The influence of intravenous L-tryptophan on plasma melatonin and sleep in men

The mammalian gastro-intestinal tract is a NOT a major extra-pineal source of melatonin

In 1992, a paper reported that the melatonin content of the rat duodenum was 24 000 ± 2000 pg/g tissue (range: 4000-100 000 pg/g) while the pineal melatonin content was 580 000 ± 36 000 pg/g. The data has been used for the last 30 years to infer that the gut produces 400 hundred times more melatonin than the pineal gland and that it is the source of plasma melatonin during the daytime. No-one has ever challenged the statement. In this review, evidence is summarised from the literature that pinealectomy eliminates melatonin from the circulation and that studies to the contrary have relied upon poorly validated immunoassays that overstate the levels. Similarly studies that have reported increases in plasma melatonin following tryptophan administration failed to account for cross reactivity of tryptophan and its metabolites in immunoassays. The most extraordinary observation from the literature is that in those studies that have measured melatonin in the gut since 1992, the tissue content is vastly lower than the original report, even when the methodology used could be overestimating the melatonin content due to cross reactivity. Using the more contemporary results we can calculate that rather than a 400:1 ratio of duodenum: pineal melatonin, a ratio of 0.05-0.19: 1 is likely. The gut is not a major extra-pineal source of melatonin; indeed it may well not produce any.

Dietary supplementation with tryptophan increases the plasma concentrations of tryptophan, kynurenine, and melatonin in Yili mares

Context Tryptophan (Trp) is the precursor of melatonin (MT) and the latter plays vital physiological roles in mares. Aims The purpose of this experiment was to investigate the effects of dietary Trp supplementation on the plasma Trp, kynurenine (Kyn), 5-hydroxytryptophan (5-HT), and melatonin (MT) concentrations in female Yili horses. Methods Twenty Yili mares aged 2 years with mean bodyweight (BW) of 263.5 ± 14.77 kg and of similar stature were selected and randomly allocated to the control (CON; basal diet), basal diet plus Trp at 20 mg/kg BW (TRP1), basal diet plus Trp at 40 mg/kg BW (TRP2), or basal diet plus Trp at 60 mg/kg BW (TRP3) group. Key results The plasma total Trp, Kyn, and MT concentrations in all Trp groups steadily increased, reached their peak values, and gradually decreased after Trp supplementation between 0 h and 12 h. However, the plasma 5-HT concentration displayed the opposite trend. Peak plasma total Trp and 5-HT concentrations were attained between 1 h and 3 h, while those of KYN and MT appeared between 4 h and 6 h after Trp supplementation. The plasma total Trp and Kyn concentrations were significantly higher in TRP2 and TRP3 than in CON between 1 h and 12 h (P < 0.05) after Trp supplementation. The plasma 5-HT concentration was significantly (P < 0.05) lower in TRP1 than in CON at 3 h, 4 h, 6 h, 9 h, and 12 h after Trp supplementation. The plasma MT concentrations in TRP1 and TRP2 were significantly (P < 0.05) higher than in CON at 3 h, 4 h, and 12 h, and at 0 h, 1 h, and 12 h after Trp supplementation (P < 0.05). Conclusions Dietary Trp supplementation can increase the plasma total Trp, Kyn, and MT concentrations in Yili mares and the optimal Trp dosage was 20 mg/kg BW. Implication The addition of Trp to a basal diet or feed may increase the plasma total Trp, Kyn, and MT concentrations in female horses.

One-week sleep hygiene education improves episodic memory in young but not in older adults during social isolation

Memory formation is a dynamic process that comprises different phases, such as encoding, consolidation and retrieval. It could be altered by several factors such as sleep quality, anxiety, and depression levels. In the last years, due to COVID-19 pandemic, there was a reduction in sleep quality, an increase in anxiety and depressive symptoms as well as an impairment in emotional episodic memory encoding, especially in young adults. Taking into account the profound impact of sleep quality in daily life a series of rules has been developed that are conducive to consistently achieving good sleep, known as sleep hygiene education. These interventions have been shown to be effective in improving sleep quality and duration and reducing depressive and anxiety symptoms. Here we propose the implementation of a brief sleep hygiene education to improve sleep quality and memory performance as well as to diminish anxiety and depressive scores. For that, participants were divided into two groups: Sleep hygiene education and control group. After that, they were evaluated for anxiety, depression, and sleep quality levels and trained on an episodic memory task. They were tested immediately after (short-term test) and also 1 week later (long-term test). This procedure was also performed before the sleep hygiene education and was taken as baseline level. We found that episodic memory performance for young adults improved for the SHE group after intervention but not for older adults, and no improvements in emotional variables were observed. Despite not observing a significant effect of the intervention for young and older adults regarding the sleep quality scores, we consider that there may be an improvement in sleep physiology that is not subjectively perceived, but would also have a positive impact on memory processes. These results show that even a sleep hygiene education of 1 week could improve cognition in young adults when acute memory and sleep impairment occurs, in this case, due to the isolation by COVID-19 pandemic. However, we suggest that longer interventions should be implemented for older adults who already experience a natural decline in cognitive processes such as episodic memory formation.

Nutritional Modulation of Sleep Latency, Duration, and Efficiency: A Randomized, Repeated-Measures, Double-Blind Deception Study

PURPOSE

This study aimed to test the hypothesis that a novel nutritional blend composed of tryptophan, glycine, magnesium, tart cherry powder, and l -theanine enhances subjective and objective measures of sleep during free living conditions.

METHODS

In a randomized, repeated-measures crossover and double-blind deception design, participants ( n = 9 males and 7 females, age = 24 ± 3 yr, body mass = 69.8 ± 11.6 kg, stature = 170.8 ± 9.1 cm) completed a 3-d familiarization period, followed by 3-d intervention and placebo trials. Subjective Pittsburgh Quality Sleep Index, Core Consensus Sleep Diary, and Karolinska Sleepiness Scale survey tools, alongside objective actigraphy measures of sleep, were assessed, with daily nutritional intake, activity, and light exposure standardized between trials. Participants provided daily urine samples for assessment of targeted and untargeted metabolomes.

RESULTS

The intervention trial reduced sleep onset latency (-24 ± 25 min; P = 0.002), increased total sleep time (22 ± 32 min; P = 0.01), and increased sleep efficiency (2.4% ± 3.9%; P = 0.03), while also reducing morning sleepiness ( P = 0.02). Throughout the study, 75% of participants remained blinded to sleep assessment as a primary outcome measure, with 56% subjectively indicating improved sleep during the intervention trial. Metabolomic analysis highlighted several significantly altered metabolomes related to sleep regulation between trials, inclusive of 6-sulfatoxymelatonin, d -serine, and l -glutamic acid.

CONCLUSIONS

Data demonstrate that using the proposed blend of novel nutritional ingredients during free living conditions reduced sleep onset latency, increased total sleep duration, and increased sleep efficiency, leading to reduced perceptions of morning sleepiness. These effects may be mediated by the upregulation of key metabolites involved in the neurophysiological modulation of the sleep/wake cycle.

