Effects of dietary tryptophan levels on growth, feed/gain, carcass composition and liver glutamate dehydrogenase activity in rainbow trout (Salmo gairdneri)

1. The tryptophan requirement of rainbow trout (initial body wt, 13 g) was estimated by feeding diets containing varied levels of tryptophan from 0.06 to 0.5% of diet for 6 weeks. 2. The estimated tryptophan requirement was 0.20-0.25 (0.57-0.71)% of diet (dietary proteins). 3. Nitrogen retention increased and feed/gain decreased with dietary tryptophan levels up to 0.14%, but no further effect was observed at levels above 0.14%. 4. Carcass protein content gradually increased and lipid and ash contents decreased with increasing dietary tryptophan levels. 5. Dietary tryptophan levels did not affect hepatosomatic index or liver glutamate dehydrogenase activity.     

Response of plasma and gastrointestinal melatonin,plasma cortisol and activity rhythms of European sea bass (<Emphasis Type="Italic">Dicentrarchus labrax</Emphasis>) to dietary supplementation with tryptophan and melatonin

Melatonin is an effective antioxidant, immunostimulant, gonadal maturating regulator and antistress indoleamine that may be potentially useful for fish farmers. We have explored two possible ways of increasing plasma melatonin levels through the diet: direct melatonin supplementation (ME diet) and supplementation with the melatonin precursor tryptophan (TRP diet). To this end, a group of sea bass was fed a commercial diet (STD diet) at a regular time for 16 days, after which plasma, intestine, and bile samples were taken at four different time points: 120 min before, and 15, 180 and 480 min after feeding. Locomotor activity, intestinal and biliary melatonin, and plasma melatonin, serotonin and cortisol levels were measured. This same sampling process and analyses were also carried out after feeding sea bass TRP diet or ME diet for 1 week. Our results show that melatonin, but not tryptophan supplementation of the diet increases plasma, intestine and bile levels of melatonin. Plasma serotonin levels, on the other hand, were increased by dietary tryptophan, but not by melatonin, confirming the availability of supplemented tryptophan for serotonin synthesis. Both treatments were equally effective in reducing the high cortisol levels observed with the STD diet.     

Effect of dietary protein and calorie deficiency on tryptophan levels in the developing rat brain

The pattern of development of brain tryptophan in the rat was studied in the progeny of mothers fed a 7.5% protein diet ad lib., a 20% protein diet ad lib. and those fed a 20% protein diet pair-fed with mothers who received the 7.5% protein. The pattern of development was similar in all three groups. Starting with a high brain tryptophan content at birth, all animals showed a progressive reduction during the next 3 weeks. However, tryptophan levels at birth were several fold higher in the brains of pups born to mothers receiving either the low protein diet fed ad lib. or those born to mothers who received the 20% protein diet in restricted amounts. From the 14th day after birth, tryptophan concentration of brain in undernourished pups was significantly lower until the 35th day. The implications of this finding are discussed.     

Influence of Feeding Paradigm in Rats on Temporal Pattern of: I. Macronutrient Intake and Arterio-Venous Differences in Plasma Glucose, Insulin and Tryptophan

Relationships among feeding paradigm (single diet vs food selection) and arterio-venous differences (δAV) of glucose, insulin and tryptophan were studied by measuring the temporal patterns of food intake and plasma parameters during 8 hr feeding cycles in rats. Adult male Sprague-Dawley rats were offered a single diet of fixed composition (20% casein) or a choice between two isocaloric diets (0% and 60% casein) for 2 weeks under 8-hr daily feeding conditions, food being offered during the dark cycle. Groups of animals were then killed at the beginning and at 2-hourly intervals throughout the feeding period. With both feeding paradigms, rats showed temporal patterns of energy, carbohydrate and protein intakes with a peak at the beginning and a trough at the end of the feeding period. However, in rats offered a dietary choice the intake of carbohydrate was significantly lower, and the intakes of energy and protein significantly higher than those found in rats offered a single diet. Throughout the feeding period, these differences between single and choice diets became less accentuated in the case of carbohydrate intake, but more accentuated for energy and protein intakes. Paradoxically, rats fed a choice of diets had a significantly lower weight gain than rats fed a single diet. The temporal variation of insulin secretion and tryptophan absorption varied inversely with the two diet paradigms. Moreover, in rats offered a choice of diets, macronutrient intake was significantly correlated with insulin secretion and venous glucose concentration. The opposed physiologic and metabolic responses to the feeding paradigms suggest the need for future studies to examine the possibility that such can function as synchronizers of biological rhythms.     

