Nail Melatonin Content: A Suitable Non-Invasive Marker of Melatonin Production.

Melatonin plays multiple physiological roles in the human body. Evaluation of melatonin production by the determination of urinary 6-sulfatoxymelatonin in 24-h samples has important drawbacks which hinder the successful evaluation of melatonin production in large cohorts. Here, we evaluated the potential of nail analysis for estimating melatonin production. Firstly, mass spectrometry methodology for the determination of melatonin in nails was optimized and successfully validated. The method was found to be linear in the range 6.5-830 fg/mg with intraday and interday accuracy in the range 100-104 %, precision below 15 % and a LOD of 3.5 fg/mg. Secondly, nail melatonin concentrations from 84 volunteers (age 5-96) were determined. The expected correlation between melatonin and age was obtained (correlation coefficient -0.615; p < 0.001). Additionally, we showed that fingernails are preferable to toenails to determine nail melatonin content. Finally, fingernails collected for 180 days after melatonin administration (two volunteers, 1.9 mg/night during 5 days) were analyzed. Nail melatonin concentrations immediately rose after administration and went back to pre-administration values after ≈100 days in both volunteers. Our results suggest that melatonin determination in nails is a suitable non-invasive tool for the estimation of global melatonin production. Due to the easy collection and storage of nails, the long-term information obtained and the multiple functions of melatonin, nail melatonin content might complement dim light melatonin onset, which is commonly measured from plasma/saliva samples, paving the way for melatonin research.

Simultaneous determination of melatonin and trans-resveratrol in wine by dispersive liquid-liquid microextraction followed by HPLC-FLD.

The discovery of melatonin (Mel) in wines triggered a new interest in the paradigm of health benefits and wine consumption, usually ascribed to trans-resveratrol (trans-RSV). In this context, a dispersive liquid-liquid microextraction for the analysis of Mel and trans-RSV in wines by LC-FLD was developed. A 26-1 factorial design was used to identify the significant variables (p < 0.05) and Central Composite Design was used to achieve the optimal conditions: 300 µL of chloroform (extracting solvent), 1500 µL of acetonitrile (disperser solvent) and 1500 mg of NaCl (ionic strength). Excellent linearity (R2 > 0.9999), repeatability (<3.55%), and accuracy (<7.18%) were obtained using a blank matrix and recoveries (>91.9%) using wines. The method was successfully applied to the analyses of Mel (0.63-7.44 ng mL-1) and trans-RSV (169-2616 ng mL-1) in different wine varieties. Comparison with literature point the overall advantages of the new method.

Effects of Melatonin and Flavonoid-Rich Fractions of Chromolaena odorata on the Alteration of Proinflammatory Cytokines and Nitric Oxide Induced by Aflatoxin B1 in the Gastric Mucosa of Wistar Rats.

In this study, we investigated serum interleukin-1 beta (IL-1ß) and tumor necrosis factor alpha (TNF-α) after ingestion of aflatoxin B1 (AFB1) in rats. We also studied the effects of nitric oxide (NO) on the stomach after consumption of AFB1. Therefore, we hypothesized that a standard anti-inflammatory agent-melatonin (MEL), and the flavonoid-rich fractions from Chromolaena odorata (FRFC) could counteract the deleterious effects of IL-1ß, TNF-α, and NO after consumption of AFB1. Thirty-five Wistar rats (211.86 ± 27.23 g) were randomly selected into 5 groups, with 7 rats in each group. Group A (control); all rats in groups B, C, D, and E received 2.5 mg/kg AFB1 each orally on day 5, whereas those of groups C, D, and E received oral administration of 10 mg/kg MEL, 50 mg/kg FRFC1, and 100 mg/kg FRFC2, respectively, for 7 days. All of them were killed on the 8th day, 24 h after last treatment. Serum samples were analyzed for IL-1ß and TNF-α, whereas stomach tissue was evaluated for NO level. Significant (P < 0.5) increase in serum IL-1ß and TNF-α in rats given AFB1 only was recorded when compared with those in the control group. Conversely, we observed significant reduction in serum IL-1ß and TNF-α in all the groups that received MEL, FRFC1, and FRFC2 after pretreatment with AFB1 when compared with those that were given AFB1 only. In addition, there was a significant increase in NO in rats given AFB1 only when compared with control, whereas reduction in NO was significant in the groups C, D, and E that were given MEL, FRFC1, and FRFC2, respectively, when compared with AFB1 group. MEL and FRFC may be responsible for the prevention of increased gastric mucosal NO and inflammatory effects of proinflammatory cytokines induced by AFB1.

