[Second generation SSRIS: human monoamine transporter binding profile of escitalopram and R-fluoxetine]. / Inhibiteurs spécifiques de la recapture de la sérotonine (ISRS) de deuxième génération: profil de liaison du transporteur de l'escitalopram et de la R-fluoxétine chez l'homme.

BACKGROUND: Single isomers of the selective serotonin reuptake inhibitors citalopram (escitalopram, S-citalopram) and fluoxetine (R-fluoxetine) are currently under development for the treatment of depression and other psychiatric disorders. Previous studies conducted in laboratory animals have revealed that the biological effects on serotonin reuptake for citalopram reside in the S enantiomer. In contrast, both enantiomers of fluoxetine contribute to its biological activity. METHODS: In the present study, the potency and selectivity of escitalopram, R-fluoxetine, and all of the other currently available selective serotonine reuptake ihibitors were compared for binding affinity at the human serotonin, norepinephrine, and dopamine transporters and several select neurotransmitter receptors using radioligand binding assays. RESULTS: Both escitalopram and R-fluoxetine were potent inhibitors of the serotonin transporter (Ki=1,1 and 1,4 nmol/L, respectively). escitalopram was the most serotonin transporter-selective compound tested and was approximately 30 fold more potent than R-citalopram. CONCLUSIONS: As noted previously, paroxetine and sertraline possess moderate affinity (<50 nmol/L) for the human norepinephrine transporter and dopamine transporter, respectively. R-fluoxetine, unlike the other selective serotonin reuptake inhibitors, possesses moderate affinity (Ki=64 nmol/L) for the serotonin 2C receptor. Potential clinical correlates of these unique attributes of escitalopram and R-fluoxetine are discussed. (Biol Psychiatry 2001; 50: 345-350 " 2001 Society of Biological Psychiatry).

Second-generation SSRIs: human monoamine transporter binding profile of escitalopram and R-fluoxetine.

BACKGROUND: Single isomers of the selective serotonin reuptake inhibitors citalopram (escitalopram, S-citalopram) and fluoxetine (R-fluoxetine) are currently under development for the treatment of depression and other psychiatric disorders. Previous studies conducted in laboratory animals have revealed that the biological effects on serotonin reuptake for citalopram reside in the S enantiomer. In contrast, both enantiomers of fluoxetine contribute to its biological activity. METHODS: In the present study, the potency and selectivity of escitalopram, R-fluoxetine, and all of the other currently available selective serotonin reuptake inhibitors were compared for binding affinity at the human serotonin, norepinephrine, and dopamine transporters and several select neurotransmitter receptors using radioligand binding assays. RESULTS: Both escitalopram and R-fluoxetine were potent inhibitors of the serotonin transporter (K(i) = 1.1 and 1.4 nmol/L, respectively). Escitalopram was the most serotonin transporter-selective compound tested and was approximately 30-fold more potent than R-citalopram. CONCLUSIONS: As noted previously, paroxetine and sertraline possess moderate affinity (<50 nmol/L) for the human norepinephrine transporter and dopamine transporter, respectively. R-Fluoxetine, unlike the other selective serotonin reuptake inhibitors, possesses moderate affinity (K(i) = 64 nmol/L) for the serotonin 2C receptor. Potential clinical correlates of these unique attributes of escitalopram and R-fluoxetine are discussed.

Effects of sodium valproate on corticotropin-releasing factor systems in rat brain.

We hypothesized that divalproex sodium, an anticonvulsant effective in the acute treatment of mania, may act upon neuropeptide systems that utilize corticotropin-releasing factor (CRF). Pharmacokinetic studies demonstrated that valproate has an apparent elimination half life of 17 minutes in rats after acute administration and that there is a nonlinear relationship between chronic dose and serum drug concentration. Acute valproate treatment neither altered plasma adrenocorticotropic hormone (ACTH) or corticosterone concentrations nor produced changes in CRF concentration in any of 10 brain regions examined. Subchronic treatment via SC-implanted osmotic minipumps (875 mg/kg/day x 7 days) resulted in decreased CRF concentrations in the median eminence and raphe nuclei. Moreover, CRF mRNA expression was decreased in the central nucleus of the amygdala (CeA) and paraventricular nucleus (PVN) of the hypothalamus. The benzodiazepine alprazolam, also a positive modulator of GABAergic function, similarly decreases CRF mRNA expression in the CeA. These results suggest that the mood stabilizing effects of valproic acid may be mediated in part by alterations in CRF neuronal activity.

