Serum Free Tryptophan Research Articles

Amino acid availability of processed Brassica carinata meals in hybrid striped bass Morone chrysops ♀ x M. saxatilis ♂

An earlier study showed that hybrid striped bass (Morone chrysops ♀ x M. saxatilis ♂) diets containing 20 % animal meals and up to 30 % aerobically fermented (AF) carinata meal (Brassica carinata, CM) followed by a single wash with water (AFCM) or 30 % CM double-washed with water without AF (WCM), resulted in similar growth. However feed utilization and Fulton’s condition factor of 30 % WCM were better. The current study investigated effects of AFCM and WCM on amino acid digestibilities using naive fish. Effects of AFCM and WCM on trypsin activity, and amino acid availability were determined using hybrid striped bass fed experimental diets for 127 and 148 days, respectively (after a growth trial). High (30 %) AFCM reduced all essential amino acids (EAA) and conditionally EAA (CEAA) except histidine, methionine and threonine. However, all EAA and CEAAs except lysine and cysteine were digested better in 30 %WCM than 30 % AFCM. High (30 %) CMs resulted in generally high serum free methionine and tryptophan, but less leucine for the first 9 h. However, 30 % WCM resulted in generally more serum free arginine and valine than 30 % AFCM. High CMs increased muscle free histidine. Generally, WCM resulted in more muscle lysine and valine than AFCM. Muscle methionine was increased by CMs. Both serum and muscle free total EAAs in hybrid striped bass fed 30 % WCM were elevated continuously over a longer period above the baseline levels. Using EAA:lysine, only muscle histidine were adequate for muscle synthesis over the 36-h period. Overall, amino acids were more available in WCM than AFCM.

Serum Levels and Removal by Haemodialysis and Haemodiafiltration of Tryptophan-Derived Uremic Toxins in ESKD Patients.

Tryptophan is an essential dietary amino acid that originates uremic toxins that contribute to end-stage kidney disease (ESKD) patient outcomes. We evaluated serum levels and removal during haemodialysis and haemodiafiltration of tryptophan and tryptophan-derived uremic toxins, indoxyl sulfate (IS) and indole acetic acid (IAA), in ESKD patients in different dialysis treatment settings. This prospective multicentre study in four European dialysis centres enrolled 78 patients with ESKD. Blood and spent dialysate samples obtained during dialysis were analysed with high-performance liquid chromatography to assess uremic solutes, their reduction ratio (RR) and total removed solute (TRS). Mean free serum tryptophan and IS concentrations increased, and concentration of IAA decreased over pre-dialysis levels (67%, 49%, −0.8%, respectively) during the first hour of dialysis. While mean serum total urea, IS and IAA concentrations decreased during dialysis (−72%, −39%, −43%, respectively), serum tryptophan levels increased, resulting in negative RR (−8%) towards the end of the dialysis session (p < 0.001), despite remarkable Trp losses in dialysate. RR and TRS values based on serum (total, free) and dialysate solute concentrations were lower for conventional low-flux dialysis (p < 0.001). High-efficiency haemodiafiltration resulted in 80% higher Trp losses than conventional low-flux dialysis, despite similar neutral Trp RR values. In conclusion, serum Trp concentrations and RR behave differently from uremic solutes IS, IAA and urea and Trp RR did not reflect dialysis Trp losses. Conventional low-flux dialysis may not adequately clear Trp-related uremic toxins while high efficiency haemodiafiltration increased Trp losses.

Interaction of Small Zinc Complexes with Globular Proteins and Free Tryptophan

A series of eight water soluble anionic, cationic, and neutral zinc(II) complexes were synthesized and characterized. The interaction of these complexes with bovine serum albumin (BSA), human serum albumin (HSA), lysozyme, and free tryptophan (Trp) was investigated using steady-state fluorescence spectroscopy. Static and dynamic fluorescence quenching analysis based on Stern-Volmer kinetics was conducted, and the decrease in fluorescence intensity of the Trp residue(s) can be ascribed predominantly to static quenching that occurs when the Zn complex binds to the protein and forms a nonfluorescent complex. The role played by the nature of the ligand, the metal, and complex charge in quenching Trp fluorescence was investigated. The binding association constants (Ka) ranged from 104to 1010 M−1and indicate that complexes with planar aromatic features have the strongest affinity for globular proteins and free Trp. Complexes with nonaromatic features failed to interact with these proteins at or in the vicinity of the Trp residues. These interactions were studied over a range of temperatures, and binding was found to weaken with the increase in temperature and was exothermic with a negative change in entropy. The thermodynamic parameters suggest that binding of Zn complexes to the proteins is a highly spontaneous and favorable process.

