Effect of amino acid supplementation on whole-body protein turnover in Holstein steers

We used the [15N]glycine single-dose urea end-product technique to measure whole-body protein turnover in six Holstein steers (250 +/- 18 kg). Steers were implanted with Revalor-S and continuously infused abomasally with water (4 L/d) or amino acids (AA; in 4 L/d water) in a crossover experiment (two 14-d periods). The AA infusion contained the following (g/d): lysine (5.3), methionine (3.3), threonine (3.2), tryptophan (1.0), histidine (2.1), and arginine (5.5). Steers were fed a diet containing 85% rolled corn, 10% prairie hay, and 1.1% urea (DM basis) at 2.16% of body weight. Nitrogen retention tended (P = .15) to increase with AA infusion, from 27.9 to 32.9 g N/d. Amino acid infusion numerically increased whole-body protein turnover from 168.6 to 183.2 g N/d, protein synthesis from 152.6 to 169.3 g N/ d, and protein degradation from 124.7 to 136.4 g N/d. Enhanced protein accretion may have resulted from a larger increase in protein synthesis than in degradation. The tendency for increased N retention is interpreted to suggest that the implanted, lightweight Holstein steers fed a corn-urea diet in our study were able to respond to AA supplementation, suggesting that at least one of the infused AA was limiting in the basal diet. Protein turnover data suggest that cattle, like other animals, may increase protein synthesis and protein degradation in response to supplementation with limiting AA. The [15N]glycine single-dose urea end-product technique for measuring whole-body protein turnover in cattle may be useful.

Determination of kynurenic acid by capillary electrophoresis with laser-induced fluorescence detection

Kynurenic acid (KA) is an excitatory amino acid receptor antagonist that is believed to play an important role in a host of diseases of the neuropsychiatric and central nervous system. A method for the determination of KA in microdialysate samples using capillary electrophoresis (CE) separation with laser-induced fluorescence (LIF) detection is described. CE is advantageous for the analysis of microdialysis samples due to its short analysis times and small sample volume requirements. Three complexation approaches were evaluated in an attempt to achieve the best limit of detection. The best approach was found to be pre-column complexation with inclusion of Zn(II) in the background electrolyte. After optimization of the zinc acetate concentration and pH, a limit of detection of 1 nM KA was achieved. However, when KA was present in the dialysate, the limit of detection increased 50-fold. Even though the endogenous levels of KA in rat brain are below this limit of detection, this methodology could be used to monitor the increase of KA levels in rat brain following dosing with its precursors, tryptophan and kynurenine.

Tryptophan and suicide

A measure of tryptophan intake in 30 nations was not associated with their 1980 suicide or homicide rates.

Lack of relapse with tryptophan depletion following successful treatment with ECT

OBJECTIVE

Although the antidepressant mechanism of ECT is unknown, there are considerable data to support serotonergic involvement. The effects of tryptophan depletion were studied in patients with major depression treated successfully with ECT.

METHOD

Five patients who had been successfully treated with ECT for major depression were studied in a randomized, double-blind, crossover design comparing tryptophan depletion to a placebo procedure.

RESULTS

No effect of tryptophan depletion on mood symptoms was observed despite more than an 85% decrease in total serum tryptophan.

CONCLUSIONS

These data suggest that presynaptic serotonin availability may not be necessary for the acute maintenance of an antidepressant response to ECT.

Rapid tryptophan depletion in drug-free depressed patients with seasonal affective disorder

OBJECTIVE

Brain serotonin systems might be involved in the pathophysiology of seasonal affective disorder. The authors tested whether tryptophan depletion alters the mood of depressed patients with seasonal affective disorder.

METHOD

Eleven drug-free depressed patients with seasonal affective disorder underwent tryptophan depletion in a placebo-controlled, double-blind crossover study. Tryptophan depletion was induced by a 24-hour low-tryptophan diet and by ingestion of a tryptophan-free amino acid beverage. During control testing the diet and the beverage were supplemented with tryptophan. Behavioral ratings and plasma total and free tryptophan levels were obtained before the diet started and several times after administration of the beverages.

RESULTS

The diet and the tryptophan-free amino acid drink reduced plasma total and free tryptophan levels by 79.0% and 87.5%, respectively. Both levels increased during control testing. No significant behavioral changes were induced by tryptophan depletion or control testing.