Paroxetine binding to the rat norepinephrine transporter in vivo.

BACKGROUND: The norepinephrine transporter (NET)/uptake site is an antidepressant-sensitive transporter located on plasma membranes of noradrenergic neurons and other specialized cells that remove norepinephrine (NE) from the synapse to terminate the actions of NE. The antidepressant paroxetine is believed to produce its therapeutic effects primarily by acting as a highly selective antagonist of the serotonin transporter (SERT). However, in vitro data indicates that paroxetine inhibits the NET. The present study was designed to determine whether paroxetine inhibits in NET in vivo. METHODS: Rats were administered paroxetine (6.5, 10.0, or 15.0 mg/kg/day) via osmotic minipumps for 1 week. Following attainment of steady state serum concentrations, cortical NET function was assessed by both [3H]-nisoxetine binding and [3H]-norepinephrine uptake assays conducted ex vivo. RESULTS: In unwashed brain homogenates, serum paroxetine concentrations greater than 100 ng/mL were positively correlated with the observed Kd for [3H]-nisoxetine. At [3H]-nisoxetine concentrations associated with 50% transporter occupancy in vehicle treated rats, [3H]-nisoxetine binding was decreased 21% and 34% in rats exhibiting serum paroxetine concentrations > 100 ng/mL and > 500 ng/mL, respectively. CONCLUSIONS: Although paroxetine is a very potent inhibitor of the SERT, paroxetine also inhibits the NET at serum concentrations > 100 ng/mL. This novel finding may underlie the broad therapeutic utility of paroxetine in mood and anxiety disorders.

Chronic administration of the triazolobenzodiazepine alprazolam produces opposite effects on corticotropin-releasing factor and urocortin neuronal systems.

In view of the substantial preclinical evidence that supports a seminal role of central corticotropin-releasing factor (CRF) neuronal systems in the physiology and pathophysiology of stress and anxiety, it is reasonable to suggest that the anxiolytic properties of benzodiazepines are mediated, at least in part, via regulation of CRFergic function. To begin to test this complex hypothesis, we examined the effects of acute and chronic administration of the triazolobenzodiazepine agonist alprazolam on CRF peptide concentrations, receptor-binding density, and mRNA expression in the CNS. Additionally, we measured mRNA expression for urocortin, a recently discovered neuropeptide that is generally considered to be a second endogenous ligand for CRF receptors. Both acute and chronic alprazolam administration was found to decrease CRF concentrations within the locus coeruleus. Furthermore, chronic alprazolam decreased basal activity of the hypothalamic-pituitary-adrenal axis, CRF mRNA expression in the central nucleus of the amygdala, and CRF(1) mRNA expression and receptor binding in the basolateral amygdala. In marked contrast, urocortin mRNA expression in the Edinger-Westphal nucleus and CRF(2A) receptor binding in the lateral septum and ventromedial hypothalamus were increased. Similar findings of an inverse relationship between the CRF(1) and CRF(2A) receptor systems have been reported in an anxiety model based on adverse early-life experience, suggesting the intriguing possibility that CRF neuronal systems may be comprised of two separate, but interrelated, subdivisions that can be coordinately and inversely regulated by stress, anxiety, or anxiolytic drugs.

Platelet 5-hydroxytryptamine (5-HT) transporter and 5-HT2A receptor binding after chronic hypercorticosteronemia, (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane administration or neurotoxin-induced depletion of central nervous system 5-HT in the rat.

There is considerable evidence that the number of platelet 5-hydroxytryptamine (5-HT) transporter binding sites, as measured by [3H]imipramine binding, are significantly decreased, and platelet 5-HT2 receptor density is increased, in drug-free patients with major depression. To investigate whether these changes in the platelet 5-HT transporter or 5-HT2 receptor sites resulted from known or hypothesized biochemical changes observed in major depression, we examined, in the rat, whether a chronic hyperglucocorticoid state, or decreases or increases in central nervous system 5-HT neurotransmission, altered binding of the selective ligands [3H]citalopram and [125I] (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane to platelet and brain 5-HT transporters and 5-HT2 receptors, respectively. Chronic (6 weeks) hypercorticosteronemia did not alter either brain or platelet 5-HT transporter or 5-HT2A receptor binding. Similarly, 8-week administration of the 5-HT2A/5-HT2C agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, at a dose which down-regulates brain 5-HT2A/2C receptors, did not alter brain or platelet 5-HT transporters or platelet 5-HT2A receptors. Additionally, para-chloroamphetamine-(11 weeks) or fenfluramine-induced chronic (1.5-10 weeks) depletion of central nervous system 5-HT did not alter platelet 5-HT transporter or 5-HT2A receptor binding. Finally, there was no correlation between the number of 5-HT transporters in brain and platelets in any of the control or treatment groups. These findings suggest that the observed changes in platelet 5-HT transporter and 5-HT2A receptor binding in depressed patients are more apt to be of genetic origin (i.e., trait-dependent) rather than an epiphenomenon of hypercortisolemia or altered central nervous system 5-HT status.

