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Antisera raised against the drug imipramine.

Antisera against 2-aminoimipramine covalently coupled to albumin have been raised in two rabbits. Both antisera bind imipramine and related tricyclic compounds as if to a single class of sites with high affinity and high titres. Displacement/inhibition assays showed that the affinities of various tricyclic compounds for the antisera showed a good correlation with the affinities of these drugs for the tricyclic antidepressant inhibitory sites on plasma-membrane 5-hydroxytryptamine carriers of human platelets and rat brain cortex. 5-Hydroxytryptamine and 5-hydroxytryptamine-uptake-selective drugs did not inhibit [3H]imipramine binding to antisera. The anti-imipramine antibodies were purified using imipramine-Sepharose affinity chromatography and were shown to be IgG class by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and protein A-Sepharose precipitation.

Animals↗

[3H]imipramine binding of protein nature in human platelets: inhibition by 5-hydroxytryptamine and 5-hydroxytryptamine uptake inhibitors.

The nature of [3H]imipramine binding to human platelets was investigated. Desipramine and 5-hydroxytryptamine (5-HT) displaced the same amount of binding and the binding was sensitive to protease treatment. The nature of pharmacological inhibition of [3H]imipramine binding was investigated in saturation experiments. Increases in KD without changes in Bmax were noted with the addition of 5-HT, desipramine, norzimeldine, or 5-methoxytryptoline. Reductions in Bmax without alterations in KD were obtained when citalopram or clomipramine was added. It is concluded that the [3H]imipramine binding site in human platelets is of protein nature and that this binding site contains the substrate recognition site for 5-HT uptake. In addition, [3H]imipramine and other 5-HT uptake inhibitors have bonds to other parts of the 5-HT uptake carrier or to the surrounding lipid membrane. This additional binding outside the substrate recognition site is not one single site but most likely represents sites that are specific for the chemical structure of each uptake inhibitor, respectively.

Binding Sites↗

Metabotropic glutamate receptors and neuroadaptation to antidepressants: imipramine-induced down-regulation of beta-adrenergic receptors in mice treated with metabotropic glutamate 2/3 receptor ligands.

Antidepressant drugs have a clinical latency that correlates with the development of neuroadaptive changes, including down-regulation of beta-adrenergic receptors in different brain regions. The identification of drugs that shorten this latency will have a great impact on the treatment of major depressive disorders. We report that the time required for the antidepressant imipramine to reduce the expression of beta-adrenergic receptors in the hippocampus is reduced by a co-administration with centrally active ligands of type 2/3 metabotropic glutamate (mGlu2/3) receptors. Daily treatment of mice with imipramine alone (10 mg/kg, i.p.) reduced the expression of beta-adrenergic receptors in the hippocampus after 21 days, but not at shorter times, as assessed by western blot analysis of beta1-adrenergic receptors and by the amount of specifically bound [3H]CGP-12177, a selective beta-adrenergic receptor ligand. Down-regulation of beta-adrenergic receptors occurred at shorter times (i.e. after 14 days) when imipramine was combined with low doses (0.5 mg/kg, i.p.) of the selective mGlu2/3 receptor agonist LY379268, or with the preferential mGlu2/3 receptor antagonist LY341495 (1 mg/kg, i.p.). Higher doses of LY379268 (2 mg/kg, i.p.) were inactive. This intriguing finding suggests that neuroadaptation to imipramine--at least as assessed by changes in the expression of beta1-adrenergic receptors--is influenced by drugs that interact with mGlu2/3 receptors and stimulates further research aimed at establishing whether any of these drugs can shorten the clinical latency of classical antidepressants.

Adaptation, Physiological↗

Effects of imipramine and desipramine on responses of single cortical neurones to noradrenaline and 5-hydroxytryptamine.

