Tryptophan modulates exocrine secretory function in rat pancreatic acini

We investigated the effect of tryptophan (Trp) on exocrine secretory function, using isolated rat pancreatic acini. Trp inhibited cholecystokinin-octapeptide (CCK-8)-stimulated amylase secretion, causing a downward shift in the dose-response curve. The inhibitory effect of Trp was dose-dependent and was observed only on the sustained secretion, there being no effect on the initial phase of amylase secretion. Trp (10mM) also inhibited amylase secretion in response to carbachol and bombesin, as well as fluoride, a potent activator of guanine-nucleotide binding proteins. Since Ca2+ influx is necessary for sustained secretion, we examined the effect of Trp on Ca2+ influx and efflux. Trp increased the CCK-8-stimulated Ca2+ influx rate without affecting Ca2+ efflux, suggesting that Trp elevates intracellular Ca2+ levels. Increasing intracellular Ca2+ levels with A23187 resulted in the inhibition of CCK-8-stimulated amylase secretion. These results indicate that Trp inhibits CCK-stimulated sustained amylase secretion, in part by increasing Ca2+ influx into acinar cells.

Decreases in aggression in tryptophan-supplemented broiler breeder males are not due to increases in blood niacin levels

In previous studies with feed-restricted broiler breeders, it was found that supplementation with dietary Trp decreases aggressive activity more in socially dominant males than in socially subordinate males. Although it is probable that this effect is mediated centrally by serotonin, an alternative possibility is that it is associated with other metabolic products of Trp such as niacin. The objectives of this study were to determine whether 1) supplemental dietary niacinamide decreases aggression in broiler breeder males, 2) elevated blood niacin levels are associated with a decrease in aggression, and 3) social status influences any of these effects on behavior. Using a randomized complete block design, a control (0.19% Trp, 22 mg niacin/kg), Trp (1.5% Trp, 22 mg niacin/kg), or niacinamide (0.19% Trp, supplemented with 140 mg niacinamide/kg) diet was assigned to each pen. There were 16 birds per pen and three pens per treatment. Birds were maintained on skip-a-day feed restriction throughout, and behavioral observations were conducted until the social hierarchy in each pen was determined. Treatment diets were then fed from 15 through 18 wk of age, and the number of aggressive pecks and threats per pen recorded in three 20-min observation periods/wk. Blood samples were collected from dominant and subordinate birds and assayed for niacin using Tetrahymena pyriformis. Supplementing the diet with Trp significantly (P < 0.05) decreased aggression. Niacinamide-treated birds did not differ from either Trp-treated or control-treated birds, and no decreases in aggression were seen in birds with elevated blood niacin levels. Blood levels of niacin were, however, higher in dominant niacin-treated birds than in dominant control birds (P < 0.05), although there were no differences among subordinate or Trp-treated birds. Thus, the modulatory effect of Trp on aggression does not appear to be mediated by increased niacin synthesis.

Influence of diet free of NAD-precursors on acetaminophen hepatotoxicity in mice

Recently, we demonstrated the hepatoprotective effects of nicotinic acid amide, a selective inhibitor of poly(ADP-ribose) polymerase (PARP; EC 2.4.2.30) on mice suffering from acetaminophen (AAP)-hepatitis, suggesting that the AAP-induced liver injury involves a step which depends on adenoribosylation. The present study investigates the effects of a diet free of precursors of NAD, the substrate on which PARP acts, in female NMRI mice with AAP hepatitis and evaluates the influence of simultaneous ethanol consumption in these animals. Liver injuries were quantified as serum activities of glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT). While AAP caused a 117-fold elevation of serum transaminase activities in mice kept on a standard laboratory diet, which was significantly exacerbated by ethanol and inhibited by nicotinic acid amide (NAA), adverse effects were noted in animals fed a diet free of precursors of NAD. In these animals, only minor increases of serum transaminase activities were measured in the presence of AAP, and unlike the exacerbation caused by ethanol in mice on a standard diet, the liver damage was inhibited by 50% by ethanol. A further 64% reduction of hepatitis was observed, when NAA was given to ethanol/AAP-mice. Our results provide evidence that the AAP-induced hepatitis and its exacerbation by ethanol can either be reduced by end-product inhibition of PARP by NAA or by dietary depletion of the enzyme's substrate NAD. We see the main application of NAA as for the combinational use in pharmaceutical preparations of acetaminophen in order to avoid hepatic damage in patients treated with this widely used analgesic.