Is there a relationship between baseline and treatment-associated changes in [3H]-IMI platelet binding and clinical response in major depression?

A peripheral model for the central 5-HT neuron is the characterization of platelet imipramine binding. We studied an outpatient major depressive cohort who fulfilled Research Diagnostic Criteria for agitation. After a 1-week placebo lead-in, subjects were blindly randomized to either imipramine (IMI) or fluoxetine (FLU) during an 8-week, double-blind study period. Thirty-three subjects (15 IMI, 18 FLU) provided both baseline and endpoint samples for the platelet [3H]-IMI assay. Depression efficacy was comparable across the two treatments, whereas FLU was significantly more effective in reducing secondary anxiolysis (p = .023). Discontinuations due to an adverse event were significantly more frequent with IMI than FLU (p < .01). Baseline affinity (KD) was mildly predictive of change in the HAMD (r = -.22; p = .07). Whereas baseline to endpoint density (Bmax) changes (delta) were similar for IMI (183 +/- 329 fmol/mg) and FLU (196 +/- 402 fmol/mg), a statistically significant treatment difference in delta KD emerged (IMI -0.005 +/- 0.010 pmol/ml versus FLU 0.008 +/- 0.013 at p = 004). Moreover, the changes in KD and HAMD17 trended to a positive correlation among only the FLU-treated subjects (4 = 0.406, p = .095). The clinical effects of 5-HT-based selective antidepressant may be reflected by dynamic changes in the platelet 5-HT uptake apparatus. These data suggest that the baseline confirmational status of the [3H]-IMI:5-HT transporter may reflect a "capacity" for a treatment response.

The simultaneous determination of neurotensin and its major fragments by on-line trace enrichment HPLC with electrochemical detection.

An HPLC assay using on-line cation exchange trace enrichment and acetonitrile gradient elution, ion pair reverse phase separation with electrochemical detection (EC) is described for the simultaneous determination of the tridecapeptide neurotensin (NT) and six of its fragments. Cyclic voltammetric analysis indicated that the oxidative electrochemical properties of NT and its fragments is not merely a function of the sum of its electroactive amino acids (i.e. tyrosine) but reflects the presence and association of other amino acids (e.g. the arginine-arginine pair at position 8-9). Using the described method, NT1-6, NT1-8, NT1-10, NT1-11, NT8-13, NT9-13 and NT1-13 were baseline resolved within 20 min with a limit of detection varying from 1 to 5 ng peptide/injection. Other structurally similar or quantitatively significant neuropeptides (e.g. substance P, somatostatin, bombesin) did not interfere. Initial application of this on-line trace enrichment HPLC-EC assay to the question of the molecular nature of NT in unprocessed human CSF indicated the predominance of NT1-13 with an apparent formation of NT1-8 and NT9-13 resulting from more vigorous sample preparation techniques. The improvements in assay specificity, signal-to-noise ratios, biomatrix compatibility and assayable sample volume compared to non-enrichment HPLC-EC are discussed.

The serotonergic antidepressant nefazodone inhibits the serotonin transporter: in vivo and ex vivo studies.

