Measurement of 5-hydroxytryptophol and 5-hydroxyindoleacetic acid in human and rat brain and plasma

Quantification of serotonin and eight of its metabolites in plasma of healthy volunteers by mass spectrometry

Serotonin is transformed into melatonin under the control of the light/dark cycle, representing a cornerstone of circadian rhythmicity. Serotonin also undergoes extensive metabolism to produce 5-hydroxyindoleacetic acid (5-HIAA), a biomarker for the diagnosis and monitoring of serotonin secreting neuroendocrine tumors (NETs). While serotonin, melatonin and their metabolites are part of an integrated comprehensive system, human observations about their respective plasma concentrations are still limited. We report here for the first time a multiplex UHPLC-MS/MS assay for the quantification of serotonin, 5-HIAA, 5-hydroxytryptophol (5-HTPL), N-acetyl-serotonin (NAS), Mel, 6-OH-Mel, 5-methoxytryptamine (5-MT), 5-methoxytryptophol (5-MTPL), and 5-methoxyindoleacetic acid (5-MIAA) in human plasma. Analytes were extracted by protein precipitation and solid phase extraction. Plasma concentrations for these analytes were determined in 102 healthy volunteers. The LLOQ of the assay ranges from 2.2 nM for serotonin to 1.0 pM for 6-OH-Mel. This sensitivity enables the quantification of circulating serotonin, 5-HIAA, NAS, Mel, and 5-MIAA, even at their lowest diurnal concentrations. This assay will enable specific, precise and accurate measurement of serotonin, Mel and their metabolites to draw a detailed picture of this complex pineal metabolism, allowing a dynamic understanding of these pathways and providing promising biomarkers and a metabolic signature for serotonin-secreting NETs.

Serotonin pathway in carcinoid syndrome: Clinical, diagnostic, prognostic and therapeutic implications

Carcinoid syndrome represents the most common functional syndrome that affects patients with neuroendocrine neoplasms. Its clinical presentation is really heterogeneous, ranging from mild and often misdiagnosed symptoms to severe manifestations, that significantly worsen the patient's quality of life, such as difficult-to-control diarrhoea and fibrotic complications. Serotonin pathway alteration plays a central role in the pathophysiology of carcinoid syndrome, accounting for most clinical manifestations and providing diagnostic tools. Serotonin pathway is complex, resulting in production of biologically active molecules such as serotonin and melatonin, as well as of different intermediate molecules and final metabolites. These activities require site- and tissue-specific catalytic enzymes. Variable expression and activities of these enzymes result in different clinical pictures, according to primary site of origin of the tumour. At the same time, the biochemical diagnosis of carcinoid syndrome could be difficult even in case of typical symptoms. Therefore, the accuracy of the diagnostic methods of assessment should be improved, also attenuating the impact of confounding factors and maybe considering new serotonin precursors or metabolites as diagnostic markers. Finally, the prognostic role of serotonin markers has been only evaluated for its metabolite 5-hydroxyindole acetic acid but, due to heterogeneous and biased study designs, no definitive conclusions have been achieved. The most recent progress is represented by the new therapeutic agent telotristat, an inhibitor of the enzyme tryptophan hydroxylase, which blocks the conversion of tryptophan in 5-hydroxy-tryptophan. The present review investigates the clinical significance of serotonin pathway in carcinoid syndrome, considering its role in the pathogenesis, diagnosis, prognosis and therapy.

Simultaneous electrochemical determination of dopamine and 5-hydroxyindoleacetic acid in urine using a screen-printed graphite electrode modified with gold nanoparticles

