Accumulation of 1-methyl-tetrahydro-Β-carboline-3-carboxylic acid in blood and organs of rat. A possible causative substance of eosinophilia-myalgia syndrome associated with ingestion ofl-tryptophan

1-Methyl-tetrahydro--carboline-3-carboxylic acid (MTCA) may cause eosinophilia-myalgia syndrome (EMS) associated with ingestion ofl-tryptophan. The distribution and excretion of MTCA were studied in rats which had received perorally a single 1.6 mg/kg dose of MTCA. MTCA concentrations in blood, kidney, liver, brain, heart, spleen, lung and gastrocnemius muscle were measured by HPLC combined with fluorometric detection. The concentration of MTCA in each organ reached a maximum at 1 h and then gradually declined. However, a significant level of MTCA still remained at 5 h, when 52% of ingested MTCA remained in the contents of the large intestine. Twenty-nine percent of the ingested MTCA was excreted in urine over the course of 24 h. A higher dose (10 mg/kg) of MTCA resulted in significant elevations in the concentrations and amounts of MTCA in the various organs. In addition, chronic treatment with a 10 mg/kg dose of MTCA for 6 weeks further increased the concentrations and amounts of MTCA in each organ. However, no histological changes were observed in any of the organs after chronic treatment. This is the first report which demonstrates accumulation of MTCA in the blood and various organs, including muscle, of rats.     

Endogenous formation of 1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid in man as the possible causative substance of eosinophilia-myalgia syndrome associated with ingestion ofl-tryptophan

1-Methyl-1,2,3,4-tetrahydro--carboline-3-carboxylic acid (MTCA) is now thought to be a possible causative substance of eosinophilia-myalgia syndrome associated with ingestion ofl-tryptophan. In the present study a factor affecting endogenous formation of MTCA in 32 healthy men is studied. Urinary excretions of MTCA and 1,2,3,4-tetrahydro--carboline-3-carboxylic acid (TCCA) were measured by high-performance liquid chromatography (HPLC) with fluorometric detection after administration of a high or low protein diet as well as peroral tryptophan (0.5 g) or ethanol (0.4 g/kg). Blood ethanol and acetaldehyde levels were determined by gas chromatography after ethanol consumption. Both, the high protein diet and tryptophan resulted in a significant rise of urinary TCCA. In contrast, ethanol intake caused increased excretion of MTCA, though a relationship between blood acetaldehyde level and urinary excretion of MTCA was not shown. We showed for the first time that an elevation of urinary excretion of MTCA following ethanol consumption in man without ingestion ofl-tryptophan tablets implicated eosinophilia-myalgia syndrome.     

Tryptophan antidepressant ‘physiological sedative’: Fact or fancy?

Some recent publications relating to the allegedly antidepressive and sedative effects of L-tryptophan the precursor of 5-HT have been reviewed.The evidence to date suggests that the amino acid is as effective as standard tricyclic drugs in alleviating the symptoms of depression, especially those cases presenting with mainly psychomotor retardation, and is synergistic with MAOIs. L-Tryptophan would also appear to be a physiological sedative. This action, however, appears to be related to the time of administration and at present has only been demonstrated at night, when endogenous levels of 5-HT are at their peak.In terms of practical therapeutics L-tryptophan would appear to have greater potential as an antidepressant than as a sedative.     

Kinetics of l-tryptophan in depressive patients: A possible correlation between the plasma concentrations of l-tryptophan and some psychiatric rating scales

The plasma concentration and flux of l-tryptophan are abnormal in primary depressive patients, according to the literature. The plasma concentrations of l-tryptophan over a 6-h period after ingestion of 5 g l-tryptophan were investigated and did not differ significantly between depressive patients and controls during the absorption, distribution, and elimination phases. There was no correlation between the plasma concentrations with anxiety or depression scores, or with the excretion in urine of 17-hydroxycorticosteroids and xanthurenic acid during the 24 h after l-tryptophan. Treatment with either 125 mg pyridoxine (three times daily with meals) and l-tryptophan (3 g at 10 PM) or with maprotiline (100 mg at 10 PM) had no influence on the plasma concentrations of l-tryptophan after 2 or 4 weeks of treatment. This excludes l-tryptophan deficiency as a pathogenic factor of depression in the patients studied. No kinetic differences could be demonstrated in the depressive patients, making differences in body compartments or flux of l-tryptophan unlikely to be of pathogenic importance to depression.     