Nefazodone HCl (Serzone) is a new antidepressant with a chemical structure unrelated to selective serotonin reuptake inhibitors (SSRIs), tricyclics, tetracyclics, or monoamine oxidase inhibitors (MAOIs). Nefazodone is active in a number of preclinical tests for antidepressant activity and shows clinical efficacy in the treatment of depression with a more favorable side-effect profile than the structurally similar antidepressant trazodone. Previous studies have shown that nefazodone is a potent antagonist of 5-HT2A receptors and binds to the serotonin transporter in vitro and in vivo. Nefazodone also binds to the norepinephrine transporter in vitro and in acute ex vivo studies. To further investigate the ability of nefazodone to modify serotonergic transmission, the ability of systemically administered nefazodone to inhibit the serotonin transporter was assessed by investigating the ability of nefazodone to prevent p-chloroamphetamine- (PCA) induced depletions of cortical 5-HT concentrations. In addition, the ability of acute and subchronic nefazodone administration to inhibit ex vivo [3H]-5-HT uptake was assessed. Acute administration of nefazodone (30, 100, and 150 mg/kg) antagonized PCA-induced depletion of cortical 5-HT concentrations in a dose-dependent manner at 1, 2, and 3 hours post-treatment. This effect was directly correlated with serum nefazodone concentrations. Both 100 mg/kg and 150 mg/kg of nefazodone were equipotent with fluoxetine (10 mg/kg) over the course of the experiment with respect to sparing of 5-HT depletion. Acute administration of nefazodone (100 and 150 mg/kg s.c.) significantly increased the Km for [3H]-5-HT uptake in rat cortical synaptosomes from 60 nmol/L in controls to 230 and 242 nmol/L in nefazodone-treated rats, respectively. Subchronic administration of nefazodone (100 and 150 mg/kg, s.c., b.i.d. x 5.5 days) reduced [3H]-5-HT uptake by 24% and 29%, respectively. Sub-chronic dosing with fluoxetine (5 mg/kg, s.c., b.i.d. x 5.5 days) reduced [3H]-5-HT uptake by 65%. These experiments confirm and extend previous reports concerning the ability of nefazodone to inhibit the 5-HT transporter in vivo.

Further studies on platelet serotonin transporter binding in depression.

OBJECTIVE: There is an impressive literature implicating abnormalities in serotonergic neural systems in depression. Many investigators, but not all, have reported low numbers of platelet and brain serotonin (5-HT) transporter sites in drug-free depressed patients. In the present study the authors sought to determine whether the low platelet 5-HT transporter binding in depressed patients is due to previous antidepressant drug exposure. In addition, the binding of both [3H]imipramine and the more specific ligand [3H]paroxetine to the platelet 5-HT transporter was compared in drug-free depressed patients and age- and sex-matched normal comparison subjects. METHOD: In the first experiment blood samples were obtained from 12 depressed patients who had never received antidepressant drugs and 12 normal comparison subjects, and platelet 5-HT transporter binding was measured by using [3H]imipramine. In the second experiment blood samples were obtained from 28 drug-free depressed patients and 28 age- and sex-matched comparison subjects, and platelet 5-HT transporter binding was assessed by using both [3H]imipramine and [3H]paroxetine. RESULTS: In the first experiment the never-medicated depressed patients exhibited fewer platelet [3H]imipramine binding sites than did the comparison subjects. In the second experiment the drug-free depressed patients had fewer platelet binding sites for both [3H]imipramine and [3H]paroxetine than did the comparison subjects. CONCLUSIONS: The low number of platelet [3H]imipramine binding sites does not appear to be due to prior antidepressant drug exposure. The Bmax of platelet binding sites for both [3H]imipramine and [3H]paroxetine, ligands used to measure 5-HT transporter binding, is abnormally low in depressed patients.

Reduced platelet tritium-labeled imipramine binding sites in women with premenstrual syndrome.

OBJECTIVE: We studied the possible role of serotonergic systems in the cause of premenstrual affective symptoms. STUDY DESIGN: The binding of tritium-labeled imipramine to platelets is thought to parallel central nervous system binding and to indicate serotonergic activity. We measured platelet tritium-labeled imipramine binding sites in the follicular and luteal phases in 12 controls and in 9 women with well-documented late luteal phase dysphoric disorder. In statistical analyses we used repeated measures analysis of variance, with Student-Newman-Keuls and Duncan's one-tailed t tests, and Pearson's r. RESULTS: The values of subjects with late luteal phase dysphoric disorder were lower than those of controls (F [1,39] = 5.13, p = 0.03). Both follicular and luteal phase level were lower in subjects with late luteal phase dysphoric disorder but reached statistical significance only in the follicular phase. CONCLUSION: Lower platelet tritium-labeled imipramine binding in women with late luteal phase dysphoric disorder supports the hypothesis that alteration of central serotonergic systems may contribute to premenstrual dysphoric symptoms.

