A Transcriptome-Based Drug Discovery Paradigm for Neurodevelopmental Disorders

Advances in genetic discoveries have created substantial opportunities for precision medicine in neurodevelopmental disorders. Many of the genes implicated in these diseases encode proteins that regulate gene expression, such as chromatin-associated proteins, transcription factors, and RNA-binding proteins. The identification of targeted therapeutics for individuals carrying mutations in these genes remains a challenge, as the encoded proteins can theoretically regulate thousands of downstream targets in a considerable number of cell types. Here, we propose the application of a drug discovery approach originally developed for cancer called "transcriptome reversal" for these neurodevelopmental disorders. This approach attempts to identify compounds that reverse gene-expression signatures associated with disease states. ANN NEUROL 2021;89:199-211.

In Vitro and In Vivo Pipeline for Validation of Disease-Modifying Effects of Systems Biology-Derived Network Treatments for Traumatic Brain Injury-Lessons Learned

We developed a pipeline for the discovery of transcriptomics-derived disease-modifying therapies and used it to validate treatments in vitro and in vivo that could be repurposed for TBI treatment. Desmethylclomipramine, ionomycin, sirolimus and trimipramine, identified by in silico LINCS analysis as candidate treatments modulating the TBI-induced transcriptomics networks, were tested in neuron-BV2 microglial co-cultures, using tumour necrosis factor α as a monitoring biomarker for neuroinflammation, nitrite for nitric oxide-mediated neurotoxicity and microtubule associated protein 2-based immunostaining for neuronal survival. Based on (a) therapeutic time window in silico, (b) blood-brain barrier penetration and water solubility, (c) anti-inflammatory and neuroprotective effects in vitro (p < 0.05) and (d) target engagement of Nrf2 target genes (p < 0.05), desmethylclomipramine was validated in a lateral fluid-percussion model of TBI in rats. Despite the favourable in silico and in vitro outcomes, in vivo assessment of clomipramine, which metabolizes to desmethylclomipramine, failed to demonstrate favourable effects on motor and memory tests. In fact, clomipramine treatment worsened the composite neuroscore (p < 0.05). Weight loss (p < 0.05) and prolonged upregulation of plasma cytokines (p < 0.05) may have contributed to the worsened somatomotor outcome. Our pipeline provides a rational stepwise procedure for evaluating favourable and unfavourable effects of systems-biology discovered compounds that modulate post-TBI transcriptomics.

Shifts in metabolic parameters surrounding glucose homoeostasis resulting from tricyclic antidepressant therapy: implications of insulin resistance?

This study displayed the physiological effects the tricyclic antidepressants amitriptyline or trimipramine have on glucose homoeostasis in male Wistar rats. An insulin secreting cell line (INS-1) was also used to determine effects tricyclic antidepressants have on insulin secretion and insulin displacement. Thirty rats each received a 1 mg kg−1 dose of amitriptyline or trimipramine for a period of 14 weeks; another 14 rats served as the control group. Blood glucose, serum insulin and muscle and liver glycogen levels were determined. Kidney, liver and muscle insulin degradation was measured and compared with insulin degrading enzyme concentrations in the latter two tissues. INS-1 cells were used to determine the effect 1μM amitriptyline has on insulin secretion. Displacement studies for [3H]glibenclamide by amitriptyline or trimipramine were undertaken on INS-1 cells. A significant increase in blood glucose (P &lt; 0.01) was found for both test groups after 6 and 14 weeks of receiving the medication, which may be related to a significant decrease in liver and muscle glycogen levels (P &lt; 0.001). Serum insulin levels remained unchanged, although a significant increase in insulin degradation was observed in the muscle, liver and kidney, which may be related to a significant increase in insulin degrading enzyme (P &lt; 0.001) that was found. A significant increase in insulin secretion was observed for the INS-1 cells treated with amitriptyline, although no significant displacement for the [3H]glibenclamide was evident for amitriptyline or trimipramine. The significant alterations in glucose homoeostasis observed, as well as the significant changes associated with insulin secretion and degradation associated with amitriptyline or trimipramine treatment, imply that prolonged use of these medicines may lead to insulin resistance and full blown diabetes.

Receptor occupancy of mirtazapine determined by PET in healthy volunteers

RATIONALE

Molecular tools are needed for assessing anti-depressant actions by positron emission tomography (PET) in the living human brain.

OBJECTIVES

This study determined whether [(11)C]mirtazapine is an appropriate molecular tool for use with PET to estimate the magnitude of neuroreceptor occupancy produced by daily intake of mirtazapine.

METHODS

This study used a randomised, double-blind, placebo-controlled, parallel-group, within-subject design. Eighteen healthy volunteers were PET-scanned twice with [(11)C]mirtazapine; once under baseline condition and again after receiving either placebo or mirtazapine (7.5 or 15 mg) for 5 days. We determined kinetic parameters of [(11)C]mirtazapine in brain regions by the simplified reference region method and used binding potential values to calculate receptor occupancy produced by mirtazapine.

RESULTS

Serum concentrations of mirtazapine ranged from 33 to 56 nmol/l after five daily doses of 7.5 mg mirtazapine and were between 41 and 74 nmol/l after 15 mg mirtazapine. Placebo treatment failed to alter the binding potential of [(11)C]mirtazapine from baseline values, whereas daily intake of mirtazapine markedly decreased the binding potential in cortex, amygdala and hippocampus. Receptor occupancy ranged from 74 to 96% in high-binding regions of the brain after five daily doses of 7.5 mg or 15 mg mirtazapine, whereas 17-48% occupancy occurred in low-binding regions.

CONCLUSIONS

[(11)C]Mirtazapine together with PET can determine the degree of receptor occupancy produced by daily doses of mirtazapine in regions of the living human brain.

The involvement of endogenous opioid mechanisms in the antinociceptive effects induced by antidepressant drugs, desipramine and trimipramine

The present study was designed to investigate the involvement of endogenous opioid systems in the antinociception induced by the antidepressant drugs, desipramine and trimipramine. For this purpose, the antinociceptive effects of desipramine (7.5 and 15.0 mg/kg i.p.) and trimipramine (5.0 and 10.0 mg/kg i.p.) were compared to that induced by morphine (0.2 and 2.0 mg/kg i.p.) in the tail-clip model in mice. Naloxone (0.3 and 3.0 mg/kg i.p.), a non-specific opioid receptor antagonist, inhibited morphine-induced antinociception in mice, whereas the antinociceptive effects of antidepressant drugs were found to be resistant to naloxone blockade to some extent, since only the higher concentration of naloxone (3.0 mg/kg i.p.) caused significant inhibition of the effects of antidepressant drugs. In contrast, naltrindole (1.0 mg/kg i.p.), a specific delta-receptor antagonist, inhibited antinociception induced by desipramine and trimipramine in this test, while it inhibited the antinociceptive effect of morphine only partly. None of the opioid antagonists produced a significant effect in the tail-clip experiment when they were injected alone. Based on these findings, we concluded that endogenous opioids are involved in the antinociceptive effects of the antidepressant drugs using different mechanisms.