Melatonin: Both a Messenger of Darkness and a Participant in the Cellular Actions of Non-Visible Solar Radiation of Near Infrared Light

Throughout the history of melatonin research, almost exclusive focus has been on nocturnally-generated pineal melatonin production, which accounts for its circadian rhythm in the blood and cerebrospinal fluid; these light/dark melatonin cycles drive the daily and seasonal photoperiodic alterations in organismal physiology. Because pineal melatonin is produced and secreted primarily at night, it is referred to as the chemical expression of darkness. The importance of the other sources of melatonin has almost been ignored. Based on current evidence, there are at least four sources of melatonin in vertebrates that contribute to the whole-body melatonin pool. These include melatonin produced by (1) the pineal gland; (2) extrapineal cells, tissues, and organs; (3) the microbiota of the skin, mouth, nose, digestive tract, and vagina as well as (4) melatonin present in the diet. These multiple sources of melatonin exhibit differentially regulated mechanisms for its synthesis. Visible light striking the retina or an intense physical stimulus can suppress nocturnal pineal melatonin levels; in contrast, there are examples where extrapineal melatonin levels are increased during heavy exercise in daylight, which contains the whole range of NIR radiation. The cumulative impact of all cells producing augmented extrapineal melatonin is sufficient to elevate sweat concentrations, and potentially, if the exposure is sustained, to also increasing the circulating values. The transient increases in sweat and plasma melatonin support the premise that extrapineal melatonin has a production capacity that exceeds by far what can be produced by the pineal gland, and is used to maintain intercellular homeostasis and responds to rapid changes in ROS density. The potential regulatory mechanisms of near infrared light (NIR) on melatonin synthesis are discussed in detail herein. Combined with the discovery of high levels of melanopsin in most fat cells and their response to light further calls into question pineal centric theories. While the regulatory processes related to microbiota-derived melatonin are currently unknown, there does seem to be crosstalk between melatonin derived from the host and that originating from microbiota.

Assessing the potential for drug interactions and long term safety of melatonin for the treatment of insomnia in children with autism spectrum disorder

INTRODUCTION

Melatonin preparations are emerging first-line pharmacotherapy for insomnia in children and adolescents with autism spectrum disorder (ASD), but quality, formulation, consistency, dosing, and limited long-term safety data are of concern. The recent approval of pediatric-appropriate prolonged-release melatonin (Ped-PRM) addresses these aspects.

AREAS COVERED

A systematic search of PubMed and web of science for prospective, randomized, and controlled trials (RCTs) of melatonin preparations vs placebo in children and adolescents with ASD and the European public assessment report on Ped-PRM was conducted.

EXPERT OPINION

Melatonin is rapidly absorbed and undergoes first pass hepatic metabolism by cytochrome CYP1A2; over 80% is excreted in the urine as 6-sulfatoxymelatonin (inactive). Immediate-release melatonin (IRM) is short-acting (3-4 h), whereas PRM provides therapeutic levels throughout the night. Drugs interacting with CYP1A2 are likely to slow-down melatonin metabolism. High variability in bioavailability among subjects calls for dose optimization. Melatonin was essentially safe for short-term use (up to 3 months). Long-term data available for Ped-PRM demonstrate fatigue (6.3%), somnolence (6.3%), and mood swings (4.2%) with no evidence of effects on height, BMI, or pubertal development, tolerance or withdrawal effects following long-term use of this product. Studies on long-term safety of IRM and oversight of melatonin supplement manufacture are warranted.

Sleeping Disorders in Healthy Individuals with Different Dietary Patterns and BMI, Questionnaire Assessment

The COVID-19 pandemic and abiding restrictions have affected every life domain. Sleep disturbances are a major health issue that is linked with a higher prevalence of metabolic syndrome, obesity, and psychological burdens. Research of sleeping disorders among vegetarian and non-vegetarian subpopulations is limited. The aim of the study was to assess the prevalence of sleeping disorders during the COVID-19 pandemic among people with different dietary patterns. Using a web-based cross-sectional survey, data were collected from 1987 people. A total of 1956 respondents met all study conditions. The questionnaire consisted of sociodemographic information, assessment of dietary habits, and assessment of the prevalence of insomnia and sleepiness, based on the Athens Insomnia Scale (AIS) and Epworth Sleepiness Scale (ESS). A total of 36.04% (n = 705) respondents declared that they noticed a change in the quality of their sleep during the last year. According to AIS and ESS, non-vegetarians suffered from insomnia or sleepiness more often than vegetarians. Insomnia and sleepiness were also more prevalent among those respondents who declared consumption of fruit and vegetables less often than once a day compared with those who consumed fruit and vegetables daily. Respondents with BMI within the recommended limit (18.5–24.99) suffered from insomnia less often when compared with underweight (BMI < 18.5) or obese (BMI ≥ 25) respondents. Those results may be useful for public health workers and medical professionals in terms of establishing new instruments that help treat sleeping disorders.

[L-tryptophan as dietetic supplement and treatment for hot flashes, astenia, and insomnia in cancer patients]

Introduction

Introduction: in women with breast cancer and gynecologic cancer, as well as in men with prostate carcinoma, hot flashes, asthenia, and insomnia are common and bothersome symptoms that impair quality of life. Objective: to evaluate the effectiveness of tryptophan intake as a treatment for hot flushes, asthenia, and insomnia in patients with prostate, breast, and uterine cervical cancer. Materials and methods: intervention study without a control group at the HUCA Radiation Oncology Service, from July 2018 to July 2019. A total of 60 patients with prostate, breast, or uterine cervical cancer who had received treatment with radiotherapy and hormone therapy, and who presented with hot flushes, asthenia, and insomnia were included. L-tryptophan was administered at a dose of 3 g per day. Results: a significant increase in serum tryptophan levels at the end of the study (p < 0.001) and a significant decrease in the scores of the study symptoms were reported. Although statistical significance was not found, a significant improvement in each symptom was observed, as well as an improvement in quality of life (p < 0.001). Conclusions: the study suggests that, in patients with breast, prostate, or uterine cervical cancer, and symptoms such as hot flushes, asthenia, and insomnia, the administration of tryptophan as a nutritional supplement is well tolerated, improves quality of life, and is associated with improvement in the scale scores of the symptoms of interest, although no statistically significant relationship with increased blood tryptophan levels was found.

Thymus-Pineal Gland Axis: Revisiting Its Role in Human Life and Ageing

For years the thymus gland (TG) and the pineal gland (PG) have been subject of increasingly in-depth studies, but only recently a link that can associate the activities of the two organs has been identified. Considering, on the one hand, the well-known immune activity of thymus and, on the other, the increasingly emerging immunological roles of circadian oscillators and the rhythmically secreted main pineal product, melatonin, many studies aimed to analyse the possible existence of an interaction between these two systems. Moreover, data confirmed that the immune system is functionally associated with the nervous and endocrine systems determining an integrated dynamic network. In addition, recent researches showed a similar, characteristic involution process both in TG and PG. Since the second half of the 20th century, evidence led to the definition of an effectively interacting thymus-pineal axis (TG-PG axis), but much has to be done. In this sense, the aim of this review is to summarize what is actually known about this topic, focusing on the impact of the TG-PG axis on human life and ageing. We would like to give more emphasis to the implications of this dynamical interaction in a possible therapeutic strategy for human health. Moreover, we focused on all the products of TG and PG in order to collect what is known about the role of peptides other than melatonin. The results available today are often unclear and not linear. These peptides have not been well studied and defined over the years. In this review we hope to awake the interest of the scientific community in them and in their future pharmacological applications.

