The effect of l-tryptophan administration on the concentration of probenecid in plasma and cerebrospinal fluid in patients

The administration of large doses of probenecid has been used to study the central nervous system metabolism of catecholamines and indoleamines in patients with affective disease. It has been reported that alterations of the binding of l-tryptophan to plasma albumin binding sites occur during probenecid administration. The present study sought to determine if the administration of large doses of l-tryptophan affected probenecid concentrations in cerebrospinal fluid and/or plasma. The data indicate that during l-tryptophan treatment, plasma probenecid concentrations are reduced but that no significant alterations in cerebrospinal fluid probenecid concentrations occur. This would suggest that the kinetics of the probenecid blockade of transport of acidic biogenic amine metabolites out of cerebrospinal fluid are not altered by l-tryptophan loading.     

The effects of alcohol on laboratory-measured impulsivity after l-Tryptophan depletion or loading

Rationale Indirect evidence supports a link between serotonergic activity and individual differences in the behavioral response to alcohol, but few studies have experimentally demonstrated that an individual’s biological state can influence the sensitivity to alcohol-induced behaviors. Objective Our purpose was to temporarily modify serotonin synthesis in healthy individuals to determine how altered biological states may interact with alcohol administration to affect impulsive behavior. Materials and methods In a repeated-measures design, 18 normal controls consumed a 50-g l-tryptophan (Trp) depleting (ATD) or loading (ATL) amino-acid beverage that temporarily decreased or increased (respectively) serotonin synthesis before receiving either a moderate dose of alcohol (0.65 g/kg) or placebo. All participants completed three impulsivity testing sessions on each of the five experimental days. Session one was a baseline session. Session two included testing after ATD-only or ATL-only. Session three included: (1) placebo after ATL (ATL+PBO); (2) placebo after ATD (ATD+PBO); (3) alcohol after ATL (ATL+ALC); (4) alcohol after ATD (ATD+ALC); and (5) Alcohol-only conditions. Impulsivity was assessed using the Immediate Memory Task (Dougherty et al., Behav Res Methods Instrum Comput 34:391–398, 2002), a continuous performance test yielding commission errors that have been previously validated as a component of impulsive behavior. Results Primary findings were that ATD-only increased impulsive responding compared to ATL-only, and ATD+ALC increased commission errors to levels higher than either the ATL+ALC or Alcohol-only conditions. Conclusions These findings demonstrate that reduced serotonin synthesis can produce increased impulsivity even among non-impulsive normal controls, and that the behavioral effects of alcohol are, in part, dependent on this biological state. This research was sponsored by grants from the National Institutes of Health (R01-AA12046, R01-AA014988, and T32-AA07565).     

Effect of monoamine precursors on the forced-swimming test in mice

The antidepressant properties of monoamine precursors were evaluated by the forced-swimming test for mice developed by Porsolt et al. DOPA but not 5-hydroxy-tryptophan (5HTP) shortened immobility at doses that did not increase locomotor activity. Although l-threo-dihydroxyphenylserine (DOPS), an artificial norepinephrine (NE) precursor, did not change immobility in intact mice, DOPS significantly reduced immobility in mice pretreated with the selective NE neurotoxin DSP4. These results suggest possible antidepressant properties of DOPA and DOPS, the latter of which may act as an antidepressant in a certain NE-depleting condition.     

Formation of dopamine from 3-methoxytyrosine

Summary l-3-Methoxytyrosine-¹⁴C was given intravenously to mice, alone or following inhibitors of monoamine oxidase, catechol-O-methyl transferase or dopa decarboxylase. ¹⁴C-noradrenaline and ¹⁴C-dopamine in brain and heart were determined 2 h after the administration of the labelled compound. The results were very similar to those obtained in previous studies after a small dose of labelled dopa. Therefore, a careful paperchromatographic analysis of the l-3-methoxytyrosine-¹⁴C was made. It was found that 1.5% of the total radioactivity corresponded to dopa. Attempts to make a preparative separation of ¹⁴C-dopa from ¹⁴C-3-methoxytyrosine failed due to the appearance of another labelled impurity interfering with the determination of dopamine. Thus, the question whether dopamine can be formed from 4-methoxytyrosine in vivo could not be definitely answered. However, the serious interference of small amounts of radioactive impurities when working with labelled material in biological systems has been demonstrated once more.     