The authors describe a disposable screen-printed graphite electrode (SPGE) modified with gold nanoparticles (AuNPs). The electrode, designated as AuNPs-SPGE, was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The AuNPs-SPGE combines the electrochemical features of graphite and the disposability of screen-printed electrodes. It displays excellent electrocatalytic activity towards dopamine (DA) and 5-hydroxyindoleacetic acid (5-HIAA). Two well-defined, sharp, and fully resolved voltammetric peaks (at 525 mV for DA and at 415 mV for 5-HIAA, both vs. Ag/AgCl) were found. Square wave voltammetry was used to simultaneously determine DA and 5-HIAA in mixtures and in urine. The linear working range extends from 0.1 to 120.0 μM for both DA and 5-HIAA, and the limits of detection (based on 3× the baseline noise) are 14.0 and 5.7 nM, respectively. The fabrication method for the AuNPs-SPGE is highly reproducible. The performance of the AuNPs-SPGE was evaluated by analyzing spiked human urine, and the recoveries were found to be well over 94.0 % for both compounds. These results indicate that the AuNPs-SPGE represents a highly selective and sensitive sensor for simultaneous determination of DA and 5-HIAA in urine. Graphical Abstract Fabrication, characterization and electrochemical behavior of gold nanoparticles modified screen-printed graphite electrode towards dopamine and 5-hydroxyindoleacetic acid in human urine.

Determination of glucuronidated 5-hydroxytryptophol (GTOL), a marker of recent alcohol intake, by ELISA technique

OBJECTIVES

To compare markers of alcohol consumption.

DESIGN AND METHODS

Measurement of urinary ethyl glucuronide, 5-hydroxytryptophol, 5-hydroxytryptophol glucuronide, 5-hydroxyindole acetic acid in 10 patients during alcohol withdrawal.

RESULTS

5-Hydroxytryptophol glucuronide was measured by ELISA with good analytical precision, its diagnostic specificity and sensitivity was better than that of 5-hydroxytryptophol and its correlation was closer to ethyl glucuronide than to 5-hydroxytryptophol.

CONCLUSION

Determination of 5-hydroxytryptophol glucuronide by ELISA offers promising results in detection of previous alcohol consumption.

Liquid chromatographic and tandem mass spectrometric assay for evaluation of in vivo inhibition of rat brain monoamine oxidases (MAO) A and B following a single dose of MAO inhibitors: application of biomarkers in drug discovery

A simple and selective assay for the evaluation of in vivo inhibition of rat brain monoamine oxidases (MAO) A and B following a single dose of MAO inhibitors was developed through the simultaneous determination of endogenous 5-hydroxy tryptamine, 5-hydroxyindole-3-acetic acid (5-HIAA), tryptophane, and 2-phenethylamine (PEA) in rat brain using liquid chromatography-tandem mass spectrometry (LC/MS/MS). These analytes were separated on a Zorbax SB-C18 column using a gradient elution with acetonitrile and 0.2% formic acid and detected on an electrospray ionization mass spectrometer in positive-ion multiple-reaction-monitoring mode. The susceptibility and variability of these analytes as potential biomarkers in response to MAO inhibition in vivo were evaluated after application to three MAO inhibitors, tranylcypromine, clorgyline, and pargyline. A dramatic increase (about 40-fold) in PEA brain level and a decrease in 5-HIAA by more than 90% were observed after administration of 15 mg/kg of the nonselective MAO inhibitor tranylcypromine. As expected, the brain level of PEA escalated to about 6-fold, while the 5-HIAA level remained unchanged following a dose of the MAO B inhibitor pargyline at 2mg/kg. In contrast, the brain level of 5-HIAA reduced by approximately 53%, but the PEA level was unaffected following the same dose of the MAO A inhibitor clorgyline. The results indicated that 5-HIAA and PEA were susceptible and effective biomarkers in the rat brain in response to MAO A and B inhibition, respectively. The LC/MS/MS method is useful not only for the determination of inhibitory potency but also for the differentiation of the selectivity of a MAO inhibitor against rat brain MAO A and B in vivo.