1 The technique of microelectrophoresis was used in order to study the effects of imipramine and desipramine on single neurones in the somatosensory cortex of the cat, anaesthetized with halothane.2 Imipramine and desipramine, when applied for a brief period, did not affect the firing rate of the vast majority of the neurones tested.3 Both potentiation and antagonism of excitatory responses to noradrenaline could be observed after a brief application of either of the antidepressants. Four drug-interaction patterns could be distinguished: potentiation of immediate onset; potentiation reaching its maximum after a delay; antagonism followed by potentiation; antagonism followed by recovery.4 When different doses of the same antidepressant were applied, it was found that the drug-interaction patterns were related to the dose of antidepressant applied, a lower dose causing potentiation, and a higher dose antagonism of the response.5 Both potentiation and antagonism of depressant responses to noradrenaline could be observed.6 Both excitatory and depressant responses to 5-hydroxytryptamine were modified by imipramine and desipramine: a smaller dose of the antidepressant potentiated, and a higher dose antagonized the responses.7 Excitatory responses to glutamate were not affected by imipramine and desipramine.

Action Potentials↗

The effect of chlorpromazine, metyrapone, imipramine and SKF 525-A on the hepatic first pass elimination of propranolol in the pithed rat.

1 The effect of chlorpromazine, metyrapone, imipramine and SKF 525-A on the hepatic first pass elimination of propranolol has been studied in the pithed rat. 2 The effect of chlorpromazine, metyrapone, imipramine and SKF 525-A on the inhibition caused by propranolol of an elicited electrically induced tachycardia has also been studied. 3 The hepatic first pass elimination of propranolol was reduced following pretreatment with chlorpromazine, imipramine and SKF 525-A but was not affected by pretreatment with metyrapone. 4 Chlorpromazine, imipramine and SKF 525-A all resulted in an increased propranolol blood concentration after hepatic portal vein administration which was associated with decreased formation of metabolites and an enhanced inhibition of an electrically induced tachycardia.

Animals↗

Potentiation by TRH of the effect of imipramine on the forced-swimming test.

Discovery of the potentiation of thyrotropin releasing hormone (TRH)-induced hyperthermia in mice by antidepressants which activate alpha-adrenergic systems instigated investigation of other relations between TRH and antidepressants. For this study the forced-swimming test using mice was chosen since this test is more sensitive for selection of antidepressants which modify catecholaminergic systems than for those affecting 5-hydroxytryptaminergic systems. The effects of imipramine were potentiated by TRH. The involvement of alpha-adrenergic systems was then investigated in this effect since it is already known that these systems are directly implicated in the potentiation of TRH-induced hyperthermia by some antidepressants. Then the involvement of opiate systems was investigated since endogenous opiates are implicated in the action of some antidepressants, and some interactions between TRH and opiate systems are known to exist. TRH made effective a completely inactive dose of imipramine as small as 2 mg kg-1 (i.p.) or 1 microgram per mouse (i.c.v.). Pretreatment by both alpha 1- and alpha 2-adrenoceptor antagonists (phenoxybenzamine, 8 mg kg-1 i.p.; phentolamine, 4 mg kg-1 i.p.) or by a alpha 1-adrenoceptor antagonist (prazosin, 2 mg kg-1 i.p.) did not prevent this potentiation. In contrast the alpha 2-adrenoceptor antagonist (Yohimbine, 2 mg kg-1 i.p.) blocked the TRH effect. The imipramine potentiation by TRH was blocked by pretreatment with an opiate antagonist (naloxone, 1 mg kg-1 i.p.) and the potentiation was decreased in morphine-tolerant mice. 5 These data indicate that potentiation of the effects of imipramine on the forced-swimming test does not seem to be associated with an increase of effective levels of noradrenaline in the synaptic clefts and suggest an interaction between TRH and the opiate systems.

Animals↗

Biphasic effects of imipramine in experimental models of epilepsy.