Evidence for the role of nitric oxide in nicotine-induced locomotor sensitization in mice

Rationale Nitric oxide (NO) is implicated in both acute effects of addictive drugs and development of dependence to them. We investigated the role of NO in nicotine-induced locomotor sensitization.Objectives The effects of N-nitro-l-arginine methyl ester (l-NAME), a NO synthase inhibitor, and a combination of a NO precursor l-arginine and l-NAME on nicotine-induced locomotor sensitization were investigated in Swiss Webster mice.Methods Sensitization to psychomotor stimulating effect of nicotine was rendered by seven injections of nicotine (1 mg/kg) on every other day. To investigate their effect on the development of sensitization to nicotine, l-NAME (15–60 mg/kg) and l-arginine (1 g/kg) were given before nicotine administration during the first seven sessions. To investigate the effect of these compounds on the expression of nicotine sensitization, after a 4-day drug-free period another group of mice received a challenge injection of nicotine on day 18.Results Nicotine (1 mg/kg) produced a robust locomotor sensitization in mice. The doses of 30 mg/kg and 60 mg/kg of l-NAME blocked the development of sensitization to nicotine; and, l-arginine (1 g/kg) pretreatment reversed this effect of l-NAME. Likewise, the doses of 30 mg/kg and 60 mg/kg of l-NAME inhibited the expression of sensitization to nicotine on day 18; and, l-arginine (1 g/kg) pretreatment reversed this inhibitory effect of l-NAME.Conclusions Our results suggest that NO is implicated in the development and expression of nicotine-induced locomotor sensitization in mice.     

Demethylation of l-3-methoxytyrosine in vivo

Summary After administration of purified l-¹⁴C-3-methoxytyrosine (l-¹⁴C-3-MTO) to rats, the fractions of labelled amino acids, catecholamines and phenolcarboxylic acids of urine and brain have been separated by column chromatography. Prior to performing the quantitative determinations, the individual metabolites of each urinary fraction and of the cerebral catecholamine fraction were isolated by paper chromatography using different systems. Susbtantial amounts of ¹⁴C-3,4-dihydroxyphenylacetic acid (¹⁴C-DOPAC) as well as some ¹⁴C-3,4-dihydroxyphenylalanine (¹⁴C-DOPA) and traces of dopamine (DA) appeared in the urine. Furthermore, small amounts of ¹⁴C-DA and ¹⁴C-norepinephrine were found in the brain with two different chromatographic systems. The urinary excretion of ¹⁴C-DOPAC and ¹⁴C-DA was increased by pretreatment with dopacetamide, an inhibitor of catechol-3-O-methyl-transferase. A possible contamination of the l-¹⁴C-3-MTO with traces of l-¹⁴C-DOPA as a major source of the dihydroxylated metabolites has been ruled out. It is concluded that part of l-3-MTO undergoes demethylation in vivo and that the finding of DA in brain and urine after administration of l-3-MTO is not an artifact.     

Nitric oxide synthesis,epileptic seizures and kindling

Nitric oxide (NO) has been implicated in synaptic changes underlying long-term potentiation and some forms of learning. It is unclear, however, whether NO contributes to long-term changes associated with the kindling of epileptic seizures. In the present study rats were treated, on the first 6 days of kindling, withl-arginine (l-Arg), the endogenous donor from which NO derives, or withl-nitro-arginine (l-No-Arg), a competitive inhibitor of NO synthesis, or with vehicle. Drugs were given in doses previously shown to affect learning or other behaviour.l-Arg (750 mg/kg IP) did not affect kindling or seizure severity.l-No-Arg (100 mg/kg) prolonged the duration of afterdischarges and convulsions on treatment days but did not advance kindling or affect seizures on subsequent days. A second experiment examined the possible rôle of NO in the development of resistance to seizures following prior seizures. Six or more stimuli were administered at 10-min intervals to fully-kindled rats after injection ofl-No-Arg or vehicle. Vehicle-treated rats became progressively more resistant to afterdischarges and convulsions with successive stimulations butl-No-Arg-treated rats failed to do so. Rats injected withl-No-Arg also showed an unexpected high mortality in the ensuing 24 h.l-No-Arg appeared to have no direct effect on the course of kindling but impaired the development of postictal resistance, and increased the duration and lethal after-effects of closely repeated seizures. The results do not support suggestions that antagonists of NO might prove clinically useful as anticonvulsants.     

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.     