CONCLUSIONS

The failure of tryptophan depletion to exacerbate the depressive syndrome suggests that dysfunctional serotonergic activity does not play a primary, direct role in the pathogenesis of winter depression.

Marginal efficiency of free or protected crystalline L-tryptophan for tryptophan and protein accretion in early-weaned pigs

We conducted an experiment to determine the efficiency of dietary tryptophan (Trp) for protein and Trp accretion in 4-kg (live weight) pigs. Five Trp-deficient diets were fed for 18 d after weaning. The basal diet contained 23.4% protein and .14% Trp. The four other diets were similar to the basal diet but were supplemented with .06 or .12% free or protected crystalline Trp. No differences were found between the two crystalline Trp forms for all variables under study. Equal amounts of all diets were fed by intragastric tube feeding. Daily weight gain (P < .10), gain:feed (P < .05), and daily protein retention (P < .01) increased linearly as dietary Trp increased. Similarly, retention and gross efficiency (retained: intake) of almost all amino acids increased. Tryptophan retention also increased linearly (P < .05), but gross efficiency was maximal (40.1%) with protein-bound Trp from the basal diet, and it decreased linearly as dietary Trp increased. This important reduction was the result of a low marginal efficiency for crystalline (13.6 +/- 3.3%) free or protected Trp.

Free amino acid supplementation to steers: effects on ruminal fermentation and performance

Three studies were conducted to evaluate amino acid utilization by cattle. In Exp. 1, five steers (580 kg) were fed 86% rolled corn diets with mixtures of amino acids containing up to 6 g/d DL-Met, 24 g/d L-Lys, 6 g/d L-Thr, and 3 g/d L-Trp. Treatments had little effect on ruminal fermentation, diet digestibility, N flow to the duodenum, or microbial efficiency. Ruminal concentrations of Met and Lys increased linearly (P < .05) with amino acid supplementation, whereas Thr responded quadratically, and Trp was not altered. In Exp. 2, four steers (414 kg) were used to measure effects of dietary monensin or laidlomycin propionate in high-grain diets supplemented with amino acids. Ionophores had no significant effect on ruminal fermentation or outflows of amino acids from the rumen. In Exp. 3, 100 steers (287 kg initial BW) were fed diets containing 1% of a nonprotein N source. Treatments were 1) no supplemental N (UREA), 2) UREA plus soybean meal (SBM), 3) UREA plus 2 g/d DL-Met, 8 g/d L-Lys, 2 g/d L-Thr, and 1 g/d L-Trp, or 4) UREA plus 4 g/d DL-Met, 16 g/d L-Lys, 4 g/d L-Thr, and 2 g/d L-Trp. During the growing period (diets based on whole-plant milo silage), gains were higher for SBM-supplemented steers than for UREA steers and intermediate for steers supplemented with amino acids. Few significant differences in performance were observed among treatments during the finishing phase (diets based on dry-rolled corn) or for the entire experiment, but cattle fed SBM or amino acids tended to be fatter and have better marbling scores and quality grades. Amino acids did not greatly alter ruminal fermentation or cattle performance.

Positron emission tomography measurement of cerebral metabolic correlates of tryptophan depletion-induced depressive relapse

BACKGROUND

Short-term depletion of plasma tryptophan has been shown to result in depressive relapse in patients with remission of major depression. Positron emission tomography and single photon emission computed tomography studies implicated the dorsolateral prefrontal cortex, orbitofrontal cortex, thalamus, and caudate nucleus in the pathogenesis of depression. The purpose of this study was to measure cerebral metabolic correlates of tryptophan depletion-induced depressive relapse.

METHODS

Patients diagnosed as having major depression (N = 21) who clinically improved with serotonin reuptake inhibitors underwent 2 test days involving tryptophan depletion or placebo, followed 6 hours later by positron emission tomography scanning with fludeoxy-glucose F18. Brain metabolism was compared in patients with (n = 7) and without (n = 14) a tryptophan depletion-induced depressive relapse.

RESULTS

Tryptophan depletion resulted in a decrease in brain metabolism in the middle frontal gyrus (dorsolateral prefrontal cortex), thalamus, and orbitofrontal cortex in patients with a depletion-induced depressive relapse (but not in patients without depletion-induced relapse). Decreased brain metabolism in these regions correlated with increased depressive symptoms. Baseline metabolism was increased in prefrontal and limbic regions in relapse-prone patients.