Trimipramine in primary insomnia: results of a polysomnographic double-blind controlled study

In recent years, sedating antidepressants have been increasingly used to treat primary insomnia. Up to now, only one open pilot study with trimipramine and one double-blind placebo-controlled study with doxepin have provided scientific support for this approach in treating primary insomnia. In order to test the hypothesis that sedating antidepressants are useful in the treatment of primary insomnia, the effect of trimipramine on objectively and subjectively measured parameters of sleep was investigated in a double-blind placebo- and lormetazepam-controlled study in a sample of 55 patients with primary insomnia attending outpatient sleep-disorder clinics. Trimipramine was selected since it has shown positive effects on sleep continuity with a lack of REM sleep suppression in studies on depressed patients and in one pilot study on patients with primary insomnia. Trimipramine at an average dose of 100 mg over a period of 4 weeks significantly enhanced sleep efficiency, but not total sleep time (which had been the primary target variable) compared to placebo as measured by polysomnography. Changes in objective sleep parameters were paralleled by changes in subjective sleep parameters. Trimipramine did not suppress REM sleep. Lormetazepam decreased wake time and sleep stage 3 and increased REM sleep compared to placebo. After switching trimipramine to placebo, sleep parameters returned to baseline. There was no evidence of any rebound effect from trimipramine. Side effects from trimipramine were only marginal. This first double-blind placebo-controlled study with trimipramine suggests its efficacy in the treatment of primary insomnia. However, due to the large intra- and interindividual variance in the parameters of interest before and during treatment a larger sample size would have been necessary to strengthen the validity of our findings.

Effects of the atypical antidepressant trimipramine on neuronal excitability and long-term potentiation in guinea pig hippocampal slices

Acute effects of the atypical tricyclic antidepressant (TCA) trimipramine on long-term potentiation (LTP) were investigated in this study. Electrically evoked population spikes (PS) were tested under the influence of trimipramine in the CA1 region of the hippocampus. A concentration of 10 microM trimipramine reduced PS amplitudes to 85.1 +/- 8.8%. They were reduced to 12.2 +/- 8.5% with 50 microM trimipramine. In experiments with LTP, trimipramine 10 microM was applied. Only 8 of 10 tested slices showed LTP. These potentiations were smaller than in the control experiments. LTP could not be induced with 50 microM trimipramine. In conclusion, the influence of trimipramine on LTP is similar to other TCA. It is contended that this contributes to the antidepressant effect of the drug.

Effects of chronic antidepressant treatments on 5-HT and NA transporters in rat brain: an autoradiographic study

Tricyclic antidepressants and serotonin (5-HT) uptake inhibitors rapidly block uptake sites, or transporters; however, their therapeutic effects are only seen after 2-3 weeks of treatment. Thus, direct blockade of 5-HT and noradrenaline (NA) transporters cannot account entirely for their clinical efficacy, and other long-term changes may be involved. Adult Sprague-Dawley rats were treated for 21 days with daily injections of either desipramine, trimipramine, fluoxetine, or venlafaxine; a fifth group that was used as a control, received daily saline injections. Identified cortical areas, hippocampal divisions and nuclei raphe dorsalis, raphe medialis and locus coeruleus were examined by quantitative autoradiography using either [3H]citalopram to label 5-HT transporters, or [3H]nisoxetine for NA uptake sites. Increases in [3H]nisoxetine binding were found in the cingulate, frontal, parietal, agranular insular, entorhinal and perirhinal cortices as well as in the hippocampal divisions CA1, CA3, dentate gyrus and subiculum, and in nucleus raphe dorsalis of trimipramine-treated animals compared to the control rats. Also, densities of NA transporters decreased in temporal cortex, CA2 and nucleus raphe dorsalis in fluoxetine-treated rats as compared to the controls. Also, there was a decrease in NA transporters in the locus coeruleus of the desipramine-treated animals as compared to the densities measured in the control group. Chronic treatment with desipramine or trimipramine, which do not directly inhibit 5-HT uptake, compared to fluoxetine and venlafaxine, lead to increases in 5-HT transporter densities in cingulate, agranular insular and perirhinal cortices. The present study shows differential region-specific effects of antidepressants on 5-HT and NA transporters, leading to distinct consequences in forebrain areas.

Clomipramine and related structures as inhibitors of the skeletal sarcoplasmic reticulum Ca2+ pump

The Ca2+-pumping activity of skeletal sarcoplasmic reticulum vesicles is half-maximally inhibited by 120 microM clomipramine, 250 microM desipramine, and 500 microM imipramine or trimipramine. The inhibition is attributed to the dihydrodibenzazepine moiety, since 3-(dimethylamino)propionitrile, reproducing the aliphatic amine chain, has no inhibitory action. The inhibition is shown as a marked decrease of Ca2+ binding at equilibrium in the absence of ATP and as a reduction of phosphorylation of the Ca2+-free conformation by inorganic phosphate. Therefore, the drug effect is consistent with preferential interaction of tricyclic antidepressants with the Ca2+-free conformation of the nonphosphorylated enzyme. An additional decrease in the apparent rate constant of enzyme dephosphorylation, i.e., in the release of phosphate from ATP during enzyme cycling was also noticed.

Trimipramine fails to exert antimanic efficacy: a case of the discrepancy between in vitro rationale and clinical efficacy

Standard mood stabilizers, such as lithium and haloperidol, and anticonvulsants show effectiveness in a maximum of 60%-70% of acutely manic patients. Obviously, there is a clinical need to evaluate other treatment options. Current pathophysiologic concepts suggest that substances with an ameliorating effect on dopaminergic hyperfunction, serotonergic hypofunction, or GABAergic hypofunction might be useful, as may be substances with calcium-antagonistic effects. In vitro, the antidepressant trimipramine exerts dopamine- and calcium-antagonistic properties. Therefore, we conducted an open trial to screen it for antimanic action. We found no clinical benefit in four acutely manic patients receiving up to 400 mg/d of trimipramine. It is concluded that, at least in the case of trimipramine, the pharmacologic profile is not helpful in predicting potential effectiveness in mania.

