Effects of the beta3-adrenoceptor (Adrb3) agonist SR58611A (amibegron) on serotonergic and noradrenergic transmission in the rodent: relevance to its antidepressant/anxiolytic-like profile.

SR58611A is a selective beta(3)-adrenoceptor (Adrb3) agonist which has demonstrated antidepressant and anxiolytic properties in rodents. The present study confirmed the detection of Adrb3 mRNA transcript in rodent brain sub-regions and evaluated the effect of SR58611A on serotonergic and noradrenergic transmission in rats and mice in an attempt to elucidate the mechanism(s) underlying these properties. SR58611A (3 and 10 mg/kg, p.o.) increased the synthesis of 5-HT and tryptophan (Trp) levels in several rodent brain areas (cortex, hippocampus, hypothalamus, striatum). Moreover, SR58611A (10 mg/kg, p.o.) increased the release of 5-HT assessed by in vivo microdialysis in rat prefrontal cortex. Systemic (3 mg/kg, i.v.) or chronic administration of SR58611A (10 mg/kg, p.o.), in contrast to fluoxetine (15 mg/kg, p.o.), did not modify the activity of serotonergic neurons in the rat dorsal raphe nucleus. The increase in 5-HT synthesis induced by SR58611A was not observed in Adrb3s knockout mice, suggesting a selective involvement of Adrb3s in this effect. SR58611A (3 and 10 mg/kg, p.o.) did not modify norepinephrine synthesis and metabolism but increased its release in rat brain. Repeated administration of SR58611A (10 mg/kg, p.o.) did not modify basal norepinephrine release in rat prefrontal cortex whereas it prevented its tail-pinch stress-induced enhancement similarly to reboxetine (15 mg/kg, p.o.). Finally SR58611A increased the firing rate of noradrenergic neurons in the rat locus coeruleus following systemic (3 mg/kg, i.v.) or local (0.01 and 1 microM) but not chronic (10 mg/kg, p.o.) administration. These results suggest that the anxiolytic- and antidepressant-like activities of SR58611A involve an increase of brain serotonergic and noradrenergic neurotransmissions, triggered by activation of Adrb3s.

New perspectives for the treatment of disorders of sleep and arousal.

A variety of molecules with novel mechanisms of action are currently being evaluated for their potential as treatments for sleep disorders. The GABA-A receptor complex remains an important target for hypnotic drugs (eg gaboxadol, indiplon). However, drugs acting through histamine, calcium channels and serotonin receptors may also be of interest for the treatment of insomnia. In the case of the 5HT2A subtype of serotonin receptors, several molecules which improve sleep maintenance and modify sleep architecture by increasing slow wave sleep are currently being tested (eg eplivanserin). Two new drugs with efficacy in excessive sleepiness (modafinil, sodium oxybate) have improved the treatment of this condition. However, the mechanisms of action of these agents are poorly understood. The recent discovery of the hypocretin arousal system in the hypothalamus may aid the identification of additional new drugs. An agonist at receptors for the pineal hormone melatonin is available in some countries (ramelteon) but is currently used only for the treatment of insomnia associated with difficulties of sleep onset. Additional melatonin receptor agonists are being developed and may have potential for treating several conditions including circadian rhythm disorders and depression.

SSR181507, a dopamine D(2) receptor antagonist and 5-HT(1A) receptor agonist, alleviates disturbances of novelty discrimination in a social context in rats, a putative model of selective attention deficit.