Determination of free tryptophan in serum with aptamer—Comparison of two aptasensors

Two aptasensors based on graphene oxide (GO) and molecular beacon were designed for the detection of L-tryptophan (L-Trp) using L-Trp aptamer (Trp3a-1). The fluorescein (FAM) labeled Trp3a-1 was absorbed by GO, which resulted in the fluorescence quenching, and exhibiting minimal background fluorescence. Upon the addition of L-Trp, Trp3a-1 was not absorbed quickly. This effect allows for a quantitative assay of L-Trp over the concentration range of 10–500μM and with a detection limit of 6.84μM. However, due to the unspecific adsorption of GO, the GO based aptasensor can׳t be applied in complex matrixes. In respect of molecular beacon based aptasensor, FRET between Trp3a-1 labeled with FAM and CS-Trp3a-1 labeled with BHQ-1(black hole quencher-1) which is partially complementary with the aptamer was used to detect L-Trp. L-Trp binding could induce the disassociation of CS-Trp3a-1, resulted in the enhancement of fluorescence in solution. With an excellent linear relationship in 10–500μM and a detection limit of 6.97μM in 25% serum, the aptasensor is expected to be improved for the detection of free L-Trp in other complex samples.

Static quenching of tryptophan fluorescence in proteins by a dioxomolybdenum(VI) thiolate complex

Abstract The binding of cis-dioxobis(dithiocarbamato) molybdenum(VI) with the proteins bovine serum albumin, human serum albumin, lysozyme, and free tryptophan was studied using fluorescence spectroscopy and Stern–Volmer kinetics. The quenching of tryptophan fluorescence was determined to be static with binding constants on the order of 104–105 M−1, and with a binding site number of one. The interaction was studied over a range of temperatures, and the binding was found to be exothermic with a negative change in entropy. Quantum chemical calculations were also conducted to identify optimal spatial contacts and the resulting energetic contributions between the complex and free tryptophan.

Disturbed Tryptophan Metabolism in Cardiovascular Disease

Atherosclerosis (AS), a major pathologic consequence of obesity, is the main etiological factor of cardiovascular disease (CVD), which is the most common cause of death in the western world. A systemic chronic low grade immune- mediated inflammation (scLGI) is substantially implicated in AS and its consequences. In particular, proinflammatory cytokines play a major role, with Th1-type cytokine interferon-γ (IFN-γ) being a key mediator. Among various other molecular and cellular effects, IFN-γ activates the enzyme indoleamine 2,3-dioxygenase (IDO) in monocyte-derived macrophages, dendritic, and other cells, which, in turn, decreases serum levels of the essential amino acid tryptophan (TRP). Thus, people with CVD often have increased serum kynurenine to tryptophan ratios (KYN/TRP), a result of an increased TRP breakdown. Importantly, increased KYN/TRP is associated with a higher likelihood of fatal cardiovascular events. A scLGI with increased production of the proinflammatory adipokine leptin, in combination with IFN-γ and interleukin-6 (IL-6), represents another central link between obesity, AS, and CVD. Leptin has also been shown to contribute to Th1-type immunity shifting, with abdominal fat being thus a direct contributor to KYN/TRP ratio. However, TRP is not only an important source for protein production but also for the generation of one of the most important neurotransmitters, 5-hydroxytryptamine (serotonin), by the tetrahydrobiopterin-dependent TRP 5-hydroxylase. In prolonged states of scLGI, availability of free serum TRP is strongly diminished, affecting serotonin synthesis, particularly in the brain. Additionally, accumulation of neurotoxic KYN metabolites such as quinolinic acid produced by microglia, can contribute to the development of depression via NMDA glutamatergic stimulation. Depression had been reported to be associated with CVD endpoints, but it most likely represents only a secondary loop connecting excess adipose tissue, scLGI and cardiovascular morbidity and mortality. Accelerated catabolism of TRP is further involved in the pathogenesis of the anemia of scLGI. The pro-inflammatory cytokine IFN-γ suppresses growth and differentiation of erythroid progenitor cells, and the depletion of TRP limits protein synthesis and thus hemoglobin production, and, through reduction in oxygen supply, may contribute to ischemic vascular disease. In this review we discuss the impact of TRP breakdown and the related complex mechanisms on the prognosis and individual course of CVD. Measurement of TRP, KYN concentrations, and calculation of the KYN/TRYP ratio will contribute to a better understanding of the interplay between inflammation, metabolic syndrome, mood disturbance, and anemia, all previously described as significant predictors of an unfavorable outcome in patients with CVD. The review leads to a novel framework for successful therapeutic modification of several cardinal pathophysiological processes leading to adverse cardiovascular outcome.