EVALUATION OF 5-HYDROXYTRYPTOPHOL AND OTHER ENDOGENOUS SEROTONIN (5-HYDROXYTRYPTAMINE) ANALOGS AS SUBSTRATES FOR UDP-GLUCURONOSYLTRANSFERASE 1A6

Serotonin is a specific in vitro substrate for human UDP-glucuronosyltransferase (UGT) 1A6. In this study, the contribution of UGT1A6 to the glucuronidation of endogenous structural analogs of serotonin, including 5-hydroxytryptophol, N-acetylserotonin, and 6-hydroxymelatonin, was evaluated using available recombinant human UGT isoforms, human liver microsomes, and liver microsomes from animals that do not express functional UGT1A6 (Gunn rats and cats). Only UGT1A6 and UGT1A9 were found to glucuronidate 5-hydroxytryptophol at a concentration of 2 mM, although the glucuronidation rate with UGT1A6 was over 10 times that of UGT1A9. K(m) values for human liver microsomes (156, 141, and 134 microM) were most similar to that of expressed UGT1A6 (135 microM) but vastly different from that of UGT1A9 (3674 microM). 5-Hydroxytryptophol glucuronidation by human liver microsomes (n = 54) correlated well with serotonin glucuronidation (R(s) = 0.83) and UGT1A6 protein content (R(s) = 0.85). 5-Hydroxytryptophol also competitively inhibited serotonin glucuronidation by human liver microsomes (K(i) = 291 microM) and UGT1A6 (K(i) = 200 microM). N-acetylserotonin was glucuronidated most extensively by UGT1A6, although UGT1A9 and UGT1A10 showed moderate catalysis. 6-Hydroxymelatonin was glucuronidated largely by UGT1A9 and UGT1A10 but not at all by UGT1A6. Gunn rat liver glucuronidation rates for serotonin, 5-hydroxytryptophol, N-acetylserotonin, and 6-hydroxymelatonin were 11, 5, 32, and 3%, respectively, of that of normal rat liver. Cat liver microsomes did not glucuronidate serotonin, whereas relatively low activities were observed for the other indole substrates. In conclusion, these results indicate that human UGT1A6 plays a predominant role in the glucuronidation of 5-hydroxytryptophol and N-acetylserotonin, whereas 6-hydroxymelatonin is not a substrate for this enzyme.

5-hydroxytryptophol as a marker for recent alcohol intake

AIMS

To review the mechanism behind the alcohol-induced shift in serotonin metabolism, and the use of urinary 5-hydroxytryptophol (5-HTOL) as a biochemical marker of acute alcohol consumption.

BACKGROUND

The serotonin metabolite 5-HTOL is a normal, minor constituent of urine and is excreted mainly in conjugated form with glucuronic acid. The formation of 5-HTOL increases dramatically after alcohol intake, due to a metabolic interaction, and the elevated urinary excretion remains for some time (>5-15 hours depending on dose) after ethanol has been eliminated. This biochemical effect can be used for detection of recent alcohol intake.

RESULTS

5-HTOL is determined by the gas chromatography-mass spectrometry (GC-MS) or liquid chromatography and mass spectrometry (LC-MS) techniques. A new ELISA method for 5-HTOL glucuronide provides a promising clinical assay. The most robust way to use the marker is by measuring the ratio of 5-HTOL to 5-hydroxyindoleacetic acid, because this compensates for urine dilution and dietary intake of serotonin. 5-HTOL is a very sensitive and specific indicator of recent alcohol consumption and, as such, a valuable complement to self-report. In clinical use, 5-HTOL is effective for monitoring lapses into drinking during out-patient treatment and for objective evaluation of treatment efforts. Other applications include detection of high-risk patients in elective surgery, monitoring of disulfiram treatment and a method to rule out artefactual ethanol formation in forensic toxicology. 5-HTOL can also be used as a sensitive reference method for validation of self-report data in clinical alcohol research.

CONCLUSIONS

An elevated urinary 5-HTOL level can serve as a sensitive and reliable marker for recent alcohol intake with a number of clinical and forensic applications.

Chromatographic methods for the determination of markers of chronic and acute alcohol consumption

The development in chromatographic methods for the determination of markers of alcohol consumption is summarized in this review. The markers included in this article are ethanol in body fluids, ethanol congeners, fatty acid ethyl esters (FAEEs), ethyl glucuronide (EtG), cocaethylene (CE), carbohydrate-deficient transferrin (CDT), phosphatidylethanol (PEth), 5-hydroxytryptophol (5-HTOL), dolichol, ketone bodies, acetaldehyde-protein adducts, and salsolinol (SAL). Some of these markers for alcohol consumption do not only indicate previous ethanol ingestion, but also approximate the amount of intake and the time when ethanol ingestion last occurred. Basic information about the procedures, work-up, and chromatographic conditions are summarized in tables. Also the main metabolic pathways and reaction schemes are demonstrated in figures. Some examples of typical applications are presented. The author points out that in many of the reviewed papers validation data of the procedures as well as specificities and sensitivities were not clearly presented and consequently were not comparable.