RATIONALE: Selective attention deficit, characterised by the inability to differentiate relevant from irrelevant information, is considered to underlie many cognitive deficits of schizophrenia, and appears to be only marginally responsive to treatment with current antipsychotics. OBJECTIVES: We compared the activity of the putative atypical antipsychotic SSR181507 (a dopamine D(2) receptor antagonist and 5HT(1A) receptor agonist) with reference compounds, on disturbances of novelty discrimination in a social context in rats, a behavioural paradigm that putatively models selective attention deficit. METHODS: A first (familiar) juvenile rat was presented to an adult rat for a period (P1) of 30 min. A second (novel) juvenile was then introduced at the end of P1 for a period (P2) of 5 min. The ability of the adult rat to discriminate between the two juveniles, presented at the same time, was evaluated by measuring the ratio of the time spent in interaction with the novel vs the familiar juvenile during P2. RESULTS: Adult rats spent more time exploring the novel than the familiar juvenile. This novelty discrimination capacity was disrupted by: (1) parametric modification of the procedure (reduction of time spent in contact with the familiar juvenile during P1); (2) acute injection of psychotomimetics that are known to induce schizophrenia-like symptoms in humans, such as phencyclidine (PCP; 3 mg/kg, i.p.) and d-amphetamine (1 mg/kg, i.p.) and (3) neonatal treatment with PCP (three injections of 10 mg/kg, s.c.), a model based on the neurodevelopmental hypothesis of schizophrenia. The potential atypical antipsychotic SSR181507 (0.03-3 mg/kg, i.p.) and the atypical antipsychotics clozapine (0.1-1 mg/kg, i.p.) and amisulpride (1-3 mg/kg, i.p.) attenuated deficits in novelty discrimination produced by parametric manipulation and by acute or neonatal treatment with PCP. The typical antipsychotic haloperidol (up to 0.3 mg/kg, i.p.) attenuated only deficits in novelty discrimination produced by parametric modification. CONCLUSION: Collectively, these results suggest that SSR181507 can alleviate disturbances of novelty discrimination in a social context in rats, and that this paradigm may represent a suitable animal model of selective attention deficits observed in schizophrenia.

High doses of haloperidol in schizophrenia. A clinical, biochemical, and pharmacokinetic study.

The effects of high doses of haloperidol on clinical status and plasma neuroleptic and prolactin concentrations and CSF levels of homovanillic acid (HVA) and gamma-aminobutyric acid (GABA) were investigated in three paranoid schizophrenic patients over six weeks. The patients had been receiving haloperidol. Oral dosages were increased at weekly intervals from 10 to 200 mg/day and then reduced to 10 mg/day. The increase did not affect paranoid symptoms. Neurological side effects were slightly increased in two patients and moderately reduced in one. Plasma prolactin levels, initially high, increased when the dosage was increased to 100 mg/day but did not increase further. The CSF levels of HVA and GABA increased to day 7 but returned to initial values on day 28 in two patients; they were decreased to day 28 in one patient.

Lack of correlation between plasma DOPEG and urinary MOPEG levels in depressed patients.

Twenty-four-hour urinary excretion of 3-methoxy,4-hydroxyphenylethyleneglycol (MOPEG) and levels of free and conjugated plasma 3,4-dihydroxyphenylethyleneglycol (DOPEG) were measured in 56 depressed patients to find a possible correlation between these two peripheral indices of cerebral noradrenergic activity. Plasma DOPEG was measured at 9:00 AM on the same day that urine was collected for the measurement of MOPEG. All depressed patients were diagnosed as having affective disorders according to DSM-III. No correlation was found between plasma free or conjugated DOPEG levels and urinary MOPEG output. This lack of correlation was found in the total sample of depressed patients (56), in 45 patients diagnosed as having major depressive episodes, and in 24 depressed patients diagnosed as major depressive with melancholia. The authors discuss the significance of this lack of correlation between two peripheral indices of central noradrenergic metabolism.

Serotonergic neuron stimulation modulates thalamocortical glucose use in the conscious rat.

We have studied the effects, in the conscious rat, of electrical stimulation of the dorsal or median raphe nuclei on integrated functional activity, as assessed by the quantitative 2-deoxyglucose autoradiographic technique. Stimulation of serotonergic neurons elicits metabolic changes in cortical and thalamic regions that are not limited to those structures known to receive the densest serotonergic innervation. The thalamic nuclei that are activated by raphe stimulation include those that subserve the processing of somesthetic, accessory visual, and limbic information. Raphe stimulation increased cortical glucose use in a laminar and columnar pattern, but only in a highly circumscribed region that corresponds to the somatotopic representation of the rat's face and head. These findings indicate that ascending serotonergic neurons play an important modulatory role in the regulation of thalamocortical glucose use, observations that may be of value in the understanding of the etiology and expression of classic migraine.

Concentrations of putative neurovascular transmitters in major cerebral arteries and small pial vessels of various species.

