Serum Free Tryptophan Research Articles

Complex temporal changes in 5-hydroxytryptamine synthesis in the central nervous system induced by experimental polyarthritis in the rat

The purpose of this study was to investigate modifications of 5-HT synthesis in a chronic pain model, the arthritic rat, at different times after the inoculation with Freund's adjuvant. This study confirms our previous findings that experimental induced polyarthritis is associated with a marked increase in free tryptophan levels in serum. During the acute phase of the disease (15–21 days after the adjuvant), the general increase in 5-HT synthesis observed in the CNS appeared to be related to an increase in tryptophan availability due to the elevation of free tryptophan in serum. During the post-acute phase of the disease (28–42 days after the adjuvant), the level of free tryptophan in the serum remained markedly increased but the levels in the CNS tended to return to normal values in all areas examined. At 42 days, 5-HT synthesis in the brain had also returned to normal values but was further increased at the spinal level. In addition, although 5-HT levels and 5-HT synthesis were increased in the dorsal as well as in the ventral part of the cord, an increase in the rate of disappearance of the amine after blockade of the decarboxylase (benserazide) was only observed in the dorsal part. This result tends to suggest that the descending serotonergic system projecting to the dorsal horn is preferentially activated during chronic pain.

High-performance liquid chromatographic determination of total and free tryptophan in serum from control subjects and liver patients

High-performance liquid chromatographic determination of total and free tryptophan in serum from control subjects and liver patients

Effect of lindane on brain monoamine metabolism

1. 1. The effect of the oral administration of the organochlorinate pesticide Lindane (γ-hexachlorociclohexane) in doses of 30, 60 and 120 mg/kg on the cerebral metabolism of 5-HT and catecholamines in female rats was studied 24 hr after the administration of the pesticide. 2. 2. All the doses tested caused a decrease in the concentration of cerebral and free serum tryptophan, with no significant change in the cerebral levels of 5-HT, although its rate of synthesis was inhibited at the lowest dose. 3. 3. The variations in the levels of 5-HIAA appears to be linked to its elimination from the brain. 4. 4. The higher doses cause increases in NA levels and turnover rates.

Tryptophan Determination in Tissue Homogenates and Biological Fluids Using HPLC-EC

Abstract A method for quantitating tryptophan in tissue homogenates and biological fluids using 6-hydroxy-tryptamine as internal standard is described. Tryptophan in CSF and free tryptophan in serum or plasma can be quantitated by directly injecting CSF or ultrafiltrate into the HPLC system with the internal standard. Serum, plasma, amniotic fluid, and saliva are deproteinized by addition of equal volume of acetonitrile. Urine samples are processed through Biorex-70 columns. Cross validation was done by comparing the values of column procedures with direct injection method.

Effect of combined administration of tryptophan with putative tryptophan pyrrolase inhibitors, DL-3-pyridylalanine, allopurinol or nicotinamide, on brain serotonin concentration.

1) Single administration of tryptophan (25-200 mg / kg) to Wistar male rats resulted in a dose-related increase in liver tryptophan pyrrolase (TP) activity. The increase in brain serotonin (5-HT) concentration was not proportional to the dose given, and brain 5-HT concentration rapidly fell to the control (saline-treated) level or below. 2) The tryptophan-induced increase in liver TP activity was clearly prevented by DL-3-pyridylalanine (3-PA, 100 mg/kg). Serum free tryptophan and brain 5-HT concentrations increased more markedly and maintained higher levels after the combined administration of tryptophan with 3-PA than after a single administration of tryptophan. 3) Although allopurinol (20 mg/kg) reduced liver TP activity under control and tryptophan-treated conditions, it did not increase serum free tryptophan and brain 5-HT concentrations. 4) Nicotinamide also failed to alter the catabolism of tryptophan and the concentration of brain 5-HT in control or tryptophan-treated rats. 5) These data suggest that 3-PA would increase the therapeutic effect of tryptophan given to treat depressive illness, but that allopurinol and nicotinamide would not be suitable drugs for this purpose.

Tryptophan metabolism in liver cirrhosis: influence of oral antibiotics on neuropsychiatric symptoms.