Nicotinamide adenine dinucleotide immobilized tungsten trioxide nanoparticles for simultaneous sensing of norepinephrine, melatonin and nicotine.

Herein, we report the anionic surfactant, ethylene diamine tetraacetic acid (EDTA), mediated synthesis of WO3 nanoparticles and its subsequent modification through gamma irradiation (GI) and electrochemical immobilization with nicotinamide adenine dinucleotide (NAD). Glassy carbon electrode (GCE) modified with GI-WO3 NPs and the enzyme NAD exhibited strong electro-oxidation of three important biomolecules such as norepinephrine (NEP), melatonin (MEL) and nicotine (NIC) in 0.1 M phosphate buffer saline (PBS) at physiological pH of 7. Square wave voltammetry (SWV) studies exhibited three well-defined peaks at potentials of 120, 570 and 840 mV, corresponding to the oxidation of NEP, MEL and NIC respectively, indicating that simultaneous determination of these compounds is feasible at the NAD/GI EDTA-WO3/GCE. The proposed sensor displayed a wide linear range of 0.010-1000 µM with the lowest detection limit of 1.4 nM for NEP, 2.6 nM for MEL and 1.7 nM for NIC respectively. Furthermore, the modified electrode was successfully applied to detect NEP, MEL and NIC in pharmaceutical and cigarette samples with excellent selectivity and reproducibility.

Melatonin and derived l-tryptophan metabolites produced during alcoholic fermentation by different wine yeast strains.

Melatonin is a neurohormone involved in the regulation of circadian rhythms in humans. Evidence has recently been found of its occurrence in wines and its role in the winemaking process. The yeast Saccharomyces cerevisiae is consequently thought to be important in Melatonin synthesis, but limited data and reference texts are available on this synthetic pathway. This paper aims to elucidate whether the synthetic pathway of Melatonin in Saccharomyces and non-Saccharomyces strains involves these intermediates. To this end, seven commercial strains comprising Saccharomyces cerevisiae (Red Fruit, ES488, Lalvin QA23, Uvaferm BC, and Lalvin ICV GRE) and non-Saccharomyces (Torulaspora delbrueckii and Metschnikowia pulcherrima) were monitored, under controlled fermentation conditions, in synthetic must, for seven days. Samples were analysed using a UHPLC-HRMS system (Qexactive). Five out of the seven strains formed Melatonin during the fermentation process: three S. cerevisiae strains and the two non-Saccharomyces. Additionally, other compounds derived from l-tryptophan occurred during fermentation.

Application of optimized dispersive liquid-liquid microextraction for determination of melatonin by HPLC-UV in plasma samples.

Melatonin (N-acetyl-3-(2-aminoethyl)-5-methoxyindole) is biologically active as a neurohormone and antioxidant agent. The optimized dispersive liquid-liquid microextraction (DLLME) followed by high-performance liquid chromatography-ultra violet detection (HPLC-UV) was used for the analysis of melatonin in human plasma. Influence variables such as volume of extracting (carbon tetrachloride: CCl4) and dispersing solvents (acetonitrile: ACN), pH and ionic strength, extraction time and centrifugation time were screened in a 2(6-2) fractional factorial design (FFD) and then the significant variables were optimized by using a central composite design (CCD). At optimum conditions values of variables set as pH 6.0, 1.5 mL ACN, 140 µL CCl4, 1.0 min extraction time and 3.0 min centrifugation at 4,500 rpm. At optimum conditions method has linear response over 2.0-500.0 ng mL(-1) with detection limit of 0.5 ng mL(-1) with relative standard deviations (RSDs) less than 5.0%. The values of intra-day and inter-day RSD were 4.3% and 8.5%, respectively. The method was applied successfully for the analysis of melatonin in plasma sample.

An interlaboratory comparison between similar methods for determination of melatonin, cortisol and testosterone in saliva.