The levels of noradrenaline, neuropeptide Y, 5-hydroxytryptamine, and substance P were measured and compared between the large arteries of the circle of Willis and the small cerebral vessels of the pia mater in the rat, rabbit, cat, and monkey. In all species, noradrenaline and neuropeptide Y concentrations were greater in the larger arteries than in small pial vessels. Noradrenaline concentrations were dramatically reduced following cervical sympathectomy, with the extent of diminution differing greatly in the various species; the effects of cervical ganglionectomy on neuropeptide Y concentrations were less pronounced. 5-Hydroxytryptamine concentrations in rats, cats, and rabbits were significantly greater in the small pial vessels, although measurable concentrations existed in the circle of Willis. In cats and monkeys, substance P was found in major arteries, but was not detectable at the level of the small pial vessels. The differences in the regional distribution of the various neurotransmitter candidates in the cerebrovascular bed may reflect their physiological significance.

Differential effects of electrical stimulation of the dorsal raphe nucleus and of cervical sympathectomy on serotonin and noradrenaline concentrations in major cerebral arteries and pial vessels in the rat.

The levels of noradrenaline (NA), serotonin (5-HT), and 5-hydroxyindoleacetic acid were measured by HPLC and compared between the large arteries of the circle of Willis and the small pial vessels in the rat, following either electrical stimulation of the dorsal raphe nucleus or bilateral superior cervical ganglionectomy. With electrical stimulation, the 5-HT concentrations were reduced (-48%) in the small pial vessels, but were unchanged in the major cerebral arteries. NA concentrations were dramatically reduced following cervical sympathectomy in the large arteries (-77%), though the reduction was less pronounced (-34%) in the small vessels. Sympathectomy caused a significant decrease in the 5-HT concentration of the major cerebral arteries (-33%), but was without effect on the 5-HT levels of the small pial vessels. These results show that an appreciable fraction of the perivascular 5-HT measured in the small pial and the large cerebral arteries originates from different sources.

Dopamine deficiency in the cerebral cortex in Parkinson disease.

We measured the concentrations of dopamine, 3,4-dihydroxyphenylacetic acid, and homovanillic acid in several cortical areas from controls and parkinsonian patients. Substantial amounts of dopamine and its metabolites were detected in hippocampus and entorhinal, cingulate, and frontal cortex of controls. In parkinsonian patients the levels of dopamine and its metabolites were reduced in these neocortical areas and hippocampus. Diminution of cortical dopaminergic transmission may play a role in the mental impairment of some Parkinson patients.

Parkinson's disease and dementia: norepinephrine and dopamine in locus ceruleus.

Norepinephrine, 3-methoxy 4-hydroxyphenylethyleneglycol and homovanillic acid levels were similar in the locus ceruleus of 13 controls and 8 parkinsonian patients with no intellectual deterioration, but were decreased in 7 demented patients. The concentration of dopamine was similarly diminished in non-demented and demented parkinsonians, and binding of 3H-desmethylimipramine and 3H-rauwolscine was not abnormal in parkinsonians. These data indicate that norepinephrine metabolism in the locus ceruleus is subnormal only in demented parkinsonians.

Zolpidem functionally discriminates subtypes of native GABAA receptors in acutely dissociated rat striatal and cerebellar neurons.

The whole-cell patch-clamp technique was used to compare the properties of native GABAA receptors in Purkinje and striatal neurons acutely dissociated from neonatal rat brains (7-11 days old). In symmetrical chloride concentrations and at a negative holding voltage, GABA induced inward currents in a concentration-dependent manner with EC50 values of 4 and 8 uM in Purkinje and striatal neurons, respectively. Diazepam potentiated the current induced by 1 uM GABA in Purkinje and striatal neurons with EC50 values of 28 and 42 nM and maximal potentiations of 128 and 182%, respectively. Zolpidem potentiated this GABA-induced current in Purkinje and striatal neurons with EC50 values of 33 and 195 nM and maximal potentiations of 189 and 236%, respectively. These results show that zolpidem, in contrast to diazepam, functionally discriminates subtypes of native GABAA receptors. Zolpidem has greater affinity for GABAA receptors containing omega 1 (Purkinje cells) than for those with omega 2 (striatum) sites and has higher intrinsic activity at these receptors than diazepam. These properties of zolpidem may contribute to its hypnoselective profile.

Autoradiographic distribution of the D1 agonist [3H]SKF 38393, in the rat brain and spinal cord. Comparison with the distribution of D2 dopamine receptors.