Influence of Feeding Paradigm in Rats on Temporal Pattern of: I. Macronutrient Intake and Arterio-Venous Differences in Plasma Glucose,Insulin and Tryptophan

Relationships among feeding paradigm (single diet vs food selection) and arterio-venous differences (δAV) of glucose, insulin and tryptophan were studied by measuring the temporal patterns of food intake and plasma parameters during 8 hr feeding cycles in rats. Adult male Sprague-Dawley rats were offered a single diet of fixed composition (20% casein) or a choice between two isocaloric diets (0% and 60% casein) for 2 weeks under 8-hr daily feeding conditions, food being offered during the dark cycle. Groups of animals were then killed at the beginning and at 2-hourly intervals throughout the feeding period. With both feeding paradigms, rats showed temporal patterns of energy, carbohydrate and protein intakes with a peak at the beginning and a trough at the end of the feeding period. However, in rats offered a dietary choice the intake of carbohydrate was significantly lower, and the intakes of energy and protein significantly higher than those found in rats offered a single diet. Throughout the feeding period, these differences between single and choice diets became less accentuated in the case of carbohydrate intake, but more accentuated for energy and protein intakes. Paradoxically, rats fed a choice of diets had a significantly lower weight gain than rats fed a single diet. The temporal variation of insulin secretion and tryptophan absorption varied inversely with the two diet paradigms. Moreover, in rats offered a choice of diets, macronutrient intake was significantly correlated with insulin secretion and venous glucose concentration. The opposed physiologic and metabolic responses to the feeding paradigms suggest the need for future studies to examine the possibility that such can function as synchronizers of biological rhythms.     

Tryptophan requirement of juvenile Asian sea bass Lates calcarifer

The dietary requirement of tryptophan for juvenile Asian sea bass (Lates calcarifer Bloch) was studied. The juveniles (mean initial weight, 5.30 ± 0.06 g) were given semi‐purified test diets containing fish meal, gelatin, squid meal, and crystalline amino acids, for 12 weeks. Each set of isonitrogenous and isocaloric test diets contained graded levels of tryptophan. Fish (15 per tank) were reared in 250‐L fiberglass tanks provided with continuous flow‐through sea water at 26°C and salinity of 28 p.p.t. Fish were fed twice daily at a feeding rate of 8% of the body weight day^?1 for the first 4 weeks and at 3.5–2.5% of the body weight day^?1 from 5 to 12 weeks. The experiment was in a completely randomized design with two replicates per treatment. Mean percentage weight gains and feed efficiency ratios were significantly different in fish fed varying tryptophan levels. Survival was 100% in all treatments. On the basis of break‐point analysis of the growth response, the dietary tryptophan requirement of juvenile Asian sea bass is 0.41% of the dietary protein. This information will be useful in further refinement of practical feed formulations for the Asian sea bass.     

Decrease in the levels of NGF and BDNF in brains of mice fed a tryptophan-deficient diet

The roles of dietary tryptophan (Trp) were evaluated in regulation of production of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin (NT)-3 in the various brain regions in ddY mice. Feeding the mice a Trp-deficient diet for 2 weeks significantly decreased in the hippocampal level of NGF but not those of BDNF and NT-3, as compared with feeding an adequate Trp diet. The mice fed excess Trp did not have different levels of any of these neurotrophins than in the mice fed an adequate Trp diet. The levels of BDNF in the cerebral cortex were also significantly lower in the mice fed on a Trp-deficient diet, while the levels of NGF and NT-3 in the region were not modulated upon feeding of the diet. The dietary Trp level had no significant effect on the levels of NGF, BDNF, or NT-3 in the entorhinal cortex nor septum of the mice. These results demonstrate that the brain levels of NGF and BDNF are dependent on the dietary content of tryptophan.     