Effects of the atypical antidepressant trimipramine on field potentials in the low Mg2+-model in guinea pig hippocampal slices

Trimipramine has been classified as an atypical tricyclic antidepressant, because only weak inhibitory effects on serotonin and/or noradrenaline reuptake have been found. Since some antidepressive drugs (e.g. imipramine) and other agents used in the treatment of affective disorders (e.g. carbamazepine) modulate neuronal calcium channels, trimipramine was tested on field potential changes (fp) in the low Mg2+-model of epilepsy which has been shown to be affected by calcium antagonists. Trimipramine reduced the frequency of occurrence of fp in a dose dependent manner (5-100 microM). The threshold concentration of trimipramine which did not decrease the firing rate was approximately 1 microM. Simultaneous application of subthreshold concentrations (2 microM) of the organic calcium antagonist verapamil with trimipramine decreased the firing rate to 37.0+/-22.7% (means+/-SEM, n=7) with respect to baseline values. In contrast, no additive effects of N-methyl-D-aspartate antagonists and trimipramine were observed. In conclusion, the data suggests that the antidepressive effects observed with trimipramine treatment may be due to its inhibitory action on neuronal calcium channels.

Repeated trimipramine induces dopamine D2/D3 and alpha1-adrenergic up-regulation

Trimipramine (TRI), which shows a clinical antidepressant activity, is chemically related to imipramine but does not inhibit the reuptake of noradrenaline and 5-hydroxytryptamine, nor does it induce beta-adrenergic down-regulation. The mechanism of its antidepressant activity is still unknown. The aim of the present study was to find out whether TRI given repeatedly was able to induce adaptive changes in the dopaminergic and alpha1-adrenergic systems, demonstrated by us previously for various antidepressants. TRI was given to male Wistar rats and male Albino Swiss mice perorally twice daily for 14 days. In the acute experiment TRI (given i.p.) does not antagonize the reserpine hypothermia in mice and does not potentiate the 5-hydroxytryptophan head twitches in rats. TRI given repeatedly to rats increases the locomotor hyperactivity induced by d-amphetamine, quinpirole and (+)-7-hydroxy-dipropyloaminotetralin (dopamine D2 and D3 effects). The stereotypies induced by d-amphetamine or apomorphine are not potentiated by TRI. It increases the behaviour stimulation evoked by phenylephrine (given intraventricularly) in rats, evaluated in the open field test as well as the aggressiveness evoked by clonidine in mice, both these effects being mediated by an alpha1-adrenergic receptor. It may be concluded that, like other tricyclic antidepressants studied previously, TRI given repeatedly increases the responsiveness of brain dopamine D2 and D3 (locomotor activity but not stereotypy) as well as alpha1-adrenergic receptors to their agonists. A question arises whether the reuptake inhibition is of any importance to the adaptive changes induced by repeated antidepressants, suggested to be responsible for the antidepressant activity.

Clozapine in bipolar disorder: treatment implications for other atypical antipsychotics

Traditional neuroleptics are often utilized clinically for the management of bipolar disorder. Although effective as antimanic agents, their mood stabilizing properties are less clear. Additionally, their acute clinical side effect profile and long term risk of tardive dyskinesia, particularly in mood disorder patients, portend significant liability. This review focuses on the use of atypical antipsychotics in the treatment of bipolar disorder focusing on clozapine as the prototypical agent. Although, preclinical research and clinical experience suggest that the atypical antipsychotics are distinctly different from typical antipsychotics, they themselves are heterogeneous in profiles of neuropharmacology, clinical efficacy, and tolerability. The early clinical experience of clozapine as a potential mood stabilizer suggests greater antimanic than antidepressant properties. Conversely, very preliminary clinical experience with risperidone suggests greater antidepressant than antimanic properties and some liability for triggering or exacerbating mania. Olanzapine and sertindole are under investigation in psychotic mood disorders. The foregoing agents and future drugs with atypical neuroleptic properties should come to play an increasingly important role, compared to the older classical neuroleptics, in the acute and long term management of bipolar disorder.

Selective activation of postsynaptic 5-HT1A receptors induces rapid antidepressant response

It has been reported that the 5-HT1A autoreceptor antagonist pindolol can accelerate the antidepressant response to the selective serotonin (5-HT) reuptake inhibitor (SSRI) paroxetine, presumably by preventing the initial decrease in firing activity of 5-HT neurons produced by the SSRI. The present study was aimed at further exploring this treatment strategy in three groups of 10 patients with unipolar major depression allocated sequentially to three treatment arms for 28 days. The administration of the selective 5-HT1A agonist buspirone (20 mg/day for 1 week and 30 mg/day thereafter) with pindolol (2.5 mg TID) was used to activate selectively postsynaptic 5-HT1A receptors. This combination produced a greater than 50% reduction of depressive symptoms in the first week in 8 of 10 patients and the response was sustained for the remainder of the trial. In contrast, the combination of tricyclic antidepressant drugs devoid of effect on the 5-HT reuptake process (desipramine or trimipramine, 75 mg/day for 1 week and 150 mg/day thereafter) with pindolol resulted in only one of ten patients achieving a 50% improvement after 28 days. The combination of the SSRI fluvoxamine (50 mg/day for 1 week and 100 mg/day thereafter) with pindolol produced a marked antidepressant effect but did not act as rapidly as the buspirone plus pindolol combination with none, four, and eight patients achieving a 50% amelioration after 7, 14, and 21 days of treatment, respectively. These results provide further evidence that pindolol may accelerate the antidepressant effect of drugs that alter the function of the 5-HT neurons and that the selective activation of postsynaptic 5-HT1A receptors may induce a rapid and robust antidepressant response.