An interlaboratory comparison study for melatonin, cortisol and testosterone in saliva in which five laboratories participated is reported in this study. Each laboratory blindly measured eight samples prepared from natural saliva spiked with melatonin, cortisol and testosterone in the range 0-579 pmol/L for melatonin, 0-90 nmol/L for cortisol, and 0-622 pmol/L for testosterone. The recovery of spiked material for melatonin ranged from 91-110%, from 83-100% for cortisol and from 80-94% for testosterone. The content of natural hormone in saliva was estimated to be between 0.278 and 6.90 pmol/L for melatonin, 0.56 and 6.72 nmol/L for cortisol and 11.9 and 73.8 pmol/L for testosterone. This indicates a large interlaboratory variation. The present study emphasizes the importance of external quality control for the analysis of melatonin, cortisol and testosterone in saliva.

Determination of melatonin and its isomer in foods by liquid chromatography tandem mass spectrometry.

This study aimed to develop a reliable analytical method for the determination of melatonin and its isomers in various food products. The method entails ethanol extraction of solid samples (or dilution of liquid samples) prior to liquid chromatography coupled to triple quadruple mass spectrometry (LC-MS/MS) analysis of target analytes. The method was in-house validated and successfully applied to various food matrices. Recovery of melatonin from different matrices were found to be 86.0 ± 3.6%, 76.9 ± 5.4%, 98.6 ± 6.4%, and 67.0 ± 4.5% for beer, walnut, tomato and sour cherry samples, respectively. No melatonin could be detected in black and green tea, sour cherry, sour cherry concentrate, kefir (a fermented milk drink) and red wine while the highest amount of melatonin (341.7 ± 29.3 pg/g) was detected in crumb. The highest amounts of melatonin isomer were detected in yeast-fermented foods such as 170.7 ± 29.9 ng/ml in red wine, 14.3 ± 0.48 ng/ml in beer, and 15.7 ± 1.4 ng/g in bread crumb.

Optical sensing of urinary melatonin with molecularly imprinted poly(ethylene-co-vinyl alcohol) coated zinc oxide nanorod arrays.

In this work, aligned zinc oxide (ZnO) nanorods were selectively hydrothermally grown on acetate-seeded spots on a gold substrate; the nanorods had an average length and diameter of 1.7µm and 240nm, respectively. Melatonin was imprinted into poly(ethylene-co-vinyl alcohol), EVAL, which was coated onto ZnO nanorod arrays. The ZnO nanorods not only increased the surface area for sensing target molecules, but also constituted an optical sensing element, as the ZnO fluorescence decreases when targets bind to the imprinted EVAL film; the fluorescence decrease, as a function of melatonin concentration, is well fit by a Langmuir adsorption isotherm. Poly(ethylene-co-vinyl alcohol) with 44mol% ethylene showed the best imprinting effectiveness (ratio of the fluorescence decrease on binding melatonin to imprinted vs. non-imprinted EVAL-coated ZnO nanorod arrays) among the several compositions studied. In real urine analysis, the MIP films responded linearly to added (exogenous) melatonin, even in the presence of many possible interfering compounds in urine. This demonstrates the feasibility of using these MIPs as part of a total urinalysis MIP system.

High-performance liquid chromatography with fluorescence detection and ultra-performance liquid chromatography with electrospray tandem mass spectrometry method for the determination of indoleamine neurotransmitters and their metabolites in sea lamprey plasma.

We present a comparison of two sensitive methods, HPLC with fluorescence detector (HPLC/FLD) and UPLC with electrospray tandem mass spectrometry (UPLC/MS/MS), for the determination of indoleamine neurotransmitters (NTs) and their metabolites in sea lamprey plasma samples. Liquid-liquid extraction (LLE) and solid-phase extraction (SPE) were also tested for recovery and matrix effect. The recoveries of SPE determined by HPLC/FLD and UPLC/MS/MS ranged from 75 to 123% and 78 to 105%, respectively, while the recoveries of LLE ranged from 45 to 73% and 48 to 75%, respectively. SPE combined with HPLC/FLD and UPLC/MS/MS to determine the target analytes in plasma samples were validated of the sensitivity, reproducibility, accuracy and precision. Both methods exhibited excellent linearity in the range of 0.2-50 ng mL(-1) for all analytes. The limits of detection (LOD) varied from 0.04 ng mL(-1) to 0.13 ng mL(-1) for HPLC/FLD method and 0.003 ng mL(-1) to 0.02 ng mL(-1) for UPLC/MS/MS method. The inter-day accuracy ranged from 82.5 to 127.0% for HPLC/FLD and 93.0 to 113.0% for UPLC/MS/MS. The inter-day precision ranged from 9.9 to 32.3% for HPLC/FLD and 5.4 to 13.2% for UPLC/MS/MS. These results demonstrated that the values obtained by both methods were within the satisfactory range and the UPLC/MS/MS method provided more accurate and precise measurements than HPLC/FLD method. The comparison is of great importance to determine the available detectors, considering the complexity and expensiveness versus quality parameters. These two methods were applied to the analysis of four important indoleamine neurotransmitter analytes (5-hydroxytryptamine, 5-hydroxyindole-3-acetic acid, tryptamine and melatonin) in sea lamprey plasma samples.

