Sleep-inducing effects of L-tryptophan

Possible roles of excess tryptophan metabolites in cancer

Tryptophan is metabolized through serotonin, indole, and kynurenine (KN) pathways. Uptake of an excess amount of tryptophan accompanied with vitamin B6 deficiency may result in the accumulation of higher concentrations of metabolites mainly from the KN pathways in the bladder. These metabolites could interact with nitrite to become mutagenic nitrosamines. They could be a promoter in the initiator-promoter model of carcinogenesis. They produced bladder cancer when implanted in the bladder. They also interact with transition metals copper or iron to form reactive radicals or reactive oxygen species (ROS). Some metabolites, 3-hydroxy-anthranilic acid, were autooxidized to mutagenic cinnabarinic and anthranilyl radical intermediates. These radical intermediates could also be ligands that interact with aryl hydrocarbon receptor (AhR) and induce xenobiotic metabolizing enzymes (XMEs) to metabolize contaminated carcinogens. When tryptophan is exposed to either visible or UV light, a photoproduct of 6-formylindolo[3,2b]-carbazole is formed, which has a very high affinity for the AhR that plays a role in carcinogenesis. This review gives an insight into various mechanisms through which tryptophan metabolites cause carcinogenesis. It could be concluded that tryptophan metabolites play a complementary role in promoting carcinogenesis along with carcinogens like aflatoxin, CCl(4) , 2-acetylaminofluorene, 4-aminobiphenyl, 2-naphthylamine, or N-[4-(5-nitro-2-furyl)-2-thiazolyl] formamide. The underlying mechanisms could be their autoxidation, exposure to either visible or UV light, interaction with nitrite or transition metals to form reactive intermediates, serving as ligands to interact with an AhR that is known to play a role in carcinogenesis through induction of XMEs. Further research is warranted.Environ.

Kinetics of drug action in disease states. XLIII: Potentiating effect of L-tryptophan on the hypnotic action of phenobarbital and ethanol in rats

The essential amino acid L-tryptophan has been widely used as a sleeping aid because it can produce drowsiness and decrease sleep latency. Its concentrations in plasma and brain and its binding to plasma protein are markedly altered in hepatic encephalopathy and renal failure. The purpose of this investigation was to determine if L-tryptophan can enhance the sensitivity of the central nervous system to the hypnotic actions of a barbiturate and an alcohol. Female rats weighing approximately 200 g received an intravenous infusion of L-tryptophan (0.8 or 0.08 mg/min) for 30 min and then an infusion of phenobarbital (0.824 mg/min) with L-tryptophan (0.8 or 0.08 mg min-1) until the onset of loss of righting reflex (LRR). Control animals received an infusion of saline solution for 30 min and then phenobarbital without the amino acid. Similar experiments were performed with ethanol (16.3 mg/min), with and without L-tryptophan (0.8 mg/min). L-Tryptophan infused alone at a rate of 3.8 mg/min for 84 min did not cause LRR. Administration of L-tryptophan at a rate of 0.8 mg/min with phenobarbital was associated with statistically significant reductions in the total dose and concentrations of phenobarbital in serum, serum water, brain, and cerebrospinal fluid (CSF) at onset of LRR. The 0.08 mg/min infusion of L-tryptophan had a less pronounced effect, with statistically significant reductions of phenobarbital concentrations at onset of LRR in brain and CSF. L-Tryptophan also significantly reduced the total dose and the concentrations of ethanol in serum, brain, and CSF required to produce LRR.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of L-tryptophan and other amino acids on electroencephalographic sleep in the rat

Electroencephalographic sleep was quantitated in adult male Sprague-Dawley rats following single injections of the methylesters of tryptophan, valine or alanine. The amino acids were administered at the onset of the daily light period (09.00 h); electrographic data were collected for the succeeding 6-h period. Saline served as the injection control, and fluoxetine, a serotonin-reuptake blocker, as a positive control. The injection of tryptophan methylester (125 mg/kg) caused a delay in rapid eye movement (REM) sleep onset, and significantly reduced the amount of REM sleep during the first 2 h postinjection. Tryptophan produced no effect on sleep onset, nor did it influence total sleep time. Fluoxetine (2.5 mg/kg) produced similar effects, as previously observed. The methylesters of valine and alanine were without effect on REM sleep, when injected at a molar dose equivalent to that for tryptophan. No consistent effects of any of the test substances were noted on non-REM (NREM) sleep or waking time, or on any of the other sleep indices quantitated. Together, the data indicate that tryptophan selectively reduces REM sleep; the effect is not due to a non-specific action of amino acids or their methylesters. The effect on REM sleep may be the consequence of a tryptophan-induced stimulation of 5-HT synthesis and release, since it is like that produced by fluoxetine, a drug that enhances transmission across serotonin synapses.