Male reproductive systems under chronic fluoxetine or trimipramine treatment

Adult male Long-Evans rats (n = 9 per group) received daily exposure for 4 weeks to fluoxetine (0.75 mg FLUOX/kg body weight) or trimipramine (1.6 mg TRIMI/kg body weight). Separate tests of copulation, sexual motivation, and intermale aggressive behaviors were used to evaluate functional changes during chronic exposure to either typical or atypical antidepressant drugs with more or less serotonin specificity. Circulating hormones, primary and secondary sex structures, and concentrations of dopamine (DA) and serotonin (5-HT) from mesolimbic tissue were assessed at necropsy. Results of tests with estrous females and untreated males revealed progressive disruption to sexual performance and aggressive responsiveness over time of treatment with TRIMI and, to a lesser extent, with FLUOX. By contrast, motivation, testosterone, and all measures of reproductive physiology were indistinguishable from controls. Ratios of transmitter metabolites relative to the parent compounds indicated similar reductions of 5-HT turnover with FLUOX and TRIMI. However, influences on DA turnover were significantly less with FLUOX than with TRIMI. Conclusions are that long-term intervention with antidepressant drugs may disrupt sociosexual exchanges without compromising male rats' interest in sexual contact or integrity of their reproductive physiology. Lessened disruption of sociosexual behaviors with this regimen of chronic FLUOX treatment may be related to the greater selectivity on serotonin relative to dopamine turnover.

Inhibition of lysosomal acid sphingomyelinase by agents which reverse multidrug resistance

An increasing body of evidence appears to implicate the lipid bilayer of multidrug resistant (MDR) cells with P-glycoprotein activity. Several cationic amphiphilic drugs (CADs) have been extensively described as modulators of MDR. These same agents are also known to (1) inhibit lysosomal acid sphingomyelinase (ASmase), a phospholipid degrading enzyme, and/or (2) induce phospholipidosis in animal tissues or cultured cell lines. In this report, we randomly selected 17 CADs and evaluated their potency in modulating MDR in the murine MDR P388/ADR leukemia cell line. We compared these results with their ability to inhibit ASmase and observed a significant dose-dependent linear relationship (95% central confidence interval), between ASmase inhibition and MDR reversal. This approach permitted us to identify three new modestly potent chemosensitizers: trimipramine, desipramine, and mianserine. Modulation of MDR was not cell line specific, since CADs at 10 microM increased doxorubicin (DOX) and vinblastine (VBL) (but not methotrexate, MTX) cytotoxicity in both P388/ADR and the human MDR cell lines MES-SA/Dx5 and K562/R7, but not in the parental drug-sensitive cells. Although all chemosensitizing CADs at 10 microM significantly increased Rhodamine-123 (Rho-123) accumulation in the human leukemia MDR cell line K562/R7 and most presented significant displacement of the photoaffinity labelling probe iodoarylazidoprazosin, no correlation between these observations and the ability of CADs to sensitize MDR cells to DOX and VBL was found. In conclusion, our study strongly suggests that the chemosensitizing potency of agents such as CADs may be due to a dual mechanism of action: direct antagonism of P-gp activity and indirect modulation of P-gp activity through the disruption of cellular lipid metabolism.

Effect of long-term administration of antidepressant drugs on the 5-HT3 receptors that enhance the electrically evoked release of [3H]noradrenaline in the rat hippocampus

The present study investigated the effects of various classes of antidepressant drugs (10 mg/kg per day, s.c. during 21 days) on the electrically evoked release of [3H]noradrenaline and on its modulation by the 5-HT3 receptor agonist 2-methyl-5-hydroxy-tryptamine (2-methyl-5-HT) using preloaded rat hippocampal slices. Treatments with either fluoxetine, a selective serotonin (5-HT) reuptake inhibitor, or moclobemide, a reversible type A monoamine oxidase inhibitor, increased the evoked release of [3H]noradrenaline. These two antidepressant treatments did not change, however, the magnitude of the enhancing effect of 2-methyl-5-HT on the electrically evoked release of [3H]noradrenaline. Desipramine produced a much larger increase of the electrically evoked release of [3H]noradrenaline than fluoxetine or moclobemide, and desensitized the 5-HT3 receptors that modulate this release. Trimipramine, which like desipramine has a tricyclic structure but does not block the reuptake of noradrenaline or that of 5-HT, did not increase the evoked release of [3H]noradrenaline and did not desensitize the 5-HT3 receptors that enhance the release of [3H]noradrenaline. Maprotiline, a selective noradrenaline reuptake inhibitor, did not produce the same changes as desipramine, but maprotiline inhibited noradrenaline reuptake to a lesser extent (50%) than desipramine (80%). These results suggest that the high potency noradrenaline reuptake blocker desipramine desensitizes 5-HT3 receptors modulating [3H]noradrenaline release, but that this effect is not common to all antidepressant drugs.

Modulation of the AMPA receptor by phospholipase A2: effect of the antidepressant trimipramine

Previous results have shown that chronic administration of the antidepressant trimipramine prevents the formation of long-term potentiation in the rat hippocampus. In the present study, we compared the effects of chronic administration of trimipramine on the binding properties of hippocampal glutamate receptors and on the modulation of the DL-alpha-amino-3-hydroxy-5- methyl-isoxazolpropionic acid (AMPA) receptors by phospholipase A2 (PLA2). Whereas the binding characteristics of various agonist and antagonist ligands to the N-methyl-D-aspartate and the AMPA receptors were not modified by trimipramine treatment, there was a significant reduction in the increase in 3H-AMPA binding elicited by PLA2 treatment. Since activation of PLA2 has been reported to play a critical role in the formation of long-term potentiation, possibly mediated through a modification of the AMPA receptors, the results strengthen the hypothesis that PLA2-induced modification of 3H-AMPA binding is an important component of synaptic plasticity.

A comparison of the cardiac safety and therapeutic efficacy of trimipramine versus doxepin in geriatric depressed patients

OBJECTIVE

To compare the cardiac safety and therapeutic efficacy of trimipramine and doxepin.

DESIGN

A 1-week single-blind placebo period followed by a 5-week randomized double-blind parallel group clinical trial.

SETTING

Psychiatric out-patient clinic of a general hospital.

PATIENTS

37 young-elderly patients with a diagnosis of Major Depressive Episode (DSM-III criteria).

INTERVENTIONS

Placebo for 1 week, 2 weeks of titration with either drug in the dosage range of 75 mg/day up to a maximum of 200 mg/day.

MEASUREMENTS

We measured the psychiatric effects with the Hamilton Rating Scale for Depression, the Hamilton Anxiety Rating Scale, and the Clinical Global Impression Scale. Cardiovascular effects were assessed on 12-lead standard electrocardiograms plus 1-minute rhythm and high speed recordings; orthostatic (lying/standing) blood pressures were also taken. Physical exams, lab tests, cognitive functions (Buschke Selective Reminding Test, Hierarchic Dementia Scale, Word Fluency) and adverse reactions were also noted.