Urinary excretion patterns of 5-hydroxyindole-3-acetic acid and 5-hydroxytryptophol in various animal species: implications for studies on serotonin metabolism and turnover rate

The concentrations of the serotonin metabolites 5-hydroxyindole-3-acetic acid (5HIAA) and 5-hydroxytryptophol (5HTOL) were determined in spot urine samples of 12 mammalian and one fish species (cat, cow, dog, ferret, golden hamster, guinea pig, horse, monkey, mouse, rabbit, rainbow trout, rat, sheep) and compared with human data. The highest urinary concentrations of 5HTOL were found in the Sprague-Dawley rat (mean 9.5 micromol/L) and NMRI mouse (8.2 micromol/L), and the lowest in rainbow trout, cynomolgus macaque, and human urine (approximately 0.1 micromol/L). The highest 5HIAA concentrations were found in hamster (89.3 micromol/L) and mouse (85.2 micromol/L), and the lowest in rainbow trout, horse and sheep (range 2.0-3.7 micromol/L). Several species showed 5HIAA concentrations similar to that normally observed in human urine (approximately 5-40 micromol/L). This study demonstrated wide inter- and intra-species variations in the urinary concentrations of 5HIAA and 5HTOL, both separately and in the sum of concentrations. The 5HTOL/5HIAA ratio, which is used as an easily accessible index of the relative importance of the reductive and oxidative pathways for serotonin metabolism, also varied considerably between different species. This observation confirms that the much higher urinary 5HTOL/5HIAA ratio in rats (mean 0.35) compared with humans (< 0.01) is due to a higher baseline formation of 5HTOL in the rat. The monkey, ferret, hamster, and rabbit most closely resembled humans in this respect, and at least the two latter species appear to be more suitable than rats as animal models for studying serotonin metabolism and turnover rate, and the metabolic interaction with ethanol.

Studies on the interaction between ethanol and serotonin metabolism in rat, using deuterated ethanol and 4-methylpyrazole

The metabolic interaction between ethanol and serotonin (5-hydroxytryptamine) via alcohol dehydrogenase (ADH; EC 1.1.1.1) was studied in tissue homogenates of Sprague-Dawley rats by following the transfer of deuterium from deuterated ethanol over endogenous NADH to 5-hydroxytryptophol (5HTOL). Homogenates of whole brain, lung, spleen, kidney, liver, stomach, jejunum, ileum, colon, and caecum were incubated in the presence of [2H2]ethanol and 5-hydroxyindole-3-acetaldehyde (5HIAL), and the [2H]5HTOL formed was identified and quantified using gas chromatography-mass spectrometry. ADH activity was most abundant in liver, kidney, and within the gastrointestinal tract. The highest incorporation of deuterium was obtained in homogenates of kidney, lung, and colon, whereas in brain, which contains very low ADH activity, no incorporation could be demonstrated. Addition of extra NAD+ (2.4 mM) increased the formation of [2H]5HTOL 2.6-fold in liver homogenates, but only 1.2-fold in kidney homogenates. 4-Methylpyrazole, a potent inhibitor of class I ADH, inhibited the 5HIAL reduction in homogenates of lung, kidney, jejunum, ileum, and colon, and caused a marked drop in 5HTOL oxidation in all tissues except stomach and spleen. These results demonstrate that in the rat a metabolic interaction between ethanol and serotonin via the ADH pathway may take place in several tissues besides the liver, which is the main tissue for ethanol detoxification.