Central pharmacological control of corticosterone secretion in the intact rat. demonstration of cholinergic and serotoninergic facilitatory and α-adrenergic inhibitory mechanisms

A method is described for demonstrating the hypothalamic control of corticosterone in the intact rat. Oxotremorine 0.01–0.05 mg/kg IP and 5-hydroxy-l-tryptophan 1–50 mg/kg IP raise plasma corticosterone levels in dose-related fashion. The oxotremorine response is blocked by atropine 1 mg/kg SC and the 5-hydroxy-l-tryptophan response by mianserin 10 mg/kg IP. -Methylparatyrosine methyl ester 400 mg/kg IP raises plasma corticosterone levels 14–16 h later. This rise can be suppressed by clonidine 0.01–0.05 mg/kg IP and this suppression is antogonized by piperoxane 5–50 mg/kg IP. Apomorphine 5 mg/kg IP does not lower plasma corticosterone levels in rats pre-treated with -methylparatyrosine.The response to oxotremorine cannot be blocked by atropine methylbromide or by mianserin. The response to 5-hydroxy-l-tryptophan is unaffected by benserazide or atropine sulphate.These data suggest separate cholinergic and serotoninergic facilitation of corticosterone release in the intact rat. The stimulating drugs used appear to be acting centrally. The data also support the presence of a noradrenergic inhibitory system mediated by -adrenoceptors. Dopaminergic receptors appear to play no part in the central control of corticosterone secretion after pre-treatment with -methylparatyrosine.     

The effect of repeated electroconvulsive shock on corticosterone responses to centrally acting pharmacological stimuli in the male rat

The effect of repeated and single electroconvulsive shocks (ECS) on the corticosterone response to pharmacological stimuli has been studied in male rats. Plasma corticosterone concentrations are elevated by oxotremorine, a muscarinic agonist, and by 5-hydroxy-l-tryptophan, a precursor of serotonin. Both these agonists probably stimulate corticotrophinreleasing-factor release from the hypothalamus. The log dose-response curves of the corticosterone response to oxotremorine and to 5-hydroxy-l-tryptophan are shifted to the left after a single ECS given daily for 10 days compared with sham-shocked controls. Plasma corticosterone concentrations are elevated by treatment with -methyl-p-tyrosine methyl ester (400 mg/kg IP). This rise is suppressed by clonidine. The log dose-response curve for the corticosterone response to clonidine after -methyl-p-tyrosine methyl ester is also shifted to the left by repeated ECS, compared with controls. There is no difference in the corticosterone response of ECS and sham-treated groups given vasopressin, which is thought to act directly on the pituitary to release ACTH.A single ECS produces a slight enhancement of the response to 5-hydroxy-l-tryptophan, a slight decrease in the response to oxotremorine and no change in the response to clonidine after -methyl-p-tyrosine.The disappearance of the difference in response between ECS and sham-treated animals was also studied 1,3, and 6 days after a series of ten ECS or sham procedures. Significant differences in the corticosterone responses to oxotremorine, 5-hydroxy-l-tryptophan and clonidine after -methyl-p-tyrosine between ECS and sham-treated animas were found 24 h after the last ECS or sham shock. These differences were in decline 3 days after the last procedure and had completely disappeared by day 6. The decline was largely due to an increase in plasma corticosterone responsiveness to pharmacological stimuli of the shamshocked controls. Responses in the ECS-treated groups remained constant.It is apparent that the anaesthetic procedure suppresses the effect of oxotremorine, 5-hydroxy-l-tryptophan and clonidine after -methyl-p-tyrosine on corticosterone concentrations in plasma. This effect is spontaneously reversible. Repeated ECS reverses the effect of the anaesthetic procedure but produces no reversible enhancement of its own.     