CONCLUSION

Specific brain regions, including the middle frontal gyrus, thalamus, and orbitofrontal cortex, may mediate the symptoms of patients with major depression.

L-tryptophan augmentation of light therapy in patients with seasonal affective disorder

OBJECTIVE

Up to one-third of patients with seasonal affective disorder (SAD) do not have a full response to light therapy. Given the evidence for serotonergic dysregulation in SAD, we examined the possible role of l-tryptophan as an augmentation strategy for nonresponders and partial responders to light therapy.

METHOD

Eligible drug-free patients meeting DSM-IV criteria for SAD were treated for 2 weeks using a standard morning light therapy regimen (10,000 lux cool-white fluorescent light for 30 minutes). Partial and nonresponders were treated for 2 weeks with open-label l-tryptophan (1 g 3 times daily) while light therapy was continued. Ratings at baseline and follow-up included the 29-item Structured Interview Guide for the Hamilton Depression Rating Scale, SAD version (SIGH-SAD) and the Clinical Global Impression (CGI) scale.

RESULTS

Sixteen patients began the l-tryptophan augmentation phase. Two patients discontinued medications within 3 days because of side effects. In the 14 patients completing treatment, the addition of l-tryptophan resulted in significant reduction of mean depression scores. Nine of 14 patients (64%) showed very good clinical responses to combined treatment and minimal side effects.

CONCLUSION

This open-label study suggests that l-tryptophan may be an effective augmentation strategy for those patients with SAD who show limited or poor response to bright ligh therapy. Further placebo-controlled studies are warranted to demonstrate efficacy.

Tryptophan needs of lactating sows fed diets supplemented with crystalline lysine

Large White x Landrace primiparous and multiparous sows (n = 115) were used to evaluate the tryptophan needs of lactating sows fed diets supplemented with crystalline lysine to contain .75% lysine. Sows were fed 1.8 kg of their allotted diets from d 110 of gestation until parturition and then were allowed ad libitum access to diets analyzed to contain either .12 (n = 58) or .17% (n = 57) tryptophan during a 21-d lactation. Diets were created by crystalline tryptophan and lysine additions to a corn-soybean meal basal diet that contained .12% tryptophan. Tryptophan level in the lactation diet did not affect number or weight of pigs at 21 d (P > .10). Sows fed .17% tryptophan were heavier at d 21 of lactation than those fed .12% tryptophan (P = .09) due to less weight loss during the 21-d lactation (P = .09). Feed intake was greater (P < .05) for sows fed .17% tryptophan than for sows fed .12% tryptophan. A reference diet analyzed to contain .11% tryptophan and .63% lysine was fed to an additional 11 sows only as a baseline for measuring plasma urea nitrogen and amino acids. Plasma tryptophan concentrations were higher (P < .05) for sows fed .17% tryptophan than for sows not fed added L-tryptophan. Among sows fed the low-tryptophan diets, sows fed the reference diet (.60% lysine) had higher (P < .05) plasma phenylalanine and valine concentrations than sows fed .75% lysine. Diet did not affect plasma concentrations of any other essential amino acid (P > .10). Plasma urea N levels were lower (P = .11) for sows fed the diet supplemented with tryptophan. Lactating sows allowed ad libitum access to diets containing .75% lysine benefited from higher feed intake and lower weight loss when dietary tryptophan levels were increased from .12 to .17%.

Effects of tryptophan depletion on drug-free patients with seasonal affective disorder during a stable response to bright light therapy

BACKGROUND

A dysfunction of the serotonin system may play a major role in the pathogenesis of seasonal affective disorder. Bright light therapy has been shown to be effective in the treatment of winter depression in patients with seasonal affective disorder. Light therapy-induced remission from depression may be associated with changes in brain serotonin function.

METHODS

After at least 2 weeks of clinical remission, 12 drug-free patients who had had depression with seasonal affective disorder underwent tryptophan depletion in a double-blind, placebo-controlled, balanced cross-over design study.