Acute interaction between ethanol and serotonin metabolism in the rat

The effect of acute ethanol on peripheral serotonin (5HT) metabolism was studied in Sprague-Dawley rats. Four hours after a single dose of ethanol (1.0 g/kg) administered into the stomach, a significant increase in the 5HT level in stomach tissue and a decrease in ileum was observed. The level of 5-hydroxyindole-3-acetic acid (5HIAA) was increased in urine, while increased concentrations of 5-hydroxytryptophol (5HTOL) occurred in jejunum, ileum, spleen and urine. After 7-9 h when the blood ethanol concentration had returned to zero, 5HTOL levels were still higher than control values in jejunum, ileum and urine. At 4 h, an elevated ratio of 5HTOL to 5HIAA was observed in urine and ileum (by approximately 2-fold), liver (approximately 3-fold), and spleen (approximately 5-fold), whereas the ratio was reduced in stomach. In urine and spleen, this metabolic shift persisted after 7-9 h. The 5HTOL level in bile was increased by approximately 3.5-fold after 8 h. 5HIAA was not detectable in bile. The present results indicate that the rat has a much higher proportion of 5HTOL formation than man under normal conditions. The rat does not appear to be an ideal model for studying the interaction between ethanol and 5HT metabolism in man.

Determination of 5-hydroxytryptophol in urine by high-performance liquid chromatography: application of a new post-column derivatization method with fluorometric detection

The aim of the present study was to develop a high-performance liquid chromatographic (HPLC) method for determination of the serotonin metabolite 5-hydroxytryptophol (5HTOL) in human urine. 5HTOL was liberated from its conjugated form by enzymatic hydrolysis and isolated by a sample clean-up procedure on a small Sephadex G-10 column. The eluate was injected onto an isocratically eluted C18 reversed-phase column and 5HTOL was converted into a fluorescent oxazole derivative by on-line post-column reaction with benzylamine in the presence of potassium hexacyanoferrate(III). The limit of detection was about 10 nM and the intra-assay coefficients of variation were below 4% with urine samples and standard solutions. The results indicate that the method can be used as a screening method to discriminate between normal and elevated levels of total (free + conjugated) 5HTOL in urine.

Time course of ethanol-induced changes in serotonin metabolism

The effect of acute ethanol consumption on serotonin metabolism was examined in healthy volunteers in the fasted and fed state by determination of plasma and urinary levels of the serotonin metabolites 5-hydroxyindole-3-acetic acid (5-HIAA) and 5-hydroxytryptophol (5-HTOL). The plasma and urinary levels of 5-HIAA were reduced by about 40% and 25%, while the 5-HTOL levels were increased on an average 7-fold and 50-fold, respectively, after oral intake of ethanol (0.8 g/kg) over 30 min in a fasted state. The maximal effect on both 5-HIAA and 5-HTOL levels was found 4-6 h after starting drinking. Urinary 5-HTOL and the 5-HTOL/5-HIAA ratio did not return to baseline until 19 h after the start of the administration (i.e., about 10 h after ethanol reached zero level). The mean 24-h excretion of 5-HTOL was increased 15-fold by the ethanol intake, while the 5-HIAA excretion was not significantly different. A clear dose dependent effect was observed in one individual who also ingested a lower amount of ethanol (0.5 g/kg). When ethanol (0.8 g/kg) was ingested over 3 h together with food, the urinary level of 5-HTOL and the 5-HTOL/5-HIAA ratio did not return to baseline until after 20-22 h. In other subjects who had unlimited access to ethanol and ingested between 1.3-2.3 g/kg together with food, the time to reach baseline 5-HTOL/5-HIAA ratio in urine ranged from 20 h to over 26 h.

Urinary excretion of 5-hydroxyindole-3-acetic acid and 5-hydroxytryptophol after oral loading with serotonin