Food policy, nutrition and nutraceuticals in the prevention and management of COVID-19: Advice for healthcare professionals

BACKGROUND

The 2019 novel coronavirus (2019-nCoV) represents an ongoing major global health crisis with a potentially unprecedented death toll and socio-economic impact in the modern era. Measures taken to reduce the rate of transmission are too unprecedented, but are deemed necessary. The extensive strain on public health services has meant that individual agency is increasingly called for. To support this, there is a need to review policy and procedure governing the food and commerce industries in particular. Additionally, it is necessary to convey a more comprehensive and nuanced understanding of relevant diet and lifestyle factors to both healthcare practitioners and the general public.

SCOPE AND APPROACH

To our knowledge, a review of possible additional measures for healthcare proffesionals, which includes the possible nutritional management COVID-19 pandemic does not yet exist.Key Findings and Conclusions: This review identifies i) changing trends in consumer awareness and purchasing patterns in response to COVID-19, and their potential future implications for the food and food-commerce industry ii) problematic elements of policy relevant to the outbreak of COVID-19, including the handling of wild-life and food-commerce, ii) newly emergent technologies in food science which represent viable and cost-effective means to reduce the risk of transmission of coronavirus, such as anti-microbial packaging, iii) important nutritional considerations with regard to coronavirus disease prevention and management, including nutrition in early infancy, and the role of select micronutrients (vitamins and minerals), phytochemicals and probiotics in conferring protection against both viral infection and pathogenicity.

Randomized Double-Blind Controlled Trial on the Effect of Proteins with Different Tryptophan/Large Neutral Amino Acid Ratios on Sleep in Adolescents: The PROTMORPHEUS Study

Disturbed sleep is common in adolescents. Ingested nutrients help regulate the internal clock and influence sleep quality. The purpose of this clinical trial is to assess the effect of protein tryptophan (Trp)/large neutral amino acids (LNAAs) ratio on sleep and circadian rhythm. Ingested Trp is involved in the regulation of the sleep/wake cycle and improvement of sleep quality. Since Trp transport through the blood-brain barrier is competing with LNAAs, protein with higher Trp/LNAAs were expected to increase sleep efficiency. This randomized double-blind controlled trial will enroll two samples of male adolescents predisposed to sleep disturbances: elite rugby players (n = 24) and youths with obesity (n = 24). They will take part randomly in three sessions each held over a week. They will undergo a washout period, when dietary intake will be calibrated (three days), followed by an intervention period (three days), when their diet will be supplemented with three proteins with different Trp/LNAAs ratios. Physical, cognitive, dietary intake, appetite, and sleepiness evaluations will be made on the last day of each session. The primary outcome is sleep efficiency measured through in-home electroencephalogram recordings. Secondary outcomes include sleep staging, circadian phase, and sleep-, food intake-, metabolism-, and inflammation-related biochemical markers. A fuller understanding of the effect of protein Trp/LNAAs ratio on sleep could help in developing nutritional strategies addressing sleep disturbances.

Relation of plasma tryptophan concentrations during pregnancy to maternal sleep and mental well-being: The GUSTO cohort

BACKGROUND

Evidence suggests a relation between plasma tryptophan concentrations and sleep and mental well-being. As no studies have been performed in pregnant women, we studied the relation of plasma tryptophan concentrations during pregnancy with sleep quality, and mood during and after pregnancy.

METHODS

Pregnant women (n = 572) from the Growing Up in Singapore Towards healthy Outcomes study completed the Pittsburgh Sleep Quality Index (PSQI), the Edinburgh Postnatal Depression Scale (EPDS) and the State-Trait Anxiety Inventory (STAI) at 26-28 weeks gestation and three months post-delivery. Plasma tryptophan concentrations were measured at 26-28 weeks gestation. Poisson regressions estimated prevalence ratios (PR) for the association between tryptophan and poor sleep quality (PSQI global score > 5), probable antenatal depression (EPDS ≥ 15) and probable anxiety (STAI-state ≥ 41) were calculated adjusting for covariates.

RESULTS

Mean plasma tryptophan concentrations was 48.0µmol/L (SD: 8.09). Higher plasma tryptophan concentrations were associated with a lower prevalence of antenatal poor sleep quality adjusting for covariates [PR: 0.88 (95% CI 0.80, 0.97) per 10µmol/L], especially in those participants who also suffered from anxiety symptoms [PR: 0.80 (95% CI 0.67, 0.95)]. No associations were observed between tryptophan concentrations during pregnancy and postnatal sleep quality or mental well-being.

LIMITATION

Subjective measures were used to assess sleep and mental well-being.

CONCLUSIONS

We observed that higher plasma tryptophan concentrations were associated with a 12% lower prevalence of poor sleep quality during pregnancy, in particular among those with anxiety symptoms. These findings suggest the importance of having adequate tryptophan concentrations during pregnancy.

Tryptophan Intake in the US Adult Population Is Not Related to Liver or Kidney Function but Is Associated with Depression and Sleep Outcomes

BACKGROUND

Tryptophan is an indispensable amino acid and is a precursor of the neurotransmitter serotonin. Tryptophan metabolites, such as serotonin and melatonin, are thought to participate in the regulation of mood and sleep and tryptophan is used to treat insomnia, sleep apnea, and depression.

OBJECTIVE

This study examined the intake of tryptophan and its associations with biochemical, behavioral, sleep, and health and safety outcomes in adults in a secondary analysis of a large, publicly available database of the US population.

METHODS

Data from the NHANES 2001-2012 (n = 29,687) were used to determine daily intakes of tryptophan and its associations with biochemical markers of health- and safety-related outcomes, self-reported depression, and sleep-related variables. Data were adjusted for demographic factors and protein intake. Linear trends were computed across deciles of intake for each outcome variable, and P-trends were determined.

RESULTS

The usual tryptophan intake by US adults was 826 mg/d, severalfold higher than the Estimated Average Requirement for adults of 4 mg/(kg ⋅ d) (∼280 mg/d for a 70-kg adult). Most health- and safety-related biochemical markers of liver function, kidney function, and carbohydrate metabolism were not significantly (P-trend > 0.05) associated with deciles of tryptophan intake and were well within normal ranges, even for individuals in the 99th percentile of intake. Usual intake deciles of tryptophan were inversely associated with self-reported depression measured by the Patient Health Questionnaire raw score (0-27; P-trend < 0.01) and calculated level (1 = no depression, 5 = severe depression; P-trend < 0.01) and were positively associated with self-reported sleep duration (P-trend = 0.02).

CONCLUSIONS

Tryptophan intake was not related to most markers of liver function, kidney function or carbohydrate metabolism. Levels of tryptophan intake in the US population appear to be safe as shown by the absence of abnormal laboratory findings. Tryptophan intake was inversely associated with self-reported level of depression and positively associated with sleep duration.