Acute tryptophan depletion and increased food intake and irritability in bulimia nervosa

OBJECTIVE

Data suggest that serotonin activity is reduced in women at normal weight who have bulimia nervosa. The authors tested whether acute perturbations in serotonin activity could alter short-term eating behavior and mood.

METHOD

They examined the effect of acute tryptophan depletion in 10 women with and 10 women without bulimia nervosa.

RESULTS

Women with bulimia nervosa exhibited an increase in caloric intake and mood irritability after acute tryptophan depletion.

CONCLUSIONS

These results indicate that women with bulimia nervosa have an exaggerated or pathological response to transient alterations in serotonin activity.

Effect of feeding reduced protein, amino acid-supplemented diets on nitrogen and energy balance in grower pigs

Two experiments were conducted to determine the effect of feeding reduced CP, amino acid (AA)-supplemented diets on the nitrogen (N) and energy (E) balance of grower pigs. In Exp. 1, 24 barrows (22.2 kg BW) were fed corn-soybean meal (C-SBM) diets containing either 16% CP, 12% CP, or 12% CP supplemented with lysine (LYS), tryptophan (TRP), and threonine (THR). After 6 d of adaptation to the diets and feeding frequency, a 5-d N and E balance trial was conducted. Supplementation of the 12% CP diet with LYS, TRP, and THR improved N retention ( P < .01) but failed to improve N retention to the level attained by pigs fed the 16% CP diet (P < .01). Efficiency of N retention was similar between pigs fed the AA-supplemented 12% CP diet and pigs fed the 16% CP diet (P > .10). Energy retention was increased by AA-supplementation of the 12% CP diet ( P < .10) to a level higher than that of pigs fed the 16% CP diet (P < .01). In Exp. 2, 60 barrows (21.7 kg BW) were fed one of the following diets: 16% CP; 12% CP diet supplemented with indispensable AA (IDAA) to simulate the 16% CP diet; 12% CP supplemented with LYS, TRP, THR, and dispensable AA N (DAAN); 12% CP supplemented with LYS, TRP, and THR; or a 12% CP negative control diet. After 6 d of adaptation to the diets and feeding frequency, a 5-d N and E balance trial was conducted. Nitrogen retention was improved (P < .01) by supplementing the 12% CP diet with LYS, TRP, and THR but remained inferior (P < .01) to that obtained when pigs were fed the other three diets. Pigs fed the 12% CP diet with LYS, TRP, THR, and DAAN supplementation retained less N (P < .07) than pigs fed the 16% CP but retained an amount similar (P > .10) to pigs fed the 12% CP diet with IDAA and DAAN supplementation. Pigs fed the 12% CP diet with LYS, TRP, and THR supplementation exhibited the highest efficiency of N retention (P < .01). Pigs fed the 12% CP diet supplemented with LYS, TRP, THR, and DAAN retained more (P < .01) E than pigs fed the 12% CP diet supplemented with IDAA and DAAN and more (P < .07) E than pigs fed either the 12% CP diet supplemented with LYS, TRP, and THR or the unsupplemented 12% CP diet. Pigs fed the 16% CP diet retained more (P < .06) E than pigs fed the 12% CP diet with IDAA and DAAN supplementation. Although the data show that the efficiency of N retention is greatest when LYS, TRP, and THR are supplemented to the 12% CP diet, maximal N retention is achieved only when the 12% CP diets are supplemented with both the deficient AA and a source of N for dispensable AA synthesis.