Correlation between brain tryptophan and plasma neutral amino acid levels following food consumption in rats

Brain tryptophan increases significantly within two hr of the time that rats begin to consume a diet containing carbohydrate and fat, but fails to rise if the diet also contains 18–24% protein. The effects of particular diets on brain tryptophan are not well correlated with plasma tryptophan concentrations alone, but do correlate well with the ratio of plasma tryptophan to individual neutral amino acids (leucine, isoleucine, valine, tyrosine, phenylalanine) or to their sums. (These amino acids compete with tryptophan for uptake into the brain.) Carbohydrate ingestion raises brain tryptophan by elevating plasma tryptophan and depressing the plasma levels of the competing neutral amino acids; protein consumption prevents an increase in brain tryptophan by raising the plasma concentrations of the competing amino acids more than of tryptophan.     

Estimates of dietary threshold levels for crude protein and amino acids to obtain plateau values of apparent ileal crude protein and amino acid digestibilities in newly weaned pigs

This study was conducted to estimate dietary threshold levels for crude protein (CP) and amino acids (AA) at which apparent ileal digestibilities (AID) of CP and AA in assay diets for newly weaned pigs reach plateaus. A total of 14 (12 + 2 for replacement) three-week old barrows were fitted with simple T cannulas at the distal ileum. Corn starch-based diets containing six graded levels of CP from casein, 90, 155, 220, 285, 350, or 415 g CP/kg assay diet (as-fed), were formulated. At 28 days of age, the pigs were randomly allocated to the six dietary treatments with two pigs per CP level in four weekly repeated measurement periods. They were fed twice daily a total of 30 g (as-fed) per kg of individual body weight at 8:00 and 20:00 h. The dietary CP and AA levels affected AID of CP and most AA (p = 0.005 to p = 0.040) in the assay diets. The AID of CP and AA were higher at 155 and 220 compared to 90 g CP/kg assay diet (p < 0.001 to p = 0.047). Initially, the AID of CP and AA increased sharply then gradually reached, at individual break points (p < 0.001 to p = 0.047), their plateaus (p < 0.001), which did not change up to dietary CP levels of 415 g/kg assay diet and the AID values became independent of the dietary AA levels. The piglets' capacity to digest CP and absorb AA was not limiting under these experimental conditions. There was no effect of age on AID of CP and AA (p = 0.056 to p = 0.899) except for a linear increase (p = 0.045) in AID of glycine from Period 1 to 4. Segmented quadratic with plateau relationships between the AID of CP and AA and their dietary contents were fitted for CP and each AA. The lower end points of 95% confidence intervals of the plateau AID values were defined to represent the initial plateau AID. The dietary CP and AA contents, corresponding to the initial plateau AID values, represent the dietary threshold levels. For CP and the indispensable amino acids, the plateau AID [%] and the dietary threshold levels [g/kg DM], respectively, in casein were: CP, 94.2 and 176; arginine, 95.1 and 7; histidine, 96.0 and 5; isoleucine, 96.4 and 8; leucine, 96.8 and 16; lysine, 96.8 and 12; methionine, 97.9 and 5; phenylalanine, 96.2 and 10; threonine, 93.4 and 9; tryptophan, 94.3 and 2; valine, 95.9 and 11. For the determination of plateau AID in piglets, the crude protein and amino acid contents in the assay diets should meet or exceed the corresponding dietary threshold levels.     

The influence of sulphur,molybdenum and cadmium exposure on the growth of goat,cattle and pig

A three factorial designed feeding experiment with common carp (Cyprinus carpio L.) was carried out in an intensive experimental rearing system. Fish (initial body weight 200 g) were fed on two different levels of dietary energy (16 and 18 MJ DE/kg DM), two different levels of protein (320 and 420 g CP/kg DM) and also two different feeding intensities (100% and 75% of the maximum intake). The experiment was terminated when fish reached a mean body weight of 1300 g.