A Perspective on the Safety of Supplemental Tryptophan Based on Its Metabolic Fates

Over the past 50 y, tryptophan has been ingested in amounts well in excess of its dietary requirement. This use is based on extensive findings that ingesting tryptophan increases brain tryptophan concentrations, which stimulates the synthesis and release of the neurotransmitter serotonin, from which it is derived. Such increases in serotonin function may improve mood and sleep. However, tryptophan ingestion has other effects, such as increasing serotonin production in the gut, increasing serotonin concentrations in blood, stimulating the production of the hormone melatonin (a tryptophan metabolite), stimulating tryptophan metabolism via the kynurenine pathway, and possibly stimulating the production of tryptophan metabolites in the gut microbiome. Several of the kynurenine metabolites have actions on excitatory glutamate receptors in the gut and brain and on cells of the immune system. In addition, metabolites of tryptophan produced by colonic bacteria are reported to cause adverse effects in some species. This review examines each of these tryptophan pathways to determine if any of the metabolites increase after tryptophan ingestion, and if so, whether effects are seen on target body functions. In this regard, recent research suggests that it may be useful to examine kynurenine pathway metabolites and some microbial tryptophan metabolites to determine whether supplemental tryptophan consumption increases their concentrations in the body and amplifies their actions.

Tryptophan-enriched cereal intake improves nocturnal sleep, melatonin, serotonin, and total antioxidant capacity levels and mood in elderly humans

Melatonin and serotonin rhythms, which exhibit a close association with the endogenous circadian component of sleep, are attenuated with increasing age. This decrease seems to be linked to sleep alterations in the elderly. Chrononutrition is a field of chronobiology that establishes the principle of consuming foodstuffs at times of the day when they are more useful for health, improving, therefore, biorhythms and physical performance. Our aim was to analyze whether the consumption of cereals enriched with tryptophan, the precursor of both serotonin and melatonin, may help in the reconsolidation of the sleep/wake cycle and counteract depression and anxiety in 35 middle-aged/elderly (aged 55-75 year) volunteers in a simple blind assay. Data were collected for 3 weeks according to the following schedule: The control week participants consumed standard cereals (22.5 mg tryptophan in 30 g cereals per dose) at breakfast and dinner; for the treatment week, cereals enriched with a higher dose of tryptophan (60 mg tryptophan in 30 g cereals per dose) were eaten at both breakfast and dinner; the posttreatment week volunteers consumed their usual diet. Each participant wore a wrist actimeter that logged activity during the whole experiment. Urine was collected to analyze melatonin and serotonin urinary metabolites and to measure total antioxidant capacity. The consumption of cereals containing the higher dose in tryptophan increased sleep efficiency, actual sleep time, immobile time, and decreased total nocturnal activity, sleep fragmentation index, and sleep latency. Urinary 6-sulfatoxymelatonin, 5-hydroxyindoleacetic acid levels, and urinary total antioxidant capacity also increased respectively after tryptophan-enriched cereal ingestion as well as improving anxiety and depression symptoms. Cereals enriched with tryptophan may be useful as a chrononutrition tool for alterations in the sleep/wake cycle due to age.

The metabolites in the tryptophan degradation pathway might be useful to determine the tolerable upper intake level of tryptophan intake in rats

L-Tryptophan (L-Trp) is a rate-limiting amino acid for growth in people from underdeveloped countries. Because L-Trp is also a precursor to nicotinamide, administration of the free form of L-Trp is a very good method of preventing pellagra. Furthermore, L-Trp has shown some effectiveness for the treatment of a variety of other conditions typically associated with low serotonin levels in the brain. Therefore, information about the no-observed-adverse-effect level and lowest-observed-adverse-effect level of L-Trp is needed. However, it is not possible to experimentally obtain such data in humans due to ethical considerations. The aim of the present workshop was to identify biomarkers that could be used before the appearance of adverse effects of L-Trp. We reviewed the published research using rats to develop an index of the metabolic upper intake level for L-Trp to be used instead of the tolerable upper intake level (UL). These results show that the urinary excretory ratio of anthranilic acid:kynurenic acid is potentially the most sensitive and appropriate surrogate breakpoint index to predict the UL of L-Trp.

Effects of tryptophan supplementation on cashmere fiber characteristics, serum tryptophan, and related hormone concentrations in cashmere goats

This study was designed to investigate the effects of tryptophan (Trp) supplementation on cashmere fiber characteristics and on serum Trp, melatonin (MEL), prolactin (PRL), insulin-like growth factor 1 (IGF-1), triiodothyronine (T3), and thyroxine (T4) concentrations in cashmere goats during the cashmere fast-growth period. Thirty-six Liaoning cashmere wether goats were stratified on the basis of body weight (28±0.8 kg) and assigned randomly to 1 of the following 4 rumen-protected Trp treatments: 0, 2.0, 4.0, and 6.0 g per goat per day. The experimental period lasted 137 d. Blood samples were collected monthly during the daytime (8:00 AM) and at night (8:00 PM). Tryptophan supplementation improved cashmere growth rates, cashmere weight, and body weight (P=0.001) and increased serum Trp levels, nighttime MEL concentrations, IGF-1, and T3 and T4 concentrations (P<0.05). Across the treatments and sampling months, a highly positive correlation between cashmere growth rate and nighttime serum MEL concentrations was observed (r=0.879, P=0.001). A moderately negative correlation between cashmere growth rates and serum PRL concentrations during the day and at night (rday=-0.645, P=0.007; rnight=-0.583, P=0.018) was observed. A moderately positive correlation between the cashmere growth rate and the daytime serum IGF-1 concentration (r=0.536, P=0.032) was observed, and no correlation was found between the cashmere growth rate and the other serum hormone concentrations. These data indicate that changes in serum concentrations of MEL, IGF-1, and PRL are related to cashmere growth in Liaoning cashmere goats during the cashmere fast-growth period. Under the experimental conditions of the current trial, we suggest that Trp may promote cashmere growth by increasing daytime IGF-1 and nighttime MEL secretion.

Melatonin independent protective role of l-tryptophan in experimental reflux esophagitis in rats

Melatonin is implicated in sustaining the esophageal integrity in gastro-esophageal reflux disease. However, the role of its synthetic precursor l-tryptophan is not clear in this pathology. The present study was designed to explore the effects of l-tryptophan on esophageal damage following reflux esophagitis (RE)-establishment and concurrent alterations in factors possibly influencing esophageal integrity such as esophageal melatonin level, luminal acidity, H(+)K(+)-ATPase activity, mucin and gastric PGE(2) levels. RE was established in rats by simultaneous ligation of pylorus region and fore-stomach. RE significantly decreased the esophageal-melatonin level and the expression of its synthesizing enzymes: arylalkylamine-N-acetyltransferase (AA-NAT) and hydroxyindole-O-methyltransferase (HIOMT). Administration of l-tryptophan significantly decreased the RE-induced esophageal mucosal damage, without altering the levels of melatonin. l-Tryptophan pretreatment also normalized the esophageal mucosal damage caused by melatonin receptor antagonist-luzindole. Simultaneously, l-tryptophan significantly increased the RE-decreased expression of AA-NAT with insignificant effect on HIOMT gene expression. In contrast, l-tryptophan per se caused a significant elevation in the esophageal melatonin level, with no significant effect on the expression of AA-NAT and HIOMT enzymes. Further, l-tryptophan significantly normalized the RE-induced changes in the gastric juice volume, acidity and pH. However, it did not significantly inhibit the H(+)K(+)-ATPase activity in vitro. Also, l-tryptophan significantly increased the RE-reduced mucin level, COX-2 activity and thereby PGE(2) levels. Interestingly, indomethacin (PGE(2) synthesis blocker), aggravated the RE-induced tissue injury with simultaneous changes in the gastric volume, acidity, pH and mucin content, which l-tryptophan failed to reverse, suggesting that the attenuating effect of l-tryptophan on gastric secretions could be PGE(2) driven. Thus the current study provide evidences that protective functions of l-tryptophan against RE is independent of its conversion into melatonin, and possibly involve mobilization of factors such as COX-2 derived PGE(2) and mucin that counterbalance the detrimental effect of gastric acid on esophageal mucosa, signifying the therapeutic efficacy of l-tryptophan against the esophageal pathologies.