In a variety of laboratory models of experimental epilepsy, imipramine exerts a biphasic action on the CNS as manifested by antiepileptic properties at low doses and convulsant effects at higher doses. In mice, imipramine (17.5-25 mg/kg, i.p.) blocks maximal electroshock seizures while exerting little or no effect on pentylenetetrazol-induced seizures. In cats, imipramine (2.5-15 mg/kg, i.v.) reduces penicillin and estrogen-induced epileptiform discharge, shortens afterdischarge duration and elevates afterdischarge threshold. Higher doses in mice induce neurotoxicity, including clonic seizures. In cats, doses above 20 mg/kg intensify chemically and electrically induced seizures and induce spontaneous epileptiform episodes. Such a biphasic action of imipramine may limit the drug's clinical utility as an antiepileptic agent and may provide an interesting tool for studies of catecholamines and brain excitability.

Animals↗

Age effects on alpha-1-acid glycoprotein concentration and imipramine plasma protein binding.

Alpha-1-acid glycoprotein concentration and imipramine binding to plasma proteins were determined in a cohort of 69 subjects, aged 20-97 years. No subject had evidence of acute or chronic inflammatory disease or malignancy, or was receiving tricyclic antidepressant therapy. Alpha-1-acid glycoprotein concentration increased significantly with increasing age (r = 0.28; P less than 0.02). Imipramine percentage not bound to plasma proteins was negatively related to alpha-1-acid glycoprotein concentration (r = -0.30; P less than 0.01); however, there was no relationship between subject age and percentage imipramine unbound. Though alpha-1-acid glycoprotein concentration increases with advancing age, because only a small proportion of the variability is explained by age, with other undefined factors being more important, drugs predominantly bound to alpha-1-acid glycoprotein such as imipramine may not have a clinically or statistically significant change in protein binding with increasing age in the absence of overt clinical illness.

Adult↗

Antimalarial properties of imipramine and amitriptyline.

Dietary riboflavin deficiency is known to diminish malarial parasitemia. In this study, we determined whether imipramine and amitriptyline, drugs which inhibit riboflavin metabolism, have antimalarial efficacy. In addition, we evaluated whether these drugs, like other antimalarial agents, increase the hemolytic response to ferriprotoporphyrin IX (FP). The growth of Plasmodium falciparum (FCR3) in the absence and presence of these drugs (10 to 75 microM) was measured by determining (3H)hypoxanthine uptake by intra-erythrocytic parasites for 48 h in RPMI 1640 medium. The uptake of (3H)hypoxanthine was significantly reduced in a dose-dependent manner by both imipramine and amitriptyline. The IC50 values of imipramine and amitriptyline at 48 h were 56 and 45 microM, respectively. Both drugs enhanced hemolysis induced by FP (10 or 20 microM). No hemolysis by these drugs was detected in the absence of FP. It is concluded that the tricyclic antidepressants, imipramine and amitriptyline, possess substantial antimalarial properties.

Amitriptyline↗

Investigation of the orthostatic reaction after intravenous administration of imipramine, chlorimipramine, and inimpramine-N-oxide.

Three age- and sex-matched groups of 10 patients were treated intravenously with imipramine, chlorimipramine, and imipramine-N-oxide respectively, in increasing doses from 25 mg to 150-175 mg given as single daily infusions during 1 hour. No systemic changes of heart frequency and blood pressure were found during the infusions in spite of the high dosage of tricyclic antidepressants given such a short period as 1 hour. The patients were examined regarding orthostatic reactions as well as ECG changes before, after 4-5 infusions and after 8-10 infusions. There were more orthostatic abnormalities and ECG changes in the patients treated with imipramine than in those treated with imipramine-N-oxide and there were practically no changes in the chlorimipramine group. However, no statistically significant orthostatic changes were found.

Adult↗

Symptom reduction in depression after treatment with L-tryptophan or imipramine. Item analysis of Hamilton rating scale for depression.