The urinary excretion patterns of the serotonin (5-hydroxytryptamine; 5-HT) metabolites 5-hydroxyindole-3-acetic acid (5-HIAA) and 5-hydroxytryptophol (5-HTOL) were examined after ingestion of bananas, a food rich in 5-HT. The bananas contained on an average 25 micrograms 5-HT/g pulp. Both urinary 5-HIAA and 5-HTOL increased markedly (15- to 30-fold) shortly after eating 3-4 bananas, with the highest concentrations found in urine specimens collected after 2-4 h, and did not return to normal until after 8-10 h. The excretion of 5-HIAA increased from a control mean value of 3.9 mg/24 h to 12.7 mg/24 h, when conventional diets were supplemented with 3-4 bananas. The corresponding results for 5-HTOL were 16.8 micrograms/24 h and 60.7 micrograms/24 h, respectively. Of the banana-derived 5-HT ingested, 60-80% was recovered in the urine as 5-HIAA and only 0.3-0.5% as 5-HTOL. However, since both the time-course and relative increase in 5-HTOL was similar to that of 5-HIAA, there was no effect on the urinary 5-HTOL to 5-HIAA ratio. By contrast, acute alcohol consumption produced a considerable elevation of this ratio.

Determination of urinary 5-hydroxyindole-3-acetic acid by high-performance liquid chromatography with electrochemical detection and direct sample injection

A method for the routine quantitative determination of the major serotonin metabolite 5-hydroxyindole-3-acetic acid (5-HIAA) in urine is described. 5-HIAA was analyzed without prior sample cleanup, using an automated high-performance liquid chromatography system with isocratic elution and electrochemical detection (+0.60 V versus a Ag/AgCl reference electrode). The urine samples were mixed with a solution of the internal standard (5-hydroxyindole-3-propionic acid) and centrifuged. The supernatant was transferred to sealed glass vials, and a 2-microliters aliquot was injected directly onto a C18 reversed-phase analytical column, using an automatic sample injector. Samples of urine could be stored for several months at -80 or at +7 degrees C for 2 days without loss of 5-HIAA. However, a gradual decline with time occurred in crude samples stored at room temperature or above, as well as in urine samples diluted with the mobile phase. The detector response was linear in the range of 0-65 mumol/l 5-HIAA, and the intra- and interassay coefficients of variation were about 5 and 7%, respectively (n = 10).

Simultaneous measurements of tryptophan and its metabolites, kynurenine and serotonin, in the superficial layers of the spinal dorsal horn. A study in normal and arthritic rats

It has been demonstrated that 5-hydroxytryptamine (5-HT) is not the only neuroactive metabolite of tryptophan (TRP) in the CNS. The presence of kynurenine (KYN) and its metabolites has been reported in the brain of several mammalian species and the neuroactive properties of these compounds are now well established. In the present study, we report the identification of KYN in the superficial layers of the rat spinal dorsal horn. KYN was measured simultaneously with TRP. 5-hydroxytryptophan, 5-HT, 5-hydroxyindoleacetic acid and 5-HT-O-sulfate by means of liquid chromatography with coulometric electrode array detection. The results observed in the normal rat and in an animal model of persistent pain, the arthritic rat, are discussed in view of the hypothesis relating to the involvement of the bulbospinal serotonergic system in pain mechanisms and of the possible participation of KYN and its metabolites in these mechanisms.

5-Hydroxytryptophol and 5-hydroxyindoleacetic acid levels in rat brain: effects of various drugs affecting serotonergic transmitter mechanisms

The effect of various pharmacological treatments on the levels of free and total 5-hydroxytryptophol (5-HTOL) and 5-hydroxyindoleacetic acid (5-HIAA) in rat brain were investigated using a gas chromatographic-mass spectrometric technique. The disappearance of 5-HTOL following monoamine oxidase (MAO) inhibition induced by pargyline was more rapid (t1/2 10-15 min) than that of 5-HIAA (t1/2 30-40 min) in all regions investigated, indicating a rapid turnover of 5-HTOL. The selective MAO-A inhibitor chlorgyline produced a more pronounced reduction of 5-HTOL than of 5-HIAA, while the MAO-B inhibitor deprenyl was without effect on both serotonin metabolites. The MAO-A inhibitor amiflamine which is selective for serotonin neurons, was also more effective in reducing free 5-HTOL levels than of 5-HIAA levels, suggesting that the formation of 5-HTOL is closely associated with serotonin neurons. Neonatal treatment with the serotonin neurotoxin 5, 7-dihydroxytryptamine (5,7-HT) led to a more pronounced reduction of 5-HTOL levels in cerebral cortex than that of 5-HIAA levels, while the increase of 5-HTOL levels in pons-medulla was more marked than of 5-HIAA levels. Probenecid treatment increased several fold both conjugated 5-HTOL and 5-HIAA levels in brain tissue. An increase was also noted for free 5-HTOL, although of less magnitude. Treatment with the serotonin receptor active agents methiothepin and d-lysergic acid diethylamide produced similar alterations of free 5-HTOL and 5-HIAA. The present results have demonstrated that free 5-HTOL has a rapid turnover in rat brain and that free 5-HTOL levels may serve as a useful index for serotonin turnover.