RESULTS

Both drugs were equally effective in relieving symptoms of depression and anxiety. The cardiovascular effects of both drugs were minimal. Trimipramine did lower blood pressure but this was without clinical significance. Three trimipramine patients and five doxepin patients developed occasional premature ventricular or atrial contractions. Of these, two trimipramine patients and one doxepin patient were among those with abnormal ECG's at entry. The doxepin patient was withdrawn from the study after 21 days of treatment when the PVC's became increasingly frequent.

CONCLUSIONS

Trimipramine and doxepin are equally safe and effective antidepressants in the young-elderly.

[3H]paroxetine binding and serotonin content of rat brain: absence of changes following antidepressant treatments

The high affinity binding of [3H]paroxetine was measured in rat cerebral cortex following chronic treatment (21 days) with imipramine (5 mg/kg), trimipramine (5 mg/kg) and fluoxetine (2 mg/kg), in adult (3-4 months) or neonatal (7 days of age) rats. Tissue concentrations of serotonin and of its metabolite 5-hydroxyindole-3-acetic acid were also determined by high-performance liquid chromatography in cingulate cerebral cortex, rostral neostriatum, hippocampus and midbrain raphe nucleus region. No differences were found in any of the parameters of [3H]paroxetine binding after antidepressant administration, in either adult or neonatal animals. In addition, endogenous serotonin and 5-hydroxyindole-3-acetic acid levels were not different from control values in any of the regions examined. The present study shows that the serotonin uptake recognition site is resilient to changes after chronic treatment with therapeutic doses of antidepressants, and emphasizes the potential usefulness of uptake site ligands as markers to quantify innervation densities within the brain.

Chronic effects of trimipramine, an antidepressant, on hippocampal synaptic plasticity

The effects of trimipramine (TRIM), an antidepressant agent, on both the induction and the maintenance of long-term potentiation (LTP) was investigated in area CA1 of hippocampal slice preparations. Chronic administration (7-9 days) of TRIM in rat caused a large reduction in the magnitude of LTP induced by a theta burst stimulation (TBS) paradigm. Results indicate that the reduction of LTP produced by trimipramine does not seem to result from major changes in the physiological properties of the slice preparations. First, paired-pulse facilitation was not impaired following the drug administration suggesting that transmitter release was not modified in TRIM-treated slices. Second, the burst responses evoked by high-frequency stimulation exhibited the typical buildup of depolarization, which is due to both a reduction of IPSPs and the activation of NMDA receptors. Finally, the treatment did not change the amount of short-term potentiation induced by TBS nor did it modify the component of excitatory postsynaptic potentials (EPSPs) mediated by the activation of NMDA receptors, suggesting that the NMDA receptor functions remained intact in TRIM-treated slices. Taken together the present data suggest that the loss of LTP maintenance in TRIM-treated animals is more likely the result of the disruption by trimipramine of cellular processes that follow LTP induction. In addition, the results provide evidence for a possible correlation between the reduction in LTP expression and learning deficits produced by chronic administration of trimipramine.

Lysosomal glycosphingolipid storage in chloroquine-induced alpha-galactosidase-deficient human endothelial cells with transformation by simian virus 40: in vitro model of Fabry disease

Human umbilical venous endothelial cells were transformed with a temperature-sensitive mutant of simian virus 40, tsA640, and a cell line, subcultured for over 20 serial passages, was established at a temperature permissive for the virus. Treatment of transformed endothelium with 3 micrograms/ml chloroquine caused a specific reduction of alpha-galactosidase activity, without cell injury, and revealed several electron-dense materials surrounded by single unit membranes. Crystalline lamellae in lysosomes with a periodicity of 6.5 nm, which are typically seen in various tissues in Fabry disease, were produced in the presence of a glycosphingolipid mixture. These cells should be useful for in vitro pathophysiological studies on Fabry endothelium.

Effect of some stereoisomeric tricyclic antidepressants on 45Ca uptake in synaptosomes from rat hippocampus

The present study has examined the inhibition of synaptosomal 45calcium uptake by trimipramine, oxaprotiline and doxepin, and their stereoisomers, in synaptosomes from the rat hippocampus. No significant difference in potency could be established for inhibition of net depolarization-induced 45calcium uptake for any pair of antipodes, and the IC50 values for calcium channel blockade were in the vicinity of 30 microM for this group of compounds. Trimipramine, doxepin and oxaprotiline also inhibited the 45calcium uptake mediated by Na(+)-Ca2+ exchange, with IC50 values of 71 microM, 110 microM, and 100 microM, respectively. The similar potency of doxepin isomers for inhibition of voltage-dependent calcium channels is in harmony with their reported similar potency in the clinic. A slight difference in potency is reported between the isomers of oxaprotiline in the behavioral despair test in rats, and the dextrorotatory isomer of trimipramine is reported to be a much more potent antidepressant than the levorotatory isomer: these order of potencies do not correspond perfectly with the similar potency of the antipodes against voltage-dependent calcium channels. The present study of stereoisomeric tricyclic antidepressants therefore fails to provide unequivocal support for the hypothesis that calcium channel blockade by tricyclic antidepressants is involved in their therapeutic effect.

Effect of trimipramine on depolarization-induced and Na(+)-Ca2+ exchange-induced 45calcium uptake in synaptosomes from the cortex of the rat brain

The present study examined the inhibition of synaptosomal uptake of 45calcium by racemic trimipramine and nortrimipramine and by enantiomers of trimipramine. Trimipramine, nortrimipramine, (+)-trimipramine and (-)-trimipramine inhibited the net K(+)-induced uptake of 45calcium with IC50 values of 31, 39, 17 and 95 microM, respectively. No significant difference could be detected between the parent compound trimipramine and the metabolite nortrimipramine; however, the levorotatory isomer had an IC50 value significantly larger than the dextrorotatory isomer. At normal therapeutic doses, a 25-40% inhibition of net K(+)-induced uptake of 45calcium, could be expected with trimipramine or 30-50% inhibition for trimipramine and nortrimipramine combined; these data, therefore, do not exclude the possibility that inhibition of voltage-dependent calcium channels could contribute to the therapeutic effect of trimipramine. The order of potency of stereoisomers of trimipramine, for inhibition of calcium channels, was the same as their reported order of potency in the clinic; this parallelism adds support to the possible involvement of blockade of calcium channels in the antidepressant effect. With respect to uptake of 45calcium induced by the Na(+)-Ca2+ exchange process, all drugs inhibited this mechanism with a similar potency (IC50 74-91 microM); the drugs are not expected to have a significant effect on this exchange process, at therapeutic antidepressant doses.