The regional distribution of the specific D1 agonist [3H]SKF 38393 (SKF 38393, 2,3,4,5-tetra-hydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine) has been studied autoradiographically in the rat CNS. The binding of [3H]SKF 38393 to striatal sections was saturable, stereospecific, reversible, of high affinity (Kd = 9.9 nM) and partly sodium sensitive; it occurred at a single population of sites and possessed the pharmacological characteristics of the dopamine D1 receptor. The highest levels of [3H]SKF 38393 binding sites were found in the caudate-putamen, nucleus accumbens, olfactory tubercle and substantia nigra. Moderately high concentrations of the [3H]ligand were observed in the amygdala, endopyriform nucleus, nucleus olfactorius anterior, lateral septum, primary olfactory cortex, cerebellum (molecular layer) and spinal cord. An intermediate labelling was found in the thalamus, habenula, subthalamic nucleus, hypothalamus, ventral tegmental area, superior colliculus, hippocampus and cerebral cortex. Moderate levels of [3H]SKF 38393 binding were observed in the globus pallidus and arcuate nucleus. The autoradiographic distribution of [3H]SKF 38393 overlapped with that of [3H]N,n-propylnorapomorphine, a radioligand which labels the D2 dopamine receptors, in a number of dopamine-rich brain areas but there were several areas which exhibited a high density of [3H]SKF 38393 binding sites but undetectable concentrations of [3H]N,n-propylnorapomorphine. Moreover, in the spinal cord, the subregional localization of these [3H]ligands clearly differed. Intrastriatal injection of ibotenic acid caused a large decrease in [3H]SKF 38393 and [3H]N,n-propylnorapomorphine binding in the striatum and provoked a reduction of [3H]SKF 38393 but not [3H]N,n-propylnorapomorphine binding in the substantia nigra confirming the view that nigral D1 but not D2 receptors are located on striatonigral fibres.

Antagonism by NG-nitro-L-arginine of L-glutamate-induced neurotoxicity in cultured neonatal rat cortical neurons. Prolonged application enhances neuroprotective efficacy.

The effects of NG-nitro-L-arginine on L-glutamate-induced neurotoxicity have been evaluated on primary cultures of neonatal rat cortical neurons. Treatment of cultures with increasing concentrations of L-glutamate during 5 min produced a delayed neuronal death, as measured by lactate dehydrogenase release in the medium 24 h later. Maximal toxicity was obtained with 500 microM of L-glutamate. Substantial nitric oxide synthase activity was detected in these cortical cultures. Nitric oxide synthase activity and cellular L-glutamate-induced cyclic guanosine 3',5'-monophosphate accumulation were totally inhibited by 100 microM NG-nitro-L-arginine. Addition of NG-nitro-L-arginine (100 microM) to the medium either 5 min prior to and during L-glutamate exposure (500 microM, 5 min) or for 24 h after L-glutamate exposure decreased the amino acid-induced neurotoxicity by 23% (not significant) and 43%, respectively. When added 5 min before L-glutamate and just after L-glutamate removal and kept in contact with neurons for the following 24 h, NG-nitro-L-arginine (100 microM) antagonized by 74% the L-glutamate-induced neurotoxicity. This effect was not reversed by a co-application of L-arginine (1 mM). The neuroprotective effect of NG-nitro-L-arginine was concentration-dependent, a half-maximal inhibition of L-glutamate-induced neurotoxicity being observed with the addition (before and after L-glutamate) of 4 microM of the drug. These results suggest that the neuroprotective effect of NG-nitro-L-arginine previously observed in vivo is exerted at the neuronal level.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of monoaminergic, cholinergic, and GABAergic markers in the human cerebral cortex.

Mapping of a number of biochemical markers for noradrenergic, dopaminergic, serotoninergic, cholinergic and GABAergic systems was undertaken in 93 samples removed from the human cerebral cortex. The right hemisphere of brains from two subjects with no known history of neurological and psychiatric diseases was examined. Neurotransmitter markers were present in all cortical samples analysed, suggesting a widespread distribution of the corresponding neurons throughout the cerebral cortex. Each marker distributed heterogeneously in a distinct pattern. Noradrenaline concentrations were highest in the frontoparietal region and lowest in prefrontal and occipital areas. Markers for dopaminergic neurons (dopamine levels, dopamine/noradrenaline ratio and homovanillic acid levels) seemed denser in the prefrontal and temporal regions. 5-Hydroxyindolacetic acid levels were particularly high in the occipital area and decreased along the caudorostral axis. Choline acetyltransferase activity was highest in temporal and frontal lobes, at variance with muscarinic receptor distribution, which was highest in occipital cortex. Glutamate decarboxylase activity, an index of GABAergic innervation, did not vary markedly among the different areas of the cerebral cortex. The different biochemical markers investigated were detected in all cerebral cortical regions; their distribution was not homogeneous. A mismatch was observed between the distribution of cholinergic neuronal systems and receptors.