The effects of alprazolam on corticotropin-releasing factor neurons in the rat brain: acute time course, chronic treatment and abrupt withdrawal.

Considerable evidence indicates that corticotropin-releasing factor (CRF) is responsible for integrating not only the endocrine, but the autonomic and behavioral responses of an organism to stress. We have investigated the time course of action of the anxiolytic triazolobenzodiazepine, alprazolam, on the activity of the hypothalamic-pituitary-adrenal (HPA) axis and of CRF neurons after acute and chronic administration. In addition, because many of the signs and symptoms observed in animals and humans after abrupt discontinuation of benzodiazepines resemble the stress response, we examined the effect of alprazolam withdrawal on CRF neurons and HPA axis activity. Alprazolam decreases CRF concentrations in the locus coeruleus between 0.5 and 3.0 h following acute injection. The half-life of alprazolam in rats is less than 1 h in both plasma and brain. Similarly, chronic (14 days) alprazolam administration also results in decreased CRF concentrations in the locus coeruleus. CRF concentrations return to control values 24 h after abrupt withdrawal. Moreover, abrupt alprazolam withdrawal results in increased plasma adrenocorticotrophic hormone and corticosterone concentrations and decreased anterior pituitary CRF receptor concentrations 24 h after drug discontinuation. These indices return to control values by 48 h postwithdrawal. These results support the hypothesis that both acute and chronic alprazolam administration alters CRF-containing neurons innervating the locus coeruleus. Additionally, abrupt alprazolam withdrawal profoundly activates the HPA axis.

Platelet [3H]-imipramine binding and leukoencephalopathy in geriatric depression.

We examined the relationship between platelet [3H]-imipramine binding and leukoencephalopathy as assessed by 1.5 Tesla Magnetic Resonance Imaging (MRI) in 21 elderly depressed patients who satisfied DSM-III criteria for major depression. Both drug-free platelet [3H]-imipramine binding and brain MRI studies were obtained during the same episode of depression. Our findings show a significant inverse relationship between frequency of subcortical hyperintensity (SCH) and the number (Bmax) of platelet [3H]-imipramine binding sites. Patients with Bmax less than 850 fmol/mg protein had significantly larger SCH compared with patients with a higher Bmax. These data provide further support to the potential use of platelet [3H]-imipramine binding studies and brain MR imaging as diagnostic adjuncts in geriatric depression and suggest, moreover, that these two biological markers may be linked in geriatric patients with depression.

Alterations in the hypothalamic-pituitary-adrenal axis in a proposed animal model of depression with genetic muscarinic supersensitivity.

Rats from the Flinders Sensitive Line (FSL) and Flinders Resistant Line (FRL), which have been bred for differences in sensitivity to cholinergic agonists, were killed by decapitation under quiet, nonstressful conditions and the concentrations of corticotropin-releasing factor (CRF) in various brain regions, the concentrations of CRF receptors in the anterior pituitary, and plasma ACTH and corticosterone concentrations were determined. A first study revealed that the cholinergically hypersensitive FSL rats exhibited lower concentrations of CRF in the median eminence, locus ceruleus, and prefrontal cortex, but no such changes in some 13 other brain regions. In this first study, the FSL rats had significantly lower plasma ACTH concentrations. However, there were no differences in plasma corticosterone concentrations between the two groups. A second study confirmed the results of the first study and revealed that the density of anterior pituitary CRF receptor binding sites was elevated in the FSL rats. The observed pattern of alterations in these measures of HPA axis activity suggest that the cholinergically supersensitive FSL rats may possess diminished HPA activity.

The 5-hydroxytryptamine2 agonist, (+-)-1-(2,5-dimethoxy-4-bromophenyl)-2-aminopropane stimulates the hypothalamic-pituitary-adrenal (HPA) axis. I. Acute effects on HPA axis activity and corticotropin-releasing factor-containing neurons in the rat brain.