RESULTS

Short-term tryptophan depletion induced a significant decrease in plasma free and total tryptophan levels (P < .001 for both, repeated measures analysis of variance), with peak effects occurring 5 hours after ingestion of a tryptophan-free amino acid drink. It emerged that tryptophan depletion leads to a transient depressive relapse, which was most pronounced on the day after the tryptophan-depletion testing. No clinically relevant mood changes were observed in the control testing.

CONCLUSIONS

The maintenance of light therapy-induced remission from depression in patients with seasonal mood cycles seems to depend on the functional integrity of the brain serotonin system. Our results suggest that the serotonin system might be involved in the mechanism of action of light therapy.

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.

[L-tryptophan. An essential amino acid for structural and functional metabolism]

Since the nineteen-sixties, L-Tryptophan has been used with success to treat depressive states and sleep disorders. When, in 1989, the substance was suspected of causing severe adverse reactions (EMS), approval for its use was initially suspended. It has since been shown that the undesired side effects were due not to L-Tryptophan itself, but to contaminations of the basic substance, and the suspension of approval was therefore lifted. In September 1996, L-Tryptophan was re-introduced onto the market as Ardeytropin. The present paper takes a look at the substance L-Tryptophan and discusses in particular its biochemical significance and its biokinetics/pharmacokinetics. The pharmacological basis for the use of L-Tryptophan to treat sleep disorders and depression is examined.

Acute dietary tryptophan depletion: effects on schizophrenic positive and negative symptoms

Because brain serotonin levels depend directly on the amounts of exogenous tryptophan (TRP) available for its synthesis, amounts of TRP in the diet may be manipulated to alter the corresponding levels of serotonin. This technique has been used for probing the role of serotonin in mediating various forms of pyschopathology. In this study, 16 patients meeting DSM III-R criteria for schizophrenia (n = 14) or schizoaffective disorder (n = 2) were assessed for the effects of acute dietary TRP depletion under controlled conditions. The hypothesis was that lowering of serotonin would result in a diminution of 'positive' and/or 'negative' symptoms of psychotic disorders. No clinically or statistically significant improvement compared to baseline occurred when TRP depletion was imposed. Indeed, there was a statistically significant deterioration on measures of negative symptoms. The results are discussed in the context of the methodological issues.

The role of tryptophan in DON-induced feed rejection

Deoxynivalenol (DON, vomitoxin) commonly produced by Fusarium fungi can alter feeding behaviour of pigs and other farm animals. The effects of dietary tryptophan (TRP, precursor of brain amine serotonin) in combination with DON were examined in mice to determine if TRP can modulate DON toxicity. Results indicated that brain TRP can be influenced by dietary TRP, but no evidence of TRP potentiating DON toxicity was observed. Higher TRP levels likely induced amino acid imbalance leading to weight gain suppression.

Effects of tryptophan depletion in drug-free adults with autistic disorder

BACKGROUND

The primary objective of this study was to investigate the behavioral and biochemical responses to acute tryptophan depletion in drug-free adult patients with autistic disorder.

METHODS

Twenty drug-free adults with autistic disorder (16 men and 4 women) (mean [+/- SD] age, 30.5 +/- 8.5 years) underwent short-term tryptophan depletion in a double-blind, placebo-controlled, randomized crossover design. Patients received a 24-hour, low-tryptophan diet followed the next morning by an amino acid drink. Behavioral ratings were obtained on the morning of the amino acid drink (baseline) and 180, 300, and 420 minutes after the drink. Plasma free and total tryptophan levels were obtained at baseline and 5 hours after the drink. The active and sham testing sessions were separated by 7 days.

RESULTS

Eleven (65%) of the 17 patients who completed both test days showed a significant global worsening of behavioral symptoms with short-term tryptophan depletion, but none of the 17 patients showed any significant change in clinical status from baseline after sham depletion (P = .001). Tryptophan depletion led to a significant increase in behaviors such as whirling, flapping, pacing, banging and hitting self, rocking, and toe walking (P < .05). In addition, patients were significantly less calm and happy and more anxious. No significant change was observed in social relatedness or repetitive thoughts and behavior. Plasma total and free tryptophan levels were reduced 86% and 69%, respectively, 5 hours after the tryptophan-deficient amino acid drink. Patients who had a significant global exacerbation of symptoms had significantly higher baseline plasma total tryptophan levels (P < .001) and Autism Behavior Checklist scores (P = .005) than did patients who showed no significant change in symptoms after tryptophan depletion.