Investigation of circadian rhythms for pineal 5-hydroxytryptophol and other indoles in the rat

5-hydroxytryptophol (5HTL) occurs in the pineal gland of the rat at levels comparable to those of melatonin, yet few studies have been conducted to investigate 5HTL as a potential alternative pineal hormone. In this study the pineals of 90-day-old male Sprague Dawley rats have been assayed by high performance liquid chromatography coupled with electrochemical detection. Significant (P less than .0001) circadian variation was measured in 5HTL levels, and a fivefold plateau elevation occurred during the middle of the light period. By comparison with the timing of the variations in N-acetyl serotonin and melatonin levels, it is suggested that 5HTL may not be regulated by simple competition with N-acetyl transferase for the common substrate 5HT but may, in fact, be regulated independently. Literature supporting such a suggestion, and a model incorporating it, are presented for discussion.

Human alcohol dehydrogenases and serotonin metabolism

Human liver alcohol dehydrogenases (ADH) may participate in serotonin (5-hydroxytryptamine) metabolism. Class I and II isozymes catalyze the oxidation of 5-hydroxytryptophol (5-HTOL) with kcat/Km values ranging from 10 to 100 mM-1 min-1 compared to 4-66 mM-1 min-1 for that of ethanol at pH 7.40, 25 degrees C. The product, 5-hydroxyindoleacetaldehyde, was purified as its semicarbazone and identified by mass spectrometry. Ethanol competitively inhibits 5-HTOL oxidation by beta 1 gamma 2 ADH with a Ki of 440 microM, a value similar to the Km of ethanol, 210 microM. The inhibition constants for 1,10-phenanthroline and 4-methylpyrazole are 20 microM and 80 nM respectively, essentially identical to those obtained with ethanol as substrate, 22 microM and 70 nM, respectively. The competition between ethanol and 5-HTOL for ADH can explain observations of ethanol induced changes in serotonin metabolism in vivo.

Pineal indoles: significance and measurement

Despite intensive investigation, particularly over the past fifteen years, many aspects of pineal function with respect to mammalian physiology remain obscure. Much of this work is reviewed and particular attention focussed on indole metabolism within the pineal gland. Emphasis is placed on the development of new analytical techniques with special reference to high performance liquid chromatography coupled with electrochemical detection. The growth in knowledge regarding pineal indole synthesis which can be attributed to the use of this technique is discussed. The possibility that pineal indoles other than melatonin may function as hormones or neuromodulators is considered. A functional role for 5-hydroxytryptophol as a neuromodulator, possibly associated with diffuse neuroendocrine function (amine precursor, uptake and decarboxylation, APUD) is suggested.

5-Hydroxyindoleacetic acid and 5-hydroxytryptophol levels in rat brain: effects of ethanol, pyrazole, cyanamide and disulfiram treatment

The two serotonin metabolites 5-hydroxyindoleacetic acid (5HIAA) and 5-hydroxytryptophol (5HTOL) were measured in two regions of rat brain (pons medulla and diencephalon) using a gas chromatographic-mass spectrometric (GC-MS) method. Acute ethanol intoxication effected an elevation of 5-hydroxytryptophol levels, while 1 week of treatment with ethanol appeared to have no effect on either metabolite when measured 24 h after the last dose. Disulfiram and cyanamide treatment produced an approximately 2-fold increase in 5-hydroxytryptophol and a slight reduction in 5-hydroxyindole-acetic acid. Pyrazole treatment produced an increase in both metabolites. This effect was, however, counteracted by the simultaneous administration of ethanol.