Growth, feed utilization and nutrient composition of the whole body and fillet were observed. The highest growth was obtained when the fish were fed on the diet containing high dietary energy and high dietary protein with satiation feeding. High dietary energy, high dietary protein and restriction of feed intake improved feed conversion ratios. High dietary energy, low dietary protein and restrictive feeding increased energy utilization. Low dietary protein and restrictive feeding resulted in better protein utilization.

Fish fed with high dietary energy contained more fat and less protein in their carcasses. A lower fat content but higher protein and higher ash content in fish carcasses was shown when fish were fed with a diet high in protein and fed restrictively.     

Interaction and imbalance between indispensable amino acids in young piglets

Lowering protein level in diets for piglets urge to have knowledge on the piglet’s requirements for essential amino acids (AA) and their interactions. The present studies aimed to determine the interaction between the dietary level of valine (Val) and tryptophan (Trp) and the effect of AA imbalance at two levels of dietary Val on the growth performance of post-weaning piglets. In Experiment 1 (duration 4 weeks), the effects of supplementation of free l-Val (1.0 g/kg) and/or l-Trp (0.5 g/kg) in a low-CP diet (CP 17.7%), marginal in Trp and Val, was studied in a 2×2 factorial design and using an additional reference treatment (CP 19.5%). In Experiment 2 (duration 5 weeks), the influence of a stepwise increase in excess supply of isoleucine (Ile), histidine (His) and leucine (Leu), up to 10, 10% and 30% relative to their requirement values respectively, was evaluated at 60% or 70% standardized ileal digestible (SID) Val relative to SID lysine, using a 3×2 factorial design. In Experiment 1, over the whole experimental period, feed intake (FI) was affected by dietary Trp level (P<0.05) and feed conversion ratio (FCR) by both the level of Trp and Val in the diet (both P<0.05). Increasing Trp level increased FI and decreased FCR while increasing dietary Val level reduced FI and increased FCR. For BW gain (BWG), there was an interaction between dietary level of Trp and Val (P<0.05). Valine supplementation decreased BWG using a diet marginal in Trp, whereas it increased BWG when using a Trp sufficient diet. Piglets fed the low-CP diet with adequate levels of Val and Trp showed at least same performance compared to piglets fed the high CP reference diet. In Experiment 2, increasing dietary Val improved FI and BWG (P<0.001) and tended to improve FCR. Dietary AA excess for Ile, His and Leu reduced FI and BWG (P<0.05) and only affected FCR (P<0.01) in the 1^st week of the study. Dietary level of Val and AA excess did not show interactive effects, except for FCR over the final 2 weeks of the study (P<0.05). In conclusion, an interaction exists between dietary supply of Val and Trp on the zootechnical performance of post-weaning piglets and dietary AA excess for Ile, Leu and His, reduces growth performance of piglets in low-protein diets, independent of the dietary level of Val.     

Influence of dietary protein levels and water temperature on growth,body composition and nutrient utilization of Cirrhinus mrigala (Hamilton, 1822) fry

The experiment was conducted to determine the protein requirement of Cirrhinus mrigala fry at three different water temperatures, 28, 30 and 32 °C, and to investigate the influence of dietary protein levels and water temperatures on weight gain, body composition, food and nutrient utilization. The 36% protein concentration in the diet yielded highest weight gain at all temperatures from 28 to 32 °C. However, daily protein intake was lower at 28 °C than at 30 and 32 °C. The diet with 36% dietary protein and 32.17% carbohydrate produced the best weight gain and gross conversion efficiency (GCE) at 30 °C. The protein-sparing effect was observed at temperatures 30 and 32 °C in diets 1 and 2, having carbohydrate levels 37.36–44.91%. Highest protein efficiency ratio (PER) was recorded at 28% dietary protein level, while it was lowest at 40% dietary protein level in all three temperatures. Lipid in the body of fishes increased at the end of the experiment in comparison to the initial body lipid. The body protein was found to be related to daily protein intake at 30 and 32 °C. Significant difference (P<0.05) was also noted between temperatures, the hepatosomatic index (HSI) and viscerosomatic index (VSI). The diet with 36% dietary protein and 32.17% carbohydrate was observed to be the best diet for C. mrigala fry at 28–32 °C.     