Melatonin distribution reveals clues to its biological significance in basal metazoans.

Although nearly ubiquitous in nature, the precise biological significance of endogenous melatonin is poorly understood in phylogenetically basal taxa. In the present work, we describe insights into the functional role of melatonin at the most "basal" level of metazoan evolution. Hitherto unknown morphological determinants of melatonin distribution were evaluated in Nematostella vectensis by detecting melatonin immunoreactivity and examining the spatial gene expression patterns of putative melatonin biosynthetic and receptor elements that are located at opposing ends of the melatonin signaling pathway. Immuno-melatonin profiling indicated an elaborate interaction with reproductive tissues, reinforcing previous conjectures of a melatonin-responsive component in anthozoan reproduction. In situ hybridization (ISH) to putative melatonin receptor elements highlighted the possibility that the bioregulatory effects of melatonin in anthozoan reproduction may be mediated by interactions with membrane receptors, as in higher vertebrates. Another intriguing finding of the present study pertains to the prevalence of melatonin in centralized nervous structures. This pattern may be of great significance given that it 1) identifies an ancestral association between melatonin and key neuronal components and 2) potentially implies that certain effects of melatonin in basal species may be spread widely by regionalized nerve centers.

Melatonin as an antioxidant and its semi-lunar rhythm in green macroalga Ulva sp.

The presence and role of melatonin in plants are still under debate owing to difficulties of identification and quantification. Accordingly, although it has been frequently proposed that melatonin acts as an antioxidant in phototrophic organisms, experimental data on its physiological role are scarce. This study describes the use of a rapid and simple new method for quantification of melatonin in the marine macroalga Ulva sp., organisms routinely exposed to tide-related environmental stresses and known for their high tolerance to abiotic conditions. The method was used here to show that exposure to oxidative stress-inducing environmental conditions (elevated temperature and heavy metals) induced a rise in melatonin level in the algae. Addition of exogenous melatonin alleviated the algae from cadmium-induced stress. Interestingly, although the algae were taken from a culture growing free floating and kept under constant photoperiod and water level, they exhibited a semi-lunar rhythm of melatonin levels that correlated with predicted spring tides. The correlation can probably be interpreted as reflecting preparation for predicted low tides, when the algae are exposed to increasing temperature, desiccation, and salinity, all known to induce oxidative stress. Given the simplicity of the described method it can easily be adapted for the study of melatonin in many other phototrophic organisms. These results provide, for the first time, experimental data that support both an antioxidant role for melatonin and its semi-lunar rhythm in macroalgae.

Interactions between dopamine and melatonin organize circadian rhythmicity in the retina of the green iguana.

Circadian physiology in the vertebrate retina is regulated by several neurotransmitters. In the lateral eyes of the green iguana the circadian rhythm of melatonin content peaks during the night while the rhythm of dopamine peaks during the day. In the present work, the authors explore the interaction of these 2 neurotransmitters during the circadian cycle. They depleted retinal dopamine with intravitreal injections of 6-hydroxydopamine (6-OHDA) and measured ocular melatonin content in vivo throughout 1 circadian cycle. The circadian rhythm of ocular melatonin not only persisted but increased 10-fold in amplitude. This increase was substantially reduced by the intraocular administration of dopamine. 6-OHDA-treated retinas, unlike those from untreated animals, did not express a circadian rhythm of melatonin synthesis in vitro. To deplete retinal melatonin, the authors pinealectomized iguanas and blocked retinal melatonin synthesis by depleting serotonin with intraocular injections of 5,6-dihydroxytryptamine. In animals so treated, they found that the circadian rhythm of retinal dopamine content was abolished, the levels of dopamine were lowered, and the levels of dopamine metabolites were greatly increased. The data suggest that in iguanas, the amplitude of the circadian rhythm of melatonin synthesis in the eye is suppressed by dopamine while the rhythm of dopamine depends, at least in part, on the presence of melatonin.