L-tryptophan: a rational anti-depressant and a natural hypnotic?

L-tryptophan is an essential amino acid which is the metabolic precursor of serotonin. Because of the evidence that serotonin deficiency may be an aetiological factor in some sorts of affective disorder and that serotonin is important in the biochemistry of sleep, L-tryptophan has been suggested as a "rational" anti-depressant and as a "natural" hypnotic. This paper reviews the biochemistry and pharmacology of L-tryptophan as well as the literature of the clinical trials that have been conducted with it and suggests that, by itself, L-tryptophan may be useful in mild cases of depression accompanied by endogenous features and cases of bipolar disorder resistant to standard treatments. It also potentiates the monoamine oxidase inhibitors and possibly the serotonergic tricyclic drugs. L-tryptophan may improve the depressed mood of Parkinsonian patients and has a clinically useful hypnotic action. There is evidence it may be useful in organic mental disorders induced by levodopa. Dosage schedules, contraindications and complications are discussed.

Short-term effects of fluoxetine and trifluoromethylphenylpiperazine on electroencephalographic sleep in the rat

Fluoxetine and trifluoromethylphenylpiperazine (TFMPP) were studied for their short-term effects on electroencephalographic sleep in male rats. Following single injection, each drug produced a sizeable, dose-related suppression of rapid-eye-movement (REM) sleep that persisted for 4-5 h (fluoxetine, 0.625-5 mg/kg; TFMPP, 0.10-1.25 mg/kg). TFMPP also consistently increased non-REM (NREM) sleep during the second hour after drug injection, though this effect was not dose-related (it was seen at all doses tested). Fluoxetine produced small effects on NREM sleep that varied non-systematically with dose and time after drug injection. TFMPP, but not fluoxetine, also increased at all doses the number of delta waves per minute of NREM sleep in the second hour. A structural analog of TFMPP that is inactive at serotonin (5-HT) receptors [4-(m-trifluoromethylphenyl)piperadine; LY97117] was also tested, and found to be devoid of effects on NREM and REM sleep. Both fluoxetine (a 5-HT reuptake blocker) and TFMPP (a 5-HT agonist) enhance transmission across 5-HT synapses, though by different mechanisms. Because they have the common effect of suppressing REM sleep, and in a dose-related manner, the data support the notion that 5-HT neurons in the brain, when active, can suppress REM sleep.

Alteration of human pain thresholds by nutritional manipulation and L-tryptophan supplementation

Pain perception and tolerance thresholds of 30 normal subjects were determined by electrical stimulation of dental pulps before and after dietary manipulation which included either tryptophan supplementation or placebo. Perception threshold levels were similar in tryptophan and placebo subjects; however, pain tolerance levels were significantly higher in the group receiving tryptophan. Side effects such as nausea, skin itching, weight loss and mood elevation were more common in the tryptophan group than in the placebo group.

Sleep suppressant action of quipazine: relation to central serotonergic stimulation

Administration of quipazine maleate (1-10 mg/kg, IP), a proposed 5-hydroxytryptamine (5-HT) receptor stimulant to rats produced a dose-related suppression of both slow-wave sleep (SWS) and rapid-eye-movement sleep (REMS) accompanied by an increase in head-shaking behavior. These effects were observed during the first 6 hr of a 12-hr EEG recording session. The latencies to the sleep states were markedly prolonged and correlated with the duration of head-shaking behavior induced by the drug. A significant inverse relationship was found between the amount of SWS or REMS and the number of head-shakes occurring during the first 6-hr period. Since head-shaking behavior in rodents has been proposed as a quantitative, behavioral model of central 5-HT activation, the data suggest a causal relationship between enhanced 5-HT activity and sleep suppression. This assumption is further supported by the observation that pretreatment with metergoline (2.5 mg/kg, IP) a 5-HT receptor blocker, reduced quipazine's effects on both SWS and head-shaking behavior.