Possible involvement of l-arginine-nitric oxide pathway in modulating regional blood flow to brown adipose tissue of rats

To evaluate whether the l-arginine-nitric oxide (NO) pathway is involved in the regulation of regional blood flow to brown adipose tissue (BAT), the effects of two specific NO synthase inhibitors, N^G-nitro-l-arginine methyl ester (l-NAME) and N^G-monomethyl-l-arginine (l-NMMA), on the blood flow to interscapular brown adipose tissue (IBAT) were studied in urethane-anesthetized rats. Regional blood flow in MAT was measured with laser-Doppler flowmetry.An intravenous injection of l-NAME and l-NMMA, but not of either d-enantiomer, caused a transient and dose-dependent increase in IBAT blood flow. Dose-response curves for these NO synthase inhibitors showed that l-NAME was more potent than l-NMMA in increasing IBAT blood flow. We also observed a concomitant pressor effect accompanied by a slight decrease in heart rate following intravenous injection of l-NAME and l-NMMA. An elevation of IBAT blood flow and blood pressure induced by both l-NAME and l-NMMA was reversed by l-arginine in an enantiomerically specific manner. The increase in IBAT blood flow induced by NO synthase inhibitors was of shorter duration and less sensitive to l-arginine than the increase in blood pressure.Our results show that the WAY blood flow is increased by inhibition of NO synthase and that the response of IBAT vasculature to NO synthase inhibitors is different from that of the resistance vessels which regulate blood pressure. The involvement of l-arginine-NO pathways in modulating microcirculation in IBAT is suggested. Correspondence to: Y. Uchida at the above address     

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.     

Propriétés différentielles d'un inhibiteur de la décarboxylase envers la l-Dopa et le l-5-HTP. Données polygraphiques et biochimiques

This study, comparing polygraphic data and biochemical dosages with a short term rabbit EEG recording technique, shows that Ro 4602 does not have the same quantitative (or even qualitative) effect whether combined with l-Dopa or l-5-HTP. Thus minimal and optimal doses of this inhibitor of the decarboxylase are not the same for the two precursors. Using equimolar doses, clinical effects on the whole appeared to be much more evident with the association Ro 4602-l-5-HTP than with Ro 4602-l-Dopa.

     

Evidence that the large neutral amino acidl-valine decreases electrically-evoked release of 5-HT in rat hippocampus in vivo

l-Valine competes with tryptophan for transport into the brain and has previously been shown to decrease brain 5-HT synthesis. In the present study, the effect ofl-valine on electrically evoked hippocampal 5-HT release was determined in the anaesthetized rat using microdialysis. In control animals two electrical stimulations of the dorsal raphe nucleus 120 min apart (S1 and S2, respectively) released similar amounts of 5-HT. In contrast, in animals which receivedl-valine (200 mg/kg) between stimulations, S2 released a significantly smaller amount of 5-HT than did S1, although basal 5-HT release was unchanged. The data demonstrate thatl-valine decreases the electrically-evoked release of 5-HT in hippocampus in vivo.     

Association l-Dopa,désipramine et inhibiteur de la décarboxylase dans le traitement de la dépression

The use of l-Dopa in the treatment of depressions has been suggested by pharmacological hypotheses and by observations made during the treatment of Parkinson's disease. The authors discuss the first results of their experiences using a combination of l-Dopa, a decarboxylase inhibitor, and desipramine. Some types of depression were rapidly relieved by such treatment, while those types associated with anxiety and agitation did not respond.

     

Neurochemical and behavioural investigations of the NMDA receptor-associated glycine site in the rat striatum: Functional implications for treatment of parkinsonian symptoms

The glutamatergic cortico-striatal and subthalamo-entopeduncular pathways are both overactive in parkinsonism. Previous behavioural investigations have shown that intra-entopeduncular injection of either NMDA-site or glycine-site antagonists results in alleviation of parkinsonian symptoms, although injection of the former is associated with the appearance of anaesthetic-like side effects. These behavioural differences may be mediated by action on different NMDA receptor subtypes. Recent neurochemical and molecular pharmacological studies have indicated the existence of NMDA receptor subtypes which display differential modulation by glycine. In the present study, three potential modes of NMDA antagonism were differentiated in vitro by effects on [³H]-glycine binding to striatal sections. Specific [³H]-glycine binding was totally displaced by the glycine partial agonist (R)-HA-966; the NMDA-site antagonistd-CPP had no effect; and the NMDA-site antagonistd-AP5 displaced [³H]-glycine binding in a subpopulation of glycine sites. The anti-parkinsonian effects of (R)-HA-966,d-CPP andd-AP5 were assessed by intra-striatal injection in reserpine-treated rats and 6-OHDA-lesioned rats. Injection of (R)-HA-966 andd-CPP resulted in alleviation of parkinsonian akinesia, although the latter elicited anaesthetic-like side effects;d-AP5 was ineffective as an anti-parkinsonian agent. (R)-HA-966 was also effective as an anti-parkinsonian agent when administered systemically in the reserpine-treated rat. These data suggest that different classes of NMDA antagonist mediate different behavioural responses within the parkinsonian striatum. The behavioural response produced may depend on the exact nature of the conformational change induced by the antagonist and the location of the subtype most sensitive to that class of compound. Selection of a specific mode of NMDA receptor antagonism or targeting of striatal NMDA receptor subtypes may form the basis of a novel therapeutic approach to Parkinson's disease.     