Synthesis and antidepressant evaluation of five novel heterocyclic tryptophan-hybrid derivatives

This study aimed at evaluating the reactivity of L-Tryptophan (TRP) 1 towards various chemical reagents to produce new bi- and tri-heterocyclic systems providing basic pharmacological activities. Indol-3-yl hydroxyoxazol-2-yl acetonitrile derivatives 5 and 6, indol-3-yl-hydroxyoxazol-2-yl-1,2,4-triazine derivatives 8 and 9, indol-3-yl-hydroxyoxazol-2-yl-aminopyrazole derivatives 11a, b, and indol-3-yl-hydroxyoxazol-2-yl-aminoisoxazole derivative 12 were synthesized via straightforward and efficient methods. The structures were characterized by spectral data (IR, (1)H-NMR, (13)C-NMR, and MS) and the purity was ascertained by microanalysis. Also, this work was extended to study the potential role of the novel synthesized TRP derivatives 5, 6, 9, 11a, and 12 as antidepressant and sedative agents in comparison with TRP. All compounds showed significant antidepressant activity in the forced-swimming test at two doses (50 or 100 mg/kg). Also, all tested compounds (at 50 or 100 mg/kg) produced a significant decrease in locomotor activity of mice during a 30 min observation period. The most potent antidepressant and sedative effect was produced by the tri-heterocyclic compounds 9 and 12, followed by 11a and TRP.

Chronic melatonin treatment and its precursor L-tryptophan improve the monoaminergic neurotransmission and related behavior in the aged rat brain

Melatonin has an important role in the aging process as a potential drug to relieve oxidative damage, a likely cause of age-associated brain dysfunction. As age advances, the nocturnal production of melatonin decreases potentially causing physiological alterations. The present experiments were performed to study in vivo the effects of exogenously administered melatonin chronically on monoaminergic central neurotransmitters serotonin (5-HT), dopamine (DA) and norepinephrine (NE) and behavioral tests in old rats. The accumulation of 5-hydroxy-tryptophan (5-HTP) and L-3,4-dihydroxyphenylalanine (DOPA) after decarboxylase inhibition was used as a measure of the rate of tryptophan and tyrosine hydroxylation in rat brain. Also neurotransmitters 5-HT, DA and NE and some metabolites were quantified by HPLC. In control rats, an age-related decline was observed in neurochemical parameters. However, chronic administration of melatonin (1 mg/kg/day, diluted in drinking water, 4 wk) significantly reversed the age-induced deficits in all the monoaminergic neurotransmitters studied. Also, neurochemical parameters were analyzed after administration of melatonin biosynthesis precursor L-tryptophan (240 mg/kg/day, i.p., at night for 4 wk) revealing similar improvement effects to those induced by melatonin. Behavioral data corresponded well with the neurochemical findings since spatial memory test in radial-maze and motor coordination in rota-rod were significantly improved after chronic melatonin treatment. In conclusion, these in vivo findings suggest that melatonin and L-tryptophan treatments exert a long-term effect on the 5-HT, DA and NE neurotransmission by enhancing monoamine synthesis in aged rats, which might improve the age-dependent deficits in cognition and motor coordination.

Improving the quality of infant sleep through the inclusion at supper of cereals enriched with tryptophan, adenosine-5'-phosphate, and uridine-5'-phosphate

The present study evaluated whether the administration of cereals enriched with nutrients that are facilitators of sleep could help improve the sleep of infants who had sleep disorders at night time. Thirty infants aged 8-16 months with sleep disorders involving at least three nocturnal waking episodes took part in the study. They were given a night-time 'sleep facilitating cereal' product containing 225 mg tryptophan, 5.3 mg adenosine-5'-P, and 6.3 mg uridine-5'-P per 100 g of product. These cereals were given in a double-blind procedure lasting 5 weeks, with ingestion of the cereal between 18:00 and 06:00. In the control week, the children received a standard cereal (75 mg tryptophan/100 g product without nucleotides) dissolved in a standard formula milk (231.5 mg tryptophan, 2.6 mg adenosine-5'-P, 5 mg uridine-5'-P, per 100 g product). In one experimental week, the children received the night-time sleep facilitating cereal together with the standard formula milk. In another week, they received the sleep facilitating cereal together with a night milk specially formulated to attain the sleep rhythm (480 mg tryptophan, 8.8 mg uridine-5'-P, and 7.6 mg adenosine-5'-P per 100 g product). The three experimental weeks were separated by two wash-out weeks in which the milk and cereal administered was identical in composition to that of the control week. All the infants received a programmed writer actimeter which they wore continually, attached to their ankles, to record their motor activity. The recorded activity was used to calculate information about the time in bed, assumed sleep, actual sleep, sleep efficiency, sleep latency, immobility, and total activity. The infants receiving the enriched cereal during the time of darkness showed improvements in their sleep parameters, regardless of whether the milk they took at night was standard or enriched with tryptophan, adenosine-5'-P, and uridine-5'-P. In summary, the administration of enriched cereals led to an improvement in sleep, regardless of the type of infant milk used. These results support the concept of chrononutrition since they confirm that the sleep/wake rhythm can be influenced by diet.

New approaches in the management of insomnia: weighing the advantages of prolonged-release melatonin and synthetic melatoninergic agonists

Hypnotic effects of melatonin and melatoninergic drugs are mediated via MT(1) and MT(2) receptors, especially those in the circadian pacemaker, the suprachiasmatic nucleus, which acts on the hypothalamic sleep switch. Therefore, they differ fundamentally from GABAergic hypnotics. Melatoninergic agonists primarily favor sleep initiation and reset the circadian clock to phases allowing persistent sleep, as required in circadian rhythm sleep disorders. A major obstacle for the use of melatonin to support sleep maintenance in primary insomnia results from its short half-life in the circulation. Solutions to this problem have been sought by developing prolonged-release formulations of the natural hormone, or melatoninergic drugs of longer half-life, such as ramelteon, tasimelteon and agomelatine. With all these drugs, improvements of sleep are statistically demonstrable, but remain limited, especially in primary chronic insomnia, so that GABAergic drugs may be indicated. Melatoninergic agonists do not cause next-day hangover and withdrawal effects, or dependence. They do not induce behavioral changes, as sometimes observed with z-drugs. Despite otherwise good tolerability, the use of melatoninergic drugs in children, adolescents, and during pregnancy has been a matter of concern, and should be avoided in autoimmune diseases and Parkinsonism. Problems and limits of melatoninergic hypnotics are compared.