Fluorescent differentiation and quantificational detection of free tryptophan in serum within a confined metal–organic tetrahedron

A metal-organic cerium tetrahedron having size constraints and cooperated interactions within its cavity was used to selectively recognize tryptophan over other natural amino acids and Trp-containing peptides. It was applied in quantificational detection of free tryptophan in serum.

Static and Dynamic Quenching of Tryptophan Fluorescence in Various Proteins by a Chromium (III) Complex

ABSTRACT The interaction of a chromium (III) complex, (R,R)-N,N′-Bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diaminochromium (III), with human serum albumin, bovine serum albumin, lysozyme, and free tryptophan was studied using steady-state fluorescence spectroscopy. Dynamic and static quenching constants were calculated using Stern-Volmer kinetics. The complex bound more tightly to the serum albumins than to lysozyme or free tryptophan, but only one binding site was determined in all systems. The interaction was also determined to be thermodynamically favorable, and the binding constants were on the order of 103–106. The fluorescence quenching was static in nature with Forster distances in the 1.8–2.0 nm range.

Increased serum free tryptophan in patients with diarrhea-predominant irritable bowel syndrome

Irregularities of serotonin function in irritable bowel syndrome (IBS) may be due to changes in the metabolism of the serotonin precursor l-tryptophan. Dietary alteration of tryptophan intake may impact upon the mood and bowel symptoms of IBS. We hypothesized that diarrhea-predominant irritable bowel syndrome (d-IBS) patients would exhibit an increase in plasma tryptophan due to alterations in tryptophan metabolism. We also hypothesized that a diet low in tryptophan would reverse this change and reduce symptoms. Thirteen patients with d-IBS had fasting serum free and total tryptophan, large neutral amino acids, and 6 kynurenine metabolites measured before and after 2 weeks of a strict dairy-free diet. Baseline tryptophan parameters were compared with an age- and sex-matched control group. Changes in the specific tryptophan parameters before and after dairy-free diet were correlated with symptoms of IBS and mood. Compared with the control group, d-IBS patients at baseline exhibited significantly higher free serum tryptophan (10.5 ± 4.35 vs 4.75 ± 2.43 μmol/L [means ± standard deviation], P = .006) and significantly lower tryptophan dioxygenase and total tryptophan oxidation as measured by the kynurenine to free tryptophan and total kynurenines to free tryptophan ratios (23.37 ± 10.12 vs 55.33 ± 16.02, P < .001 and 49.34 ± 17.84 vs 258.46 ± 98.67, P < .001, respectively). Dairy-free diet did not modulate metabolites of the kynurenine pathway or symptoms. Tryptophan metabolism along the kynurenine pathway is inhibited in d-IBS, and a dairy-free diet does not alter this. Our findings are consistent with possible enhanced serotonin activity in d-IBS.

Serotonergic function, substance craving, and psychopathology in detoxified alcohol-addicted males undergoing tryptophan depletion

Alcohol addiction is associated with alterations of central nervous dopaminergic and serotonergic functions. Acute tryptophan depletion has not yet been applied in detoxified alcohol-addicted patients in order to investigate its impact on psychopathology, psychoneuroendocrinology, and substance craving behaviour. 25 alcohol-addicted males randomly either received a tryptophan-free or tryptophan-containing amino acid drink and 7 days later the respective other drink. Anxiety, depression, and craving were assessed before and 5 h after the drink. Tryptophan, 5-HIAA, dopamine, norepinephrine, epinephrine, and HVA in serum were measured before and after both treatments. Nocturnal urinary cortisol measurements and genotyping for the HTTLPR polymorphism of the SLC6A4 gene were performed. Tryptophan depletion resulted in a significant reduction of total and free serum tryptophan while the tryptophan-rich drink increased serum levels. Both treatments caused a significant increase of serum serotonin levels, however, serum 5-HIAA was decreased after depletion but increased after sham depletion. Dopamine and norepinephrine were elevated after tryptophan depletion and sham. Depletion increased depression scores (MADRS), while the full amino acid drink improved state and trait anxiety ratings (STAI) and substance craving. Urinary cortisol excretion was not affected by both treatments. Patients with the ll genotype of the serotonin transporter gene displayed lower baseline tryptophan levels compared to patients with the heterozygous genotype. Results suggest an impaired serotonergic function in alcohol-addicted males.