Trimipramine: pharmacological reevaluation and comparison with clozapine

Trimipramine has been reported to differ from other typical tricyclic antidepressant drugs in several aspects, for instance it does not inhibit neuronal transmitter uptake and does not cause down-regulation of beta-adrenoceptors. Moreover, it may possess antipsychotic activity in schizophrenic patients. In the present investigation it was found that trimipramine did not alter the electrically-induced release of [3H]noradrenaline and [3H]5-hydroxytryptamine, from slices of the cerebral cortex of the rat, in concentrations of less than 1 microM. It did not antagonize the inhibitory effect of noradrenaline and 5-hydroxytryptamine on the release of transmitter, mediated by presynaptic autoreceptors. In radioligand binding studies, D,L-trimipramine showed fairly high affinities (KI 10-60 nM) for some dopamine (DA), noradrenaline and 5-hydroxytryptamine (5-HT) receptor subtypes (5-HT2 receptors = alpha 1A/B-adrenoceptors greater than or equal to D2 receptors), intermediate affinities (300-550 nM) for D1 receptors, alpha 2B-adrenoceptors and 5-HT1C receptors but only low affinities (greater than 1000 nM) for alpha 2A-adrenoceptors, 5-HT1A, 5-HT1D and 5-HT3 receptors. It may thus be classified as an atypical neuroleptic drug. Especially, its affinities for dopamine receptors, alpha 1-adrenoceptors and 5-HT2 receptors closely resembled the values measured for clozapine. The L-enantiomer of trimipramine showed higher affinities for these binding sites than D-trimipramine. The present findings may explain the mechanism of the potential antipsychotic action but not the antidepressant effect of trimipramine.

Effects of diazepam and Ro 15-1788 on duodenal bicarbonate secretion in the rat

Bicarbonate secretion by duodenal mucosa just distal to the Brunner's glands area and devoid of pancreatic secretions was titrated in situ in anesthetized rats. Intravenous injection of diazepam (0.1 and 0.5 mg/kg) significantly increased the secretion; this stimulation was abolished by proximal bilateral vagotomy. Ro 15-1788, a benzodiazepine antagonist that also has well-known intrinsic activity, caused similar stimulation of the secretion when administered IV (0.01 and 0.1 mg/kg). Intracerebroventricular infusion of Ro 15-1788 (10 micrograms/h) resulted in a greater increase in secretion; again, this stimulation was prevented by vagotomy. Adrenoceptor blockade by phentolamine increased basal alkaline secretion but did not affect the stimulation by diazepam. The tricyclic antidepressant trimipramine (2.5 mg/kg IV) did not affect the duodenal bicarbonate secretion. For comparison, effects of diazepam and Ro 15-1788 (10(-6)-10(-4) mol/L) were also tested in isolated bullfrog duodenal mucosa. Neither drug effected the alkaline secretion in vitro. The combined results strongly suggest that benzodiazepines, as previously shown for certain brain peptides, influence the central nervous control of duodenal mucosal alkaline secretion and that their stimulation of secretion is vagally mediated. This action benzodiazepines might be used in modulating mucosal protection against acid.

Increased deep sleep after trazodone use: a double-blind placebo-controlled study in healthy young adults

The effects of trazodone on sleep were compared with those of placebo and the sedating tricyclic antidepressant trimipramine in a double-blind crossover study in six healthy young men. Only trazodone significantly increased deep sleep without otherwise altering the normal architecture of sleep. The alpha-adrenergic receptor-blocking property of trazodone and a relative lack of noradrenergic reuptake blocking and the lack of anticholinergic effects are hypothesized to be responsible for the effects on sleep.

Effect of trimipramine, an atypical tricyclic antidepressant, on the activities of various enzymes involved in the metabolism of biogenic amines

1. The mechanism of action of trimipramine, a clinically efficacious tricyclic antidepressant, is not well understood. In order to investigate whether it might affect the activities of different enzymes involved in biogenic amine metabolism we have undertaken a comparative study of it along with amitriptyline. 2. Neither trimipramine nor amitriptyline, at concentrations up to 1 mM, exhibited any significant effect on phenylalanine hydroxylase, tyrosine hydroxylase, L-aromatic amino acid decarboxylase, dopamine-beta-hydroxylase, phenylethanolamine-N-methyltransferase, catechol-O-methyltransferase, phenylsulfotransferase or tyrosine aminotransferase. 3. Monoamine oxidase, however, was inhibited by both drugs with the greatest effect being on MAO-B. The inhibition was reversible, non-competitive and relatively weak.

The effects of chronic trimipramine treatment on biogenic amine metabolism and on dopamine D2, 5-HT2 and tryptamine binding sites in rat brain

1. Two week chronic administration of trimipramine increased the brain concentration and metabolism of dopamine and 5-hydroxytryptamine. 2. The treatment also produced a reduction in dopamine D2 and 5-hydroxytryptamine 5-HT2 receptors but no change in tryptamine binding was observed. 3. These findings suggest that trimipramine induces adaptive changes in dopamine and 5-hydroxytryptamine neurotransmission.

Effects of scopolamine, trimipramine and diazepam on explicit memory and repetition priming in healthy volunteers

The effects of scopolamine, an anticholinergic drug, of trimipramine, a tricyclic antidepressant with both anticholinergic and sedative properties, of diazepam and a placebo, on explicit memory and repetition priming were assessed using a free-recall task and a word-stem completion task. Forty-eight healthy volunteers took part in this double-blind study. Diazepam provoked a dissociation between free recall, which was profoundly impaired, and word completion, which was spared. No significant changes in memory performances were observed in the scopolamine group; however, a significant correlation between explicit and implicit memory performances was observed in this group. At the low dose used, the effects of trimipramine on memory were mild. The results suggest that the cholinergic system is involved in the priming effect.

Effects of antidepressant drugs on inositol phospholipid hydrolysis in rat cerebral cortical slices

The effects of several different types of antidepressant drugs on phosphoinositide hydrolysis by slices of rat cerebral cortex was investigated by prelabeling inositol phospholipids with [3H]inositol and then measuring the formation of [3H]inositol phosphates (a total fraction consisting of the mono- and poly-phosphates was collected) in the presence of 10 mM LiCl. All of the drugs tested (amitriptyline, trimipramine, mianserin, desipramine, tranylcypromine, and citalopram) inhibited NE-stimulated [3H]inositol phosphate formation. This inhibition appeared to be due to antagonism of alpha 1-receptors. In addition to inhibiting the effects of NE, the tricyclic antidepressants themselves were able to stimulate [3H]inositol phosphate formation. This stimulation occurred at drug concentrations higher than that needed to inhibit stimulation by NE. Stimulatory effects of the antidepressants themselves were not blocked by the alpha 1-antagonist, prazosin. An examination of the types of inositol phosphates formed revealed that formation of inositol monophosphate was stimulated, but that inositol biphosphate production was decreased by tricyclic antidepressants compared to control.