Mode of action of l-DOPA on central noradrenaline mechanisms

Summary Changes in central noradrenaline receptor activity were correlated with changes in dopamine and noradrenaline concentrations in rats after treatment with l-3,4-dihydroxyphenylalanine (l-DOPA) in combination with different drugs. The noradrenaline receptor activity was tested by means of flexor reflex increase and blood pressure reduction.After depletion of the endogenous noradrenaline stores by reserpine, and inhibition of the monoamine oxidase by nialamide, the l-DOPA treatment produced increases in flexor reflex activity and in both dopamine and noradrenaline concentrations. Pretreatment with the dopamine--hydroxylase inhibitor FLA-63 revealed that both catecholamines were of importance for this functional effect. Without monoamine oxidase inhibition, the administration of l-DOPA (after inhibition of the peripheral l-DOPA decarboxylase by l--methyldopa hydrazine) did not cause any functional effect, despite almost the same accumulation of dopamine.Injection of l-DOPA (after inhibition of the peripheral decarboxylase) into rats with intact noradrenaline stores evoked increased flexor reflex activity concomitant with a small but significant disappearance of noradrenaline and reduced the mean arterial blood pressure by 24–35 mm Hg. A second dose of l-DOPA had a much smaller effect on flexor reflex activity and on blood pressure, when given 90 min–12 h after the first one. This tachyphylaxis coincided with a fractional loss of endogenous noradrenaline and was not due to desensitization of the effector cells.In conclusion, the dopamine and noradrenaline formed from l-DOPA after monoamine oxidase inhibition act directly on the central noradrenaline receptors. Without monoamine oxidase inhibition, the l-DOPA treatment elicits a central noradrenaline receptor activation via release of endogenous noradrenaline, presumably by displacement of a small noradrenaline store with dopamine.     

The cytosol of N1E-115 neuroblastoma cells synthesizes an EDRF-like substance that relaxes rabbit aorta

Summary The cytosolic fraction of N1E-115 neuroblastoma cells catalysed the l-arginine- and NADPH-dependent formation of a substance that relaxed endothelium-denuded strips of rabbit aorta. Relaxations in response to this substance were enhanced in the presence of superoxide dismutase. N-Nitro-l-arginine and N^G-monomethyl-l-arginine, two inhibitors of EDRF synthesis, markedly attenuated the relaxations. Hemoglobin, a scavenger of EDRF, and methylene blue, an inhibitor of soluble guanylate cyclase, completely abolished the relaxation to N1E-115 cytosol. In contrast, the cyclo-oxygenase inhibitor indomethacin did not alter the relaxations. These data demonstrate that the cytosol of a neuronally-derived cell line is able to synthesize a substance with pharmacological properties similar to EDRF.This work was supported in part by Research Grants AM 30787 and HL 28474 from the National Institutes of Health, USA     

Intestinal decarboxylation of L-Dopa in relation to dose requirement in Parkinson's disease

Summary The magnitude of the decarboxylation of L-Dopa in the intestinal organs was determined by a method based on oral and intravenous administration of L-3,4-dihydroxyphenylalanine-1-¹⁴C (carboxyl labelled L-Dopa) and analysis of the radioactivity in urine.In 11 parkinsonian patients studied under standardized conditions 74% of L-Dopa given orally as a 0.5 g tablet was decarboxylated in the intestinal organs. Thus less than 26% of the ingested L-Dopa reached the general circulation.The possibility that individual variations in the magnitude of intestinal decarboxylation might be at least partly responsible for the individual variations in the dose requirement of parkinsonian patients was tested. There was neither any correlation between dose requirement of L-Dopa and the intestinal decarboxylation nor between that dose and the plasma disappearance rate of L-Dopa.It is concluded that other factors than those responsible for the peripheral metabolism of L-Dopa determine the individual dose requirement.     