Chemical and biological characteristics of a west African weaning food supplemented with compea (Vigna unguiculata)

The effects of cowpea and amino acid supplementation on the protein quality and chemical characteristics of a maize-based West African traditional weaning food were studied. Process optimization for improved nutritive value was also determined. Supplementation of the traditional weaning food with cowpea increased the lysine, tryptophan and threonine content while the sulphur-amino acids decreased with increasing levels of cowpea. Further supplementation of 70:30 maize/cowpea blends with lysine, threonine or methionine did not significantly improve (p > 0.05) protein quality in terms of the biological value (BV) and net protein utilization (NPU), although significant increases in the protein scores were noted. However, considerable improvements in the BV and NPU were recorded in blends fortified with either tryptophan alone or a combination of lysine, tryptophan, methionine and threonine. Cooking whole cowpea seeds for 45 min before incorporating in the blend formulation also significantly improved (p < 0.05) the protein quality of maize/cowpea blends. The BV and NPU of blends containing 30% pre-cooked cowpea increased from 52 to 76% and 50 to 71% respectively compared to pure maize porridge. The protein content increased from 10 to 14% and the utilizable proteins more than doubled. The weight increase of experimental rats fed with these blends was comparable to that of rats on casein diet. A 30% supplementation of the maize-based weaning food with cowpea therefore greatly enhances the nutritive value especially when the cowpea is pre-cooked for 45 min. Use of chemical scores alone for such blends cannot be a reliable index of blend quality.

The effects of a novel and selective inhibitor of tryptophan 2,3-dioxygenase on tryptophan and serotonin metabolism in the rat

The effects of a novel inhibitor 680C91 ((E)-6-fluoro-3-[2-(3- pyridyl)vinyl]-1H-indole) of the key enzyme of tryptophan catabolism tryptophan 2,3-dioxygenase (TDO) (EC 1.13.11.11), were examined on tryptophan catabolism in vitro and in vivo and on brain levels of tryptophan, serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA). 680C91 was a potent (Ki = 51 nM) and selective TDO inhibitor with no inhibitory activity against indoleamine 2,3-dioxygenase (EC 1.13.11.17), monoamine oxidase A and B, 5-HT uptake and 5-HT1A,1D,2A and 2C receptors at a concentration of 10 microM. 680C91 had no effect on the binding of tryptophan to serum albumin in plasma and inhibited TDO competitively with respect to its substrate tryptophan. 680C91 inhibited the catabolism of tryptophan by rat liver cells and rat liver perfused in situ. The catabolism of L-[ring-2-14C]-tryptophan and a load dose of tryptophan (100 mg/kg) in vivo were inhibited by prior administration of 680C91. Administration of 680C91 alone produced marked increases in brain tryptophan, 5-HT and 5-HIAA. A load dose of tryptophan (100 mg/kg), producing increases in brain tryptophan 4-fold greater than that seen with 680C91, did not increase brain 5-HT and 5-HIAA to levels greater than those seen with 680C91 and produced a shorter-lasting increase in these parameters. These data therefore demonstrate the importance of TDO as a regulator of whole-body tryptophan catabolism and brain levels of tryptophan and 5-HT and suggest that a greater antidepressant efficacy might be achieved with inhibitors of TDO than tryptophan administration alone.