Effects of dietary arginine levels on growth performance and body composition of juvenile grouper Epinephelus coioides

An 8‐week feeding trial was conducted to determine the effects of dietary arginine levels on growth performance and body composition of juvenile grouper Epinephelus coioides (initial weight: 16.10 ± 0.26 g per fish) in 500‐L indoor flow‐through circular fiberglass tanks. Diets contained six levels of l ‐arginine ranging from 1.78% to 3.31% of dry diet in 0.30% increments. The diets, in which 25% crude protein came from fishmeal and soybean protein concentrate, and 23% from crystalline amino acids, were formulated to simulate the amino acid profile of 48% whole chicken egg protein except for arginine. Each diet was assigned to three tanks (20 fish per tank) in a completely randomized design. Grouper were fed to apparent satiation (about 5% body weight per day at the initial 1–4 weeks and 3% body weight per day in the following 5–8 weeks) twice daily on weekdays and once daily on weekends. Weight gain (WG) and specific growth rate (SGR) showed an incremental trend with increasing dietary arginine levels from 1.78% to 2.72% and remained thereafter relatively constant. Productive protein value (PPV) was poorest in fish fed the lowest arginine diet (P < 0.05) and showed no significant differences among other treatments (P > 0.05). Dietary arginine contents significantly influenced body composition. With the increase in dietary arginine, contents of total essential amino acids (EAAs), total non‐EAAs and total amino acids of whole body significantly increased (P < 0.05). The retention of dietary EAA in whole body of juvenile grouper was significantly influenced by dietary arginine. Arginine retention increased with increasing dietary arginine levels from 1.78% to 2.72%, then declined above the level of 2.7% (P < 0.05). Based on broken‐line regression analysis of WG against dietary arginine levels, the dietary arginine requirement of juvenile grouper E. coioides was determined as 2.7% of the diet (corresponding to 5.5% of dietary protein).     

Dietary valine requirement of juvenile blunt snout bream (Megalobrama amblycephala Yih, 1955)

An 8‐week feeding trial was carried out to test the hypothesis that adequate dietary valine might improve growth, feed utilization and protein content in blunt snout bream, whereas a valine deficiency might have adverse effects on these parameters. Six isonitrogenous (34% crude protein) and isoenergetic (14.2 MJ kg^?1 digestible energy) experimental diets were formulated to contain graded valine levels (0.66, 0.95, 1.26, 1.55, 1.87 and 2.16% of dry weight) at about 0.30% increments replaced by equal proportions of glycine. At the end of the experiment the survival rate was not significantly affected by the dietary valine level. Final weight, weight gain (WG), specific growth rate (SGR), feed efficiency ratio (FER) and protein efficiency ratio (PER) increased with an increasing dietary valine level up to the 1.26% diet, and thereafter remained relatively constant. Dietary valine levels significantly affected the viscerosomatic index, but not the hepatosomatic index or condition factor. The dietary valine levels significantly affected the protein contents of whole body and plasma. Dietary valine supplementation significantly increased the plasma valine concentration, but not the levels of other branched‐chain amino acids (isoleucine and leucine). Based on SGR and FER, the optimal dietary valine requirements of juvenile blunt snout bream were determined to be 1.32% of the diet (3.88% of dietary protein) and 1.26% of the diet (3.71% of dietary protein), respectively, using broken‐line regression analysis.     