Thirty-eight in-patients with endogenous- and 20 in-patients with non-endogenous depression, took part in a multi-centre 3-week double-blind trial where patients were randomly allocated to treatment with either 6 g L-tryptophan or 150 mg imipramine daily. Item analysis of Hamilton ratings, before the investigation and weekly during the trial period demonstrated few statistically different mean scores on individual items between the two treatment groups. After 3 weeks' treatment a statistically significant item mean reduction on the 0.1% level was found in the item Agitation in favour of imipramine-treated, and in the item Work and Activities in favour of L-tryptophan-treated endogenously depressed patients. After 3 weeks' treatment a statistically significant item mean reduction on the 5% level was found in the item Suicide in favour of imipramine-treated non-endogenously depressed patients. The present study has shown that, after 3 weeks' treatment, imipramine and L-tryptophan has decreased the mean score on individual items of HRS in about the same degree.

Adolescent↗

Tryptophan-nicotinamide, imipramine and their combination in depression. A controlled study.

In a double-blind controlled study lasting 4 weeks 25 newly admitted severely depressed patients were randomly assigned to tryptophan-nicotinamide or imipramine or tryptophan-nicotinamide-imipramine combination. Nicotinamide was given to reduce peripheral breakdown of tryptophan. Although there were no substantial differences between the three treatments, the efficacy of tryptophan-nicotinamide tended to diminish after 2 weeks when the dose of tryptophan was increased from 4 g/day to 6 g/day and that of nicotinamide from 1.0 g/day to 1.5 g/day. The therapeutic response of patients treated with tryptophan-nicotinamide was significantly correlated with the rise in plasma tryptophan. For the tryptophan-nicotinamide-imipramine group, however, therapeutic response and rise in plasma tryptophan were negatively correlated, implying that tryptophan levels were too high in some patients. The data suggest that tryptophan-nicotamide may be as effective as imipramine in unipolar patients providing the dose is kept within the therapeutic window, and that at low doses it could also potentiate the action of tricyclic antidepressants. Bipolar patients seem to require higher doses of tryptophan than unipolar patients.

Adult↗

Why some depressed patients may have low platelet 3H-imipramine binding.

Human platelet membranes were incubated with 3H-imipramine, 3H-paroxetine or 3H-chlorimipramine. It was found that chlorimipramine remained in the membranes, as it was impossible to remove this antidepressant drug by normal washing procedures. Similar results, although to a lesser degree, were found with paroxetine, whereas imipramine could be washed away from the membranes. Treatment of volunteers with chlorimipramine strongly reduced platelet imipramine binding probably due to the presence of chlorimipramine in the membranes during the binding assay. These results suggest that the low imipramine binding reported in depressed patients, at least in some cases, may have been caused by antidepressant drugs or drug metabolites remaining in the platelet membrane preparations.

Antidepressive Agents↗

Relapse prevention by means of paroxetine in ECT-treated patients with major depression: a comparison with imipramine and placebo in medium-term continuation therapy.

In-patients with severe major depression were treated in the acute phase with electroconvulsive therapy (ECT) in combination with antidepressants. The drug treatment consisted of two randomized trials which were both extended into the post-ECT continuation phase. Patients with electrocardiological impairment were randomized to either 30 mg paroxetine daily or placebo under blind conditions. Patients without electrocardiological impairment were randomized to either 30 mg paroxetine daily or 150 mg imipramine daily. There was a high level of agreement between the Hamilton Depression Scale and the Melancholia Scale, demonstrating that the patients treated with ECT plus imipramine in the acute phase showed greater symptom reduction than those treated with ECT plus paroxetine. However, in the post-ECT phase paroxetine was superior to both imipramine and placebo in preventing relapse. Thus in the post-ECT phase 65% of the placebo-treated patients relapsed, compared to 30% of the imipramine-treated patients and 10% of the paroxetine-treated patients. The psychometric analysis of the Melancholia Scale in the continuation or post-ECT phase showed that relapsing patients displayed a pattern with lack of interests, impaired concentration, depressed mood and anxiety among the less severe symptoms (first-compartment symptoms). In other words, these symptoms represent the gate to full-blown depression (second-compartment symptoms). Serotonin-selective antidepressants such as paroxetine appear to be more effective in controlling the first-compartment symptoms.

Adult↗

Serotonin receptors in the brain of rats treated chronically with imipramine or RU24969: support for the 5-HT1B receptor being a 5-HT autoreceptor.