Oral tryptophan loading tests were performed on patients with cirrhosis of the liver before and after treatment with an oral antibiotic practically unabsorbed from the gastrointestinal tract. After antibiotic therapy, neuropsychiatric manifestations evoked by the oral administration of tryptophan were reduced in duration by about 50% and in severity as well despite a slightly enhanced elevation of serum total and free tryptophan levels, compared to pre-treatment loading tests. The urinary indican output also showed a significantly greater decrease in the post-treatment test (p less than 0.05) whereas no appreciable difference was observed in urinary 5-hydroxy-indoleacetic acid excretion between the pre- and post-treatment tests. The data suggest that neuropsychiatric manifestations seen following oral administration of tryptophan may be attributed to intestinal tryptophan metabolites rather than to this aromatic amino acid itself and/or its metabolites in the brain.

Role of precursor availability in control of monoamine biosynthesis in brain.

Role of precursor availability in control of monoamine biosynthesis in brain.

Tryptophan and neutral amino acid concentrations in serum of rats after salmon calcitonin injection.

After a single injection of salmon calcitonin (2 MRC units/kg b.wt) marked decreases in both calcium and neutral amino acids in rat serum were observed. In turn, free tryptophan in serum and serotonin (5-hydroxytryptamine) in the whole brain were greatly enhanced during the initial period.

Effects of amitriptyline on serum glutamate and free tryptophan in rats.

In rats, chronic amitriptyline (14 days, 10 mg/kg, IP) administration resulted in a significant increase in the serum glutamate concentration and concomitant increase in the serum free tryptophan. In contrast, amitriptyline had no effect on the total serum tryptophan or CSF glutamate level. The data confirmed that antidepressant drugs may induce an increase of the serum glutamate concentration in depressive patients.

Tryptophan and tryptophan pyrrolase in haem regulation. The role of lipolysis and direct displacement of serum-protein-bound tryptophan in the opposite effects of administration of endotoxin, morphine, palmitate, salicylate and theophylline on rat liver 5-aminolaevulinate synthase activity and the haem saturation of tryptophan pyrrolase.

1. The increase in the haem saturation of rat liver tryptophan pyrrolase caused by tryptophan administration was previously shown to be associated with a decrease in 5-aminolaevulinate synthase activity. 2. It is now shown that similar reciprocal effects are caused by palmitate and salicylate, both of which increase tryptophan availability to the liver by direct displacement of the serum-protein-bound amino acid. 3. The reciprocal effects on the former two parameters caused by endotoxin and morphine are associated with an increase in liver tryptophan concentration produced by a lipolysis-dependent, non-esterified fatty acid-mediated, displacement of the serum-protein-bound amino acid. 4. All these changes and those caused by another lipolytic agent, theophylline, are prevented by the beta-adrenoceptor-blocking agent propranolol and by the opiate-receptor antagonist naloxone, whose anti-lipolytic nature is demonstrated. 5. High correlation coefficients have been obtained for one or more pairs of the following parameters: serum non-esterified fatty acid concentration, free serum tryptophan concentration, liver tryptophan concentration, liver 5-aminolaevulinate synthase activity, liver holo-(tryptophan pyrrolase) activity and the haem saturation of liver tryptophan pyrrolase. 6. It is suggested that liver tryptophan concentration may play an important role in the regulation of 5-aminolaevulinate synthase synthesis, and that the latter may be subject to control by changes in lipid metabolism and may be influenced by pharmacological agents that affect tryptophan disposition. 7. Preliminary evidence suggests that tryptophan may be bound in the liver and that such a possible binding may control its availability for its hepatic functions.