Blood Substrates and Hormonal Response to Increased Egg White Protein Intake Prior to a 12,000m Run in Heat

This study was undertaken to investigate the effects of isoenergetic and increased amounts of egg white protein one hour before a run on the changes in the post-exercise blood biochemistry and the rating of the perceived exertion (RPE). Twenty-four male distance runners were divided into four groups. Venous blood samples were collected at three time points: just before the experiment (Pre), just after a 12,000 m run (Post 0 h) and one hour after the run (Post 1 h). After the first blood sampling, each participant consumed one of the four isoenergetic supplements (86 kcal); 0 g, 5 g, 10 g, or 20 g of egg white protein. The blood glucose, free amino acid, and branched chain amino acid (BCAA) levels in the 0 g, 5 g, and 10 g protein groups were higher at Post 0 h than at Pre. The pre-exercise intake of the 20 g protein group showed the smallest changes in the blood biochemicals. The RPE scores were significantly higher at Post 0 h, and did not vary among the four protein groups. Accordingly, the pre-exercise carbohydrate intakes significantly altered the post-exercise blood biochemisty findings, but the pre-exercise protein intake did not. Furthermore, the changes in the RPE scores in our present study were not explained by changes in the serum free tryptophan or the BCAA levels, and an increased dietary intake of egg white protein might not prevent post-exercise increases in the RPE scores.

Effects of treatment with chromium picolinate on peripheral amino acid availability and brain monoamine function in the rat.

Elemental chromium (Cr) is an essential micronutrient. It is required for optimal insulin activity and normal carbohydrate and lipid metabolism. Tri-valent chromium (Cr3+) is recommended for the treatment of diabetes and obesity. There is evidence that Cr3+ may have antidepressant properties, possibly by enhancement of monoamine function through its ability to increase amino acid transport to the brain. The aim of the present study was to investigate further the possible effects of Cr3+ treatment on peripheral amino acid availability and brain monoamine function in the rat. We undertook three studies in rats. The first was a time-course study in which animals were administered single doses of 50 mg/kg of Cr3+ picolinate and the second a dose-response study in which animals were given either 20 or 50 mg/kg Cr3+ picolinate versus vehicle alone via the intra-peritoneal route. In the third, animals were fed a diet containing Cr3+ picolinate (100 mg/kg) or a similar control diet for two weeks and were then sacrificed. Blood was sampled and brains were removed for later analysis. Results from the Cr3+ time-course study defined an optimal time for sampling of two hours after dosing. Results from the second study showed dose-related responses to Cr3+ treatment for a number of measured biochemical parameters including serum corticosterone. In the sub-chronic treatment study Cr3+ significantly increased serum free tryptophan (TRP), non-esterified free fatty acids (NEFFAs), corticosterone, together with brain TRP, serotonin (5-hydroxytryptamine, 5-HT), noradrenaline (NA) and pineal melatonin. From other studies in our laboratory we have shown that Cr3+ treatment can modify brain 5-HT function, perhaps by altering the sensitivity of central 5-HT2A receptors. The peripheral effect of Cr3+ picolinate treatments and their consequential central effect on increased serotonergic and noradrenergic function may suggest that Cr3+ could have some antidepressant-like actions. Future studies to confirm this are to be done.

Interferon-gamma-induced conversion of tryptophan: immunologic and neuropsychiatric aspects.

Tryptophan is an essential amino acid and the least abundant constituent of proteins. In parallel it represents a source for two important biochemical pathways: the generation of neurotransmitter 5-hydroxytryptamine (serotonin) by the tetrahydrobiopterin-dependent tryptophan 5-hydroxylase, and the formation of kynurenine derivatives and nicotinamide adenine dinucleotides initiated by the enzymes tryptophan pyrrolase (tryptophan 2,3-dioxygenase, TDO) and indoleamine 2,3-dioxygenase (IDO). Whereas TDO is located in the liver cells, IDO is expressed in a large variety of cells and is inducible by the cytokine interferon-gamma. Therefore, accelerated tryptophan degradation is observed in diseases and disorders concomitant with cellular immune activation, e. g. infectious, autoimmune, and malignant diseases, as well as during pregnancy. According to the cytostatic and antiproliferative properties of tryptophan-depletion on T lymphocytes, activated T-helper type 1 (Th-1) cells may down-regulate immune response via degradation of tryptophan. Especially in states of persistent immune activation availability of free serum tryptophan is diminished and as a consequence of reduced serotonin production, serotonergic functions may as well be affected. Accumulation of neuroactive kynurenine metabolites such as quinolinic acid may contribute to the development of neurologic/psychiatric disorders. Thus, IDO seems to represent a link between the immunological network and neuroendocrine functions with far reaching consequences in regard to the psychological status of patients. These observations provide a basis for the better understanding of mood disorder and related symptoms in chronic diseases.