Corticotropin-releasing factor (CRF) is the major physiological regulator of adrenocorticotrophic hormone (ACTH) secretion from the anterior pituitary. In vivo and in vitro studies have suggested that hypothalamic CRF secretion is under stimulatory serotonergic control, although the receptor subtype(s) responsible have not been definitely determined. The acute effects of the 5-hydroxytryptamine2 agonist, (+-1-(2,5-dimethoxy-4-bromophenyl)-2-aminopropane (DOB), were examined on a number of biochemical indices of hypothalamic-pituitary-adrenal axis activity in vivo. DOB increased plasma ACTH and corticosterone concentrations at doses greater than 0.1 mg/kg. This effect is dose-dependent. Peak effects occurred 30 min postinjection and returned to basal levels by 4 hr after DOB injection. These effects of DOB are hypothesized to be mediated by the release of hypothalamic CRF because pretreatment with the CRF receptor antagonist (alpha-helical CRF9-41) significantly attenuated the ACTH response to DOB. Median eminence CRF content was also decreased following DOB administration in the presence of the protein synthesis inhibitor, cycloheximide (200 mg/kg i.p.), suggestive of release of CRF from median eminence terminals as a result of DOB activation of CRF neurons. DOB administration was without effect on brain CRF concentrations in all of the 12 extrahypothalamic brain regions studied 60 min after injection. These results, taken together, support a stimulatory role for 5-hydroxytryptamine2 receptors on hypothalamic CRF secretion.

The 5-hydroxytryptamine2 agonist, (+-)-1-(2,5-dimethoxy-4-bromophenyl)-2-aminopropane stimulates the hypothalamic-pituitary-adrenal (HPA) axis. II. Biochemical and physiological evidence for the development of tolerance after chronic administration.

In order to investigate the long term effects of the 5-hydroxytryptamine2 (5-HT2) receptor agonist, (+-)-1-(2,5-dimethoxy-4-bromophenyl)-2-aminopropane (DOB), on hypothalamic-pituitary-adrenal (HPA) axis activity, DOB (0.35 mg/kg/day) was administered via osmotic minipumps to rats for 7 days at which time plasma adrenocorticotrophic hormone (ACTH), corticosterone and regional brain corticotropin-releasing factor (CRF) concentrations were measured. In addition, anterior pituitary CRF and frontal cortical 5-HT2 receptor binding was measured. Seven-day infusion of DOB resulted in tolerance to the stimulatory actions of the drug on the HPA axis as evidenced by the return of plasma ACTH and corticosterone concentrations to base-line values. Moreover, rats treated chronically with DOB exhibited decreased numbers of both anterior pituitary CRF and cortical and hypothalamic 5-HT2 receptor. These receptor changes were physiologically significant as challenges doses of DOB or CRF resulted in blunted ACTH responses. Chronic DOB infusion was without effect on CRF concentrations in all hypothalamic and extrahypothalamic brain regions studied. A series of time course experiments revealed that DOB-induced increases in plasma corticosterone returned to base-line by 2-days postimplantation. This effect was apparently associated with down-regulation of the 5-HT2 receptor because high-affinity cortical [3H]DOB and hypothalamic (+-)-[125I]-1-(2,5-dimethoxy-4-iodophenyl)-2-amino-propane binding were decreased at this time as well. Although median eminence CRF content was unchanged at all time points, anterior pituitary CRF receptor binding was significantly decreased 7 days postimplantation.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevated plasma concentrations of alpha 1-acid glycoprotein, a putative endogenous inhibitor of the tritiated imipramine binding site, in depressed patients.

The plasma concentration of alpha 1-acid glycoprotein, a putative endogenous inhibitor of the site labeled by tritiated imipramine, was measured by a radial immunodiffusion assay in 36 normal human volunteers and 51 drug-free patients who fulfilled DSM-III criteria for major depression. The depressed patients exhibited a significant elevation in the plasma concentration (+/- SEM) of alpha 1-acid glycoprotein (79.6 +/- 4 mg/dL) when compared with the age- and sex-matched controls (61.7 +/- 3 mg/dL). Fourteen of the 51 patients with major depression had plasma alpha 1-acid glycoprotein concentrations that were higher than the highest values of the normal controls. There was no relationship between plasma alpha 1-acid glycoprotein concentrations and sex or affinity of platelet tritiated imipramine binding of either the normal volunteers or the depressed patients. In the depressed patients, there was a significant positive correlation between plasma concentrations of alpha 1-acid glycoprotein and postdexamethasone plasma cortisol concentrations, and two measures of depression severity, the Montgomery-Asberg Rating Scale for Depression and the Center for Epidemiologic Studies-Depression Scale, and a significant negative correlation with age. These data provide the first evidence of alterations of an endogenous inhibitor of the tritiated imipramine binding site/serotonin transporter in depressed patients.