[Age-related changes of exercise capacity and some biochemical indices of rat muscles under influence of different light conditions and pineal preparations].

The influence of different light conditions (standard--12 h light : 12 h darkness-- LD; 24-hour constant light--LL, light deprivation--DD, natural light regimen of the North-West of Russia--NL) and substances with geroprotective effect (melatonin and epitalon) on age-related dynamics of exercise capacity, lactate dehydrogenase (LDH) isoenzymes spectrum, enzymatic and non-enzymatic system of generation and utilization of oxygen reactive substances, activity of key antioxidant enzymes in skeletal musculature were investigated during 2 years. The decrease of exercise capacity, changes of energy production strategies and antioxidant protection during animals ageing in dependence on different light conditions was found. LL lead to earlier decrease of exercise capacity with synchronous increasing content of less effective anaerobic LDH fraction and decreasing of catalase activity in comparison with DL. Similar decreasing of exercise capacity, changes in LDH spectrum and antioxidant status in NL condition coincide in time with autumn season what indicates that seasonal changes of illumination is natural disturber of circadian rhythm. Melatonin and epitalon applied from 4-month age did not influence on exercise capacity in young rats. Both substances had similar stimulate effect on age-related physical activity of mature and senescent animals such as reducing of exercise capacity depression and normalization of antioxidant protection.

Chiral resolution of melatoninergic ligands by EKC using highly sulfated CDs.

EKC methods for the enantiomeric resolutions of melatoninergic ligands were developed using anionic CDs (highly S-alpha-CD, highly S-beta-CD, and highly S-gamma-CD) as chiral selectors at acidic pH 2.5. The optimization of the various operational parameters (nature and concentration of the CD, phosphate buffer concentration, addition of organic modifiers in the BGE, and temperature) allows baseline enantioresolutions (superior to 2) in short analysis times (inferior to 7 min) for all studied analytes. Some analytical characteristics of the optimal method were then studied for each analyte: repeatability, linearity, and LOD and LOQ. Lastly, determination of the apparent binding constants for the 18 complexes formed between the six analytes and the three CDs led us to rationalize the complexation mechanisms.

Micellar electrokinetic capillary chromatography for fast separation and sensitive determination of melatonin and related indoleamines using end-column amperometric detection.

MEKC was used in conjunction with end-column amperometric detection (AD) at a carbon disc electrode (0.3 mm diameter) for the selective and sensitive determination of melatonin and its five related indoleamines including its precursors and metabolites in the pineal gland. The introduction of a sample stacking technique in injection and the buffer additive SDS in the buffer solution system provided the rapid and sensitive analysis. Optimal buffer conditions (10 mmol/L phosphate containing 20 mmol/L SDS, pH 7.2), detection potential (+1.0 V vs. Ag/AgCl), and electrokinetic injection 10 s with the separation voltage of 24 kV were employed to achieve the baseline separation of six pineal hormones within 15 min. The peak currents and the analyte concentrations have a good linear relationship over the range of 6.0 x 10(-8) 6.0 x 10(-5 )mol/L. The detection limits for six pineal hormones by AD are 9.7 to 41.8 nmol/L (equal to 2.0 to 9.7 ng/mL) (S/N = 3), respectively. It is proved to provide about 30- to 250-fold improvement over UV, and be comparable with the sensitive fluorescence detection, which needs pre-column derivatization. The proposed method has been applied for analysis of melatonin and related indoleamines in rat pineal glands. A very simple sample pretreatment procedure, merely involving the homogenization step in perchloric acid, was enough to achieve recoveries in the range of 71 to 127% for all the analytes in the pineal gland.

Rapid method for accurate analysis of melatonin, serotonin and auxin in plant samples using liquid chromatography-tandem mass spectrometry.

Currently, the information available on the physiological functions of melatonin in higher plants is rather limited and the role of plant melatonin in human health remains undetermined. Research in this area has been slow due to lack of efficient analytical methods for rapid identification and quantification of the melatonin and related compounds in complex plant matrices. In this communication, we report the development of a rapid, accurate method for extraction, detection and quantification of plant melatonin, serotonin and indole-3-acetic acid (IAA) by Liquid chromatography-tandem mass spectrometry (LC-MS/MS) with electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photoionization (APPI), respectively. The limit of detection (LOD) of melatonin in the plant extraction was 5 pg/ml and the limit of quantification (LOQ) was 0.02 ng/ml, as well as LOD for serotonin was 100 pg/ml and the LOQ was 5 ng/ml, LOD for IAA was 50 pg/ml and the LOQ was 0.7 ng/ml. There was a linear relationship between melatonin, serotonin, and IAA concentration and peak area over a quantifiable range of 0.02 ng/ml to 0.1 mg/ml, 5 ng/ml to 0.1 mg/ml, and 0.7 ng/ml to 0.1 mg/ml, respectively, in the plant extract.