Rats were treated by intraperitoneal injection for four weeks with either RU24969, a 5-HT1B and 5-HT1A agonist or imipramine, a 5-HT uptake inhibitor. Pre- and postsynaptic 5-HT receptors were measured to compare the effect of direct or indirect stimulation of the 5-HT autoreceptor (5-HT1B receptor). The 5-HT transport protein (5-HT uptake site), labelled with [3H]paroxetine, was unaffected after treatment with either one of the drugs. The density of 5-HT2 receptors, labelled with [3H]ketanserin, we found increased after treatment with RU24969 (Bmax = 161 fmol/mg protein) and decreased after treatment with imipramine (Bmax = 109 fmol/mg protein) as compared with control rats (Bmax = 134 fmol/mg protein). The 5-HT1B receptor was found decreased both by the imipramine treatment (Bmax = 106 fmol/mg protein) and the treatment with RU24969 (Bmax = 105 fmol/mg protein), compared with control rats (Bmax = 130 fmol/mg protein). The 5-HT1A receptor was found to be decreased after treatment with RU24969 (control: Bmax = 62 fmol/mg protein; RU24969-treated: 49 fmol/mg protein), but unchanged after treatment with imipramine (Bmax = 58 fmol/mg protein). These results correspond to what could be expected, if the 5-HT1B receptor is the 5-HT autoreceptor.

Animals↗

Effects of thioridazine and diazepam on the pharmacokinetics of [14C]imipramine in rat: acute study.

The pharmacokinetics of [14C]imipramine (10 mg kg minus 1) were tested in male Wistar rats for interaction with thioridazine (16 mg kg minus 1) or diazepam (10 mg kg- minus 1). All drugs were administered orally with the test substances being given 40 min before [14C]imipramine dosing. Bile and urine were collected for 90 min after the radioactive drug was given. The animals were then killed and the tissues removed. Thioridazine reduced the excretion of radioactivity into the bile and urine, and increased the weight of the contents within the gastrointestinal tract. These effects were interpreted as being mainly due to a reduction in gastrointestinal motility resulting in a slower stomach emptying of [14C]imipramine. No effect on metabolism was detected. Diazepam pretreatment reduced the concentration ratio of radioactivity in the small intestinal contents to that of plasma, but did not alter the tissue distribution, metabolism or excretion of [14C]imipramine.

Animals↗

Suppression of ventricular arrhythmias resulting from acute coronary artery ligation in rat by imipramine.

The potential antiarrhythmic activity of imipramine against ventricular arrhythmias induced by coronary artery ligation in rats has been investigated and compared with procainamide. Imipramide (1 and 5 mg/kg-1) or procainamide (5 and 10 mg/kg-1) or solvent were injected intravenously 30 min before ligation. Imipramine reduced the total number of ventricular ectopic beats as well as the incidence and duration of ventricular tachycardia and ventricular fibrillation. The drug did not significantly affect the blood pressure but reduced the heart rate. The antiarrhythmic activity of imipramine is postulated to be due to a quinidine-like effect and/or alpha-adrenergic blocking activity. The study confirms the potential utility of imipramine as an antiarrhythmic drug.

Animals↗

A comparative study on desipramine pharmacokinetics in the rat brain after administration of desipramine or imipramine.

Chronic intraperitoneal administration of desipramine led to an extensive cumulation of the drug in brain and blood compared with that after a single dose treatment, while chronic treatment with desipramine by the oral route produced a brain concentration comparable with its level after a single oral dose. Comparison of the present results with the corresponding data of published imipramine pharmacokinetics indicated that the cumulation of desipramine in the rat brain was nearly the same when rats received desipramine or imipramine twice a day for two weeks at a dose of 10 mg kg-1 orally, or imipramine, twice a day for two weeks at a dose of 10 mg kg-1 intraperitoneally. It is suggested that these three experimental paradigms may be used as models for differentiation of the pharmacological effects of imipramine and desipramine in-vivo.

Administration, Oral↗