Acute effects of caffeine injection on neutral amino acids and brain monoamine levels in rats

The injection of caffeine (100 mg/kg, i.p.) into male rats acutely increased brain levels of trytophan, serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA). Blood levels of glucose, nonesterified fatty acids (NEFA) and insulin also increased, while those of the aromatic and branched-chain amino acids fell. Serum tryptophan levels either did not fall, or increased. Consequently, the serum ratio of trypthopahn to the sum of other large neutral amino acids (LNAA) increased. Less consistently noted were increases in serum free tryptophan levels. Brain tyrosine levels were not appreciably altered by caffeine, nor was the serum tyrosine ratio. In dose-response studies, 25 mg/kg of caffeine was the minimal effective dose needed to raise brain tryptophan, but only the 100 mg/kg dose elevated all three indoles in brain. In no experiments did caffeine, at any time or dose, alter brain levels of dopamine or norepinephrine. Caffeine thus probably raises brain tryptophan levels by causing insulin secretion, and thereby changing plasma amino acid levels to favor increased tryptophan uptake into brain. The rises in brain 5-HT and 5-HIAA may follow from the increase in brain tryptophan, although further data are required clearly to establish such a mechanism.

Long lasting effects of intrauterine growth retardation on 5-HT metabolism in the brain of developing rats

Intrauterine growth retardation (IUGR) was achieved by ligating the artery and vein supplying one uterine horn in pregnant rats on the 5th day before delivery. At birth, the weight of the whole body and of the forebrain (but not that of the brain stem of about half of the offspring) were significantly lower than those of normal controls. This deficit persisted for at least the first 3 postnatal weeks. During the immediate period following birth, the concentrations of norepinephrine, dopamine, serotonin and 5-hydroxyindoleacetic acid (5-HIAA) were significantly higher in IUGR rats than in controls. Increased levels of serotonin and 5-HIAA were still observed in the forebrain and brain stem of 15-day-old IUGR rats and were associated with parallel increases in brain and serum free tryptophan levels. These results indicate that a transient insult in the fetal life could result in long-lasting alterations in 5-HT metabolism in CNS of developing rats.

Total and free serum tryptophan levels and brain 5-hydroxytryptamine metabolism in arthritic rats

In rats suffering from experimentally induced arthritis produced by Freund's adjuvant, there is a marked decrease in total serum tryptophan levels and a marked increase in plasma-free tryptophan levels at both 15 and 21 days after the administration of the adjuvant. Tryptophan, 5-hydroxytryptamine and 5-hydroxyindoleacetic acid levels are increased in the brain and the spinal cord at 15 days. However, 21 days after administration of the adjuvant these levels returned to normal values in the brain, but remained increased in the spinal cord. These results are in agreement with investigations suggesting the possible involvement of the raphe-spinal system in response to pain stimuli but are contrary to the observation that there is a large decrease in plasma-free tryptophan levels in arthritic human patients. These opposite results still question the hypothesis of a relationship between changes in plasma-free tryptophan levels and the severity of pain.

Clinical evaluation of serum levels of tryptophan in hepatobiliary disease

Fasting serum levels of total and free tryptophan, and free fatty acids and albumin, were measured and compared by blood biochemical analysis in patients with hepatobiliary disease and neuropsychiatric symptoms. The serum total tryptophan level tended to be elevated in patients with chronic active hepatitis, hepatic coma and obstructive jaundice, but not significantly. The serum free tryptophan level was significantly elevated in patients with chronic active hepatitis, liver cirrhosis, primary hepatocellular carcinoma and obstructive jaundice. The free tryptophan level was related to the decreased serum albumin level and elevated serum free fatty acid levels, which seems to indicate a connection with liver parenchymal function. The level, however, seemed not to correlate with neuropsychiatric symptoms.

Effect of valproic acid on serotonin metabolism

The effect of valproic acid (2- n-propyl-pentanoic acid) on serotonin metabolism was examined in rats and mice, since this anticonvulsant has beneficial therapeutic action on human myoclonic disorders which have been associated with brain serotonin deficiency. A single intraperitoneal injection of 400 mg/kg valproic acid decreased total serum tryptophan and increased free serum tryptophan, brain tryptophan and brain 5-hydroxyindoleacetic acid (5HIAA) but had no effect on brain serotonin levels. Brain tryptophan levels returned to normal in mice after chronic administration of valproic acid (400 mg/kg daily for 7 days) but the changes in serum tryptophan and brain 5HIAA persisted. Valproic acid potentiated the anti-myoclonic action of chlorimipramine in a p, p'-DDT-induced animal myoclonus model. Valproic acid may displace protein-bound serum tryptophan thereby increasing brain tryptophan which is converted to serotonin.