Melatonin in Glycyrrhiza uralensis: response of plant roots to spectral quality of light and UV-B radiation.

Melatonin (N-acetyl-5-methoxytryptamine) is known to be synthesized and secreted by the pineal gland in vertebrates. Evidence for the occurrence of melatonin in the roots of Glycyrrhiza uralensis plants and the response of this plant to the spectral quality of light including red, blue and white light (control) and UV-B radiation (280-315 nm) for the synthesis of melatonin were investigated. Melatonin was extracted and quantified in seed, root, leaf and stem tissues and results revealed that the root tissues contained the highest concentration of melatonin; melatonin concentrations also increased with plant development. After 3 months of growth under red, blue and white fluorescent lamps, the melatonin concentrations were highest in red light exposed plants and varied depending on the wavelength of light spectrum in the following order red >> blue > or = white light. Interestingly, in a more mature plant (6 months) melatonin concentration was increased considerably; the increments in concentration were X4, X5 and X3 in 6-month-old red, blue and white light exposed (control) plants, respectively. The difference in melatonin concentrations between blue and white light exposed (control) plants was not significant. The concentration of melatonin quantified in the root tissues was highest in the plants exposed to high intensity UV-B radiation for 3 days followed by low intensity UV-B radiation for 15 days. The reduction of melatonin under longer periods of UV-B exposure indicates that melatonin synthesis may be related to the integrated (intensity and duration) value of UV-B irradiation. Melatonin in G. uralensis plant is presumably for protection against oxidative damage caused as a response to UV irradiation.

Quantification of melatonin in phototrophic organisms.

Melatonin, the chief secretory product of the vertebrate pineal gland is also known to occur in numerous photoautotrophic organisms. The indoleamine is suspected to act as a transducer of photoperiodic information and/or to participate in antioxidative protection. In higher plants and other photoautotrophic organisms, contradictory results for melatonin content for samples from the same species show that further improvement of methods for reliable quantification is required. In the present study, melatonin was quantified in tomatoes, ginger and the marine green macroalga, Ulva lactuca, after extraction with three different extraction methods based on ether, acetone or perchloric acid. Melatonin was determined by enzyme-linked immunosorbent assay (ELISA) in high-performance liquid chromatography (HPLC)-purified extracts. The same HPLC system used for purification of extracts was used for parallel quantifications after derivatization of melatonin under alkaline conditions in the presence of hydrogen peroxide (HPLC-PD). Both quantification methods gave similar results with a high correlation [f(x) = 0.99x + 3.01; R(2) = 0.99]. In ginger, the melatonin concentration was below 5 pg/g (fresh weight, f.w.), whereas in tomatoes about 1200 pg/g (f.w.) were found, and in the green alga, U. lactuca, approximately 12 pg/g (f.w.). Taking into account the recovery rates for synthetic melatonin added prior to extraction, no substantial differences were observed in melatonin quantification between different extraction methods. The demonstrated methods based on HPLC purification and subsequent quantification by ELISA and HPLC-PD allow highly sensitive melatonin determinations in diverse photoautotrophic organisms with a low risk of overestimations by false-positive results.

Melatonin: a growth-stimulating compound present in lupin tissues.

Melatonin (N-acetyl-5-methoxi-tryptamine), a well-known animal hormone synthetised by the pineal gland, plays a key role in the circadian rhythm of vertebrates. An exhaustive bibliographical revision of studies on melatonin in plants published since 1990 points to very few studies (around 20), of which only 8 have a clear plant physiological focus. The data presented in this study demonstrate that melatonin plays a physiological role in plant tissues. Melatonin is seen to be a molecule that promotes vegetative growth in etiolated Lupinus albus L. hypocotyls, in a similar way to IAA. The measurements of melatonin and IAA in lupin hypocotyls by high-performance liquid chromatography with electrochemical detection, and their identification by tandem mass spectrometry, point to a different distribution of these molecules in etiolated hypocotyls.