CONCLUSIONS

The results of this study are consistent with previous research that has implicated a dysregulation in serotonin function in some patients with autism. These data suggest that the short-term reduction of serotonin precursor availability may exacerbate some symptoms characteristic of autism in some patients. Continued investigation into the role of serotonin in the pathogenesis and treatment of autistic disorder is warranted.

Comparison of the effects of the M1-receptor antagonist telenzepine and the CCK-receptor antagonist loxiglumide on the pancreatic secretory response to intraduodenal tryptophan in dogs

In six conscious dogs with chronic gastric and pancreatic fistulas we compared the action of different doses (20.25 to 81.0 nmol/kg/h) of the muscarinic M1-receptor antagonist telenzepine, the cholecystokinin (CCK) antagonist loxiglumide (2.5 to 10.0 mg/kg/h) and several combinations of both drugs on the pancreatic secretory response to intraduodenal perfusion of graded loads of tryptophan (0.37-10.0 mmol/h) given against a background of secretin (20.5 pmol/kg/h i.v.). Except for 20.25 nmol/kg/h telenzepine, all tested doses of telenzepine and/or loxiglumide decreased the 180-min integrated bicarbonate response to tryptophan by 55 to 119%. Except of 20.25 nmol/kg/h telenzepine and/or 2.5 mg/kg/h loxiglumide, all tested doses of telezepine and/or loxiglumide inhibited the tryptophan stimulated integrated pancreatic protein responses by 54 to 88%. While telenzepine mainly inhibited the bicarbonate and protein response to the lower loads of tryptophan (0.37-1.1 mmol/h), loxiglumide decreased the response to all loads of tryptophan. The inhibition evoked by the combinations of telenzepine and loxiglumide was not significantly greater than that by single infusion of either drug. The CCK plasma levels basally and in response to tryptophan were not significantly altered by telenzepine and/or loxiglumide. These findings indicate that (1) both enteropancreatic cholinergic reflexes and the hormone CCK are mediators of the protein response to intraduodenal trytophan (2) enteropancreatic cholinergic reflexes are probably the dominant mediators of the response to low amounts of tryptophan, whereas CCK is the major mediator of the response to high loads of tryptophan, (3) the two mediators seem to act independently of each other, and (4) the release of CCK by intestinal trytophan is not influenced by telenzepine or loxiglumide.

Differential potentiation of L-tryptophan-induced head-twitch response in mice by cocaine and sertraline

Using selective monoamine uptake blockers and appropriate selective monoamine receptor antagonists, we have previously shown that cocaine enhances the frequency of 5-HT2A receptor-mediated 5-hydroxytryptophan (5-HTP)-induced head-twitch response (HTR) in mice via inhibition of serotonin uptake. Concomitantly, cocaine prevented the maximal producible HTR frequency via simultaneous indirect stimulation of the inhibitory presynaptic 5-HT1A and postsynaptic alpha 2 receptors. In the present study, we have investigated the effects of cocaine and the selective 5-HT (sertraline), norepinephrine (nisoxetine) and dopamine (GBR 12935) uptake inhibitors on the L-tryptophan-induced HTR in the presence of a nonselective monoamine oxidase inhibitor, tranylcypromine. We utilized two experimental protocols where cocaine or sertraline were administered either after (protocol 1) or prior to (protocol 2) L-tryptophan injection. Cocaine potentiated the ability of L-tryptophan to induce HTR to a greater extent in protocol 1, whereas sertraline induced a greater effect in protocol 2. However, in our earlier study cocaine (and also sertraline) up to 10 mg/kg produced a similar degree of potentiation in both experimental protocols on the 5-HTP-induced HTR. Furthermore, as in the latter study on the 5-HTP-induced HTR, in the present investigation nisoxetine potently attenuated whereas GBR 12935 did not modulate the induced HTR. The results show that the respective serotonergic and noradrenergic effects of cocaine also operate on the L-tryptophan-induced HTR. The differential effects of cocaine and sertraline in experimental protocols 1 and 2 on the L-tryptophan- versus 5-HTP-induced HTRs suggest that cocaine has additional effects on the conversion of L-tryptophan to 5-HT.