Comparison of two dose-response techniques to study the pancreatic secretory response to intraduodenal tryptophan in the absence and presence of the M1-receptor antagonist telenzepine

To answer the questions if the type of continuous dose-response technique influences the pancreatic secretory response to intraduodenal tryptophan and if the M1-receptor antagonist telenzepine influences the intestinal absorption of tryptophan, we determined, in 12 conscious dogs with chronic gastric and duodenal fistulas, pancreatic bicarbonate and protein secretion and tryptophan plasma concentrations following intraduodenal tryptophan perfusion using two dose-response techniques. With an ascending continuous dose-response technique (aDRT), tryptophan was perfused in loads ranging from 0.12 to 10.0 mmol h-1, starting with the lowest load and tripling it every 45 min. With the descending continuous dose-response technique (dDRT), the order of tryptophan loads was reversed, with the highest load being given first. All studies were done on a fixed background of intravenous secretin (20.5 pmol kg-1 h-1) and repeated in the presence of the anticholinergic M1-receptor antagonist telenzepine (243 nmol kg-1 h-1). The bicarbonate and protein response as well as tryptophan plasma concentrations to the same loads of tryptophan did not differ significantly between the two techniques. Using both techniques, telenzepine significantly (p < 0.05) inhibited the overall pancreatic protein response by 65% (dDRT) to 81% (aDRT). The overall bicarbonate response was only numerically, and not statistically significantly, inhibited by telezepine. Tryptophan plasma concentrations after duodenal perfusion with tryptophan were neither influenced by the order of tryptophan loads nor altered by telenzepine.(ABSTRACT TRUNCATED AT 250 WORDS)

Continuing occurrence of eosinophilia myalgia syndrome in Canada

Eosinophilia myalgia syndrome (EMS), was defined by the Centers for Disease Control (CDC) as eosinophilia > 1000 mm3 and incapacitating myalgia without infection or neoplasm. Studies suggested that use of L-tryptophan (L-T), was a risk factor. We conducted a pharmacoepidemiological survey in Canada where access to L-T is limited. Using the active surveillance method, a 100% sample of potentially involved specialists and a 15% sample of family physicians from Ontario and Quebec were surveyed regarding treatment of patients with severe myalgia within the past year. Follow-up amplified clinical and laboratory information. Overall response rates were 61.4%. Thirty-eight per cent of respondents reported at least one patient. Of 6423 patients assessed, 19 'definite' and 25 'possible' EMS cases were identified. Information from physicians did not suggest use of L-T in patients with definite or possible EMS. It was considered that the cases found an underestimate of the incidence of EMS. Its continuing occurrence in Canada brings causal interpretations of earlier studies into question.

Tryptophan deficiency and alcohol consumption in rats as a model for disadvantaged human populations: a preliminary study

Choice of diet is a combination of socioeconomic, psychological, and biological factors. This article reports on a preliminary study using an animal model and approximating the dietary conditions found on some Native American reservations. The results suggest that alcohol consumption in these disadvantaged populations may be a result of tryptophan deficiency. Tryptophan-deficient rats consumed more alcohol under ad-libitum conditions, perhaps to compensate for the lack of this essential amino acid. Tryptophan is the biological precursor of serotonin, a central neurotransmitter that has been implicated in mood elevations and declines. Alcohol has been found to mimic the effects of tryptophan or serotonin. We suggest that alcohol consumption may act to compensate for the dietary deficiency of this amino acid. The model attributing alcohol consumption to tryptophan deficiency thus connects socioeconomic, psychological, and biological factors.

L-tryptophan and the eosinophilia-myalgia syndrome: a clinical and laboratory study

Case notes of 202 patients who were prescribed a single brand of L-tryptophan (Optimax, manufactured by Merck) between January 1987 and December 1991 were examined. Fourteen patients' notes indicated that they had clinical or laboratory findings suggestive of a diagnosis of eosinophilia-myalgia syndrome (EMS). However, results of clinical examination and measurement of serum aldolase, total eosinophil count and antinuclear antibodies did not support the diagnosis of EMS in any of the 14 patients. Although a further study of 50 consecutive patients on L-tryptophan at the time of the investigation revealed that 5 had mild eosinophilia, none reached the criteria for EMS established by the US Centers for Disease Control and Prevention.

Stereospecific effects of intraduodenal tryptophan on pyloric and duodenal motility in humans

BACKGROUND

L-Tryptophan delays gastric emptying in animals to a greater extent than D-tryptophan, but none of the possible motor mechanisms responsible for this stereospecific effect have been evaluated.