Interferon-gamma-induced tryptophan degradation: neuropsychiatric and immunological consequences.

Tryptophan is a constituent of proteins and in parallel it represents a source for mainly two pivotal biochemical pathways: the generation of 5-hydroxytryptamine (serotonin), and the formation of kynurenine by the enzymes tryptophan pyrrolase (TP) and indoleamine 2,3-dioxygenase (IDO). IDO is induced by interferon-gamma (IFN-gamma) in a broad variety of cells. Therefore, enhanced tryptophan degradation is observed in diseases and disorders concomitant with cellular immune activation, e.g. infectious diseases, autoimmune diseases, malignant diseases as well as in pregnancy. IFN-gamma-derived tryptophan degradation may represent an effector mechanism within in the comprehensive network of immune stimulation. In addition, the cytostatic and, respectively, antiproliferative properties on e.g., T-lymphocytes may contribute to the immunomodulatory function of IFN-gamma. However, especially in states of persistent immune activation increased tryptophan catabolism leads to the depletion of free serum tryptophan and to the accumulation of neuroactive kynurenine metabolites. As a consequence, serotonergic functions may be affected, and the neurotoxic properties of kynurenine derivatives may lead to neuronal disorders evoking neurological/psychiatric symptoms. This notion provides a basis for the better understanding of mood disorders and related syptoms in chronic diseases. Moreover, IDO could represent a link between the immunological network and neuroendocrine functions with far reaching consequences regarding to the psychological status of patients.

Differences in Tryptophan Binding to Hepatic Nuclei of NZBWF1 and Swiss Mice: Insight into Mechanism of Tryptophan's Effects , ,

We have observed that in NZBWF1 mice the affinity for L-tryptophan binding to hepatic nuclei in vitro is markedly less than that of Swiss mice. In vitro binding of [3H]tryptophan to hepatic nuclei from both strains was determined without and with unlabeled L-tryptophan(10−4 mol/L). The relative specific binding of L-tryptophan to hepatic nuclei in vitro was 60.9 ± 4.4% for Swiss mice and 35.8 ± 5.4% (P < 0.01) in NZBWF1 mice. The total specific binding (bound radioactivity/mg nuclear protein) of L-tryptophan to hepatic nuclei in vitro was 74.9% (P < 0.05) lower in NZBWF1 mice than in Swiss mice. Other strains (DBA, SJL and BALB/c) had specific binding affinities similar to that of Swiss mice. Serum and hepatic free tryptophan concentrations and hepatic tryptophan dioxygenase activity in mice that were food-deprived overnight or 1 h after tube-feeding L-tryptophan (20 mg/100 g body weight) were similar in the strains of mice. In vitro [14C] leucine incorporation into protein using hepatic microsomes of mice 1 h after tube-feeding L-tryptophan (20 mg/100 g body weight) revealed a significantly greater (P < 0.05) increase relative to food-deprived controls in Swiss mice (76.8 ± 19.2%) than the increase in NZBWF1 mice (26.5 ± 2.6%). Nuclear [14C]-labeled RNA release in vitro was increased 77.2 ± 18.0% by tube-feeding of L-tryptophan in Swiss but only 7.6 ± 5.8% (P < 0.02) in NZBWF1 mice. Liver nuclear poly(A)-polymerase and nucleoside triphosphatase activities were variably increased by the administration of L-tryptophan in both strains. In summary, compared with Swiss mice, NZBWF1 mice have a lower specific binding affinity for L-tryptophan by hepatic nuclei, and this alteration may account for the other differences in responses to L-tryptophan by the two strains.

Elevated tryptophan levels in post-withdrawal alcoholics.