Intravenous cocaine self-administration in rats is reduced by dietaryl-tryptophan

Rats were trained to self-administer intravenously-delivered cocaine. Four lever-press responses resulted in a cocaine infusion (0.2 mg/kg) during daily 24-h sessions. The rats were also trained to obtain water from tongue-operated solenoid-driven drinking spouts. Ground food and water from a standard drinking bottle were also available. When cocaine injections reached stable levels,l-tryptophan was mixed with the rats' food for 5 days. Three concentrations ofl-tryptophan (2, 4, and 8%) were tested in different groups of five rats each. Three other groups of five rats each received the samel-tryptophan treatments; however, in these rats saline was substituted for cocaine and a sweet drinking solution consisting of glucose and saccharin (G + S) replaced water in the automatic drinking device. Two other groups consisting of five rats each self-administered a higher (0.4 mg/kg) or lower (0.1 mg/kg) unit dose of cocaine and food adulterated with 4% tryptophan. At the two higher concentrationsl-tryptophan reduced cocaine infusions by at least 50% during the 5 days of treatment, and cocaine infusions returned to baseline levels within 48 h after the regular diet was restored. Responding reinforced by the G + S solution was not altered by any of thel-tryptophan concentrations. Food intake was substantially lowered by the 8%l-tryptophan concentration; however, water intake, responding on an inactive lever, and the number of saline infusions were not affected by addition ofl-tryptophan to the food.l-Tryptophan had the same magnitude of effect on self-administration of the 0.1 and 0.2 mg/kg unit doses of cocaine, but behavior maintained by the highest cocaine dose (0.4 mg/kg) was resistant to the effect ofl-tryptophan. The results of this experiment indicate thatl-tryptophan reduces behavior reinforced by IV cocaine infusions.     

Interaction of β-adrenoceptor agonists with the serotonergic system in rat brain

Summary The effect of -adrenoceptor agonists on the behavioral effect of l-5-HTP in rats and mice was studied. All -agonists potentiated the behavioral syndrome elicited by l-5-HTP. However no indication for a correlation between their potencies to stimulate peripheral beta-receptors and their potencies to enhance l-5-HTP effects was found. The potentiating effect of salbutamol in rats was intensified by the MAO A inhibitor clorgyline, completely inhibited by (±)-propranolol and partly inhibited by WB-4101, while practolol was without effect. Lesions of 5-HT pathways by i.c.v. injections of 5,7-DHT impaired the potentiating effect of salbutamol in rats. In contrast, 6-OHDA lesions or alphamethyl-p-tyrosine pretreatment were without effect. A central site of action of salbutamol is suggested by the fact that it intensified l-5-HTP effects also after i.c.v. administration. Therefore the results suggest that salbutamol facilitates 5-HT transmission in rat brain probably via stimulation of central beta receptors.A part of this study was presented at the meeting of the Deutsche Pharmakologische Gesellschaft in Mainz, March 18–21, 1980     

Chronic administration of citalopram in olfactory bulbectomy rats restores brain 5-HT synthesis rates: an autoradiographic study

Rationale The olfactory bulbectomized (OBX) rat model is widely accepted as an animal model of depression with a proposed serotonergic imbalance in the brain.Objective To study the effects of chronic administration of citalopram on serotonin (5-HT) synthesis rates.Method Serotonin synthesis was evaluated using the -[¹⁴C]methyl-l-tryptophan (-MTrp) autoradiographic method in OBX rats. Citalopram was administered continuously (10 mg kg^–1 day^–1) for 14 days using a subcutaneous osmotic minipump.Results The OBX rats treated with citalopram (OBX-CTP) have the same 5-HT synthesis rates as the sham-operated rats treated with citalopram (Sham-CTP). The OBX-CTP rats, relative to the OBX rats treated with saline (OBX-SAL), showed a reduction in the majority of the terminal brain structures, suggesting a normalization of 5-HT synthesis in the OBX-CTP rats following treatment. The OBX-SAL rats have significantly greater synthesis than the Sham-SAL rats in a majority of the terminal structures, but lower rates in the dorsal raphe. A few structures in the OBX-CTP group have lower synthesis than in the Sham-SAL group (e.g., dorsal raphe, hippocampus, amygdala). The data suggest that receptors in some brain areas are likely still responsive to the elevated levels of the extracellular 5-HT produced by citalopram.Conclusion There is no significant global or individual structure difference in the synthesis between the Sham-CTP and OBX-CTP groups. The similarity in the synthesis between the OBX-CTP, Sham-CTP and Sham-SAL groups is likely a result of changes in the sensitivity of the receptors through which 5-HT synthesis is controlled. Because of some of the differences in the synthesis between the Sham-CTP and Sham-SAL groups, the data suggest that receptors throughout the brain are not fully desensitized.     