METHODS

In 11 healthy volunteers antropyloroduodenal pressures were recorded in the fasted state with a sleeve/sidehole manometric assembly during 20-min intraduodenal infusions (2 ml.min-1) of isotonic L- and D-tryptophan (50 mM, pH 5.7) and normal saline (pH 5.5), given in randomized order.

RESULTS

Intraduodenal L-tryptophan increased basal pyloric pressure (p < 0.05), whereas D-tryptophan had no effect. In contrast, L- and D-tryptophan both stimulated (p < 0.05) localized phasic pyloric pressure waves, and there was no significant difference in the responses. The number of duodenal pressure waves was greater during infusion of L-tryptophan than during D-tryptophan (p < 0.05).

CONCLUSION

We conclude that intraduodenal tryptophan has stereospecific effects on pyloric and duodenal motility. Although the precise contribution of these differential effects to gastric emptying remains to be clarified, they may be partially responsible for the differences in gastric emptying of D-tryptophan and L-tryptophan.

Serotonin and the neurobiology of depression. Effects of tryptophan depletion in drug-free depressed patients

OBJECTIVE

To investigate the effects of tryptophan depletion in untreated depressed patients. Rapid dietary depletion of the precursor of serotonin synthesis, tryptophan, causes a transient return of depression in 67% of patients who have had a therapeutic antidepressant response.

METHOD

Forty-three untreated depressed patients underwent tryptophan depletion in a double-blind, placebo-controlled cross-over study. After testing, they received open sequential antidepressant treatment.

RESULTS

Mood did not change when tryptophan was depleted but did change on the day after the depletion test. Relative to the control test, 37% of the patients had 10-point or greater decrease in Hamilton Depression Rating Scale (Ham-D) score, while 23% had a 10-point or greater increase in Ham-D score on the day after the tryptophan depletion test. Change in mood was correlated to treatment response after testing. Patients whose condition worsened proved to be highly refractory to treatment while those who showed improvement were more likely to respond.

CONCLUSIONS

That tryptophan depletion did not rapidly worsen depression argues that serotonin function is not linearly related to the level of depression and if reduced serotonin function does cause depression, then it is either as predisposing factor or due to a postsynaptic deficit in the utilization of serotonin.

Tonic immobility and high-intensity calls in a precocial chick as a function of age, diet, and time of day

Tonic immobility (TI) and high-intensity vocalizations are two antipredator behaviors employed by domestic chicks (Gallus gallus) which vary in their function and the proximate mechanisms that govern them. In the present study, we sought to determine the influence of age (3 or 10 days old), diet (control or tryptophan-free), and time of testing (A.M. or P.M.) on the duration of TI and the number of calls produced in domestic chicks. Older chicks remained immobile significantly longer than younger chicks as did subjects on the control diet or those tested at night. However, 3-day-old chicks had significantly shorter TI durations only when tested in the A.M.: TI did not differ between age groups when subjects were tested in the P.M. Three-day-olds called significantly more than 10-day-olds when given the control diet and when tested in the P.M. but vocalization frequencies did not differ between age groups during the A.M. testing or when given the tryptophan-free diet (T-). Vocalization rate (calls/TI duration), however, was significantly greater during the A.M. testing. These results emphasize the importance of considering circadian rhythms and behavioral development. Furthermore, an integrative view of the proximate mechanisms and adaptive functions of TI and high-intensity vocalizations is presented.

Acute tryptophan depletion aggravates premenstrual syndrome

The dietary technique of acute tryptophan depletion was used to suppress brain serotonin synthesis in 16 women with documented premenstrual syndrome. Each subject was tested at distinct phases of each of two menstrual cycles. Baseline amino acid levels did not vary across the menstrual cycle, except for tyrosine which showed a significant premenstrual decrement. Compared to a sham procedure, actual tryptophan depletion caused a significant aggravation of premenstrual symptoms, particularly irritability. Symptom magnitude was correlated with diminution of tryptophan relative to other amino acids. This result supports other evidence implicating serotonin in premenstrual syndrome.