Changes in serotonin function and disturbances in tryptophan availability have been implicated in many psychiatric disorders, including alcoholism. In the present study we took serum free tryptophan samples from 31 healthy volunteer controls and from 42 DSM-III-R alcohol-dependent subjects who had abstained from alcohol for at least 2.5 weeks (range 2.5-104 weeks). We also measured the basal serum cortisol level at 09.00 hours for the same subjects and controls. There was a significant increase in the serum tryptophan level of the alcoholic subjects, by 43.7 mumol l-1 (range 29-63 mumol l-1), regardless of age of onset of alcoholism, family history of alcoholism or sociopathic traits, compared to the controls (33.0 mumol l-1, range 19-60 mumol l-1). There was also an increase in the basal serum cortisol level in the alcoholic subjects compared to the controls, but this was not related to the increase in tryptophan levels. These findings indicate a disturbance in serotonin precursor availability in post-withdrawal alcoholics, and contribute to the evidence for involvement of the serotonin system in alcoholism.

Free and protein-bound tryptophan in serum of untreated patients with chronic renal failure

In fasting sera from 46 untreated patients with chronic renal failure and in 22 normal subjects, non-protein-bound tryptophan, F, was separated by pH-controlled equilibrium dialysis. Total tryptophan, T, and F were measured by HPLC. Results in patients were related to gender, severity of chronic renal failure (as measured by radioisotopic glomerular filtration rate), protein intake (as measured by 24-hr urinary urea N excretion), and protein nutrition (as measured by serum concentrations of albumin and transferrin). T was subnormal in 59% of the patients. In seven hypoalbuminemic patients, F/T was markedly increased (approaching unity) but F was normal. In 39 non-hypoalbuminemic patients, F was again normal but F/T was often increased at glomerular filtration rates below 30 ml/min/3 m2 of height2, especially in females. T was significantly correlated with estimated protein intake (r = 0.54, P = 0.0004), even though neither F nor serum protein levels were correlated with it. We conclude that the serum level of free tryptophan is well-maintained in chronic renal failure, being uninfluenced by severity of renal insufficiency, voluntary protein intake, or serum protein concentrations. On the other hand, protein-bound tryptophan varies with protein intake, decreases markedly in hypoalbuminemic patients, and also decreases in many nonhypoalbuminemic patients (especially females) when the glomerular filtration rate falls below approximately 30 ml/min/3 m2 of height2.

Determination of tryptophan in human serum by high-performance liquid chromatography with pre-column fluorescence derivatization using phenylglyoxal

A high-performance liquid chromatographic method based on pre-column fluorescence derivatization with phenylglyoxal is described for the sensitive and selective quantification of total (free plus albumin-bound) and free tryptophan in serum. Serum was deproteinized with perchloric acid for total tryptophan and by ultrafiltration for free tryptophan, and then subjected to fluorescence derivatization. The reaction mixture was separated on a reversed-phase column by isocratic elution and the tryptophan derivative was then detected by fluorimetry. The method was at least ten-fold more sensitive than other conventional chromatographic methods with no derivatization. The lower limit of determination (signal-to-noise ratio = 3) for endogenous tryptophan in human serum was 72 nmol/l, which corresponds to 200 fmol on-column.

Fluorometric Determination of Tryptophan in Human Serum Using Phenylglyoxal

A simple fluorometric method is described for the determination of the total (free + albumin-bound) and free tryptophan in human serum. After deproteinization of the serum (perchloric acid precipitation for total tryptophan; ultrafiltration for free tryptophan), the samples are treated with phenylglyoxal in dilute perchloric acid to develop fluorescence. The method is sensitive and fairly selective for tryptophan in serum; the limit of detection is 0.84 nmol ml−1 in serum, thus giving a fluorescence intensity that is twice that of the blank.

Distribution of 5-hydroxytryptamine and related compounds in various brain regions of rainbow trout (Oncorhynchus mykiss)

The levels of tryptophan (Try), 5-hydroxytryptamine (serotonin, 5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were determined in the brain regions of rainbow trout (Oncorhynchus mykiss) by high performance liquid chromatography with electrochemical detection (HPLC-EC). Brain tryptophan concentrations varied from 3.972 ± 357 ng/g cerebellum) to 8.841 ± 772 ng/g (hypothalamus). The 5-HT concentrations varied from 69 ± 7 ng/g (optic tectum) to 573 ± 34 ng/g (hypothalamus). The concentrations of 5-HIAA varied from 29 ± 3 ng/g (medulla oblongata) to 68 ± 7 ng/g (hypothalamus). Total and free serum tryptophan levels were also determined; in adult rainbow trout 92% of the serum tryptophan was observed to be free i.e., not protein-bound.