Central effects of baclofen on thel-dopa induced hyperactive urinary bladder of the rat

Summary Cystometric recordings were performed in pentobarbitone anaesthetized rats and the effects of baclofen on urinary bladder function were evaluated as their influence on bladder hyperactivity induced by 1-dihydroxyphenylalanine (l-dopa) after peripheral decarboxylase inhibition. The bladder response was inhibited by intracerebroventricularly (i.c.v., 4th ventricle, 0.1 g) as well as by systemically administered (10 mg/kg i.v.) baclofen. Intravenous naloxone but not i.v. bicuculline i.c.v. substance P or i.c.v. glutamate antagonized the inhibitory actions of i.c.v. or/and i.v. baclofen.It is suggested that baclofen depresses the hyperactive bladder by a central action that is unrelated to bicuculline sensitive gamma aminobutyric acid mechanisms, substance P or glutamate neurotransmission but that is possibly related to interference with opioid mechanisms.     

Tryptophan tolerance and metabolism in endogenous depression

The concentration of free and total tryptophan and kynurenine in plasma from 49 female depressives and 26 female controls was measured following oral loading with l-tryptophan, 100 mg/kg body weight. There was no significant difference between five depressives and six controls in the area under curve for free or total tryptophan or kynurenine in plasma. The peak concentration of kynurenine occured 4 h after loading and it correlated significantly with the area under curve for kynurenine. There was no significant correlation between the l-tryptophan dose (g) and the plasma concentration of kynurenine at 4 h in the 49 depressives or 26 controls. The mean plasma levels of tryptophan and kynurenine at 4 h in the depressives were not significantly different from control levels. There was no clear relationship between the plasma levels of tryptophan or kynurenine at 4 h and the therapeutic response in 13 depressives treated with l-tryptophan for 14 days.It is concluded that the absorption, the plasma clearance, and the degradation to kynurenine of loading doses of l-tryptophan are normal in depressed patients. Results further-more suggest that the plasma levels of tryptophan and kynurenine at 4 h are poor predictors of the response to l-tryptophan treatment in depressives.     

Involvement of central GABA receptors in the regulation of the urinary bladder function of anaesthetized rats

Summary Cystometric recordings were performed in pentobaribitone anaesthetized rats and the effects of gammaaminobutyric acid (GABA) mechanisms on urinary bladder function were evaluated as their influence on a bladder hyperactivity induced by 1-dihydroxyphenylalanine (l-DOPA) after peripheral decarboxylase inhibition. The bladder response was inhibited by intracerebroventricular (i.c.v., 4th ventricle) injections of GABA (250 g), muscimol (0.2 g) and glycine (1,000 g) as well as by systemically administered muscimol (4 mg/kg) and diazepam (2 mg/kg). Intravenous (i.v.) bicuculline, but not i.v. strychnine, antagonized the inhibitory actions of intraperitoneal (i.p.) and i.c.v. muscimol and i.v. diazepam while the opposite was true for the inhibitory action of i.c.v. glycine. In rats not pretreated with l-DOPA, i.p. administration of bicuculline (4 mg/kg) after 15 min caused prominent detrusor contractions that were prevented by an infracollicular brain transection.It is suggested that GABA synapses in the pontinemesencephalic brain region may be involved in the modulation of urinary bladder function.     