Dietary niacin deficiency lowers tissue poly(ADP-ribose) and NAD+ concentrations in Fischer-344 rats

Poly(ADP-ribose) is synthesized in response to DNA strand breaks, using NAD+ as substrate, and has been implicated in the process of DNA repair. Because NAD+ can be synthesized from niacin or tryptophan, both of these components must be manipulated to alter niacin status. Six dietary treatments were used, including niacin-deficient (ND) diets and niacin-replete (NR) diets consumed ad libitum and the NR diets pair-fed (PF) to the ND intake. The ND, NR and PF diets contained either 80 g casein + 50 g gelatin/kg diet (8-5 diets) or 70 g casein + 60 g gelatin/kg diet (7-6 diets) to control tryptophan content. The 8-5ND and 7-6ND diets induced mild and severe symptoms of niacin deficiency, respectively, over a 3-wk period in male weanling Fischer-344 rats. Food intake and weight gain were suppressed in both of the ND groups compared with their respective NR controls. Weight gain was not different between ND animals and their PF counterparts. At 3 wk, blood, liver, kidney, heart and lung NAD+ concentrations for both 8-5ND and 7-6ND animals were all significantly lower than those for their respective PF groups. In the groups fed the 8-5 diets, liver poly(ADP-ribose) was lower in the ND group (64% of PF), with no difference between the NR and PF groups. In rats fed the 7-6 diets, poly(ADP-ribose) levels were further decreased in the ND group (43% of PF), but food restriction also exerted an independent effect (PF levels were 46% of NR levels).(ABSTRACT TRUNCATED AT 250 WORDS)

[The effect of tryptophan on the regulation of food intake in normal and overweight persons]

The neurotransmitter serotonin significantly contributes to the regulation of food intake and appetite behaviour. The cerebral serotonin synthesis depends on the availability of the precursor tryptophan. To examine how diets with different carbohydrate, protein and tryptophan content affect food preferences and the mood, healthy obese and non-obese male adults consumed the following isocaloric diets at breakfast: standard diet (60% carbohydrate), protein-rich diet (35% carbohydrate, 40% protein), carbohydrate-rich diet (80% carbohydrate), tryptophan supplemented diet (standard diet + 1.5 g tryptophan). The plasma concentration of tryptophan (TRP) and large neutral amino acids (LNAA) is determined by their uptake with the diet. In obese and non-obese adults the TRP/LNAA-quotient rose significantly by upto 0.40 to 0.57, following the tryptophan supplemented breakfast. The protein-rich diet reduced the TRP/LNAA-quotient. The preference of protein-rich food after the consumption of carbohydrate-rich diets (60-80% carbohydrate) was diagnosable with the non-obese person and not with the obese person. No obvious connection was detected between nutrient preferences and plasma TRP/LNAA-quotient. There was no influence of the plasma TRP/LNAA-quotient after meals with different nutrient relation on mood. Therefore it is concluded that different carbohydrate and protein content and also additional tryptophan supplementation of single meals is not able to modify the brain serotonin synthesis and release in healthy people in a kind that serotonin induced behaviour would be changed, at least on a short time basis.

Identification of four metabolites of 3-(phenylamino)alanine, a constituent in L-tryptophan products implicated in eosinophilia-myalgia syndrome, in rats