Increase in large neutral amino acid transport into brain by insulin.

Abstract—The administration of oral glucose to fasted rats produced a decline of all large neutral amino acid levels in serum, including that of the free fraction of tryptophan. In addition to this well known effect, it also decreased the brain concentrations of leucine, isoleucine and valine, while increasing those of tryptophan, tyrosine and phenylalanine. The total concentration of large neutral amino acids in serum was decreased by 44%, while it was slightly increased in brain. Analogous results were obtained in 4 rats injected with exogenous insulin. Moreover, the administration of either glucagon or isoproterenol to rats force‐fed with glucose produced a decline in total serum tryptophan concentration proportional to that of the rise in FFA, while it increased free serum tryptophan and brain tryptophan levels. It can be concluded that insulin stimulates the transport of large neutral amino acids from blood to brain and that the level of free serum tryptophan also controls the entry of tryptophan into the brain under the influence of insulin.

Role of free serum tryptophan on brain tryptophan concentration after oral glucose administration

Role of free serum tryptophan on brain tryptophan concentration after oral glucose administration

Daily variations of various parameters of serotonin metabolism in the rat brain. II. Circadian variations in serum and cerebral tryptophan levels: Lack of correlation with 5-HT turnover

Rats submitted to regular 12 h cycles of light and darkness for three weeks were sacrificed at various times of the day. 5-HT, 5-HIAA and tryptophan levels were estimated in the fronto-parietal cerebral cortex. Tyrosine and free and total tryptophan levels in serm were estimated in parallel. Significant circadian variations in 5-HT and 5-HIAA levels were found in cerebral tissues. The peaks of 5-HT and 5-HIAA levels were detected during the light and dark periods respectively, the maximal fluctuations being seen between 17.00 h and 21.00 h, two times separating the light off. Important significant circadian variations in free and total serum tryptophan levels were also observed. In both cases, the maximal levels were found during the middle of the dark phase after the peak of 5-HIAA levels. The circadian rhythm of tyrosine levels in serum was in opposite phase with that of tryptophan (free or total). The diurnal changes in tryptophan content in cerebral tissues seemed thus related to those found in serum. Taking in consideration results obtained in previous studies 16,17 carried out in similar experimental conditions, it was concluded that the parallel increase in serum free tryptophan and in tissues 5-HIAA levels seen during the night were not related to a stimulation of 5-HT turnover. Indeed 5-HT synthesis is minimal at this time 16.

Evidence that only free serum tryptophan exchanges with the brain

Summary Following the administration of 3,5- 3 H-L-tyrosine (TYR- 3 H), brain tyrosine specific activity (S.A.) reaches values similar to those of serum, while, following 3 H-L-tryptophan (TRY- 3 H) injection, serum S.A. remains about twice as high as that of the brain, suggesting that a compartment of serum tryptophan does not exchange with the brain. The AA. conclude that this compartment is tryptophan bound to albumine.

Characteristics of tryptophan binding in the serum of the newborn rat.

During the very first period of postnatal life, tryptophan is almost entirely free in the serum of rats. This situation is in sharp contrast with the well-known ability of serum albumin to bind the essential amino acid in the adult. Three main factors accounted for the relative lack of binding during the early postnatal life when compared to the adult: (1) the lower concentration of serum albumin, the binding protein; (2) the inhibition of binding by nonesterified fatty acids, which were at a high level in the serum of young rats until weaning, and (3) the decreased number of available binding sites for tryptophan on the defatted serum albimin, whereas the apparent association constant of tryptophan binding to serum albumin was similar in newborn and adult. Since immunological characterization of newborn and adult serum albumins did not reveal a specific fetal serum albumin, we suggest that discrete changes at the association site for tryptophan are sufficient to induce large alteration in the binding capacity of the protein. In contrast to the situation observed in adult rats, serotonin synthesis in the brain of newborn animals is therefore not dependent on the equilibrium between bound and free tryptophan in serum.