PET study of carbon-11-PK 11195 binding to peripheral type benzodiazepine sites in glioblastoma: a case report.

The utility of the peripheral type benzodiazepine site ligand 11C-PK 11195, for imaging human glioma in conjunction with Positron Emission Tomography, relies on a high specific binding of the tracer to tumoral peripheral type benzodiazepines sites. In a patient with glioblastoma, we found that 11C-PK 11195 binding was two-fold higher in the tumor than in normal gray matter and that 30% of tumoral binding could be displaced by a large excess of unlabeled drug. These findings suggest that tumoral retention of the ligand is due, in part, to specific binding.

Neuroprotective effects of eliprodil in retinal excitotoxicity and ischemia.

PURPOSE: To evaluate whether eliprodil (SL82.0715), a NR2B-selective N-methyl-D-aspartate (NMDA) antagonist, is protective of retina subjected to an excitotoxic or ischemic insult. METHODS: To evaluate protection against retinal excitotoxicity, eliprodil was administered intraperitoneally before and after the injection of NMDA (5 microl, 20 nmol) into the vitreous of rats. Integrity of the retina was assessed by counting cells in the retinal ganglion cell layer (GCL) and measuring choline acetyltransferase (ChAT) activity. In a subsequent experiment, total retinal ischemia, as measured by a cessation of electroretinographic (ERG) activity, was induced in anesthetized rabbits by elevating intraocular pressure above systolic blood pressure for 65 minutes. After ischemia, recovery of ERG activity was assessed at 24 and 48 hours in animals treated with vehicle or eliprodil (1.0-10.0 mg/kg). RESULTS: Intravitreal NMDA injection resulted in a dose-related decrease in cells of the GCL and in ChAT activity. Eliprodil administered intraperitoneally at 10 mg/kg completely prevented the loss of ChAT and the loss of cells in the GCL. Twenty-four hours after retinal ischemia, A and B waves of vehicle-treated animals were suppressed by 60% to 70%. Eliprodil administered intraperitoneally at 10 mg/kg ameliorated the A- and B-wave depression throughout the 48-hour experiment. CONCLUSIONS: Eliprodil is neuroprotective of retinae subjected to either an excitotoxic or ischemic challenge and may be useful for treating a variety of retinal and optic nerve head disorders.

Benzodiazepine-induced intestinal motor disturbances in rats: mediation by omega 2 (BZ2) sites on capsaicin-sensitive afferent neurones.

1. The central and peripheral effects of the omega (benzodiazepine) site ligands, clonazepam, alpidem, zolpidem, triazolam, flumazenil, ethyl beta carboline-3-carboxylate (beta-CCE) and N-methyl beta carboline-3-carboxylate (beta-CCM) on intestinal myoelectrical activity were evaluated in conscious rats, chronically fitted with Nichrome electrodes implanted on the duodenum and jejunum. The localization of the omega (benzodiazepine) receptors involved in these effects was evaluated by use of systemic and perivagal capsaicin treatments. 2. When administered intraperitoneally (i.p.) the omega site inverse agonists beta-CCE and beta-CCM, and the omega site antagonist flumazenil, did not affect the duodeno-jejunal motility. Alpidem and zolpidem, two selective omega 1 site agonists induced an inhibition of migrating myoelectric complexes (MMCs) only at a high dose (5 mg kg-1). In contrast, clonazepam (a mixed omega 1/omega 2 agonist) and triazolam (a preferential omega 2 site agonist) disrupted the MMC-pattern at doses as low as 0.05 mg kg-1, the effect of trizolam being of much longer duration than that of clonazepam. None of these drugs altered MMC-pattern when administered centrally (i.c.v.). 3. Administered i.p. or i.c.v. prior to triazolam, alpidem blocked the effect of triazolam on duodenojejunal spike activity. Administered i.p. prior to triazolam, flumazenil suppressed the triazolam-induced MMC-disruption. Previous systemic but not perivagal capsaicin treatment suppressed the effects of clonazepam on MMCs. 4. It is concluded that omega-site agonists but not, antagonist or inverse agonists, administered systemically induced intestinal motor disturbances which may be linked to activation of omega 2 (BZ2) sites located on nonvagal capsaicin-sensitive afferent neurones.