A contaminant of L-tryptophan enhances expression of dermal collagen in a murine model of eosinophilia myalgia syndrome

The eosinophilia-myalgia syndrome was associated with the ingestion of L-tryptophan products containing a number of contaminants, one of which has been identified as 1,1'-ethylidene-bis-(L-tryptophan) (EBT), also known as peak E or peak 97. In earlier studies, we demonstrated that EBT induces inflammation and fibrosis in dermal and subcutaneous tissue of C57BL/6 mice. Others have shown EBT to be a potent stimulus for fibroblast activation and collagen synthesis in vitro, and dermal tissue from EMS patients reveals evidence of enhanced collagen gene expression. In the present study using Northern blot analysis and in situ hybridization, we demonstrate enhanced expression of genes for types I, III, and VI collagen in the dermis and subcutis of C57BL/6 mice treated with EBT for 3-21 days. Increased type I procollagen mRNA was noted on day 6 of EBT treatment and was followed by enhanced expression of type III and VI procollagen mRNA at day 21. L-Tryptophan, free of contaminants associated with the eosinophilia-myalgia syndrome epidemic, increased dermal collagen mRNA to a lesser extent than did EBT. Increased procollagen gene expression was accompanied by evidence of enhanced TGF-beta 1 expression in the dermis and subcutis. This animal model provides additional evidence for EBT as a causal agent of the eosinophilia-myalgia syndrome and should prove useful in the study of the pathogenesis of that syndrome.

Vitamin B-6 status of women with a constant intake of vitamin B-6 changes with three levels of dietary protein

To determine the effect of varying levels of dietary protein with a constant intake of vitamin B-6 (B-6) on B-6 status, nine women were fed diets providing daily intakes of 1.25 mg B-6 and 0.5, 1.0 and 2.0 g protein/kg body weight. After an 8-d adjustment period, the women consumed each level of dietary protein for 14 d in a Latin-square design. Several direct and indirect B-6 status indicators were measured in blood and urine. Significant differences among protein levels were found for urinary 4-pyridoxic acid (4-PA) excretion (P < 0.01), plasma pyridoxal 5'-phosphate (PLP) concentration (P < 0.05), and urinary excretion of volatile amines (VA, kynurenine plus acetylkynurenine) after a 2-g L-tryptophan load (P < 0.05). Nitrogen intake was significantly negatively correlated with urinary 4-PA excretion (r = -0.619, P < 0.001) and plasma PLP concentration (r = -0.549, P < 0.01), and positively correlated with erythrocyte alanine aminotransferase percentage stimulation (r = 0.418, P < 0.05) and urinary post-tryptophan load excretion of xanthurenic acid (r = 0.535, P < 0.05), kynurenic acid (r = 0.563, P < 0.05) and VA (r = 0.626, P < 0.01). Compared with men consuming diets with similar B-6 to protein ratios In a previous study, the women excreted a greater percentage of the B-6 intake as 4-PA, had lower plasma PLP concentrations and excreted greater amounts of postload urinary tryptophan metabolites at all three protein levels. If the Recommended Dietary Allowance (RDA) of vitamin B-6 is to be based on the dietary B-6 to protein ratio, gender differences in response to varying protein intakes should be considered. For the levels of protein intake used in this study and a B-6 intake of 1.25 mg/d, a B-6 to protein ratio of greater than 0.020 mg/g is required for adequate vitamin B-6 status in women.

Comparison of the effects of two cholecystokinin-receptor antagonists, loxiglumide and L-364,718, on the pancreatic secretory response to intraduodenal tryptophan in dogs

BACKGROUND

The aim of the study was to compare the effects of the cholecystokinin (CCK)-receptor antagonists loxiglumide and L-364, 718 on the endogenously stimulated pancreatic exocrine secretion.

METHODS

In six conscious dogs with chronic gastric and pancreatic fistulas we compared the action of different doses of loxiglumide (2.5 to 10.0 mg/kg/h) and L-364, 718 (0.025 to 0.1 mg/kg/h) on the pancreatic secretory response to intraduodenal perfusion of graded loads of tryptophan (0.37-10.0 mmol/ h), given against a background of secretin (20.5 pmol/kg/h intravenously).