Effects of antidepressants on alcohol-induced gastric mucosal injury in rats

The purpose of the present report is to study the effects of antidepressants such as trimipramine, amitriptyline, maprotiline and mianserin on severe gastric mucosal lesions produced by ethanol in comparison with cimetidine (H2-antihistamine) and dexchlorepheniramine (H2-antihistamine). The percentage of macroscopic mucosal lesions caused by alcohol affects 15% of the mucosal area. But pretreated with cimetidine the affected area was 9.18%, with dexchlorepheniramine 5.01%, with trimipramine 14.46%, with amitripytline 7.94%, with maprotiline 3.8%, and with mianserin 4.07%. Microscopic evaluation reveals that ethanol produces destruction of glandular cells and injures medial and basal layers. All drugs used previously to ethanol produce a decrease of microscopical lesions. A direct relation was found between micro and macroscopical lesions in rats treated with maprotiline, mianserin and dexchlorepheniramine.

Trimipramine and other antipsychotics inhibit Campylobacter pylori in vitro

A series of conventional anti-ulcer drugs, tricyclic antidepressants and neuroleptics (and some CNS non-active isomers) were tested in vitro for possible inhibition of Campylobacter pylori. These bacteria are claimed to play an etiological role in peptic ulcer disease, at least in gastritis B. While cimetidine, famotidine, ranitidine and pirenzepine were inactive, all the antipsychotic agents and their isomeric derivatives were active to various degrees with IC50 of 26-59 microM. Of special interest is trimipramine (Surmontil) that has been demonstrated to be effective against duodenal ulcers in some trials. The activity of the non-neuroleptic stereo-isomers of clopenthixol and chlorprothixene may lead to investigation in patients with peptic ulcer disease of this kind of agents. However, a firm connection between the antimicrobial activity of these compounds, their possible anti-ulcer effect and the etiological role of Campylobacter pylori in peptic ulcer disease must first be established.

Action of trimipramine on sleep and pituitary hormone secretion

Trimipramine is unlike other antidepressants in that it does not suppress REM sleep and possesses an atypical pharmacological profile. This antidepressant was administered in the evening to 10 depressed patients at a dosage of 75 mg on night 1 with 25 mg increments each night, up to 200 mg on night 6 and at this dosage thereafter. Sleep parameters were measured at baseline and on nights 2, 11 and 21. On nights 11 and 21, there was a significantly improved sleep pattern as shown by increases in sleep period time, total sleep time and sleep efficiency, and there was a decrease in sleep onset latency. No suppression of REM sleep occurred, and an increase was even noted; this, however, may have been due to a particularly low baseline value. Subjective assessments in which self-ratings of sleep quality were used also demonstrated an improvement in sleep. In addition, the neuroendocrine effects of trimipramine were investigated in 8 healthy volunteers after a single oral 75 mg dose. After 3 hours, a significant fall in plasma cortisol concentration from 117 to 43 micrograms/L and a significant rise in plasma prolactin concentration from 6 to 16.3 micrograms/L were observed, but there was no significant effect on plasma human growth hormone concentration. These results further support the effectiveness of trimipramine therapy in normalising a disturbed sleep pattern in depressed patients, and it may be of use in non-depressed insomniacs. The acute neuroendocrine effects of trimipramine are similar to those observed with neuroleptics and further indicate its atypical pharmacological profile.

Modulation of sleep by trimipramine in man

We have studied the acute effect of trimipramine (25, 50 and 75 mg) on nocturnal sleep in 6 young men. Fluoxetine (60 mg) and diazepam (10 mg) were included as controls for the potential changes in sleep measures. Trimipramine reduced awake activity, Stage 1 (drowsy) sleep, and the duration of rapid eye movement (REM) sleep. Non-REM (Stage 2) sleep was increased. Residual effects of trimipramine were present the next morning (9 h after ingestion) with impaired coding ability. The effects of trimipramine on sleep and daytime alertness are consistent with its complex pharmacological profile. Reduced wakefulness and sedation are most likely due to synergism between histamine H1, alpha 1-adrenoceptor, and dopamine receptor antagonism. Anticholinergic activity and possibly blockade of alpha 1-adrenoceptors would disturb the balance of transmitter activities which facilitates the optimal appearance of REM sleep. In this way the effects of trimipramine on nocturnal wakefulness and REM sleep are similar to drugs which inhibit the uptake of noradrenaline.

Clinical originality and new biology of trimipramine

Trimipramine differs from other antidepressant drugs in a number of ways. Although trimipramine shares equivalent efficacy with doxepin, imipramine, maprotiline and amitriptyline, as evidenced by double-blind studies, it possesses a different side-effect profile. Trimipramine is considered to be less cardiotoxic, and data presented in this paper support its minimal effect on orthostatic hypotension, as compared with clomipramine. In addition, trimipramine has less epileptogenic potential than other antidepressants such as imipramine, amitriptyline and maprotiline. Besides this different side-effect profile, trimipramine exerts differing effects on neurotransmitter functions and their reuptake. For example, trimipramine does not inhibit reuptake of noradrenaline and serotonin, and does not down-regulate beta 1-adrenoceptors. Furthermore, in common with lithium, trimipramine produces enhancement of antidepressant action in treatment-resistant depressed patients. There is evidence that trimipramine enhances the sensitivity of cortical neurons to noradrenaline after prolonged administration and may also increase the activity of serotonin neurons.

Effects of trimipramine on sleep EEG, penile tumescence and nocturnal hormonal secretion. A long-term study in 3 normal controls

Sleep EEG, nocturnal penile tumescence (NPT) and nocturnal endocrine activity were studied in 3 male control subjects during placebo, under trimipramine (TR) and after withdrawal. TR did not change the sleep structure. NPT activity tended to increase under TR. Nocturnal plasma cortisol levels decreased markedly while the early morning rise of cortisol appeared delayed under 200 mg TR. After withdrawal the changes of the cortisol secretion rebounded. Nocturnal secretion of GH, testosterone, LH and FSH remained unaffected, but plasma prolactin levels increased under TR and returned to normalcy after cessation. Our data illustrate that the neurobiological effects of TR are different from those of other antidepressants. We suggest that some of the psychotropic effects of TR are mediated by suppression of cortisol.