Strain differences in paroxetine-induced reduction of immobility time in the forced swimming test in mice: role of serotonin

We studied the antidepressant-like effect of paroxetine in strains of mice carrying different isoforms of tryptophan hydroxylase-2 (TPH-2), the enzyme responsible for the synthesis of brain serotonin (5-HT). The effect of paroxetine alone and in combination with pharmacological treatments enhancing or lowering 5-HT synthesis or melatonin was assessed in the forced swimming test in mice carrying allelic variants of TPH-2 (1473C in C57BL/6 and 1473G in DBA/2 and BALB/c). Changes in brain 5-hydroxytryptophan (5-HTP) accumulation and melatonin levels were measured by high-performance liquid chromatography. Paroxetine (2.5 and 5 mg/kg) reduced immobility time in C57BL/6J and C57BL/6N mice but had no such effect in DBA/2J, DBA/2N and BALB/c mice, even at 10 mg/kg. Enhancing 5-HT synthesis with tryptophan reinstated the antidepressant-like effect of paroxetine in DBA/2J, DBA/2N and BALB/c mice whereas inhibition of 5-HT synthesis prevented the effect of paroxetine in C57BL/6N mice. The response to paroxetine was not associated with changes in locomotor activity, brain melatonin or brain levels of the drug measured at the end of the behavioral test. These results support the importance of 5-HT synthesis in the response to SSRIs and suggest that melatonin does not contribute to the ability of tryptophan to rescue the antidepressant-like effect of paroxetine.

Urinary excretory ratio of anthranilic acid/kynurenic acid as an index of the tolerable amount of tryptophan

Some people may take excessive tryptophan as a supplement in the expectation that the tryptophan metabolite, melatonine, will help to induce sufficient sleep. We investigated the basis for a useful index to assess the risk of a tryptophan excess. Young rats were fed on a 20% casein diet with 0, 0.5, 1.0, 2.0 or 5.0% added tryptophan for 30 d the apparent toxicity and growth retardation was observed in the 5.0% tryptophan-added group. Metabolites of the Tryptophan-nicotinamide pathway and such intermediates as kynurenic acid (KA), anthranilic acid (AnA), xanthurenic acid, 3-hydroxyanthranilic acid and quinolinic acid in 24-h urine increased in a dose-dependent manner. Of those metabolites and intermediates, the urinary excretion of KA progressively increased, and that of AnA dramatically increased in the 2.0 and 5.0% tryptophan-added groups. The urinary excretory ratio of AnA/KA was a high value for both the groups. These results suggest that the urinary ratio of AnA/KA could be a useful index to monitoran excessive tryptophan intake.

Chrononutrition: use of dissociated day/night infant milk formulas to improve the development of the wake-sleep rhythms. Effects of tryptophan

Three different lactation experiments have been tested in a double blind procedure for 3 weeks, to improve sleep-wake patterns in infants. In a control experiment, standard infant commercial milk (1.5% tryptophan) was administered without changes during the day. In a second control (inverse), enriched milk (3.4% tryptophan) was given during light-time (06.00-18.00h), and standard commercial milk during night-time (18.00-06.00h). During the experimental week, the infants received standard milk during light-time and tryptophan enriched milk during night-time. The infants receiving the enriched formula during dark time showed improvements in the sleep parameters studied, and no statistical differences were found between the two control lactations. The urinary metabolites of serotonin suggest that the observed improvements were due to an increased use of serotonin to melatonin synthesis. In conclusion, the chronobiological changes in the normal components of the diet can improve infantile development of sleep/wake rhythms.

Tryptophan Modulates Cell Viability, Phagocytosis and Oxidative Metabolism in Old Ringdoves

The decrease of melatonin with age contributes to immunosenescence. Its restoration via tryptophan may have immuno-enhancing effects. Therefore, we determined the effect of tryptophan administration on circulating serotonin, melatonin, cell viability, phagocytic function and levels of free radical generation of blood heterophils from old ringdoves (Streptopelia risoria), aged 11-13 years. The animals received a single oral capsule of l-tryptophan 1 hr after the onset of the light period. The tryptophan treatment significantly increased serum melatonin and serotonin levels, cell viability, phagocytosis index and phagocytosis percentage. Superoxide anion levels decreased significantly with respect to vehicle values, with the nocturnal reduction being greater than that which occurred during the light period. This suggests that orally administered tryptophan at the beginning of the day enhanced heterophil viability, phagocytic response and detoxification of superoxide anion radicals deriving from this immune function, as a result of the immunoregulatory action of melatonin and serotonin.

Tryptophan increases nocturnal rest and affects melatonin and serotonin serum levels in old ringdove

The sleep promoting functions of melatonin have gained wide scientific attention due to the ability of this indole to provide relief from sleep inefficiency and the temporal relationship between its nocturnal rise in the blood and the "opening of the sleep gate" at night. However, little is known about the effects exerted by its precursor, the amino acid tryptophan. We studied the effect of a 7-day administration of two concentrations of tryptophan (125 and 300 kg b.w.) on the activity/rest rhythms of ringdove, aged 2-3 (young) and 10-12 (old) years, and on the serum levels of serotonin and melatonin. Activity pulses were logged before, during, and up to 5 days after the treatments. The animals received 125 or 300 mg/kg b.w. per animal/day at 09:00 h or at 19:00 h. Subsequently we chose the treatment which gave the best results in terms of nocturnal rest without affecting diurnal activity, i.e., 300 mg/kg b.w. administered to old animals at 09:00 h, 1 h after lights on, for the serotonin and melatonin measurements. During this treatment, the nocturnal and diurnal levels and amplitudes of serotonin and melatonin were all significantly higher than the corresponding levels before and after the treatment. In sum, our results point to an improvement of nocturnal rest in this animal model of old ringdove when administering 300 mg/kg tryptophan 1 h after lights on.

L-Tryptophan administered orally at night modifies the melatonin plasma levels, phagocytosis and oxidative metabolism of ringdove (Streptopelia roseogrisea) heterophils

The essential amino acid tryptophan is the precursor in the anabolic pathway of melatonin, a hormone with immunomodulatory properties. The present study shows the in vivo effect of tryptophan on the phagocytic function and oxidative metabolism of heterophils from Streptopelia roseogrisea of < 1 year of age, with a parallel evaluation of the plasma levels of melatonin. The L-tryptophan was administered orally (125 and 300 mg/kg b.w.) at 19:00, before the beginning of the period of darkness, for 7 days. At the end of the tryptophan treatment, determinations were made at 21:00 and 02:00 of the Phagocytosis Index, the Phagocytosis Percentage, the Phagocytic Efficiency and the superoxide anion levels in heterophils isolated from blood and of the plasma levels of melatonin. The results showed, for the determinations at 21:00 in the animals that had received 125 mg L-tryptophan/kg b.w., enhanced heterophil phagocytic function and raised levels of plasma melatonin, with no affect on the oxidative metabolism of the phagocytes. For the administration of the greater concentration of tryptophan (300 mg/kg b.w.), there were raised plasma melatonin levels together with increases in heterophil phagocytic capacity and phagocyte oxidative metabolism at 02:00. The results indicate that tryptophan administered orally at night to diurnal animals of less than 1 year in age affects the circulating levels of melatonin at the same time as inducing stimulation of the innate immune function.