Reduction in brain glucose utilization rate after tryptophol (3-indole ethanol) treatment

3-Indole ethanol has been recently identified as the hypnotic agent in trypanosomal sleeping sickness, and because it is formed in vivo after ethanol or disulfiram treatment, is also associated with the study of alcoholism. When administered intraperitoneally to rats (250 mg/kg) tryptophol induced a sleep-like state that lasted less than an hour (no righting reflex was apparent 2 min after injection, but it returned at 11 min in bovine serum albumin solution, and 47 min in 40% ethanol solution). In ethanol solutions, tryptophol reduced brain cortical glucose utilization by 55% to the basal brain metabolic rate, and this effect lasted less than 1 h. Synergistic effects of tryptophol and ethanol were suggested by the observation that in albumin solution, tryptophol reduced brain glucose utilization by 35%, but a normal rate was not observed until 2 h postinjection.

Changes in the rat sleep-wake cycle produced by DL-6-fluorotryptophan, a competitive inhibitor of tryptophan hydroxylase

DL-6-Fluorotryptophan (6-FT), a competitive inhibitor of tryptophan hydroxylase, produced a transient disruption of sleep in rats chronically implanted with EEG recording electrodes. In the 4 h period following the administration of 6-FT (120 mg/kg) awake time was increased, paradoxical sleep time was decreased and slow-wave sleep remained unchanged. These sleep changes were accompanied by significant reductions in brain 5-HT levels. L-Tryptophan (100 mg/kg) co-administration with 6-FT prevented the major sleep changes whereas L-leucine (100 mg/kg) was without effect. The major sleep changes produced by 6-FT were prevented by the pineal indole melatonin (20 mg/kg) but not by L-5-hydroxytryptophan (5 mg/kg). These neurochemical and drug interaction data raise the possibility that 5-hydroxytryptamine is involved in the control of paradoxical rather than slow-wave sleep in the rat.

Hypnotic effect of tryptophan analog in rats

The effects of DL 2-amino-3-(1-naphthyl) propanoic acid, a tryptophan analog, on sleep and brain chemistry were investigated in rats. Similar to previous findings with tryptophan, the tryptophan analog (30 mg/kg, IP) reduced slow-wave sleep (SWS) latency. The reduction in SWS latency occurred at a time when 5-hydroxytryptamine (5-HT) concentration was reduced in the cortex, pons-medulla and striatum-thalamus with no change in the concentration of 5-hydroxyindoleacetic acid, a major metabolite of 5-HT. At the same time, norepinephrine concentration was reduced in the cortex, hippocampus and striatum-thalamus with a marked reduction (40%) in cortical dopamine (DA). The reduction of cortical DA coincided with a 53% decrease in homovanillic acid, a major metabolite of DA. The behavioral effect of tryptophan analog for six hours, as monitored by the EEG, was an increase in SWS by 25 min and a decrease in waking by 29 min. These data suggest that the effects of the tryptophan analog on sleep may be due to the attenuation of the activity of brain catecholamines and imply that tryptophan may as well produce its hypnotic effect via a similar mechanism.

Effects of L-tryptophan and ethanol on sleep parameters in the rat

Sleep parameters were monitored following (1) a single 2 g/kg oral dose of ethanol, (2) an oral dose of L-tryptophan (600 mg/kg), and (3) administration of both drugs simultaneously. Ethanol reduced REM and increased slow wave significantly. The effects of L-tryptophan were apparent only in the case of one parameter, REM latency. Administration of both drugs resulted in a significantly shorter REM latency than that observed for ethanol alone. Results are discussed in terms of possible changes in the biosynthesis of 5-HT.

The insomnia of 'sleeping in a strange place': effects of l-tryptophane

Forty-two normal human subjects were studied in the sleep laboratory for one night each. Fourteen were given placebo at bedtime, 14 took l-tryptophane 1 g, and 14 took l-tryptophane 3 g. Both tryptophane groups had significantly lower sleep latency than the placebo group. The usually discarded 'first laboratory night' produces a mild situational insomnia in normal persons and thus can be useful in certain sleep studies.