双低菜粕替代豆粕对青鱼幼鱼生长及生理生化指标的影响

以初始体重(5.77±0.05)g 的青鱼(Mylopharyngodon piceus)为研究对象, 以双低菜粕蛋白分别替代饲料中0 (对照)、25%、50%、75%和100%的豆粕蛋白, 配制双低菜粕含量分别为0、11%、22%、33%和44%的5 种等氮等能的实验饲料, 研究双低菜粕对青鱼生长、消化酶、消化率、体组成和部分生理生化指标的影响。实验在室内养殖系统中进行, 每水族箱(300 L)饲喂25 尾, 每处理组3 个重复, 以鱼体重3%—5%投喂量, 日投喂2 次, 试验持续8 周。实验结果表明, 当饲料中双低菜粕含量大于11%时, 其特定生长率、干物质和蛋白质表观消化率、肠道蛋白酶、淀粉酶和脂肪酶活性均显著低于对照组, 当双低菜粕含量达到44%时, 饲料系数显著高于对照组(PP<0.05)。饲料菜粕对鱼体水分和蛋白含量无显著影响, 但鱼体脂肪随菜粕含量的增加而降低、脏体比指数和灰分含量有随菜粕含量的增加而升高的趋势, 肝体比指数有随菜粕含量的增加而有先升高后降低的趋势。上述结果表明, 青鱼幼鱼饲料中双低菜粕含量以不超过11%为宜。       

Effect of feeding different protein to energy (P/E) ratios on the growth performance and body composition of Oreochromis niloticus fingerlings

This study evaluated the growth performance and body composition of Oreochromis niloticus fingerlings (average initial weight 16.53 ± 0.44 g) fed 9 experimental diets (A, B, C, D, E, F, G, H and I) containing three different levels of protein (26, 31 and 36 g 100 g^?1) at three different gross energy (GE) levels (16, 19 and 22 MJ kg^?1) for a period of 64 days. Significant differences were observed in the feed consumption, body weight gain, specific growth rate (SGR), condition factor (k), feed conversion ratio (FCR), protein efficiency ratio (PER), net protein retention (NPR) and apparent net energy retention (ANER) values of fish when the energy level of diet was increased at different protein levels. The maximum weight gain, SGR and k were observed on diet F containing 36% protein and an energy level of 19 MJ kg^?1 of dry feed with a protein to energy (P/E) ratio of 18.96 (g protein MJ^?1 GE). A further increase in the energy content of the diet (22 MJ kg^?1) at the same protein level (Diet I) did not produce any improvement in the growth performance. Lowering the energy level at the same protein level significantly affected the growth performance. Fish fed diet B containing 31% protein and a lower energy level of 16 MJ kg^?1 with the same P/E ratio of 18.61 as diet F showed significantly lower weight gain and growth performance than diet F. Diets E and H containing 31% crude protein at all three energy levels produced similar results as diet B. The poorest FCR was observed when the diet contained both lower levels of protein and energy. Fish fed diet G, containing 26% protein at high energy level (22 MJ kg^?1), showed the best PER and NPR values. The PER and NPR were the poorest on diet C containing 36% protein at low energy level (16 MJ kg^?1). The body moisture content at all protein levels decreased (P < 0.05) with the increasing level of dietary energy whereas the body fat content increased (P < 0.05). Similar trends were observed in the body ash and energy content. Increasing the dietary energy content at lower protein levels did not show any difference (P > 0.05) in body protein content. Our results indicated the optimum P/E ratio for O. niloticus as 18.96 g protein per mega joule of gross energy at 36% dietary protein level and a dietary gross energy value of 19 MJ kg^?1.     

Circadian Rhythm Variations in the Adult Rat Induced By Low and High Protein Diets Administered at Various Stages of Development

Hypothalamic tryptophan (TP), serotonin (5HT) and 5-hydroxy-indoleacetic acid (5HIAA), serum tryptophan (free and total), and circulating corticosterone and aldosterone were measured over 24 hr in 60-day-old male rats fed high (60%) and low (6%) protein diets. The diets were administered during specific stages of rat growth: fetal phase and suckling (when the process of mitosis is most rapid), post-lactation, and from the fetal phase through to the adult stage. In all groups, there was a direct correlation between protein intake and hypothalamic and serum TP levels. Remarkable decreases in the amplitude and mesor of the aldosterone rhythm were observed when the hyperprotein diet was administered in the fetal and suckling phases, or from the fetal phase until the adult stages. The rhythm of the serotonin system was significantly altered by a low protein diet: decreased 5-HT amplitude (low protein diet in the fetal stage and suckling), decreased 5-HT amplitude and deranged S-HIAA rhythm (low protein in the post-lactation period), deranged 5-HIAA rhythm (low protein diet throughout the experiment). Lastly, there was a remarkable increase in the corticosterone mesor in rats administered a low protein diet after weaning and in rats constantly given this diet. Growth was greatly inhibited in these two groups of animals, therefore, it cannot be excluded that the high levels of circulating hormone resulted from their debilitated condition.     