Interaction of antidepressants and neuroleptics with histamine stimulated parietal cell adenylate cyclase and H+ secretion

The tricyclic antidepressants trimipramine and doxepin, and the neuroleptic agents trifluoperazine and haloperidol were tested for their effect on histamine H2-receptor-mediated adenylate cyclase activity and H+ secretion in guinea-pig parietal cells. All compounds inhibited histamine-stimulated adenylate cyclase and H+ secretion in a concentration-dependent manner. The antisecretory potency was 1-2 orders of magnitude higher than that for adenylate cyclase inhibition. All drugs caused a rightward shift in the concentration-response curves of histamine-induced adenylate cyclase activation with Schild-plot lines having a slope significantly different from unity. Histamine-stimulated H+ secretion was inhibited by the drugs in a noncompetitive fashion. These results demonstrate that antidepressants and neuroleptics interfere noncompetitively with the parietal cell histamine H2-receptor and that this receptor blocking activity is not related to the antisecretory activity of the drugs.

Effects of some polycyclic drugs on gastric secretion and on the healing of duodenal ulcers

Polycyclic drugs such as the dibenzazapine trimipramine have been shown to accelerate the healing of gastric and duodenal ulcers, possibly by inhibiting gastric secretion. We have therefore compared the effects of three polycyclic drugs (trimipramine, mianserin and quisultidine) on nocturnal and pentagastrin-stimulated gastric secretion. The patterns of the effects of the three drugs on gastric secretion differed. Although pentagastrin-stimulated secretion of acid was inhibited by trimipramine (13%), mianserin (38%), and quisultidine (29%), overnight gastric secretion was inhibited by mianserin (37%) and quisultidine (78%) but increased by trimipramine (16%). In view of its gastric inhibitory actions, the effects of mianserin on the healing of duodenal ulcers have been studied. In a pilot open trial seven out of eight duodenal ulcers healed after four weeks of treatment with mianserin 60 mg at night. A controlled, randomized long-term study is now scheduled in order to assess the role of mianserin in the management of ulcer disease.

Effects of subchronic administration of psychoactive substances on the circadian rhythm of urinary corticosterone excretion in rats

Abnormal function of the hypothalamo-pituitary-adrenocortical (HPA) axis has been observed in depressed patients. Experiments with laboratory rats were performed to test whether psychoactive substances (among them clinically effective antidepressants) influence circadian HPA activity. For this purpose, corticosterone was measured in urine collected for 24 h at 4 h intervals. Maprotiline, fluoxetine, imipramine, trimipramine, clorgyline and pargyline were given once daily for at least 13 days, by either intraperitoneal or subcutaneous (clorgyline) injection. Only two substances produced significant changes in the circadian pattern of corticosterone excretion: pargyline distinctly delayed the phase of circadian HPA activity, and trimipramine prolonged the nocturnal increase in urinary corticosterone. The present results suggest that psychoactive drugs have no effects in common on the circadian rhythm of HPA activity in rats.

The effect of trimipramine (Surmontil) on the gastric secretion of acid and pepsin in patients with duodenal ulceration

Twenty-three patients with endoscopically proven, symptomatic duodenal ulceration were randomized to receive trimipramine 50 mg daily or placebo. Maximal acid output studies and estimations of pepsin levels were performed before treatment, for 4 weeks while on drug or placebo and for 4 weeks after cessation of treatment. Gastric acid secretion was significantly reduced after 3 weeks treatment with trimipramine and this reduction was maintained for the duration of the study. Gastric pepsin levels were unaffected by the administration of the drug.

An increase in sensitivity of rat cingulate cortical neurones to substance P occurs following withdrawal of chronic administration of antidepressant drugs

The sensitivity of neurones in the cingulate cortex of the rat to iontophoretically applied substance P (SP) was tested one hour after a single dose of various antidepressant drugs and also 1 day following the termination of a chronic dosing schedule (14 once daily injections) of the same agents. One hour after a single injection of desipramine (DMI), chlorimipramine (CMI), trimipramine (TMI) or zimelidine ( ZIM ) (all at 10 mg kg-1 i.p.) there was no change in the mean size of excitatory responses to SP compared to those before the injection. There was a tendency towards a decrease in the TMI group. One day following the last of 14 consecutive daily injections (10 mg kg-1 i.p.) of the above agents there was a significant increase in the size of excitatory responses to SP compared to those in rats receiving daily saline injections. However, 14 days of treatment with DMI did not alter the responses to L-glutamate. Similar chronic dosing schedules with either diazepam (5 mg kg-1) or fluphenazine (5 mg kg-1) did not affect the responses to SP. Thus chronic but not acute administration of antidepressant drugs results in an increase in the sensitivity of neurones, in the cingulate cortex of the rat, to SP.

Serum concentration of pancreatic polypeptide after infusion of histamine and the effect of cimetidine, trimipramine, and atropine in man

Histamine was given intravenously to eight human subjects, and the PP concentration in serum increased significantly from 14.8 (7.2-29.3) pM to 27.5 (9.6-39.3) pM and then decreased to the basal level. This histamine-induced PP release was not altered when trimipramine or cimetidine was given in addition to histamine. This PP release could not mediated through histamine-receptor mechanisms, and since atropine prevented this PP release, we conclude that the release of PP after histamine reflects a cholinergic stimulus.

The effect of trimipramine, cimetidine, and atropine on gastric secretion

In the present study a comparison was made of the effect of increasing doses of trimipramine (0.05, 0.10, 0.20, 0.40 mg/kg/h), atropine (7, 14, 21, 28 microgram/kg/h), and cimetidine (0.3, 0.6, 1.2, 2.4 mg/kg/h) on the gastric secretion stimulated by 3 microgram/kg/h of histamine dihydrochloride as continuous infusion, each dose step lasting 30 min. In nine healthy individuals it was found that trimipramine had a stimulating effect on the volume and output of acid during one of eight 15-min periods. The largest dose of atropine caused a reduction of the volume and acid output by 68% and 77%, respectively, whereas cimetidine reduced the volume by 74% and the acid output by 89% during the last five 15-min periods, thus having the most pronounced effect. The study may suggest that the healing effect of trimipramine on peptid ulcer is not linked to the effect on submaximal histamine-stimulated secretion and that a different mechanism of action is probably present for the effect of trimipramine, compared with atropine and cimetidine, on the gastric secretion.