Opposite effects of tryptophan intake on motor activity in ring doves (diurnal) and rats (nocturnal)

The role of l-tryptophan as precursor of serotonin and melatonin synthesis on activity-rest rhythm was studied in ring doves, Streptopelia risoria, as a representative of diurnal animals and rats, Rattus norvegicus, as a typical nocturnal one. The animals were housed in cages equipped for horizontal activity recording in a thermostatized chamber and submitted to a 12/12h light/dark photoperiod (lights on at 08:00 h). After acclimatization, the animals received vehicle (methylcellulose) and l-tryptophan (240 mg/kg) by esophagic cannula 2h before the onset of either light or dark phase. Also, oral melatonin (2.5mg/kg) was tested for comparative purposes. After nocturnal l-tryptophan administration, rats showed increased activity (149%), while the opposite occurred in ring doves (39% decrease). No significant changes were found after diurnal l-tryptophan intake in either species. Melatonin produced effects similar to those of l-tryptophan. These results suggest that the effects of l-tryptophan administration are dependent on the nocturnal/diurnal habits of the studied species and, most probably, are mediated by increased melatonin synthesis.

Age related changes in the activity-rest circadian rhythms and c-fos expression of ring doves with aging. Effects of tryptophan intake

Age related changes in the circadian rhythms and sleep quality has been linked with impairment in the function of the suprachiasmatic nucleus (SCN) and melatonin secretion. The precursor of melatonin, serotonin (5-HT) is a neurotransmitter involved in the synchronisation of the circadian clock located in SCN, which shows decreased levels with age. The present work studied the effects of L-tryptophan, the precursor of 5-HT, on the circadian activity-rest rhythm and c-fos expression in the SCN of young and old ring doves, animals diurnal and monocyclic as humans. Two hours before the onset of dark phase, animals housed in cages equipped for activity recording and maintained under 12/12 L/D conditions, received orally L-tryptophan (100 and 240 mg/kg) and, for comparative purposes, melatonin (2.5 and 5 mg/kg). The administration of both L-tryptophan and melatonin reduced the nocturnal activity of all ring doves although only the highest doses were effective in old ones. A reduced amplitude in the activity-rest rhythm was observed in old animals in comparison to youngest, but it was increased after the treatments. Sleep parameters, calculated from the activity data, indicated a worsened sleep quality in old animals but it was improved with the treatments. In addition, the expression of c-fos in the SCN was reduced after both mentioned treatments. The results point to the SCN as a target for the observed nocturnal effects of L-tryptophan and melatonin, and support the supplemental administration of the essential amino acid L-tryptophan to reverse the disturbances of the circadian activity-rest cycle related with ageing.

Serotonin, but not melatonin, plays a role in shaping dominant-subordinate relationships and aggression in rainbow trout

The aim of this study was to clarify to what extent the effects of elevated dietary L-tryptophan (Trp) on aggressive behavior and stress responsiveness in rainbow trout are mediated by circulating melatonin and central serotonin (5-HT), respectively. Isolated rainbow trout were paired for 1h a day for 7 days in order to create fish with experience of being dominant and subordinate. Following this week, the fish were tested for aggressive behavior using a resident-intruder test after which they were subjected to one of four treatments: (1) tryptophan, (2) the selective serotonin reuptake inhibitor (SSRI) citalopram, (3) melatonin, and (4) no treatment (controls). After 7 days of treatment, the fish were subjected to a second resident-intruder test. Trp-supplemented feed resulted in a suppression of aggressive behavior in fish with experience of being dominant. Moreover, fish fed Trp-supplemented feed, regardless of social experience, also displayed lower plasma cortisol levels than controls. These effects of elevated dietary Trp were closely mimicked by citalopram treatment, whereas exogenous melatonin had no effect on either aggressive behavior or plasma cortisol. Thus, the effect of elevated dietary Trp on aggressive behavior and stress responses does not appear to be mediated by melatonin even though elevated dietary intake of Trp resulted in an increase in plasma melatonin concentrations.

Effect of orally administered L-tryptophan on serotonin, melatonin, and the innate immune response in the rat

To assess the effects of external administration of L-tryptophan on the synthesis of serotonin and melatonin as well as on the immune function of Wistar rats, 300 mg of the amino acid were administered through an oral cannula either during daylight (08:00) or at night (20:00) for 5 days. Brain, plasma, and peritoneal macrophage samples were collected 4 h after the administration. The accumulation of 5-hydroxytryptophan (5-HTP) after decarboxylase inhibition was used to measure the rate of tryptophan hydroxylation in vivo. Circulating melatonin levels were determined by radioimmunoassay, and the phagocytic activity of macrophages was measured by counting, under oil-immersion phase-contrast microscopy, the number of particles ingested. The results showed a diurnal increase (p < 0.05) in the brain 5-HTP, serotonin (5-hydroxytryptamine, 5-HT), and 5-hydroxyindolacetic acid (5-HIAA) of the animals which had received tryptophan at 08:00 and were killed 4 h later. In the animals which received tryptophan during the dark period, the 5-HT declined but the 5-HT/5-HIAA ratio remained unchanged. There was also a significant increase (p < 0.05) in nocturnal circulating melatonin levels and in the innate immune response of the peritoneal macrophages in the animals which had received tryptophan at 20:00. The results indicated that the synthesis of serotonin and melatonin, as well as the innate immune response, can be modulated by oral ingestion of tryptophan.

Time-course of the effect of dietary L-tryptophan on plasma cortisol levels in rainbow trout Oncorhynchus mykiss

Isolated juvenile rainbow trout were fed a feed supplemented with L-tryptophan (TRP) for 3, 7 or 28 days, after which they were either sampled directly (undisturbed) or subjected to a standardised stressor prior to sampling. Controls (stressed and undisturbed) received the same feed but without any supplementary TRP. Stress resulted in a significant elevation of plasma [cortisol] in fish fed control feed and in fish fed TRP-supplemented feed for 3 and 28 days. However, fish fed TRP-supplemented feed for 7 days did not show any significant elevation of plasma [cortisol] in response to stress. Plasma levels of adrenocorticotropin followed the same general pattern as cortisol. Plasma and brain [TRP] were elevated in fish fed TRP-supplemented feed. The amino acid TRP is the precursor of the monoamine neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) and the brain 5-HT system is known to be involved in the control of the hypothalamic-pituitary-interrenal (HPI) axis. Fish fed TRP-supplemented feed showed elevated levels of 5-hydroxyindoleacetic acid (5-HIAA, a major 5-HT metabolite) in the hypothalamus and optic tectum. However, TRP treatment did not appear to result in any effects on brain dopaminergic activity and the effects on brain norepinephric activity do not support a role of norepinephrine in mediating the effects of TRP on HPI axis reactivity in rainbow trout.