The effects of dl-p-chlorophenylalanine and dl-α-methyl-p-tyrosine on the brain catecholamine,serotonin and free amino acid contents in rat

The changes in the brain levels of catecholamines, serotonin and free amino acids have been considered as a factor in the development of the physical dependence on and tolerance to some drugs. In order to show the relationships among the brain levels of these substances, three groups of rats were given i.p. dl-MpT alone, dl-pCPA alone, or dl-MpT and dl-pCPA together, twice a day for three days. Another group was kept as control. The brain levels of catecholamines, serotonin and free amino acids were determined. Although dl-MpT and dl-pCPA alone caused a decrease in the levels of catecholamines and serotonin respectively, the administration of dl-MpT and dl-pCPA together did not. The changes in the levels of free amino acids which were found were related to the metabolism of catecholamines and serotonin.     

Modification of spontaneous ECoG and behavior in cat by monoamine precursors

The effects of increasing the brain monoamine content on the three types of localized rhythms identified in somatic area I (mu-type rhythms) were studied in freely moving cats.Increases in brain monoamines (catecholamines and serotonin) were produced by injecting l-Dopa and 5-HTP. l-tyrosine, l-tryptophan and tryptamine were also tested.It is concluded that the two subsets of rhythms, one accompanying high levels of alertness and vigilance and the other appearing during quiet wakefulness, are related to the catecholaminergic systems, while those characterizing drowsiness seem to be controlled by a serotoninergic system. The latter, however, is distinct from that controlling slow sleep.     

Supersensitivity to l-5-hydroxytryptophan after 5,7-dihydroxytryptamine injections in desmethylimipramine- and nomifensine-pretreated rats: Behavioral evidence for postsynaptic supersensitivity

The behavioral syndrome induced by l-5-hydroxytryptophan (l-5-HTP) in rats was used to study the supersensitivity to l-5-HTP and 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) which develops after unilateral intracerebroventricular (ICV) injections of 200 g 5,7-dihydroxytryptamine (5,7-DHT). Pretreatment of the animals with a combination of desipramine and nomifensine was found to protect dopamine neurones better than desipramine alone. Maximal behavioral supersensitivity to l-5-HTP and 5-MeODMT was found as early as 24 h after injection of the neurotoxin, even in the presence of the specific 5-HT uptake inhibitor CGP 6085 A, or the MAO-A inhibitor clorgyline. The results indicate that a quickly occurring postsynaptic event contributes to the development of behavioral supersensitivity after ICV injections of 5,7-DHT.     

Lisuride,a potent drug in the treatment of muscular rigidity in rats

Summary Persistent and transient muscular rigidities were induced by 6-aminonicotinamide (6-AN) and reserpine, respectively, in rats and recorded electromyographically.Very low doses of lisuride (25 or 50 g/kg) reduced or abolished the increased electromyographic activity in the gastrocnemius muscle. Similar results were obtained with the combination of L-DOPA (100 mg/kg) plus benserazide (25 mg/kg). Methysergide was inactive. It is suggested that lisuride could be of value in the therapy of Parkinson's disease.N-(D-6-methyl-8-isoergolenyl)-N,N-diethylcarbamide hydrogen maleate     

Striatal dopamine turnover and l-dopa treatment after short-term exposure of rats to manganese

The turnover rate of striatal dopamine (DA) and the effect of l-dopa treatment was investigated in rats after the daily oral administration of MnCl₂ · 4H₂O for a period of 30 days. The turnover rate of striatal DA, as determined by the administration of -methyl-p-tyrosine, increased significantly in manganese-exposed rats. l-Dopa administration resulted in a significant elevation in the levels of DA and its metabolite, homovanillic acid, in manganese-exposed rats, but these neurochemical changes could not be correlated with the concentration of manganese in the striatum. We therefore advise that l-dopa therapy should not be tried in early manganese intoxication, as it may aggravate manic symptoms due to marked increase in brain DA.