RESULTS

Both loxiglumide and L-364, 718 inhibited the secretin-stimulated pancreatic bicarbonate output by up to 47% and 48%, respectively. The pancreatic protein output during secretin was significantly inhibited by all doses of L-364,718 (by 65% to 82%) but not by loxiglumide. All doses of loxiglumide and L-364, 718 abolished the 180-min integrated bicarbonate response to tryptophan. The two higher doses of loxiglumide (5.0-10.0 mg/kg/h) and L-364,718 (0.05-0.1 mg/kg/h) significantly decreased the 180-min integrated response to tryptophan by 59% and 79% (loxiglumide) and by 72% and 97% (L-364, 718). The plasma CCK-like immunoreactivity basally and in response to tryptophan was not significantly altered by loxiglumide or L-364, 718.

CONCLUSIONS

These findings indicate that in dogs 1) the pancreatic bicarbonate response to secretin is augmented by the hormone CCK; 2) L-364, 718 but not loxiglumide decreases pancreatic protein output during secretin; 3) endogenous released CCK is involved in the pancreatic bicarbonate response and is a major mediator of pancreatic protein response to intraduodenal tryptophan; and 4) the release of CCK by intraduodenal tryptophan is not influenced by loxiglumide and L-364, 718.

Crude protein and supplemental dietary tryptophan effects on growth and tissue neurotransmitter levels in the broiler chicken

Indian River male broiler chickens growing from 7 to 28 d of age were fed on diets containing 120, 210 and 300 g crude protein/kg diet and 0, 1.67 or 16.7 g added tryptophan (TRP)/kg diet. The hypothesis tested was that crude protein levels and TRP would affect both growth and neurotransmitter metabolism. Heart, brain and pancreatic neurotransmitter (noradrenaline (NA), dopamine (DA), serotonin (5-HT) and 5-hydroxy-indole-3-acetic acid (5-HIAA)) concentrations were determined by HPLC separation and electrochemical detection. Malate dehydrogenase (2-oxoglutarate decarboxylating) (NADP+) (MDH(NADP+); EC 1.1.1.40), isocitrate dehydrogenase (NADP+) (ICD(NADP+); EC 1.1.1.42) and aspartate aminotransferase (AAT; EC 2.6.1.1) activities were also measured. Supplemental TRP decreased growth and feed intake. Increasing dietary crude protein decreased MDH(NADP+), but increased (ICD(NADP+) and AAT activities. Additional dietary TRP decreased MDH(NADP+) activity, but had no effect on other enzyme activities. Cardiac NA concentrations were directly related to dietary crude protein levels while pancreatic levels were inversely related. An increase in dietary crude protein decreased both brain NA and DA. Supplemental dietary TRP increased both 5-HIAA and 5-HT. Changes in feed intake caused by different levels of both dietary crude protein and TRP are accompanied by altered levels of neurotransmitters. The present study indicates that much larger amounts of TRP are required to make simultaneous changes in feed intake and neurotransmitters.

Toxic effect of valproic acid on tryptophan binding to rat hepatic nuclei

This study evaluated whether valproic acid, a branched-chain fatty acid which has been used in the treatment of seizures, would influence the binding Of L-tryptophan to rat hepatic nuclei. Previous studies have indicated that binding of L-tryptophan to hepatic nuclear envelope protein was saturable, stereospecific, and of high affinity. In this study, we investigated whether valproic acid, which under certain conditions is heptatoxic, would influence L-tryptophan binding to rat hepatic nuclei as assayed by in vitro L-(5-3H)tryptophan binding. Our results indicate that the addition of valproic acid to hepatic nuclei or nuclear envelopes in vitro has little influence on their L-(5-3H)tryptophan binding. On the other hand, when valproic acid (80 mg/100 g body weight) is tube-fed 2 h before killing, the isolated nuclei show decreased specific L-tryptophan binding (total binding minus non-specific binding using unlabeled L-tryptophan (10(-4)M), at 2000-fold excess) compared with controls. Other fatty acids (oleic, palmitic or linoleic acid at 10(-4)M) when added with excess, unlabeled L-tryptophan (10(-4)M) in vitro to hepatic nuclei revealed some (but less than with valproic acid) decreased specific binding compared with controls. At high doses, valproic acid (80 mg/100 g body weight) appears to decrease tryptophan-induced stimulation of hepatic protein synthesis, probably in a hepatotoxic manner.