HR and BP on exercise demonstrating that certain individuals may be more prone to have withdrawal effects than others. 5. The length of time during which withdrawal phenomena can occur is probably longer than has previously been realised. 6. Hormonal changes were found in the withdrawal period (Walden et al., 1990).     

Sleep disturbances and depression: a challenge for antidepressants

Sleep disturbances are commonly experienced by depressed patients, and abnormalities of sleep architecture are among the most robust psychobiological correlates of major depression. Most antidepressants alter the physiological patterns of sleep and eventually improve sleep symptoms, along with other symptoms of depression. However, many antidepressants also have unwanted adverse effects on sleep, notably by causing or worsening insomnia, daytime sleepiness or sedation. This article briefly reviews the biology of sleep, the sleep disturbances associated with depression, and the therapeutic and adverse effects of antidepressants on sleep. It also describes a novel antidepressant, agomelatine, which improves symptoms of depression and rapidly relieves sleep complaints without sedative effects.     

Effects of dihydroergotamine on psychomotor function, neuroendocrine parameters and blood pressure, in healthy volunteers

Following the infusion of 15 micrograms/kg of dihydroergotamine (DHE) a 50-fold rise in growth hormone plasma levels was observed in 9 healthy volunteers. Prolactin (PRL) secretion was depressed 240 minutes post infusion. For 170 min, diastolic blood pressure was increased reaching a peak of +19 mmHg at the end of the infusion. Mild sedation and nausea were induced by the treatment for a total duration of 60 min.     

Effect of pindolol on endocrine and temperature responses to buspirone in healthy volunteers

Ten healthy subjects received buspirone (30 mg orally) with and without pre-treatment with the 5-HT1A receptor antagonist, pindolol (80 mg over 3 days). Following pindolol treatment the growth hormone and hypothermic responses to buspirone were significantly decreased. There was also a delay in the onset of the prolactin response to buspirone but the total amount of prolactin secretion, calculated as area under the curve, was not significantly reduced. The data suggest that the growth hormone and hypothermic responses to buspirone in humans are mediated by 5-HT1A receptors, but an explanation founded on pharmacokinetic factors cannot presently be excluded. Both this latter possibility and the lack of selectivity of pindolol for 5-HT receptors indicate the need for the further neuroendocrine studies of the mode of action of buspirone, preferably with more selective 5-HT1A receptor antagonists.     

Effects of labetalol and propranolol on responses to adrenaline infusion in healthy volunteers

The effects of labetalol and propranolol were compared in eight healthy human volunteers using pulse rate and blood pressure changes in response to low rates of adrenaline infusion. Propranolol not only blocked but reversed the positive chronotropic and vasodepressor effects of adrenaline. Labetalol appeared to block these effects only partially. The alpha blocking property of labetalol may have contributed to this difference and hence is unlikely to cause alpha receptor mediated side-effects of endogenously released adrenaline in stress. This model is able to differentiate with great sensitivity between pure beta blockers and alpha beta blocking agents.