Effects of clonidine, prazosin and phentolamine on heart rate and coronary sinus catecholamine concentration during cardioaccelerator nerve stimulation in spinal dogs.

1 In spinal dogs, continuous electrical stimulation of the cardioaccelerator nerve produced a transient rise in aortic blood pressure and a sustained increase in both heart rate and coronary sinus blood flow. The latter effects were accompanied by a significant elevation in the coronary sinus plasma noradrenaline concentration without significant changes in the levels of dopamine and adrenaline. The concentrations of the three catecholamines in thoracic aorta plasma were not significantly changed by cardioaccelerator nerve stimulation.2 Clonidine (20 mug/kg, i.v.), given during cardioaccelerator nerve stimulation, increased both mean aortic blood pressure and coronary sinus blood flow and decreased heart rate and coronary sinus venous plasma noradrenaline overflow.3 Phentolamine (0.3 mg/kg, i.v.) completely antagonized these effects of clonidine. Prazosin (0.3 mg/kg, i.v.) inhibited by only 43 and 38% the respective reductions in heart rate and noradrenaline overflow elicited by clonidine.4 On termination of cardioaccelerator stimulation (about 10 min after either prazosin or phentolamine), heart rate and coronary sinus noradrenaline overflow returned to control prestimulation levels.5 Phentolamine or prazosin, administered alone during stimulation of the cardioaccelerator nerve, increased heart rate and noradrenaline overflow into the coronary sinus plasma. However, intravenous phentolamine and prazosin, in contrast to desipramine (0.3 mg/kg, i.v.) or tyramine (1.0 mg, i.a.), failed to change the tachycardia resulting from the local administration of noradrenaline into the sinus node artery (i.a.).6 These results show that in spinal dogs the clonidine-induced reduction in heart rate (elevated by electrical stimulation of the cardioaccelerator nerve) is accompanied by a fall in the quantity of noradrenaline overflowing into the coronary sinus plasma. The latter effect is presumably the result of an action of clonidine on cardiac presynaptic alpha-adrenoceptors, the activation of which is followed by a reduction in the release of noradrenaline per nerve impulse. Phentolamine and prazosin are both antagonists of cardiac presynaptic alpha-adrenoceptors in spinal dogs, as suggested by their action against clonidine and by their positive chronotropic effect when administered during stimulation of the cardioaccelerator nerve.

Decrease in plasma levels of 3,4-dihydroxyphenylethyleneglycol in major depression.

Plasma levels of free and sulfoconjugated 3,4-dihydroxyphenylethyleneglycol (DOPEG), the main deaminated metabolite of norepinephrine, were measured in a group of 45 hospitalized patients presenting a major depression and a group of 45 healthy subjects, matched for sex and age. Compared to healthy subjects, depressed patients had significantly lower plasma levels of free and sulfoconjugated DOPEG. The ratio of free over conjugated DOPEG was not statistically different in the two groups. The reduction of plasma DOPEG levels in the depressed patients did not appear to be related to the duration of drug-free period and was similar in males and females. There was no statistically significant correlation between plasma DOPEG levels and total score on the Hamilton Rating Scale for Depression. Finally, plasma DOPEG levels did not differ in unior bipolar patients. The present data provides further evidence for a reduced CNS noradrenergic transmission in major depression.

Lack of circadian rhythm in plasma levels of 3,4-dihydroxyphenylethyleneglycol in healthy human subjects.

In order to investigate the possible existence of a circadian rhythm in plasma free and sulfate-conjugated 3,4-dihydroxyphenylethyleneglycol (DOPEG), the plasma levels of this metabolite (and for comparison, of melatonin and cortisol) were measured in seven healthy volunteers at 4-h intervals over a period of 24 h. Plasma concentrations of melatonin and cortisol showed distinct diurnal variations with acrophases at 2.5 h and 8.5 h, respectively. In contrast, plasma free DOPEG levels were relatively stable over the 24-h period studied. Sulfate-conjugated and free + sulfate-conjugated DOPEG levels showed a slight, non-significant increase in the early afternoon. These results indicate that in contrast to plasma 3-methoxy 4-hydroxyphenylethyleneglycol, plasma free and conjugated DOPEG levels do not exhibit a circadian rhythm.