Different diets and amino acid supplementation do not affect the voluntary consumption of ethanol by rats

The effects of four different diets (control diet: 19.5% protein, 60.5% carbohydrate, 10% fat; diet I: 65% protein, 10% carbohydrate, 10% fat; diet II: 5% protein, 76% carbohydrate, 10% fat; diet III: 20% protein, 69% carbohydrate, 1% fat; diet IV: 69% protein, 15% carbohydrate, 1% fat) and supplementation with 3 amino acids (tryptophan: 150 mg/kg/d; arginine: 400 mg/kg/d; taurine: 380 mg/kg/d) on the voluntary consumption of ethanol were investigated in rats using the 2 bottle method. First, rats received the control diet and diets I, II, III and IV for 20 days with a choice of ethanol for the last 6 days only. Ethanol consumption was similar in all dietary groups. Second, rats received the control diet for 8 days followed by diets I, II and IV for another 8 days. Ethanol was offered throughout both periods. The switch to the special diets did not affect ethanol consumption. Third, rats received a control diet with arginine, tryptophan or taurine added to the drinking fluids for 16 days with a choice of ethanol for the last 5 days; thereafter supplementation stopped but the ethanol choice remained. No difference in the voluntary intake of ethanol was noted but ethanol consumption fell after cessation of arginine supplementation. In conclusion, diets differing greatly in their composition or supplementation with these 3 amino acids did not affect the voluntary choice of ethanol by rats in a significant manner.     

Effect of dietary tryptophan on plasma and brain tryptophan, brain serotonin, and brain 5-hydroxyindoleacetic acid in rainbow trout

In order to determine the effect of dietary tryptophan level on plasma and brain tryptophan, brain serotonin, and brain 5-hydroxyindoleacetic acid levels, juvenile rainbow trout (Salmo gairdneri) were raised for 16 weeks on semipurified diets containing 0.06%, 0.16%, 0.21%, 0.26%, 0.39%, or 0.59% tryptophan. After 14 weeks, feed intake was depressed in fish fed the diets containing 0.06% or 0.16% tryptophan. No further differences in feed intake were noted between the remaining treatments. In addition, body weight was lower in fish fed diets containing 0.06%, 0.16%, or 0.21% tryptophan compared with fish fed higher levels. After 16 weeks of feeding the test diets, plasma tryptophan levels were found to be directly related to dietary tryptophan levels. Similarly, increased dietary levels of tryptophan resulted in increased brain levels of tryptophan, serotonin, and 5-hydroxyindoleacetic acid. These results demonstrate that in rainbow trout, as in mammals, altered dietary levels of tryptophan result in alterations in plasma and brain tryptophan, brain serotonin, and brain 5-hydroxyindoleacetic acid.     

Changes in cerebrospinal fluid and plasma amino acid concentrations with elevated dietary protein concentration in dogs with portacaval shunts

Effects of dietary protein concentration on plasma and cerebrospinal fluid (CSF) amino acids (AA) in dogs with portacaval shunts (PCS) were examined. An 18% protein purified diet (18P) was fed to 4 PCS dogs and 2 controls; at week 10, 2 of the PCS dogs were switched to 36% protein (36P) until week 28. Effects of the diet switch on plasma and CSF AA in 8 normal dogs were determined in another experiment. Neither surgery nor protein level significantly affected average food intake (weeks 10-28). Plasma amino acid patterns typical of PCS animals were observed: phenylalanine and tyrosine increased and branched chain AA decreased with shunting (p less than 0.05). Plasma phenylalanine increased further with 36P in PCS dogs (p less than 0.05), but was not affected by dietary protein concentration in controls. With 36P: CSF arginine, serine, histidine, tryptophan, phenylalanine, glutamate and glutamine increased in PCS dogs; but only arginine decreased in CSF of controls (p less than 0.05). In PCS dogs, significant CSF AA changes with elevated dietary protein were unrelated to plasma AA changes.