3-(Phenylamino)alanine (PAA), a contaminant found in L-tryptophan tablets, has been discussed as a possible cause of eosinophilia-myalgia syndrome (EMS). We administered PAA (100 mg/kg) by gastric gavage to Wistar rats to determine its distribution and metabolism. We developed a purification procedure, using Bond Elut SCX cartridges followed by high performance liquid chromatography (HPLC) in order to determine levels of PAA. The level of PAA in blood was 4.22 micrograms/ml at 5 h and urinary excretion was 21.7 micrograms for 5 h and 84.6 micrograms between 5 and 24 h. The amount of PAA in the contents of the large intestine at 5 h was 0.76 microgram, indicating poor transfer of PAA to the large intestine. However, the highest concentration of PAA was 12.3 micrograms/g in the brain, indicating the passage of PAA through the blood-brain barrier. In addition to detecting PAA in the blood and organs, we also detected four metabolites of PAA in urine. We used gas chromatography mass spectrometry to identify PAA in rat liver, as well as N-(hydroxyphenyl)glycine, N-phenylglycine, 3-(pheylamino)lactic acid, and 3-(hydroxyphenylamino)-lactic acid in rat urine. These results suggest that the degradation pathway of PAA is similar to that of phenylalanine.

Eosinophilia-myalgia syndrome in Germany: an epidemiologic review

OBJECTIVE

To review the epidemiologic features of eosinophilia-myalgia syndrome (EMS) in Germany.

DESIGN

We determined the incidence of EMS in Germany through May 1992 and analyzed the dose of L-tryptophan used, the duration of intake, and the concurrent medications.

MATERIAL AND METHODS

All patients receiving L-tryptophan preparations in Germany were already under medical supervision before the onset of the disease; thus, information on patient history and other potential risk factors was readily available. Because of the drug status of L-tryptophan preparations, brands could be accurately traced back to suppliers of raw materials. Statistical differences in age and gender of patients, dose of L-tryptophan, eosinophil count, and skin involvement were sought between patients with and those without concurrent medications.

RESULTS

On the basis of guidelines established by the Centers for Disease Control and Prevention, 105 patients fulfilled the criteria for EMS. No apparent correlation was found between the incidence of EMS and the dose of L-tryptophan or the duration of intake before onset of EMS. Assessment of the study group showed that 45% were taking various other medications, whereas 55% were taking L-tryptophan only. Analysis by type of pharmaceutical agent showed no preponderance of a specific concurrent drug (in particular, psychotropic drugs). Thus, concurrently used medications did not seem to be an important variable. All cases of EMS were associated with L-tryptophan from formulators that had used raw materials from the previously implicated source.

CONCLUSION

This study supports the pathophysiologic role of a contaminant in L-tryptophan in the occurrence of cases of EMS in Germany.

The effects of energy source and tryptophan on the rate of protein synthesis and on hormones of the entero-insular axis in the piglet

The present experiment was designed to study the influence of dietary energy source (fat or carbohydrate) and tryptophan (TRP) on protein synthesis and plasma insulin concentrations in the piglet. Six dietary regimens, based on either a high-fat (F) or a high-carbohydrate (C) diet with three levels of TRP (deficient, 1; adequate, 2; excess, 3), were used. Fractional protein synthesis rate (ks; % per d) was measured in the liver, Longissimus dorsi (LD), Semitendinosus (ST), skin, femur, brain, pancreas, stomach, mucosa of the duodenum and jejunum, and the whole body, using a 'flooding dose' of 3H-phenylalanine. Mean integrated insulin, gastric inhibitory polypeptide (GIP) and glucose concentrations were higher after the C diets compared with the F diets, TRP supplementation globally augmented ks linearly in the liver, ST, skin and whole body, while it had quadratic effects in the LD (ks highest in the TRP-adequate diet groups) and jejunal mucosa (ks lowest in the TRP-adequate diet groups). Pancreatic ks was increased by TRP addition up to a plateau. Ks was highest after the F diets in the digestive tissues while in the skin and LD ks was highest after the C diets. Fasting concentrations of gluconeogenic amino acids were lower (and urea higher) with the F than the C diets, suggesting their use as precursors for glucose synthesis. In conclusion, we have confirmed the depressive effects of TRP deficiency on ks, RNA activity and growth. We could not establish a relationship between plasma insulin and muscle ks. This may be related to the way in which we manipulated plasma insulin concentrations.