The amino acid <Emphasis Type="SmallCaps">l</Emphasis>-lysine blocks the disruptive effect of phencyclidine on prepulse inhibition in mice

Rationale The cognitive and attentional deficits observed in schizophrenic patients are now considered central to the pathophysiology of the disorder. These deficits include an inability to filter sensory input as measured by, e.g., prepulse inhibition (PPI) reflex. Administration of phencyclidine (PCP), a drug that can induce a schizophrenia-like psychosis in humans, disrupts PPI in experimental animals. In rodents, this PCP-induced deficit can be blocked by pretreatment with nitric oxide (NO) synthase inhibitors. This suggests that some of the behavioral effects of PCP are mediated via NO. The substrate for in vivo NO production is l-arginine, and active transport of l-arginine via the cationic amino acid transporter may serve as a regulatory mechanism in NO production. Objectives The aim of the present study was to study the effects of l-arginine transport inhibition, using acute and repeated l-lysine treatment, on PCP-induced disruption of PPI in mice. Results Subchronic, and to some extent acute, pretreatment with l-lysine blocked a PCP-induced deficit in PPI without affecting basal PPI. Conclusions l-lysine has been shown to block l-arginine transport in vitro, most likely via a competitive blockade and down regulation of cationic amino acid transporters. However, the importance of l-arginine transport as a regulatory mechanism in NO production in vivo is still not clear. The present results lend further support to the notion that some of the effects of PCP in the central nervous system are mediated via NO and that l-arginine transport may play a role in the regulation of NO production in the brain.     

Limbitrol (amitriptyline plus chlordiazepoxide) revisited

The effect of increased central serotonergic levels on motor activity was investigated in rats neonatally treated with 6-hydroxydopamine (6-OHDA) in the lateral ventricles. Regional brain assays of monoamine levels in 90-day-old rats showed depletion of catecholamines, but not of serotonin, in the forebrain accompanied by a large elevation of norepinephrine, and minor elevation of serotonin, in the hindbrain. Measures of behavioral activity in adulthood were taken after treatment with saline, pargyline, l-tryptophan, or pargyline given 30 min before l-tryptophan. The combined treatment of pargyline plus l-tryptophan produced hyperactivity in controls and this effect was blocked in the 6-OHDA-treated animals. These findings indicate that the serotonergic system is capable of influencing motor activity, but that this influence is blocked in animals permanently depleted of catecholamines in their terminal field regions.     

Pre- and postjunctional actions of endothelin in the rat iris sphincter preparation

Effects of endothelins (ETs) were studied in the rat iris sphincter preparation. Three peptides (ET1, ET-2 and ET-3) caused contractile responses, and the rank order of agonist potency was: ET-1 = ET-2 > ET-3. The concentration-response curve to ET-1 was shifted to the right by the ET_A receptor antagonist cyclo [d-Asp-l-Pro-d-Val-l-Leu-d-Trp] (BQ-123: 10^–7 M), the pA₂ value of which was 7.41 ± 0.09 (n = 4).ET-1 and ET-3, at the concentration of 10^–9 M, potentiated cholinergic contractions evoked by electrical field stimulation (5 and 20 Hz) without affecting the postjunctional sensitivity to carbachol. This potentiating effect was not influenced by BQ-123 (10^–6 M). The ET-evoked percentage increase in the stimulation-induced contraction observed at 5 Hz was significantly greater than that at 20 Hz. A release of immunoreactive ET was detected when the preparation was stimulated at 20 Hz (1.81 ± 0.36 pg/sphincter n = 6). ET release evoked by 20 Hz stimulation was completely abolished by tetrodotoxin (10^–7 M).In conclusion, ET interacts with two different receptor types, ET_A and non-ET_A receptors (probably ET_B) which exist post- and presynaptically at cholinergic neuroeffector junctions of the rat iris preparation. Stimulation of ET_A receptor results in a direct muscle contraction and non-ET_A receptor activation facilitates the acetylcholine output from cholinergic nerve endings. It is suggested that ET released from a tetrodotoxin-sensitive site is involved in the modulation of acetylcholine release in the rat iris sphincter preparation. Correspondence to: I. Takayanagi at the above address     