Serial cerebrospinal fluid tryptophan and 5-hydroxy indoleacetic acid concentrations in healthy human subjects

The role of the serotonergic system in the pathogenesis of behavioral disorders such as depression, alcoholism, obsessive-compulsive disorder, and violence is not completely understood. Measurement of the concentration of neurotransmitters and their metabolites in cerebrospinal fluid (CSF) is considered among the most valid, albeit indirect, methods of assessing central nervous system function in man. However, most studies in humans have measured lumbar CSF concentrations only at single time points, thus not taking into account rhythmic or episodic variations in levels of neurotransmitters, precursors, or metabolites. We have continuously sampled lumbar CSF via subarachnoid catheter in 12 healthy volunteers, aged 20-65 years. One ml (every 10 min) CSF samples were collected at a rate of 0.1ml/min for 24-hour (h), and the levels of tryptophan (TRP) and 5-hydroxy indoleacetic acid (5-HIAA) were measured. Variability across all 12 subjects was significantly greater (P < 0.0001) than the variability seen in repeated analysis of a reference CSF sample for both 5-HIAA (32.0% vs 7.9%) and TRP (25.4% vs 7.0%), confirming the presence of significant biological variability during the 24-hr period examined. This variability could not be explained solely by meal related effects. Cosinor analysis of the 24-hr TRP concentrations from all subjects revealed a significant diurnal pattern in CSF TRP levels, whereas the 5-HIAA data were less consistent. These studies indicate that long-term serial CSF sampling reveals diurnal and biological variability not evident in studies based on single CSF samples.

Serotonin and sleep

For 50 years, serotonin has been in the centre of the search for the mechanisms and control of sleep. Serotonergic neurotransmission is related to the behavioural state of the animal and plays an important role in modulation of the behavioural state, by interacting with other brain areas modulating circadian rhythm, sleep and waking. Serotonergic activity may be accompanied by waking or sleep depending on the brain area and receptor type involved in the response, on the current behavioural state and on the concomitant agonism/antagonism of other neurotransmitter systems.

Suppression of aggression in rainbow trout (Oncorhynchus mykiss) by dietaryl-tryptophan

Juvenile rainbow trout Oncorhynchus mykiss were isolated in individual compartments in observation aquaria and allowed to acclimate for 1 week, during which they were fed commercial trout feed. Thereafter, the fish were tested for aggressive behaviour using a resident/intruder test. Following this first resident/intruder test, the feed was exchanged for an experimental wet feed supplemented with 0.15 % or 1.5 % l-tryptophan (by wet mass). Controls received the same feed but without l-tryptophan supplementation. The fish were fed to satiety daily, and their individual feed intake was recorded. Aggressive behaviour was quantified again after 3 and 7 days of l-tryptophan feeding using the resident/intruder test. Feeding the fish l-tryptophan-supplemented feed for 3 days had no effect on aggressive behaviour, whereas feeding the fish l-tryptophan-supplemented feed for 7 days significantly suppressed aggressive behaviour in the fish, an effect seen at both levels of l-tryptophan supplementation. Fish fed l-tryptophan-supplemented feed showed elevated plasma and brain levels of l-tryptophan. The amino acid l-tryptophan is the precursor of serotonin, and supplementary dietary l-tryptophan was found to elevate levels of 5-hydroxyindoleacetic acid (5-HIAA) and the 5-HIAA/serotonin concentration ratio in the brain. Neither feed intake nor plasma cortisol level was significantly affected by dietary l-tryptophan. Central serotonin is believed to have an inhibitory effect on aggressive behaviour, and it is suggested that the suppressive effect of dietary l-tryptophan on aggressive behaviour is mediated by an elevation of brain serotonergic activity.

Nocturnal melatonin secretion and its modification by treatment in patients with sleep disorders

Data on the circadian melatonin secretion in sleep disordered patients and effects of sleep medication on melatonin are still missing. We studied plasma melatonin concentration, sleep, and effects of some hypnotics in 15 patients and 10 controls. Nocturnal melatonin levels were significantly decreased in patients with a more than five years history of sleep complaints compared to controls or patients with a shorter duration of illness. Independent of their sleep promoting properties drugs increased or decreased nocturnal melatonin in controls and patients. Patients with chronic sleep-wake rhythm disorders showed altered relations between their circadian melatonin secretion pattern and sleep. We conclude that nocturnal melatonin secretion is primarily independent of sleep regulation but represents a neuroendocrine feature of chronically disturbed sleep.

Fibromyalgia--a syndrome associated with decreased nocturnal melatonin secretion

OBJECTIVE

Most patients with fibromyalgic syndrome (FMS) complain of sleep disturbances, fatigue, and pain. These symptoms might be a consequence of changed melatonin (MT) secretion, since MT is known to have sleep promoting properties. Moreover, serum concentrations of two MT precursors (tryptophan and serotonin)--affecting both sleep and pain perception--appear to be low in patients with FMS. Therefore, the objective of this investigation was to study whether serum MT (s-MT) level is also low in these patients.

DESIGN

Eight patients with FMS and 8 healthy sex-, BMI-, and age-matched controls were included in the study. s-MT concentrations were determined every second hour between 1800 and 0800 h. Urine was collected between 2200 and 0700 h for determination of urinary MT excretion. To evaluate total MT secretion between 1800 and 0800 h and MT secretion during the hours of darkness (between 23 and 07 h) individual MT areas under the curve (AUC) were calculated and expressed as group means.

RESULTS

The FMS patients had a 31% lower MT secretion than healthy subjects during the hours of darkness (MT AUC 2300-0700 h (mean +/- SEM): 1.70 +/- 0.17 vs 2.48 +/- 0.38 nmol/l; P < 0.05). Also the s-MT peak value was significantly lower in the patient group: 0.28 +/- 0.03 vs 0.44 +/- 0.06 nmol/l; P < 0.05).

CONCLUSION

Patients with fibromyalgic syndrome have a lower melatonin secretion during the hours of darkness than healthy subjects. This may contribute to impaired sleep at night, fatigue during the day, and changed pain perception.

Guidelines for prescribing melatonin

Although compelling logic suggests that melatonin may be effective for a variety of disorders, there are few empirical clinical studies. The optimal dose of melatonin is not clear; most studies have used doses that produce supraphysiological blood levels. The timing of melatonin administration is important. Melatonin has few immediate side-effects except drowsiness, but the effects of chronic administration are unclear. Melatonin may be effective in reducing jet lag. In elderly patients with poor sleep and documented low melatonin production, melatonin may be helpful. In several studies, melatonin has been shown to shorten sleep latency. Further studies are needed to clarify the efficacy and safety of melatonin.

Nocturnal plasma melatonin concentrations in healthy volunteers: effect of single doses of d-fenfluramine, paroxetine, and ipsapirone

The effect on nocturnal melatonin secretion of acute administration of the indirectly acting serotonin (5-HT) receptor agonists d-fenfluramine (30 mg) and paroxetine (20 mg) and a partial 5-HT1A receptor agonist ipsapirone (20 mg) was investigated in healthy male volunteers and compared to a placebo condition. Each subject (n = 8) received each drug on one occasion over a 4 week study period, with drug administration separated by 1 week. A randomized, counter-balanced design was used. Drugs or placebo were administered at 2,000 hours in the light, and all blood samples were collected throughout the night in the dark at regular intervals until 0600 hours. Neither d-fenfluramine, paroxetine, or ipsapirone following acute dosage had a statistically significant effect on nocturnal melatonin synthesis. The lack of effect seen with d-fenfluramine, paroxetine, and ipsapirone may be due to limitations imposed by the dose requirements.