N-ccetyl-S-(1-cyano-2-hydroxyethyl)-l-cysteine,a new urinary metabolite of acrylonitrile and oxiranecarbonitrile

Two mercapturic acids, i. e., N-acetyl-S-(1-cyano-2-hydroxyethyl)-l-cysteine (CHEMA) and N-acetyl-S(2-hydroxyethyl)-l-cysteine (HEMA), were isolated from the urine of rats dosed with four successive doses of oxiranecarbonitrile (glycidonitrile, GN), 5 mg/kg, a reactive metabolic intermediate of acrylonitrile (AN). GC-MS analysis of methylated urine extracts from both AN- and GN-dosed rats showed another mercapturate which was identified as N-acetyl-S-(1-cyanoethenyl)-l-cysteine (1-CEMA) methyl ester using an authentic reference sample. The mass spectrum of this compound was very similar to that of a methylated metabolite of AN tentatively identified by Langvardt et al. (1980) as N-acetyl-3-carboxy-5-cyanothiazane (ACCT). In contrast, no ACCT was found in rats dosed with either GN or AN. Hence, there is no evidence for the formation of ACCT or its isomers in rats dosed with AN or GN. The methyl ester of 1-CEMA is formed artificially by dehydration of CHEMA methyl ester in the injector of the gas chromatograph.Details of the synthetic procedures and NMR-spectra are available from the authors on request     

A dose-response study of nitric oxide synthase inhibition in different vascular beds in man

Background and objective Nitric oxide (NO) is an almost ubiquitous messenger molecule and is implicated in several disorders. N^G monomethyl l-arginine (l-NMMA:546C88) is an inhibitor of all three NO synthases (NOS), the enzymes that catalyse the production of NO. The present study was performed to evaluate the dose-response relation of l-NMMA to improve the design and interpretation of studies in migraine sufferers and other diseases.Methods In a double-blind, placebo-controlled, cross-over design, six healthy volunteers were randomised to receive three different doses of l-NMMA (0.3 mg/kg, 1 mg/kg, 3 mg/kg) or placebo (5% dextrose) intravenously (iv) over 5 min on four different days. On a fifth study day, in an open design, the same subjects received l-NMMA in the dose 6 mg/kg iv over 15 min. The effect of l-NMMA on the maximal mean blood velocity (V_mean) in the middle cerebral artery (MCA) (transcranial Doppler), the luminal diameter of the radial artery (high-frequency ultrasound), mean arterial blood pressure (MAP), heart rate and electrocardiogram were repeatedly followed every 5 min until 60 min after start of the infusion, then every 15 min during the following hour, and at 3 h and 4 h.Results Inhibition of NOS had no effect on V_mean in MCA or on the diameter of the radial artery, but MAP increased and heart rate decreased dose dependently. With a dose of 6-mg/kg l-NMMA infused over a 15-min period, the maximum MAP increase was 20% 20 min after the start of l-NMMA infusion. The maximum decrease of heart rate was 24% 15 min after start of the l-NMMA infusion.Conclusion l-NMMA in a dose that caused marked changes in systemic blood pressure and heart rate had no effect on cerebral and radial arteries in man.     

Toxic effect of various selenium compounds on the rat in the early postnatal period

The toxic effect of selenium compounds (sodium selenate,d,l-selenomethionine,d,l-selenocystine, dimethyl selenide, and trimethylselenonium ion) was tested in 10-day old male rats. Increasing doses of the compounds were administered an s.c. injection and control animals were not injected. All compounds tested were lethal. Eye lens cataract was induced by the administration of selenate,d,l-selenomethionine, andd,l-selenocystine, while dimethyl selenide and trimethylselenonium ion failed to cause cataract. The cataractogenic effect of the above compounds may be attributed to their interference with glutathione metabolism.